formulaF302

I don't know if those carbs I sold you guys woulda had those stumbles or not on a hard take off....at the time I was running props that would broke loose on a hard take off...so all of my takeoffs were rather slow events with the tabs all the way down with twin engines. The electric fuel pumps that came with those cargs were only abut 3 1/2 lbs as I recall though in case that helps you at all... Glenn

Madmax

Forgot to write back in, Glenn........ I got the stumble cleared up by moving the pump cam to the first hole. That took care of it. Runs perrrrrrrrfect now. Still dialing in jetting tho. Does anybody know, if the primarys and secondarys both have power valves, should they be jetted evenly? I'm at 82's all around, and it seems to run pretty terrific, just didn't know if the secondary's should be richer than the primary's? I'm gonna try and play with it more this week.

Thanks Glenn........cured my problems.! Now if Badhabit can get his fixed...

BAD-HABIT

Yea they have power valves front and rear....Stock they are the 6.5's....I think that most times jetting is higher in the rears.....

BH

Bulldog

When you dump the sticks, the throttles open and your vacuum falls to almost atmospheric. The idle and main jet circuits will almost completely stop flowing fuel. At this point the accelerator pump and power valve are what lets the motor accelerate.

The larger accelerator pump squirters will allow more fuel to flow. You can fine tune this with the various pump cams, but you have to have enough flow through the squirters first or it will always be lean.

The accelerator pump can only deliver fuel for a short period of time, then runs out. Hopefully, by the time the pump runs out, the motor is pulling enough vacuum to establish flow through the main jets. The 50 CC pump will maintain a larger flow volume and for a longer period of time, but will also run out eventually.

The power valve is there in case the engine is heavily loaded- the vacuum will be lower that for a normal running condition. The power valve opens at a specific vacuum level, and stays open until vacuum returns to normal. The number on a Holley power valve indicates the point at which it opens- I think a 6.5 will start to open at about 13 lbs vacuum.

I would first verify that the main jets are approximately correct, check the pump squirter nozzles for size number and operation. and the power valve does not leak by applying a vacuum (haha)

If it stumbles during the acceleration only, and the main jets are even close to correct, it is probably the nozzles. They are cheap and are right at the top of the carb, next to the air filter screw hole. Be careful not to drop it, and watch for a small seal underneath. I have gotten away without that seal so don't worry if it's not there. I would buy the next 2 sizes larger than the one you have.

See if there is a 4 digit 'list' number stamped in the air horn area- for example 8410, and post it. Holley has a listing of these with all factory jets, nozzles, etc that the carb was built with.

Good luck!
Bulldog aka Ronnie

Madmax

That's kinda the problem.........the squirters aren't adjustable on the 4010 Holley.......

BAD-HABIT

Yeah this is the downside of these carbs I think. Outherwise I think its a GREAT carb. I think you can drill the shooters out if need be........Ive got a couple of books that describe the procedure.

BH

richard

do you have a adjustable fuel pressure regulator by any chance? If so could it have slowly adjusted through engine vibrations?

I would also change the fuel filter, and check the pump diaphram if its got one +clean out fuel lines.

Silicone gasket sealer is what I would use, as its compressible and formes a good seal.

Everything else I can currently think of has been said.

BAD-HABIT

No regulator....Fuel filter/seperator changed,pump diaphram changed(new fuel pump) and fuel lines cleaned out...........Still working on the stumble.

BH

richard

Did you check fuel flow? I read that fuel pressure can be fine but flow still bad.

Can you post a pic of where you think the leak is, and have you tried surfacing the mainfold with a flat file, as this works quite well and doesnt require expensive machining. Move the file forward and sidwards at the same time to achieve a perfect flat. then file again but at a 90% angle across the previous filed grain, and repeat till no low spots are present. they are visible as areas which dont catch the file.

Have you siliconed the manifold as yet?

kmm4951

Recall that there may be a filter (sock) and/or a check valve in the fuel tank. Sometimes these get partially plugged and may cause these symptoms when you need the fuel most.

KM