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Hey guys, I took the RMX out today. The weather is now 30* warmer since my last post. When it was cooler I'd notice it would ping very little and just under certain loads. Now my bike was pinging/knocking badly. . Last summer it didn't ping at all! The only thing different with bike is a new topend and I swapped out the PJ for a pwk, I'm running same jetting. Any suggestions? E

Ignition timing.

I think it's unlikely that the ignition timing just mysteriously got out of whack if you have not had the flywheel off. Couldn't hurt to check it though! I would lean towards jetting, especially since replace top end / swap carb is all you have done between running well and pinging. Compression should be better on a new top end, which would require revisiting the jetting anyway. Maybe raise the needle up a clip or two and see if there's a difference. If so, you know you're on the right track.

I would look at the jetting. A different carb with the same jets is not the same flow.

Is it fresh gas or old. The older fuel gets the less octane it has,especially fuel with ethanol .

Thank you guys for all the suggestions.

I pulled the Carb apart lastnight and upon inspeecting I noticed that the someone previous has modified the slide. The cutout has been ground bigger. I compared to another pwk 38mm #7 to confirm. Could/would this make the bike ping? Correct me if I'm wrong. But the bigger/taller cut on slide would make it essentially a "leaner" slide right?

took it out today, checked the plug, nice mocha to dark mocha. before first ride, swapped out the shaved slide to non shaved #7, no difference. pulled card. raised the needle 1 position still pinging. back to truck, raised needle to 4th slot still pinging, thou not quite as bad. went back to truck, put in 1 size larger MJ, better accel. but the ping is still there. Frustrated, I guess i'll put the ole PJ back on and see if its any difference. Unless you guys can throw some more suggestions?

Detonation is a octane issue. You need to raise octane or lower compression or retard timing. Unless your old carb is electric I can't see it making a difference. If it is, it probably changes the ignition curve in the cdi.

put in 1 size larger MJ, better accel. but the ping is still there

Might be onto something there....IE still lean. Brown color means noting, you have to read a brand new plug immediately after a WOT plug chop run. Search plug chop on here. Did the RMX ever come with a 38mm PWK on it? If so, look up the jet specs for stock. If no dice find the closest year RM that had one. I was able to do this for my WR....Came with a Mikuni VM, but other year YZ's used the PWK. The PWK I got for it had everything wrong. Slide, needle, jets, etc.

its all psycosomatic
there is no actual knocking of pinging of the engine...your mind just cant comprehend that you would be riding a yellow bike instead of a green one so your own mind is making up these noises to replicate the KIPS rattle so it can pretend you are on a KDX and all is well

diymirage wrote:its all psycosomatic
there is no actual knocking of pinging of the engine...your mind just cant comprehend that you would be riding a yellow bike instead of a green one so your own mind is making up these noises to replicate the KIPS rattle so it can pretend you are on a KDX and all is well

my rm has a kips rattle :):), although it is green powered.lol

diymirage wrote:its all psycosomatic
there is no actual knocking of pinging of the engine...your mind just cant comprehend that you would be riding a yellow bike instead of a green one so your own mind is making up these noises to replicate the KIPS rattle so it can pretend you are on a KDX and all is well

Yeah, I wish. Funny thou.

Is it hard to start? I'm thinking you might have an air leak.

Goofaroo wrote:Is it hard to start? I'm thinking you might have an air leak.

No, starts up easily always.

Does it slowly return to idle?

Goofaroo wrote:Does it slowly return to idle?

No, it does hang just abit thou.

I'm guessing you have an air leak. You replaced the top end, are you sure about the base gasket and intake gaskets? Was it running fine before you freshened up the top end?

Goofaroo wrote:I'm guessing you have an air leak. You replaced the top end, are you sure about the base gasket and intake gaskets? Was it running fine before you freshened up the top end?

Yeah, the bike was running fine. Freshened up topend for piece of mind. Also, swapped out stock keihin. PJ Carb for the pwk.....as mentioned.

Switch back to the stock carb and see what happens. While you have the carb off take a close look at the boot and make sure it isn't torn. Then report back to us.

I'm with royadams that it needs more octane. I had the same thing happen with a YZ250 after a rebuild, pinged like crazy with 87 and 89, had to run 92. Of course I used a higher compression piston.