jetting help, please!

C

cvx16

New member
Hi guys,
Last year I bought a 1995 vmax4 800, and second time out it burnt down piston #1. Replaced the piston,rings, replated the cylinder. The carbs were dirty, and the jets full of crap, so cleaned the carbs, tank, replaced the pick up filter, and replaced the fuel pumps. The sled has a trail port from Bender, Aaen quad pipes, Mikuni 38mm flatslide carbs and has a comet clutch.
This year, I ran it once and the plugs look very lean. The carbs have 640 main jets. After the run this year, I moved the needles to the highest position. I have ordered the next size up jets, but this all seems to be guess work. Any help would be very appreciated. I want to run the sled on the lake only. Also, another thing is hook up, the track is picked with ice chisels and it'll still break loose at 80mph?
The previous owner used it for grass drags. Is there any info out there on setting up the suspension for snow/ice? Sorry for going on, but I love this sled and always wanted one. Now that I have it, I'd like to use it reliably.
Thanks,
Bob
 

Ok, if i where in your shoes;

1, Clean carbs again, if they where that filthily it can take a couple of cleans to get them right.

2, With the sled running spray carb cleaner around the carb manifolds, paying particular attention to the manifold of the last burnt piston any rise in rpm will show a bad manifold or seal.

3.Long distance jetting is a real stab in the dark due to the variables, but we can get you close;
Your carbs if stock probably have #140 jets as there is no 640 main jets. Move the needles back to stock. fit some #150 jets and do a WOT run and post pictures of your plugs. pick up 4 x 147.5 and 4 x 145 jets at the same time. You are set up for summer and way lean, i would think you would end up around 145, but jets are cheap so start high and work your way down
 
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Thanks for responding. The carbs are not stock, they are Mikuni 38 mm flatslides, with open element filters on each carb ( that's the way it was when I bought it). I did clean the carbs more than once, and put in new main jets to be safe even after cleaning them. They are 640's, or at least that is what is stamped on them. They look like sewer pipes, but I'm not interested in fuel economy, just don't want to hurt this motor again. I've ordered the next jet size up (660's), but there is only a few sizes left after that. The plugs look grey?, not tan or brown. Thanks again.
Bob
 
Also check your gearing if it was for dragracing it will be geared down and for jetting like 2stroke said start fat! if it was used for grass it will be very lean what is your compression was the head cut?
 
This may be harder than expected! The sled is at my camp in Maine, and I'm at home in Chelmsford, Ma. The sled feels very stout (All Vmax4's do), but untill I go back this weekend, I will not have compression #'s for you. As far as if the heads were cut, I can't say for sure. I just got the sled last year from the second owner who didn't know too much about the original owner. All he told me was that the original owner used to grass drag it and take it out once or twice a winter to spank his friends then put it back away. I love this beast, but I would like to ride it too, not just wrench on it.
 
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