mag rotor

Last night I made the first run of the year. launched motor felt like it had no power. popped out the exhaust on number 2. burnt the ground strap off the plug. found the magneto rotor the tip was bent back as if the little screw was loose. burnt the rotor into the plastic. there was no signs of the rotor hitting the cap. the cap looked perfectly fine. tried a new rotor new plugs. fired it ran for a very short time then shot out number 2 exhaust again. acting like the timing was retarded. im at a loss in which direction to go to try and fix this thing.

 

Is it a large cap mag? Maybe the rotor jumped out of phase.

 

ok so here is a little more info. I can give a little better run down of what happened. warmup went fine. on the first run, went through the burnout. the car launched very poorly with very little power. now I do not pull power away on the launch. 1.4 seconds in egt on number 2 was 1250 and by 2.5 seconds it was up at 1510. now my egts on my computer generally run about 1250 at the finish line. 2.7 seconds in it fire out of the exhaust. loud pop and the motor shut itself off. back to the pits we pulled the plugs, number 2 burned the ground strap off. then we pulled the mag cap and found the tip of the rotor twisted back as if the screw came loose and the tip has retarted itself by a lot. thinking we found the problem, we put new plugs in, new rotor. fired right up. ran about 10 seconds and backfired out of the exhaust again. we tried a new ignition box and tried it again. same thing. last thing we tried was bypassing the crank trigger going straight off of the mag. and it did the same thing.

moving to today. I pulled the head found number 2 cylinder with a crack in the piston and black soon on the head gasket between number 2 and 4.

this was my first run this year. did not change any of the wiring over the winter. the only thing I have changed is the 2 batteries from optima to rock racing batteries. I did some welding on the chassis but made sure I disconnected the grounds. or at least thought I disconnected them all.

will the cracked piston cause the backfire on number 2? will the ignition kill itself upon the backfire through the exhaust?

 

- missing
- popping
- piston damage
- head gasket

I think you might try looking for a lean problem like blocked injector, bad line etc.
The rotor may be a red herring that you only found because you were looking. I figure if there was a rotor problem you would see it in more cylinders - probably all of them
As normal - $.02

 

Any chance of water in your alky, from sitting over the off season?

 

I suppose that is possible. But the mag pointer came loose and was bent back way off where it should be. I imagine this caused timing to be fully retarded and finally back fired out of the exhaust. I do not have ground straps which i will be putting on now. May have been a grounding issue maybe? We tried firing it off the mag and was still popping with a new rotor.

 

2 other reasons that I've had engines pop out the exhaust are plug wires on wrong and a problem in the valvetrain.

I'd run the valves to see if something shows up.

 

after talking with my engine builder today, we think the number 2 cylinder was not getting any fuel. first thought was the port hose started collapsing. detonation caused the piston to crack, and the intake and exhaust valves are damaged. I pulled apart the hoses and check valve on the port side. the hoses all appear good to me. i opened the poppet and found small metal shavings coming apart inside the openings of it. i am guessing a piece of metal got inside the jet blocking off the fuel to number 2 causing a lean condition. the mag rotor caused the timing to be retarded to the point we were firing all cylinders out of the exhaust. just so happened number 2 got so lean it burnt up the valves and was leaking through the head gasket from 2 to 4. detonation caused backfire and the motor to shut itself off.

this is the way i am looking at it and understand it. let me know your thoughts if that makes sense or i am wording it improperly. Im always an ear to learn.

 

so I just pulled apart my port lines. it looks like the poppet inside the check valve has some metal pieces flaking off. im guessing this got in and blocked the port on number 2. I will be cleaning this all out and replacing the poppet.

 

i found my problem!!!! like an idiot it was something stupid. the fuel shutoff was only half open. the lever full open was only opening the valve half way. apparently the cable must have been loose and from moving it around while working on the car all winter, it must have changed. this caused a crack piston, leaking head gaskets, and quite a few valves that were replaced. could have been much worse. that you all for listening and I can be the dummy of the month. isn't the first, and wont be the last dumb thing I do that's for sure.

 

Put an over Center bracket on shut off at pump.