crank seal, plug readings. - Snowmobile Forum: Your #1 Snowmobile Forum

mustang_gt_350 · 01-02-2013, 09:31 PM

Ok, short story. Purchased the 91 mach 1 617 a few years ago. Took it out and first time out it blew up. Tore it down it melted the ex. port area of the piston. Rebuild it and took it back out, did a throttle chop and read the plugs. The pull start side was very lean, the primary side looked fine. So it has been sitting for the last 2 years, now that we have snow and i have some land to ride on of my own I'm getting the itch. So Is it possible that a bad crank seal would only show on one cylinder and not the other? I didn't notice any cracks in the carb boots, but i could have missed it. I want to dig into it again in the next day or 2 after i drag it back into the garage that i can mess with it. I also finnaly located that dang anti torque mount bolt so it won't eat belts, it will need a new ski or maybe both and a new track soon as i had to go max on adjustment but i don't want to drop money into the skis or a track until i can get it running properly.

thanks

mikemalibu · 01-02-2013, 11:15 PM

I would make sure that the carbs are well cleaned. Had that happen to my venture sure enough I had a clogged jet. Something I check now every season. A crank seal could cause it but before tearing it all apart I would check carb and boots and do a proper compression test with the throttle wide open.

mustang_gt_350 · 01-03-2013, 12:04 AM

Alright i will go through the carbs again. i did it when i had it torn down for the rebuild but maybe i missed somthing. any good links to the main cleaning parts of the carbs? Just to make sure i dont miss anying. I'm sure the compression is fine, its a bear to pull.

mikemalibu · 01-03-2013, 02:40 AM

I figured u may have gone thru them. In the how to section is some good info on carb cleaning. Basically make sure all the passages are clean. I use a small copper wire to clean the jets and carb cleaner. Then blow out with air. A small piece is all it takes. A compression check could help track down a bad seal in the case. I had checked my boys xlt when we bought it with 150 across all three jugs. First ride something told me pto bearings were out. A retest showed a 9lbs drop. Not enough to worry about but that and the noise told me what's up. You may want to check the jet sizes to be sure the po didn't do something funny. I'm no expert on skidoo's so maybe someone who is can give heads up what to look for on your specific sled.

mikemalibu · 01-03-2013, 02:42 AM

Link to the how to
http://www.snowmobileforum.com/engin...-tos-here.html

**smallengineguy** · 01-03-2013, 03:48 AM

A bad crank seal would indeed only affect one side. The cylinders also have a center seal to separate them.

**kccats** · 01-03-2013, 06:26 AM

If the Plug Chop showed the 1/4 throtle was lean, the pilot get as well as the center needle is likely plugged! Remove the pilot jet (up the tube) and floss it with a strand of wire!

mustang_gt_350 · 01-03-2013, 04:36 PM

Alright thanks for all of the info, i had figured it would be side specific on the seal but i wasn't sure. And i didn't know it had a center seal. Thanks for the help. I won't probable be able to pull the carbs until sat/sun. But when i do i'll let you know. I have a gallon paint can of carb cleaner from napa i'm going to soak them in and clean them both and check the boots. I do know they are not the OEM sized carbs, they are a little larger but I can't remember how much larger or why the PO changed them as it has a stock pipe/can. I do remember checking the jet sizes tho and i don't rememer any being way out of line from what should be in there, from the carb side that is fine compared to the bad side. Anyway i'll post back and let you know. If i find nothing in the carbs or boots i'll check out the crank seal. Hoping its just a bad boot and i missed it.

**smallengineguy** · 01-03-2013, 07:36 PM

Stock carbs are 40's. The Mach 1 X had 44's.

mustang_gt_350 · 01-08-2013, 04:18 PM

Pulled the carbs and tore them down, Didn't see any obvious problems with the boots. And i checked over the carb on the lean side and didn't notice anything clogged. I have the lean side carb pulled apart and soaking in a can of carb dip. I figure since they are off why not go over them again. If i get them back together tomorrow i'll toss them on and try to get it fired (primer is bad also) and take it for a run and check the plugs again. If its still lean I'm just going to pull the motor and take it into the house where i can tear it down and check out the seals, and replace them while its apart.

mustang_gt_350 · 01-09-2013, 07:08 PM

Pulled the engine today, ordered a clutch puller and a full gasket set.