Carb Indentification?

pj sportfire · Post by **pj sportfire** » Thu Jan 22, 2009 1:51 am

Other than the obvious size measurement and external design que's to reference; how do I find out exactly what model of Mikuni VM34/231 I have on my 1980 SF 440 engine now? I know the "34" number means 34mm in size, but what does the "231" number mean? According to the manuals, the model of carb for this sled is a AM55055, but how do I tell one model from the other? I can't find any markings to identify it with (or any other Mikunis on my other sleds) either?

Any help is appreciated.

pj

pj sportfire · Post by **pj sportfire** » Thu Jan 22, 2009 11:26 am

Anyone?

harleysportster · Post by **harleysportster** » Thu Jan 22, 2009 11:31 am

I am not sure if there is actual documentation but it seems like the carb model # corresponds to the factory jets installed for a particular model sled.

pj sportfire · Post by **pj sportfire** » Thu Jan 22, 2009 8:12 pm

I figured that too, but here in the shop now, I currently have a 1979 JD/TF 340, two 1979 JD/TF 440's, and two 1980 JD/SF 440's. The carbs on all the 340/440 TF's look alike from their exterior w/ respective jetting for each engine, but the two SF's have two different carb exterior designs between themselves *AND* they are different from all three TF's...

I don't lnow which is which and what's supposed to go on what, so I'd like to sort it all out to make sure I have the right parts on this thing. Maybe someone swaped out those carbs at some point??

The carb on my running SF is the clean one pictured and it looks pretty much like the TF carbs regarding fuel bowl design, fuel inlet spigot, etc; except it has a larger air inlet throat than the TF's do?

The carb on my non-running SF does have the same air inlet throat size as all the TF's do, but it has a different fuel bowl design and a different fuel inlet spigot??

Something amiss here I think.......

Attached are pics of what I'm talking about~ Hopefully someone can help.

pj

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pj sportfire · Post by **pj sportfire** » Thu Jan 22, 2009 8:13 pm

Non-running carb design...

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harleysportster · Post by **harleysportster** » Thu Jan 22, 2009 11:56 pm

The VM34/231 appears to have been used on the '80, '81 and '82 sportfires looking at the service manual.

JoeRainville · Post by **JoeRainville** » Fri Jan 23, 2009 12:20 am

The Sportfire used a 34mm Power Jet Mikuni with a separte high speed fuel circuit that only worked at 3/4 to WOT. It's a smaller version of the 36mm Power Jets used on the 80-84 Liquifire. The 34mm Mik on a Trailfire is a standard type, simular to what was used on the 76-78 Liquifire and Cyclones.

Do not run a power jet equipt sled w/o the air box. It needs some pressure drop to pull fuel out the float bowl through the external fuel line and nozzle.

Does that help?
-Rainville

pj sportfire · Post by **pj sportfire** » Fri Jan 23, 2009 9:33 am

Thank you guys' for the info, that surely helps!

After a bit of digging around on the internet and measuring with calipers- I think I found the problem... The dirty carb that is on the non-running SF is only a 32mm Mikuni and I have no idea what it came off of originally, as it looks like the past owner must have switched it out at some point. Damn...

The second clean carb on my running SF is a 34mm Mikuni, but it doesn't have the high speed power valve circuit that Joe spoke of on it, therefore, it's also the wrong carb for this engine. Damn, Damn....

The only saving grace I have here is that the running carb is jetted right, so I think I'll still be able to go riding on Saturday like I planned, but I'll need to source the correct carb for this machine to make it right and then another later on for my other SF once I get it running. Damn, Damn, Damn...

Anyone have a complete (correct) 1980 JD Sportfire 440 VM34/231 carb for sale? I need one...

pj

Post by **ICCSF 108** » Fri Jan 23, 2009 10:29 am

PJ I don't believe that Deere used a carb ( Like in your second set of pics ) with the main jet coming out the side of the bowl that looks to be like an old Polaris carb to me..
I believe that the Deere Mikuni's were just like any of the standard replacement VM carbs except for the / numbers

Kenny

pj sportfire · Post by **pj sportfire** » Fri Jan 23, 2009 2:25 pm

You're probably right Kenny and I'll just clean it real good, rebuild it and put it up for sale on Ebay- maybe someone can used a good, used, rebuilt 32mm carb for something.

I'm still on the hunt for the correct carbs for my machines.

pj

pj sportfire · Post by **pj sportfire** » Fri Jan 23, 2009 9:17 pm

Well, been searching for an original 1980 Sortfire carb today online and haven't found one yet, so I decided to dial-in the current 34mm "whatever-it-is" Mikuni carb on my running Sportfire as accurate as can be to make the sled run at its max performance.

I verified that it had the correct needle, needle jet, main jet and idle jet installed first. Then I set the float levels, adjusted the idle mixture screw to factory spec and set the engine RPM to where it liked to run cleanly...

After a few thrashes through the yard, it ran pretty good, but still bogged when warm. It should run better.... So, I changed out the fuel pump w/ a new one (the old one was questionable) and changed out the fuel filter again- just to be safe. I switched to 93 octane pump fuel using Valvoline 2-stroke premix at 50:1 and refilled the tank. Did some more thrashing and it ran better yet, but still bogged just a ***little*** bit. I thought it could be better yet still...

I took the carb slide back out again to lean the fuel needle one click and gues what I found...A BENT FUEL NEEDLE!!! (see pic) That can't be good, so I swaped it out with another good one I had here and installed it one click leaner than stock, so now its two notches down from the top. Re-installed everything, fine-tuned the fuel mixture, idle speed settings and throttle slide height a bit to compensate for the change and took her out again for a few more thrashes.....

HOLLYYYYY SHIZNITTTT! This thing flat screams now!!!!! WhoooooooHoooooooooo!!!!!

I can pin the throttle to WOT from a dead idle and the engine spins up IMMEDIATELY, the clutch kicks in hard and this thing pulls the skis a little light when the shift occurs it pulls so darn hard through the mid-range!! Now **THIS** is getting fun!!!

I'm going to leave everything just the way it is and run the machine like this for the rest of the year while I'm searching for the correct carb for this engine. I'll then use this carb on my Sportfire #2 when I get it done, so I don't have to find two carbs that are already hard to find.

Anyway, just wanted to let you guys' know how this mess was going in case you were interested and we're off to Buffalo Trails in Northern Indiana tomorrow for a day of riding.

BTW- I still need a correct carb if someone runs across one.

Cheers!
pj

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bent_needle.jpg (110.93 KB)

jdsledwheelman · Post by **jdsledwheelman** » Fri Jan 23, 2009 10:24 pm

Don't forget to check the color of the plugs for being to lean. We were out riding a few days ago and a friend said his sled never ran so good

. I asked him when he last had the carbs cleaned. He said its been a few years

. I told him I had heard the saying "they run the best right before they blow up"
:eek: . Later that night after we parked our sleds he rode home. 15 min. later he calls me to haul his sled off the road

. He made it half way home and melted the right side piston

. So I'm not saying your carb is dirty, you had yours apart, cleaned and gone through. But you did make some adjustments, and said the magic phrase about running better than ever

. So good luck and be cautious

.

nick

pj sportfire · Post by **pj sportfire** » Fri Jan 23, 2009 11:32 pm

We'll do and thanks for the heads-up!

I think it's correct now though, because when it ran before, it rich-bogged pretty bad where it smoked heavily, fouled plugs easily and it made your eyes water just being around the thing. When I get back from riding tomorrow, I'm going to install a wide-band AFR bung into the header pipe so I can actually measure the air/fuel ratio in real time- just like we do with the cars we build here. Then I can nail down the AFR with dead-on accuracy.

PJ

400brian · Post by **400brian** » Sat Jan 24, 2009 4:06 am

When I get back from riding tomorrow, I'm going to install a wide-band AFR bung into the header pipe so I can actually measure the air/fuel ratio in real time- just like we do with the cars we build here. Then I can nail down the AFR with dead-on accuracy.

PJ

Very interesting, post some photos and school us on this set up.

Mean Green · Post by **Mean Green** » Tue Jan 27, 2009 9:29 pm

Dunno if your'e interested, but I found a carburetor for your sportfire. VM 34 PJ. You won't believe how much pick-up in the midrange you will get with one.

http://cgi.ebay.com/ebaymotors/Single-MIKUNI-snowmobile-slide-carb-34-231_W0QQcmdZViewItemQQ_trkparmsZ66Q3a2Q7c65Q3a7Q7c39Q3a1Q7c240Q3a1318QQ_trksidZp3286Q2ec0Q2em14QQhashZitem250363935660QQitemZ250363935660QQptZSnowmobileQ5fPartsQ5fAccessories

Tracy