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Vanquish66

YZ400F Problems - you guessed it. Carb Related.

12 posts in this topic

Problem:

-Bike won't start without choke AND hot start. Once started, It will run without the hot start but it must have the choke on.

Bike:

-1999 YZ400F, obviously 39mm Keihin Flat CR.

-FMF Powercore 4 exhaust on a stock header.

Carburetor:

-All jets cleaned well and reinstalled.

-Jets all at stock numbers (starter 65, main 175, pilot 45) and Pilot screw adjusted for the exhaust pipe (2.5 turns out)

-Float bowl height checked and reset to stock 9mm level

-Accelerator Pump diaphragm looks great.

-Yeah, my slide is square side down.

Yeah.... carb issues like the rest of everyone. Looking for a little direction. I will admit.... Passageways not given the attention they need. When it comes off again, I will take care of that. I'm looking for other possible problems to look out for while i'm in there.... The bike seems like its breathing hard and not getting enough gas OR too much air. Where are possible trouble areas for all these issues? This is the last time I work on this carb.... If I rip it out again its going to the shop and getting completely worked over.

Thanks ahead of time for all the help I may or may not get. Haha.

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Do a search for 'FCR hanging idle' or 'FCR pilot circuit', all the info you'll ever want to read. :ride:

Search in all the makes too, this carb is used on other bikes with the same problems. Could also be an air leak between the carb and head or the hot start.

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I didn't necessarily mean for him to go to my thread, just steer him in the direction I went to fix mine. When I was trying to fix my problem, I tried a lot of different search terms. The two search terms I suggested are the ones that came up with the best results.

There is a lot of suggestions from members that overlap between just the pilot circuit problem and the guys that had a hanging idle. A lot of times, one leads to the other. Some guys with a hanging idle had throttle cable problems that would not really be his problem, but others had issues with air leaks that could be his problem. I think most hanging idle problems come from people trying to adjust the idle knob to compensate for an air leak or tight valves or a clogged pilot circuit, which was my problem. I also found answers in other makes forums like KTM or Husky or the exotics, that's why I mentioned searching all makes.

I never knew much about it until I had to deal with it, now I just try to help. Considering how many threads are on this, I still find it surprising that there isn't one big, all inclusive, every conceivable solution FCR idle problem thread as a sticky somewhere. LOL

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I still find it surprising that there isn't one big, all inclusive, every conceivable solution FCR idle problem thread as a sticky somewhere. LOL
Well, for one thing, there's a 10,000 character limit on individual posts. :ride::lol:

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Check the hoses to the remote hot start for vacuum leaks.
...as well as the hot start itself, to be sure it closes entirely.

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Thanks Guys.... ripped the thing apart, put it back on, no luck. Checked all of my hoses, cleared all of my passages.... Gave the thing a solid going through but no luck. Unfortunately I may be on my way to the shop If I don't find a vaccum leak somewhere.

If.... just hypothetically speaking.... I wanted to put a new carburetor on there.... where can I find a basic aftermarket carb to fit my bike?

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You can buy complete modernized replacement Keihin carbs from Sudco , or buy a used unit from a later YZF.

Ebay has a bunch of '00 to '09 FCR-MX carbs. If I had known they would directly replace the earlier FCR, that's what I would have bought.

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