Hi Guys,

im new to the sport. Been an avid motorcyclist for 39 years, but have just embarked on a new avenue. I purchased a 2000 GasGas 321. Unsure of mileage or hours used. The bike starts in one kick, runs well, and appears to have been well taken care of.. After the bike gets hot, (after 30 or 45 minutes) it has a knock that I would equate to a spark knock. The bike idles smoothly. It makes this spark knocking noise under these conditions. ....

when idling and you bump the throttle, letting off the throttle, and when the engine is revved up about 3 times idle, its does it continuously until you let off the gas.

You can shut the bike off for 5 or 10 minutes and when restarted, it’s quiet again until it gets hot again. 

I run 100LL AV Gas at 75:1 with AMSOIL. 

*Also, id like to install a magnetic kill switch to replace the current button. Looks like theres only one wire running from the button to inside the frame. I assume that's the power wire and the button grounds against the bar to shut it off.  
is it as simple as connecting the power wire to the existing and then attaching the ground wire on the new kill switch to a frame ground?

 
Thanks everyone!

Greg
 

My first trials bike was a 321.  Letting off the throttle will not produce "spark knock" (detonation).   I'd be wiggling bearings.   Sometimes you can isolate the source of the noise with one end of a hose (maybe 3/4 - 1" ID) held to your ear and probing the engine with the other end.

And yes, one side of the kill button goes to the chassis ground.

Sounds electrical, failing ignitions start to break down as temperature rises. 

If it is electrical, you should be able to feel that while riding.  It will feel like it's missing combustion cycles.

Thanks for the help guys.

 

It does get much worse the hotter it gets. I will explore the electrical idea as well. In your opinion, should I start with a new coil?

 

Thanks Again

Don't think it will be the coil, they tend to work or not work. But worth eliminating if you can borrow one. 

 

Edited January 28, 20197 yr by b40rt

1 hour ago, Bankerman said:

Hi Guys,

i

 
is it as simple as connecting the power wire to the existing and then attaching the ground wire on the new kill switch to a frame ground?

 
Thanks everyone!

Greg
 

Yes.

Ignition coils can work ok when cold but when they get hot any minor internal wiring or insulation fault will manifest itself be it in the primary or secondary winding. This usually ends up as a weakening spark.....poor high tension levels....causing misfiring and stuttering/hesitation. Vibration can cause coil breakdown along with impact damage causing internal damage to wire and insulation. 

I had one of these and loved it. however it in your case it sounds like it needs a decoke. If there is a sufficient build up of 'carbon' deposited on the piston and combustion chamber it will increase the compression ratio and as the bike gets hot the symptoms get much worse causing the problem you described, Just drain the coolant take the head off and clean the top of the piston and the combustion chamber. The bigger bore bikes are more susceptible to this problem as they tend to run hotter anyway and the compression ratio and cooling system are pretty much right on the limit.

Edited January 28, 20197 yr by sherpa325
spelling

12 hours ago, sherpa325 said:

I had one of these and loved it. however it in your case it sounds like it needs a decoke. If there is a sufficient build up of 'carbon' deposited on the piston and combustion chamber it will increase the compression ratio and as the bike gets hot the symptoms get much worse causing the problem you described, Just drain the coolant take the head off and clean the top of the piston and the combustion chamber. The bigger bore bikes are more susceptible to this problem as they tend to run hotter anyway and the compression ratio and cooling system are pretty much right on the limit.

Exactly, thus causing detonation or in laymans terns ‘pinking’. Only needs a tiny edge of the excess carbon to become hot enough to create alternative ignition source other than the plug.