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Old 05-23-2010, 06:56 PM   #1
F1 Flathead
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Default Holly 94 jet recommendation for a flathead running open exhaust?

I'm running a mostly stock 40 Merc flathead with a mild cam in my 29 roadster. I'm running stock exhast manifolds with a just a short, 3 foot open pipe on each side. The engine missfires at high rpm. I've gone through the ignition and am now thinking I need to richen up the jets a bit. Can someone recommend a jet number for me? Also, I'm just running the holly powervalve that comes in the standard kit. I remember reading that it is not really correct. I've forgotten which of you has the proper powervalve available for that carb. Can you let me know? I know this was all available on the old Fordbarn but I didn't find anything when I searched this new setup.
Thanks guys!
Dan
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Old 05-23-2010, 07:31 PM   #2
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

As for the power valve, try a 5.5. The kits come with a 7.5. Ken ct. has a "drop in" pv, but if you don't mind grinding a little on the inside of the fuel bowl, you can use a modern Holley pv.
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Old 05-23-2010, 10:06 PM   #3
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

Most Holley 94's I've taken apart have #51 jets.
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Old 05-23-2010, 10:50 PM   #4
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

You say you have gone through the ignition. What exactly did you do?
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Old 05-24-2010, 06:56 AM   #5
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

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You say you have gone through the ignition. What exactly did you do?
I'm running a "diver helmet" dist. I took it off, cleaned and lubed it, got the vacuum break operating, installed and gapped new points. It would run reasonable well until the coil would heat up and then begin to run very poorly. I made my own coil adapter out of the coil base and installed a remote Echlin 6 volt coil and matching condenser. That took care of 90% of the symptoms. It now runs strong to high rpms and does not get worse as it warms up. In fact, it gets better. it just missfires some. My theory is that I am running borderline lean because of the open pipes (which tend to lean out an engine). I'm planning to get some jets and begin richening the mixture to see what effect it has. I was just hoping that one of you could say "been there, done that, start with a number whatever jet". I haven't completely ruled out ignition trouble. I really have only set the timing by feel, as I usually do on my engines. I set the base timing by vacuum level and then backed the vacuum break all the way out and still don't have any knock, so I'm thinking I can't be too far off. This winter I will pull the dist. and get it curved but don't want to leave the car down now since I am having loads of fun driving it.
Thanks,
Dan
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Old 05-24-2010, 06:59 AM   #6
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

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Originally Posted by 1952henry View Post
As for the power valve, try a 5.5. The kits come with a 7.5. Ken ct. has a "drop in" pv, but if you don't mind grinding a little on the inside of the fuel bowl, you can use a modern Holley pv.
Can you point me to the procedure for grinding the bowl to use a modern pv? That sounds like the procedure for me since I am a cheap bastard and never want to pay for anything I can do myself. I know I have seen it before on Fordbarn or somewhere but don't know how to find it now.
Thanks,
Dan
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Old 05-24-2010, 07:16 AM   #7
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

You don't need to grind the bowl or turn the bottom of the power valve as some have suggested. You need the right gasket. The gasket that comes with a Holley Performance valve is triangular shaped and don't seal on the old carbs. You need a gasket the fits snug on the power valve threads and is about .080 to .090 thick and is not bothered by fuel and has some give to it so it shapes to the power valve and seat as it is tightened. I have used a 100 of them and never have any leaking problem. Try some Marvel Mystery oil down both sides of the carb when it is running and a 1/2 quart in the fuel tank the first treatment and 1/2 pint with every fill up. This new fuel causes sticky valves. The distributor needs to be set on a strobe machine, feeler gauges don't work. G.M.
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Old 05-24-2010, 07:31 AM   #8
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

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You don't need to grind the bowl or turn the bottom of the power valve as some have suggested. You need the right gasket. The gasket that comes with a Holley Performance valve is triangular shaped and don't seal on the old carbs. You need a gasket the fits snug on the power valve threads and is about .080 to .090 thick and is not bothered by fuel and has some give to it so it shapes to the power valve and seat as it is tightened. I have used a 100 of them and never have any leaking problem. Try some Marvel Mystery oil down both sides of the carb when it is running and a 1/2 quart in the fuel tank the first treatment and 1/2 pint with every fill up. This new fuel causes sticky valves. The distributor needs to be set on a strobe machine, feeler gauges don't work. G.M.
GM, I like the gasket idea. I admit I was mystified by the triangular gasket that came with the kit. I think I reused the one that was on the carb instead. I'm not sure I know what I'm trying to seal from your describtion. The flange (hat brim) of the valve should be sealed tight to the carb body, right? I will try some MM oil. I do think that sticky valves is a real possibility on this motor. It was rebuilt in the 70s and then sat for most of the time until I bought it a few years back. All I did was change the oil and and give it a fresh coat of paint. Here's a clip of it starting for the first time. I'm the dorky looking guy who didn't bother to change out of his work (office) clothes before heading to the garage after work.
https://www.youtube.com/watch?v=UpGQa0SjPNg
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Old 05-24-2010, 07:32 AM   #9
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

Not sure your on the lean side,could be too rich.I have the 5.5 PV with the correct gasket. 7.5 open too quick. I have bigger jets but dont think thats your problem.I would run .050 in it.ken ct. 1-203-260-5945 or igadore@sbcglobal.net.
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Old 05-24-2010, 07:55 AM   #10
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

Quote:
Originally Posted by G.M. View Post
You don't need to grind the bowl or turn the bottom of the power valve as some have suggested. You need the right gasket. The gasket that comes with a Holley Performance valve is triangular shaped and don't seal on the old carbs. You need a gasket the fits snug on the power valve threads and is about .080 to .090 thick and is not bothered by fuel and has some give to it so it shapes to the power valve and seat as it is tightened. I have used a 100 of them and never have any leaking problem. Try some Marvel Mystery oil down both sides of the carb when it is running and a 1/2 quart in the fuel tank the first treatment and 1/2 pint with every fill up. This new fuel causes sticky valves. The distributor needs to be set on a strobe machine, feeler gauges don't work. G.M.
Yes GM, you do. Your information is false. If he was to buy a HOLLEY power valve, as "some" suggested, the brass spring retainer at the top is TOO big to fit in the fuel bowl well. It WILL bind against the bowl and the valve will NOT work.

Following your advice, a fellow could buy an aforementioned power valve, get the "right" gasket, and not know why his carb isn't working. And no, MMO would not free this valve up.
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Last edited by 1952henry; 05-24-2010 at 08:18 AM.
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Old 05-24-2010, 08:06 AM   #11
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

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Originally Posted by 1952henry View Post
Yes GM, you do. You information is misleading. If he was to buy a HOLLEY power valve, as "some" suggested, the brass spring retainer at the top is TOO big to fit in the fuel bowl well. It WILL bind against the bowl and the valve will NOT work.
So I need to check the fit of the brass spring retainer to the float bowl and open the hole up a bit if it is binding, correct?
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Old 05-24-2010, 08:16 AM   #12
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

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So I need to check the fit of the brass spring retainer to the float bowl and open the hole up a bit if it is binding, correct?
Yes, if you buy a modern Holley power valve. Remove the airhorn and watch as you screw the Holley power valve in. Almost right away you will see the brass retainer make contact with the well. If you screw it in tight, you will not be able to push it down like you should be able to. I use a carbide Dremel bit to remove some material, then try again. It doesn't take much, and you have plenty of "wall" to work with.

For gaskets, I like to use viton square-shouldered o-rings. They aren't bothered by fuel, offer a great "crush" (sealing), work with either the older-style pvs, or the new Holleys with their odd gasket surface.

IF, you do use a Holley that requires grinding, be careful to cover up the jets and thoroughly rinse out the bowl. You don't want any chips getting into the plumbing.
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Old 05-24-2010, 08:31 AM   #13
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

I wouldn't bother with the grinding crap.Buy the proper PV and gasket.Also all MJ's marked .051 dont even mike out to .051. there in the range of .048-.049. they use a diff measuring system than strom ones which are exact size of the hole. ken ct.
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Old 05-24-2010, 08:35 AM   #14
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

I will check this out ASAP. If my power valve is not able to open, that would exactly explain the issue I am experiencing. After I fix this issue, I may move to a second problem of my powervalve opening too soon due to the reduced vacuum levels with my cam so I think I'll make the jump to the 5.5 PV at the same time. Thanks for the help. I'll post some feedback just as soon as I can check this out.
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Old 05-25-2010, 06:38 AM   #15
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

Here's an update on this issue. I pulled the carb apart last night. It has .051 jets as predicted. The power-valve is the correct style in that it does not interfere with the carb body, but it is not labeled other than it is stamped "Keller". It appears to function properly. It is normally open and closes when I apply vacuum, although I can't tell exactly when it is closing. I think I'm back to square one since this valve appears to be doing it's job. I've got another carb I can throw on just as a test. Other than that, does anyone have any suggestions?
Thanks,
Dan
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Old 05-25-2010, 07:08 AM   #16
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

About 75% of the carb related misfiring can be traced to the ignition system.
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Old 05-25-2010, 07:20 AM   #17
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

JWL is correct, sounds like ign. maybe points are floating a high rpm's ?
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Old 05-25-2010, 07:51 AM   #18
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

F1, The Holley Performance power valves work better then the stock type valves. The stock valves have generic springs and open at differant vacume values then marked. The Performance valves are adjusted after they are assembled opening at exactly where they are marked. They are also manufactured recently with modern materials not some barrel of valves that was found sitting in a warehouse for 40 years. I did fail to mention that the round adjustment nut on the top of the valve is a little larger in diameter and the flat spot above the threads in the bowl must have a few thousanths of material removed with a die grinder to clear. There is close to 3/16" of material there so it don't hurt anything. And Henry the right gasket does seal the valves and these valves have a much longer life then the stock valves. I have never had to replace one in over 15 years. G.M.
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Old 05-25-2010, 08:26 AM   #19
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

GM, thanks for the detail on the powervalve. I will pick up a 5.5 Holley and make the modifications so it fits. The one in there now is an unknown so I need to replace it.
JWL and jdl, I think some new points is a good next step. It's been a while since I put this pair in and I can't swear as to their origin. I might have filed a used set and reused them, since I'm a cheap bastard, as previously mentioned. I picked up a set of Echlins from NAPA and will but them in to answer the point bounce issue. It sure could be that. I've been putting off installing them because I have to pull my radiator to get at them with that darned "diver's helmet" dist. and I've been too lazy to tackle it.
Thanks for all the good advice. I'll keep you posted.
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Old 05-25-2010, 08:59 AM   #20
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Default Re: Holly 94 jet recommendation for a flathead running open exhaust?

Boy lazy and cheap what a combo.You dont have to modify my power valves they fit right out of the box and have the correct gasket nor grind the bodys to fit. Also carry American made points but as you say your a cheap bastard who dosn.t take anyones advice anyway. ken ct. Do as you wish/ good luck
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