99 YZ400 Carb Question


7 replies to this topic
  • Extrapolate

Posted November 07, 2005 - 10:16 PM

#1

Was plagued with infamous Yamabog, noticed fuel leaking around AP linkage, figured bad AP diaghram. Removed AP cover and yes, bad diaphram. Have one on order along with spring and o-rings.

Question: While I have the carb off, should I re-build it, or just take it apart and clean it, or anything else? If I should take apart and clean is there a gasket set that I can buy? I am fearing that the bog will not clear up with the repair of the diaphram (based on reading lots of yamabog posts here!). I know the first response to the bog is "clean the carb", so I'm thinking a pre-emptive strike may be in order. I'm hesitating though 'cause I don't have any experience with carbs and don't want to make things worse! Also don't want to get into it and then find out that I need something that's gonna take a week to order.

I don't have many hours logged on this bike as I bought used only a few months ago, but I'd say I'm happy with power everywhere but right off idle. Don't know the status of any jets, I'm assuming stock. FS was out just a touch over 2 1/2 turns.

Any advice at this point from you "YZer" folks would be great.

  • srhines67

Posted November 07, 2005 - 11:03 PM

#2

Sorry, I can't offer any advice but I do have a question for you as I have a 99 YZ 400. Does your YZ kind of smell hot after a few hours of riding and have you ever had it loose coolant? I was just wondering.

Good luck with the carb.

  • Eric824

Posted November 07, 2005 - 11:25 PM

#3

Was plagued with infamous Yamabog, noticed fuel leaking around AP linkage, figured bad AP diaghram. Removed AP cover and yes, bad diaphram. Have one on order along with spring and o-rings.

Question: While I have the carb off, should I re-build it, or just take it apart and clean it, or anything else? If I should take apart and clean is there a gasket set that I can buy? I am fearing that the bog will not clear up with the repair of the diaphram (based on reading lots of yamabog posts here!). I know the first response to the bog is "clean the carb", so I'm thinking a pre-emptive strike may be in order. I'm hesitating though 'cause I don't have any experience with carbs and don't want to make things worse! Also don't want to get into it and then find out that I need something that's gonna take a week to order.

I don't have many hours logged on this bike as I bought used only a few months ago, but I'd say I'm happy with power everywhere but right off idle. Don't know the status of any jets, I'm assuming stock. FS was out just a touch over 2 1/2 turns.

Any advice at this point from you "YZer" folks would be great.

I purchased a 400 last year and had a bog also. I got tired of trying to fix it so I had the carb completely rebuilt. The bike runs real strong and starts easy. Apparently there was some damage to some hard to find o rings deep in the carb. Also, put a 2003 450 cam in it and eliminate your compression release, its the best $160 I ever spent.

  • Extrapolate

Posted November 08, 2005 - 07:30 AM

#4

The bike will get real hot real fast if you just let it sit and idle. I never do that though. I have only been riding it since sept, and the weather has been pretty mild here, have not lost a drop of cooland and I have done some fairly slow trail riding, where I half expected some overheating problems. Mine's been very well behaved with regard to overheating. They do get hot though.

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  • Hick

Posted November 08, 2005 - 12:35 PM

#5

Was plagued with infamous Yamabog, noticed fuel leaking around AP linkage, figured bad AP diaghram. Removed AP cover and yes, bad diaphram. Have one on order along with spring and o-rings.

Question: While I have the carb off, should I re-build it, or just take it apart and clean it, or anything else? If I should take apart and clean is there a gasket set that I can buy?



Cleaning it wouldn't hurt, but if it was running okay save for the a/p problems and you are worried about this job skip it.

But you should address the problem that led to the demise of you a/p, on the 400s the push rod that operates the pump is exposed, I'm not sure if this rod is removable, I think it may be, if so remove it and clean it ane the passage into the a/p.

What normally happens to the a/p on these bikes is dirt running down the pump rod does them in.


Hope this helps.

  • buick

Posted November 08, 2005 - 01:54 PM

#6

I had the bog on my 99 yz400 and alomst got it out. I switched to a 2002 fcr 39mm but had a hell of a time with tjetting it, it ran like a 125. Sold both of the carbs and replaced it with the edelbrock quicksilver. Night and day difference. Its the best upgrade for the bike IMO. I bought mine on ebay for $200, you can sell your 99 fcr for about 200-250 as many drz riders want it...

  • VOODOOCHILD

Posted November 08, 2005 - 02:00 PM

#7

I have a 98' and it was popping and such. I asked myself the same question and decided to take it all apart and clean it while looking for other problems. I'm not a carb GOD myself. I just stuck to the manual and it was very simple. It only took an hour or so. Just take your time. :banghead:

  • Extrapolate

Posted November 08, 2005 - 08:58 PM

#8

Thanks for the replies, I'm just going to clean out the passage for the AP shaft this time around and change the diaphram as planned. I will put back together and do the smoke test if the bog persists (see if it is blasting smoke during the bog), then I'll post the results and hope to hell someone helps me proceed. It really drives you nuts, especially learning 'cause you don't know if your gonna wheelie or not when you crank the throttle. The bike has me on my toes enough, I gots to get the bog outta there!

And to the TTer who said they replaced the carb completely with an edlebrock, you stated that it is "almost" cured??? You mean its still there even after replacing the carb?

Anyone who feels like giving a history lesson on these earlier YZ's and their bog problems, I'd be real interested. I'm just baffled how prevalent this problem seems to be. Was it there when these bikes were new, or is it something that creeps in slowly and all us guys that are buying used are having to deal with?

Thanks for all the help with the Exorcising the bog!





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