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Old 07-08-2010
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Bulla Bulla is offline
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XR400 with Mikuni carb running rich and Swingarm Bearing question

Looking at the plug today whilst doing the valves on the bench while the frame is being painted I noticed the plug is black and sooty like it's running rich. It has been a fuel guzzler with a bit of a deceleration backfire of late. Adjusted the pilot jet on the Mikuni TM36 which originally decreased the backfire considerably however the running rich is still there.

Anyone else running a Mikuni out there that can point me in the right direction on what to adjust on the carb to solve this issue.

Swingarm wise I've got the old bearings out with the special tool (big hammer and drift) and have noticed the kit I have has two sets of different width bearings in it. It appears I have a choice of fitting 4 of the same size bearings or fitting 4 slightly wider bearings (This will give me more surface area for the bushes to roll in so would be better). Both sizes will fit just not sure if I have missed some bearings or its just the way they come in a kit with different sizes.

Thanks in advance

Bulla
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Old 07-08-2010
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You got it out.. :0

Lucky you hehe..

I guess I should have another go at mine
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Old 07-08-2010
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Quote:
Originally Posted by geoffyboy View Post
You got it out.. :0

Lucky you hehe..

I guess I should have another go at mine
Huge steel piston sort of drift pin, big sledgehammer and the young fella holding the pin. Took about 2 hours overall but finally came out. Might pay to chase up a replacement bolt as mine didnt survive the ordeal.

try to get it to rotate using a impact socket or something every now and then as well. Mine didnt move then one hit later it began to. Tokk about 20 hits after that to get it out.

Good Luck
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Old 07-08-2010
rideo rideo is offline
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Congrats on getting the pin out.
As to the carby, you could try the fix i'm real close to applying, and that's to chuck the fkn thing on Feebay.
I think i did say to you to get some smaller jets when you bought the carby as the yank jetting is too rich for here.
I've tried just about everything including - --- --- ----- ----- ------, that didn't work either as it stuffed up the choke due to less/no vacuum.
Smaller pilot wouldn't tune up right, mucking around with the squirter duration and initial working point didn't do a lot either.
It's not just the crap running for the first 1/4 throttle, it's the shocking economy that i get now that i can't handle, used to get roughly 90-110 before reserve, now i get 60-70 before reserve, no good for any real riding at all.
You can get a smaller squirt jet apparently, that may help and it's my last move before it goes.
I don't see me getting satisfactory economy however no matter what i do to it...

i also have the issue of the squirter mechanism on the throttle shaft suffering a delay due to the spring mount setup when i snap the throttle open, one of the main reasons imo for using a pumper is to have that instant lunge when the message is given, and when i do it now it actually has more lag than a stock carb, how fkd is that?

I only fitted mine up when i was chasing a popping/snuffing issue, that turned out to be recessed inlet valves so i may just go back to the OEM carby as at least i could get that to within 99%, even the known bog off idle wasn't a big issue with mine. I guess i got sucked in with the hype over pumpers on xr's as being the best thing since sliced bread, maybe it is with a diff. carb and indeed if you could get it running right it would be awesome as it does offer more go over the stock carb,, but again, i've nearly had enough i reckon.

Plenty of suckers, i mean xr owners out there that would be happy to get this as a bargain on ebay [wont part with it for less than what i paid and i dont see any trouble getting that]

Good luck and sorry i don't have the cure for ya woes.
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Old 07-08-2010
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Know what you mean re the fuel economy, mine is like 1/2 tank to 40km but a lot more responsive. When I bought the carb I asked for the next size down jets so might pull it apart and see what I got. Also has an XR's Only competition exhaust on it which came with extra jets so will see what size they are. No issue with the accelerator pump as yet, mine is set just under 1/4 throttle. Broke the pull cable for the throttle last ride so just checking whether the oem cables will fit, can't seem find anyone who sells them separately. If I can't find a fix for this issue I might also put it on feebay and go back to the stock carb as well.

Just have to get a bigger tank to do the longer rides lol
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Old 07-08-2010
rideo rideo is offline
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My squirter used to work well, but i have adjusted it back so as to be throwing less fuel in there ie: it now stops squirting at 1/2-2/3 throttle whereas it used to squirt up to 3/4 or even closer to full throttle.
I certainly don't miss the squirt up higher in the range and economy came back a tad, it's just the crap running at up to 1/4 twist that is getting me, and economy.

What do you mean by 'mine is set just under 1/4 throttle'?
Does it squirt for 1/4 then stop or does it start at 1/4 position?


With your cable, take your busted one [all bits of it] to a bike shop and they should be able to make a new inner to go in it, brass ends soldered and everything.

Btw, got no idea re: the swing arm bearings, maybe ring Honda on Monday and ask them?
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Old 07-08-2010
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Quote:
Originally Posted by rideorberidden View Post
My squirter used to work well, but i have adjusted it back so as to be throwing less fuel in there ie: it now stops squirting at 1/2-2/3 throttle whereas it used to squirt up to 3/4 or even closer to full throttle.
I certainly don't miss the squirt up higher in the range and economy came back a tad, it's just the crap running at up to 1/4 twist that is getting me, and economy.

What do you mean by 'mine is set just under 1/4 throttle'?
Does it squirt for 1/4 then stop or does it start at 1/4 position?


With your cable, take your busted one [all bits of it] to a bike shop and they should be able to make a new inner to go in it, brass ends soldered and everything.

Btw, got no idea re: the swing arm bearings, maybe ring Honda on Monday and ask them?
Unfortunately I left the damn broken cable at Manar park when I was sizing up potential replacements. The stock cable seems to be the same length as the Mikuni push side just havent checked the fittings to see if they will fit.

My carb seems to activate the pumper around 1/4 throttle maybe slightly less. Amost close to what yours was originally.

been looking at site: http://www.iwt.com.au/mikunicarb.htm They also sell the jets as well. Going to ring on Monday and get some prices. In the meantime Ill pull the carb to pieces and check what sizes are in their now - probably not the ones I asked for afetr we spoke a while back about the jetting issues.
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Old 07-08-2010
rideo rideo is offline
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That would be good if you could, if you DID get smaller jets as you asked and they are still too rich then i need to look at going down more than what i have tried as my starting point should be higher than what you have.
I have been putting a bit of faith in xrsonly knowing what they were doing with jetting it for us, maybe they are miles off?
Certainly seem to be at this stage.
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Old 07-08-2010
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I dont have too much faith in them, they never answered my emails when I bought the carb and exhaust, and the tip has only just arrived for the exhaust 3 months after it arrived. The tip alone (which was part of the exhaust package) took 2 phone calls and about 5 additional emails to begin its journey here.

Will let you know what I find out when I check the jets - hopefully they have numbers on them.
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Old 07-08-2010
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I really must get around to posting my 'How to install a FCR carb on a XR 400' thread.

Why anyone pays top dollar for second best (Mikuni) is beyond me.

Which carb has been fighting off the progression of EFI on dirtbikes? The FCR!!

And spare jets/needles? Every man and his dog has 'em laying round in the shed.

Cables no worries either.

You can bling it too

Mine punches out wheelies in 4th. I run 14/40 gearing. About 130 odd to reserve. It has hot start, BK mod, O-Ring mod, homemade KeroNow and a 50mm PVC spigot adapter.......

WHOOOPS!!

I gave away the secret.


All you need to make it fit.

Impossible!!! they said on TT.

FCR's dont fit XR 400's they said on TT.

I made it fit.

With good old fashioned Aussie ingenuity.

And some 50mm PVC pipe.

Go on fella's, get amongst it.
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