Hi guys.Hope you guys are doing great.Well I just wanna start off by thanking you guys for all the help you guys have given me I appreciate it. These last couple of days have been pretty good I finally got my truck out for the year.

I have a question which I've done research on different websites and fourms. So if you don't know i have a holley 470 truck avenger carb and it runs great when your just chugging along around town. I just have a problem when I'm at full throttle or part full throttle in 2nd or 3rd gear there is a stutter that happens.

I noticed it a week ago. Today my brother asked if I could help him go get a couple of boxes of wood for his house anyway on the way there I noticed my truck wasn't running so hot WOT stutter but she was giving it her best. I proceeded to drive normally. There was a point where I had it in fourth gear and it wasn't moving granted it was windy and 86 isn't the most aerodynamic truck around but I've never had a problem like this before.

I was thinking it may be my power valve due to the fact that from factory they come with a 2.5 power valve and I make at least 21 at idle and I did the whole equation that Holley gives you and I need at least a 8.5 power valve. The carburetor has been rebuilt and my truck has DUI distributor. When I got home I was curious about how my plugs were looking so I checked them out and they were okay. 1, 4, and 6 were not so nice I cleaned the build up on those plugs and regapped all the plugs.

Which brings me to my question would a incorrect power valve cause this problem?

Sorry for the long post just wanna keep you guys on the up and up. I'm almost positive that it would be a conviction on my plugs and maybe a power valve issue. But I wanna be clear. I'm still learning about carburetors so please bear with me.

Thanks always!

 

If your carb is set up near stock specs it should not produce the symptoms described. I think you may have ignition system issues.

 

I kinda find it hard to believe I didn't have ignition problems when I had a edelbrock on there. Maybe I should mention it doesn't do it all the time only sometimes. When I checked the plugs 4 out of the 6 plugs weren't in the specified gap. One plug was at .025 kinda scared me.

When I switched to the Holley it didn't do it at first then after I did a little tuning that's when I noticed it.

 

You did not say how many miles are on the plugs and the motor?
How is the truck used? Around town on weekends or on the high way for 30+ min. or 15+ miles?
I find Holleys do run a little rich but you would see this on all plugs not just 2 or 3.
Other than the 1 gap closing up what did the plugs look like?
Black & sooty, hard & light brown in color?
Could it be the gap was closed when installed?


If me and I found half the plugs in question I would replace them all, and maybe the cap, rotor and wires if I did not know the shape of them.
Put a 1000 miles on them and see what they look like. If the same cly are showing signs like before I would check deeper with a leak down test to see what is bad and the cause of the plugs going bad.
Dave ----

 

UPDATE ! SO yesterday my brother in law and I spent the day trying to figure this thing out and found out that the secondaries are not opening up. We switched back to the edelbrock to cross off that the igntion is working properly and it did so it was the Holley.

Did the whole paper clip test with the Holley before swapping it out and paper clip didn't move that was with the vacuum diaphragm that came with the carb. We changed it out with a diaphragm from a 600 holley still no dice. We also changed out the power valve with a 6.5. Still nothing the primary side of the carb work flawless love it I could tell the holley winds up way quicker then the edelbrock it's just the secondary side of it that giving me problems.

I'll keep you guys updated on what happens. Thanks.

 

Don't quote me here but I.I.R.C.,..Holley's have two different lengths shafts for their secondary diaphragms. One size secondary vacuum diaphragm fits most Holley's but not all.

 

Do you have a gasket between the secondary vacuum pot and main body?

You probably don't need the secondaries anyway - the primaries on a 600 are plenty big.

 

We did this on larger Ford truck engines, 361's, 370's to test operation of Holley secondaries to save numerous road test. Looking down the curbside primary barrel sorta on an angle toward the front of the right fender, you will see a small hole in the wall of the barrel. Air rushing by this hole creates the vacuum signal to open the secondaries.

ENGINE OFF, BEWARE, you will create a vacuum that will cause gas to spray around. Take you shop air hose and blowgun, with primaries held wide open aim the blow gun down the barrel, hugging the wall, but above the small hole. Squeeze the blow gun and hold. In 3-4-5 seconds the secondaries will start to open and go to completely open IF ALL IS WELL. Two reasons we did these tests. 1- When there was a complaint of lack of power and the operator said "It runs real good, but it won't pull". 2- We rebuilt our own carbs. When done we would bench test the secondaries to make sure we put the diaphragm, check ball and all gaskets in properly and that it worked properly.

Fordboy300, As your carb is off now, you can do some bench testing this way. Tricks
1- On installing diaphragm, cover off, press center down against the spring, use a small vise grip against the shaft where it come thru the housing to lock and hold the diaphragm level as when assembled. Then you can put the cover on effortlessly.
2- The little check ball should be used. It allow the secondaries to open smoothly. The different colored springs from the spring kit, you have to choose the one that lets the secondaries open fastest with out bogging.
3- Usually there is a safety that will not allow the secondaries to open if the choke is not open ALL THE WAY and there maybe a piece on the linkage side that will not let the secondaries open IF the primaries are not open all the way.

You need to check all and on the bench is the ideal/safest way. Good Luck and let us know how you make out.