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Old 12-03-2011, 12:17 PM   #1 (permalink)
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'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.
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Old 12-03-2011, 09:39 PM   #2 (permalink)
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I believe a carb off of like a 600 triple would be 36mm and you would want the carb boot to go with it! Also have to find a different throtle cable and chock cable??
I would barrow a differnt compression tester! That is too low to even start! Most wont start below 100-110#! You should get it up to 120-125#!
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Old 12-04-2011, 06:56 PM   #3 (permalink)
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Smile parts on order

I picked up a VM34 today from a Polaris 583. Owner says it has a 200 main and 35 pilot jet. He has the same carb with a 260 main and 35 pilot on his 340, so I'm hoping the 200 main is somewhat close to what I need for this 275cc engine.

I'm gonig to have to figure out a throttle and choke cable as kccats mentioned. Not sure what sleds came with a single round slide from the factory, but my initial thought is I need to figure out a model with the cables I need so I can get them on order. Anyone have a suggestion?

I'll have to figure out if someone else has a gage to tech cylinder pressure. I don't believe there is any issue with my gage. May just put it on my air compressor to confirm. It sounds like if I really have 55-58psi cyl pressure that is probably the root cause for my hard starting problems and the reason it doesn't idle very well.

I have a set of rings and a gasket kit on its way to see if I can do something about the cylinder pressure. If nothing else I know it could use a reringing from 16+ years of running without a rebuild.
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Old 12-04-2011, 09:17 PM   #4 (permalink)
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It does have an oil pump right? Then a throtle cable off of like a Jag should work? And a single choke cable is universal!
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Old 12-05-2011, 11:54 AM   #5 (permalink)
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It does have an oil pump right? Then a throtle cable off of like a Jag should work? And a single choke cable is universal!
I have no idea if there is an oil pump or not. The sled is a Jag, so are you implying that my current throttle cable should work? Sounds like my choke cable should work.

Keep in mind I'm going from a B34 to a VM34 and I do not have the VM34 in my hands yet.
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Old 12-05-2011, 12:00 PM   #6 (permalink)
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I do not see an oil pump shown on the FA engines.
If it did have one, it would be right below the carb on the lower block.
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Old 12-05-2011, 08:13 PM   #7 (permalink)
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OK well I was thinking of a 85 Jag! It has a 34vm single carb, but it has an oil pump!
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Old 12-09-2011, 04:22 PM   #8 (permalink)
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Parts are in

I received the carb, it looks really good. It has a port on the intake manifold side that had a vacuum hose plug on it that will be a perfect point to run a primer. I am going to use a primer instead of choke. I'm going to try this carb as it arrived with a 200 main jet, 35 pilot, and the c-clip on the middle groove in the jet needle. Lots to do before that point in time though.

I also received a primer kit, universal throttle cable, fuel pump rebuild kit, gasket kit including crank seals, spark plugs, and 54mm rings.

Parts still needed are a new belt since the belt I have is old and should probably be retired for spare use. I also need a new air filtering system since the new carb has an airbox side diameter that is less than the factory 59mm. I think this one is about 45-48mm. Probably just grab a K&N filter for it.

I pulled the engine out this evening. Next I and am preparing to take the clutch off with a home made tool (thanks for the tips in the other threads) and also remove the magneto wheel.
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Old 12-10-2011, 09:46 AM   #9 (permalink)
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Make an adapter from some PVC so that you can use the airbox.
Heck, I have made adapters by just wrapping electrical tape on the carb until it fits the box opening.
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1980 AC Pantera (donor engine to the 90 wildcat)


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Old 12-10-2011, 05:02 PM   #10 (permalink)
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Make an adapter from some PVC so that you can use the airbox.
Heck, I have made adapters by just wrapping electrical tape on the carb until it fits the box opening.
I would, but one of the good things about the new carb not fitting is that I can ditch the factory airbox since it is in pretty bad shape. I don't like that there isn't a real filter anywhere either. I had the discussion with my local dealer about a filter and he claims they don't need one. I don't like that answer.

I picked up a
K&N R-1090 K&N R-1090
on Amazon along with a precharger. A good portion of the sledding we will do will be through fields and prairie grass, so I want a filter to keep the corn stalk pieces and grass seeds out.

I also picked up a new puller and a 9/16:18x2-1/2" bolt to pull the clutch, as well as a 2-1/4" brush hone. Work to commence this evening.
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Old 12-10-2011, 08:53 PM   #11 (permalink)
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Crank seal help needed

I used the bolt and water trick to remove the clutch and it worked beautifully. Once the clutch was gone I was alarmed by the seal that I saw behind it. The seal was protruding the cases by ~1/8" and when I grabbed the edge it slid right off! I sure that is a contributor to my running issues. I feel pretty lucky that I never burned a hole in anything.

I used the other puller I have to remove the stator wheel and it worked excellent as well. Once the stator wheel was gone I noticed that there are a few tick marks on top of the magneto than line up with a tick mark on the aluminum housing, so I made sure to record the angular location of the magneto WRT the housing so I can set the timing back where it was.

I have a couple of questions about this side of the engine.
1. Should I remove the aluminum magneto housing before attempting to remove this seal?
2. Is this one typically a bear to remove because of its metal structure and does anyone have any tips or warnings about removing this seal?
3. Which way does the new seal get installed? (it is a bit different looking, though the same size) I would guess the spring goes toward the rods.
4. Do both seals install dry or should they be greased or oiled?

Seal spring side:

Seal metal side:
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Old 12-10-2011, 09:03 PM   #12 (permalink)
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5. Does anyone have the torque sequence/specs for the stator wheel nut, clutch bolt, cylinder nuts, and head nuts?
6. Are there any bolts/nuts besides the exhaust header that should be loc-tited?

Here are a couple of pictures showing the difference between the Mikuni B34 and my newly acquired VM34. The airbox sides are 59mm and 47mm, respectively.




I'm starting to really get into this thing. At first I was taking it apart just to do what was necessary to get it running. Now I'm really enjoying it and it's been going surprisingly smoothly. We haven't had any snow yet but it sure seems like it could let loose any day now.
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Old 12-10-2011, 09:06 PM   #13 (permalink)
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7. What should I do with the choke feature on this carb? I was going to hook my primer to the engine side of the carb in that nipple that can be seen in the pics above. For that reason the choke won't be needed. Should I just install the original choke cable into the carb and zip tie the cable up to the back of the dash to keep the choke circuit closed off? Is there a purpose made plug for the choke circuit that I can install to disable choke?

By choke I mean enrichment, obviously.
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Old 12-11-2011, 06:49 AM   #14 (permalink)
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There is a close off plug, but the easier fix would be to just take the slug and spring and the brass fitting [minus cable] and just install that.
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Old 12-11-2011, 08:40 AM   #15 (permalink)
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There is a close off plug, but the easier fix would be to just take the slug and spring and the brass fitting [minus cable] and just install that.
Good idea. I didn't notice that those parts could be removed from the cable.

Anyone have some information on the other questions, specifically the seal questions? I'm half tempted to leave the stator side crank seal in place because it appears from the outside to be in good shape. There was/is not any oil or fuel in the stator hoising to lead me to believe that it was leaking like the clutch other side.
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Old 12-11-2011, 09:09 AM   #16 (permalink)
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Replace it! The age alone would Mandate that! A harmonic ballance puller will pull the flywheel!
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Old 12-11-2011, 12:08 PM   #17 (permalink)
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Replace it! The age alone would Mandate that! A harmonic ballance puller will pull the flywheel!
Alrightythen.

Pulled the cylinders off today and they look good. Are these steel sleeved or just aluminum? Sure seems like 100% aluminum to me. I can't find a parting line between the aluminum fin structure and the steel sleeve if they are indeed sleeved.

Pistons look bad. Both have side wear on them where some of the piston has balled up and gouged itself. One piston has both ring alignment pins missing so both rings can spin freely. The other piston has both ring alignment pins worn down almost completely and just barely keeps the rings from spinning. I am going to order a new set of pistons today because I'm not comfortable trying to use these, and I'm pretty sure they are originals.

Next up, seal install.
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Old 12-11-2011, 02:45 PM   #18 (permalink)
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Plated aluminum cylinders.
If you decide to bore it out, they will have to be replated.
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'93 Wildcat 700EFI
w/ Comet 108 Pro-4 clutch & 01 ZR skid

'90 Wildcat Project in progress.

Vintage (sorta)
1980 Indy Trail 440 (for sale)
1980 AC Pantera (donor engine to the 90 wildcat)


http://www.dcdrifters.net/


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http://www.masonicdryden472.org/

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Old 12-11-2011, 05:49 PM   #19 (permalink)
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How do the cylenders look? any gouges in them that you can snag your fingernail on?
Don't forget you will have to remove the flywheel and then the stator and stator plate! Be sure to mark the stator for timing!
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Old 12-11-2011, 07:20 PM   #20 (permalink)
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How do the cylenders look? any gouges in them that you can snag your fingernail on?
Don't forget you will have to remove the flywheel and then the stator and stator plate! Be sure to mark the stator for timing!
Cylinders are fine. I have both seals out now and cleaned the cases out as best I could with some parts cleaner and compressed air. Things are looking good. I am waiting on pistons and small-end bearings which are due in Wednesday. I think I'll be ready to reassemble once these parts arive.
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