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mxmaddman

carb comparison question

7 posts in this topic

I have an 04 atv carb and a 07 dirt bike carb.

why does the 04 have some type of pilot diaphragm and the 07 doesn't?

Is the 04 supposed to have a hot start plunger? It just has a cap with nothing in the hot start hole.

Its running lean and i found a missing o ring in the diaphragm and no hot start plunger in the hole. I'm thinking its def the problem.

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Yes, there's supposed to be a hot start plunger, and if it's missing, you'll have a huge air leak.

The pilot diaphragm is the same as that on a WR450 carb. It's part of the air cut valve, which is an element of the air injection system.

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Yes, there's supposed to be a hot start plunger, and if it's missing, you'll have a huge air leak.

The pilot diaphragm is the same as that on a WR450 carb. It's part of the air cut valve, which is an element of the air injection system.

I figured you would know if anyone would. Does the air valve need to be on the carb or can it be removed and blocked off?

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It can be, but there is some compensation that must be made for its absence, and I'm not clear on the details. In a YZ450, air is fed to the pilot circuit through a single jet and passage. In a WR/YFZ, the air passage is forked, with one side bringing air in through a pilot air jet, and the other through the ACV. When the ACV is blocked off, the PAJ needs to be larger. See the WR450 forum for more info.

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OK thanks gray, Apparently you can flip the diaphragm and block the passage then add a larger paj or maybe smaller PJ.

I know the standard yz passage pulls from the paj, do you know where the second passage draws its air from?

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ok, thanks gray.. It looks like it might go up into the top of the carb above the slide...

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