mikebyz

Member
Apr 25, 2006
4
0
Hey, My name is Mike and I'm a Newbie. I have a 99 yzf400 with a 'rebuild' carb, starts great, I have that routine down. But the bike is loosing power when accelerating, sounds like porky pig (stuttering and sputtering). D&E Yamaha said to pull the choke (richen up the mix, to see if it was jetting??) to see if the problem would go away, and it didn't. Their next suggestion was that the timing was off, maybe a valve out of adjustment.
The bike idles great. when not under load, I can blip the throttle and it sounds great. Air filter is in good shape, I have yet to pull the plug, but I don't think that the plug is the main issue.

Any suggestions?
 

B

biglou

I think the symptoms would be the same at idle, but is it possible the slide is in the carb upside down? I've heard it's easy to do by mistake. Outside of that, valve clearance, timing, air leak, clogged passage in the carb...
 

Ol'89r

LIFETIME SPONSOR
Jan 27, 2000
6,961
45
mikebyz said:
But the bike is loosing power when accelerating, sounds like porky pig (stuttering and sputtering).QUOTE]

Mike.

Other than what biglou suggested check your hot start button.

Make sure the rubber boot under the hot start button is seated all the way down. If it is not seated, it will hold the hot start button open a little bit causing the condition you described. If the boot is seated then check the hot start valve itself. Remove the hot start valve and inspect the rubber seal on the end of the plunger for damage.

Just my $ .02
 

mikebyz

Member
Apr 25, 2006
4
0
Biglou - dumb question - to check the slide in the carb, pull the carb and just look (also reference the manual)? or Is there another way without removing the carb?

Mike
 
B

biglou

I've never done it. I've read about it though. Apparently it's easily installed upside down and can cause some sypmtoms like you listed, but I think those symptoms should be present at idle also. If I remember, there's a marking or something to signify which side is up on the slide. I'd take the entire thing out and look at it along with what 89r suggests, also.
 

mikebyz

Member
Apr 25, 2006
4
0
89r and Biglou - Thanks for the advice and help!!! I worked on the beast for a few hours on Saturday. Checked the Hot Start valve first, it was fine, looked at the carb and it was fine. That left timing. Pucker factor was really high as I took off the valve cover. Looked at the Clymer book and saw the intake cam was off by two teeth. With pucker factor level at 10, I took the cam chain tensioner loose and adjusted the cam. Long story short the cam jumped after the tensioner was removed, I put together wrong and ended up taking the bike appart twice :bang: . The second time I turned the page and found the correct starting position for the cams and once back together, my world is MUCH happier. :ride: :laugh: :laugh: The bike runs better that it ever has!!!

Glad I stuck with it and finished the job!!
 

TaylorC

Member
Jun 29, 2008
1
0
I have the same bike and had a similar problem, it ended up being the throttle plate, something to keep in mind for next time

my bike is burbling when i go over woops and sometimes when im in the air, i have had the carb apart and check by a mechanic, i even took it in to a few different shops but no one can figure out the problem, i am gettin my cam chain replaced cause apparently that needs to get done every couple years anyways, but if that doesnt fix it do you know of anything else?
 

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