sb tuning problems
- Thread starter ap6street
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Hey mate,
I think there a few issues going on here:
1st. Can you borrow a smaller carb even a 750 would be enough. Ill make the assumption that your running the Indy single plane manifold? You might find that it fixes most of your problems and picks a bit of torque in the lower speed ranges and better throttle response. Its not only about the volume of fuel your engine gets from the carb but the quality as well. A smaller carb will atomise the fuel better.
You've got a very large carb feeding into a large plenum so low speed running really isnt going to be that good compared to a smaller carb. Alternatively and a cheaper option to try is you can turn the manifold into a dual plane by installing a metal/alloy plate in the middle of the plenum to halve what your engine sees from the carb improving signal. Like this:
http://www.hotrod.com/how-to/engine/0806phr-david-kauffung-308-chevy-small-block-rebuild/
Quick Fuel carbs also place Idle Feed Restriction (IFR) in the top of the meterig block. It should be relocated to the lower position as per this thread:
http://racingfuelsystems.myfunforum.org/Relocating_the_Holley_Idle_Jet_about18.html
2nd. You need initial timing, 18 is the minimum you should start at. Put the black bushing in and go from there. You can make bushings but i couldn't be arsed so i bought a Mallory which looks to be a better built unit and i get a vacuum advance too. Your cam isnt really big for the cubes your running so i dont think you've got excessive overlap and the problems that with it even though the manifold and carb dont help.
What are your cam specs?
If your stalling after running for 20-30 minutes it might be heat issue as the carb is aluminuim and theres very little room in an AP6 engine bay. Also post some pics please! I have an AP5 with a 360 by the way.
What control box and coil are you using? This can affect idle quality as well.
Try a smaller carb 1st!
Hysteric
I think there a few issues going on here:
1st. Can you borrow a smaller carb even a 750 would be enough. Ill make the assumption that your running the Indy single plane manifold? You might find that it fixes most of your problems and picks a bit of torque in the lower speed ranges and better throttle response. Its not only about the volume of fuel your engine gets from the carb but the quality as well. A smaller carb will atomise the fuel better.
You've got a very large carb feeding into a large plenum so low speed running really isnt going to be that good compared to a smaller carb. Alternatively and a cheaper option to try is you can turn the manifold into a dual plane by installing a metal/alloy plate in the middle of the plenum to halve what your engine sees from the carb improving signal. Like this:
http://www.hotrod.com/how-to/engine/0806phr-david-kauffung-308-chevy-small-block-rebuild/
Quick Fuel carbs also place Idle Feed Restriction (IFR) in the top of the meterig block. It should be relocated to the lower position as per this thread:
http://racingfuelsystems.myfunforum.org/Relocating_the_Holley_Idle_Jet_about18.html
2nd. You need initial timing, 18 is the minimum you should start at. Put the black bushing in and go from there. You can make bushings but i couldn't be arsed so i bought a Mallory which looks to be a better built unit and i get a vacuum advance too. Your cam isnt really big for the cubes your running so i dont think you've got excessive overlap and the problems that with it even though the manifold and carb dont help.
What are your cam specs?
If your stalling after running for 20-30 minutes it might be heat issue as the carb is aluminuim and theres very little room in an AP6 engine bay. Also post some pics please! I have an AP5 with a 360 by the way.
What control box and coil are you using? This can affect idle quality as well.
Try a smaller carb 1st!
Hysteric
The only starting points I've seen published are here.
http://www.demoncarbs.com/Tech/DemonSelectionGuide.asp
(You're basically already there, so just for future reference.)
Then tweak to what your combo wants.
Crackedback and Hysteric have provided good info. I'd hold off on advancing the total timing until you've made a pass or two. Then if no knock and plugs look OK, bump it up.
Not getting full throttle? Now that is an all too common, even from shops. Get someone to help you or a big rock to hold the pedal down...
So the car ran fine before when first in i hadnt driven it much 34 total with the 850cfm quickfuel.
Took to a chassis dyno shop to get it tuned. Pretty reputable shop (lol) they said at WOT i i have 2.5" of bacuum so which i guess makes sense needs a bigger carb . They said go with a 1050cfm i realise at this stage this carb is massive for the cubes/cam setup . Everyone advised against but i gave the boys a chance to prove me wrong and put on a 1050.
The printout showed 330hp now up to 350hp 20 extra all the way up the curve.
Took it home and drove it . Sounded a lot crisper . Especially coming off the throttle while cruising . But a bit gutless. Checked the throttle and was only going half way. Fixed it up now and it went hard . I called the place and they said they were 99% that it was fine . (Very strange)
But since then at cruising the car dies at idle . Definitely plenty of power and torque downlow and no stumble or heaistation anywhere. Just the stalling .
About the heat changed fuel pump location and recently added the 1/2" plastiv spacer.
http://s1190.photobucket.com/user/ap6street/library/Mobile Uploads?sort=3&page=1
Took to a chassis dyno shop to get it tuned. Pretty reputable shop (lol) they said at WOT i i have 2.5" of bacuum so which i guess makes sense needs a bigger carb . They said go with a 1050cfm i realise at this stage this carb is massive for the cubes/cam setup . Everyone advised against but i gave the boys a chance to prove me wrong and put on a 1050.
The printout showed 330hp now up to 350hp 20 extra all the way up the curve.
Took it home and drove it . Sounded a lot crisper . Especially coming off the throttle while cruising . But a bit gutless. Checked the throttle and was only going half way. Fixed it up now and it went hard . I called the place and they said they were 99% that it was fine . (Very strange)
But since then at cruising the car dies at idle . Definitely plenty of power and torque downlow and no stumble or heaistation anywhere. Just the stalling .
About the heat changed fuel pump location and recently added the 1/2" plastiv spacer.
http://s1190.photobucket.com/user/ap6street/library/Mobile Uploads?sort=3&page=1
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If the problem with the throttle only opening 1/2 way was there with when you ran the 850 that would explain the vacuum reading. Now that you have fixed the throttle issue try the 850 again.
Hysteric
P.s Thats not much of a pic, lets see her in all her glory!
I added a few pics there now .
No see thats why i didnt believe they checked the throttle coz the same way the throttle bracket and cable was setup i switched it iver back on the 850 again and it had full throttle.
It was the difference in the carb .
No see thats why i didnt believe they checked the throttle coz the same way the throttle bracket and cable was setup i switched it iver back on the 850 again and it had full throttle.
It was the difference in the carb .
Marcohotrod
Well-Known Member
are U saying that the 850 with full throttle was 330 hp and the 1050 with 1/2 throttle was 350 hp? no way. how dark are the plugs lookin? and forget about larger headers, I have run 1 5/8", 1 3/4", and 1 7/8" on several engines, not much difference
Plugs are completely blackthe very tip sometimes has some colour lol.
Yes they said it makes no sense to pick up 20hp if there was only half throttle. They said take it back if i like they were quite sincere about it. Took me ages to get the throttle correct on the raceq model . The throttle arm is longer and needed a light spring for return . No way they had it correct short of doing it via the carb which they said they never do.
Msd 6al . Msd blaster 2 coil.
Is there anyway to tell directly if the spark has enough power ??
Could ignition parts get too hot . They are on the inside of the firewall in the cabin.
Yes they said it makes no sense to pick up 20hp if there was only half throttle. They said take it back if i like they were quite sincere about it. Took me ages to get the throttle correct on the raceq model . The throttle arm is longer and needed a light spring for return . No way they had it correct short of doing it via the carb which they said they never do.
Msd 6al . Msd blaster 2 coil.
Is there anyway to tell directly if the spark has enough power ??
Could ignition parts get too hot . They are on the inside of the firewall in the cabin.
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I ran the same set up you have now and was told to ditch it for a crane HI-6 6000 6440 and the PS92 coil. All i can say is what a difference, the idle was instantly better. Gapped the plugs to cranes recommendation i think 45 thou and what a different engine!
Im getting rid of all my MSD stuff.
Hysteric
Marcohotrod
Well-Known Member
plugs are black=too cold or too rich. why do U not want to go to a hotter plug? when it was on the dyno did they measure A/F ratio? go 1 step down on the primary jets please
Well i was gonna try a hotter plug . But last time when i asked someone they said def not and try add in more timing with a colder plug.
Ill probably the high initial timing when i get the new bushes.
If thats not doing much then maybe a hotter plug.
Will a smaller jet possibly cause it to lean out inder acceleration tho??
Ill probably the high initial timing when i get the new bushes.
If thats not doing much then maybe a hotter plug.
Will a smaller jet possibly cause it to lean out inder acceleration tho??
Jet it down, adjust idle mixture for highest vacuum reading or highest smooth engine rpm. Timing should be no more than 36 degrees at 3000 rpm. Don't use any sort of heavy springs in the distributor, medium to lightweight. You should be able to run at 14-16 initial without any problem. Betting a majority of your issues are carb related, possibly a vacuum leak showing up when the engine warms up... What's your fuel delivery system, line size, pump, regulator, return line?
If you are still running the 1050 you have way more carb than you need. Put that 850 back on / stock jetting / 4.5 pv or block the power valve and put the same size jets in the primaries and secondaries. If any of your carbs are edelbrocks throw them up in the classifieds and let them become someone elses nightmare
If you are still running the 1050 you have way more carb than you need. Put that 850 back on / stock jetting / 4.5 pv or block the power valve and put the same size jets in the primaries and secondaries. If any of your carbs are edelbrocks throw them up in the classifieds and let them become someone elses nightmare
yeah,because,its,been,doing,some,idling,at,the,moment,im,not,suprised,it,has,the,black,plus.
but,when,i,cruise,it,with,some,revs,and.get,the,revs,up,eventually,at,a,set,of,lights,it,will,stall,short,of,foot,brake,and,revs.
but,when,i,cruise,it,with,some,revs,and.get,the,revs,up,eventually,at,a,set,of,lights,it,will,stall,short,of,foot,brake,and,revs.
The real problem being is the stalling .
The 1050 when i got the car back idles and drives fantastic . Idling at 750rpm like a dream. And all the way through the revs and stabs on the throttle.
I dont see how the carb size is a problem when it goes through so well.
Except running rich by the plugs , which may be causing it to stall after not getting enough spark.
The 1050 when i got the car back idles and drives fantastic . Idling at 750rpm like a dream. And all the way through the revs and stabs on the throttle.
I dont see how the carb size is a problem when it goes through so well.
Except running rich by the plugs , which may be causing it to stall after not getting enough spark.
Lol well most of the people at the beginning said need at least 20 initial timing. Now people are saying its not timing and plugs its the jets and carb size. Different opinions is why i swapped the 850 and bought the 1050 in the first place .
Telling you the 1050 is too big without a doubt. You might have some issues with the 850, take it a step at a time fix one issue and move on to the next. What's the story on the 850, buy it new / used etc...?
sorry to sounds rude before, i dont doubt you. when the dyno place told me 1050 i asked at least 20 different people, friends and people from my facebook who constantly are racing and they all said no way. 1050 is way too big.
both carbs were brand new.
im not sure of the jet sizes. id have to take it apart.
the idle speed screw is one turn away from the engine stumbling to a stall as in turned out ? dono if that makes a difference.
idle mixtures are 1/2 turn out from fully wound in .
jets id have to open up and take a look.
850 diamond series quickfuel q
1050 race q quickfuel
both carbs were brand new.
im not sure of the jet sizes. id have to take it apart.
the idle speed screw is one turn away from the engine stumbling to a stall as in turned out ? dono if that makes a difference.
idle mixtures are 1/2 turn out from fully wound in .
jets id have to open up and take a look.
850 diamond series quickfuel q
1050 race q quickfuel
Just because people are recommending more timing and others say the carb is too big or at least needs smaller jets doesn't mean any of them are wrong. They are all correct IMHO. Doing one or the other won't fix all your issues. One solution might improve your issues but you really need to more initial timing with less advance and a correctly jetted properly sized carb to get the best performance/driveabilty out of your engine.
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