More 300 Jetting - Lean enough to ping?

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May 4, 2000
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#1
Installed the following jetting in my new '01 300EXC for riding 4-7000', 90 degrees.

Hand-cut slide about 7.5, CGK middle clip, 40 pilot, 178 main

Bike ran great no richness anywhere, but I think I was hearing it ping slightly at 1/4 to 1/2 throttle. But it didn't overheat even on the 1st gear hills when the weather was hot. Next day I upped the pilot to 42, seemed like less pinging but not gone. Next ride I went back to my 7.0 slide and now we are starting to run rich at 1/8 to 1/4 and response is not as smooth, still have a pinging sound.

Strick mentioned that the 6.5 slide can be made to work on the '01, but it is in my '99 which I traded in so I don't have it to test with.

I fit my old Gnarly pipe to this bike and it is very close to the frame in two places, so maybe it is contacting the frame at certain rpms and creating this sound. I plan to put the stock pipe back on see what happens.

As another test, I opened the choke while on the road getting back to the truck and the pinging seemed to lessen, this makes me think I am still too lean, but why the loss in power with the richer jetting then compared to my first setup? :think

If it was pinging, what other signs would I have? I think if it was a ping that the bike would tend to overheat, but the '01 jug does have the bigger water jacket so maybe not. Any thoughts?
 

Strick

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#2
This suggestion can be expensive, and habit forming!

Race gas. I run 50/50 race gas in my 300. I have gone out to a riding area, rode one loop with pump gas. I then drained the tank, and put in 50/50 race gas/pump gas. There was a noiticeable performance gain. This mixture may also aid your pinging woes.

When you went to the 42 did you experience any loss on the bottom (loading up), or any more spooge?

I will also say this about that. You have what I consider a fairly lean needle, and a very lean slide. How about this: if your 42p is performing well, move the needle up one postition (move clip down). If you have richer needles (CGJ, CGH) try one of those.

Finally, do you experience and run-on when you chop the throttle and coast to a stop?
 

KTM Mike

Mi. Trail Riders
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#3
My 97 300 pinged a bit, also surged on trailing throttle, even after i had cleaned up my jetting to spot on. - using 50/50 race/pump gas mix ended the pinging a surging. It is expensive but I felt worth it.
 
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#4
The question about run-on, it didn't do that or exhibit any other symptom of being lean, just a ping. The power delivery was very good too, had I not heard what I think is predetonation, I wouldn't have changed a thing. The powerband has gotten less desirable as I have richened it up.

I really don't want to resort to a race gas mixture, maybe if nothing else works I could go with a thicker base gasket to drop the compression. Would one of those additives that increases octane held me to end the pinging? Is so, that could be a short term fix. I have big ride this weekend and I don't want to burn a hole in the top of my piston!

On needles, I wanted a CEK, but all Carb Parts had in stock was the CGK, so that is what I have for now. Maybe the richer needle is worth a try.

On spooge, I am running the TCII and there is nearly none.

Another thought, maybe fitting the old Gnarly pipe is not a good idea on the '01, hmm...
 
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#5
Ok I am going to buy race gas. I don't mind buying it, its the special trip that I don't look forward to every few weeks. Also I understand it must go in a metal can, not plastic.

I read in my manual and it says to run '95'. Is the octane rating system the same for Europe as the States?

I will run a 1:1 mixture of race to super this weekend and post the results.
 
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#7
I ran a 2:3 race to pump gas mixture and a 1:1 race to pump this weekend. It still pinged slightly with the 2:3, but almost not at all with the 1:1. I like the change in the motor with the new fuel mixture but it wasn't really that big of a change IMO. Not enough more power to convince me to run a race gas mixture full time.

One of the guys I rode with has a commerical hop-up shop for bikes and sleds and he offered his services to increase the squish area in my cylinder head to get her to run on pump gas. I think I will do that.