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Discussion Starter · #1 ·
Hey guys,

I tried to search on this forum and on google, but maybe i can't see the forest for the trees... i have also no real knowhow about it either.

So i have a skidoo mx470 rotax type 467 from 1993. It has 2 Mikuni carburetors with a indication H3 6 2

It stood still for years but it looks almost brand new.

So we took the old gasoline out. Put in new. I cleaned the carburetors, removed the all the jets. cleaned them out, the pilotjet was really full of dirt but it is now perfect clean. Put everything back in its place, we used the settings of

air. 1,5 turn out

idle-screw: 3 turns in

So now we are at the point, the scooter starts perfect! and as long as we hold the gas, we can go on forever. Full Trottle or mid trottle no problem. But as soon as we leave the trottle, the motor dies instantly

We tried differend settings on the carbs, but we dont get a feeling that it helps.

So what is next to try and to look at ? The fuelpomp , what is best way to test it ? or something else ?

Thanks guys !
 

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You may have to screw in both idle screws till you have her running at 1800 rpms at idle. They do screw in a long way to get it to idle.
 
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Turn the Air Screws in 1 turn to start.

How were the Carb Boots? No cracks?

Did you get the Carbs back on well seated?

The Idle Circuit has 3 small holes, Engine Side of the Carb Slides. Check to make sure they are Clear of any debris. Use an Air Gun, Blowing both threw the Air Screw Holes, and Carb Throat.
 

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Discussion Starter · #5 ·
Okay little update, removed the carbs and checked them again but they are perfect clean. i readjusted the airscrew, it was at 1 and 1/3, i put it at 1,5 now.

So now the scooter starts again perfectly + it idles perfect at 1500 rpm !!

Except if you try to give trottle it dies -_- , so now it is the other way around

perfect idle, but stalls when giving gas
 

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Turn the Air Screws in 1 turn to start.

How were the Carb Boots? No cracks?

Did you get the Carbs back on well seated?

The Idle Circuit has 3 small holes, Engine Side of the Carb Slides. Check to make sure they are Clear of any debris. Use an Air Gun, Blowing both threw the Air Screw Holes, and Carb Throat.
No the carb boots seems fine. Yes carbs are well seated.

i have to say, the battery is broken and we start the ski doo with jumper wires and second battery. When it was running on idle, i detached the second battery to try to drive and then we noticed that if we put in trottle it would stall. So can this broken battery be the problem on not being able to give trottle ?
 

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I can't see a weak battery making it stall off idle, but when in doubt just disconnect it. Your engine does not rely on the battery of power to the ignition circuit. I am assuming it has a functioning recoil. I notice you had set the idle screws 3 turns IN as opposed to OUT. I usually gently seat the screw and back it off by 3-4 turns as a starting point. Make sure that your slides are raising off the idle pins at the same time and that one isnt staying closed due to slack in the cable. There are different methods of syncing your carbs using drill bits or a manometer but by eye should give you a reasonable starting point.

Even though you just cleaned the carbs, there is a change your pilot circuit may have become plugged up again due to debris in the fuel system. If your floats are not adjusted correctly, a lack of fuel in the bowl could be your problem. Be sure you didnt reinstall the float arm upside down. There should be a little wear "dot" wear it contacts the needle and seat. Float arm height should be 22-24mm measured from the carb body to the float arm while holding the carb upside down with the bowl off.
 

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Maybe a little lean on the needle jets if she bogs off idle. lower the circlips on the needles jets and see if that helps?
 

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Discussion Starter · #9 ·
I can't see a weak battery making it stall off idle, but when in doubt just disconnect it. Your engine does not rely on the battery of power to the ignition circuit. I am assuming it has a functioning recoil. I notice you had set the idle screws 3 turns IN as opposed to OUT. I usually gently seat the screw and back it off by 3-4 turns as a starting point. Make sure that your slides are raising off the idle pins at the same time and that one isnt staying closed due to slack in the cable. There are different methods of syncing your carbs using drill bits or a manometer but by eye should give you a reasonable starting point.

Even though you just cleaned the carbs, there is a change your pilot circuit may have become plugged up again due to debris in the fuel system. If your floats are not adjusted correctly, a lack of fuel in the bowl could be your problem. Be sure you didnt reinstall the float arm upside down. There should be a little wear "dot" wear it contacts the needle and seat. Float arm height should be 22-24mm measured from the carb body to the float arm while holding the carb upside down with the bowl off.
- Slides are in sync , i checked it

- float arm is installed correctly, i indeed looked at the little wear dot

- all Jets are clear

about the idle screws, i dont understand "seat the screw"

This is how i do it: i turn the idle screw out so i am sure it doesnt hit the slide. then i turn untill i can feel with my finger it hits the slide. And then i turn the screw 3 more turns IN. That is how i saw it on Youtube.

It is just weird, first we couldnt idle but trottle was no problem, we solved the idle problem, and now we cannot trottle -_- , tomorrow we need to get new battery, we will buy also some new sparks just to be sure.

And then we check again the carbs
 

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If it idles at 1500 rpm, you need not worry about the Idle Screws.

The Air Screw, then Pilot Jet, control upto about 1/3 throttle. The Air Screw is in the side of the Carb Body engine side of the slide. A small Brass Screw, that are Not Jets, they are Air Screws, Leaner farther out, richer closer in. So try turning them in 1/2-3/4 a full turn.

If that doesn't help coming Off Idle, it is most likely Pilot Jets, Dirty/Too Small/or the openings in the Carb Throat past the Slides.
 

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- Slides are in sync , i checked it

- float arm is installed correctly, i indeed looked at the little wear dot

- all Jets are clear

about the idle screws, i dont understand "seat the screw"

This is how i do it: i turn the idle screw out so i am sure it doesnt hit the slide. then i turn untill i can feel with my finger it hits the slide. And then i turn the screw 3 more turns IN. That is how i saw it on Youtube.

It is just weird, first we couldnt idle but trottle was no problem, we solved the idle problem, and now we cannot trottle -_- , tomorrow we need to get new battery, we will buy also some new sparks just to be sure.

And then we check again the carbs
By "gently seating the screw" I mean to turn it all the way in until it will no longer turn but don't tighten it too much as to not damage anything. After this, back the screw out by 3-4 turns. If you screw in until it hits the slide and then in 3 turns, there is no way to know exactly where each carb is really at. The adjustment will vary randomly based on the amount of slack in the throttle cables. Idle screws are the first adjustment, throttle cables are the second. When I sync carbs, I connect a manometer to my primer fittings, then set the idle using the idles screws. Next, I bring the engine off-idle to make sure the slides are both hanging from the throttle cables (3000 RPMish) and adjust the slack in the cables until my pressure is even. Just make sure you have the back of the sled off the ground for your start-up in case it wants to take off on you. Most dual carb sleds I have worked on end up at roughly 3.5 turns out from seated on the idle screw.
 

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Discussion Starter · #12 ·
So little update

Just to be sure, i took the fuel pomp out to clean and bought a repair kit for it to replace the gaskets and diaphragms. It is an Mikuni df52-73 with a weep hole. When i took it out, it had the weep hole on the top.

But as i was searching on the internet i found a document ( i think it is about little airplanes but maybe it is the same)

https://m.cps-parts.com/cps/pdf/Part53.pdf

Figure #3 - When mounting a fuel pump vibration isolation is a prime concern. Here a dual pump is mounted on two #260-657 Rotax Radiator mounts.

This also puts the weep hole at the bottom point where it belongs.
With a snow scooter does the weep hole needs to be up side down ?
 

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I think the weep hole is dependant on the style pump you have.

The single rectangular is up and with some dual outputs it is down.

Your mounting location usually allows the pump to be only bolted in one orientation which determines up or down.

IMO it is not that important as long as writing on the pump is upwards, or thereabouts.
 

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Discussion Starter · #14 ·
okay, little update ,

So i installed a gasoline filter, i re-installed the fuel pump with the new kit. double-checked everything cross-double-triple checked everything !!

I did the correct settings on the carb.

It took some time to get the fuel lines back full, but in the end, my god, it worked! Idle is perfect on 1500rpm, i can give trottle, no problem !

But then i think i flooded it xD, i primed when the motor was warm and it wouldnt start anymore. So tomorow new start test but i think i tackeld the problem !

Thanks guys !
 

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Discussion Starter · #16 ·
No everything is ok !! i just forgot about the ignition break button :rolleyes:

It starts like a pro, everything is ok !!
 
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