: Engine troubles
01-02-2002, 07:16 PM
I have a 93' Storm with updated 96' Cylinders and heads. the heads are milled 25 thousandths and the cylinders have light trail porting. Problem is, I have hardly any getup and go, alot of low end bog, and hardly no top end. It maxes around 6k to 7k if im lucky. Thats about 60-70mph. We didn't change anything in the carbs, should the jetting be changed? Anybody have a good setup? It just got a new comet 108exp and a different secondary spring. We went from a real weak blue to a black (needed to ride). Any suggestions? Everything else I believe is stock. Thanks
01-04-2002, 12:43 AM
Did you check the jetting? If it is using the stock jetting then you might have already cooked the motor because it should have been changed if those mods were added.Could also be losing compression somewhere,not firing on all 3 lots of different things to check.Reply with what you have checked already and I will see what else to try.
01-04-2002, 04:37 PM
I believe the motor is still to the stock 750 Jetting. Would you happen to know what needs to be purchased for rejetting? I cannot get an answer out of any of the 4 local dealers. If I could get some part numbers or something, that would really make my day. (440 arctic cats are beating me!!) Thanks for the help.
01-05-2002, 01:05 AM
The only things you would need to buy are new jets.The size I am not sure of that you owuld need.I would say at least 5 sizes maybe.Do you know how to properly jet the machine? start it somewhere you can get a good run.Hit the throttle wide open until then engne shifts and you reach top rpm then hit the kill switch whith the trhottle open.Check you plugs for the color on the bottom.To be safe they should be a chocolat brown.The darker they are you are too rich and need to go down in jet size,the lighter it is you need to go up in size.If it is very light be careful and dont hold the mahcine wide open until you rejet the machione because you iwll definatly melt a piston.if anyone else can add to this be welcome
01-05-2002, 10:44 AM
Have you ever ran the sled with the '96 cylinders before? Were they ported when you got them? A bad port job will kill an engine's top end OR bottom end performance.
01-05-2002, 12:12 PM
Yes, they were ported when I got them, the mechanic I had put the motor together stated that they were lightly ported. As for plugs, you can barely see any color change. I can have someone change the jetting, I just need someone to tell me what to get. Thanks for the help.
01-05-2002, 05:11 PM
I beleive the first part of your problem may be the clutching. The 96 specs call for 8250 rpms. You stated that you have changed some springs and the clutch. I know that with the updates that the sled has a fairly narrow power band. If I remember correctly it would come on somewhere just below 7 grand. I would start there first. You may have to light a primary spring or to heavy weights. The stock Polaris spring was blue with 10-62 bushed weights. The helix was 34 degree and spring in 2nd hole. The stock jetting with the updates is 380-390-420. This was up to 900' elevation and good to -20 degrees F. The Jet Needle is 6CGY3-3. The pilot jet-45. Air screw 1 turn. As I stated earlier start with your clutching. One more thing, with the shaved heads only run premium. What is your compression when cold?
01-05-2002, 07:36 PM
Ok, just went and picked up the mains and the pilots are on backorder. Let you know on the powerband/clutching after i get the jetting done. And I don't have a compression tester.
01-06-2002, 05:38 AM
Did you check your main jets before you picked up the new ones? The 93 storm came with 390-390-410 (P-C-M). They both run the same VM38SS carburators. This is pretty close to the 96 specs. The difference between the 2 is not enough to cause your problem. Also note that the stock timing on the 93 model is 28 degrees at 3000 RPM's. The 96 updated specs call for 24 degrees at 3000 RPM's. At 8000 The 93 is suppose to operate at 12 degrees. The 96 update at 11 degrees. This tells me that if you adjust yours for 24 degrees then your 8000 rpm will be around 7 degrees.They both list a different CDI box which would have different timing at 8000 rpms. I would try turning back my current timing just a little bit, Maybe 26 or 27 degrees at 3000. The CDI box identification on my 95 with updates was CU2508. I wouldn't run right out and buy one until the last thing. Hope this info helps and doesn't add more confusion. CONFIRM YOUR CLUTCHING FIRST!
01-06-2002, 06:07 AM
I talked to the dealership, and they said the 93 750 had 330s for mains and 35s for pilots. And the 96 had 400's and 45s for pilots. This right? He got this right off his computer. Stock jetting. Thanks for the help.
01-06-2002, 09:45 AM
Your jetting depends on your elevation and temperature. I did make a mistake on my first post. I put up to 900 feet. That should of been meters. Actually that jetting is up to 3000' elevation. If you are going to run 330's you better watch your piston wash and plugs. I hope you would be over 3000' and not below 10 degrees.
Also after thinking about it are you sure you have the 96 updates and not the 95 updates? If they are 96 then your cylinders will be nicasil. The 95's had the sleaves. I beleive for the 96 to fit on the 750 the cases had to be modified. the 95 cylinders fit right on.
01-06-2002, 04:03 PM
Yes, they are 96. We had to take 5mm off the bottom of the cylinder skirt. I got the new jets today and the old ones were 220, 250, 300. With 35 pilots. Putting it back together now, should be done tonight or tommorrow. THanks again for the help, wasn't sure on anything.
01-06-2002, 04:27 PM
Besides all the jetting Q/A I am wondering if you have bad gas from last year. *Old gas even a *month or two at the most is useless.
01-07-2002, 03:46 PM
Ok, got the jets in and another problem. The motor will only turn 5000 rpm. that is the max. So is this a timing/cdi problem? And it won't idle. What do you think?
01-07-2002, 04:11 PM
Check your compression, Are you sure you had 220,250,300? Sounds way to lean. Borrow a compression guage. Maybe remove your pipes and check the tops of your pistons. Also the cylinder walls for scratches. Thats where I would look next. Hope it isn't what it sounds like it could be with those jets.
01-07-2002, 04:35 PM
Thats what was in the carbs when I took out the jets. The rebuild was done less than 30 miles ago. the Motor sounds like its really struggling for power, even at 5000. Current jets are 400, 400, 420. Is that right? thats what I was told for the 96 Storm. As for the Air Screw, is that one turn from all the way out? Or from where is was stock?
01-07-2002, 06:01 PM
Turn air screw in till lightly seated, then back out 1 turn. This only affects when you first open the throttle. It will not affect when the lever is wide open. Take at least one of your exhaust pipes off and look inside. It only takes about 5 minutes. Take a spark plug out and then shine a light into the motor. Look at the pistons and cylinders. If they are messed up no sense going any further.
01-07-2002, 06:29 PM
Ok, pulled of the exhaust, AND IM NOT HAPPY!!!!!!! I can only see one ring and a big chunk of piston is missing on the exhaust side of all of them. If you could, what was the problem? What could I do to make sure it doesn't happen again, and any other advice? Thanks for the help.
01-07-2002, 06:40 PM
YOUR JETTING WAS WAY TO LEAN!!!!!! I cannot understand why those jets were in there. The 1 thing I can think of, was the sled ever used for grass drags in the middle of the summer? At high altitude? There is no way that sled should of run those jets. What is the history of that machine? Sorry to hear what happened. I can feel your pain.
01-07-2002, 06:47 PM
The first jetting with the 220, 250, 300 was too lean? Remember, the dealership after I told them the motor was running like crap said that they didn't mess with the carbs. I believe that when I bought the 750 (750 Motor in 94 storm chassis) that it was an ex racer. It has MSDRA stickers on it and the clutch was setup for it. The 750 ran fine like that. (I believe) So I guess when I have the money, I'll buy another set of pistons and try again. So the jetting that I told you I just put in is ok? Just want to make sure. Hopefully it didn't mess anything else up.....
01-07-2002, 06:56 PM
Your cylinders will probably be wiped out to. Why did you have the 96 cylinders and pistons put on? Was the old ones junk from being to lean? Did a dealership do the work for you?
01-07-2002, 07:08 PM
I had the 96's put on because they were $500 for the cylinders and heads. And because the 750 melted down because the oil pump cable busted. Found that out while tearing it down. And also, for the 750 its over $100 for one piston and rings. So I guess I'll tear down the engine and see whats up.
01-07-2002, 07:10 PM
Oh, and it was a Arctic cat, doo, and polaris dealer.
01-16-2002, 09:22 PM
Ok, got it back together, alls good. Alot of snap but in all this Mi powder its hard to hook up. Thanks for the help Ninja Plumber. Runs great.
01-17-2002, 06:07 AM
Glad to hear you got it back and running. Did you have to replace more then just the pistons? Hope you got your jetting right. I'm off to Maine tomorrow morning for a long weekend. I'm finally going to try out my XCR with the HTG kit I installed this fall.
01-17-2002, 05:08 PM
One last post. I have good movement through about 5k. It seems like its chugging in the midrange. And if I let it idle, it fouls a plug. But even when its running an all 3 it still chugs at midrange-top end. It will only go 45 then it starts to chug. Got any ideas?
01-17-2002, 05:16 PM
One more thing, the jetting is 400-400-420 * I'm gonna check out the plug fouling tommorrow with some new plugs. But the sleds speedo says it tops at 65 while on the stand. goes to about 6k. I'll also try it with my belt off. Let you know tommorrow.
01-19-2002, 03:46 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (skidplate @ Jan. 06 2002, 5:27pm)</td></tr><tr><td id="QUOTE">Besides all the jetting Q/A I am wondering if you have bad gas from last year. *Old gas even a *month or two at the most is useless.[/b][/quote]
Gas is stable up to one year in a good enviornment.
One year old gas may have a slightly higher flashpoint that may be noticeable in some gas engines, but 3-6 month old fuel stored in a snowmobile tank will be 99-100% fresh. http://www.snowmobileworld.com/forums/iB_html/non-cgi/emoticons/tounge.gif