96 Polaris Indy 500 Mid-Range Bog

[JerkinLips]

My 30 year-old Indy 500 (over 8,000 miles) has been having a mid-range bog for many years now.  It is worse on warm days and when the engine is warmer.  The sled runs fine up to about 1/4 throttle, then runs extremely rich up to 3/4 throttle.  The spark plugs are dark brown (better brown than down?) but not saturated.  8 years ago I moved the clips on the jet needles from the 3rd to the 2nd groove to lean the mixture and it helped for a while.

 

Should I move the clips to the top groove (temporary solution)?

Could the jet needles, needle jets, and/or the main jets be warn and need replacement?

 

Don't think I will have time to tear the carbs apart this season for a rebuild so I may just band-aid the problem.

[Wanderer]

As soon as I started reading mind went to needles and seats.  You might want to try just replacing those first?  I’ve only done that once before in my life but it made the difference.  A carb refresh in 8,000 miles seems reasonable.

[fishingstar]

In those years Polaris was known to put buna tipped needles in there sleds. They get a ring around the seat and don't seal shut. But if that would be the case your problem would be with the motor shut off and filling the crankcase with gas. If your plugs are brown that is were they should be. I wouldn't drop that needle down to the last grove. I would replace them before I did that. I have never had a carb with that setting.

Have you looked at your clutches? They could be dirty or have a bad roller. 

Does it bog as it's accelerating or when you hit the throttle? 

 

 

[JerkinLips]

6 hours ago, fishingstar said:

if that would be the case your problem would be with the motor shut off and filling the crankcase with gas

Previous owner (22 years and 5,000 miles ago) said it was prone to flooding when sitting for a long time or trailering, so I shut the fuel off in both cases.

 

6 hours ago, fishingstar said:

Have you looked at your clutches? They could be dirty or have a bad roller. 

Primary is significantly worn.  I replaced several rollers and pins which helped.  I have two used clutches in much better condition that I could (and should) install.

 

6 hours ago, fishingstar said:

Does it bog as it's accelerating or when you hit the throttle?

It seems more like when I hit the throttle, but the bog could be from poor clutch shifting.  Will have to pay attention next time and inspect the clutches.  Thanks for the ideas.

[Wanderer]

How old is your belt?

 

My old Polaris 4 wheeler with belt drive was bogging at mid range to top end last year.  Changed the belt and that problem went away.

[SkunkedAgain]

4 hours ago, JerkinLips said:

Previous owner (22 years and 5,000 miles ago) said it was prone to flooding when sitting for a long time or trailering, so I shut the fuel off in both cases.

All of those Polaris sleds from that era were notorious for flooding and leaking. I've still got a 2003 XCSP 600 Edge that my daughter rides. As you noted, you need to shut off the fuel in those situations.

[fishingstar]

Those flooding problems are a sign of your needle and seat are leaking.  If the needle has a ring around the tip you can clean it if it's brass. If it has a black rubber tip then it needs to be replaced. You can clean the needle and seat with things like rubbing compound or even toothpaste I use a product called Semi chrome. It for polishing die pins. Just clean them up after polishing.

[JerkinLips]

I moved the clips on the jet needles up to the top groove to lean it out.  This eliminated the mid-range bog and the sled accelerates well even when warm.  The plugs are not quite dark now, but look good.  I'll have to rebuild the Mikuni carbs this summer for the permanent solution.  I'll also repair or replace the primary clutch to eliminate that issue.  Thanks for all of the suggestions.

 

[SkunkedAgain]

If you have a Mity-vac, make sure to pressure test the needle and seat before putting the carb back together. That will often solve leak/flooding issues (but I don't think that's your issue). It's a different type of fuel leak.

[Wanderer]

Glad you’re getting results!

 

I’d throw a new set of sparks in there for next season too.  Weak sparks have given people plenty of headaches.

 

I just had a deal where a friends wheeler just died while he was loading it on a trailer.  Wouldn’t restart for anything.  He and I did a lot of checks and trials to get it running but couldn’t.  I finally took it to my local small engine guy.  He repeated all the diagnostics we did, plus some, and couldn’t get it started.

 

Based on his experience, he decided to try a new set (mind you they did have spark outside the cylinder).  It fired right up.  Pretty rare for BOTH of them to go bad but it’s been running great ever since.

[JerkinLips]

On 4/9/2025 at 3:51 PM, Wanderer said:

Based on his experience, he decided to try a new set (mind you they did have spark outside the cylinder).  It fired right up.  Pretty rare for BOTH of them to go bad but it’s been running great ever since.

I'll put new plugs on the top of my list; cheap fix.  One of the plugs had the threads worn off on the cap on top and it stuck in the rubber cap.  Thought this may have been part of the problem but a new (used plug) with a tip cap didn't change the issue.  The change in one plug is why I have mixed plugs in the picture.

 

Lots of shopping to do at Haydays next fall - new belt, plugs, track, ski spindles/ bushing, clutch puller for a start.

[fishingstar]

lots of Polaris parts at haydays

[leech~~]

7 hours ago, JerkinLips said:

I'll put new plugs on the top of my list; cheap fix.  One of the plugs had the threads worn off on the cap on top and it stuck in the rubber cap.  Thought this may have been part of the problem but a new (used plug) with a tip cap didn't change the issue.  The change in one plug is why I have mixed plugs in the picture.

 

Lots of shopping to do at Haydays next fall - new belt, plugs, track, ski spindles/ bushing, clutch puller for a start.

Haydays can be fun but some times a picker nightmare to get in and out of.  I like the Outlaw grass drag and swap meet in Princeton,  MN a few weeks before Haydays.  If you don't find it there you can always then check Haydays.  I've found must everything I ever needed at the Outlaws swap!  

[fishingstar]

haydays has become to commercialized now. We started going in the early 90's. Now there is way too may people. I'm there for the swap. I don't have snowmobiles anymore but when the kids were young we had 5 cats from the 90's. We bought a lot helmets, suits and parts there. Now the boys can buy and fix there own sleds. Maybe this year we will check out the outlaw drag this year.

[leech~~]

1 hour ago, fishingstar said:

haydays has become to commercialized now. We started going in the early 90's. Now there is way too may people. I'm there for the swap. I don't have snowmobiles anymore but when the kids were young we had 5 cats from the 90's. We bought a lot helmets, suits and parts there. Now the boys can buy and fix there own sleds. Maybe this year we will check out the outlaw drag this year.

I to started out at the haydays back when it was at Waldoch.  I went to the Haydays last fall for the first time in about 6 years, only because my grandsons wanted to see the "C-Boys" some U-tub clowns that trash stuff on U-tube.  Two hours in line to see these clowns!  Not me I sat in a UTV for sale at a stand as they were in line!   I use go every fall to Princeton-Outlaws, Anoka-Rum river runners at the Anoka fairgrounds and once in a while the very small swap at the Brainard fair grounds.  I can't even remember all the stuff I bought over the years for snowmobile, 4 wheelers, and dirtbikes.  

[JerkinLips]

I started going to Haydays when I moved to Blaine in the mid-80's.  Waldoch was very convenient from Blaine.  I quit going for several years when they moved it to North Branch.  I've gone there the last 3 years and like the new layout better.  Parking and admission has gotten very pricey but the event offers a lot to do and see.  Now that I moved up north, Princeton would probably be further for me than North Branch, but maybe I will give it a try.