bog issue while starting off

stomper · Dec 7, 2013

My sons 91 indy 400 has a bog when starting off from a stand still. Once it gets going it is fine. On take off it won't even spin the track like it used to. I don't drive the sled so I didn't know about it until I took it for a spin the other day. My kid says it has been doing this for awhile now. I just had the clutches apart and for cleaning and noticed it had 10M5 (I think) weights. The manual says stock weights are 10MB. So I changed them hoping that it would make a difference. Both the primary and secondary have the proper stock springs. The belt looks fine and sits up about 1/16 - 1/8" high above the secondary sheaves. I was going to take the cabs off and clean them but thought I would get some opinions first. Does this sound like a carb issue.

treetopflyer · Dec 7, 2013

The first place id go would be clutches. The clutches probably have never been serviced. Sounds like you have belt deflection set properly. Check your primary,rollers and weight pins and weights, probably need to be replaced. Primary spring needs to be replaced. The spring sacks out with use and is probably shot. Next check your secondary clutch. Pull it apart and replace wore out or broken spring, also replace the buttons the helix rides on. more than likely they are wore out.

Sometimes if the primary hasn't been serviced your better off replacing the entire cluth, they just plain and simply wear out !!!!!!!!!

Good luck

Tim

treetopflyer · Dec 7, 2013

As for a carb issue, that is also possible. Check throttle cables, you need to make sure that the carb slides are pulling up in sync with each other. adjust them at the carbs where the throttle cables go in.

Also check compression on your motor, you may have a cylinder going down or just wore out. should be in the 115-120 pound range.

stomper · Dec 7, 2013

I will check these things. When I had the clutches apart for cleaning everything looked fine. As for the springs, I have never replaced them since I got the sled at 2100 miles and the sled has over 8000 miles on it now. I guess that would be a good place to start.

treetopflyer · Dec 7, 2013

With that many miles the clutch is probably shot. check the pins that hold the weights for wear, they get grooved and so do the weights in the bushing where the pins slide through. Also the cover bushing wears and binds the clutch. Its the the big bronze bushing in the center of the cover. Look at these areas and see if they need to be addressed.

Don't overlook the secondary clutch it needs to come apart to check the spring and to inspect the buttons. Im sure the buttons are completely gone and and the helix is wearing on the aluminum on the clutch.

stomper · Dec 12, 2013

I just bought some new springs for the primary and the secondary. I had the clutches apart for cleaning a couple weeks ago and things actualy looked not bad. The buttons in the secondary looked surprizingly good. I changed weights in the primary to the proper 10MB, it had 10M5. This helped with the performance a bit but not with the bog. I will check compressin and change the springs for starters and continue from there. Thanks for the help.

volcano buster · Dec 12, 2013

What are you comparing the bog to? These older piston port engines typically have a bog off the bottom versus a reed port engine.

Good luck eliminating as much of the bog as possible.

stomper · Dec 12, 2013

I'm comparing to what the sled used to do. It had no problem spinning the track on take off before.

stomper · Dec 12, 2013

Compression is 117 on the pto side and 112 on the mag side. Also did some checking on the oem belt. The OEM belt is suposed to be 3211042 and the belt thats on it now is 3211070. According to my research the 3211070 isn't used on anything older than a 97.

retiredpop · Dec 13, 2013

1042 has a side angle of 32 degrees while the 1070 has a 28 degree angle for 97 and up sleds. Other than that they are the same with outer circumference of 47.25" and width of 1.375". I'm not sure how much difference the angle makes but it could be your problem. I think the different angle would cause the belt to not grab the sheaves as hard as it is supposed to.

Also have you checked the belt deflection (1.25") or just gone off the amount showing above the secondary sheaves? Is the center to center clutch distance okay as well as the offset? What about belt side clearance in the primary? It should be right around .020" and no more than .035" max. Lower hp sleds are fussier on clutching imo.

stomper · Dec 14, 2013

It was mentioned on another forum about possibly being the choke cables. I did change the choke cables out near the end of last year and maybe they are not set properly. How do I check to see if they are. and how do I set them properly.

volcano buster · Dec 14, 2013

I've done it, years ago. You might check YouTube to see if there is a handy "how-to".

Red River Pig · Dec 15, 2013

Stomper, check for stuck bearings on the skid and drive axle, hyfax, and track clips. Most likely your drive belt is worn out, thus high 'gear' take off. one or two take off attempts with a froze down track, end of belt.
Or possibly mice in intake/exhaust, water/bugs in carb air/gas passages?
very easy throttling burns belts and loads up the plugs- use premium gas and synthetic oil, cheaper than new plugs...

stomper · Dec 20, 2013

Haven't had the time to get the sled out for a test run yet to see if it is working. Hopefully in the next couple days.

steepndeeper · Dec 23, 2013

I adjust the choke cable by using a small piece of wire that I put a 90 degree bed in about 1" from one end that I have sharpened to a point. Take the top cap off the carb and down on the right hand side about even with the choke there is a small hole that I insert the short end into. As you lift the choke lever you should be able to feel the wire slip under the plunger. If it won't go under the plunger when is lifted then your cable is too tight and cable needs adjusting. Then I let the lever down and see if the wire will slip out. If it comes out without lifting the choke lever then your cable is too loose and needs adjusting. If your plungers don't move then disassemble and clean.

steepndeeper · Dec 23, 2013

As far as your clutching goes the 10M B (47.5 grams) weight is the production one for elevations up to 5000'. For 5000-8000' they call for a 10M R (44 grams). What is your elevation and at what RPM does the clutch begin to engage?

mike_s · Dec 23, 2013

Has the engine ever been rebuilt? Is it harder to start than it was in the past before this bog surfaced? With that many miles it is likely that there is a piston skirt broken causing the bog, but this would also make it dificult to start. Pop the carbs off and look in through the intake boots and see if the piston is still completely in tact.

firecat99 · Dec 26, 2013

Check your pilot jet for dirt. They do clog up. If your clutches look fine I would go to the carbs there next, tare and pull them completely apart, blow them out with air. My old 488 use to do this after it got high into the miles.
I used a Cat yellow/white primary to get that thing to move out of the hole better.
Your compression seems a little low tho, could use a ring job also.

If your skirt broke I'm sure something would have been damaged by now and motor wouldn't run.

But I do agree with a rebuild. 8000miles is getting up there, I know they will do more but after that your gambling IMO.

mike_s · Dec 26, 2013

firecat99 said:
If your skirt broke I'm sure something would have been damaged by now and motor wouldn't run.

.

I have actually never had that happen. The piston is just aluminum, and the skirt pieces rarely ever find their way up to the top end. I have always just found the pieces chillin in the bottom of the case...

Cleaning the carbs is a good start though, especially if there is no filter in the fuel line. Plus, you gotta have the carbs off to look at the pistons anyways.

stomper · Dec 29, 2013

steepndeeper said:
As far as your clutching goes the 10M B (47.5 grams) weight is the production one for elevations up to 5000'. For 5000-8000' they call for a 10M R (44 grams). What is your elevation and at what RPM does the clutch begin to engage?

My elevation is around 1000' and the weights are 10MB. Not sure on the engagement never took note. I will check next time.

bog issue while starting off

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