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
ROLLINFAST

Need some carb help...

9 posts in this topic

I've got a '99 WR400 that is sumo'd. Awesome bike with all new parts. Big Gun pipe and carb is supposed to be jetted for it. I've had the bike since December and have put 900 miles on it since then. The other day, I changed the oil & filter, replaced the antifreeze with Engine Ice and all was well. I rode the bike to work that night (29 miles) and everything performed flawlessly. The next morning on my way home, I got about 3-4 miles from work and the idle got stuck high. It was almost as if the throttle was not returning to rest. After checking it, I saw the throttle had full range of motion. I had to limp it home with a high idle for about 23-24 miles, dulling my shiny ceramic header coating :banghead: Anyway, I've tried adjusting the mixture screw out, but still have a high idle. It has performed perfectly. This is an "all of the sudden" problem. Please help me guys:banghead: :)

Share this post


Link to post
Share on other sites

Pull the carb and check the slide for cracks. The Gen 1 FCR carbs on the 400s have a history of cracking, and ultimately failing, ingesting a bunch of metal into the intake. If it's cracked, it would cause an air leak, which would give you a high idle (esp if your mixture at idle is a bit rich)

Share this post


Link to post
Share on other sites

Thanks, I'll pull it when I get home this morning. I'm of the belief that the carb is from a later model bike. It has a stand-alone hotstart knob (attached at the frame, not the carb) as well as TPS. I don't know for sure, but it seems as what was passed on to me when I got it.

Share this post


Link to post
Share on other sites

If the hot start is on the frame, it's a Gen 1 carb. The Gen 2 carbs have it integrated into the carb body.

Share this post


Link to post
Share on other sites

You might also check the hot start vacuum lines for leaks...disconnect it where it ataches to the head and put a cap over the nipple. If your idle drops to normal, you have a leak in the octapus somewhere...

Share this post


Link to post
Share on other sites

Thanks for the tips guys. I didn't get to pull it today, but I will tomorrow. I'm scared that it's going to be the slide as well. I'll try the trick with the hot-start first. Thanks again, and I'll post up my results.

Share this post


Link to post
Share on other sites

Don't be too scared...you can quite often find a Gen 2 carb on e-bay for less than the cost of a new slide, and you will get better idle and off idle perfomance. If you snag a YZ carb, you also lose the Air Cut Valve from the WR carb, which makes it a bunch easier to jet. If you end up buying just a slide, there used to be a guy here on TT who sold billet aftermarket slides that eliminated the problem, but I don't really remember any of the details...

Share this post


Link to post
Share on other sites

Thanks again, I tried the hot-start trick, but the idle was still high. I guess I'll check into late-model carbs if the slide is cracked. I won't know until today when I get home. I really appreciate the speedy response!

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