1998 Trail RMK has me stumped....

[absteed]

I haven't been able to get it to start for a while, so I went with the basics--yes, I have spark, I pulled the pick-up line and it's in good shape, replaced the fuel filter.

So I cleaned the carbs being very careful not to change settings on the throttle cable or the idle screw. When I removed the bowl from the Magneto carb the main jet fell right out. It had vibrated loose and spun off. I thought for sure this was the problem, but when I reinstalled the carbs the sled still wouldn't start.

One night after pulling a few times, I turned off the fuel line. The next morning I turned the fuel back on and it started in 3 pulls. It was running great and had lots of power. The crankcase must have been full of fuel because it started dumping fuel out of the exhaust. Once that was out of the system it ran fine. For the next few days I could start it within just a couple of pulls. Then from one day to the next and without warning it was dead--couldn't start it to save my life.

So I dragged it into the shop and immediately pulled the float bowls off the carburetors again. Lo and behold, the main jet had vibrated loose again and was in the bowl. This time I put a little bit of teflon tape on the threads and reinstalled.

Since the carbs were out and the air box was off, I decided to check the synchronization of the carbs. I downloaded the service manual, watched a YouTube video, and followed the procedure precisely. The carbs were way out of adjustment. After reinstalling the carbs the machine started within 3 pulls again. It dumped a bunch of fuel out of the exhaust again, but the engine had lots of power. For the next couple of days it would start within 3 pulls consistently. I thought I had finally figured it out.

Last night I brought it home and allowed the kids to ride it around the yard for about 45 minutes. It was running great and they were having a ball. They stopped in the front yard to change drivers while the machine idled. Out of nowhere it died as though someone had hit the kill switch.

The kill switch was up. The key was on. Even the engine was warm and had been running consistently for 45 minutes, the sled refused to start. It was a little low on fuel, not empty but low, so I put a few gallons in. Nothing. I checked the spark--plenty of spark. Even when I pull the rope the headlight comes on. But it doesn't want to start. It doesn't cough or sputter like it even might start.

I was convinced that the main jet had worked itself loose again. I pulled both carbs out and the main jets are secure.

So it's either related to an electrical problem or a fuel problem.

Electrical: How many built-in safeties does this thing have for an electronic shutoff? It has a key, has a red button on the handlebars... anything else that would cause the machine to refuse to start? If the key were off or the red button were down, would the headlight still get power when trying to pull start?

Fuel: Where it has fresh fuel, a brand new filter, newly cleaned and synchronized carbs, and I removed and inspected the pick-up line and screen inside the fuel tank, the only other thing I can think of would be the fuel pump. But would a fuel pump run great or not at all intermittently if it's failing or would it just run more and more weakly over time?

I appreciate any advice you guys can give me. I'm at my wit's end here.

 

[BBP]

A cracked diaphragm in the fuel pump can fill the crankcase on one side through the impulse line. A stuck float can fill one side with fuel. There was a wire that would rub on the case under the carb & short out the ignition. I believe it was a coil wire. The stator or coil can intermittently fail when they warm up.

 

[absteed]

Thanks I'll look into that

 

[Fosgate]

I agree with BBP, Stuck float or a cracked float that is not adjusting with the amount of fuel in the bowl could easily be a reason. Fuel pump is also cheap on those via ebay. I would also look inside the fuel tank for debris. Swapping fuel filter may seem to help but can clog quickly if you got some nasties in it. Toss a little bit of heet in the fuel also. If you have water in the lines it will freeze up. Also, belt deflection, if too tight it can make it a bear to start.

 

[Jeff Schmitz]

Another common problem in other Poo sleds (Indy Lites for damn sure!) were the needle/seat assemblies in the carbs. Ever wonder why a lot of Poo sleds came with fuel shut off valves under the cowl? At best a bad one or more of these assemblies will cause major headaches. At worst they will TOTALLY fill the crankcase and hydro lock the engine. Ask me how I know. They can be intermittent. There is a simple test in the book - take the carb off, drain it and turn it upside down so the weight of the floats is pressing the needle shut. Apply 4 psi air to the fuel inlet and isolate the carb fuel line port that you are putting the 4 psi into. The 4 psi should hold nicely, in fact a really good needle/seat will hold 9 psi. If there is any steady leakage at 4 psi replace the neeele/seat assy. I have not had any luck cleaning them up but others may be able to. Note: While 4 psi is hard to see with a lot of air pressure gages the Fat Bike world has several that max out at 15 psi. Easy to see any changes with these. I've seen some just leave the carbs on the machine, take the fuel hose off the inlet to the fuel pump and put a clear plastic fuel line full of fuel up to about ceiling height. The fuel will pass thru a non operating fuel pump to the carbs and the floats will now govern fuel level as in normal operation. The ceiling height fuel column pressure is in the 3 -5 psi range which is where the fuel pumps operate from what I've been told. Any level change in the clear fuel line at the top is pretty obvious once the bowls are at calibrated level. Any continuous drop is going into the engine. Hope this helps.

 

[retiredpop]

Just curious if you pulled the crankcase drains when it quit.

 

[absteed]

Another common problem in other Poo sleds (Indy Lites for damn sure!) were the needle/seat assemblies in the carbs. Ever wonder why a lot of Poo sleds came with fuel shut off valves under the cowl? At best a bad one or more of these assemblies will cause major headaches. At worst they will TOTALLY fill the crankcase and hydro lock the engine. Ask me how I know. They can be intermittent. There is a simple test in the book - take the carb off, drain it and turn it upside down so the weight of the floats is pressing the needle shut. Apply 4 psi air to the fuel inlet and isolate the carb fuel line port that you are putting the 4 psi into. The 4 psi should hold nicely, in fact a really good needle/seat will hold 9 psi. If there is any steady leakage at 4 psi replace the neeele/seat assy. I have not had any luck cleaning them up but others may be able to. Note: While 4 psi is hard to see with a lot of air pressure gages the Fat Bike world has several that max out at 15 psi. Easy to see any changes with these. I've seen some just leave the carbs on the machine, take the fuel hose off the inlet to the fuel pump and put a clear plastic fuel line full of fuel up to about ceiling height. The fuel will pass thru a non operating fuel pump to the carbs and the floats will now govern fuel level as in normal operation. The ceiling height fuel column pressure is in the 3 -5 psi range which is where the fuel pumps operate from what I've been told. Any level change in the clear fuel line at the top is pretty obvious once the bowls are at calibrated level. Any continuous drop is going into the engine. Hope this helps.

Thank you--I think this is my next step. I've cleaned the carbs multiple times so they should be fine. I'll either come up with a tester tool somewhere or just buy a fuel pump and try it out. I've just replace every single fuel line. If the pump and fuel lines don't fix the problem, then I'll pressure test the carbs.

 

[absteed]

Just curious if you pulled the crankcase drains when it quit.

I actually never thought to do that... when it finally gets up and going it shoots all the extra gas out of the crankcase itself...

 

[absteed]

Another common problem in other Poo sleds (Indy Lites for damn sure!) were the needle/seat assemblies in the carbs. Ever wonder why a lot of Poo sleds came with fuel shut off valves under the cowl? At best a bad one or more of these assemblies will cause major headaches. At worst they will TOTALLY fill the crankcase and hydro lock the engine. Ask me how I know. They can be intermittent. There is a simple test in the book - take the carb off, drain it and turn it upside down so the weight of the floats is pressing the needle shut. Apply 4 psi air to the fuel inlet and isolate the carb fuel line port that you are putting the 4 psi into. The 4 psi should hold nicely, in fact a really good needle/seat will hold 9 psi. If there is any steady leakage at 4 psi replace the neeele/seat assy. I have not had any luck cleaning them up but others may be able to. Note: While 4 psi is hard to see with a lot of air pressure gages the Fat Bike world has several that max out at 15 psi. Easy to see any changes with these. I've seen some just leave the carbs on the machine, take the fuel hose off the inlet to the fuel pump and put a clear plastic fuel line full of fuel up to about ceiling height. The fuel will pass thru a non operating fuel pump to the carbs and the floats will now govern fuel level as in normal operation. The ceiling height fuel column pressure is in the 3 -5 psi range which is where the fuel pumps operate from what I've been told. Any level change in the clear fuel line at the top is pretty obvious once the bowls are at calibrated level. Any continuous drop is going into the engine. Hope this helps.

I finally got the right tester tools and did the air test you just described. It failed miserably, so I just ordered up a carburetor rebuild kit. Thanks for the tip.

I'm relieved to have found the problem.

 

[absteed]

Another common problem in other Poo sleds (Indy Lites for damn sure!) were the needle/seat assemblies in the carbs. Ever wonder why a lot of Poo sleds came with fuel shut off valves under the cowl? At best a bad one or more of these assemblies will cause major headaches. At worst they will TOTALLY fill the crankcase and hydro lock the engine. Ask me how I know. They can be intermittent. There is a simple test in the book - take the carb off, drain it and turn it upside down so the weight of the floats is pressing the needle shut. Apply 4 psi air to the fuel inlet and isolate the carb fuel line port that you are putting the 4 psi into. The 4 psi should hold nicely, in fact a really good needle/seat will hold 9 psi. If there is any steady leakage at 4 psi replace the neeele/seat assy. I have not had any luck cleaning them up but others may be able to. Note: While 4 psi is hard to see with a lot of air pressure gages the Fat Bike world has several that max out at 15 psi. Easy to see any changes with these. I've seen some just leave the carbs on the machine, take the fuel hose off the inlet to the fuel pump and put a clear plastic fuel line full of fuel up to about ceiling height. The fuel will pass thru a non operating fuel pump to the carbs and the floats will now govern fuel level as in normal operation. The ceiling height fuel column pressure is in the 3 -5 psi range which is where the fuel pumps operate from what I've been told. Any level change in the clear fuel line at the top is pretty obvious once the bowls are at calibrated level. Any continuous drop is going into the engine. Hope this helps.

I just posted a question in a new thread on a different machine if you have time to check it out

1996 Polaris 440 Sport Touring.... time for a top end?

My old 440 with 3000 miles has been acting up. It starts fine when it's cold. But if you shut it off or it dies while running, it won't start warm. I have to wait for it to get cool again. I cleaned the carburetors and synchronized them to factory settings. No change in the way the machine...

www.snowest.com

 

[absteed]

Just so you know, it's up and going now and I couldn't have figured it out without performing both carburetor tests.

I already mentioned that I did the dry test and both carbs failed that test so I replaced the needle and seats. Then I did the wet test. One carb held pressure. The other one wouldn't hold pressure. So I replaced the floats in that unit.

Machine starts and runs great now.

I will say that even though I've replaced every single fuel line and clamp, the fuel filter, and the fuel pump, it still seems slightly flooded if I don't shut the fuel valve off after every use.

Is that normal?