You all may remember my last flathead problem thread http://www.jalopyjournal.com/forum/...nown-reason-help.1023625/page-3#post-11591673 Well...I have a new issue I need some help with. Flathead runs great, idles smooth, blah, blah, blah. However, upon moderate to heavy throttle under LOAD (driving) it will break up badly. This started off very mild and has slowly and progressively gotten worse over the past few weeks. Upon slow and gradual acceleration, no problems. Cruising speed at 50-70 MPH no problem. Step on it and it breaks up something fierce. Evens out a bit once the load on engine gets lighter as car speeds up, but still breaks up a bit even though getting smoother as car accelerates and load on engine decreases. Plugs good, ignition wires good, coil new and good. Cap, rotor points, etc. good. Dizzy timing set on Sun machine. I'm thinking it may be a faulty vacuum brake on the crab distributor. Not exactly sure what the vacuum brake does. Does it stop the breaker plater from moving and advancing the spark under high vacuum (idle) and allow the breaker plate to advance the timing under low vacuum (acceleration)? If so, would a faulty vacuum brake (stuck in the "on" position preventing breaker plate ignition advance) be the cause of the above issues? Or does anybody else have any ideas? I strongly believe this to be an ignition issue as my carbs and fuel delivery system are spot on. This is why I am asking about how the vacuum brake on a crab dizzy works. I'm new to flatheads so I'm kinda glad to have some small issues to work out to learn from but need help on this. Thanks, Andy
I'm not well versed in that distributor so I found this http://www.vanpeltsales.com/FH_web/flathead_engines_distr-timing.htm I'd be looking at the low/mid speed circuit in the carb along with the accelerator pump circuit. And checking the fuel line for kinks or other restrictions. I had a rig back in the 70's with a pretty hot engine in it that flat fell on it's face about half way across an intersection when you nailed it hard. Let off the gas and it would pick up and go again and then stall out but once you got to the speed limit on the highway it would cruise right along for miles on end. Finally took the time to figure out the problem and it ended up being a brass fitting intended for natural gas in the fuel line to the dual carbs. It caused such a restriction that the engine ran out of gas on hard acceleration .
Hey Andy, I'm not sure what you got going on but if it's just when you step on it, could it maybe your power valves in the carbs. You say it's ok with easy gas pedal but breaks up when you step on it. Do you know what size jets and power valves you have in your carbs. If they are 97s the standard should be .045 jets and 65 power valve. From there you can fine tune your carbs. When you step on it and the power valves kick in, they can be to big "ie" too rich or too small "ie" too lean. If you can maybe hook up a volt meter in the battery that you can read from inside the car and take it for a spin. Step in it as you read the volts and see if it drops a lot under load. If the volts go higher than you know it's not a bad battery as a bad battery can send you in a wild goose chase. Good luck and let up know what's going on.
Just put a mercury flathead in a dragster chassis..fired right up ran mint until I tried to rev it up..pulled carb apart no difference new wire's to points same.ended up being the condenser I put in was bad put an old one in that I had runs mint...good luck with it
Same here on the condenser, brand new out of the box. Started acting up, degraded in a hurry. Old one fixed her right up!
Power valves new. Any info on the vacuum brake? Carbs are 94's. Remember it was running fine and this problem began to emerge slowly and now progressively getting worse. I do not believe to be a fuel problem. Pressure gauge at carb reads good and changing the fuel pressure at the regulator does not change the problem at all. New fuel lines so no kinks or restrictions. I still believe the problem is spark so I will change out the condenser even though I don't think that's it. It's an old good American condenser that I have changed out before trying to hunt down previous issues. I was kind of hoping on some insight on if a faulty vacuum brake might be the problem causing this issue. Anybody got some info on that?
The vacuum brake slows advance when accelerating. Vacuum keeps the piston away form the breaker plate. As vacuum drops when you open the throttle, a spring forces the vacuum brake piston to contact the plate and stop it from advancing. I don't think it is your problem.
....different animals,different functions....and I throw in one more vote for a bad condenser,...they are pure junk today....
Also, if you're 12 volt now, check the polarity of the coil. 12V negative ground setup means the wire from the coil to the distributor should be coming from the negative terminal of the coil. If you're still 6 volt and using a regular can type six volt coil, you'd be using the positive terminal on the coil for the wire to the distributor. Also, these coils do not require any sort of resister in the power line to the coil. The other suggestions above are all good as well.
So if you have a can type coil on your 6 volt pos earth early ford you do not have tor run power thru a resistor.???
I'm pretty sure it will say on the coil itself run with external resistor, or it will say do not use external resistor, as some coils have a built in resistor.
Adjusting the vacuum brake will be for eliminating ping. Not sure if adjusted too far in it would cause your stumble? Is the adjusting bolt pretty far down?
It's definitely not a ping. It's a stumble for sure. Coil is set up properly. Remember, this happened on an existing well running and driving vehicle. Anybody else? Thanks, Andy
As others have said, not the vacuum brake. You could hot wire from bat to coil to eliminate resistance/shorts/opens in the wiring or switch. And check grounds.
Had a flatty cut out like that two separate times. Once it was the condenser. The other, the choke closed partially during acceleration. Also what are you using for filters?? Even the expensive ones inhibit air flow. I use nylon stocking material. I too don't believe you have advance problems.
Don't rule out rotor or cap. Have you tried with new or known good ones from another car? Had problems with both before now, gave similar symptoms. Mart.
Not condensor, switched it out. No change. Not air filters, took them off. No change. Car has sat for a few days and last night problem seemed to actually be a little worse. Now upon hard acceleration, it doesn't just break up and stumble, but also seems to bog so I'm going to look at fuel delivery as a problem as per Bubba, but as "three window" said above, 90 % of carb problems are ignition. Andy
have you checked fuel pump pushrod length....and wear in pump including valves diaphram and lever pivot /spring ?
Shot in the dark here but have you done a load test on the battery. Maybe your battery has a dead cell.
Or just change out battery with a different one and see what happens. If your car is 12v you can always hook up a jumper box and see if that helps. Iv had brand new battery drop a cell in the first 20 mins in use. Drive you crazy and have you spinning gears trying to figure out what's wrong and it's just a junk battery. Hook up a volt meter to the battery and hit the throttle. See if the volts stay up high or if they fall way off. Good luck I hope you get it nailed down ASAP.
Tried some things last night late and did a couple of test drives. Car has sat for a couple days previous due to disgust at situation . The stumble has now progressed to be a definite bog upon stomping on the pedal. Leads me to think "fuel". Thinking the progressive nature of the problem may just be a progressively clogging fuel filter. Will change it out tomorrow and let y'all know what that does. Andy
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