1981 Trailfire Flooding

[LamarIda01]

Hi all, I am new to the forum and Deere snowmobiles. I have been trying to figure out a problem for some time but am stumped. It seems to me my mikuni fuel pump on my 81' Trailfire is pumping to much fuel or has too much pressure. Here is the back story - I will try to keep it brief. I put a rebuild kit in the fuel pump while I was rebuilding the sled. Once all back together, I kept flooding out the engine and thought it was the carb. I tried two other different carbs that I know are good and had the same result - too much fuel. It would not idle and wouldn't run long at higher throttle. I used a bottle to gravity feed the carb and it started right up and ran great. I had the fuel pump hose going into a jar and it half filled the jar in about 10 seconds – a lot of flow. This made me wonder if the fuel pump was creating too much pressure and overwhelming the carb floats so that it was constantly flooding. The seat/needle valve in the carb are new. Gaskets and crank seals are new. The main and pilot jet are new - carb is cleaned. Could it be the fuel pump? I was thinking of buying a new one but just wonder if that is the problem as everything else seems to be fine. My understanding is that the fuel pumps should not push beyond what the floats can push back against and usually fail all together, not the other way around. Any help is much appreciated.

[yooper360]

Have you set your float height correctly? You can have as many new parts as you want, but if the float height is wrong it will continue to let fuel in. Per the manual: "Float arm should be parallel with the carburetor body." Set it with the float bowl off and the carb upside down. Let us know if that doesn't work or if you tried that already.

[400brian]

The Fire series sleds are not my thing. But I am wondering...are the pumps used on these the typical round Mikuni pump, or were they specific to the Kawi sleds? Seems like some of these were different, but I can't remember what the deal was.

At any rate, sounds like you are beating your head against the wall. I have never been adverse to throwing good money after bad, I would probably be putting a new pump on to try if all else fails.

[400brian]

OK, from what I am being told, the single carb fire series sleds ran the rectangular Mikuni pump. The pump that was different was the 80+ liquifires, where the round pump incorporated a shut off feature. The 78 Liquifire for example ran a round pump, but did not have the shut off.

So, I have rebuilt the rectangular pumps, my recollection is that they are pretty simple. If no other explanation can be found for the over fueling issue, I would be tempted to buy a new pump as they are fairly cheap.

[yooper360]

+1 to 400brian. They do have the rectangular pumps. They are indeed simple, although I would almost think if anything went wrong with them it would cause less pressure, not more. Who knows though, I have seen weirder things on these machines:P

As far as another next step, do you have a filter in the tank or the carb? The issue could be dirt clogging up the valve seat when you are running it off the tank compared to when you run it off the gravity feed. Just a thought because I have been there, just clean the carb out and then it is full of dirt after running for two minutes because I failed to clean the tank/install a filter.

Another thought that came to mind is: Do you have the vacuum line and fuel line going to the right places? I messed that up once, filled my whole crankcase with fuel when it started. Then ran like it was overfilling with fuel.... because it was lol. Check the float arm position though, it makes a world of difference.

[400brian]

Well we have seen problems discussed here that were assumed to be carb problems, when actually it was a dirty fuel issue. More common with the steel gas tanks I would think.

Another possible issue with Mikunis is that a float could be bad. You don't hear of it very often, doesn't mean it can't happen

[yooper360]

The trailfire plastic tanks have a tendency to get a weird gunk built up in them, especially when they have had fuel sit in them for a few years. I remember reading this from the technical information page on this site:

"The #1 failure reason for JD snowmobiles is dirty carbs. The plastic JD used in their tanks seems to leech something into the gas that produces a substance similar to Tapioca pudding when a machine sits unused and the gas isn't stabilized. This clogs jets and jams floats, and the result is a burned piston on the first ride of the new season. This tends to destroy both the pistons and cylinders, and the result is a $100 snowmobile that needs an engine rebuild. Every engine failure I've seen is for this reason - JD Owners KEEP YOUR CARBS CLEAN!"

At this point I would start from the bottom up. Check everything you haven't that we mentioned and let us know what ends up happening.

Dave

[harleysportster]

Did you buy aftermarket needle/seat or Mikuni?