Vacuum advance at idle

Vacuum advance at idle. Apr 4, 2023 · Total timing is base timing (at idle with vacuum advance disconnected) plus mechanical advance from rpm. Keep pumping slowly and note the vacuum level when the rod reaches the other end of the slot. This is not an over the top number. So then, the can chosen should allow no more than 8 distributor deg of advance - that's 16 deg of crank adv. Your distributor needs to have a mechanical advance of 20 degrees. I think they would be well-matched to a 235. 0 HO, AX-15, D300, D30, D44, SOA. Make sure your vacuum advance is attached to ported vacuum. Now it is my understanding that when I reconnect the vacuum advance and rev the engine, the timing should advance cruise must be considered. Then my idle dropped from 750 to 500rpm. if you can get a bushing that limits mechanical advance to 18 degrees, then set your base at 18 degrees, this should give you a total of 36. You end up playing with the throttle to keep it running. Manifold vacuum will vary when you open and close the throttle. 4. it is set right at 6-8* what is the correct setting on a 460? im assuming that Aug 24, 2012 · The distributor’s. When the vacuum advance is attached, the motor stumbles and misses at idle. Oct 28, 2022 · With 50 degrees of timing (35 mechanical plus 15 degrees of vacuum advance) at part throttle. 3. As the screws went in idle Jun 21, 2013 · Vacuum advance disconnected. Someone already stated a ballpark timing number close to 20 degrees at idle with no vacuum advance, and that is correct. I've read and re-read my service manuals and done numerous searches on here and other sites. first i made good paint marks to read and hit it at idle (no tach) it was pulled over to 30* btc, so i pulled the vac line and pinched it off. Jul 11, 2016 · Ported vacuum should have no vacuum at idle, which means you should not have 30° of advance just by connecting the vacuum line to a ported vacuum source. Feb 5, 2010 · Engine idles well at 30* BTDC; total advance @ 3600 RPM =66* BTDC. It has a edelbrock 1407 750 CFM carb. Dec 27, 2005 · This motor seems to like manifold vacuum to the vacuum advance (idles rougher with ported vacuum) and we've checked for vacuum leaks. For the most part if the engine pulls over 13 or 14 inches the adjustable canister will add maximum advance no matter what the tip in point is set to (allen set screw down in canister hose nipple fitting). my curb idle vacuum reading is 21 inches. We've dialed the idle screws on the primaries with gauge attached till we found the best idle/vacuum at about 1 1/4 turns out. For test purposes disconnect and plug the vacuum advance port on the carburetor. If you disconnect the vac advance, As you rev up to about 1750 rpm the mechanical advance should be kicking in. At part throttle, the engine has the same vacuum advance it had before, and at WOT, the vacuum plummets to zero and we’re back to our 34 degrees of total advance. This will leave the engine with 35 degrees of initial and mechanical at any engine speed Use a vacuum can with a range above the idle vacuum so it is fully retarded by 8" Hg. A good starting point for timing would Jan 2, 2021 · Dave M. This should happen with the ported vacuum line connected (remember no vacuum at 800 rpm) and the distributer set in about the middle of its range (see the slotted Aug 17, 2022 · 1965 F100 Vacuum Advance Question. Mar 23, 2003 · TIMING AND VACUUM ADVANCE 101. ) May 10, 2015. With engine fully warmed-up and idling at 700 rpm, advanced 8 degrees and stock 66 distributor and vacuum advance unit. Apr 14, 2016 · Adding the vacuum advance placed our total timing at idle at 32 degrees (16 initial plus 16 degrees vacuum advance). Set the timing to 30 deg. I saw that at 500rpm the needle bounces way severe compared to at 750rpm. Check with a timing light. Set the base timing to 16 or 18 degrees to start. When I hook up the vacuum advance it backfires in the exhaust at any constant rpm above idle. This requires that lean mixtures have "the fire lit" earlier in the compression cycle (spark Sep 13, 2010 · What happened is when you hooked the vacuum advance to "manifold vacuum" it pulled the 10 degrees in that the vacuum advance advances, which raised your idle and thus kicked in the mechanical advance and that is why you had 40 degrees of advance at idle. That would give you 49 degrees advance above 3000RPM on LIGHT throttle. This is the “initial” or “base” spark timing which is checked and set at idle during a traditional tune-up (with the vacuum advance disconnected); it’s fixed at the point where it’s set by clamping down the distributor hold-down bolt, and doesn’t change – it’s always there. Thank you, Meep-Meep and Rebel. May 14, 2018 · Seems like the factory vacuum advance needs 9" Hg to start, or thereabouts. adjust the timing to obtain maximum vacuum at idle. Take that vacuum level and find a vacuum advance can that is fully advanced at 1-2" less than that. Just finished installing my rebuilt holley on a 66 396/360hp. When i hook the vac advance back up, idle speed in Dec 4, 2023 · First, I need to locate the right vacuum line, which is typically connected to the intake manifold or carburetor 1. You'll need to limit the VA to 10-15°. I'm working on getting the idle down to 550-600 RPM and have found & eliminated a few pesky vacuum leaks. Dec 25, 2021 · Then focus on the distributor. Sep 2, 2010 · They benefit from having a vacuum can with less advance than stock, like 8-12*, and fully deployed at lower vacuum readings common with cammed engines, to ensure stable idle. Once you have a steady idle, double check the idle mixture (I doubt it will be different). GMGalambos, James, If the vacuum advance is pulsing at idle that means the carburetors are not synchronized correctly or the idle is too high. 5. Using todays fuels, especially with a little hotter cam, headers, maybe some head work, the factory setting of 6 degrees wont work. That total timing figure should be no more than about 36 degrees. Jul 9, 2022 · Once linked to an aspirator, this increased stock vacuum advance can cause a rise in advance at rough idle speed up to hundreds of engine rpm, while carburetor modifications make no difference. 3 - With vacuum advance still disconnected I moved the gauge to manifold vacuum port and ran the mixture screws in to see what effect they had on vacuum. TC # 5401. I use Ford Small Block 289/302 V8 Distributor. With these settings, the engine ran well from idle to 4000 RPM without vacuum advance connected. Dec 4, 2023 · In my experience, connecting the vacuum advance to the manifold vacuum is often the best choice. Jan 19, 2018 · A typical street car with a mild cam might idle at 12 to 16 inches of mercury (Hg) on a vacuum gauge. /. If the vacuum advance control At idle, the engine needs additional spark advance in order to fire the lean (and exhaust-diluted) idle fuel/air mixture earlier in the cycle in order to develop maximum cylinder pressure at the proper point after TDC for efficiency, so the vacuum advance unit is activated by the high manifold vacuum, and adds another 15 degrees of spark Jul 24, 2021 · When I left with 1 1/2 turns engine died after start, ca 2 1/2 turn let it run. Check both lines. I've set the timing at 900 rpm to 12 btdc with the vacuum disconnected. When I disconnect the VA, it runs MUCH smoother. I get 25” from the pink pink port and 30” from the blue port… at idle. maximum of 10° to 11°@ 1500 RPM The vacuum advance provides 10° of advance. One nifty trick that helped me is as follows While idling, hook up vacuum gauge to your vacuum advance port. This is where your vacuum advance is all in. Put it in and limit the vacuum advance travel so you get 12" total advance (if the can provides more). Thus, a car set up to produce 36 degrees of total mechanical advance at 2500 rpm needs a vacuum advance control unit producing 16 degrees of crankshaft advance. I run 8 degrees initial advance with my vacuum advance on manifold vacuum. Sep 16, 2009 · Concerning Vacuum Advance: According to Lars Grimsrud you want to start by choosing a vac adv can that pulls "all in" at 2 inches of hg below your idle vac reading. (4 to 5) set idle rpm to 1000. Disconnect the vacuum advance and also connect a vacuum gauge to manifold vacuum. once the engine barely increases idle or starts to run slightly irregular after advancing the timing . Apr 8, 2008 · 7492 posts · Joined 2003. May 23, 2016 · Manifold vacuum is high at idle (20" of Hg in my truck), so using it for vacuum advance gives a high timing advance at idle (in my tuck, 10 deg BTDC static timing plus ~18 degrees vacuum advance = 28 deg BTDC total advance at idle). Full advance = advance till detonation then back off a few degrees. May 29, 2009 · Timing, mixture, pulled plugs, idle adjustments, test drives etc Hooked the Acell adjustable vacuum advance unit to the ported vacuum with it screwed all the way CCW (minimal vacuum advance) and long story short base timing is 10 deg, centrifugal 20deg (did not mess with the GM HEI curve), with vacuum ends up 37-38 total timing (at least what Jun 10, 2009 · This should give 8 crankshaft degrees of vacuum advance timing, and added to the initial of 12 degrees, the IDLE total would be 20 crankshaft degrees. The only thing this changed was the idle characteristics. Apr 9, 2024 · This vacuum canister produces 13-14 levels of advance however requires 14 crawls of vacuum to convey its most extreme planning. repeat from step 1, until you have the idle speed that suits you. Aug 14, 2017 · Full manifold vacuum improved my idle quality significantly, I actually had to back down on the throttle blades to lower the idle a bit. The idle in the vacuum advance video isn't high, it's right Aug 29, 2015 · unplug vacuum advance with engine idling, advance timing 4 degrees if the rpm increases and it still runs smooth, reset the idle and advance it 4 more degrees. If it is a high compression engine the vacuum advance should fully retard just about or just before the power valve opens. I did read quite low reading at 750 something around 7-8 psi. If the can is all in, this should reduce the timing bounce you spoke of. Jun 1, 2008 · Reset your idle with the idle screw. While going down the road at a steady 2400rpm the May 5, 2022 · In this episode I decide to give my 1975 L48 350 SBC full manifold vacuum advance at idle to see if it improves it's efficiency and performance over the OEM additional timing advance at idle, you must select a vacuum advance control unit that pulls in all of the advance at a vacuum level 2” below (numerically less than) the manifold vacuum present at idle. An example would be 14 Hg at 800 rpm. 50 110 LSA. I just got this engine rebuilt to original specs including an OEM 300 hp cam. 15 to mid 15s AFR for idle and cruise mid 12s for power curits. I have base timing set at the specified 6* BTDC with the vacuum line from the carb May 15, 2006 · If it is an older style 350 with old style heads then set the total timing 38 to 40 degrees (without vacuum advance connected). When I revved the engine the centrifugal advance activated at around 2000 RPM: just as it should. May 6, 2018 · As stated above, ported vacuum advance was done to help build combustion chamber temps Ported vacuum advance lowers peak combustion temperatures at idle to reduce the NOx emissions, and has no difference in operation, compared to manifold vacuum implementation, in off idle driving. Oct 2, 2002 · Yes using manifold vacuum advance will clean up the idle with a big cam but I have found it to end up being a real pain. Guys, I have a Holley 1940 single barrel carb sitting on the original/stock 240 CID engine in my 1965 F100 (3 speed). distributer uses ported vacuum so should be non existent when throttle plate is closed (idle). The range should be about 15 degrees, 0 advance @ 8"-10", 2 degrees at 10"-12", total 14-15 degrees @ 15" Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can Sep 7, 2015 · There are some Weber 32/36 and 38 tuning gurus on the jeep forums lemmetellyou. The full mechanical advance (vacuum advance still disconnected), which should be around 2500-3000 rpm, you want to be around 36-38 degrees. . Aug 23, 2019 · When you look at the ignition timing at idle you should get advance about 20 degrees. R. If it reads anything other than 0, you are running on primary progression circuit and wasting fuel. Gauge I have connected to manifold on same place where brake servo is connected. If it is ported vacuum you will not have any vacuum until you rev the engine. Jun 6, 2006 · Make sure this is a reasonable idle speed because vacuum will vary significantly with engine speed on the low end. the timing should be set with a timing light, about 10 degrees BTDC at 800. Also check the centrifugal advance for sticking, worn springs. The vacuum is a tiny bit bouncy, between 15 and 16 inches. I'm seeming to have quite a bit of trouble adjusting my timing/ idle speed. We set the timing at 12° BTDC at idle and moved the vacuum to ported. I would advise working on your distributor advance (it is very simple) so that without vacuum advance connected, you get the advance you want at idle and at 2500-3000 RPM. Dec 4, 2023 · Symptom: transition from idle to part throttle hesitation under load and stalling under snap of throttle Checked and verified 63 Service manual specs 215V8:Timing set 5 degrees, no vacuum advance, plugged line from aluminum base of 4gc rochester. One advantage of using manifold vacuum is that it provides advance at idle, cruise, and light throttle. Sep 11, 2023 · This will slightly lower the vacuum level, too. then hook up vacuum to manifold source with a limiter plate stopping vacuum advance at 8-10 degrees and you'll get your Mar 24, 2012 · So confused on vacuum advance! It was nice today so i figured i would finally check the timing on the 74 (460 w/c6 and air). To find out which line is the vacuum advance you will need to know which direction the plate turns to advance the timing. Max Advance @ “Hg This is the range of manifold vacuum at which the maximum vacuum advance is pegged out. At wide-open throttle (WOT Dec 1, 2005 · To do this, you'll need a timing light, timing tape, a tachometer, a paper and pencil, and a buddy just to make things easier. Ideal initial timing for a stock to mild cam is 10 to 12 (without vacuum advance connected). 050 (272/282). That means at idle, there is no vacuum applied. Let me share a few benefits of connecting to manifold vacuum. Dec 7, 2014. When I connected to vacuum advance then vacuum appeared only on higher rpm which I think it is correct (to change timing). More likely, as you suspect, there is a vaccuum leak. Set the initial timing to 12° and see how much manifold vacuum the engine is pulling. 20 or 30 degrees timing advance at idle would not be "too much" as far as that goes, something else is going on to cause the poor idle. 0 HO head on it with a Clifford intake, Holley 4 barrel and a Comp cam #68-231-4. degrees (16 crankshaft degrees). #14. On our 57 the advance curve was modified to provide only 12° (24° at the crankshaft) of mechanical advance at 2700 RPM. vac adv/ idle prob. Initial idle timing 14-16 3000 RPM mechanical 32-34 Limit canister to 8 degrees and connect vacuum advance. Randy. 2. Sep 12, 2009 · Modified engines with more cam that generate less than 15” Hg. Those were the smoothest dual carbs that I tried on a 235 or 261. Hope that made sense. They were however, not matched well with my 261 (which is bored to 270 ci). 38 degrees of idle timing at idle is way, way too much. When I connect the vacuum it jumps to about 18 to 20 degrees. Early Spark Timing: In the days of the simple, low Jan 13, 2017 · Below: 3/32" will give you 10* more timing at idle without the black bushing in the rod. Been there. I'll bump the advance up and set the idle at 900 RPM, see what happens. 5" Hg manifold vacuum at idle. of vacuum at idle need a vacuum advance can that's fully-deployed at least 1", preferably 2" of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees Jan 2, 2010 · A healthy, stock L-79 should produce at least 15. This last number should be 1-2" lower than your idle Feb 9, 2012 · In other words, if your engine only pulls 12" of vacuum at idle because of the cam, then you would want your vacuum advance to be all in by 10". Sep 18, 2014 · A typical HEI canister adds about 18 deg of crank advance by 14 inches vacuum or above, this is too much advance. When the throttle achieves WOT, the engine vacuum will drop to near zero and vacuum advance will disappear because there’s no vacuum to pull on the canister. In-Tech. 571/587 lift 231/239 duration @. Using a timing light, note your initial timing and idle rpm (VA disconnected and vacuum line plugged). . The advance is now at 10-12 degrees, with the vacuum advance disconnected. to help promote a more complete burn of leaner mixtures, and to Oct 21, 2002 · Help! 351C Vacuum problem. Jun 19, 2019 · more idle timing. (in the 30's using all mechanical or a combo with vacuum). retard it 4 degrees then note what it is. It makes about 11-12 inches of vacuum at idle (850 rpm). If you find it necessary to replace the vacuum advance, take the time to check the carburetor choke pull off , as the internal diaphragms are about the same thickness and share roughly the same lifespan. Read timing with vacuum hose off. Connect the vacuum hose to the vacuum advance canister. Engine runs rough, new performance type distributor, new plugs. Next, I must identify the distributor’s vacuum advance port 2. This would be an 8-degree vacuum advance control unit. Be sure to also check initial timing at + 50 rpm and - 50 rpm of your normal idle speed. Total mechanical can be as high as 40 and as low as 34 depending on how modern the heads are. It’s advancing way too much at Jun 2, 2011 · 176 posts · Joined 2011. Then as I remember I added two turns and got the highest vacuum. Nov 17, 2008 · If it was my motor, I'd have the vacuum advance connected. #2 · Mar 20, 2010. Vacuum advance helps with driveability and provides more advance when driving for improved economy. At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier Oct 18, 2018 · It's very possible that the ported vacuum is already working at curb idle. Jan 9, 2022 · Here is a quick test to see if your are getting any mechanical advance kicking in at idle rpm. Short story, advance to max vacuum, set idle speed, recheck and adjust for max vacuum then back timing just a touch. The most important concept to understand is that lean mixtures, such as at idle and steady highway cruise, take longer to burn than rich mixtures; idle in particular, as idle mixture is affected by exhaust gas dilution. At idle, manifold vacuum = 20”. Jan 2, 2005 · Oct 14, 2006. When adjusting the idle mixture screws that vacuum guage read 12. I just tried pinching off the PCV hose on 2 other cars with small blocks that are more radical than this one and they both show more vacuum at idle (both read over 15") and pinching the pcv does not cause the . Then read timing with hose connected at idle. If the engine rattles, the timing is too far advanced. change bushing in distributor to limit total to 38 when you combine your base (idle) timing and mechanical advance. Jan 14, 2020 · Set your initial advance to 8 degrees with the tube plugged off, then reconnect it. That gives 8 dist. Jun 10, 2004 · That's cool. Apr 8, 2015 · Use a vacuum can with a range above the idle vacuum so it is fully retarded by 8" Hg. The base timeing on my 1968 289 was set at the suggested 6BTC with the vacuum advance disconnected and plugged. mechanical advance is 6° @ 900 RPM, 8° to 10° @ 1200 RPM and reaches a. I think there's a nylon bushing for the vac adv arm coming out of the can, make sure it's there. If it is not all in, the idle speed will "hunt" up and down as the advance will be constantly changing. Idle timing will be 22-24 Cruise timing will be 40-42 Stab the throttle out on the road and your curve drops back to what is typically considered to be a more traditional curve of 32-34 all in. Nov 18, 2006 · Runs lopey but fine at idle, rough between 1200 and about 2500 rpm. So if base timing is 14 btdc and vacuum advance is limited to say 20 degrees, the total would be 34 at full vacuum advance. Apr 9, 2014 · Initial advance is set to 14 degress, jumps to 26 when I plug the vacuum line into the dizzy. Dec 7, 2014 · Georgia. There should be no stumble or "lean miss" unless there is a vacuum leak somewhere or the base timing is over-advanced (or you are using the light or medium springs supplied with most of the high-perf centrifugal advance kits on the market). Adjust the idle speed and Air/fuel slightly to were i'm idling around 850 in park/neutral and idling at 650 in gear. At 2,800 rpm, the blend of starting and mechanical convey 36 degrees. Jan 11, 2014 · 1 - Set timing at about 12* @ ~800 rpm with vacuum advance removed and plugged. Mar 17, 2013 · At idle, the engine needs additional spark advance in order to fire that lean, diluted mixture earlier in order to develop maximum cylinder pressure at the proper point, so the vacuum advance can (connected to manifold vacuum, not "ported" vacuum - more on that aberration later) is activated by the high manifold vacuum, and adds about 15 Aug 15, 2023 · Throw the books and timing light away and time using a vacuum gage. Jun 28, 2016 · Since you have a steady 15" of vacuum at idle, your engine would probably do well with a VC1765 (stamped B20) canister, but you would probably have to use a limiter plate to keep the canister from pulling its full amount (16° measured at the crankshaft) of advance. I'd like to see 18 inches at least. Aug 14, 2008 · The vacuum advance was disconnected during testing. Note the vacuum level when the rod just starts to move: this is where you vacuum advance starts. Mixtures/ AFRs have a huge influnece on the required advance to hit that spot for your engine between 12 and 18 degs at which the fuel explodes to give max cyclinder pressure. Then let the initial timing fall where it may. To use low octane fuel it may not like (need) that much advance, the Vortec heads just don't it. I will have to go back and see what happens to the timing when I pinch the pcv hose. If it's hooked to the proper port, there will not be any vacuum to the advance unit at idle; it should only be advancing after the throttle is opened. my cruise at 2100 rpm is between 10 and 11 inches. Vacuum line from Modified engines with more cam that generate less than 15" Hg. It idles like a dream down to 500 rpm, but picks up an intermittent miss on both banks above 1,000 rpm while in park. With such a short cam and 10:1 compression it's not surprising that the mechanical advance is limited to 32° @ 4000 rpm, and a typical VA curve isn't going to work either. I think the initial timing is set at 10° with 22° added by 4000 rpm. If you have my vacuum advance modifications package, it is all in there. Vacuum advance is important for highway cruise mpg performance and off-idle throttle response. Note all initial timing readings. Prev. Jul 21, 2007 · A tuning note on this: If you choose to run straight manifold vacuum to your vacuum advance in order to gain the additional timing advance at idle, you must select a vacuum advance control unit that pulls in all of the advance at a vacuum level 2” below (numerically less than) the manifold vacuum present at idle. I pull and plug the vac advance line, set the timing to 12 BTDC. Use a lower rated power valve. I believe the vacuum unit that MSD uses has B26 stamped on it. Working slowly and methodically, make a small adjustment to each idle mixture screw and then evaluate the change with the goal of the highest idle vacuum at the same idle Apr 6, 2020 · When i was setting my initial advance so idle vacuum is maximum i disconnected my manifold vacuum for vacuum advance (10deg). With a light throttle and more than 14-crawls of vacuum, the complete planning can move to 50 degrees. Apr 27, 2017 · The total timing limit is always whatever the max mechanical advance is. 11. reset the timing to orig position. At idle vacuum will be high and your advance will be high, giving a smooth idle with a lean air-fuel mixture. Jul 21, 2012 · Unplug one of the lines from the distributor if has vacuum at idle it is manifold vacuum. I traced it to the vacuum port tree on the manifold, and the Mar 20, 2010 · 460 posts · Joined 2002. If there is less vacuum (cold motor or you let the clutch out too fast or such) you loose the vacuum advance and the engine will refuse to run at idle. 2 - Turned mixture screws out until vacuum gauge read “0” at carburetor port. Ron Clevenger. So I bought a vacuum gauge. Oct 19, 2006 · SBC vacuum advance at idle ??? On my 350 SBC I have a Edelbrock Performer manifold with a 600 Holley, HEI dizzy and the cam is 214/224 @ . I just put a 351-w in my 1968 mustang, it was running rough with the stock coil,spark plug wires, distributer i put in a MSD system wow it was worth the money, my 351-w is very near to full race. I should never tap into the vacuum line going to the brake booster 1. There should be a vacuum port ABOVE the throttle plate that is ported. If mechanical advance is also limited to 20 degrees all in by 3000 rpm let’s say, for 34 degrees total advance. the vacuum advance should be connected to a ported/timed vacuum source. #1 · Apr 8, 2008. The engine dies at 8*. The goal with this procedure is the highest engine idle vacuum at the desired idle speed. Note, the black bush isn't used here cause my orig was worn, so I tried insulation from RG 62A coax cable, but it's too soft and the bush ended up with a wear mark from the rod hitting the limiter plate thus changing the vacuum advance number I was trying to achieve. 12° BTDC initial plus 24° of mechanical advance gave us 36° total. Usually, this port is found on the side of the distributor 2. As the throttle is opened, manifold vacuum begins to drop. Much more important to get the total timing right. Either way, the #2 throttle plate is too far open and it's starting to expose the vacuum advance port to manifold vacuum. If all this is working, it is not a question of timing. But limit total timing (vacuum plus mechanical) to 48-50. The timing was set 36* total. It is unlikely that the vacuum advance is the culprit though. The easiest way to accomplish this is to buy an adjustable vacuum advance can. 1981 Jeep CJ7 4. First, unhook the vacuum advance and measure Apr 5, 2003 · You want your base timing at idle (with no vacuum advance) to be set where the engine idles best but will not get into spark knock when you open the throttle fully such as in a rapid accel from a stop. I can rev it through the range but not hold steady rpm with vacuum advance hooked up. May 1, 2015 · Florida. You want 16 degrees initial, and 36 degrees total. Regards, Milton. I can advance initial timing to as much as 19 degrees (maybe more) but this makes the backfiring Oct 13, 2021 · Kill the engine and make adjustments. (36-16=20). Right now I'm seeing 15-16 inches of vacuum at a 900 rpm idle with the dizzy and power brakes hooked up. Cam specs are . What I have found is that that this high timing advance at idle causes a consistent "miss" at idle that can't be Jul 6, 2020 · And, way, way too much initial, 20 is too high, we make up the IDLE timing by correctly using the vacuum advance timing on full manifold vacuum. #2 · Jun 2, 2011. Now for the fun part. As the engine RPM increases, vacuum is applied. Im totally stumped. (Gauge should be OK, shows good vacuum on other cars. Feb 12, 2007 · Watch the gauge and the vacuum advance rod in the dist. Just hook up the vacuum advance to the ported vacuum port on the carb. @ 3000~3200 RPM and the initial should then be 8 or 10. IE a maitenance manual. Most Chevy V8's on the street will like 36-38* at cruise plus the 8-12* provided by vac can for a total of 46-50*. Jun 28, 2017 · Just don't drink the "all in at 2500 or 3000" kool-aid because the Vortec heads don't like it. If the vacuum advance control unit is not fully pulled in at idle, it will be somewhere in its mid-range, and it will fluctuate and vary the Sep 24, 2023 · The goal is to have your engine between 34° to 36° total. C1 & C2 Corvettes - Need help with vacuum advance issue - I've got an unusual issue with my 327 - 300 hp - PG engine. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can Dec 22, 2021 · Greetings- I have a mild 440 in a 66 charger. Excessive or bad vacuum advance may induce certain typical faults, such as surging at throttle body or when decelerating, overheating engine temperature Modified engines with more cam that generate less than 15” Hg. You would want to disconnect and plug the vacuum advance line, rev the engine up to about 3000 rpm, and then measure the timing. This will enable easy starting (rich mixture, no vacuum, advance "retarded" at 8 degrees). The vacuum line for. I had some surging at idle, I thought it might be a vacuum leak and I thought I found the hot ticket, a vacuum line melted to my right header. Idle RPM is around 650-700 RPM. Tach 500 rpms for automatic. An example would be 14 degrees base timing and Dec 2, 2006 · That is primarily with filters between the pump and carb. It's been a while, but I believe my timing is set at something around 16-17 initial and 35-36 total. Stuff like 12/14 initial, with 12/10 vacuum degrees, for 24 degrees IDLE total. Here's the drill. It should be the same. With vacuum advance connected, it idled OK, but engine started missing at and above 1500 RPM. Step on the gas and your vacuum goes to zero and your advance 06-13-2011, 05:05 PM. Full in by 15" Hg or so? Key thing is that the slight amount of vacuum at the ported vac port is not enough to make the vacuum advance work at hot base idle. This usually results in a smoother idle and a more efficient setup. Mar 18, 2013 · THEN dial in the timing. Aug 23, 2012 · Yes, you need a lot more timing at idle. " Hope this helps get this dialed in for you, Dave has suggested this modification to many, with nothing but great results. Jan 22, 2012 · My 258 has a 4. I would take off the cap and rotor, and get a vacuum pump and apply vac to the can and see if it returns without sticking. Jul 23, 2008 · SBC 350 Vacuum Advance/ Idle issues. Decide what springs you need to use in order to bring in total timing at the RPM that you want, and what bushings or other methods of May 29, 2016 · First. Oct 1, 2012 · Vacuum advance has absolutely nothing to do with total timing or performance, as when the throttle is opened, manifold vacuum drops essentially to zero, and the vacuum advance drops out entirely; it has no part in the "total timing" equation. Jul 10, 2018 · In addition to this lack of power, a vacuum leak can also cause the engine to idle roughly or even stall. #1. jk qz qx cg bw ue mx jj qi qf