misfire... carb issue??

[Kyle]

i bought a holley tuning book today and was reading through it. the stumble seems to only happen under load and im assuming thats when the manifold vac drops off.... could i have the wrong power valve or one thats set too high? maybe i need one that opens up at a lower vacuum?

[randycrane79]

yes more then likely it blew out on ya  make sure the numbers match .....yes power valve pop off valve and if ya didnt order it that way it aint in there    ya have to change out the valve body on it or ya can buy the block for it

[Kyle]

yes more then likely it blew out on ya  make sure the numbers match .....yes power valve pop off valve and if ya didnt order it that way it aint in there    ya have to change out the valve body on it or ya can buy the block for it

its a 670 street avenger... so i dont know if it has it or not. is there a way to tell without tearing it apart? why would i need a whole new body for it? does the block kit affect normal operation on it for street driving?

is this somethin that id be lookin for?
http://www.automedia.com/Holley_Power-Valve_Blowout_Protection/pht20011001cb/1

[Kyle]

turns out my carb already has that protection for it..... maybe im just lookin at a bigger power valve then?

http://holley.com/data/types/pictures/SA_IntoZOOM.jpg

[Yetti]

i have it off the upper port on the carb where holley says to use, has no vac at idle but once that throttle is moved it sucks a bunch of vac. i have the pressure set at 6(which holley reccomends i run it at 6-6.5) right now by an inline guage between the regulator and the carb

"the port on the carb" as you say is just that, ported vacuum. its what is supposed to be for the distributor. and only the distributor.
The regulator should be on manifold vacuum from the intake behind the carb or at a port lower then the throttle plates that has full manifold vacuum at idle.

Manifold vacuum should be a solid 18-21 inches at idle. if it jumps around or is low at the manifold you need to find out why. the wrong PCV can and will cause a low vacuum problem. so can a blown diaphragm in the brake booster

[Kyle]

i have it off the upper port on the carb where holley says to use, has no vac at idle but once that throttle is moved it sucks a bunch of vac. i have the pressure set at 6(which holley reccomends i run it at 6-6.5) right now by an inline guage between the regulator and the carb

"the port on the carb" as you say is just that, ported vacuum. its what is supposed to be for the distributor. and only the distributor.
The regulator should be on manifold vacuum from the intake behind the carb or at a port lower then the throttle plates that has full manifold vacuum at idle.

Manifold vacuum should be a solid 18-21 inches at idle. if it jumps around or is low at the manifold you need to find out why. the wrong PCV can and will cause a low vacuum problem. so can a blown diaphragm in the brake booster

the fp regulator does not have a vac on it. the needle does not jump at all it holds fairly steady at just a hair over 16. i dont run any pcv valve, just a breather on each valve cover. and how can ya tell a brake booster is blown? i have good brakes

[betterbeaters]

get a 2.5 power valve

[Kyle]

get a 2.5 power valve

standard flow or high flow?

[Squirell]

That 40 degrees of timing at 2500...that with the vacuum hooked up or blocked off? If its blocked off you have to much total timing. But it does seem like a lean condition

[Kyle]

That 40 degrees of timing at 2500...that with the vacuum hooked up or blocked off? If its blocked off you have to much total timing. But it does seem like a lean condition

it is with the vac hooked up. i never thought to test it with the vac blocked off

[old school truck dude]

40 is a bit much, gotta limit that total somehow

[Squirell]

Block it off and check again let me know...base timing isn't as important as total timing. But always check it with vacuum unhooked from dizzy and plugged off. The lean condition could be caused from to much timing

[Yetti]

37 is the max on timing unless your running high octane fuel. other then that you start to get detonation in the cylinders with low octane fuel. it will burn the pistons and valves if it stay that way to long.
(could be part of the problem?)
as for a bad booster they hiss under the dash if they are bad.

[Kyle]

40 is a bit much, gotta limit that total somehow

theres stop bushings i can put in. my dizzy is full adjustable

Block it off and check again let me know...base timing isn't as important as total timing. But always check it with vacuum unhooked from dizzy and plugged off. The lean condition could be caused from to much timing

will try to get to it tommorow then. does the timing curve up to full advance matter too? cuz i can put diff springs and adjust the curve a couple different ways

37 is the max on timing unless your running high octane fuel. other then that you start to get detonation in the cylinders with low octane fuel. it will burn the pistons and valves if it stay that way to long.
(could be part of the problem?)
as for a bad booster they hiss under the dash if they are bad.

well i run premium gas to compensate for the higher compression, not sure if you consider that high octane. i doubt it has burnt valves cuz it will ru fine in 3rd gear driving places, its only stumbling under load(possibly when the vac drops off). as far as the booster theres no hiss under the dash that i know of

[old school truck dude]

Clamp off the vac line to the booster and give it a few seconds to see if the rpm changes to check for that leak. yes, the curve matters ALOT. Ever seen a Sun distributor machine? Thats how we used to set them up. Premium is not high octane, 104+ is high octane. Turbo blue all the way, woohoo!!   Probably still aint rich enough on your mix, might need to go up a size on your jets. If it aint too hard, its really worth a try. Youd be surprised at the difference 

[Squirell]

ok you set timing with the vaccum advance unhooked. what it does hooked up is how it is suppose to work. but anyways set the timing at 34 degrees at 3000 rpm with the vacuum unhooked. then just check the timing at idle. it should be close to 10-14 degrees. the main concern in this is total timing<timing at 3000 rpm> if that is correct and you still have a problem. move on to them power valves. even know it has "protection" it can still happen.

[Kyle]

ok. got some numbers now....

base timing
14 degrees
advance at 2500 with vac
42 degrees
advance at 2500 no vac
24
advance at 3000 no vac
26

my dizzy has heavy springs tho so it wont reach full advance with them till bout 5k rpms but the stops are 21 degree stops. i was reading through my diagrams on what my springs give me, and i basically have 2 options: having full timing at 2500 rpms or having it full at 3k rpms(after those rpms are reached the stops engage and it is limited to 21 degrees advance)


on a different note, i ordered a jet kit from holley so i can up the jets and a new power valve, same size(6.5) just a high flow one. so once i get them in i plan on bumping up the jet size to somewheres around the 75(stock is a 65) to 85(what the 770cfm carbs run) and just changing out the power valve anyways just to be sure its working

[Kyle]

this has my instructions which shows my possible timing curves:

http://www.msdignition.com/WorkArea/DownloadAsset.aspx?id=6442451554

[Squirell]

ok you dont have near enough timing in that. you need 32-36 degrees at 3000 rpm with no vac hooked up. dont worry about the springs right now. them are only affected by the vaccum advance. at least that is how i understand it. Set your timing with vacuum advance unhooked. and it plugged off. get it to 34 degrees and I about promise that pop goes away.

[Kyle]

ok you dont have near enough timing in that. you need 32-36 degrees at 3000 rpm with no vac hooked up. dont worry about the springs right now. them are only affected by the vaccum advance. at least that is how i understand it. Set your timing with vacuum advance unhooked. and it plugged off. get it to 34 degrees and I about promise that pop goes away.

the springs have to have some affect on it..... otherwise ill have like 20 degrees base timing, so i almost have to change them out. unless theres some way to get more advance outta it that i dont know of?? this aint some regular hei distributor from a running vehicle