Need help after Mod's

To start, I just started riding two summers ago, so I am new to motorcycles. I have learned a lot from reading posts on this site. It seems there is always someone willing to help with a problem. THANKS!

I recently removed/disassembled the carb and cleaned it all up. The bike ran ok last summer, but after sitting for a few months it was difficult to start and it ran terrible after it did start. It wanted to die when you would snap the throttle while in neutral. The mods on the bike last summer were airbox lid removed, exhaust unplugged, and throttle stop shaved. While I had the carb off, I did the "Taffy Mod" and disconnected the Grey Wire. The bike still wants to die when snapping the throttle while in neutral, and now after riding up and down the street, it does die when I pull up to the house after shifting down to first gear and pulling in on the clutch lever. It is also spitting/popping out the pipe after down shifting. Unfortunately I have to have the plug in while testing on the streets near the house. I am pretty sure it is all a jetting thing now, but I wanted to get some ideas from anyone willing to help on this site. I did not change the jetting from last summer.

Jetting is as follows:

Main Jet = 158

Pilot Jet = 45

Pilot Screw = 2 turns out

Starter Jet = 60

Main Air Jet = 200

Pilot Air Jet-1 = 75

Pilot Air Jet-2 = 90

Jet Needle = Clip on groove #2 (second position from top)

I live near Boulder Colorado. My riding is between 6 and 12k elevation.

MrLee.First make sure you're running fresh fuel & a fresh spark plug before you go any further.Then if you still have problems do a search on jetting for your altitude.LarryCO should have some tips for your area,sorry I'm near sea level.If it ran good before it's probably something simple.BTW what needle are you running?

I knew I was going to forget some info. I replaced the plug and gas as well. The needle is stock (DTM).

I noticed my accelerator pump is somewhat prone to fail if the bike is stored for a period of time. You may want to check yours.

First off, you NEED to disassemble the carb for a VERY THOROUGH cleaning. The 98’s and 99’s have an inferior accelerator pump design and the AP is notorious for filling up w/ dirt and water resulting with corrosion and SEIZING!

Before you pull the carb off your bike, run the bike dry by shutting off the fuel petcock on your tank. As the bike starts sucking the float bowl dry of fuel keep blipping the throttle. This will drain the fuel out of your accelerator pump reservoir if it not seized.

Work over a VERY CLEAN area. A cardboard box may be ideal. You can very easily drop some o-rings and you will very hard-pressed to find them. Be sure you seal up any areas in the box where tiny o-rings can roll/slide into. EXPECT fuel to still be in the carb. You can rotate the carb upside down/sideways/every which way several times. This will cause most of the residual gas to flow out the carbs vent lines.


You will want to disassemble the carb completely. The AP has two o-rings in it. One ALWAYS falls out.

I recommend doing the following:

ENTIRE carb disassembly, cleaning, and blowing out w/ compresssed air.

Including: both main and pilot air jets – these are under the air horn on the airbox end of the carb. It is common these two jets plug up w/ air filter oil if you do not wait enough time after oiling your air filter

ALL jets on the underside (inside the float area of the carb).

The accelerator pump in it’s entirety.

Your fuel screw >> WARNING,WARNING WILL ROBINSON!! When you pull your fuel screw out, there is a tiny o-ring and tiny washer, along w/ the spring in the hole. DON'T LOSE THEM!!

Set your float height.

Remove your air cut valve (the octopus), plug the two brass nipples or fill w/ silver soldier

Perform either the Taffy mod or KL mod to your accelerator pump linkage.

Re-jet your main jet, pilot jet (if necessary), needle jet, main air jet, pilot air jet (or adjustable pilot air screw -available only from SUDCO)

I agree with NH, however I do not recomend his method of removing fuel from your bike. Shutting off the fuel supply and running the bike creates a lean condition that can last as long a 3 minutes. This could be enough to burn an exhast valve.

1. Shut the fuel off and lay the bike on its side. (the vent hoses will allow most of the fuel to run out of the carb.)

2. When you remove the accelerator pump basin there are 2 o-rings that are very easily lost. Be careful.

3. Inspect the accelerator pump diaphram for cracks. Mine had set in gas so long that it had hairline fractures in it that prevented it from pumping fuel properly.

4. Clean accelerator pump actuator arm of rust and dirt. (it will be rusted) are regrease with a litium based water proof grease.

5. Check fuel flow passages for rust pieces. Most likely you will find a small pond of rust and water on the top side of the accelerator pump diaphram.

6. Make sure when you reinstall the carb that the air boots are put on TIGHT. These bikes create a tremendous vaccum on the air boot when you close the throttle from WOT.

Thanks for all the advise! I did take the carb completely apart. I didn't loose any O Rings, just mixed up the O Ring and washer that went with the pilot screw. Yes the accelerator pump was very dirty and rusted. I actually put it all back together and didn't have any left over parts. Just ran aweful when it was all said and done. I have PM'd LarryCo a couple times and I am going to try his jetting setup. I will post after I get it all put back together and try it out. Just got all the required jets and needles and so forth tonight.


I completed the jetting (copied LarryCo's setup) and the bike is still acting up. It takes awhile to get it started, after it does start it dies when I snap the throttle. I took it up and down the street once, and it is backfireing on deceleration. It also died after I downshifted to 1st and held the clutch in. Now it doesnt want to start again.

So carb has been completely cleaned.

Taffy Mod done.

New plug.

New gas.

New air filter.

LarryCo jetting.

Pipe uncorked.

What Next? Any help is appreciated.

Sounds like it is rich or possibly OVERFUELING or you have installed the plate on the carb slide backwards.

If it is overfueling or FLOODING it could be a bad needle & seat (attaches to the float at the fuel inlet-(rubber tipped) or a misajusted/defective float.

Correct me if I'm wrong but the symptoms you are having are the same as when you started?These problems exsisted before the jetting changes? You will more than likely have to clean or replace the plug if it is fouled.We would also need to know the condition of the plug.Did it smell excessively rich when it was idling?Don't worry someone will set you straight!


Can the plate be installed backwards? I thought it would only fit in one way. I am not sure what you mean with the needle and rubber tipped seat. I will look at the service manual. Is this the Jet needle? I installed a new (EKP) needle.

The symptoms were the same before jetting. The plug is new with the exception of up and down the street twice. I will look at it again though. It doesn't smell excessively rich, but I can't ell if it is too rich or too lean so who knows. Thanks.

Mrlee,Yes the plate that fits onto the slide CAN be installed backwards,I think that all of us here have done it at one time or another.If you don't pay close attention to the way it came out & put it in backwards it will run like crap.If you suspect this has happened,just flip it the opposite way.You will know if that is your problem immediately.The manual description that shows the plate is'nt exactly clear.I believe If I remember correctly the lettering goes toward the air box side,don't quote me on this though.Maybe someone can chime in that remembers for sure,but it is important that you verify this first.

The needle & seat I'm referring to attaches to the tang on the float.The neoprene needle can become brittle & cause carb flooding.The float rises to its adjusted point (float level)the fuel should stop flowing.If the needle is defective it leaks fuel into the carb bowl.That problem can cause a gas smell at idle from the tail pipe.(among other things)Did you check your float level? & set it to specs?I hope we are getting somewhere :smirk:Check that slide plate first though OK Maybe we'll get lucky with that. :)

Mr Lee,I just noticed you have a 99 close attention to the slide when you inspect it it COULD be CRACKED.Let us know what you find.


Me and the carb along with the fumes spent way too much time in the garage last night. I was having long conversations with myself.

I checked the slide it is not cracked. I DID have it on the correct way. I tried it every other way and it did not slide smoothly. I also checked the needle valve. It looked great. The float was in spec as well-(Fun reading in the service manual). I did not recheck my plug yet, but like I mentioned, it is new with the exception of up and down the street a couple times.

Thanks again for your help!

So which way was the slide installed when you checked it?It can be installed wrong & the slide will move.Did you make any more progress on the diagnosis?

The only way I can describe the slide (or throttle valve per service manual) is that the hole on the throttle valve plate is at the bottom. If I'm not mistaken, the only other way it would go on is if the hole was at the top. I tried that and the thing only goes down about half way. The way it is installed now, there is free movement.

I have another question though.

What is the correct installation for the adjusting screw and locknut that goes on top of the arms and roller assembly which moves the throttle valve up and down? There isn't much in the manual about this. To me it looks like it slightly raises or lowers the throttle valve position at idle. Do I need to have this adjusted so the plate is down as far as possible or up a little from the bottom of the carb?

Hope this makes sense. Hard to discribe. THX

Ok-The slide plate is installed on the engine side of the slide,hole facing downward.The hole should face toward the engine per manual.Normally you should'nt take off the throttle cables by loosening the lock nuts,this messes with your throttle free play.If you indeed did do this you need to follow procedure in the manual under inspection/adjustment,look for throttle grip free play adjustment.Once you get that adjusted remove the mounting bracket for the cables with the 2 screws that hold the bracket to the carb if you need to remove the carb again.

That is good advice for the throttle cables. I will do that next time. The adjusting screw and locknut I was talking about is actually inside the carb at the top. This slightly adjusts the height of the slide. I was wondering what the correct adjustment for this is? It does not state it in the manual.

I cleared a ton of problems on my bike by removing the small cylindrical spacers on the 2 hose clamps that hold the carb in place.

This was causing the bike to gulp a lot of unnecessary air and I had the issue where you would gas it and it took forever to go back to low idle when you let off---and some popping. This was one simple cure for my woes.

Sorry,I misunderstood you.My 2002 WR does'nt have that adjustment,The idle screw controls the slide air gap to the best of my knowledge.Did you happen to check the archives for the WR 400?


I did check the archives and found a couple posts on the slide adjuster screw,Thanks.

Sounds like this little screw is pretty touchy. I put it to the number of turns out that it was when I took it apart. Don't think that was the problem because I had already done that anyway.

I did however do a bunch of electrical checks and got bad readings from the coil. Hope to get a new one tomorrow. Any experiance with the coil or electrics in general? Think that would cause the problems my bike has?


Thanks for the tip. I left those spacers off this time when I put the carb back on. It was missing from one side anyway.

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