1973 JD 400 Lacks power

[bills2010]

Hello,

New to the vintage sled world so I will try my best to sum up my issue. I have a 1973 John Deere 400. It has a 339 CCW engine & a Comet clutch which I am assuming was added aftermarket. I have finally got it running and got snow but it just wont go. If i put it on blocks the engine revs & track spins just fine. The Primary and secondary Clutches seem to function as the should at high speed. When I sit on it it will go on hard pack snow or no snow but not at full speed. When I hit the powder it just seems to stop. Would this be a clutch issue? Please help.

Thanks

[Matt]

Have you replaced/have the correct belt? When you say it stops, please be more specific - does the engine bog, or does the engine rev up but the track isn't spinning, etc.

Many of original Salsbury clutches were replaced by Comets, some by a recall from Deere, so having a Comet is not incorrect.

[bills2010]

The belt is 1 & 3/16" X 43". It is what the specs called for. It does bog down when it stops as if it is dtrying to engage the clutch. I put it on blocks and got the rpm's up enough to see if the primary & secoundary engage and they do. The track spins just fine. had it out on snow covered pavement yesterday but it just doesn't seem to have the power it should & it doesn't appear the belt is slipping. The chaincase seems fine I have had those slip before and it doesn't seem to be that.

[Matt]

Your clutches may need some service. It may not be shifting correctly when under a load.

[tmartin]

i put a comet 102 c on my 400. it came off a trailfire lx. mine acted the same way as yours does. i figured it to be in the clutching or the carb. i first removed the secondary and dissassembled it. it was gummed up with grease. clutches should always be dry. this helped with backshifting but it still shifted and lugged down at about 20 mph. i tried the clutch set up that is recomended and it worked great but with comets ordeal right now i cannot find the parts i need. i am currently putting a tillotson carb on it and this should cure all my troubles. if you have a 102-c clutch i would try a white spring and f-2 cam arms. it made a huge difference over the silver spring and u arms. if u have a 94-c duster i cant help u. good luck.

[bills2010]

How do I know what kind of comet it is? I don't see any markings on it other that it is a comet? Did you only disassemble the Secondary clutch? Is that were the spring your refering to is? Thanks so much for your help!

[bills2010]

So I finally got some time to test on some good snow, packed. Seems the clutch engages just fine. When I start from the base of Carb adjustment (Walboro) with High out 3/4 and low 1 turn it will run just fine for a bit but as it gets hotter it will start to bog down. I have tried various adjustments to the carbs to correct this but nothing seems to work. The guide to adjusting these doesn't seem very clear. Could it be something else?Please help. Thanks

[SpitfireKing]

get it somewhat warmed up and in a spot where you would ride it...warm it up on a stand so you can rev the motor out a few times....then stop it and put new clean plugs in and then try to ride..let it bog and die, and then pull the plugs right away and see what they look like...if their black and wet then your way to rich and if their white or clean then likely lean....screw in is lean and out is rich if my mind serves me correctly, but also make sure you check your compression and spark.....maybe your loosing a cyl under load or something?