Jetting/plug chop opinion.

[13B-RX3]

Last weekend I did a plug chop to verify jetting, these are the plugs. L&R were at full throttle, through the gears to the top of 5th (102mph). 3/8 was through the gears at 3/8 throttle for about a mile, and 3/4 was through the gears at 3/4 throttle, for a mile as well. Both 3/8 and 3/4 were only done on the left cylinder. IMO both the right and left cylinders looked lean at full throttle, the right more so than the left. I went up one main size on the left and two on the right. It also looked lean at 3/8, compared to 3/4. I went one taper shallower and dropped a clip on the needle. Picked up a little low end and dropped a little top end (seat of the pants) as expected by me. This weekend I wanted to get another plug chop in just for giggles. Everything was done the same other than the location and it appears to be leaner everywhere, even though I had richened 3/8 and full throttle. For the first test it was 77f and today it was 80f. I don't understand why it seems like I'm getting the opposite results of what I'm expecting. The only thing I can think of is that I did the chop today after a longer ride to warm it up. Maybe it was a little hot, I did notice a small amount of boiling in the fuel lines. The first pic is from the previous weekend and the rest were from this weekend.

 

Oh, p.s. Let's pretend that this is an air cooled Yamaha twin

 

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[13B-RX3]

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[13B-RX3]

A little better pic

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[Killacaviar]

A little better pic

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Provide build and jetting specs.

You are very lean.


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[13B-RX3]

The bike is an RD400 (air cooled) mild port, pipes, stock compression.

Carbs are pwk 30mm (oko) needle is a GJH. When I originally started the bike I had 155 main jets. I put about 100 miles on the bike before I started running it hard. With the 155 it seemed very rich, didn't want to come on the pipe at all. 1 dropped down to a 150 and it got better but still wasn't 100% clean. Went to a 148 and it was clean and felt good. I put about another 300 miles on it, not running it too hard, while I dialed the needle in. Once it felt like everything was good, I wanted to make sure before I started adding timing. After the first plug chop I realized it was lean. I went up one size on the L and 2 on the R (150L, 152R) after I did another chop it seemed even leaner. I just got back from a third chop. I put 155 mains in just to see what would happen and it ran good. Didn't come on the pipe as violently but seemed like it pulled harder. I'm guessing it's still a little lean, but y'all have way more experience at this than me. I don't know why it wouldn't run before with the 155mj but does now. Either the rings weren't seated or the needle was way off to begin with (JJH). it seems like it's responding to a jet change now, so if it's still lean I'll order some more jets. Sorry if I'm talking in circles. Any advise would be greatly appreciated!

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[kawa110]

I would like those jjh needles.
Lol


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[Mattchev]

2 hours ago, kawa110 said:

I would like those jjh needles.
Lol


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You would like them as in you want some? I have some laying around

[kawa110]

Please
Looking for two jjh and two n68a’s as well for pwk28.

I am clueless... the needles will work on pwk 28 and 35’s?


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[13B-RX3]

I would like those jjh needles.
Lol


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Jetsrus sells the JJH for like $6 each.

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[Stingray]

If it changed that much you need to do a leak down test those plugs are extremely lean they should have a 2 mm soot ring and yours are not even close. At least start it and spray starter fluid around all gaskets and intakes and listen for rpm change better safe than sorry

[13B-RX3]

Thanks for the advise, I'll do another leakdown while I'm swapping the jets.

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[13B-RX3]

Did a primary leakdown and everything looks good. The right cylinder consistently reads leaner than the left, I guess I'll run a little larger jet on the right, I don't know if that's common or not, but with these knockoff carbs it doesn't suprise me. After laying all the plugs side by side, it does appear that is getting richer with each jet change. It's hard to measure but I'm guessing the smoke ring is between 1mm-1.5mm, but I'd love a second opinion on weather or not I should keep fattening it up. Thanks in advance.

 

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[kawa110]

I have read that the knock off jets are not the correct measurements and originals....
Maybe.


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[13B-RX3]

I'm out of ideas. Went ahead and rejetted. The smoke ring isn't getting any wider, only darker. I exhausted everyone's supply of br8es so the last chop was done with 9s. It gets more and more sluggish with each jet change, with the current jetting I can't go full throttle off the pipe, it just loads up and misfires. Any suggestions, I'm out of ideas.

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[13B-RX3]

I have read that the knock off jets are not the correct measurements and originals....
Maybe.


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All the mains, pilot, and needles are authentic keihin from jetsrus.

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