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Discussion Starter · #1 ·
2001 MXZ700, ran fine last winter and when put away.

Before last winter I rebuilt both carbs with all new jets (stock) and floats, float valves & float seats. Replaced both reeds at that time too. So now it's just geysering out spark plug hole on left bank only. Thinking the float valve seat was compromised I tore apart both bowls, removed and cleaned everything and swapped floats when reinstalling thinking the problem would move. It didn't, still the left bank ejects fuel 6' high out spark plug hole. I hope the video attached plays it's actually quite impressive. Couldn't shrink the video down enough to attach here so here's a link to the video on Youtube.


Checked reeds next and they look fine. My plan is to swap those going back in as well and see if the problem moves, but I paused there in case anyone has any advice while still apart.

What else could it be? Strange it ran fine last year..... could it need another carb rebuild already? That would be odd. Oh, I used non-ethanol fuel. Out of probably 10 tankfuls I had to use an emergency tank of ethanol but that was about the sixth tank out of ten. So I would imagine that ethanol would be long gone with 4 more tankfuls of non-ethanol running through it.

Thanks in advance!
 

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Don't let it geyser as it would only take a tiny spark to ruin your whole day/winter.

Still thinking the float is stuck. If the float is working, it would shut off fuel flow.

When you have the carb off, turn it upside down and blow into the fuel input line. You should not be able to.

The other possibility is that the fuel pump diaphragm is leaking and pushing fuel through the pulse line directly into the crank case.

And the last possibility is one of your hoses is not connected to the right spot. While this isn't usually the case because the lines are all different sizes, I've actually seen someone put the fuel input line on the vent hole.
 

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All of that and more. Because of the recent maintenance I'm thinking there in the problem lies. Lines not hooked up correctly or the suspect side float needle is not seating. New float as mentioned would require float height to be set. That needle may not be seating because the float height is way off.

Lots of time before the snow flies. You'll get it.
 

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Discussion Starter · #4 ·
DARWIN AWARD TO ME!!! WOOO HOOOOO! I finally win something! But that geyser is so cool to watch, especially in slow-mo LOL.

Thank you, not only did I not think of that, but that fuel pump diaphragm sounds like it could be the culprit. I took it apart last fall and "cleaned" it. And although it ran well, I wouldn't doubt it's seen better days and is injecting directly into the crank.

I'll try the line test with carbs upsidedown, but my money is on the diaphragm.

Thank you tons!

Don't let it geyser as it would only take a tiny spark to ruin your whole day/winter.

Still thinking the float is stuck. If the float is working, it would shut off fuel flow.

When you have the carb off, turn it upside down and blow into the fuel input line. You should not be able to.

The other possibility is that the fuel pump diaphragm is leaking and pushing fuel through the pulse line directly into the crank case.

And the last possibility is one of your hoses is not connected to the right spot. While this isn't usually the case because the lines are all different sizes, I've actually seen someone put the fuel input line on the vent hole.
 

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Yeah, you want to be very careful with fuel like that flying around.... DON'T ask me how I know, too embarrassing.

Sent from my moto g(6) using Tapatalk
I was lucky more didn't go wrong. My experience was with a riding lawnmower. Pulled the spark plug out, even removed from the cap, figured I was safe to turn the motor over. It blows lots of fuel straight out of the open garage door right onto my mini-van and something sparked and it was like a jet engine blasting the front of that van. Lucky it only scorched the paint on plastics.

Too bad I didn't have the video cameras then, that would have made a good one for youtube.
 

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Discussion Starter · #7 ·
OK just an update to this, it's still a problem. I know for a fact I didn't swap fuel lines LOL, but I can see how that could happen. I like to take a LOT of pictures before and during any disassembly, even set up the gopro for the more in depth repairs. Not to say I can't screw up, cuz I do, but I know these fuel pump lines are correct.

OK, with that out of the way, I rebuilt the fuel pump with a kit from DennisKirk. I didn't see any smoking guns during this rebuild, and in fact the problem still exists after reassembly. Just to make sure I wasn't losing it, I went out to my other sled today, yanked plugs and pulled. No fuel of any kind spraying out of either hole. Then put plugs back in and it started first pull (like usual). Just for giggles I even put full choke on to see if I could get a geyser, but even full choke no perceptible gas coming out of the holes at all. That sled is a 2000 MXZ700, the problem sled is a 2001 MXZ700. They changed carbs, pump and boots/reeds for 2001 so I can't swap any of those in unfortunately.

Last fall I after I rebuilt the carbs I replaced the floats/valve/seat in both carbs. They're 100% plastic, everything, and I don't see any type of adjustment at all. But the more I think about this, the more I rebuild/change/troubleshoot without success I'm thinking it really sounds like a stuck float valve, especially since it's only one side. I swapped carb boots & reeds but the problem didn't move. It's always the left bank.

Problem is I wrecked my MX bike overjumping a 65'er (this happens frequently LOL) so I banged up my right shoulder and it's hard to pull. So I have to make my pulls count. Of course with the plugs out it pulls a ton easier, but it still is painful ugh.

I'll link the original video of the SERIOUS geyser again...

Yes, there still is plenty of time to get this fixed before the snow flies so at least I've got that going for me.

Thanks guys, I know we'll get it, I'm stubborn and will never relent. So hang in there with me please. And of course once we get it I'll definitely post the fix for the next guy (likely me next year LOL).
 

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Swap carbs around. Guessing the problem will follow which tells you it is a carb problem.
Definitely do this.

They're 100% plastic, everything, and I don't see any type of adjustment at all.
Hmmm, you have to check float adjustment. It's so primitive a caveman can do it. Sounds like you need a maintenance manual. Float adjustment is clearly outlined there. PM your email and I'll send it.
 

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Discussion Starter · #11 ·
Swap carbs around. Guessing the problem will follow which tells you it is a carb problem.
I'm not home right now but those carbs are connected and I don't think interchangeable. Are they?
 

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Manual on the way. 4 volumes in that pdf. Yours is vol 3. Click on the banner in the upper left margin to see volume selections. Download the file. It will expire on the web in a couple days.

Pretty sure your issues are with the work you did on the carbs. The float needle can get hung up on the float tab easily during reassembly. This can cock the needle at an odd angle and keep it open. Hence flooding.

Also, doesn't take much of a bend on the float tab to leave the needle open even when the bowl is full.
 

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Discussion Starter · #14 ·
Maybe try swapping floats.
Thanks, Sorry I meant to mention that but I typed that up in a couple sittings and forgot that piece. I have cleaned and swapped floats the problem did not move. I will tear into the floats a more, I mean it's GOT to be that.
 

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Discussion Starter · #15 ·
Manual on the way. 4 volumes in that pdf. Yours is vol 3. Click on the banner in the upper left margin to see volume selections. Download the file. It will expire on the web in a couple days.

Pretty sure your issues are with the work you did on the carbs. The float needle can get hung up on the float tab easily during reassembly. This can "edit for bad language" the needle at an odd angle and keep it open. Hence flooding.

Also, doesn't take much of a bend on the float tab to leave the needle open even when the bowl is full.
David, you're my hero, thank you for the manual!

What is killing me is I rebuilt the carbs last fall, before the season, ran it all winter then parked them both in March. Now I go to start them and the geyser is there. The other (one year older) sled started within a few pulls. Sure, I could have messed them up after cleaning them a week ago, but I mean they just SAT for 5 months! I use leaded gas, even put stabilizer in tanks.

Damn I want to EFI these friggen sleds LOL.

It's got to be the bend you speak of, as the float swap didn't move the problem. Time to do some more cleaning and check that adjustment now that I've got the manual :)
 

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Hmmm, If the float adjustment was off it should have moved with the swap. Check it anyway but it's likely the needle/seat at this point. As mentioned above, I also think the float needle is not seating.

If all is assembled properly and floats adjusted correctly and needle is seating then I'm just guessing...Fuel pump?

For smarter guys, does the pulse line come off the pto side on this sled?
 

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Discussion Starter · #17 ·
Hmmm, If the float adjustment was off it should have moved with the swap. Check it anyway but it's likely the needle/seat at this point. As mentioned above, I also think the float needle is not seating.

If all is assembled properly and floats adjusted correctly and needle is seating then I'm just guessing...Fuel pump?

For smarter guys, does the pulse line come off the pto side on this sled?
Rebuilt fuel pump after "ruling out" float not seating. (gonna revisit this)

Yes, off PTO side. (and no, my lines are not crossed) The only other thing I could be talked into believing is a bad oil injector? But I don't know anything about that part.
 

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Rebuilt fuel pump after "ruling out" float not seating. (gonna revisit this)

Yes, off PTO side. (and no, my lines are not crossed) The only other thing I could be talked into believing is a bad oil injector? But I don't know anything about that part.
Oil injectors are not part of this problem.

Sent from my moto g(7) using Tapatalk
 

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Take a closer inspection of circled O-ring. If that is pooched, fuel has a path to bypass the needle/seat assembly and flood the crankcase.

Can't say I've run into it on the 01-up MXZ TMX rack carbs, but definitely have on other mikunis with this sealing method on the seat body.
 

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i had an issue like that on my 69 olympic opposing twin, i took pictures of everything when i took it apart... so i had a camera laying near by. went to start the beast, hydro locked. took the plug out, pulled, plug was close to the hole (for some reason i put the plug in the cap?) so she sparked and blew a 10ft ball of flame at my workbench. 2 weeks later my wife is asking why the camera wont work, it smells like gas and looks like it's melted. I walk over to look at it... "oh" ooops. ha ha.
 
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