WR 400 Fixed hanging idle

I've seen a few posts lately on hanging idle. My 99 WR was also hanging, so I checked out the carb. Generally a hanging idle is caused by a small air leak.

I found 3 problems:

1 - a split in the small air hose that connects the hot start T to the intake manifold. I turned the hose for the pic. The crack was on the underside, so not visible.

carb1.jpg

2 - A split in one of the small air hoses on the side of the carb. The hole is on the inside of hose near the tip of the screwdriver.

carb3.jpg

carb2.jpg

3 - Stuck plunger on the side of the carb.

carb4.jpg

I fixed all 3 at the same time, and the hanging idle was cured when I fired up the engine, so I'm not sure exactly what fixed the problem.

The cracked hotstart hose is the most likely candidate, since it lets air bypass the carb completely. If anyone has a hanging idle, this is an easy check and repair.

The other cracked hose may have had some effect, and I can't comment on the stuck plunger since I don't know what it does.

I believe (but correct me if I'm wrong) the plunger is the air cut valve, when you decellerate, it's supposed to stop/surpress the backfiring from being too lean, this part does not exist on YZ carbs - it's just left open - no diaphram or cover.......

I've seen a few posts lately on hanging idle. My 99 WR was also hanging, so I checked out the carb. Generally a hanging idle is caused by a small air leak.

I found 3 problems:

1 - a split in the small air hose that connects the hot start T to the intake manifold. I turned the hose for the pic. The crack was on the underside, so not visible.

carb1.jpg

2 - A split in one of the small air hoses on the side of the carb. The hole is on the inside of hose near the tip of the screwdriver.

carb3.jpg

carb2.jpg

3 - Stuck plunger on the side of the carb.

carb4.jpg

I fixed all 3 at the same time, and the hanging idle was cured when I fired up the engine, so I'm not sure exactly what fixed the problem.

The cracked hotstart hose is the most likely candidate, since it lets air bypass the carb completely. If anyone has a hanging idle, this is an easy check and repair.

The other cracked hose may have had some effect, and I can't comment on the stuck plunger since I don't know what it does.

LOL, all three of your fixes got you on the right path. That bike must of been a pain to cold start!

I believe (but correct me if I'm wrong) the plunger is the air cut valve, when you decellerate, it's supposed to stop/surpress the backfiring from being too lean, this part does not exist on YZ carbs - it's just left open - no diaphram or cover.......

The YZ (some models) have the same casting but none of the passage ways. Much cheaper to cast all the carbs the same, then machine each to suit the customer/bike.

You'll notice in the picture, that ACV (Automatic Coast Enricher) is actually an add on. Early style carbs did not have it as FCR's were originally designed as race carbs.

Guess you don't "coast" when racing - hehe...

Yes, I was pretty sure YZ's didn't make use of it.

i had the same problem it was the stuck plunger

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