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TR2/3/3A Missfire and Backfire
- Thread starter Ken H
- Start date
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When my misfiring problem began several years ago, I tore the distributor down and cleaned and lubricated everything. It seemed in good condition considering it's the original distributor. At that time, I was convinced that the problem was in the distributor, so I found an advance curve for Lucas distributors and bought a set of springs to "calibrate" my distributor to match the original manufacturer's specs. I never got it perfect, but it wasn't bad. Eventually I replaced it with a Pertronix electronic distributor which was slightly better, but not the performance the engine should have. I retired, moved, and the car sat for a few years with me starting it once or twice a month. Now I have the original distributor back in the car and trying to debug the problem I've had for years.
Thanks for your help. I started at 15 flats and after warming used the "lift the piston" method which eventually took me to the 18 and 15 flat combination. That made me wonder if the needle was correct. When I tried to lean the carbs, I reached a point when the engine suddenly stopped firing and stalled. I was idling around 600 rpm. I like to idle at 450 when adjusting carbs, but the engine was rough when below 600.
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Hi Charlie, This morning I checked the fuel pump flow again and it's ok. I rechecked the jet centering and they were ok. I opened the jets with SM needles to 12 flats and the engine would only run with the choke pulled. I opened the jets one flat at a time and finally got the engine to run around 800 rpm with the jets opened 18 flats. Using the lift method per the manual, the engine ran it's best at 20 flats. It still idled around 600-700 rpm with some misfiring. The engine hunted back and forth between 600 and 700 rpm which makes me wonder what is changing causing the hunting? Distributor?
Yes. I have two coils that I've been swapping. Both are fairly new. Resistance measurements are ok.
Visually, all valves are opening and closing and appear to have full travel. Right now, the valves are set at .012 rather than .010 and .012. This was at the recommendation of someone in the forum. What symptoms would a flat lobe create? Will measuring valve travel with a drop dial indicator provide useful information?
I checked for arching today and everything was ok.
With a flat lobe the valve will not open not correctly or even at all. In this case the valve can be adjusted as normal because the valve will always be up and close. The problem happens because the spring does not compress and open the valve for fuel to get in.
When I have a problem like you have, I pull the plugs often and try to see something on the plugs that might be happening. Sometimes if the plugs are too clean there is no gas going to that plug or those cylinders. I had a clog in a float bowl chamber once that turned out to be a piece of the rubber seal had came lose worked its way into carb and blocked off fuel getting from the float bowl to the body of the carb. There is a 2 inch long by about 3/16 round hole in the base of the carb body that feeds fuel to the jet. When that plugged the spark plugs looked new because there was no fuel and the engine would idle, but not receive enough fuel to have any power.
Do you have a different distributor you can try.
steve
When I have a problem like you have, I pull the plugs often and try to see something on the plugs that might be happening. Sometimes if the plugs are too clean there is no gas going to that plug or those cylinders. I had a clog in a float bowl chamber once that turned out to be a piece of the rubber seal had came lose worked its way into carb and blocked off fuel getting from the float bowl to the body of the carb. There is a 2 inch long by about 3/16 round hole in the base of the carb body that feeds fuel to the jet. When that plugged the spark plugs looked new because there was no fuel and the engine would idle, but not receive enough fuel to have any power.
Do you have a different distributor you can try.
steve
I have a new condenser and the float levels are good.
The plugs are new and I haven't been able to run the engine enough to really get it hot (other than at idle) When I start it, I have to leave the choke on for about five minutes to keep it from stalling. After that, it runs ten minutes while I adjust carbs and timing. After cool down, the plugs have a light coating of black soot. I don't know if the black soot under those conditions tells me anything. I don't have another distributor to try. I ordered a new timing light so I can measure spark advance with changes in rpm to see if the distributor is advancing smoothly and matches original distributor advance curves. I can measure valve lift with a drop dial, but don't know how much lift I should be getting on a good cam. Do you have any information about valve lift with a stock cam?
When I cleaned the carbs about six months ago, I ran wires down all the passageways to make sure they were clear. I think it's good, but you never know what can happen. I wonder if I can watch mist coming from the jets at idle with a borescope camera.
They are now. About a month ago, I was convinced the carbs were running rich and it turned out to be one of the jets was sticking open in the choked position. That prompted me to tear down the carbs and replace jets, needles, and cork gaskets with neoprene o rings Moss sells. Since then the jets fully return.
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I've been lurking for a while and finally decided to join the thread.
My immediate reaction, on reading the initial post, was valve timing. I agree with Graham on that. It's difficult to check this without a degree wheel. One thing you might try--and I don't know for sure if this will work--measure the amount that the #1 valves are open at TDC on the exhaust stroke. They should be the same. The intake valve will be opening and the exhaust closing, but at that point they should be the same distance from fully closed. Be sure to approach this point turning the engine CW as seen from the front.
Another possibility: adjusting the carbs should be done with the engine fully hot. Just warming it up in the driveway generally is not enough. But, I suspect that would leave it too rich, and the popping indicates a lean mixture.
My immediate reaction, on reading the initial post, was valve timing. I agree with Graham on that. It's difficult to check this without a degree wheel. One thing you might try--and I don't know for sure if this will work--measure the amount that the #1 valves are open at TDC on the exhaust stroke. They should be the same. The intake valve will be opening and the exhaust closing, but at that point they should be the same distance from fully closed. Be sure to approach this point turning the engine CW as seen from the front.
Another possibility: adjusting the carbs should be done with the engine fully hot. Just warming it up in the driveway generally is not enough. But, I suspect that would leave it too rich, and the popping indicates a lean mixture.
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