Arctic Cat Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
4 Posts
Discussion Starter #1
I have found that some free-air Cats tend to get finiky when the weather gets warmer. And I've found that it's hard to tune the finiky-ness out with carb adjustments. I know that being free air engines; there's only so much you can do to help air flow over the engine to keep it cool. Running with the hood removed only helps a little...and to be honest, I likda like running with the hood installed haha.

I'd like to think that part of the problem is carburetor related. Does anyone have any experience with carb upgrades on free air cats? I feel like a nice mikuni flat slide would probably offer better tunability and better performance. Thoughts?
 

·
Registered
Joined
·
1,227 Posts
its rather common that a snowmobile made to run in cold air will run poorer in warm air, air changes, so yes, you can I am sure adjust carb to run better in warm air, but then will need to again when its cold again?

its why EFI is so liked, it solves this issue's
as well as with altitude changes that also effect running due to again air changes!

adding more vents to the hood can help a little, re jetting and or carb adjustments,
maybe can try adding a electric fan if one wanted to ?? fill engine bay with ice or?? LOL
better heat shields on exhaust to get heat out and away from motor faster?
these are about all I can think of?
 

·
Registered
Joined
·
4 Posts
Discussion Starter #4
its rather common that a snowmobile made to run in cold air will run poorer in warm air, air changes, so yes, you can I am sure adjust carb to run better in warm air, but then will need to again when its cold again?

its why EFI is so liked, it solves this issue's
as well as with altitude changes that also effect running due to again air changes!

adding more vents to the hood can help a little, re jetting and or carb adjustments,
maybe can try adding a electric fan if one wanted to ?? fill engine bay with ice or?? LOL
better heat shields on exhaust to get heat out and away from motor faster?
these are about all I can think of?
I thought about completely removing the vents from the rear side of the hood. I do have a spare hood that I could cannibalize if necessary. As far as a fan goes....I guess I could go F/C haha.


I would wrap the pipe with DEI wrap, https://deipowersports.com/products/exhaust-wraps-accessories. Then you will need to rejet way lean depending on temps. A flatslide won't benefit that much more than a roundslide on a small engine. What machine a engine do you have?
Its a 1979 Jag 3000. I've put flat slides on other small 2 strokes and there is a noticeable difference. Especially on dirtbikes. More snappiness.

I should also add that I am worried about locking up the engine as well. Seems like free air sleds have a reputation of blowing up when its warm...sometimes even idling. I may get some cylinder head temp sensors as well.
 

·
Registered
Joined
·
4,903 Posts
DO not under any circumstances go "lean". You'll seize it for shure. In the free-air days we would go rich to cool the combustion temp down when it got warmer. Did the same thing in my old Panhead too. You lean it out and you will melt a piston on a warm day.

Get head temp pyrometers I had them on my Z. You'll see how they react as which way the wind is blowing. So you know, when it's cooling it's actually warping the cylinder wall. The heads the hottest part
 

·
Registered
Joined
·
2,068 Posts
79 Jag says its a fan motor not up real good on the small stuff though. Regardless early Cats suck air under hood which is hotter. Ducting carbs to outside air would help. Never heard F/A blowing up because its warm out I've had plenty, they richen as it warms. Make less power and clutch drags RPM down and makes sluggish. Reclutch for less power is in the mix also with carbs when it gets warm. Small motor just more pronounced. Got a pic maybe someone removed your ducting from your motor
 

·
Registered
Joined
·
1,594 Posts
Over the years I made up my mind that flat-slides are a pain in the arse, that the common round-slide are more tuneable.
The only thing that I ever found to make a free-air ever-so-slightly less temp sensitive are Swaintech coatings. Every engine I rebuild gets at least the pistons and heads coated.
 

·
Registered
Joined
·
4,903 Posts
79 Jag says its a fan motor
OP says it's a free air

Heres a 79 Jag 3000 340 Free Air. Looks like a free air to me


Anyways I do know you don't want to jet way lean thats rolling the dice
 

·
Premium Member
Joined
·
786 Posts
Anyways I do know you don't want to jet way lean thats rolling the dice[/QUOTE] Jetting lean accordingly. If your jetting anything, you read your plugs. If your running a snowmobile with factory jetting, your running rich even in sub zero temps, the factory does that so the regular Joe won't burn it up. If your going to run in 30+ temps, you need to lean it down or it will run like a pooch. I race, and even a 10 degree temp change requires rejetting. A trail rider doesn't need to get that finicky, but a 30 degree difference will improve engine performance with jetting. As a side note, back in the 60's and 70's to present, i don't recall any free air's blowing up or melting pistons for no reason. Running too lean, an air intake leak, not the right oil/gas mixture, gaskets, can all contribute to a melt down. That's why you read your plugs. To cut down on heat, because the whole exhaust is in front of the engine, wrap the exhaust with heat wrap. It will cut the heat under the hood over 50%.
 

Attachments

·
Registered
Joined
·
4,903 Posts
I've built many engines, and I know how to read plugs, a sensitive altimeter and water grains, And you wrap the exhaust not to keep your under hood temperatures cooler, thats not the reason. You can do as you prefer tho
 

·
Premium Member
Joined
·
786 Posts
I've built many engines, and I know how to read plugs, a sensitive altimeter and water grains, And you wrap the exhaust not to keep your under hood temperatures cooler, thats not the reason. You can do as you prefer tho
That is true. Pipes are wrapped to keep the pipe hot. That helps the 2 stroke exhaust to scavenge better. The other plus with a wrapped pipe is, it reduces heat under the hood. I was not telling you "how to read plugs". I was only stating that for most people, learning to read plugs is a quick way to adjust jetting. Now the OP could run one step colder plug for better heat transfer also. It all depends on how warm of temperature he plans to run in. Is he trail riding in 30+ degree temps? Or putting wheels on and riding all summer. You seem to be hell bent on not leaning out a free air according to plug color for some reason. I wonder what moto cross guy's with 2 stroke free air engines used to do? I dunno This is for the OP,
 

·
Administrator
Joined
·
19,796 Posts
That is true. Pipes are wrapped to keep the pipe hot. That helps the 2 stroke exhaust to scavenge better. The other plus with a wrapped pipe is, it reduces heat under the hood. I was not telling you "how to read plugs". I was only stating that for most people, learning to read plugs is a quick way to adjust jetting. Now the OP could run one step colder plug for better heat transfer also. It all depends on how warm of temperature he plans to run in. Is he trail riding in 30+ degree temps? Or putting wheels on and riding all summer. You seem to be hell bent on not leaning out a free air according to plug color for some reason. I wonder what moto cross guy's with 2 stroke free air engines used to do? I dunno This is for the OP,
Changed my pre-mix ratio
 

·
Registered
Joined
·
4,903 Posts
78 is listed as a F/A 79 is a fan according to the fiche. Thats what regardless means
Ok regardless;
Here IS what the fiche shows, might not be what your looking at but it is what the company built.

here is the "Parts Fiche" showing the 1978 Arctic Cat Jag 3000 FREE AIR engine assembly.
It looks like a free air to me;


Ok here is the "Parts Fiche" showing the 1979 Arctic Cat 3000 Free Air engine assembly


Don't know what other parts fiche is out there but this is what they made, both years Pick one
 

·
Registered
Joined
·
474 Posts
Jags came in two flavors for 1978 model year both free air. 2000 and 3000 twins of 275cc and 340 cc displacement. For 1979 model year they branched out and added a third model. The 3000 FC fan cooled 340. They also made plenty of 1979 2000 and 3000 Free Airs as well . I’ve owned all of them over the years. When the free air engine starts running warm and you start changing jetting and don’t get the usual reaction you were expecting, that’s when I find that a gasket or a seal is going somewhere. Many years ago I had a modified 2000, a 1978. I did a lot of work on that engine trying to wring more power for my growing body. Where it wanted to spring a leak was usually the PTO head gasket or the intake manifold gaskets where it meets the cylinders. We are talking almost 40 year old engines now. Is the engine properly buttoned up with good seals and gaskets? My motor usually wanted all the studs torque checked every season because I rode the snot out of it and usually I would find something had loosened. If something got loose that started blow by and that meant a new gasket was needed because now it had a a tear or a scorch mark. I ran a factory head temp gauge and a tach. I’d check all the seals and do a compression check and a torque check of all head studs and jug bolts and intake bolts. Then recheck when warm .Make sure it’s not leaking air first. Only costs you time.
 
1 - 15 of 15 Posts
About this Discussion
14 Replies
8 Participants
gbarchives-eltigre
Arctic Cat Forum
Arctic Cat forum is a community to discuss Arctic Cat 400, 440, 500, 650, snowmobiles, sleds, ATV's and more. Join the fun!
Full Forum Listing
Top