OK, I am a factual guy, so I'll lay the groundwork first. 1953 BelAir, 235 Blue Flame, PowerGlide, 36K miles. Car sat for 30 years, and then was revived. Motor is bone stock, except for dual exhaust. Before getting it on the road, I replaced the following: - Converted to 12V - New Battery and cables - Carb re-built - New fuel Pump - fresh oil (a few changes) - Air Cleaner - Points/Condenser - Plugs - Wires - Cap - Rotor - leads to dizzy replaced - 2 fuel filters (1 before pump, 1 before carb) Car has run great for about 300 to 400 miles. Now when it gets hot (outside), it starts to misfire only under a load. Just a constant misfire under load, no backfire, no pops, fine at part throttle and while reving in neutral until very high RPM's. It's not overheating at all. Runs great when cold (er), in the morning. Any pointers?
If you put new points in 300 miles or so ago they probably need to be re-gapped. The rubbing block will wear real quick at first. Recheck your timing while your at it. If those items check o.k., pull a couple of plugs and take a look. They should be fairly clean, dry, and have a brownish color to them.
adjust the valves...maybe has not been done in 40 years You need to do it even if that's not what was wrong.
It occasionally has a really light lifter tap at hot idle....very light. Brand new Accel (sorry, forgot to add that tid-bit) Yes sir, they are Champion. I run NGK in everything else, but wanted to keep it OG on this car and went with champions. Checking plugs tomorrow, but wont the "running right" time clean off the "running poor" part? What is Factory Timing on this motor? It has exhaust and air cleaner, no other mods. Yeah, that's on the list, probably sooner more than later. I thought the Blue Flame valvetrains were maintainence free with the hydraulic lifters?
Just my two cents, but I had a similar problem on an old Chrysler and it turned out to be a cracked (hardly visible) distributor cap.
The timing mark is a ball about the size of a BB imbedded in the flywheel. When timed correctly, the ball will line up with the pointer that is in the bell housing hole, just above the starter. Check point gap first though (.018 I believe).
A find that its usually best to find out just what is missing. If you short out each cylinder separately at idle and watch a tach, one will usually drop more rpm than the others. That gives you your weak cylinder. If that isn't decisive, then set the brake, preferably with someone inside to hold the brakes, and short them out one at a time again. If you still don't have a weak cylinder, you'll have to chase electrical problems. If you find a weak cylinder, pull the plug , check it , then run a compression test. If your not pumping at least 100lbs, squirt some oil in the cylinder and try again. If it comes up you've got a ring problem, if not, you have a valve problem. If compression is fine and the plug isn't fouled, then check resistance on the plug wire. look for carbon tracking inside and outside the cap, check the points while your in there. As someone said, good looking plugs can be bad. try a spare. Have fun. Think like an engine.
Check your timing and put in a new fuel line. mine did that after sitting for 25 years and I just recently did all that except put in a new line and clean the tank. Did that and 600 miles later still runnin like a champ!
bdr1 said: I thought the Blue Flame valvetrains were maintainence free with the hydraulic lifters? Maintenance free in the 1953 world. Compared to mechanical lifters that you touch maybe every 5000 miles. It really would not hurt to adjust the valves after 57 years. Even thou this is not your problem. <!-- / message --><!-- sig -->
It's an Accel 8140 or 8145 (don't remember which one, but it is the correct one for the car). I will check the dwell tonight. I will check the gap, but that is roughly where I set it when I did points on it. This will be the tought part. It's only doing it under a load, on very hot days after it has been driven for some time. I cannot get it to misfire in the driveway. Isn't that the way it always goes?
I had a similar problem with mine a few years ago. Mine ran fine at idle and up to a certain RPM... when it got ready to shift gears (hydramatic) or under a load it would misfire. I did a complete tune up on it and rewired the distribtuor and the problem was still there. I had a spare distributor laying around and just changed them out and it fixed the problem. I believe it ended up being the distributor shaft wore on mine.
You don't say if the misfire is random or regular. Random could indicate a lean condition in the fuel department. Regular would be ignition.
If you're using typical universal type fuel filters,just use one,between the pump and carb. Sounds like a lean misfire under load,fuel pumps push better than they ****.And take off the carb top off ( Rochester)and check to be sure the power valve piston is free to move and the power vavle check ball and jet at the end of the "stand" is clean.Of course it could be ignition or typical case of 235 hydraulic lifters pumping up at low RPM's.
Sounds spark related. Coil and condenser will go bad as they heat up. Being new means squat to a condenser and a bad one will make you swear you have a fueling problem. They can and will fail at any time for no apparent reason. Put the old condenser in, see what happens. If that doesn't help, try the old coil. Are you running a coil with internal resistor? If not, do you have the external resistor? Shooting 12v. to the coil can kill it, sometimes rather quickly. Bill
Once it is warmed up, it seems pretty consistant. Now, again, this is only when it gets screaming hot out. FOr example, I drove around in it for a good part of saturday and it was 102 out. I was moving all the time, water temps were lower, and had no issues until I started to sit in traffic. I am running a filter before the pump because it killed a pump diaphram before and was dumping gas into the oil. I just left the one before the carb on. It's pretty simple to yank one off, so I can try that pretty easily.
I second the answer about the play in the distributor shaft (I had one do that). But, the heat issue makes me think the coil is breaking down under load.
I had the same problem on my 54 sedan 5 years ago. It was also a car that hadn't seen regular use in 30 years. I called Tom Langdon of Stovebolt 6 and got one of his converted electronic distributors. No points, 12V and 5 years plus 10K of maintenance free driving. Distributor issues sounds possible. My .02. Good luck.
When you converted to 12V the coil needs a resistor, so you feed the ignition wire through a resistor, this will keep the coil from overheating and breaking down, then you take a wire from the starter to the + of the coil ,this is called COLD START, the starter wire must be hot when cranking but be dead when not cranking. When an engine is cold it won't start without full 12v, the resistor prevents this, but the Cold Start wire from the starter will provide the shot of 12v to fire a cold engine and then shut off after the starter is disengaged. This is why early GM starters had the extra terminal on the sollenoid, one engaged the starter the other was the COLD START wire to the + of the coil. What you are describing sounds like a coil beraking down from overheating caused by too much voltage. You are running a 12v condenser, a 12v will work on a 6v system, but a 6v will not work on a 12v system.
So how did they ever start 6v cars? 6v engines will start when cold, but things get dicey when the temps get below zero. His car will never need 12v for starting. There is no such thing as a 12v condenser as all points systems operate on 6v. Coils with an internal resister are usually marked as 12v and cannot use an external resister. That means the system operates 100% of the time on 6v. Bill
Check the coil disconnected. Should have 3-4 ohms. A 0 ohm coil won't have enough resistance and will put to much heat at the points and cause misfire and excessive scaring. Is the coil really hot to the touch while running?
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