Giving up on my 380!!!!

[Craighjr]

Am I thinking about the timing wrong? I am using 2.99mm BTDC from the later models because I though that was to fight pinging.

In any case after 65 miles she gave up on me and started running like crap, I think the plugs are oil fouled. I’m going to back off the pump, drain the crank case of any oil, put in some fresh plugs and try again.

[Craig380]

Personally, I think 2.99mm BTDC is too far advanced. The timing spec for the L/M models was 2.25mm BTDC and for the A/B models, 2.05mm BTDC. The thing is, the piston and combustion chamber profile never changed across ALL models from '72 to '78 and the compression ratio was the same across all models too.

The original timing spec of 2.99mm was intended to boost mid-range torque but I believe it's too risky if you run the engine above 5,000rpm for any length of time. My '76 M model was happiest at 2mm BTDC.

[Craighjr]

Ok good to hear I am going to try to reset it this weekend.

[Craighjr]

Reset the timing to 2.0mm btdc and the bike starts and runs better but I’m fouling plugs every 15 miles. It runs well then just loads up and looses cylinders. Do you run less oil with the modern 2-stroke oil vs the 1970’s stuff?

[jabcb]

Are you having fouling troubles with all 3 cylinders or just one?


Your first post mentions a NOS oil pump.

The oil pump for the GT380, GT550 & GT750 look the same. Might you have the wrong oil pump?
There is a number stamped on the control arm, which I think indicates which one you have. What is that number?

It’s possible to install the control arm 180 degrees out from the correct position. Doing that will cause full oil output to occur at idle.
If your pump actually was a rebuilt pump, then the arm might be 180 degrees out.
There is a procedure to check this. Will look for it if this might be an issue.

[Craighjr]

Are you having fouling troubles with all 3 cylinders or just one?


Your first post mentions a NOS oil pump.

The oil pump for the GT380, GT550 & GT750 look the same. Might you have the wrong oil pump?
There is a number stamped on the control arm, which I think indicates which one you have. What is that number?

It’s possible to install the control arm 180 degrees out from the correct position. Doing that will cause full oil output to occur at idle.
If your pump actually was a rebuilt pump, then the arm might be 180 degrees out.
There is a procedure to check this. Will look for it if this might be an issue.

My pump was 180 out, interesting that the pumps are different. I have replaced it with an eBay one not knowing where it came from. As for the fouling it feels like fouled plugs but they look good. I need to dig around some more. I put in some B8ES plugs and set the timing at 2.0mm BTDC and the bike feels pretty darn good, now to see if I can put more than 15 miles on it before it bogs down and starts missing.

[jabcb]

The GT380, GT550 & GT750 pumps are the same except for different oil flow rates. The casting is the same. The control arm & internal bits differ.

I have a 72 GT380 & 72 GT550. I can check to see if your control arm number matches with mine.