Plug Fouling Continues
Posted November 18, 2002 - 06:00 AM
I posted a few times a couple of months ago about my plug fouling problem and got some great ideas to try but nothing worked. Heres the skinny! My bike is a 1998 WR 400 used as a dual sporter. It is fairly low mileage and in excellent, clean, well maintained condition. The bike ran fine until early this summer when it started fouling spark plugs at least each ride. It continued to get worse until it now fouls a plug after about 2 minutes of running. I have replaced all electronic components including the CDI, Stator, Ignition coil and plug cap, Unhooked the grey wire, tried it witht he stop switch and TPS unhooked. Still no difference. I went torough the carb with a fine tooth comb and dropped the needle all the way. Checked float height and even ran it without the air filter to be sure it was not causing too much restriction. No Change. It fouls a $3 plug after only a few minutes of operation. Yes the plugs are black but I cant get enough time on the engine to take a proper plug reading. I believe they are sooting up while in the start-up mode. It runs great with no black smoke until it fouls the plug a few minutes later. Some of you said re-jet the carb but, it ran flawlesly for 3 years and probably on the same plug and all of a sudden started this. My dealer is no help, Yamaha customer service has been no help. This bike is un-ridable. If anyone has any ideas please help. I would buy a new 450 if I could get this one to run long enough to trade it in.
Posted November 18, 2002 - 07:41 AM
Posted November 18, 2002 - 08:02 AM
Posted November 18, 2002 - 08:50 AM
Thanks for the replys!
Posted November 18, 2002 - 09:59 AM
If we rule out electrical, which seems prudent given you replaced just about everything, it must be that your carb is leaking fuel into the motor somehow. I think there is a gasket between the top and bottom halves of the FCR.
It sounds to me like you need to find a bike to swap carbs with. A KTM four stroke or DRZ should work as a donor if you can't find another 400/426.
If you swap carbs and the fouling goes away I'm thinking it must be the accelerator pump or a leak between venturi and carb bowl or emulsion tube or something.
Hope this helps.
Posted November 18, 2002 - 03:19 PM
Let us know.
Posted November 18, 2002 - 09:26 PM
how about air mixture jets?
I dunno, I had a clogged pilot air and my bike would not even idle, and I gave it plenty of time to foul a plug before I finally yanked the carb.
What you and Bill say about needle valve etc. is a guess I'd also like to endorse as the culprit.
Posted November 19, 2002 - 12:15 AM
next time you attempt to get it running, don't do it in the shed-do it at the beginning of the trail and get going immediately. even start it with your lid and gloves on the lot.
try and cover a few miles. disconnect the APJ if you can and you should burn a lot of the carbon off.
if the bike runs ok and but for what you'd call carb glitches it's fine then i suggest you drastically alter the jetting on it and come right down on your settings to the stuff they use here.
watch out for the coil wire being a bit loose as well...
Posted November 19, 2002 - 04:10 AM
Posted November 19, 2002 - 08:30 AM
what is the APJ?
He's wanting you to ride it with the accelerator pump disconnected.
Probably the easiest way to do this on your carb is to take off the pump cover (on the bottom of carb bowl), watch out for two very tiny o-ring seals, and remove the pump diaphragm and spring.
You can also remove the pump actuating rod, but I'm not sure how difficult that is to do on your carb, the throttle shaft may have to come off...
Posted November 19, 2002 - 11:02 AM
what you need is running time with no problems, get some heat into the engine and burn all that carbon off. get fresh fuel through it etc etc.
then every little glitch needs putting down in your memory and briing it back here. we'll do our best.
now don't do what one bloke did and that is to find a bog in the acceleration "ah he said, it nearly jumped off the paddock stand as well!"
you have to smile
Posted November 19, 2002 - 12:46 PM
Is the choke circuit closing?
From your descriptions the jetting is nearly stock:
?? turns out
#75 pilot air jet
#200 main air jet
Is this correct?
Posted November 19, 2002 - 01:42 PM
Posted November 20, 2002 - 09:32 AM
I will try running it with the Acc Pump non functional. What if I try to ride it with the hot start valve pulled out. Wouldn't this lean it out and possibly eliminate rich fuel fouling the plug. The mixture screw is out 1.25 turns.
I will have some time this weekend to do some testing and I just bought a whole box of plugs.
Posted November 20, 2002 - 12:53 PM
I hope you get it figured out. I don't want to see another unresolved plug fouling issue here...
Posted November 22, 2002 - 04:07 PM
Posted November 25, 2002 - 05:03 AM
I am still experimenting with this gremlin. I turned the pilot screw in to 1/4 turn out. It was set at 1 and 1/2 out before. It does not idle real well this far in but it does seem to be leaner. I ran it about 20 minutes around the yard and it has not fouled yet. Usually the second time I crank after it has had time to cool completely the plug will foul for sure. I did stop and check the plug a few times during my yard riding and most times it looked good and clean. However, a couple of times it looked good in the center but the outside rim of the plug was black. It would easily wipe off with a rag and some carb cleaner. Is this normal?? I don't put the bolts back in the gas tank or seat so it is easy and quick to pull the plug. I have not disabled the Accelerator pump yet. I am trying to do this one step at a time. I will continue to try it this week. Thanks for all the help and suggestions.
Posted November 26, 2002 - 06:34 AM