HEADS UP!!!

Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.

Sign in to follow this  
Followers 0
m2g4b

Rich/Lean Carb?????????

7 posts in this topic

Okay, I have a 98 yz400 and it just recently started to run like crap, you have to leave the choke on way longer than I've been reading about on here. It pops alot on decel, and the bog is getting worse every time I ride!! I am just now starting to look at my carb and fiddle with it enough to become somewhat familiar with it, I have it tore down right now, cleaning it out and cleaning the acel pump (man was it nasty)anyway, I have found alot of info on carbs but usually it is on newer bikes with the bk mods and so forth, what can I do to fix mine, by the way the temp has dropped dramatically here is Oklahoma, it is around 30 to 40 degrees now. Do I need to play with the fuel screw or try to re-jet the carb??? help please!!! thanks

Share this post


Link to post
Share on other sites

If you richen the pilot circuit that should clear up your decel popping. Makes sense this time of year because colder air is more dense and will require richer jetting to get the right mixture. We should post a jetting guide in the tech section because I know this has been posted before, but here goes:

-Adjust your idle per manual specs

-With bike off, count number of turn it takes to turn fuel screw all the way in. Record that as "before" setting.

-Turn screw back out to "before" setting as a starting point, fire up the bike, then begin to turn the fuel screw in until the idle begins to get rough. Note the number of turns.

-Then, back the screw out until the idle gets rough. Also note number of turns.

-You want to put the fuel screw right in between the two extremes. This should also fall within 1.5-2.5 turns out total. If you're outside that range, the pilot jet needs to be changed. If you're more than 2.5 turns out, go up a size and vice versa.

Hopefully the cleaning will clear up your bog. If you've got it this far apart, you may want to check the squirt duration and timing of your accelerator pump. Also check the stream quality. If it's a really long squirt (>2 sec) I would search this page for ways to reduce the squirt duration (what the BK mod is for on '00 and newer bikes). There is a similar mod for the older ones. Also, make sure the squirt is straight and unobstructed. Lastly, make sure the squirt doesn't hit the slide. If it does, the newer bikes have a timing adjustment screw, not sure if the old ones do, but changing the timing alone has helped some bikes eliminate the bog.

Hope this helps and I'm sorry if I've repeated a bunch of stuff you already know.

Share this post


Link to post
Share on other sites

I had the pretty much the same symptoms as you do on my 99 YZ400. I had the fuel screw out 3 turns and it still popped on decel and was a cold blooded dog when it came to starting it. I put in a 48 pilot jet in place of the 45 stocker and went 1 1/2 turns out on the fuel screw. Along with a good carb cleaning, the bike runs great now. The cold weather will affect the jetting so don't worry about changing it, just follow the post by bbeakly and change the jetting if need be.

Pat

Share this post


Link to post
Share on other sites

WELL I WENT INTO THE CARB AND THIS IS WHAT I FIND, THE SPRAY DOES NOT HIT THE SLIDE!!! BUT IT IS RATHER LONG, CLOSE TO 2 SECONDS. I PUT THE FUEL SCREW AND THE IDLE TO STOCK SETTINGS (FS=1 3/4 OUT,) AND TRIED IT ALL OUT. THE BIKE STARTS GREAT, HAS A HARD TIME IDLING,YOU HAVE TO KEEP IT CHOKED FOR AWHILE, ONCE YOU GET IT ROLLING, ITS AWESOME, STILL STUMBLING A TAD ON A QUICK FLICK OF THE THROTTLE. DO YA THINK IT COULD STILL BE FIXED BY THE FUEL SCREW OR JUST GO UP A SIZE WITH THE PILOT JET, MINE IS A 45 STOCK! THANKS FOR ALL THE HELP!!

Share this post


Link to post
Share on other sites

m2- my '00 came stock with a 42 pilot, I changed it yesterday to a 45 with mixed results. I found it ran better, with less decell popping, but it didn't really help the starting all that much. You might look at my post on my cold weather jetting experience... Where do you ride out there? A couple friends and I are planning a dune trip for next weekend if the weather gets a little better...

Share this post


Link to post
Share on other sites

MikeOK - Hey, mine comes stock with a 45 pilot and a 175 main, i tore the carb down again to make sure thats what was in it, and it was, I actually went back to stock on all the settings and it fires up on the first kick but would not run with out the choke. I finally decided to change the plug again to make sure I hadnt fouled it while tinkering, i had a cr7e in it and i went back to the cr8e plug, it fired right up and ran great all day at the track!!!??? dont ask me, im lost!!! also we ride here in duncan mostly at the mx track here, sometimes we go to munster, draper, stillwater, and some various places. thanks for all the help people!!!

Share this post


Link to post
Share on other sites

m2g4b,

I rode all last winter with the stock CR8E plug without any trouble (In New Mexico at 5000' with temps from 35-50 deg). The CR7E is a colder operating temperature plug then the CR8E. Haven't read what the operating temps should be for a CR7E. I'd suggest leaving the CR8E in until you run into problems that the CR7E can fix. It would be interesting to find out what the advertised temp ranges are for the CR7E just to see if that might have been the reason...

The duration at 2 seconds for the accel pump spray is longer than what most here recommend. There is a mod to reduce the squirt duration down to the recommended 0.3-0.5 sec on the 98-99 carbs if you want to try and eliminate what bog you still have. Look up JK mod in the search, you should be able to find all you need there.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now
Sign in to follow this  
Followers 0