Carbs, Fuel Pump, or ???

[hanson]

I have a gut feeling I know what the issue is but want some feedback before I pull too many parts out of the sled.

91 EXT 550 Special w/ twin Mikunis

This sled didn't get summerized last spring and guess what? Yep... Issues.

Started off by pulling the plugs and pouring gas directly into the cylinders. She'd fire off, putt-putt a few times, and then kill. I repeated this about 8 times at which point I realized there is a gunky carb issue. Normally if you do this a few times the carbs start pulling fuel and you are in business but not this time.

Carbs come out of the sled and oh my Lord. No gas in the float bowls but lots of green sludge algae looking stuff. Stripped the carbs all the way down- jets, needle & seat, etc and sprayed all the passages out good with carb cleaner. Got the jets looking good and clean, everything put back together, and into the sled they went.

Once back in the sled, I did the gas in the cylinder trick one more time and away we go with a nice idle. Thinking I was in business, I gave it some gas to be greeted with a nice bog. Over and over and over again. At this point I'm not happy.

Soooo... my guess is I have a fuel pump issue now. Would anyone else agree that this is the next place to check? My thought is the pump is pumping enough gas to idle the sled but when I open it up, its starved for fuel. I really can't believe there is still a carb issue as they just received the full teardown and cleaning.

After seeing how gunked up the carbs got, I have got to believe there is gunk like that in the fuel pump as well.

Thoughts??

[harvey lee]

Chris, did you put the carb parts in carb cleaner and let them soak for awhile and use air to clean and dry the parts off or just spray the parts down with carb cleaner? Is it possible that the carbs may still have a speck of dirt in there yet?

Otherwise I would lean towards the pump.

[hanson]

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Is it possible that the carbs may still have a speck of dirt in there yet?

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It is definitely possible. I'm ordering up a new gasket/diaphragm kit for the fuel pump, new fuel filter, and new fuel lines (as the old ones are rock hard) and will more than likely rip the carbs down again to re-clean them.

This sled ran like a top last winter and had no issues. The only thing that has happened to it is it has sat for nearly 9 months without being run. Another reason why I have to believe it is something in the fuel system.

[harvey lee]

I would believe that would take care of your problems as you pretty well hit every concern. Sometimes that crud can get in everything and then you need to clean the whole fuel system up. You never know, the carbs could have been clean and a piece of who knows what could have ran through the fuel line and got caught in a jet or seat.

[Macgyver55]

You may have already done this, but since you didn't mention that you had, take a look at the throttle safety override switch. It wont let the motor rev up if there is a stuck or misadjusted throttle.

[Surface Tension]

Check the fuel line connections between the tank and pump.

When they get old they get hard and even though there might be a clamp they get memory of the fitting and will leak air.

Next check the impulse line from the engine to fuel pump. Any air leak and the pump will not work.

Pull the fuel line from the tank. Will gas run out? If yes then connect that back up and remove the outlet fuel line from the pump(you might have two)and pull over the engine, hows the fuel pressure? If the gas didn't run out of the tank you could have a check valve on the drop tube in the tank. Use a section of hose and connect it to the tank. Suck on it, can you draw gas. If you can't or feel air, remove the gas tank and replace the pick up line and clean the valve or screen.

If your getting gas from the tank but no pressure off the pump and you checked the fuel and impulse lines and connections. Then your pump needs a cleaning and rebuild or your not getting that impulse and its a compression or seal deal.

[Black_Bay]

Macgyver might be on to something. I remember my buddies having issues similar to yours on their '90s Arctic Cats. There is a throttle switch that would occasionally get out of adjustment. For some reason I'm thinking it's a magnetic or electronic switch.

[hanson]

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Macgyver might be on to something. I remember my buddies having issues similar to yours on their '90s Arctic Cats. There is a throttle switch that would occasionally get out of adjustment. For some reason I'm thinking it's a magnetic or electronic switch.

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You guys might very well be right with this.

Each carb has a small wiring harness coming off of it. Browsing the schematic for these Mikuni carbs (VM-38), there is a magnetic switch on each carb.

Both of these plug into a harness and where it goes from there I don't know.

If there is an issue with this, that might make a lot of sense. Like I said, when I hit the throttle, its instant bogging. There is no chance at all for the engine to rev up. You can hold the thottle wide open and its the same bog.

I'm guessing if it was a fuel problem, there might be some intermittent increase in RPMs at a minimum.

I won't get around to wrenching on the sled until Sunday or later. I have a couple other parts to order that need to come in first. I get a little exuberant with my wrenching and made a boo-boo.

[Black_Bay]

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I get a little exuberant with my wrenching and made a boo-boo.

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LOL I know how that goes. If one click of the elbow is good, two must be better.

[vister]

how does it idle when you flip the choke? if it revs up, then give it gas. if it revs up then you're looking at dirty pilot jets, then it is only an air issue. shouldn't be a fuel pump, as they rarely go bad. considering it ran fine last time out???

clean the carbs, again, and blow all of the jets off with compressed air to do a good job, but hold on to them with a pliers. or sometimes they'll blow out of your hand, and we all know they are pretty small. and drain the gas tank before putting back together.

may be time consuming to do these things, but the bottom line is FREE, unless you bill yourself. Should take care of it.

[Macgyver55]

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Like I said, when I hit the throttle, its instant bogging. There is no chance at all for the engine to rev up. You can hold the thottle wide open and its the same bog.

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Thats a classic description of what it would do. Could be when you spun the tops off one of the cable adjusters turned and is now out of adjustment. Just having the carbs out of sync is enough to make this happen. Make sure the slides are free, resnyc the carbs, and you should be on your way. Unless one of the switches is bad.

(You did remove them when you soaked them right?)

[lawdog]

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I get a little exuberant with my wrenching and made a boo-boo.

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Boy if I had a dollar for every time I did that, I could afford a shop to work on my stuff!

I'm thinking that regardless of the end result, replacing those fuel lines and the diaphragm and all that you mentioned on a sled of that age can't be anything but a good idea. I remember my '93 EXT had some magnetic thing with the carbs too, but honestly that's way longer ago then I can remember stuff!!! Best advice I ever got about sleds (or any engine for that matter) remember: fuel, air and spark! Keep it simple before you go nuts on other stuff.

GOOD LUCK!

[hanson]

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how does it idle when you flip the choke?

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It will stall out.

The sled really idles nice. Choking it when it is idling will kill the engine. I can adjust the idle screws independently on each carb and the idle responds like it should, higher or lower depending on which way I turn the screw.

Everything seams to be running right, except when I hit the throttle.

[hanson]

Sure sounds like these magnetic switches are my problem. This is the first sled I've had thats had these so I probably should take a look at them first.

Thankfully this is just my "fun" sled so there is no hurry to get it up and running. Ever since Cat produced this one, I've always wanted one.

[vister]

have you taken the fuel pump apart yet. a diaphragm may very well have cracked or torn, if it sat dry over the summer. i would double up on a carb cleaning again though, to make sure you ruled them out. Do you have fresh gas, maybe even fresh 91 plus octane, non ethanol? does the gas tank smell right. not like varnish? Try sea-foam?