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Message started by OldTimahRider on 08/14/20 at 15:58:09

Title: MIKUNI Carb Diaphragm
Post by OldTimahRider on 08/14/20 at 15:58:09

I'm working on carb problem on my 2012. Can anyone tell me the best way to evaluate my carb Diaphragm? Looks a little misshapen but no apparent holes or tares (when viewed held up to light) plunger seems to move up and down OK. Thanx

Title: Re: MIKUNI Carb Diaphragm
Post by eau de sauvage on 08/14/20 at 16:18:22

Sounds to me that it's all good with regard to the diaphragm, others will be along soon so you may as well list as accurately as you can everything you've done so far and what exact problems you're having, at what speeds or at what throttle positions, have you set the air/fuel screw, checked for vacuum leaks etc.

Title: Re: MIKUNI Carb Diaphragm
Post by IslandRoad on 08/14/20 at 18:17:30

Here's a shot of a healthy diaphragm in situ for comparison.

Ignore the white tube in side the spring (it's an Australian thing!)

Title: Re: MIKUNI Carb Diaphragm
Post by OldTimahRider on 08/15/20 at 06:02:27

556F707D72784E737D781C0 wrote:

Here's a shot of a healthy diaphragm in situ for comparison.

Ignore the white tube in side the spring (it's an Australian thing!)

Thanx for the pic. Yours looks like mine......what I desribed as "mis-shapen." Not taught in any way, but also no visible signs of any leakage possibillities.

Title: Re: MIKUNI Carb Diaphragm
Post by OldTimahRider on 08/15/20 at 06:29:01

For my carb problem, symptoms:
1 problem intermittent
2 when runs, runs great. Otherwise won't run past minimal throttle open
3 saw fuel leaking through air filter, but only one time
Troubleshooting steps taken:
1 no fuel detected in oil
2 paseed "cap and prime test". Bought but not yet installed RAPTOR
3 removed carb, diaphragm & float bowl covers. (Brass floats appear to
look OK, move up/down OK. Need to bring carb to machine shop to
remove/drill out/replace float hinge pin. It is a press fit evidently and
won't budge. Even after trying PB BLASTER, filing down suages at
both ends, flush with body tabs that hold it.
4 after I get past this point I plan to check floats for leackage, clean all
jets with B-12 and can of compressed air

Title: Re: MIKUNI Carb Diaphragm
Post by norm92de on 08/15/20 at 10:52:26

Put the Raptor on and then see how it runs.

Title: Re: MIKUNI Carb Diaphragm
Post by ohiomoto on 08/15/20 at 13:55:21

Yeah, don't mess with 2-3 things at once. The petcock is probably the problem. Fix that first.

If you still have problems, make sure the diaphragm is properly seated (which you'll have to do anyway because you took it apart) and the slide is not worn. A sticky slide causes all kinds of problems and is often overlooked.

The float pin can only be removed in one direction.

Title: Re: MIKUNI Carb Diaphragm
Post by ckahleer on 08/15/20 at 20:13:06

I sometimes check slide functioning by connecting a shop vac to the cylinder head side of the carburetor. As you open and close the throttle, the slide should move up and down smoothly.

Title: Re: MIKUNI Carb Diaphragm
Post by OldTimahRider on 10/17/20 at 07:36:25

I solved my above mentioned problem a long time ago. Been lax at getting back. Thanx to all who offered advice. Resolution: Took carb apart and cleaned with B-12 CHEMTOOL (there was a lot of dirt in there) and jet cleaning tool sent to me by a kind member in this forum. (Was unable to remove float hinge pin, but determined that float was not leaking and worked properly.) Installed RAPTOR pet thingy. Don't know exactly what the problem was, as it was intermitant, and passed PRIME/CAP test, but I've ridden it about 500 miles now, with absolutely no recuring problem. I have since noticed a slight new problem however, what has been identified to me as LEAN SURGE. I believe there is a MOD for this somewhere in this forum, called WHITE WASHER mod, or something like that. I will investigate this further. Maybe wait 'til spring to implement this. (Getting cold up here in NH!)

Title: Re: MIKUNI Carb Diaphragm
Post by Dennisgb on 10/17/20 at 10:19:36

Diaphragms are floppy and wrinkled like that. Seems odd the first time you see it but it’s normal.