cmyc2

Went down two sizes in jets. Car still had a flat spot when giving it alot of gas to fast. Ran good if you did it slow. last night I went down two more sizes and now it runs real bad. Question is should I go up one size or go back up two and make other ajustments. What else should I do ? When yo make that big of a change do I need to ajust the float?

66BlkBB

The float level on a Holley is never affected by a change of jets. Once the level is set it should be OK unless it was altered by some outside event. Is it possible that you have the wrong power valve for you application. I would go back up the two sizes and work with something else on the carb to see if I could get the bog out.

67L36Driver

Except for drastic elevation changes smaller/larger jets than original size are seldom necessary.

Power valve has to match camshaft (vacum) characteristics.

midyearvette

which holley?? ...need more info....if a vac secondary, trouble with diaphram or wrong spring....if mechanical, pump shot......

62Jeff

If by flat spot, you mean stumble when you floor it, that's often the wrong secondary spring in a carb with vacuum operated secondaries. Going with a lighter spring cures that.

midyearvette

maybe im reading you wrong jeff but if too rich on the opening, i think he should go stronger??

JohnZ

So far, we have absolutely no information about what combination he's working with - engine, carb type, mods, current jet sizes, current power valve, etc. If we knew what he had, we could probably help him get to where he wants to be.

Astrodokk

My Holley had a stumbling upon quick acceleration as well. We rebuilt it and noticed that the cam was severely worn out. I bought a new set (bunch of different colors) and used a new one of the same color that was on there. It fixed the problem.

cmyc2

It seems to stumble before the secondaries open. No powervalve when I got it ,friend of mind put one in that he had . How do you know what valve to use . Are they numbered like jets? How how would I know to go up or down with the size. Hate to sound stupid but never worked on a carb before. Isn't working on it part of the fun of having an old vette? Thats the reason I gave my wife as to why I wanted and old vette more then a new one.

aaronz28

well... without your combination, its hard to help.. but there is alot of wrong info in this thread.


first of all.... a stumble, or bog, when the secondaries open is generally because the secondaries are opening too soon... a lighter spring will only make that worse.

if the diaphragm is setup right, you shouldn't feel the "KICK IN ***" when the secondaries open...

98% of carb problems are in the timing LOL.

make sure you have enough advance.. that often cures what appears to be a carb stumble.

jetting...unless you are 10 sizes or more out... shouldn't in anyway create a bog or flat spot...


what you should do..., get the carb set back up as it was delivered...
correct jets... correct powervalve.. correct squirter, and correct cam..

make sure your timing is doing what it is supposed to do... i.e. 36-38 WOT advance, run full manifold vaccuum advance (if so equipped)

your power valve number should be about 1/2 of the idle vaccuum... so if you engine is making 12in HG at idle... you should use a 6.5 PV

the PV opens when the vaccuum drops below the numerical value... this does two things... MAINLY, if the engine starts to stall.. while idling, when the vaccuum drops below the PV rating, it will open and allow a little more fuel into the engine to keep it running...

and 2.. when you put the engine under load, the same thing happens... the PV opens and adds a little fuel to richen up the mixture...
in all reality, the actual size of the PV is not going to make much of a difference here, because the engine typically drops to Zero Manifold Vaccuum rather quickly under load... so a 6.5 vs 8.5 is not going to yield much of a difference as you accellerate.


If you don't have a timing issue... your problem probably lies in the Squirter and Pump Cam..

make sure that the pump cam arm is properly adjusted...there should be zero lash, and as soon as you graze the throttle,, you should see fuel dripping out of the squirters. if not... then you could be creating your lean spot there.

most holley's come with 25 or 28 squirters... depending on how much cam you have. .you might need a 31

having been down this road a million times... my bet is in the timing.

Best of Luck

A

mrruffhouser

Suggest you get at least one good book like, Haynes 'Holley Carburetor Manual", #10225 at your parts store or online. This book will give you not only basic funamentals on most Holley carbureators, but rebuild, repair and tunning info. /there are several other good ones also-check Amozon.com
Holley has a good on-line site, plus you can call and talk with a tech live at #270-781-9741. Get your model # of the carb first, with is usually stamped on the side of the air horn so people can help you.
Search our Forum also for excellent information after you have the model #.

rovers2000

good info thanks

Dicecal

Vetterodder

If it bogs when the throttle is opened but recovers quickly the problem is likely an inadequate accellerator pump shot. Lean jetting can make it worse but I'd start with a larger squirter as Aaron suggested and go from there.

65 vette dude

Hesitation is usually caused by a lean mixture. I don't think going to leaner jetting will help. I had a bad hesitation in my 2818 Holley and I finally got rid of it by 1) adjusting the accelerator pump lever so the slightest movement of the throttle rod, caused the accelerator pump lever to move. 2) I also bought the cam kit from Holley. This seemed to make the biggest difference. I had a red cam existing, and after much experimenting with all the different colors, the green cam took the hesitation away the best. 3) I also changed out the squirter from a 25 to a 28.

62Jeff

Putting a lighter spring in my 65 largely cured my stumble, and allowed the secondaries to open more easily.

Maybe I solved the problem with the wrong repair though, since a Lars tuning paper I have from a few years ago says to tune your secondary opening rate you should go with a lighter spring until you get a stumble, then go one spring stiffer.

thevanshop@aol.com

accelerator pump.

PAmotorman

check the LIST number on the front of the choke housing and look this number up on the holley website to find out what is the stock setup in this carb and go there first. very seldom are these specs far off. if you can not find the LIST number on the holley website post it here and someone will have the answer

cmyc2

I went back up one size on the jets ,but didn't get a chance to try it last night. Hope to try after work today. I was trying to find a number on the carb so I could look it up ,but I don't know where to look. I have a Holley book that list all these numbers but it dosn't show where to find on the carb. Thanks for everyone trying to help.

mrruffhouser

STOP fooling with your carburetor until you know what model you have.
Your most likely wasting your time and ours too. We're more than happy to try and help-but we have to have some information-like what model carb do you have?
It's stamped on the airhorn. Take off the air cleaner and it will be right above the gasket ridge for the air cleaner. It will be 4 numbers, many times followed by a dash and another number.
Come back when you have the number.