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DR-Z250 float height

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G'day,

Can anyone tell me the float height for a 2001 DR-Z250 EK1 with the Mikuni TM28SS pumper carb, please?

I'm in the process of stripping/cleaning the carb (again) to try to fix it, but so far have found nothing obviously wrong (except the accelerator pump plunger is a bit sticky). If anyone has any useful suggestions, I'd be grateful to hear them.

The bike has two carb issues. Firstly, it has always hesitated/bogged down when opening the throttle off idle. Secondly, it often idles very fast (gets worse with time). A big blip of the throttle will sometimes make it idle normally, but then the idle speed steadily climbs again.

The only thing wrong I can see is that the A/P plunger doesn't seem to operate smoothly, sticking in the bore. I've often noticed that the A/P rod is not fully extended, that is, not up against the A/P lever. Could this be the cause of the two problems? If there is a gap between the rod and the lever, then opening the throttle will not actuate the accelerator pump. With the plunger part way through it's stroke, it could be forcing extra fuel into the carb throat at idle?

As the plunger is metal in a metal bore immersed in petrol, I don't see how I could make it slide better without sticking. Maybe a polish with very fine wet and dry paper? Fit a stronger spring? Modify the existing spring somehow?

Everything is standard: carb, exhaust and airbox, except I have replaced the air filter with a Twin Air recently (made no difference to the problem). The bike has a manual fuel tap and AFAIK the carb doesn't leak fuel at all. The throttle cables were replaced a little while ago, the air filter is clean and oiled, the spark plug was replaced and the valve clearances set recently. It has been to two different shops who've cleaned the carb: one found crud in some jets, the other raised the needle one clip. Each time it has been better for a while but not fixed.

Any help or suggestions would be gratefully appreciated.

Thanks in advance.

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Doesn't seem like anyone knows the answer, dammit! Time to experiment, I think.

I've been reading lots of the jetting FAQs, stuff on the accelerator pump, etc. Lots of good info there - my thanks to those who've taken the time to write it up. There are quite a few things for me to try in order to resolve this problem. If nothing else, I'm sure it will make me an expert in installing/removing the carb!

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You, sir, are a champion! :thumbsup:

I was planning to use how to confirm your pilot circuit setting just for my own curiosity but now you have given me good reason to do it. Currently it is set to 2.0 turns but I will check it is correct.

You have got me thinking... these bikes are shipped with an inlet restrictor. This has been removed on my bike, as on most, but I don't know if it has been rejetted to suit.

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OK so it is all back together and is much better! I've started it up in the driveway and it is idling steadily at normal speed and responding well to blips of the throttle.

I made three changes:

  1. The float height was maybe 14.3mm; raised/richened up to 13.8mm.
  2. The pilot screw was 2.0 turns, richened that up to 2.5 turns.
  3. The A/P plunger and bore were lightly polished with wet n dry paper.

About to go for a good test ride.

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