Getting a Free Air engine to run better when it's warm out? - ArcticChat.com - Arctic Cat Forum
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post #1 of 14 Old 04-15-2019, 03:21 PM Thread Starter
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Getting a Free Air engine to run better when it's warm out?

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?
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post #2 of 14 Old 04-15-2019, 04:38 PM
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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?
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post #3 of 14 Old 04-15-2019, 06:50 PM
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I would wrap the pipe with DEI wrap, https://deipowersports.com/products/...ps-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?
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post #4 of 14 Old 04-15-2019, 08:13 PM Thread Starter
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Quote:
Originally Posted by mrbb View Post
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.


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I would wrap the pipe with DEI wrap, https://deipowersports.com/products/...ps-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.
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post #5 of 14 Old 04-15-2019, 08:41 PM
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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

Owning a Thundercat is like having a totally hot wife..... All of your friends want to see it, feel it and check it out..... They all want to know what it is like to ride it, but if they only knew how much time and money it takes to keep one up, they would call you a fool!

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"Of all the 850 vs Sidewinders/Thundercat/ZR 9000's; you are the first I have ever heard that beat one. I know the 850 is strong but it's down 30 hp from the turbo sleds.
I have a low slung fully built( by a well know engine builder) 3 cylinder 800 cc that made multiple dyno pulls over 200 hp on a calibrated Land and Sea dyno and I barely pull my buddy on his stock Thundercat. And I do have video."

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Last edited by guudasitgets; 04-15-2019 at 08:45 PM.
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post #6 of 14 Old 04-17-2019, 11:32 AM
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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
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post #7 of 14 Old 04-17-2019, 04:16 PM
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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.

My new favorite bumper sticker seen outside The Bent Wrench, Fountain, MN: "Your loud can doesn't make up for your small d*ck

Think about that the next time a trail is shut down because of loud sleds.

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post #8 of 14 Old 04-17-2019, 04:35 PM
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Quote:
Originally Posted by 720 View Post
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

Owning a Thundercat is like having a totally hot wife..... All of your friends want to see it, feel it and check it out..... They all want to know what it is like to ride it, but if they only knew how much time and money it takes to keep one up, they would call you a fool!

Seen in a DOO forum

"Of all the 850 vs Sidewinders/Thundercat/ZR 9000's; you are the first I have ever heard that beat one. I know the 850 is strong but it's down 30 hp from the turbo sleds.
I have a low slung fully built( by a well know engine builder) 3 cylinder 800 cc that made multiple dyno pulls over 200 hp on a calibrated Land and Sea dyno and I barely pull my buddy on his stock Thundercat. And I do have video."

Things on NASA headphones that are not good;
"That supposed to be like that?" "What the hell was that?" "Did you just pee in your spacesuit"

Last edited by guudasitgets; 04-17-2019 at 04:41 PM.
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post #9 of 14 Old 04-17-2019, 06:29 PM
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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%.
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post #10 of 14 Old 04-17-2019, 07:40 PM
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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

Owning a Thundercat is like having a totally hot wife..... All of your friends want to see it, feel it and check it out..... They all want to know what it is like to ride it, but if they only knew how much time and money it takes to keep one up, they would call you a fool!

Seen in a DOO forum

"Of all the 850 vs Sidewinders/Thundercat/ZR 9000's; you are the first I have ever heard that beat one. I know the 850 is strong but it's down 30 hp from the turbo sleds.
I have a low slung fully built( by a well know engine builder) 3 cylinder 800 cc that made multiple dyno pulls over 200 hp on a calibrated Land and Sea dyno and I barely pull my buddy on his stock Thundercat. And I do have video."

Things on NASA headphones that are not good;
"That supposed to be like that?" "What the hell was that?" "Did you just pee in your spacesuit"
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