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Discussion Starter #1
Hey guys, I was wondering if you might help point me in the right direction. I have a 93 Ski-Doo Mach1 with the 670 Rotax / duel carb. I am having a bear of a time trying to get it started this year. I have flushed the fuel system completely, and cleaned out the carbs. I have disconnected all the kill switches and ign switch (this is a pull start only) I am getting spark (inline spark tester) and I know that I am getting fuel from the wet plugs. I can only get it to start (no belt) about every 100 pulls or so with the throttle wide open. I can feather the throttle and get it to run for about a minute or so (lots and lots of black smoke), but when I try to get it down to idle it dies. I had a friend watch the spark and he said the spark cut out before the engine died. Upon trying to restart, I can not even get it to fart unless I let it sit for an hour or so. I am thinking that there may be something wrong with the CDI box, coil, stator, or maybe the ignition trigger. Any ideas would be helpful. Thanks for any info.
Jon
 

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Unscrew your spark plug boots and cut about 1/2 inch off the ignition wires. Go to a NGK supplier (or dealer) and purchase 2 new resistor type boots. Apply some dielectric grease on the ends of the wires and spark plug nipples. Screw new boots on the wires and start that sled. Check that you didn't install the floats in upside down too.
 

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Discussion Starter #3
Unscrew your spark plug boots and cut about 1/2 inch off the ignition wires. Go to a NGK supplier (or dealer) and purchase 2 new resistor type boots. Apply some dielectric grease on the ends of the wires and spark plug nipples. Screw new boots on the wires and start that sled. Check that you didn't install the floats in upside down too.[/b]
Thanks, I'll try that tomorrow. I'm pretty sure the floats are right side up, I'm a small engine mechanic and the carbs were pretty straight forward. If it's this easy I'll....
Thanks Jon
 

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Not to hijack your thread but can you run resistor plugs BR9ES with resistor caps, or do you need B9ES plugs? My buddy said not to run resistor plugs with resistor caps.?????
 

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The factory plug boots are resistor and so are the plugs. Has no effect on available voltage to the spark plugs the resistors are only for radio and electro magnetic interference. The NGK racing wires don't have resistors in the caps. One test which is fail safe is to remove the plug boot and give it a shake next to your ear. If it rattles, the resistor is burnt out.
 

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Discussion Starter #6
Unscrew your spark plug boots and cut about 1/2 inch off the ignition wires. Go to a NGK supplier (or dealer) and purchase 2 new resistor type boots. Apply some dielectric grease on the ends of the wires and spark plug nipples. Screw new boots on the wires and start that sled. Check that you didn't install the floats in upside down too.[/b]
I now have a new HERO. Thanks Doc, I did just as you said and now my sled starts on the first or second pull everytime. :D Tomorrow I'll adjust the idle up, it's only about 1750 right now and it will die if you let it.

Next question; Seems to be ALOT of smoke from this engine, is this something that will fade as I ride and burn of any extra in the exhaust or could it be a different issue? I'm running Ski-Doo XP-S oil. Thanks Again
 

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I now have a new HERO. Thanks Doc, I did just as you said and now my sled starts on the first or second pull everytime. :D Tomorrow I'll adjust the idle up, it's only about 1750 right now and it will die if you let it.

Next question; Seems to be ALOT of smoke from this engine, is this something that will fade as I ride and burn of any extra in the exhaust or could it be a different issue? I'm running Ski-Doo XP-S oil. Thanks Again[/b]
If it's acrid smelling smoke, its probably your float levels in the carbs are off. Its worth the effort to take the carbs off again and make sure that the tang is level and 18mm higher than the bowl gasket surface. Adjust your idle mixture screws to 1 & 3/4 ~ 2 turns out from lightly seated.
 

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Discussion Starter #8
If it's acrid smelling smoke, its probably your float levels in the carbs are off. Its worth the effort to take the carbs off again and make sure that the tang is level and 18mm higher than the bowl gasket surface. Adjust your idle mixture screws to 1 & 3/4 ~ 2 turns out from lightly seated.[/b]
Quick update and question; I got the sled out on the lake today, maybe 2-3 minutes. I just couldn't help it after cleaning the raves and lubing everything. Got back in the yard and gave it a little blip on the throttle just to move it up another few inches and it stalled. Now it won't restart. This happened yesterday also, except I let it stall from lack of idle. By the time I got home last night she fired right up on the first pull. I'm not sure if this has to due with the smoking issue. BTW it really smokes at idle, but is fine once you're moving.
Here's my question; when I pulled the carbs out initially I checked the mix screw before dissasembling and it was at 2 3/4. I reassembled it the same because that's what is in my book. Any reasoning behind the your recomendation to go with 1 3/4-2 or is it just experiance. Just wondering. I'll be pulling the carbs tomorrow.
Thanks again
 

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Mostly because those 44 mm Mikunis are known to be bad on fuel consumption and they don't like to be parked on an incline (they flood easy) If you have the original 44 mm carbs the correct float level is 20 mm not 18mm for 40 mm Mikunis. The leaner low speed allows you to idle it longer but it will idle quite high. If you can get it to idle at 2 1/4 turns out without it loading up in the warm weather then leave it there.
 

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Discussion Starter #10
OK, so tonight I get home and figure I'll get in a quick ride before it's dark and I start the sled (maybe three pulls) I had to stay on the gas to keep it running and yes still smoking and yes Doc it smelled acrid. I work in a small engine shop and live in two cycle smoke. This wasn't it. After idling/holding the throttle the temp came up so I quickly threw on the helmet and it died. This happened about 4 or 5 times before I could not get it restarted. So off with the helmet and out to get some tools. I pulled the carbs and reset the float levels to 20mm (they were at 17/18) I also reset the idle mix screw to 2 turns out and then reinstalled the carbs. (floats are in with the word "up" facing up :wink: ) I put them back in the sled and tried starting it (sans airbox) and nothing, not even a fart. I stopped reinstalled the airbox and changed plugs (properly gapped) and still nothing. Now I know it may just be flooded, but with the FIRST snow of the season coming tomorrow I'm hoping to have this running.
On a side note. I believe hese are the original carbs, but there are no markings on them, other than MIKUNI. I did take a look at the PTO side main and it is marked 420 (didn't look at the other side) if that helps in identifing witch carbs I have.
Thanks for all the help. I'll probably try to restart it again before bed.
Jon
 

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I have somewhat of a similiar situation. I also have a 93 Mach 1. The machine runs fine when it is going, but at an idle it smokes quite a bit (but it will sit and idle without stalling).But one problem I find...If after a run, and I stop the machine for say an hour break..I will go to start it, I will give it a prime or two and pull the cord, usually it will fire up as long as I grab hold of the throttle quick enough..BUT!..If I miss the throttle and it stalls out I usually will have to wait around a half hour before I try to start it again..WHAT THE HELL??? Any ideas?
One of my theorys is that it just gets flooded...
Thanks
 

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OK lets first identify what sized carbs you have there before we proceed. Judging by the main jet size you describe it appears you have 40mm Mikunis. Remove the PTO side carb and look at the number stamped in the same place as the photo

[attachment=33545:IMG_0713.JPG]

As you can read on this carb The M stands for MAG side, the 381 is the production number and the 34A states the carb size in mm.
Once you have that number post it. According to my specs the carbs should be 40-54 PTO with 420 main jet and 40-55 MAG with 440 main jet.
 

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Discussion Starter #13
OK lets first identify what sized carbs you have there before we proceed. Judging by the main jet size you describe it appears you have 40mm Mikunis. Remove the PTO side carb and look at the number stamped in the same place as the photo

[attachment=33545:IMG_0713.JPG]

As you can read on this carb The M stands for MAG side, the 381 is the production number and the 34A states the carb size in mm.
Once you have that number post it. According to my specs the carbs should be 40-54 PTO with 420 main jet and 40-55 MAG with 440 main jet.[/b]
40 on top, 54 underneath
 

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Discussion Starter #16
OK I just pulled both carbs and have them inside where I can see clearly. Number wise this is what I have;

Mag side
40 over a 55 with a 440 main jet

PTO side
40 over a 54 with a 420 main jet


What should my next step be? should I return the floats to 18mm and the idle mis out to 2 3/4? This is where they were originally and I still didn't have a good idle. I'd rather wait and find out before I reinstall them. Sorry for the confusion about which carbs they were, I'm really new to this type of engine and just want to ride and have a good time with it. FYI these carbs are on a 1993 Formula Mach1 Aniversary with a 670. Compression is 148 in both cylinders.

Just a thought, but could this be a fuel pump problem? I know that it should gravity feed fairly well, but last year I filled the sled with about 11 gallons of fuel, only rode once for about 1/2 hour (no snow or ice last year) and when I drained it this year I only had about 2-3 gal left. There doesn't appear to be any leaks, nor a gas smell in or around the sled. just wondering if it was seeping through the pump gaskets and evaporating. They look moist, but there is no other visable sign of leakage.

Thanks again for all your help.
Jon
 

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Jon,

Sorry to run you around the garden path, I thought you had an X model. Here are the specs for you sled right from BRP.

[attachment=33586:1993_Mach_1_carb.doc]

Please observe the Needle clip position from the top is staggered and the idle mixture is only 1/2 turn out. That should clear up the over rich idle problems. Float height measured at the bowl gasket surface is 18.1mm.
 

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Jon,

Sorry to run you around the garden path, I thought you had an X model. Here are the specs for you sled right from BRP.

[attachment=33586:1993_Mach_1_carb.doc][/b]
You wouldn't happen to have the specs for the 96 Mach 1 would you?
 
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