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Keihin Jetting for 300.


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Hi all, I'm curious what jetting a TRS 300 runs, particularly what needle and slide they use. I'm wanting to see if it's similar or even the same as my '14 GG 300 which runs the std JJH needle.

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300 and 250 run with the same jetting from stock:

pilot jet: 45

main jet: 125

needle: JJH with clip in middle

slide: 3.5

Is almost identical in all trials engine now (maybe sherco was using a leaner pilot jet --42--) due to the almost identical thermodynamics in 2T of similar characteristics.  I bet you can swap the keihin between your GG and TRS with total success!




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Thanks, you're right, exactly the same as my GG original std jetting apart from a 122 MJ. I need to check my float height again perhaps. I only ask because my GG  seems a little lean coming onto the needle and is never a 1st kick starter and I always felt this could be due to not having the best needle fitted.

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4 hours ago, arnoux said:

RACING and GP spec non homologated Gassers are now standard with 48 pilot (up from the 45 of a few years ago)

I do believe a lot of that is to accommodate pumpgas with ethanol as well, but still the high altitude size will follow as lineaway stated.

one will find these jet sizes will apply to most all bikes with that carb, as the carb only knows how much air is going through it and not which bike it is on. mixture requirements are basically the same for all.

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12 hours ago, inchhigh said:

That's interesting, because I'm old school I've always run 50 or 60:1 believing that's richer, which it is for the engine but not in carburation terms.. I need to try 80:1 as my next step. I think I know what this means, correct me if I'm wrong please. As an example, 50:1 is actually more lean than 80:1 in carburetion terms due to having less fuel but is richer in the sense of having more oil for the engine, is that right ?  Running a fuel/oil mixture of 100:1 just sounds scary to an older bloke like me but it does make some sense when you think about it.

PS: We don't use ethanol fuels in our bikes here in Australia, unleaded 95 and 98 is readily available. My elevation above sea level is only a few hundred metres at worst.

Edited by fourex
PS added.
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1 hour ago, lineaway said:

 The clue would be even Arnoux is telling you a 45 is too lean down under.

I've been running a 48 PJ and # 3 slide for over 3 years now, but it still could be better.

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My son just got a 2018 300rr two weeks ago. The dealer had put a 120 and a 58 in it. It ran well, butmy son needed it to betterĺ, so I dropped it to a 52. In your case there isno reason not to try a 50. All bikes have there own personality.

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  • 4 weeks later...

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