96 XR400 carb issues

[CarbonCopy]

New to site! Have read alot as of late! Thanks for all the good info thus far.

Recently a friend of mine gave me his xr4. It was in horrible shape. Been sitting for 10yrs. I have bought new everything, rebuilt forks shock, rotors, sprockets, etc....everything, trust me.

I have taken the carb apart, soaked, sprayed, blown it out twice now. It has 160 and 60 jets, needle clip is in 3rd groove. And yes, pilot and main are spotless clean. I have done all Gordon mods. I have bought a carb rebuild kit, installed, diaphragm is in good shape. The bike starts and idles fine. When I give it any throttle it wants to die. It pops on the way up. It will however run well on choke prior to achiving opperating temp. I have mixture screw set at 2 1/2 out. Nothing changes when I turn mixture screw in and out. I am in Texas at 500ft.

My question is can a carb be so dirty that I cannot clean the internal passages enough to make work? The carb when i opened it up in the begining was the wost i have ever seen one varnished over. Should I just buy the Minkuni pumper and call it a day. This will be my "buddy" bike so I'm not worried about any added performance from the Minkuni. I do however want it to be a first start kicker. And no, I don't want to have to spend $400 on the pumper, but I will.

If the pumper carb is the best alternative, where can I get one other than xrs only? Ive read some bad things about customer service and people not receiving ordered parts! They seemed less that inthused to talk to me. Takes 3 weeks to get one to me.

Please advise!

[Trailryder42]

During that 10 years, was the bike stored inside or out?

 

I assume you removed the fuel screw too and cleaned that passage. Did you verify its oring was present and in good shape? Verify the fuel screws tip wasn't damaged or broken off?

 

What did you soak it in?

 

Did you run a wire thru every passage also?

 

Did you try to clean the jets or just replace them?

 

Be sure the carb vent lines are not clogged up.

 

Replaced the spark plug?

 

Make sure the spark plug cap isn't loose or corroded on the end of the coil wire. Be sure the coil ground points are corroded. Pull the CDIs electrical plug, check for corrosion and moisture.

 

Verify the intake manifold oring is present and in good shape. Should probably be replaced.

 

If you get no difference when turning the fuel screw from 2.5 turns out to all the way in, the pilot circuit is still clogged somewhere.

 

XRs Only is the only place I know of that has the Mikuni already fitted with the proper bell housing extension and comes with the proper throttle cable. It's not a magic carb that just works after installation. You still have to fine tune it just like any carb. Tho it is an easier starter once tuned and you figure out the start routine.

 

I've never had any shipping problems with XRs Only. I wouldn't use them for mechanical work, but ordering parts from them they've always been ok.

[CarbonCopy]

Thanks Trailryder!

Bike was stored inside. So I'm told. When he gave it to me it was on a stand in his barn. 95% of all bolt heads are not rusted.

I put the new mixture screw and print and washer in when I rebuilt. I made sure i put it in correctly as well. I replaced the intake oring 2 days ago. That was not it. Yes, new plug, plug cap is good and no corosion. I soaked it gallon of Chem cleaner. I only soaked it for 4 hrs each time.

The bike starts to easy and idles perfect to be a pilot issue in my opinion. I can Rev it up with the choke on. That tells me it's too lean. Is that correct? I have been doing my tests without the air filter on. Is that an issue. I don't see how it could be. Thanks for your help! I have not adjusted valves yet. Any chance it could have jump a tooth or two on timing?

[CarbonCopy]

I'm sorry, I replaced main and reused pilot. I cleaned, soaked and wired the pilot. To my eyes it looks perfectly clean. But, as with other equipment, bikes, I know those suckers are hard to clean. My rebuild kit came with a #42 pilot. I opted not to use.

[Trailryder42]

Does it still have the stock air filter and cage? The stock cage is a stainless steel cage with a wire mesh in between 2 layers of screen. Quite restrictive.

 

Yes, the air filter not being installed will make a difference. Always do your tuning with the bike set up as if you're going to ride it.

 

>>>>>>>>>>I put the new mixture screw and print and washer in when I rebuilt.<<<<<<<<<<<< Print? I suppose you meant oring? When putting the fuel screw assembly together, the spring goes on first, then washer, then oring last.

 

Be sure not to leave any orings in the carb when you're soaking it.

 

I suppose you set the float level to spec?

 

The only way I see for it to jump time is if the chain is extremely worn and the auto tensioners torsion spring is broken.

 

Doing a valve clearances inspection is a good call. Should be done anyway, carb problems or not.

Edited March 26, 2016 by Trailryder42

[CarbonCopy]

Yes, I ment oring! Yes set float level. I bought the uni filter with cage.

Can I soak the carb for a few days? Will that help with clearing internal passages? I would bet that's what's going on. The carb was unbelievably dirty whennis opened it up the first time. The float needle would not come out. I had to heat it up a bit and use needle nose! Crazy!

Will the Minkuni pumper drastically improve the performance? Other than helping with off idle throttling, is there a noticeable difference. My non riding friends will be riding this bike. I will for some vintage events. With pumper carb, will it be anywhere near the throttle response of my 350ktm? I don't want it very snappy for their saftey. And thanks again!

[Trailryder42]

How did the finish of the carb look after soaking it for 4 hours? Some cleaners like Simple Green eat the finish off the carb. You don't want your cleaner to do that. If it's coming out looking ok after 4 hours, longer would be ok I would think.

 

I suggest you find a few wires of differing sizes and go thru all passages. Pieces of guitar string work good. Look up into the passages for the main, pilot and fuel inlet needle of the float and be sure those seats are clean and smooth, no varnish or corrosion.

 

The Mikuni does have better throttle response. I always tell folks to turn the accel pump screw all the way in to bring on the accel pump as late as possible, for initial setup anyway. Then play with it later on if you want to. The Mikuni is nothing to be scared of. I don't have a KTM350, so I don't know what it's throttle is like. I don't imagine it has any off idle hesitation tho, and neither does the Mikuni when tuned right.

 

The bike will rev up on choke when it's cold, first start of the day, normal. If it does so after the engine is warmed up and hot, not good.

[CarbonCopy]

It won't stay running with choke on once warmed up. But it will rev up without dying or poping on the way up with the choke on. I'm getting ready to take off and tear down again. Is there any chance that the 60 and 160 are to lean. Also, when I took apart carb first time clip was on needle in the top setting. I moved it two notches. Could that be an issue?

Backing out of mixture screw makes carb leaner correct?

[Tryingoutdirt]

TrailRyder4 is definitely the go to guy for carb help.. the popping back sure could be tight valves , if you haven't adjusted them I would be going there next.

[CarbonCopy]

Thanks tryingout! Yes, I 100% agree. I've been reading his post as far back as 06. He is well educated it seems. I'm glad he responded. I will un screw covers later and check them. I pulled carb, tore down again and will soak for a couple days. If this does not work, I'm in for the pumper!

[Piney Woods]

Did you remove the petcock and clean it? Did you clean the tank? Did you install an inline Visufilter to keep the carb from getting new gunk in it from the tank? In my opinion the screens on the petcock are worthless, never trust them. I cleaned my carb several times and even had a buddy put it in a sonic cleaner twice at the Honda shop where he worked. Until I cleaned the tank very thoroughly and installed an in line filter  my bike acted just like the one you are working on. It would be perfectly clean then get stopped up as soon as it ran a couple minutes. :banghead:   Good luck.

Edited March 27, 2016 by YHGEORGE

[CarbonCopy]

Yhgeorge - yes I did. I put a new petcock on. I did not put an in-line filter on. I dumped tank and swished new gas in it for a few minutes, thats it. You might be onto something about gunk in tank. The old petcock had completley closed off with greyish gunk. How can I clean tank throughly I wonder? Any ideas?

[Trailryder42]

Did the new petcock include new screen filter? George has a good point about what happens when the original petcock filter disintegrates.

 

For your elevation, UNI filter, 160/60 is usually should be spot on or dang close. Does the bike still have the stock muffler? If so, still have its baffle too?

 

Somewhere along the way, someone leaned out the needle by moving it to 1st from top. 3rd from top is stock and you can leave it there.

 

No, out on the fuel screw is richer. It's a "fuel screw", it meters fuel. That may be part of your problem if you're tuning it thinking it's going leaner. You'd be right if this was a 2 strokes "air screw".

Edited March 27, 2016 by Trailryder42

[Still-learning]

It really sounds like you may have air leak at the intake manifold, I saw you replaced the 'O' ring but fire it up & while running spray carby cleaner around the manifold & see if the rpm changes. This may not be your problem but I hope it helps.

[CarbonCopy]

Yes Sir Trailryder, it did have a new screen. Also, might be something, might not, this bike the A-loop mods to it, tank and seat are that of a 99 CR250. It has 2 petcocks! One on each side. One is new, other has been torn down and cleaned. I can not find another new one to fit other side, it is a different bolt pattern in the tank.

Yes, I have removed the baffle in muffler, snorkel removed. I have not checked the header welds.

When I pulled carb again yesterday I noticed the mixture screw was bent a bit. It is the cheap aftermarket one that came with rebuilt kit. I will be replacing with stock one this time. Carb is soaking, I will pull it out this evening and blow, spray, etc....

Stir learning, good idea! I will try that. Your right. That head or plastic intake could have warped with heat damage. When I drained bike of oil, about 12 ounces came out, not 2 quarts!!

I want to thank everyone for adding comments. I appreciate it greatly! I'm the type "A" that wants to fix this without simply throwing a bunch of money at it just to solve. Once. I/we figure this out, I will buy the pumper. But, I will not let this problem beat me!! I've worked on way to many small carbs to loose to this one! It's personal now! Don't you love "free" motorcycles. $2300 in so far and counting! It needs new rims as well! Small small crack in rear and big one on front! Shit! I wish I knew how to post pictures, the carb at original pull of is comical!

[CarbonCopy]

Thought I would add this....when the bike starts, not a puff of smoke on throttle up or down - the little i get. Valve train sounds spot on at idel as well!

[CarbonCopy]

Carb 1st tear down

[Trailryder42]

You drain the oil at 2 different points. There's the engine drain bolt and there's a bolt at the bottom of the front frame tube, above the oil line banjo fitting. It sticks out from the frame at about a 45* angle.

 

The fuel screw looks stock in that picture.

 

You should be able to post more than 1 picture per reply.

Edited March 27, 2016 by Trailryder42

[CarbonCopy]

1st tear down

[CarbonCopy]

I know about the 2 drain points. I drained both points! Still about 12 oz! Yikes!

1st tear down