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Discussion Starter · #1 ·
I am having problems figuring out what is wrong with the 1979 Ski-Doo TNT 440 I just bought. It runs decent for 5-10 mins until it is warm and then it starts to bog. It doesn't matter how much throttle you give it, it stays at the same rpms once it is bogging. It doesn't produce enough power to turn the track. when i can feel it happening I usually hold the throttle half open to limp it back to my garage, after riding it around the field. If I wait ten minutes it usually fires right up revs up then once i jump on it it doesn't have the power to turn the track. Bluish/black smoke billows out from underneath and it will only sit there and idle but will not move upon giving it more throttle.

I have changed the spark plugs, had the entire carb off and cleaned, changed the needle and seat position so it would let less fuel through the carb, change the wires, drained old fuel replace with new mixed fuel (used Opti-2 and premium for the mixture). And it remains a powerless stationary sled.

I am wondering if it could be the coils? if so which ones? does this sled have more than 1 set of coils? What else could it be based on my description?
 

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What condition are the clutches in? Have you tried replacing the belt? Clutch alignment within spec? Engine mounts in good condition? So many times I have been fooled into thinking I had an engine problem when it was worn clutches/belts/alignment issues that were the root of the problem.
 

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Make sure thst your fan belt isn't broken. We had a '78 440 that had the same issue and I believe it was a broken fan belt. Engine was too warm.
 

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By the word "Bogg" I assume a "dull-flat" (rich) sound as opposed to a "cough n choke" (lean) kinda sound.
When it gets warm and does this its usually rich. Try flipping the choke, if it get worse its rich.
Like the others said, check it ain't overheating. But the fan cooled sleds with jetting set at stock ( -24 to -12and 1000' elev) end up horribly rich at -8 and 2000'.
 

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By the word "Bogg" I assume a "dull-flat" (rich) sound as opposed to a "cough n choke" (lean) kinda sound.
When it gets warm and does this its usually rich. Try flipping the choke, if it get worse its rich.
Like the others said, check it ain't overheating. But the fan cooled sleds with jetting set at stock ( -24 to -12and 1000' elev) end up horribly rich at -8 and 2000'.
Dirt Moover great point on the temps. In the past 3 years probably 75% of the riding I've done has been at temps above -5c. We just don't get te cold consistently enough around here to stick with stock jerting on a 35 year old sled
Also, 2x on double checking the clutches, a sticky secondary works just like an engine break.
 

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Discussion Starter · #6 ·
The problem is not fixed yet but I found out some interesting stuff while tinkering on it today. The sled once again ran good for a bit until it warmed up and started to bog. However, this time once it bogged I opened the hood and it took a few seconds but the sled got power and started to spin the track good again. I ripped around on it pretty good. If it started to bog I would just lift the hood and it would take a few seconds and take off again. This now seems like an air issue to me. Has anyone has similar issues with their sleds? I still haven't changed the fuel pump or anything yet.

I did pull the plugs and the vacuum hose and pull the recoil to see if I could get gas to come out of the plug holes but I didn't get any to come out and I couldn't see any in the crankcase?

If you have suggestions please let me know. I am new to the vintage sled world.
 

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bad ground wire attached to hood or its squishing the air intake shut (not sure how they are set up)
 

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The problem is not fixed yet but I found out some interesting stuff while tinkering on it today. The sled once again ran good for a bit until it warmed up and started to bog. However, this time once it bogged I opened the hood and it took a few seconds but the sled got power and started to spin the track good again. I ripped around on it pretty good. If it started to bog I would just lift the hood and it would take a few seconds and take off again. This now seems like an air issue to me. Has anyone has similar issues with their sleds? I still haven't changed the fuel pump or anything yet.

I did pull the plugs and the vacuum hose and pull the recoil to see if I could get gas to come out of the plug holes but I didn't get any to come out and I couldn't see any in the crankcase?

If you have suggestions please let me know. I am new to the vintage sled world.
Be sure the exhaust grommet is there.If not,the hot air from ex come back to carb and does what you describe.Be sure that the foam (if any)inside the cab facing the fan is well glued and not getting sucked by the fan.Engine should not exceed 7300,if more then adjust clutch.
 

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I had the exact problem with both of my 78 tnt 440s Would start right up run like a raped ape for a while or until warmed up good then they wouldn't even limp back home had to let cool down a while to get them home. Both fans were working correctly and they even didn't seem like they were getting that hot. If i remember right tho both run in the 170's for compression. I thought it could be water getting into the carbs so i took the air breathers off and that seemed to help some but still not much better. Its def acts like its flooding with fuel. but i have pulled the plugs right after and they always seem in good shape. It was the end of the season last year so i just forgot about it until now. I was going to do a complete engine overhaul to one of them to see if it helped maters.
 

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Could be allot of things. Mice build a nest in air box ? Floats lacqered up from no stabile in fuel Gas is made to break down in 3 monthes due to epa regulations these days. Stable or c foam all small engine fuel in off monthes. Crank seals? Wire shorting out seams logical? Coils are easy to remove and have tested. How due carb boots look? If cracked that is a issue. Could have a clogged jet in one carb. What do plugs look like lean or wet when it dies? One looks off that narrows down the problem cyclinder side?
 

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any luck? Did you try a leak down test (harbor freight sells the test kit reasonable) or the starting fluid check around the crank seal, case halfs and cab boot? Getting warm then loosing power sounds like an air leak... Keep us posted!
 

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I have the same thing happening with my 79 440 Everest f/c. Last year it ran perfect and now this year its been acting up the same way. Starts perfect and will idle all day but once it warms up it starts bogging out and dies. Let it sit for one minute and it will fire right up and run beautifully for about 15 seconds then start bogging and dying right away. Seems like if you hit some good powder and it starts sucking it in and steaming under the hood it will do it right away but if you hit the same powder before it has warmed up too much it will run perfect. Wondering if anyone has any suggestions what to try on this sled next. Already done plugs, cleaned and adjusted carb to what seems to be good. Clutch seems to be running fine. Tried throwing snow on all parts of the engine with it sitting and idling but it didn't affect it at all. Hoping someone on this forum will be able to help out with some suggestions because I don't know where to go from here. Thanks!
 

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Had our crank seals go on our old 250 single Elans quite regularly way back when. The biggest issue for the seals is the crankcase where the crank bearings would sit would wear as the case was made out of aluminium and the bearings would literallystart to move up and down in the crankcase there by screwing the crank seals. Remedy was to build up the aluminium bearing area on both sides of the crankcase then have it turned and then install new crank bearings and seal and it would be good again for about 3 more seasons. Keep in mind that this was the single cylinder engine and it was prone to this. I do not recall ever having to do this with a two cylinder as the crank had more support with the center bearing between both throws.

Hope this helps some people.

KC.
 

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I am having the same issue with my 1978 everest 440
One thing i have found is the pickup tube was split and very soft possibly closing up, starving the system for fuel
This just started
Would like to know what the cause is. I have read the other posts excellent ideas
 

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Discussion Starter · #17 ·
Okay so my sled is bogging after it gets warmed up again. I tweaked the jetting to solve the problem somewhat before but now that we got a lot more snow and I've been riding it way more I am convinced that it is a clutch issue like others have stated earlier. Who out there can tell me where to start with adjusting the clutches or how to check to determine if the need adjusting when you ride this sled wide open the rpm get up to 8500-9000.
 

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At 8.5 or 9k,you are way too high.Bring the engine down to 7300,not more.Going over that means more heat,danger of seized piston,etc.If you turn 8500+- ,check if you dont have flats on rollers.Levers should be C4L with a pink spring.Preload should be @ 8 lbs,more than that ,you increase rpm.Check if the "square" of the drive pulley is well aligned with the cover square.Check condition of the shaft on the drive pulley,if not worn.Look at driven sliding if you got more than normal side play.Your bogging should decrease if you bring the engine under 7300.Like i said on a previous post,bogging is caused by hot humid air inside the cab.So keep air duct clean,clean grille,a good grommet around exhaust tip.Add asbestos if you dont have any,around the joint between pipe and exhaust manifold to avoid hot exhaust inside the cab.Get the airbox duct towards the back.
 

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I am curious about lifting the hood and she gets going again. Sounds like exhaust getting sucked in. Had an old Arctic Cat (in another life) that I had to ride around holding up the cowl in order for it to run. I had a cracked manifold but it could be weak springs or something like that. Definitely worth checking out. Once it starts bogging it is a vicious circle if it is not getting fresh intake air. My 2 cents...
 

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I am curious about lifting the hood and she gets going again. Sounds like exhaust getting sucked in. Had an old Arctic Cat (in another life) that I had to ride around holding up the cowl in order for it to run. I had a cracked manifold but it could be weak springs or something like that. Definitely worth checking out. Once it starts bogging it is a vicious circle if it is not getting fresh intake air. My 2 cents...
Lifting the hood works great.Brings fresh air inside,it gives you a proof that hot humid air creates the bogging.A solution would be to get more holes on the cab but in deep snow,it brings other problem .
 
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