Snowmobile World banner

1 - 15 of 15 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #1
Okay so here is the deal... I bought a 1979 Arctic Cat Jag 340 Twin yesterday for $300. Thing looks great for the year, but it needs some work. No problem, but it was sunny and warm and lots of snow on the ground, and I have never really been snowmobiling (long time dirt biker) so I bought the damn thing and went into the woods for about 4 hrs, and even got to do some lake running.

Problem is to get the damn sled running I have to take off the spark plugs and pour some mix down in the there. It'll fire up on the first pull everytime after that - stop for a couple of hours and have to do it again. Also it idles REAL high, like 'I'm going to blow up' high. Smoke everytwhere. I tried to turn down the idle but no luck. I drove it anyway :thumbsup: because it was so nice out.

Now the guy I bought it from said the crank seals need to be done - is that the cause of my high idle? If so what is involved and what parts do I need? I have a service manual off ebay on the way and am not afraid of wrenching. I've also been over the parts microfishe this morning.

Any thoughts?
 

·
Premium Member
Joined
·
575 Posts
Okay so here is the deal... I bought a 1979 Arctic Cat Jag 340 Twin yesterday for $300. Thing looks great for the year, but it needs some work. No problem, but it was sunny and warm and lots of snow on the ground, and I have never really been snowmobiling (long time dirt biker) so I bought the damn thing and went into the woods for about 4 hrs, and even got to do some lake running.

Problem is to get the damn sled running I have to take off the spark plugs and pour some mix down in the there. It'll fire up on the first pull everytime after that - stop for a couple of hours and have to do it again. Also it idles REAL high, like 'I'm going to blow up' high. Smoke everytwhere. I tried to turn down the idle but no luck. I drove it anyway :thumbsup: because it was so nice out.

Now the guy I bought it from said the crank seals need to be done - is that the cause of my high idle? If so what is involved and what parts do I need? I have a service manual off ebay on the way and am not afraid of wrenching. I've also been over the parts microfishe this morning.

Any thoughts?[/b]
Your gas lines could be hard and letting air in, so you loose your prime, also it will run lean if you get air in it . Check your plugs, if they're white better fix it real soon before you melt a piston. Crank seal will suck air too, again a lean mixture. We used to do a quick check on seal by squirting starter fluid at the seal when the engine is running....if it speeds up the seal's bad for sure. Careful with the ether, not too much.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #3
Your gas lines could be hard and letting air in, so you loose your prime, also it will run lean if you get air in it . Check your plugs, if they're white better fix it real soon before you melt a piston. Crank seal will suck air too, again a lean mixture. We used to do a quick check on seal by squirting starter fluid at the seal when the engine is running....if it speeds up the seal's bad for sure. Careful with the ether, not too much.[/b]

I'll check the clutch side seal tonight, but assume I'd have to take the recoil off and pull the stator to check for oil? I'll also check to see if there are any cracks in the boot or gas lines.

The plugs looked fine when I looked yesterday, but they were new. After the thromping ti took, I'll check the plugs tonight too.

I'll let you guys know how it goes.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #4
I'll check the clutch side seal tonight, but assume I'd have to take the recoil off and pull the stator to check for oil? I'll also check to see if there are any cracks in the boot or gas lines.

The plugs looked fine when I looked yesterday, but they were new. After the thromping ti took, I'll check the plugs tonight too.

I'll let you guys know how it goes.[/b]

One other odd thing - no matter how much or which way I turned the throttle stop screw and air screw it just kept on idling. The darn thing idles so much if I don't stay on the brake, it'll run away from me faster than I can catch it.
 

·
Premium Member
Joined
·
575 Posts
One other odd thing - no matter how much or which way I turned the throttle stop screw and air screw it just kept on idling. The darn thing idles so much if I don't stay on the brake, it'll run away from me faster than I can catch it.[/b]
Maybe your throttle cable is adjusted too short and won't let the throttle plate close.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #6
Maybe your throttle cable is adjusted too short and won't let the throttle plate close.[/b]
I checked the throttle cable and when the throttle is released there is some slack in the cable up at the bar end - should I check inside the carb?

I looked at the plugs and such last night for the first time since I drove the crap out of it for 3 hours. I noticed an oil leak that is quite bad, as far as I can tell the header on the stator side is leaking. That side of the engine is covered in dark oil, all centered around the header.

The plug on that side was black, but wet with oil like the outside of the case. The other plug on the clutch side was dry and white. Not bright white, but definitely running lean (assuming it is pulling air somewhere). Tried twice to get it running so I could test the crank seal on that side but no luck and it was late and cold so I gave up... Checked the plugs after I tried to start it and both were wet and black now.

Time is scarce this week but I hope to get at it soon.

Anyone know if I have to pull apart the non-clutch side to check the crank seal (via the spray wd-40 trick?)

Thanks for the help so far, it is much appreciated.

Jon
 

·
Premium Member
Joined
·
575 Posts
I checked the throttle cable and when the throttle is released there is some slack in the cable up at the bar end - should I check inside the carb?

I looked at the plugs and such last night for the first time since I drove the crap out of it for 3 hours. I noticed an oil leak that is quite bad, as far as I can tell the header on the stator side is leaking. That side of the engine is covered in dark oil, all centered around the header.

The plug on that side was black, but wet with oil like the outside of the case. The other plug on the clutch side was dry and white. Not bright white, but definitely running lean (assuming it is pulling air somewhere). Tried twice to get it running so I could test the crank seal on that side but no luck and it was late and cold so I gave up... Checked the plugs after I tried to start it and both were wet and black now.

Time is scarce this week but I hope to get at it soon.

Anyone know if I have to pull apart the non-clutch side to check the crank seal (via the spray wd-40 trick?)

Thanks for the help so far, it is much appreciated.

Jon[/b]
Another way to test the seals is to pressure test the crankcase, this is a little more complicated. You have to remove the exhaust manifold and the intake manifold. Then you have to block these ports with a gasket of sorts. Leave the sparkplug in and pressurize the crankcase through the pulse port on the block below the cylinder. It should hold 15 lbs. (don't apply more than that or you will blow out the seal). This has to be done to both sides as the crankcase is separate for each cylinder. If you don't have a pulse fitting on one side you have to make up a sparkplug with an air fitting and pressurize from there.
 

·
Registered
Joined
·
8 Posts
Discussion Starter #8
Another way to test the seals is to pressure test the crankcase, this is a little more complicated. You have to remove the exhaust manifold and the intake manifold. Then you have to block these ports with a gasket of sorts. Leave the sparkplug in and pressurize the crankcase through the pulse port on the block below the cylinder. It should hold 15 lbs. (don't apply more than that or you will blow out the seal). This has to be done to both sides as the crankcase is separate for each cylinder. If you don't have a pulse fitting on one side you have to make up a sparkplug with an air fitting and pressurize from there.[/b]

So it is possible to have a seal go on one side only?
 

·
Premium Member
Joined
·
575 Posts

·
Registered
Joined
·
8 Posts
Discussion Starter #10
Talked to a freind of mine that owns a small engine repair shop... he said 1 hour labour to do the seals if I bring in the motor out of the sled. $15 for the seals.

Should I do both while it is out? Any other gaskets, seals whatever that should be done too?
 

·
Registered
Joined
·
11 Posts
Talked to a freind of mine that owns a small engine repair shop... he said 1 hour labour to do the seals if I bring in the motor out of the sled. $15 for the seals.

Should I do both while it is out? Any other gaskets, seals whatever that should be done too?[/b]
Absolutely do both for that price! Hard old seals are leaking air into the engine, the jetting on the pilot circuit is probably set rich enough to compensate for the leaking seal(s) - a 2-stroke when it gets lean will nearly "run away" and that's what you're expierencing right now. Once you replace the seals, put in a new set of plugs, then adjust the idle speed and mixture and then run it and check the high speed mixture by reading the plugs. Have him also do a quick compression test when he's done changing seals just to see what kind of shape the top end is in.

As for the hard starting - it's probably not able to create enough vacuum to pull the a/f mix into the engine as well as not enough engine pulse pressure to allow the fuel pump to work. Changing the seal will help both symptoms - then at least you've got a good base to start adjusting from.

Heck if the engine is out I'd clean the carb and start at the factory jetting and settings (recomended # of turns for each screw) and then tune from there.
 

·
Premium Member
Joined
·
575 Posts
Absolutely do both for that price! Hard old seals are leaking air into the engine, the jetting on the pilot circuit is probably set rich enough to compensate for the leaking seal(s) - a 2-stroke when it gets lean will nearly "run away" and that's what you're expierencing right now. Once you replace the seals, put in a new set of plugs, then adjust the idle speed and mixture and then run it and check the high speed mixture by reading the plugs. Have him also do a quick compression test when he's done changing seals just to see what kind of shape the top end is in.

As for the hard starting - it's probably not able to create enough vacuum to pull the a/f mix into the engine as well as not enough engine pulse pressure to allow the fuel pump to work. Changing the seal will help both symptoms - then at least you've got a good base to start adjusting from.

Heck if the engine is out I'd clean the carb and start at the factory jetting and settings (recomended # of turns for each screw) and then tune from there.[/b]
YUP, what he said!
 

·
Registered
Joined
·
8 Posts
Discussion Starter #13
YUP, what he said![/b]
\

Sounds good!

I am going to replace both crank seals, head, base and manifold gaskets (header was blowing by quite badly), new gas lines and filter, new carb boot as the old one is cracked, and carb is out and being looked at.

When I pulled the throttle out of the carb the main spring was not straight at all, and the throttle would not fully close either... so it is going to be done as well.

New belt, air filter and plugs.

Also, the brake disk hub is loose on the shaft, and the key is out of the slot. Looks like it has been like this for a while. The disk will rotate abotu 45 degrees on the shaft and the fetch up on the loose and floating key. Need to take it off tonight and see what I am in for here, but shouldn't be too bad.

I DID NOT PLAN ON REBUILDING THIS OLD CLUNKER, BUT HERE I AM! :rolleyes:

I'll have to post a pic up when she is done.


ONE more question...

I took the carb off, all the lines off and the pull cord and the exhaust. Took the two fron t engine mounts off as well (with some greif but they are off). Now for the back two mounts, they are under a bent back flange and I can't see how to get at them. My service manula I bought off ebay isn't due to the end of the week... anyone have any advice?

Thanks so far for all the help,

Jon
 

·
Registered
Joined
·
8 Posts
Discussion Starter #14
Finally got the final engine mount off last night. Not easy with only two hands when you need to use one pair of plyers to hold the nut, one to hold the flashlight, and one to turn the ratchet.. 28 years of heat cycles, rust, and someone who already stripped both of the heads of them made them a little unwilling to come out, not to mention the cross bar underneath was all bent to :cussing:

My grinder got put to use :cool:

One of the bolts was still stuck in the engine plate after I pulled it from the sled and was so curved I had to cut it out... new hardware was on the order anyways.

Off to the engine shop...
 

·
Premium Member
Joined
·
575 Posts
\

I took the carb off, all the lines off and the pull cord and the exhaust. Took the two fron t engine mounts off as well (with some greif but they are off). Now for the back two mounts, they are under a bent back flange and I can't see how to get at them. My service manula I bought off ebay isn't due to the end of the week... anyone have any advice?

Thanks so far for all the help,

Jon[/b]
bj I saw your post too late, the back engine mount plate bolts (nuts) are actually part of a rubber mount and the nuts are accessible at the front of the track in the tunnel.

[attachment=33844:Jag_engine.gif]
 
1 - 15 of 15 Posts
Top