The Carburetor from Hell

[fairmountvewe]

So for those who have been either giggling their way or rolling their eyes through my little electrical issue, I am pleased to say that we solved that one, only to be smacked in the head with a new twist on the problem. By way of background, my first ever snowmobile, a 1980 440 Trailfire was having running issues. My neighbour and I have worked on it for the last couple of days in between chores, snow removal and (his) airplane maintenance. Well we have cleaned the carb, replaced fuel lines, filters, and clamps, and tried to set the carb as described in the Service Manual, but it wouldn't run right. And it ran even worse when we replaced the air box. A couple of times, when we closed the dash the idle would change.
We putzed around for a while, and got the sled to idle decently, and run at top speed decently, but the middle was mushy, and very unresponsive. So today I bought some new jets, and seats, and (on the advice of some of you on the board) a new choke cable. Tonight was a balmy -18C with almost no wind, so a couple of layers of clothes, a hot cup of tea, and a couple of cold fingers later, and the carb is back off again, disassembled, and soaking in varsol. I also found two nice little tears in the carb boot. I will have to get a new one of them before I can continue this little odyssey. I am hoping that this is the culprit that is causing the elusive carb issue, because I really don't want to have to pull a motor, and replace crank seals - especially when my wife is non too pleased with my newest addition to my fleet of Deeres!

[SpitfireKing]

No such thing as a mikuni that's a nightmare.... Try a kehin off a 74 yamaha 433...... Now its not only from hell, its the devils second cousin Leroy! I've been fighting this thing for a month, and nw the brand new kit is all swelled up and useless. These new carb kits are just junk.... Going to be a tough road ahead for future repairs if this is all that's left for suppliers

[ihengineer76]

You said the idle would change when you close the dash? It sounds like your choke cable is either not adjusted properly, or the outer cable sheath is not fully seated in the end on the carb. Opening and closing the dash will pull the cable around and possible is unseating the plunger in the carb. When the choke is adjusted properly, you should have just a little bit of slack between the sheath and the adjuster.

[S_Kyle]

I will start by saying that I hate power jet mikunis with a passion. If your flange is leaking, replacing it is the first step. The choke moving around is a common issue. Maybe try removing it from the dash a temporally remount it more solid to eliminate that variable.

Also if you don't have a manual go to the link below and print one off. The John Deere manuals for the most part are well written. I would like to offer more help but I am not very good with carbs.

[ljm]

If your replacing the carb boot. I would strongly suggest getting a genuine Mikuni one from New Breed Parts.

They are more money, But MUCH better quality.

The Trailfire carbs are not power jet carbs so they are a little simpler than Sportfire and Liquifire carbs.

If they are CLEAN and have the close to the proper jets they work well.

If you were still at Inverhuron I would come and give you a hand.

Lloyd

[fairmountvewe]

Well good evening all and welcome back to round two with my project. I have pulled the carb off the sled (again) and disassembled it and cleaned it in varsol for a couple of days. I started to re-assemble it this evening, and have run into a couple of issues. First, is there supposed to be an atmospheric vent in the carb? The reason I ask is because when I turned the carb upside down, solvent ran out a small hole near the top of the carb. I looked where it came from, and it goes from the bowl, up on the left side of the carb as you look at it from the comfy operator's seat, 90' (so horizontal) across toward the operator and exits just right of centre in front of the slide,(pictures to come as soon as I figure out how). Is that right? I didn't think fuel should be at atmospheric pressure like that, or that there should be an entrance into the bowl like that. Should this be plugged? Help!!

[Matt]

Yes, there is supposed to be a vent there.

[fairmountvewe]

Awesome. Thanks Matt. Now how do I post pictures?

[JoeRainville]

The above post that talks about your choke cable is solid advice. My 80 LF would flood out when you closed the dash. Turns out you need to adjust the choke cable to have a small amount of play with the dash closed. Sounds like you are running rich. New choke plungers are available, and seal better than 30 year old ones of course.

I hope this helps,
-Joe

[sledder670]

'ya choke cables should have 3-5 mm of free play in them right at the carb pulling them up and down.

[JDT]

And that free play is with the dash down.

[fairmountvewe]

Well the carb is back together and on, but my brand new universal choke cable broke second time I used it, so back to the original. After reading the last two posts, I did not have it adjusted right so I guess that is tomorrows job. Thanks for the help all.

Peter

[JDT]

Well I have my carb from h*&& siting on my kitchen counter right now.

Yep, it's a Keihin. Never seen one like this. It is stamped 401 HI 407.
Real large bore. Won't pump good enough to draw fuel the whole way up to the carb.
Belly pan tank on this sled with a mid mount engine so it has to lift 18".

Standard Keihin parts kit is too small for this monster. So I am on my own.

Anyone know anything about this bad boy?

[JDT]

I figured it out!!

Found a picture in an old Interstate manual I had that showed a breakdown on this carb.

Two gaskets were revered in one section.
She pumps great now.