why would you suggest to pay $300-$500 to tune out an "engine stumbling" issue. you think it would take someone that knows what they are doing 3-5 hours to find the problem...
Not at all and I suggested it because this engine surely has more tuning issues than just a simple stumble. Unless there's a banana stuffed into the tailpipe or a rag hiding inside the intake manifold?.. this is fuel and/or ignition related. Plus, who takes their car to a chassis dyno just to fix a stumbling issue and then decides not to tune for better performance while it's all strapped down? Have to spend the time or the money, Frank. And most spend so much time trying to save money that it ends up costing them far more of both in the long run.
There is an "older" guy nearby that builds old school race engines and also is a wiz with Ford flatheads. I'll be contacting him shortly. I'm with you on the modern day mechanics. They rely on a plug and play computer to (maybe) figure out what's wrong with your vehicle.
Wolf, How did this shake out? I think I have a similar problem... idles high in park, once in drive it's fine until I really give it some gas... then gets sluggish and stalled once. Just put in new performer intake, edelbrock 600 cfm carb, pertronix coil and distributor, champion 3 core radiator and DT shorty headers and exhaust. I set initial timing to 10, air and fuel screw were all the way in and backed out 2 1/2 turns. Waiting for vacuume gauge and timing light with tach to arrive so I can learn how to tune it. But does not like it when I really give it gas. Actually stalled out on me and had to hold gas pedal in for it to start... like it was flooded. As soon as I would throw it in gear she would die again.
What would you suggest as a starting point? I was getting a backfire with factory settings, 2 1/2 turns seemed to fix that. I am also plugging the vacuume advance hose on the distributor when I set initial timing... I then hook it up to driverside of carb since I don't have any emission stuff on it.
Sounds exactly like the issue I had. I set the mixture screws by sound of the motor at idle until I got the "sweet spot", then adjusted the idle to around 600 rpm. Installed a 1/2 inch spacer under the carb and then repeated the process. Runs and starts better. Like you, I had the same issue with after running it for a while, acting like it was flooded when trying to re-start. It still needs a little tweeking to get it perfect, but much better than it was for sure. Still looking for answers.
Check your float level as well. Also, stalling when giving it gas could be an accelerator pump adjustment. Work the throttle with the car off while looking in the carb. You should see a squirt of fuel. If it is delayed, adjust the arm.
First off you'll need WAAAAAYYYYYYYYYY MORE(yeah.. a LOT) initial timing at idle. Manifold vacuum is what the carb wants and needs. You can NEVER have too much metering signal for a carb setup. Sometimes fuel curve just needs to be recalibrated to better match that stronger signal. Trick is to implement a HIGHER initial base timing setiing with vac advance pot hooked to full manifold vacuum for improving idle/light cruise(achieves higher cylinder pressure/manifold vacuum). BUT.. you have to try and do this without allowing your peak ignition advance #'s to spiral out of control in the high speed cruise ranges as the mechanical advance comes in heavier or reaches "all in @2,xxx rpm". Otherwise you'll end up with too much timing in certain portions of the powerband. Only way to sneak up on a more idealized tune with this particular parts combo is to adjust and minimize the vac pots level of supplementation by tightening it's internal diaphragm return spring with an allen wrench(5/32?) till it doesn't allow much more than 8-12° of vac assist. As a result manifold vacuum will rise drastically(often 3-5".. sometimes more with bigger cams) and the carb will begin metering properly from idle on up into the transition circuits and main metering. Higher idle/light cruise manifold vacuum levels improves the carbs signal strength and allows it to function more efficiently even if the factory calibration isn't perfect(and it rarely is). Very forgiving devices so long as everything's not too far off at the same time but inadequate spark timing lead is extremely important to getting the party started and on the right track. Get that sorted out and then you'll need to shorten up the mechanical sweep by a fairly large amount just to allow all that extra initial base timing into this mix. Here's a safer base tune for both of you to strive towards. Have to make some quick assumptions based on cams and gear ratios so I will keep it safer to reach across wider engine combo's/drivetrain variables. ........base/initial timing should be around 20°(even more if you can limit the mechanical advance sweeps contribution down closer to an idealized 10-12°) ........mechanical sweep should be around 10-16° and all in by about 2,800 rpm(lighter cars generally don't need longer delayed curves like heavier cars to avoid detonation) .......vac pot should be nearly fully tightened(careful not to over crank on that tiny little allen screw/return spring.. go till barely seated/snug and back off 1/4 turn or so) to reduce contribution levels down around 8-12° example @WOT; 22° initial + 16° mechanical @2,800 rpm = 38° total advance example @steady state; 22° initial + 16° mechanical + 8° vac assist = 46° cruise advance The next problem you will likely run into around 44° at idle and/or light cruise is the carb leaning out. Idle will begin to crackle like little rice crispies inside the carbs venturi and light throttle/steady state cruise may even begin to surge and you'll see related fluctuations/manifold vacuum losses on a vac gauge too. You will need to enrichen the idle and light cruise portions of the carbs metering.. or just forego the vac advance pots connection altogether and lose out on some added efficiency like 99% of the other people driving around you. another simple tuning option. Hook a handheld vac pump to the distributors vac advance pot with a long hose and fiddle with ignition lead while driving at various throttle transitions and also steady state speeds. It's kinda cool the first few times you try it, the hand pump can sometimes act like a secondary throttle and surge the car forward as you add timing with the diaphragm during steady state cruise. If you have a vac gauge hooked up to full manifold vacuum you will see the correlation to heavier ignition leads affect on manifold vacuum production.
If you are able to make this engine backfire with the mixture screws?.. you are WAY OFF on your ignition tune. And I seriously mean.. WAY off.
