8ba engine tuning help needed

M

ModelTbucket

Junior Member
Here is some of the specs Model T bucket 3spd, banjo, less than 2000lbs.
8ba bored .125, edelbrock head with .055” clearance, kiwi l-100 cam, .060 shims under stock springs, .016 lash Fresh rebuild, sbc points distributor with 4° initial 18° mechanical (all in at 2200rpm) 6° vacuum advance. Blue streak points and condenser dwell set at 30°.echlin cap and rotor, suppression wires. New fuel pump shimmed to 2.5lb pressure, 2 Holley 94 with 51 jets and 3.5 pv. New battery. Ngk b6hs, set idle mixture to max rpm with vacuum gauge. Also installed blue accelerator pump diaphragms
I can not for the life of me get this thing to run right. Idles great, revs up great. Take it for a drive and it has hesitation at half throttle. If I pin it sounds like it’s missing no back fire or popping. Almost like a rev limiter. It will run at 75mph no problem. It will barely spin the tires in first.Pulled the timing cover and the dots on the gears line up at tdc. I looked at another timing gear I have and the dot on the cam gear is one tooth different. It was a matched sealed power set I put in. Here are the things I have tried
Stock distributor, stock distributor with pertronix, sbc distributor, solid core wires, suppression wires, .040 plug gap, .025 plug gap.
Here are my questions
The vent in the model cap is tiny 1/16” could that cause fuel starvation?
Can the timing marks on the cam gear be different from 2 different manufacturers?
How do I know the cam gear mark is right?
Will my wife leave me if I keep complaining about this motor?hahaha
 
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Couple of things, what coil are you running and on what voltage? How is the coil wired up, as in external resistor? If you really want to know what is going on with the cam timing you need to put a degree wheel on it and check it out. You posted checking the cam gear marks at TDC, how are you establishing TDC. Just some random thoughts.
 
I am running a blue bosch 00012 as per bubba’s recommendations. No ballist resistor. Full 12v to coil from ignition. TDC was marked on the pulley at rebuild and I also just checked it as per Bruce Lancaster’s interference stop. Put a zip tie in the spark plug hole turn engine till it stops then rotate 180 the other direction then split the difference between the marks.
 
Sounds good! I would put a degree wheel on the cam and check it out.
 
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If your initial timing is only 4 degrees thats to low I find low initial timing will cause the issue your having. The initial setting should be 10 to 12 degrees. The mechanical added advance then will need to be reduced so your total stays no more than 25 degrees. Try that.
Ronnieroadster
 
With my 4° initial and 6° vacuum, would I not be at 10°? I have a brass coloured bushing on the mechanical and 1 medium and 1 light spring.
 
ModelTbucket said:
With my 4° initial and 6° vacuum, would I not be at 10°? I have a brass coloured bushing on the mechanical and 1 medium and 1 light spring.
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No the initial is a set number figuring in the the vacuum is not correct. The additional advance added by the vacuum is added to the initial.
 
I usually run 2/4 degs Initial advance. Actually the initial advance isn't very important, and is only used to start the engine. However adding the vacuum advance will give you the right advance 10/12 degrees, apron acceleration the vacuum drops to near Zero but the mechanical will come in. I like 16/18 mech all in by 2k and 8 degs vacuum for a total of 26.28 in cruse. This works with most cam as well as the L-100. I always set my main jets for economy, and let the power valve take care of the power AF. Unfortunately this doesn't work very well with the 94/97 power systems. but is more tuneable with the Edelbrock carbs. I don't see much wrong with your present settings , but their not quit there yet. 51 jets are alittle rich for cruise but might be OK for power. An AF meter would solve most of your problems. I think your fuel pressure might be alittle low
 
Thanks for the help ronnieroadster. So if I have 10 initial I have to get a bigger bushing or put a set screw in to limit my mechanical even more as Iam at 18°. That would put me at 28° which I have read is way too high. Would you suggest leaving off the vacuum advance? What do you think the chances of the timing gear being stamped wrong? Should I get a degree wheel and pull the intake? I have no idea how to check that. I have the cam card but don’t know how to use it.
 
Thanks ol’ron. I have tried to read everything you posted on these gm distributors. I checked with a timing light and timing tape to get those exact numbers. Think I might start looking at the fuel side of things. Might need a bigger vent in that model T cap. I will pull the gaskets from the stand and increase my pressure to 3psi.
 
ModelTbucket said:
Thanks for the help ronnieroadster. So if I have 10 initial I have to get a bigger bushing or put a set screw in to limit my mechanical even more as Iam at 18°. That would put me at 28° which I have read is way too high. Would you suggest leaving off the vacuum advance? What do you think the chances of the timing gear being stamped wrong? Should I get a degree wheel and pull the intake? I have no idea how to check that. I have the cam card but don’t know how to use it.
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I have not found any issues so far with the cam gears but since you notice an issue with what you wrote then anything is possible. However until you see what the actual cam timing events are taking place theres no way of knowing. A while back i posted my findings on a Isky camshaft where the actual center line was advertised at 111 degrees however I found it was actulayy at 115 degrees so theres always the cam timing mystery not a simple fix on a flathead.
As I wrote my experience with a late inital timing point on a modified Flathead such as yours will cause a problem your experiencing but its also possible its fuel related. An easy test would be advance the distributor a little more and do a road test you dont need to reach high RPM to determine if advancing some will help. If theres no improvement then i would look elsewhere and of course that could be the fuel system. But no matter what you discover you will gain a lot of experience figuring this out which will always help you in the future.
Ronnieroadster
 
After setting the engine to TDC, I noticed my crank timing mark that is supposed to be 4°btdc is actually 4° after.
So if Iam suppose to be around 10° Iam currently close to 14° off.
I checked float levels this morning and they are good.
I will check the ball valve in the tank, the vent, and fuel pressure next
 
If you have air cleaners on the carbs, see how it runs without the air cleaners. If this fixes it . try some KN filters.
 
Flatjack9 I had the engine set at TDC. When I put the timing cover back on the pointer is at the TDC (I scribed 5° marks half way around the pulley) the original timing mark is past the pointer already. If I set it to the original timing mark I would be 4° retarded.

I have those cheap chrome air filters from speedway. I have heard they are pretty restrictive. When I take them off the rpm increases. I will try running it with some scoops I have.

Just checked compression and Iam at 150# on all cylinders.

Iam pull both carbs apart again. I will try some 4.5 PV (machines flat gasket surface) I watched the Charlie Prine rebuild videos. I noticed there is a spring under the accelerator pumps. None of the 94’s I have pulled apart had these
 
The numbers I mentioned are just a starting point and every engine is different. You can add or subract a few degs with the initial , or remove some from the vac. I like to run alot of advance in cruise, so I can run a lean mixture for better gas mileage. bIT!! you must have an accurate TDC mark
 
One thing I do is run a Chevy Harmonic balancer. Sometimes the lower pulleys line up when using a narrow belt. Unfortunately you have to make one for the wide belt/ ith the balancer you get a good degree marks up to 40. I broch a new Keyway to place the TDC mark in the stock location. I know this because I check the cams or just an accurate TDC mark. I f your gona spend allot of money on the build, then tuning is very important. Remember a rich mixture will ruin RINGS. Think cruise.
 
ModelTbucket said:
Flatjack9 I had the engine set at TDC. When I put the timing cover back on the pointer is at the TDC (I scribed 5° marks half way around the pulley) the original timing mark is past the pointer already. If I set it to the original timing mark I would be 4° retarded.

I have those cheap chrome air filters from speedway. I have heard they are pretty restrictive. When I take them off the rpm increases. I will try running it with some scoops I have.

Just checked compression and Iam at 150# on all cylinders.

Iam pull both carbs apart again. I will try some 4.5 PV (machines flat gasket surface) I watched the Charlie Prine rebuild videos. I noticed there is a spring under the accelerator pumps. None of the 94’s I have pulled apart had these
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How did you determine TDC?
 
If your TDC is correct. Maybe some slippage. Always a thing to check on the couple yrs later yblocks cranks. Not that I want to go on about vacuum retard dizzies with mechanical assist. Been covered over and above.



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Flatjack9 in my second post I explain that I made a mark on the pulley at rebuild and I also did an interference check with a zip tie. Then split the difference with micrometers and it was the same as my original mark.
 
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