Need help after Mod's

Well MrLee,You should be a FCR expert by now :D

As far as your coil is concerned I would be very suspect of changing any electrical part based on ohmmeter readings that are slightly out of spec,I've really never seen an elec. part that was within printed specs.Unless you can visually inspect & condemn the coil I would not change it based on ohm readings that are slightly out of spec. IMHO.

An open curcuit would be grounds for replacement,coils can breakdown under a load (hard accel) & still show good when bench tested.Sadly the only way to verify some elecrical problems is to replace the component with a known good unit.

Other electrical things to check are TPS,CDI box & all engine/frame grounds & related connections.Keep plugging away :)

I was afraid you were going to say that. I checked on the coil this am, and it is $85. OUCH. I ran through all the checks, and everything else was in spec per manual. Coil was only one off. Guess I will take it to dealer and have them double check it for me. Pretty sure they are going to say "Ovcourse it is bad, buy a new one!" Oh well, not sure where to go from here.

If carb is right & you can't verify ANY electrical problems.The next logical step would be to check the mechanical stuff like engine compression and verify the valves are adjusted correctly and there are no valve train problems.Let us know how everything turns out,all could benefit from knowing the cause of your problems.

Some good news!

I took the coli into work along with my tester and had someone verify I was doing this correct. I did not remove the spark plug cap, resistor, and spring before doing the test. We did that, stuck a long screwdriver down in the boot to make a connection to the metal at the bottom and redid the test. Coil tests good. There is one more thing ruled out and $85 saved.

I did notice the spark plug cap was loose. I checked the archives and found that member (Rich in Orlando) had similar problems due to loose cap. I can only hope that is what it ends up being. I am already on system overload, my head is going to explode, but I will look into the valves etc next.

Thanks again for stickin with me through this.

Did you take off your tps sensor. It has to be adjusted to a certian degree. When mine was out of wack my bike ran crapy.

I did have the TPS off all the way at one point. I just did the resistance check last night with it attached to the carb. Everything was in spec. Am I missing something?

As long as you returned the TPS to its original location you should be ok.There is a voltage setting at idle for the TPS to be adjusted to(see Manual for spec)There is no test I know of to check the CDI(black box) Just make sure you go over all the connections & grounds.Check grounds for corrosion clean as necessary.Hey its a process of elimination.Don't melt down just get your self a frosty one & have a think. :D:)

Are all your o-rings and rubbers in good shape and sealing properly. If not it could be sucking air in some were. You can try letting it idle and spray wd-40 and if it finds a leak the idle will increase for a few seconds. Also did you blow out all you passage ways in side of your carb. Hope you get it fixed nothing worse then something wrong and you cant figure it out. :)

Mr lee,when you take your bike up the street for a run put a new plug in first,when you get back take it out again(wait for the motor to cool first)if it`s black,you are too rich,and a motor runing way too rich at low revs WILL foul a plug fast,it will clear a little when you get a bit of speed on,then foul up again when slowing down,checking the plug when trying to find jetting probs is very important!,it should come out with just a little soot way up inside,just where insulator meets the metal threaded part of the plug,make sure you do this it can save you a lot of stress!

TPS check in the manual only talks about ohm resistance. I dont see anything about voltage at idle. Hate to keep buggin, but I don't want to miss something in my elimination process.

captain s,

I will get another plug and check.

Your not bugging anybody,MrLee-I just keep checking back time to time between errands to see how your coming.The TPS adjustment procedure should follow the testing section in the manual.Idle should be 1700-1900 rpm.Positive tester lead to yellow wire/Neg. tester lead to black wire.Leave wires connected,start bike-voltage should be .58-.78 Volts.This is the WR 426 spec. per my book.Look toward the back of your book all info should be there.

Thanks RSA210.

I am afraid my manual doesn't have any voltage check on the TPS in it. I have done all the checks per manual and they are all ohm resistance. I am feeling pretty comfortable about the TPS.

This is where I'm at now.

When I took the bike out this spring to start it up, it had a bad bog at idle when snapping the throttle. I figured the carb needed a good cleaning because I didn't drain the gas when storing it.

So I cleaned it, left everything else alone (jetting and did no mod's). I did put in a new plug and gas though. It ran worse. This tells me I put something back together in the carb incorrectly. I should have just rechecked the carb from here but I decide to change the jetting and do the Taffy mod. Bike runs the same as previous jetting (bad). So I am thinking the carb did need a good cleaning but I put it back together wrong. I rechecked the slide and plate and there are no cracks. The needle valve and float are in good shape and in spec. I have tripple checked the Taffy Mod and I am real close to a .5 second squirt durration. The only thing I am not sure of is the adjuster screw and locknut inside the carb at the top. Looks like it slightly adjusts the slide height. Right now the slide plate (engine side) is about the thickness of a dime above the bottom of the carb. There are a couple posts about this adjuster screw. One response by Taffy says the slide plate (engine side) should be at the bottom of the carb.

I will do this next. If this doesn't work I am afraid the next step will be a mechanic. Hate to do that after all the time I have put into it. I have a ride coming up the first of May and I'm afraid if I get into the valve adjustment and so on, I will mess something else up and not know where to turn.

I will let you know how the slide adjutment works.

Are you sure you have all the o-rings back in?

There are 3. 2 in the accelerator pump, 1 on the fuel screw. There is also the rubber gasket between the air horn and the carb body, where your main AIR jet and pilot AIR jet sit.

On your fuel screw, the order is drop the spring on the screw, then the washer, then the o-ring. Then the screw inserts into the carb.

You checked your float height?

No air leaks, either on the carb, airbox boot or rubber manifold that connects the carb to the engine?

Unless I am sadly mistaken, there should be a slight gap at the bottom of your slide w/ the throttle closed. Without that gap, the engine cannot draw in enough air at idle.

I really hate to see you bring the bike/carb into an OFFICIAL YAMAHA DEALER. I know more about my bike than those guys do.

Did you happen to check the hotstart button? :) Mine stuck on me one time and did the same thing as yours is doing. I have a 98 YZ and I have to take my hotstart button apart from time to time and clean it. Hope this helps. :D Oh and when this happened the only way it would idle was if I had the choke on all the time.

NH Kevin,

Is that 2 or 3 O-Rings in the accelerator pump? I have the 2 small O Rings in there. All other O Rings are in. Float height is in spec.


Hot Start is good.

This is where I am now, I think I'm getting close.

I tightend the adjuster screw and locknut (adjuster screw first) inside the top of the carb last night all the way down putting the slide plate at the bottom of the carb. I put the carb back on and almost tightened everything when I noticed the airhorn carb joint wasn't all the way on the carb. I pushed it on all the way and tightened everything down. When I started it later this morning it started with a couple kicks with choke on. I was letting it warm up when it died after about 1 minute idleing. Then it wouldn't start with the choke on. It would almost start with the hot start. It started with 1 kick with both choke and hot start. I could then turn the hot start off, but it would die if I turned choke off also. So I had to turn idle screw as far as I could clockwise (make idle faster) before I could turn choke off. It still wouldn't idle very good after doing that. The only way it ran good was to turn idle down and have choke on.

This is telling me it is too lean???

My thoughts now are that I had an air leak at the airhorn and carb before I adjusted the slide plate down to bottom of carb (and that was my problem not the slide plate), and I should readjust the slide up a little???

Maybe now it is just a matter of adjusting the fule screw???

I am at the same jetting setup as LarryCo.

Any thoughts?

I would really like to know for sure how to adjust the slide plate with the adjuster screw and locknut.

Mr Lee

My 2000 WR400 was doing the same thing and I was blamming jetting. I spent weeks on my jetting. It ended up being the coil was not grounding to the frame. I cleaned the tabs on the frame and cleaned the coil tabs and tightened it down and my bike run better. I also cleaned the bottom wire mount. I don't know if this will help you or not but it help me.

NH Kevin,

Is that 2 or 3 O-Rings in the accelerator pump? I have the 2 small O Rings in there.

just 2 in the accelerator pump (AP). You are all set.

If you need both the bypass and choke here is what's going on:

The hot start is porting air directly from you airbox around your carb to your engine's intake. As for choke, you are getting extra fuel. If your slide is bottomed out in your carb's throat, you will need to raise it up a bit.

I will raise the slide plate a little and try it out. Maybe I just wasn't getting the carb sealed off all the way. I probably wont get a chance to get this done for a couple days, but I will post the results when done.

did you lose the rubber o-ring/gasket that sits between the air horn and carb body?

If you are talking about the O Ring/Gasket that goes between the two metal/aluminum (whatever it is made of) parts of the carb, it is installed and in good shape. If there is one that goes where the rubber airbox/airhorn meets the carb and is tightened with a clamp, I am screwed.

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