XR650l Mikuni 42mm pumper

I am having trouble with a 42mm pumper I bought from XR's Only. I figured since the folks I bought it from have been no help so far I would ask you fine folks with your infinite wisdom. Is there anyone out there that have bought this carb and are having trouble? It just seems like too much carb for my bike. I have an 06 with the smog crap removed, FMF headpipe and Q-muffler, snorkle removed with a twin-air filter. It is moving way too much fuel for the engine to swallow. Fouling plugs and popping bad on decel. It runs fair for a while until I bump a plug. I have checked for air leaks and went bigger with the pilot to try and remedy the decel pop with no luck. I turned the pump start screw all the way in to delay the pump spray (which was the fix from XR's only) but still no luck. To get this thing to run the way it should I removed the pumper and reinstalled the stock carb with Dave's mods. I hope I did not flush almost $500 down the toilet! Any help from you folks would be greatly appreciated! I am not impressed with the so-called expert help from the vendor!:banghead: Thanks! Crewdog

Sounds interesting.

I myself want to get a carb for my 650, but a couple notes on what you mentioned, and I think people will agree.

The popping on decel is from a lean condition, usually cured by a richer pilot jet, which you tried, or the needle position being changed (lower the clip to raise the needle). If it is fouling plugs else where, maybe a leaner main jet.

Not familiar with the carb, maybe it has other jets as well.

I guess your not an advocate for the carb, but I hope you get it sorted out, so if it works out in the end you can tell me what to do if i get one :banghead:

crewdog, what are your jetting specs? main/pilot #'s? needle and clip settings? have you opened up the airbox? what exhaust do you run? what is your elevation?

I have an 06 with the smog crap removed, FMF headpipe and Q-muffler, snorkle removed with a twin-air filter. : Thanks! Crewdog

got this but still give current or best jetting combo youve found with the carb. any other mods to engine you didnt say? have you checked/adjusted valves when trying to fix this? Surprised the larger pilot didnt help poping, maybe didnt go big enough

It is not to big! it is just a jetting issu. I run a 48mm mikuni Hsr on xr650r wiht no problemo!! Only tuning was fullrace exhoust and open airbox!!

Ok Just 1 problemo..D"...Losed some power in the lower end.....but run wery smood.. God mainjet on xr650 is 150 (1,5mm) So i will think 140 on 650l and 600r.

Have you changed the air jet? Go with 1.2

I would change the pump noozle and make sure the streem hits the needle. Don't be afraid to go way big on the pilot. I have ran up to 27.5 pilot, I had trouble till I change the needle jet and needle. Y-4 Needle jet, 90HJ1 Needle.

It is not to big! it is just a jetting issu. I run a 48mm mikuni Hsr on xr650r wiht no problemo!! Only tuning was fullrace exhoust and open airbox!!

Ok Just 1 problemo..D"...Losed some power in the lower end.....but run wery smood.. God mainjet on xr650 is 150 (1,5mm) So i will think 140 on 650l and 600r.

Phrase of the Day, ladies and gentlemen!

"Wery smood."

:banghead:

Phrase of the Day, ladies and gentlemen!

"Wery smood."

:busted:

LMAO :banghead:

I tired the Mikuni pumper on my XR250R (from XR's only also) and found it to be way too much carb for the motor. It is uncorked -airbox opened, aftermarket pipe etc, but it ran like sheat.

IMHO unless engine mods are made or something as simple as a cam change that increases valve duration that requires or would be better off with more fuel flow found in the big pumper carbs, you are wasting your money.

I talked to a guy at XR's only and got an exchange going for the carb and bought some other more useful items, like an IMS tank etc.

Again - and just my humble opinion do not go to a Mikuni pumper without doing some engine work and or a cam change that necessitates the need for more fuel.

well, if you think about it, the stock carb is 42.5 mm. plus you were trying a big carb on a 250 also. how big was that carb?

I had a Mikuni TM42 from a XR650R supermotard racer, AP and choke where disconnected...should I say more?I mounted it like this on a 650r last month ,bike started nice(cold or warm) ,jetting/power was nice (better than stock) with plenty more overrev. :banghead:

The AP shoots way to much fuel for a mono cylinder,cold start circuit idem. You should be able to adjust this with leaner settings and keep the pump action/choke.

Since I shelled out plenty of G.I. dollars, I will figure it out and give you a heads up on the fix. Thanks!

Crewdog, you crew chiefing a Warthog by chance???

I have to apologize as I am still trying to figure out this website. This is an 06 with 200 miles (didn't ride it much after carb problem). Stock engine, open airbox with FMF headpipe and Q. I went up to a 25 pilot and did not mess with the needle or air jet. I guess I was really disgusted with the initial product. You folks have been a great help and have given me new roads to travel. Thank-you very much! Crewdog By the way, Sweden is a very nice place with fantastic people. I thank you for your hospitality in the past.

Crewdog, you crew chiefing a Warthog by chance???

My previous career was a Warthog crewchief and loved every second of it. Some of the arm-pits of the world were not so good, especially the big mid-east sandbox. But the jet was fantastic. Hey Greybeard you sound like you know about crewing jets. :banghead:

I DoNt SpeakE IngLirs Wery Goood!! Waht is Smood ?? He,He

Crewdog---- 37 years AF/Air Guard, retired. Spent my last 25 working 135's and A-7's. Love the A-10, especially the gun. Amazing what a 30mm will do.

Hope you get some satisisfaction out of that carb. My L's motor is staying stock for another year but I might be doing the do da to it next winter and besides a piston and cam, a carb might be on the list as well. Will be watching your progress. Later, my brother. OGB

I agree,

Ive run a HSR48 (basically a TM48) on my XRL with no issues, I removed the accel pump before trying it and never fitted it as it just doesnt need it. I found it ran smoother than the VM42.5 rounslide Mikuni Id previously bored/used.

Crewdog, Its likely that you just need to rejet it to get the pumper working as Prof Mick Uni intended.

Hey guys ? I got 92 xr600r.bored 20 over. i got a 48 mm. Mikuni flat slide carb.. Im emptying the bowl. Bike works sweet till emptys bowl. And that dont take long lol any help be great

Float valve sticking or float out of adjustment. Float may be pushed up by the float bowl  closing the valve.

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