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'07 250Cc Revs Not Dropping? (Added Pics & Video!)

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Excellent. The point above about making sure the hose clamps are straight is important too. Especially since the Beta clamps are made of butter and won't take a lot of torque. The Mikuni is pretty tolerant of settings but 1 1/2 turns out for the air screw is normal. You may find the bike runs crisper with the 27.5 pilot jet and if you want it to grunt like a tractor I recommend Moto Tassinari VForce3 carbon reeds

For the vent hoses don't be too picky. Any hole that is above the float bowl is good enough to stop the tubes from acting as siphons. I just nip a hole with small wire cutters.

  • Author

Cool thanks, will take it for a bit more of a ride when I can and report back :-)

  • Author

Its still doing it after fitting the new inlet manifold, idle is set very low and air screw is 1.5 turns out. Before I get into crank seals could the float level be too low? If so how do I adjust this?

  • Author

Looking at these pictures it looks like my brass tangs are fitted updside down?! Have fitted it the correct way now and the bike definitely seems better. See the video at the bottom for how it is running currently. So my question is, is that a normal amount of over revving/pinging/revs hanging? If not which way should I move the tangs, as i've tried a little higher and also a little lower but still seem to have the hanging revs?

20130630_122906_zps01a9bac7.jpg

20130630_122836_zps6f13793c.jpg

VIDEO >>>> http://youtu.be/RWBv3JCL3_Y <<<< VIDEO

Edited by sawtooth

  • Author

Failing the carb would crank seals really cause that kind of hanging?

Yeah that's upside down. The bottom of the travel should be level and the top of the travel for the tangs should only point at the right angle formed by the top of the pilot jet housing and the main jet tower. The little tang on the side is what sets the travel.

  • Author

Well its now set like this and it moves up (down in this pic) about 5mm.

Side%20View%20-%20After.jpg

Does that sound right? It hasn't cured my issue so either its still set wrong or its my crank seals?

  • Author

If it was crank seals would that not make it run lean all the time? It seems fine while revving it (blue smoke and all), it just goes lean off throttle.

A crank seal could simply cause a lack of 'Signal Strength" that's the amount of vacuum that creates the Venturi effect

If its low it can make it lean just because it won't suck hard enough at low rpm, not because you have carb problems and not because the extra air ingested cause a lean condition

Usually the bike would be hard starting if crank seals were leaking as it just can't pull fuel through the carb

Saw tooth

I am not saying that this is your hanging up issue but your carb tangs are set wrong in these pictures. Try and find my article on what these tangs are for, notice I said these as in two tangs as there are two of them and they both serve two different purposes.

We need to start there before we go on any further.

Look for BillyT Mikuni carb article on this site.

Yeah that pic shows the most it should travel when the valve is open. At fuel valve closed it should be level. Should have explained better. If you can find Billy's article on setting up the Mikuni all the better. It was what opened my eyes to how the thing should be tuned.

  • 4 months later...

Ya I dunno

Modification in attempt to solve a running condition problem just gets you deeper into problems you can't understand

I wouldn't change the carb unless it was to test a known good runner carb on the bad running bike

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