Full throttle hesitation - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mikajo39 · 07-23-2009, 12:34 PM

OK so I got my new engine in my truck and it's doing prety great,problem is though, if I drop the hammer, it'll stumble and bumble till you let off and try and ease it into full throttle. I tried adjusting my carb (edelbrock 600cfm 1405) accelerator pump for a bigger shot of fuel but that killed it entirely, then I went to the smallest shot of fuel and once again it died. Otherwise it runs great. It's a mildly hopped up 355 (cammed, headers,vortec heads,year one crate motor woo!) with a GMPP HEI, I have the vacuum advance on the full manifold vacuum side. The problem is with the distributor is the vacuum advance can it's so big (in size) that it hits my intake manifold and I can't adjust the timing much without the can hitting , and I must be having brain fade but which way do you turn it to advance or retard. so do you think its a fuel problem or ignition? thanks in advance!

69GMCLonghorn · 07-23-2009, 01:19 PM

Definitely ignition. A couple things to look into:

1) If you can't rotate the distributor far enough, you can pull it up and move it over a tooth or 2. Just be careful not to move it too far. Then obviously adjust the timing accordingly.

2) It sounds like it's advancing too far at WOT and causing it to bog. Had the same problem on a Chevelle. If adjusting the base timing doesn't solve the problem, you need to re-arc your distributor for that motor. Basically just change the weights and springs inside to stiffer/heavier...

3) What you may find is that you need to advance the base timing after re-arcing. It's your total advance that you're more concerned with. You should probably be around 35 - 40° total advance.

mikajo39 · 07-27-2009, 10:08 PM

So I finally am back home and I have my truck home too. Now i need to set this timing. GMClonghorn what do you mean by pulling it up and moving it over? wouldnt the distributor shaft not line up with the oil pump shaft after? and if its easier how do I remove my vacuum advance can and reinstall it after I clear the intake runner?

69GMCLonghorn · 07-23-2009, 01:23 PM

BTW, once I got this fixed on my Chevelle, the first time I nailed it off the line, the clouds opened up, angels were singin' and playin' the harp (I think they were playing The Devil Went Down to Georgia). I ROASTED the tires up to 55 MPH... with a 307!! I hope you have the same results!

mikajo39 · 07-23-2009, 02:08 PM

Thanks for the quick reply! I was pretty sure it wasn't fuel related, I'm probably just going to move the dizzy a 2 teeth over to get the vacuum can cleared, it had a bit to much base timing already. The starter lugs even when the engine is cold (and it's a new starter) and when it's hot its a battle to get it started, so hopefully it's just base timing.

mikajo39 · 07-23-2009, 02:09 PM

Quote:

Originally Posted by 69GMCLonghorn

BTW, once I got this fixed on my Chevelle, the first time I nailed it off the line, the clouds opened up, angels were singin' and playin' the harp (I think they were playing The Devil Went Down to Georgia). I ROASTED the tires up to 55 MPH... with a 307!! I hope you have the same results!

This is what I'm going for

I know this engine has got some grunt, now I just need to unleash it

mclairmo · 07-23-2009, 02:15 PM

You need to carefully time the engine with a timing light and timing tape and determine what your initial, mechanical and vacuum advance is and then optimize them all by setting the initial timing and then the mechanical. You may need to limit the amount of mechanical advance. You then add the vacuum advance and adjust that for maximum efficiency without detonation. The MSD website has some good info in ignition timing/tuning.

mikajo39 · 07-23-2009, 02:27 PM

I was wondering if there would be any way I could take my vacuum advance off so i could clear the intake manifold then put it back on once it's cleared? could that work?

mclairmo · 07-23-2009, 03:48 PM

The vacuum advance canister can be removed. However, if it hits now, why will it not hit later after you remove, rotate and reinstall? Might work, might not.

mikajo39 · 07-23-2009, 05:25 PM

Quote:

Originally Posted by mclairmo

The vacuum advance canister can be removed. However, if it hits now, why will it not hit later after you remove, rotate and reinstall? Might work, might not.

The vacuum advance can just has to clear an intake runner its just a little tiny space it has to clear then i'm home free

mclairmo · 07-23-2009, 07:18 PM

Go for it and good luck. I hope you are able to get it all tuned up. Just be patient and methodical and eventually you will get the timing just where it needs to be for your engine.

faribran · 07-27-2009, 11:41 PM

please DO NOT remove the advance can... its simple to pick the dist. up and if you have to u can turn the oil pump shaft with a long screw driver..

mikajo39 · 07-27-2009, 11:54 PM

Quote:

Originally Posted by faribran

please DO NOT remove the advance can... its simple to pick the dist. up and if you have to u can turn the oil pump shaft with a long screw driver..

haha duh long screwdriver man my brain isnt working tonight. And i wouldnt be removing it permenatley just so i can clear my intake manifold and then I'd put it back on.

07-23-2009, 12:34 PM	#1
mikajo39 Gearhead and audio junkie Join Date: Aug 2008 Location: nunyah Posts: 452	Full throttle hesitation OK so I got my new engine in my truck and it's doing prety great,problem is though, if I drop the hammer, it'll stumble and bumble till you let off and try and ease it into full throttle. I tried adjusting my carb (edelbrock 600cfm 1405) accelerator pump for a bigger shot of fuel but that killed it entirely, then I went to the smallest shot of fuel and once again it died. Otherwise it runs great. It's a mildly hopped up 355 (cammed, headers,vortec heads,year one crate motor woo!) with a GMPP HEI, I have the vacuum advance on the full manifold vacuum side. The problem is with the distributor is the vacuum advance can it's so big (in size) that it hits my intake manifold and I can't adjust the timing much without the can hitting , and I must be having brain fade but which way do you turn it to advance or retard. so do you think its a fuel problem or ignition? thanks in advance!

07-23-2009, 01:19 PM	#2
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: Full throttle hesitation Definitely ignition. A couple things to look into: 1) If you can't rotate the distributor far enough, you can pull it up and move it over a tooth or 2. Just be careful not to move it too far. Then obviously adjust the timing accordingly. 2) It sounds like it's advancing too far at WOT and causing it to bog. Had the same problem on a Chevelle. If adjusting the base timing doesn't solve the problem, you need to re-arc your distributor for that motor. Basically just change the weights and springs inside to stiffer/heavier... 3) What you may find is that you need to advance the base timing after re-arcing. It's your total advance that you're more concerned with. You should probably be around 35 - 40° total advance.

07-27-2009, 10:08 PM	#3
mikajo39 Gearhead and audio junkie Join Date: Aug 2008 Location: nunyah Posts: 452	Re: Full throttle hesitation So I finally am back home and I have my truck home too. Now i need to set this timing. GMClonghorn what do you mean by pulling it up and moving it over? wouldnt the distributor shaft not line up with the oil pump shaft after? and if its easier how do I remove my vacuum advance can and reinstall it after I clear the intake runner?

07-23-2009, 01:23 PM	#4
69GMCLonghorn Registered User Join Date: Dec 2006 Location: Porter Ranch, CA Posts: 978	Re: Full throttle hesitation BTW, once I got this fixed on my Chevelle, the first time I nailed it off the line, the clouds opened up, angels were singin' and playin' the harp (I think they were playing The Devil Went Down to Georgia). I ROASTED the tires up to 55 MPH... with a 307!! I hope you have the same results!

07-23-2009, 02:08 PM	#5
mikajo39 Gearhead and audio junkie Join Date: Aug 2008 Location: nunyah Posts: 452	Re: Full throttle hesitation Thanks for the quick reply! I was pretty sure it wasn't fuel related, I'm probably just going to move the dizzy a 2 teeth over to get the vacuum can cleared, it had a bit to much base timing already. The starter lugs even when the engine is cold (and it's a new starter) and when it's hot its a battle to get it started, so hopefully it's just base timing.

07-23-2009, 02:15 PM	#7
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: Full throttle hesitation You need to carefully time the engine with a timing light and timing tape and determine what your initial, mechanical and vacuum advance is and then optimize them all by setting the initial timing and then the mechanical. You may need to limit the amount of mechanical advance. You then add the vacuum advance and adjust that for maximum efficiency without detonation. The MSD website has some good info in ignition timing/tuning.

07-23-2009, 02:27 PM	#8
mikajo39 Gearhead and audio junkie Join Date: Aug 2008 Location: nunyah Posts: 452	Re: Full throttle hesitation I was wondering if there would be any way I could take my vacuum advance off so i could clear the intake manifold then put it back on once it's cleared? could that work?

07-23-2009, 03:48 PM	#9
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: Full throttle hesitation The vacuum advance canister can be removed. However, if it hits now, why will it not hit later after you remove, rotate and reinstall? Might work, might not.

07-23-2009, 07:18 PM	#11
mclairmo Registered User Join Date: Jan 2006 Location: Take Off Posts: 1,908	Re: Full throttle hesitation Go for it and good luck. I hope you are able to get it all tuned up. Just be patient and methodical and eventually you will get the timing just where it needs to be for your engine.

07-27-2009, 11:41 PM	#12
faribran Registered User Join Date: Jul 2005 Location: AL Posts: 1,828	Re: Full throttle hesitation please DO NOT remove the advance can... its simple to pick the dist. up and if you have to u can turn the oil pump shaft with a long screw driver.. __________________ "



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