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tpars121

Carburetor Help

6 posts in this topic

I am trying to help a friend get his 06 yzf450 running that a previous mechanic screwed up. I have been able to get it idleing smooth and running good if you ease the throttle on but it bogs pretty bad if you blip it. Should i be able to see it squirt gas from the little brass thing sticking up by the slide when i blip the gas. I think you call it an accelerator pump? can this thing get stopped up or go bad? I'm not good with carbs so any hints or tips would be appreciated.

I just learned one more thing. With the engine not running i can take the cover off the throttle cable and i can push down the little black thing with my finger and it will squirt gas but if i just give it throttle it will not squirt, it does rotate down slowly but no squirt.

Edited by tparscrf250r

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Most likely a little safety wire will solve your problem. Basically you safety wire the black plastic piece to the metal piece so they both move togther. It's easy and you can do it without removing the carb.

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Correctly setting up the accelerator pump timing per the manual will solve the problem, too, and that will do so without binding up the throttle linkage short of full throttle.

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I looked at it a little more closely and the accelerator pump is only moving slightly and then stops short of full stroke. I can press it with my finger and it will move the rest of the way. I cleaned the carb but I haven't open up the part where the diaphragm is. I guess I will open that up next.

Gray, Are you not a fan of tieing the accelerator pump to the throttle?

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Gray, Are you not a fan of tieing the accelerator pump to the throttle?

No. Not with wire, at least. The stroke of the accelerator pump is limited by a button on the diaphragm itself. To allow for this, the pump operating rod is connected to the throttle linkage so that it is driven indirectly by a spring. This lets the pump come to a stop without stopping the throttle itself from opening fully.

If the pump rod is tied to the linkage in such a way as to eliminate that spring, one of two things has to be done. Either the pump stroke has to be delayed enough to allow the throttle to open entirely, in which case there will be no pump delivery until the throttle is about half open, or the button must be removed. If the button is removed, the pump duration is roughly tripled what it should be, and you end up needing a grossly oversized leak jet to compensate.

If, after trying the correct adjustment procedures, it is found that the pump delivery is inadequate due to the dive spring being weak, a much better fix is the Merge Racing accelerator pump linkage spring. The stronger spring makes the pump a little more aggressive without the need of shortening the diaphragm button. Another way to accomplish the same thing is the "O-ring mod", in which a small O-ring is used to tie the linkage together. The Merge spring is more workmanlike and permanent, and is not likely to break, fall off, and foul the linkage.

You should not need any of this, nor a $200 float bowl, nor a $150 pump cover in order to make the bike run right. If your friend doesn't have a manual for the bike, download one here:

http://www.yamaha-motor.eu/eu/services/owner-manuals/index.aspx

Look at the linkage assembly on page 4-16 to be sure all the parts are there, then review the timing procedure on page 4-20. Once done right, opening the slide should cause a fairly strong squirt that "just misses" hitting the slide as it opens.

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