Old 2 cycle engine snowmobile???

[Bubba1235]

Buddy got a free (1978) arctic cat snowmobile with a single cylinder 2 cycle engine. He tinkered with it for the past couple days and got it to run, sort of. The problem is it backfires through the carb. I've told him IMHO the only way that can happen is if the reed valves are bad / leaking. Am I off base and is there another way it can happen? He is hoping so because finding replacement reed valves is going to be a night mare and getting to them will require pulling the engine.

I am NOT a two stroke expert of any sort...

 

[Fleetwin]

Re: Old 2 cycle engine snowmobile???

Usually, running lean makes them "sneeze" through the carb. The reeds don't cause it but the sneezing certainly can damage them.

 

[rbh]

Re: Old 2 cycle engine snowmobile???

If it is anything like my old rotax 640, check the timing.
Really kinda weird way to check/set timing on those old motors, try going through this site.

Points timing for older snowmobile - ArcticChat.com - Arctic Cat Forum

 

[oldjeep]

Re: Old 2 cycle engine snowmobile???

Finding replacement reed valves is simple and definitely does not require pulling the engine

 

[Fleetwin]

Re: Old 2 cycle engine snowmobile???

This is a real "flame" coming back.

Don't doubt that!:laugh: With that open air silencer it can be a bit frightening.

Backfires occur in the exhaust and are usually the result of too RICH. Lean sneeze is what you are describing.

I agree that timing may be an issue. Did it shear the flywheel key?

 

[oldjeep]

Re: Old 2 cycle engine snowmobile???

Best bet would be to go here:
Vintage Snowmobiles, Vintage Sleds and even Vintage Snow Machines

Friend of mine does one lunger racing, there are still plenty of sleds and parts around for the old cat single cylinders

 

[Tim Frank]

Re: Old 2 cycle engine snowmobile???

I have a 1968 OMC Snow Cruiser with a one-lunger....20HP.
First thing I'd check, as suggested, is the points/timing.
Second would be the carb connection...for air-tightness.

How is the compression?
Also, check the intake vacuum.

 

[Grub54891]

Re: Old 2 cycle engine snowmobile???

I have a 1968 OMC Snow Cruiser with a one-lunger....20HP.
First thing I'd check, as suggested, is the points/timing.
Second would be the carb connection...for air-tightness.

How is the compression?
Also, check the intake vacuum.

Or crankshaft seals......

 

[nwcove]

Re: Old 2 cycle engine snowmobile???

Or crankshaft seals......

yep, i would look into the clutch side crank seal if cleaning up the ignition and carb doesnt cure it. you may also want to remove the muffler and check to see if the guts of it have come loose and are choking it on that end.

 

[Tim Frank]

Re: Old 2 cycle engine snowmobile???

Or crankshaft seals......

Which should be shown by =>

Also, check the intake vacuum.

 

[rbh]

Re: Old 2 cycle engine snowmobile???

Look at a cut away view of the cylinder, each stroke does 2 jobs.

 

[Tim Frank]

Re: Old 2 cycle engine snowmobile???

Something else I thought was weird, setting the timing. Says to take spark plug out and bring piston to top dead center, stick a measurement sick against piston top and rotate backwards until piston drops 3 mm. Once done set the points to actuate at that point with a test light and then lock them down. Alternative is to set timing at 22 degrees BTDC at 6000 RPM. No idea how you would run engine at 6000 RPM with no load on it or run along side the sled when it's at 6000 RPM so it had a load. Guess the measuring method is the way to go.

This is a lot like the PITA way to set points on many Tecumseh 4 strokes. Believe it or not when i used to do my old snow-blower engine, it was far easier to take the head off (new gasket ~ $10-, lower blood pressure ~ priceless )

To run the sled at high RPM you can use a stand hat holds the rear end off the ground/snow.

 

[Bob_VT]

Re: Old 2 cycle engine snowmobile???

Well, found a manual on line and the engine has no reed valves. Color me confused. How in the heck it works without them is beyond my two stroke knowledge.

Manual said same as you guys, timing and fuel air mixture. Gave him the specs. from the manual and said he knows fuel / air is off after he took carb. apart to clean it. That's where he is going to start.

Something else I thought was weird, setting the timing. Says to take spark plug out and bring piston to top dead center, stick a measurement sick against piston top and rotate backwards until piston drops 3 mm. Once done set the points to actuate at that point with a test light and then lock them down. Alternative is to set timing at 22 degrees BTDC at 6000 RPM. No idea how you would run engine at 6000 RPM with no load on it or run along side the sled when it's at 6000 RPM so it had a load. Guess the measuring method is the way to go.

Being an old cat it might be an old 440 Kawi motor. PLEASE do not use a stick......use a dial indicator gauge!!! Just a tiny bit off and bang ....you will have a piston with a hole.

The carbs are critical and normally cleaning them helps.

The motor is only a small part of the performance too. The clutch weights have a big factor on when the track is engaged. I had an older 440 cat that was used for hill climbs and it was horrible to ride on flat ground........ it would wind up real high then launch with a surge.

Fun machines in the right conditions.

 

[rbh]

Re: Old 2 cycle engine snowmobile???

250 cc made by Suzuki. (Called the spirit engine) Was surprised for only being 250 cc it's rated at 40 HP.

One things about these engines some where built for torque, as Bob mentioned the clutches engage and disengage with a combination of a set of weights, spring and ramp slope on the clutches helix.

You can get more out of them with a better expansion/tuned exhaust pipe and upgrade the carb.

 

[Tim Frank]

Re: Old 2 cycle engine snowmobile???

250 cc made by Suzuki. (Called the spirit engine) Was surprised for only being 250 cc it's rated at 40 HP.

Probably at 18,000 RPM

 

[nwcove]

Re: Old 2 cycle engine snowmobile???

Probably at 18,000 RPM

lol lol lol...yep, more like 18 hp, maybe 20 on a real cold day!!

 

[hungupthespikes]

Re: Old 2 cycle engine snowmobile???

Sorry Bubba, he's gone till spring.

 

[MTboatguy]

Re: Old 2 cycle engine snowmobile???

Once you are bit by the sled bug, there is no going back, he is lost until the snow turns to fishing lakes.

 

[oldjeep]

Re: Old 2 cycle engine snowmobile???

Yup - it is a great snow year, need to use the sleds as much as possible since you never know what next winter will bring.

 

[Scott Danforth]

Re: Old 2 cycle engine snowmobile???

Bubba,

those with sleds play in the snow
those with boats play in the water
those with 4x4's play in the mud or a rocky ravine
those with all 3 are single and most likely have the ice shanty as well.

there is just something about flying thru new snow