Leak Jet DR350 and 37mm Keihin FCR

So I squeezed on a FCR and it runs really well, no bog, surging, just good strong pick up. The original carb had no leak jet and I swapped bowls with another carb which did have a leak jet as the squirt was a bit too strong.

Time to fine-tune things now as the bike can still get a bit blubbery and rich with a lot of short sharp throttle action in the lower gears. Swapping the bowl with the leak jet helped considerably so I assume I just need to get a bigger leak jet to tone down the squirt a little more.

Make sense? The current leak jet is a #50, the carb bowl was off a CRF450 which obviously can handle a lot more fuel than me ol’ DR!

Any suggestions what size to go to, a #60 I guess not a huge jump, maybe a 70? I don’t know how sensitive these things are.


Edited by thedktor

You are on the right track. The LJ size change will not be real apparent UNTIL you are close. Try the 70.

Thanks William. I can only try eh!

Well it turns out that the exact leak-jets I need are not available in the UK so I got some drills instead:


Starting from #50 (0.5mm), drilled it out to 0.8mm, which was perhaps a bit much as I was getting a bit of bogging if really cracking open the throttle in an unnatural way


So a spare jet drilled to 0.7mm and then out for a proper run.


Well apart from being a beautiful day the new jetting was perfect!

Interestingly, most engines, and certainly the DR can be set very rich for that extra bit of hp, but at the expense of “crispness”. With the current leak-jet I may have lost a tiny, tiny bit of acceleration but it feels “right” now – very crisp, and no hint of wooliness or blubber.




Edited by thedktor

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