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Honda XR650R - Mikuni TM40 - Interesting

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Hey guys have had my mikuni tm40 for quite a while now and it starts alright and runs alright but recently i have noticed a little bit of an annoying issue.

This issue i have fixed a little bit with a gearing change but when going through some singletrack type sections it almost seems that after 10-20 corners or similar that the bike builds up a sort of bog where im guessing it has ingested to much fuel possibly through the accelerator pump?

I have started to adjust the start stroke for the pumper but thought id ask any of you fellas with the same carby just for reference and if its related to the start stroke or the end stroke.

It has roughly 2-3mm before the pumper starts the stroke and finishes roughly at 1/2-3/4 throttle.

As i said other then this area the snap the carby has is awesome.

Thanks

Matt.

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Warmer in OZ now maybe she's a litle rich.

2-3mm should be fine for the pump mine works straight from idle.

Does it clear out? Is it intermittent?

Things shouldn't just change for no reason.

Cracked float.

Needle and seat not shutting fuel off.

Blocked breATHER?

Is the pumper stream hitting the needle?

One other reason why bikes go rich for no reason can be muffler packing but that's more 2 strokes dude.

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Warmer in OZ now maybe she's a litle rich.

2-3mm should be fine for the pump mine works straight from idle.

Does it clear out? Is it intermittent?

Things shouldn't just change for no reason.

Cracked float.

Needle and seat not shutting fuel off.

Blocked breATHER?

Is the pumper stream hitting the needle?

One other reason why bikes go rich for no reason can be muffler packing but that's more 2 strokes dude.

I think the problems always been there just that i hadnt rode this type of tighter singletrack before, obviously if i dont ride spiritedly there isnt a problem but giving it a little squirt is fun, and yes it does clear out as soon as i get to a quicker section eg 2nd/3rd gear instead of 1st/2nd.

This weekend ill experiment a little and see what i can come up with, ill check all those things you mentioned too.

Thanks

Matt.

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You need to shorten the pump stroke a tad and adjust the squirt so it hits squarely on the middle of the needle to break the fuel up. Add a extra o-ring to the nozzle so it says in place or a slightly larger one, another thing you can do is wrap the nozzle with some teflon tape or use some Honda bond to hold it from turning.

A #45 pump nozzle works good for me.

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You need to shorten the pump stroke a tad and adjust the squirt so it hits squarely on the middle of the needle to break the fuel up. Add a extra o-ring to the nozzle so it says in place or a slightly larger one, another thing you can do is wrap the nozzle with some teflon tape or use some Honda bond to hold it from turning.

A #45 pump nozzle works good for me.

Hi there, i will definitly be having a look at the nozzle position and ensuring its in the correct position and as to the pump stroke do you mean the to shorten the beginning or the end of the stroke?

Thanks

Matt.

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Hi there, i will definitly be having a look at the nozzle position and ensuring its in the correct position and as to the pump stroke do you mean the to shorten the beginning or the end of the stroke?

Thanks

Matt.

Trial and error Joker as I said my pumper comes on straight off idle and it loves it.

One change at a time dude.

Screw the set screw for the pump in to back it off from the bottom end (think) and the one on top screw it in to take the pump away from the top end if that makes sense.

but one at a time.

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Trial and error Joker as I said my pumper comes on straight off idle and it loves it.

One change at a time dude.

Screw the set screw for the pump in to back it off from the bottom end (think) and the one on top screw it in to take the pump away from the top end if that makes sense.

but one at a time.

Ya know that was the trouble when I got mine. The carb came with no instructions whatso ever. Do you have a line on where to get an adjustment manual

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Ya know that was the trouble when I got mine. The carb came with no instructions whatso ever. Do you have a line on where to get an adjustment manual

Nope just trial and error.

Joker taking the pump out of the system and then doing say a roll on test will give you the clues as well dude,you'll c if it's the pumper end point or not.:lol:.

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Nope just trial and error.

Joker taking the pump out of the system and then doing say a roll on test will give you the clues as well dude,you'll c if it's the pumper end point or not.:lol:.

Today it seemed better i have to say, interesting because all i have adjusted so far is pumper start stroke starting a tiny bit later off idle and also a new throttle tube so that the grip does not rub on throttle housing.

Need to have a look sometime in the near future for the pumper end stroke.

Will defs post back.

Thanks.

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Sure is thats what i was referring to :lol:

XRS only didn't supply anything with carb. When I called They just said "make sure the screw on top of the white thing on your left side is screwed all the way in"

Which now I know what it is for.

So Joker is your screw #1 all the way in on the acelerator pump. ????

I'd appreciatev it if you could give your adjustments for all screws (the number of turns out from lightly seated.. So I could have a starting point.

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XRS only didn't supply anything with carb. When I called They just said "make sure the screw on top of the white thing on your left side is screwed all the way in"

Which now I know what it is for.

So Joker is your screw #1 all the way in on the acelerator pump. ????

I'd appreciatev it if you could give your adjustments for all screws (the number of turns out from lightly seated.. So I could have a starting point.

Maybe wait for wesk to reply as i have been fiddling with mine a bit and wouldn't want to put you off the right track. Having said that the one on top of the carb would still be stock as i haven't fiddled with that and the one on the side has about 1-2mm clearance before beginning the stroke.

Matt.

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Sometimes you can get a fake start point with the bike not going.

As the rod for the pump can bind and not come all the way back out.

so I when I set mine had the bike idleing so the vibrations let the rod come back out all the way.

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i've been wanting to pick one of these up.....guess its not as plug and play as powerbarn claims?

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i've been wanting to pick one of these up.....guess its not as plug and play as powerbarn claims?

It actually is, just that im being fussy :bonk:

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So who is the best vendor to buy a TM40 from?

I bought mine from XR's only . I don't know if they are the "best" but I have bought alot from them in the past and have had no issues and fast shipping. Also they pre-set up mine from sea level to 3,000 ft elevation. As I live in Fl ride here and E.Tn.

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Hi… I need help witch my XR650R.

I installed a Mikuni TM40-6 carburetor, and now it’s working, but witch out the power pump, because when I used the power pump the throttle make like a hole, and sometimes shutoff my bike, I think that the problem is the size of the jet of the power pump.

I need to know your recommendation about the size of this jet.

Note. Actually I’m using a 1.1 pilot jet air, 150 main jet, 27.5 pilot jet, 2.5 turn out (air bolt) and removed the main air jet.

My bike have: FMF full exhaust system, UNI filter, holes in the left panel and stock machine. My position: 1000 meters above sea level.

Thanks.

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Hi… I need help witch my XR650R.

I installed a Mikuni TM40-6 carburetor, and now it’s working, but witch out the power pump, because when I used the power pump the throttle make like a hole, and sometimes shutoff my bike, I think that the problem is the size of the jet of the power pump.

I need to know your recommendation about the size of this jet.

Note. Actually I’m using a 1.1 pilot jet air, 150 main jet, 27.5 pilot jet, 2.5 turn out (air bolt) and removed the main air jet.

My bike have: FMF full exhaust system, UNI filter, holes in the left panel and stock machine. My position: 1000 meters above sea level.

Thanks.

Man i'm not sure what you are saying here about remove the main air jet.Do you mean uncorked?

That's a lot of fuel for a stockish bike,but every bike is different.

A 45 pump nozzle is the go.

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