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Old 09-18-2012, 12:33 PM   #1 (permalink)
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'89 Formula mx 470

My buddy gave me this sled which i'm in the process of going through to fixing all the "defered maintainence" issues on it and one issue i'm not having much success at is getting it to idle without crapping out after 30 seconds or so. It starts on the first pull and idles good for a while but unless i prime it when the idle start dropping or blip the throttle, it'll die. I've taken the carbs apart and cleaned them. How do i adjust the idle on the carbs, the screw on the side or the cable adjustments on the tops of the carbs?

I also broke the fuel level gauge on the side of the gas tank so i need to plug those holes. Any suggestions? I was going to use the appropriate sized screws to see if can't get them plugged and i haven't had much luck with any type of epoxy when fuel's involved.
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Old 09-18-2012, 03:27 PM   #2 (permalink)
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The screw on the side of the carb that extends into the throttle body to adjust the slide is the idle screw. But the symptom your explaining screams a plugged or dirty idle jet. this is the jet that is inside the fuel bowl situated between the slide and the end that connects to the carb boot. I would pull it out and shoot carb cleaner through the jet itself and through the idle port.
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Old 09-19-2012, 03:54 AM   #3 (permalink)
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Correct. Did you remove the pilot jets when you had the carb apart?
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Old 09-19-2012, 06:47 AM   #4 (permalink)
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Yeah, i tore the thing down and specifically sprayed carb cleaner through the jet then held it up to a light to make sure it was 100% clean. Even ran a wire through it to make sure there was nothing left. I did the same thing to the passage in the carb body where the jet screw into so i know the jet and passage are free of any obstructions. It sure seems to me like it was a dirty carb issue and that's why i tore them down.

There's another screw on the other side of the carb and i assume that's the air/fuel mixture screw? Anyone know what the stock setting is? Maybe my buddy messed around with it trying to fix other problems and it's out of spec. Man, this machine had 3 broken motor mounts and the engine was flopping around in the engine bay so much the primary clutch was rubbing on the secondary.
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Old 09-19-2012, 08:41 AM   #5 (permalink)
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Wondering if you might be able to help with decoding the VIN. I'm not sure it's an '89 but the way the vin's written, i thought it was. The numbers stamped into the side of the tunnel are 3742 01086. These numbers are also on a tag on the tunnel but with additional numebrs/letters. The whole thing on the tag is 3742 01086 MAI 1989.
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Old 09-20-2012, 03:58 AM   #6 (permalink)
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Pretty sure that's a 1990. MFG date 1989 makes it a 1990 model year. The air screw should be 1 turn out from closed, but you may have to adjust it a little as you ride.
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Old 09-20-2012, 12:20 PM   #7 (permalink)
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I'm going to go through them again this weekend to make sure i didn't miss anything and check the settings. I'll also go through the fuel pump just to make sure no crap is in there and replace the fuel filter since everything's going to be out of the way. Thanks for the help.
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Old 11-19-2012, 03:37 PM   #8 (permalink)
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hi i have the same sled and i just bought a fuel pump gasket kit and i was wondering if i needed to use any sort of gasket sealer on the new gaskets?
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Old 11-19-2012, 03:54 PM   #9 (permalink)
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You shouldn't have to use a gasket sealer on gaskets, that is the purpose of a gasket.
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Old 11-19-2012, 05:12 PM   #10 (permalink)
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okay so i replaced the fuel pump gaskets and that didn't solve my problem, my sled starts up and runs for about 10 seconds until it starts to die, then i prime it and it stays running and it constantly repeats this, it doesn't appear that any fuel is getting to the carbs from the fuel pump so i was wondering what i could do yo fix that?
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Old 11-20-2012, 03:47 AM   #11 (permalink)
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Start it and remove the fuel lines from the carbs while it's running. Fuel should shoot of the lines. If not, there is a restriction or a broken line from the tank, or the pump impulse line is bad to the engine block.
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Old 11-20-2012, 06:29 AM   #12 (permalink)
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Breks, i doubt your problem, and mine, is the fuel pump. It'll take more than 10 seconds for the engine to drain both fuel bowls on the carbs, unless the float is set too low. Also, typically fuel pumps will have a hard time keeping flow up at high rpms if clogged or have other issues. I agree it's a fuel issue however most other engines i've come across adjusting the idle will help but it seems even doing that, doesn't help on these engines. I haven't touched that sled in months but i may get to it over this holiday weekend if i have extra time. I'm going to tear down the carbs again and set everything to factory specs per the manual and see what happens. This is going to be the last time i try to tackle this issue. It's just an old beater sled so i'm not going to spend a bunch of time on it when it starts up and runs good. I'll post back if i get to it.
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Old 11-20-2012, 06:39 AM   #13 (permalink)
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Quote:
Originally Posted by smallengineguy View Post
Start it and remove the fuel lines from the carbs while it's running. Fuel should shoot of the lines. If not, there is a restriction or a broken line from the tank, or the pump impulse line is bad to the engine block.
I dont think it is a bad line from the tank because fuel gets to the pump and through the line to the engine block and tbrough the smaller line to the carbs but not through the larger lines to the carbs
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Old 11-20-2012, 08:02 AM   #14 (permalink)
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Quote:
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I dont think it is a bad line from the tank because fuel gets to the pump and through the line to the engine block and tbrough the smaller line to the carbs but not through the larger lines to the carbs
I have this same motor in my sled. ('95 MX) Mine was doing this and I found a small pin hole in one of the fuel lines to the carb on the clutch side. Replaced the line and it runs great now.

If the line that travels from the block the pump has a hole or crack in it, it will suck air causing lack of vacuum for your pump. Could be your problem.

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Old 11-20-2012, 03:36 PM   #15 (permalink)
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Quote:
Originally Posted by smallengineguy View Post
Start it and remove the fuel lines from the carbs while it's running. Fuel should shoot of the lines. If not, there is a restriction or a broken line from the tank, or the pump impulse line is bad to the engine block.
okay, so now here is my new problem, i unhooked the fuel lines from the carbs and gas poured out, so now what does that mean, would my carbs be clogged?
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Old 11-21-2012, 02:11 AM   #16 (permalink)
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You may have a stuck needle and seet. Also put your finger over the lines lightly see if gas still comes out. Had one that had a tiny pin hole that would pump til under pressure

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Old 11-21-2012, 03:38 AM   #17 (permalink)
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Remove and COMPLETELY clean the carbs. There is a tutorial in the how-to's section of this forum.
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Old 11-21-2012, 04:28 PM   #18 (permalink)
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okay so i checked the lines for holes and found none, i also blew air into the spots for the gas to go in and i cleaned them, i dont know what else to do...
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