Is there a correct clip setting for the TM-40 jet needle as well as a correct main jet size for an '86 fxstc? I don't know the history of the bike, but believe the engine has had some work/upgrades done to it. If the needle was on the wrong setting, what would that do?

The bike has a 170 main jet and according to the manual 165 came from the factory. Bike doesn't want to stay idling, leaks fuel from the overflow when bike sits with the petcock in the on or reserve position. Now when riding it and letting off the throttle idle stays high as well. Choke is in and throttle plate is down. Had it to 2 indie shops and they did basically nothing for it but collect the $$$.

I'm cleaning and putting a rebuild kit in it (which wasnt done) but am unsure if its the correct main jet size and jet needle clip position. The kit has a float needle valve which I will replace and hopefully that will fix the leak.

One other thing. It occasionally will spit (fuel?) out of the carb. Anyone have any suggestions to help? Thanks

 

This is an aftermarket carb that is not commonly seen on a Harley Davidson (if ever).
The only 40mm Mikuni carb marketed for Harleys was the HS40, which was long ago replaced by the HSR series of carbs.

 

The hs40 is the tm-40. The carb was made for Harleys and from what I've read was a huge improvement on the keihin carb. I'm surprised its so rare. Guys on Suzuki forums know it inside and out for the dr650. They can tell you needle clip position, main jet size etc. for optimal performance. That is for the dr650 though and not the evo. I thought a 170 main jet would remind someone here and he'd say something like,"170 main jet means a hot can, needle clip position 2, pilot screw 3 turns out. That's how the Suzuki guys are but I guess its a rare bird on a Harley even though its made for one.

 

The 42 is popular and believe it took over on the 40 when it was introduced, a Mikuni responds well on a Evo.
Ran a 45 so can't pinpoint your jets / needle, your rebuild should take care of the fuel leak and not returning to idle is most likely a lean condition, jet blockage so cleaning and rebuild is a good start. Spitting fuel out with the air cleaner off can happen with a Harley and Mikuni will at idle, if it is coughing then a lean condition is present
Middle notch on a Mikuni is a good starting point, low jet covers a larger portion of tuning unlike a CV, other words it goes deeper into into the low speeds and then the needle takes over. The Mikuni tuning manuals are in depth and the modern 42/45 manual was written by Joe Minton (Harley Guru) for Mikuni. Another reason why you won't see post after post on Harley Mikuni tuning is the 42 out of the box can cover a wide variety of engine sizes due to being rich but known for lack of mpg.
Something you need to check for on a older Harley is intake seal leaks, it is common and can throw your carb repair / tuning into a tail spin if it is pulling air through the seals

http://www.mikuni.com/pdf/hs40_manual.pdf
http://www.mikuni.com/pdf/hsr_tuningmanual_021003.pdf

 

I didn`t know the TM 40 was the same as the HS 40.

I ran an HS 40 for many years on my `89 Sortail, and only changed out to a CV carb because the Mikuni setup stuck out too far, the CV was a much cleaner install.

The Mikuni ran great right out of the box, I never changed a jet in it.

 

Thanks for all the input. From what I've read the 42 was the improved 40. Roller bearings instead of metal on metal etc. Just curious, what do you think is the best carb for an evo?

I sprayed carb cleaner around manifolds with engine idling (does that sometimes) and idlle speed didnt change. Sounds like there are no leaks. Kind of surprising the spitting out of fuel signifies a lean condition. It did it with the cleaner off, but also with it on. With the filter off the atomization of the gas looks like a cloud about the size of a baseball coming out of the carb. I believe what you say about the lean condition but I thought it was the opposite what with the needle valve not seating and fuel coming out the overflow. The rebuild should fix the leak and I think I'll try the clip on the second notch. Do you know if a valve clearance or ignition problem would cause spitting as well?

 

You need to correct the overflow issue before you can do anything else.

A good cleaning and rebuild kit may be all you need.

 

So I've been looking at this for a little while and one thing I noticed was that the right gas cap's vent was clogged. If you're having an idling issue, that is a good first thing to check. This bike sat for many years before I purchased it so it's not that big of a surprise. I wasn't actually aware the gas cap had a vent until reading the service manual.So what I did was spray carb cleaner directly into the vent hole underneath the cap and turn it right side up while swishing it around some. This process took about 10 minutes and finally the crud broke through and the fluid started to drain from the hole to the bottom of the cap. My plastic gloves turned to shreds but the cap is venting now. Here are some pics of the cap and tank vent: I then took the carb off and tested the petcock settings of "On" and "Reserve" to the fuel line to make sure gas was flowing to the carb freely.

 

So now I've purchased a rebuild kit and taken the carb off of the bike. Noticed a couple of things. The float is kind of hanging on the pin sometimes when I turn the angle to simulate gas filling the bowl. So I purchased a bowl and pin as well. Also noticed with the float gauge that the measurements were slightly different for each side of the float. When checking the float level range make sure to measure each side of the float as they can become bent or twisted over the years -especially if you don't know the history of the bike.

A question if I may? On the Mikuni it has a dummy Main Air Jet as well as a Pilot Air Jet on the funnel that the air cleaner sits in front of. Does anyone know how many turns out (if any) from being seated for the bike to idle correctly? I had read in another thread someone mentioned it needs to be seated in order for the bike to idle. Is that correct? Mine was about a quarter turn out.

So I then purchased a can of Gunk Parts Cleaner and disassembled most of the carburetor. I left the thick plastic on near the accelerator pump adjusters, as well as a rubber plug for the pump nozzle to see if it wouldn't disintegrate while soaking. This was done for approximately 40 hours and the plastic and rubber appears ok. Carburetor came out mostly clean. Attached are pictures of the carb before and after. Btw, I know many of us here are getting up in age. I have no affiliation with the product, but in the second picture is a container of Joint Support by Arazo. From old injuries and simply age I recently have issues with torn cartilage, strained ligaments and arthritis in my hip joint. If anyone is dealing with similar issues this supplement appears to really work. It has glucosimine, chondroiton and msm. The only thing to watch is if you have diabetes to consult your doctor first before taking.
Anyway, the carb came out nice and the other parts arrived today so we'll see how it goes.

 

Where did you get that info not taking it w/diabetes?