'80 JAG 2000 F/A Carb Qs & Eng Rebuild
I have had this 1980 Arctic Cat Jag 2000 F/A 275cc for 16 years now. It's been a good sled but it's never been easy to start. I rebuilt the carb last year (thanks for your help, folks) and it ran pretty well. Late last season I started noticing a low end nock. It does not appear to be detonation because I richened the fuel screw and it didn't go away. I always add Stabil and run it through the whole fuel system before storing.
This year I am going through the engine and I'm considering ditching the B34 Mikuni butterfly carb for a VM34 (or closest equivalent) round slide Mikuni. Reasons include ease of disassembly, tuning and performance. I am told that a VM34 jetted correctly can produce much more high rpm power from additional fuel flow than my B34.
Can someone give me some guidance on what VM34 (or other size) carb specs to start with? I am prepared to do some tuning and probably some rejetting, but I would like to try and pick up a clean used carb that is very close in jetting to avoid a ton of work. Based on the carbs that I have found available there appears to be a TON of jetting and slide combinations. If someone has a suggestion about where I could source a very close carb starting point (like make & model of another sled, or maybe just some jet and slide specs for starters) that would be most excellent. I have found several sets of VM34s from 500-550cc 2-stroke engines that I thought would make a good starting point by using 1 carb since my displacement is right at 1/2 of those engines. Makes sense with 1 carb running 250-275cc worth of engine on the bigger engine, but maybe my math is oversimplifying.
For the engine, I started by measuring the cylinder pressures with WOT and both spark plugs removed. Right is 55psi and left is 58psi. What is a target cylinder pressure for this engine? I would expect pressures up in the 90-100psi range on a healthy engine. I am considering purchasing one of those good used crank sets for $125 and installing a new set of pistons, rings and gaskets with seals. Along with the used carb that would put me in the $350-$400 range for a good rebuild.
The goal is to build a good running toy for myself and my kids to play in the snow. It will never be more than a mile or so from home and speeds over 35-40 would rarely be seen....probably 20-25mph most of the time since our property is mostly rolling hills with trees. High performance is not the goal here. I look forward to your responses.
1980 Arctic Cat Jag 2000
1981 Arctic Cat el Tigre 6000