AT MY WITS END...NEED SOME HELP

Gene Fiore

Famous Member
I'm re-posting an original thread from the aluminum head section that I posted a few weeks ago. I recently switched from my 2bbl conversion log head to the aluminum head and intake using the same carb.

I have an update on how my setup is performing...and it's not all good. Here is the baseline for my Holly 500 2bbl which ran great btw on my log head.

Main jets: 73
Acc pump squirter: .031
Acc pump cam: brown on #1 hole
50cc pump( stock with the 500 Holley )
PVCR: .055 (I have the QF billet metering block which allows you to adjust the power valve channel restrictions).
Power valve: 65
Initial timing: 10 deg
Float level is good...right at the bottom of the threads while the engine is running

Car runs greats under light to medium acceleration both from a standing start and while cruising...very responsive and nice power. I put about 200 miles on it and when I checked the plugs they all looked like the day I installed them...white porcelain...no coloring. So I figured it's running a bit lean...no biggy. The real problem is at WOT acceleration...it falls flat on it's face and stalls! Here is what I have done so far with not much success.

All of the following tests are from a standing start. First thing I did was change main jets to 75 since I feel it is a bit lean...I also installed a new 65 powervalve just in case the old one was bad. WOT still stalls out but really didn't think that would have any affect. Next was to tackle the pvcr. Thinking it might be lean I installed .057 restrictor but was at least as bad as before...maybe worse. So I drastically went the other direction and installed .049 restrictor...better under 3/4 throttle acceleration...now it lays rubber and feels stronger but not great...WOT start the same...stalls out. Next I tried leaner yet on the pvcr to .047. No noticeable difference really...WOT start still stalls. Next I changed the acc pump squirter to .028. Seemed a bit better under 3/4 throttle start but WOT start the same.

UPDATE AS OF 1/20/2018:
So I thought now that I might just be getting too much pump shot so I purchased an accelerator pump cam assortment. Based on an article I had saved from fordsix I started changing the pump cams and making test runs.

The article said that the volume delivered for 10 strokes of the pump with a 50cc pump with the cam in the #1 position are:
white 17cc
blue 18cc
red 18.5cc
orange 19cc
black 19cc
green 24cc
pink 30cc
brown 36cc

So I started at the bottom and worked up. Since I already have the brown cam I started with pink and went up the list. I stopped at orange (only reason I tried this one is it had a wider cam surface very similar to the brown one that came on the carb). Each cam I tried had the same results...instant stall going to WOT from a standing start.

I'm questioning my technique for adjusting the acc pump since you need to do that each time you switch out the pump cam. Hold the throttle wide open and attempt to put a 15 thousands feeler guage between the pump lever and pump arm...adjust if necessary.

WHAT AM I MISSING OR OVERLOOKING??? I would really like to be able to use this carb as I have alot of money into it.
 
sorry no simple answer here,

What happens when accel is snapped in neutral manually under hood (no load) ?

Do you have a Vacuum gauge an it?. Idle and cruise vac normal ? , chasing a vac or porosity leak?, could accel be too RICH ?, - head flows so much better? , when all else fails, i'd first swap on another known good running carb ... .

(with the forced induction projects an AFR meter-gauge was only answer )



have fun
 
I ran into the same type of problem with my Aussie 250 2V headed 200. Seemed no matter what I did the thing would fall on its face with any load but run and idle fine. I replaced the carb with a new holley 350, changed jetting both directions. nothing cured the problem until I replace the MSD coil and MSD6LA, I even tested the MSD stuff as directed by MSD before I bought new. After changing those the thing ran perfect. dig into you ignition.
Walt
 
nothing cured the problem until I replace the MSD coil and MSD6LA,

Initial startup of the 250 Tri-Power was halting and prolonged due to a defective distributor - grounding only when turning... .
 
Gene, stick with the brown cam in the #1 position.
Install a 8.5 power valve.
Need to test what you have with a wideband A/F tester.
Also check fuel pump pressure & volume.
 
Hi, I know you probably checked this out but I keep going back to the accelerator pump.
Are you sure the weight is under the squirter, and can you see a good pump squirt at the end of the throttle opening.
Good luck
 
B RON CO":yzbjg7ig said:
Hi, I know you probably checked this out but I keep going back to the accelerator pump.
Are you sure the weight is under the squirter, and can you see a good pump squirt at the end of the throttle opening.
Good luck
Not sure...I'll have to check that out.
 
Gene, go with a .034" squirter & the 8.5 power valve. I would go with a pvcr .056-7 area.
With the aluminum head you can go with a little more initial advance. I would suggest a total of 32-34" total advance in by 2800 rpms. I don't know your total vacuum advance, but that is a final tuning deal. Bill
 
I wonder if the lack of heat in the intake manifold is part of the problem? At least, as I recall there is no heat (water) in the intake base under the carb on the AL head. Please correct me , if I am wrong.

My 4412 carb on my 200 cid engine has a #28 squirter on it. The engine does not like that : (bog) under heavy throttle from a stop. If I richen up the idle circuit a bit, then the bog is way less. The car makes your eyes water when it sits there and idles very long. LOL
 
I am thinking that the larger area of the ports and manifold is hurting your carb signal...Maybe try a 350 or a small four barrel with smaller primary's ...As said the cold manifold could be a contributor to the problem.
Ak Miller always said the turbo lag or simply lag is a fuel lag problem. and its not getting there the instant the engine needs it .
Would more base timing help , have to watch your total of course...My engine likes 20 degrees of base but it is a lot different that yours.
 
Go to a 8.5 power valve, that will bring in the enrichment circuit in sooner. You can always install a larger squiter.
 
Gene Fiore":251s0imw said:
Ive ordered an 8.5 pv and some larger acc pump squirters to try.
Good news! :D Got the parts and started doing some testing this morning. On Bill's suggestions, I went back to the original acc pump cam, installed an 8.5 power valve and .057 pvcr restrictors. I was previously running a .031 acc pump squirter and it was suggested to try a .034 (which I found is not available). So I purchased a .033, .035 and .037 squirter. Going first with the .033 results were much improved! No more stalling but still had a bog...great I am going in the right direction now! Next I changed to the .035 squirter but still had a slight bog. Changed to the .037 and very nice...no bog and peeled the tires pretty good. I still don't have a wide band to know where I am for sure but I am pretty happy at this point. Any further testing was curtailed by imminent rain here. I can still try some additional initial ignition timing to see how that affects it. My plan in the next month or so is to take it to the chassis dyno where I can check air fuel and hp. :beer: Thanks for everyone's suggestions!
 
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