Holley Carb Problem

[Garys1969RR]

Hey can anybody help me fix this 4778 Holley dbl pumper ? It is used, and I fixed a few leaks in it, and put it on my 451 today. Well it seems to be dumping an excess amount ol fuel into the primaries when I open the throttle part way. I put in a new power valve, and same thing. Seems to be going into the driver side venturi, mostly. When I look at the boost venturis when opening the throttle, just a huge amount goin in the driver side primary. And the engine sputters and misses. Passenger side seems to have a normal amount of fuel spray going in. Any suggestions appreciated. Thanks.

 

[snakeoil24]

Check float level. Also see if floats are cracked and filling with fuel. Needle seat issue.

 

[65 Plymouth Satellite 426]

X2!

 

[Meep-Meep]

As said above and possibly the o-ring around the needle and seat (center pivot bowl).

 

[Garys1969RR]

Found out the carb had 76 primary, and 80 secondary jets in it. Stock is 69 primary, and 78 secondary. Float levels are both right on. So went to the stock size of 67 pri, and 76 sec, lowered 2 sizes for altitude. Still flooding pri, on 1/4 to 3/8 throttle. But ran great wide open. So leaned the primary further by installing a power valve plug. Then it ran great on part throttle. No more sputtering. Wide open still good. So now do I re install the power valve, and drop main jet size on primary again? Could the power valve be leaking and giving it too much fuel? The carb is a 700 CFM dbl pumper. List 4778-8. The thing idles good, and all else works great. Just the part throttle sputtering as if it too rich.

 

[Jeremiah]

What power valve are you using and what is the vac. reading in gear at idle speed?

 

[Garys1969RR]

It had a 6.5 power valve stock. Then put in a new 4.5 one that came in a kit. Helped a little, so went to a 2.5 and it was worse. When I put in a P/V plug it ran the best. No more sputtering. Thought the 2.5 looked like it was gas soaked on the vacumn side. The rubber part also looked wrinkled like it had gotten gas on it. And each time I work on it, I run the bowl dry before disassembly to eliminate gas draining all over. So maybe the 2.5 had a leak?

 

[Garys1969RR]

I havent checked the manifold vacumn yet. But that my next step when I get back from N D. Has a 509 cam which is notorious for low vacumn. Hence the 2.5 P/V. Vacumn was so low I had to convert to manual brakes. Which I like better anyway. So it runs best at this point with 67 pri, 76 sec jets and P/V plugged. So may try dropping 5 jet sizes, primary side only, and re installing the power valve. Only takes 5 minutes to re jet the primary metering block now. I can do it with my eyes closed! Lol. Wonder if I could have the wrong metering block, or an internal fuel leak?

 

[Meep-Meep]

It seems that you are going around the problem by diddling with jets and PV's. The 4778 is set up with 67 / 76 jets and that should be a very good starting point and always start with the proper float level before moving on. Obviously the altitude will create a whole new set of problems, which may require an aftermarket metering block with a different emulsion tube calibration. Timing is critical as well so make sure that is correct too.

 

[67 coronet]

if you can see a variance in fuel flow from one side to the other there is an odd problem.look close at the air beeds on top(right on top by the air horn near the base of the venturies)check to see if they have been drilled to different sizes.i figure you got the carb used,so who knows what has been done.have you done a full rebuild and blown all air and fuel holes fully clear?a partialy plugged feed hole could cause a varience in fuel flow.

 

[Garys1969RR]

Total timing is set to 36 deg all in by 2500 RPM. This engine ran great with the Eddy 750 I had on it before. This Holley works a little better at WOT top end, just flows too much fuel with the power valve in and stock jetting. So going to check manifold vacumn at idle, and go 2 numbers below that with a new power valve. If I get 6.5" vacumn, then will use a 4.5 P/V. If it still feeds too much fuel then will either change the metering block, or drop 5 jet sizes in the primary. Don't know if I can find a new metering block. Maybe Atlas carburetor co. Thanks every one.

 

[Meep-Meep]

How are you measuring too much fuel flow? In order to do it right you will need a gas analyzer and check it under load. Gross effects can be felt with drivability but to dial it in you will need to put it on a dyno. A change of five jet sizes on a carb usually means you have the wrong carb or something else is wrong. Or put the Eddy 750 back on.

 

[Garys1969RR]

Well its easy to tell when the engine is running too rich. Or getting way too much fuel. It idles fine, but under partial tip in of throttle plates, like 3/8 open, it sputters and runs rough. Then when I open it up it tends to smooth out some what. Then going to a leaner mixture by eliminating the P/V enrichment circuit makes it smooth out all the way. So it seems to be way too much fuel going in. I like this carb better than the Eddy, just need to get it dialed in. Runs better wide open than the Eddy. Easier to work on, and jet. Still feel like theres a problem in the P/V enrichment circuit. Want to find out whats wrong with the carb.

 

[Garys1969RR]

I now think some previous owner may have enlarged the power valve fuel metering ports in the metering block. A Holley expert told me he has seen that happen more than once. This would flow too much fuel when the P/V opens. Will check it out and possibly change the primary metering block to one I know has the stock orifice size.

 

[RustyRatRod]

You're going in circles trying to solve a problem that you know what it is. It's dumping too much fuel into one venturi. Take a length of small wire and run it through the air bleeds on that venturi. It sounds like an air bleed is stopped up. COmmon problem on those old Holleys and will cause your malady. The jets and powervalve will not cause only one venturi to run rich. You need to concentrate on why that ONE side is doing it, instead of addressing the carburetor as a whole. You should get that malady cleared up and then see what you have for a vacuum signal. Here is Holley's instructions for choosing the correct power valve so you don't get some voodoo bad information.

http://holley.com/data/TechService/Technical/power_valves.pdf

 

[Garys1969RR]

Thanks RRR, It was hard to fathom that only 1 primary venturi was dumping excess fuel. Was'nt sure I was seeing it right. Difficult to see in there and rev the engine at same time! But thats what it looked like. So will check the air bleeds next, then proceed with vacumn reading and P/V choice. So you talking about the air bleeds on top of the carb near the booster? I can also take it apart and spray carb cleaner thru there to make sure it comes out the other side.

 

[RustyRatRod]

Thanks RRR, It was hard to fathom that only 1 primary venturi was dumping excess fuel. Was'nt sure I was seeing it right. Difficult to see in there and rev the engine at same time! But thats what it looked like. So will check the air bleeds next, then proceed with vacumn reading and P/V choice. So you talking about the air bleeds on top of the carb near the booster? I can also take it apart and spray carb cleaner thru there to make sure it comes out the other side.

That's right. You CAN spray something into them. It won't hurt. But, I've seen some so stopped up through the years that I had to run thin mechanic's wire through them. That's why you see on higher end holleys and other brands removeable air bleeds. That's why you see that change made, because stopped up or restricted air bleeds have made many a carburetor guru chunk one across the yard. So you can not only adjust the air bleeds but you can also remove them for cleaning. I would use the wire to make absolutely certain. It sure won't hurt the carburetor, but it will unblock the air bleed if something is there. ;)

 

[Garys1969RR]

Ok I will try that. The carb is pretty clean over all, but definitely could have an air bleed plugged. Wont be home to check it out till about the 31st of July. Thanks.

 

[RustyRatRod]

Ok I will try that. The carb is pretty clean over all, but definitely could have an air bleed plugged. Wont be home to check it out till about the 31st of July. Thanks.

I used to work at a local speed shop when I was a kid in school. That was back in the early 80s. You would not BELIEVE the number of new return Holleys we got back on a regular basis. I bet it was a 30% return rate. I've seen metal shavings get in the air bleeds of new carbs and make them run terribly. I'm not saying that's what it is....but certainly check for it. A lot of folks simply don't think about it.

 

[Garys1969RR]

Well found the problem, got to looking at the Power Valve Channel Restriction (PVCR) in the metering block, and it was very large compared to some other metering blocks I have from similar carbs. So I installed one with a much smaller Orifice, and it runs great now! Used same jets as before. I got this carb used, so no telling if a previous owner drilled them out, or swapped blocks. This restriction meters additional fuel to the main metering system when the power valve is open. Thanks everyone for helping me solve this Holley carb tuning problem!