Polaris 600 VES no power

[MN Mike]

Ok, you guys know I'm not a Polaris guy so I'm looking for some help on my Cousin's sled.

Its a '05 IQ with a 600 VES motor. It's losing power at around 6500 RPM, just dogs out like there's not enough fuel, it misses and powers out until you let off the throttle.

Today we pulled the Power Valves out, cleaned them up as best we could with degreaser, either and a good rag, they were a little gummed up but not what I would consider bad, they came out very easy.

Sled ran great for about 10 - 15 miles and then back to it's old self again, no power at 6500 RPM.

He says sometimes when it starts acting up he can back out of the throttle and then pin it and it takes off, wide open, all kinds of power.

Drive clutch spring is good, the belt on the driven clutch is riding up out of the shiv like it should, about 1/8" or better, belt and the tension looks good.

It has the Mikuni flat slide carbs, I've never been into them or had to mess with them so I know nothing about this carb. He says he did treat it with SeaFoam last spring.

Air box is clean.

I know the power valves run off of cylinder pressure on the Polaris's, is there more that needs to be checked? I feel we were close to the problem when we worked on the PV's and the sled ran great for a while, maybe we over looked something.

Going to run a pressure check on the cylinders tomorrow and slip in some new plugs if I can find them.

I'm all ears if you guys have any suggestions.

Are these gas tanks vented thru the cap? After thinking about it after we finished tonight, I should have loosened the gas cap and seen if that made a difference..... it's only a 5 gallon race tank.

Mike

[Meat-Run]

I'm not familiar with efi's but may sound like air s uc king, does it have a boost bottle?? I've never heard of a sled/motor act like that.

MR

[JosMN]

I had the same problem with my pro x 7. It was one of the exhaust valve bellows torn. Tell tail sign is oil splatter at the front of the exhaust valve itself.

[Surface Tension]

Since it'll bog at higher RPMs and recovery after you back off the throttle I would suspect the fuel level in the carb is low.

Weak fuel pump, air leak, improper float drop, debris restriction at the inlet valve, or if you have one, a dirty fuel filter. The last two would be the likely culprits.

[Surface Tension]

Sometimes draining the bowl will allow the float to drop down far enough for a small piece of debris to be flushed out of the inlet valve. Catch the fuel and inspect it for crud and water. Since you have a check valve on the drop tube in the gas tank, pull the engine over repeatedly by recoil or by key to pump the fuel into the carb. Be sure to have the switch on Kill. If that doesn't do it I'd remove the carb and clean it.

[leech~~]

Since it'll bog at higher RPMs and recovery after you back off the throttle I would suspect the fuel level in the carb is low.

Weak fuel pump, air leak, improper float drop, debris restriction at the inlet valve, or if you have one, a dirty fuel filter. The last two would be the likely culprits.

Plus 1 sounds like a high speed carb flow issue.

[Macgyver55]

Weak fuel pump, air leak, improper float drop, debris restriction at the inlet valve, or if you have one, a dirty fuel filter. The last two would be the likely culprits.

Or possibly a crack or leak on the pulse hose for the fuel pump?

[HNTNBUX]

Please let me know if you find out what it was because mine does the same thing.

[MN Mike]

What kind of RPM should I be seeing on this 600?

I slipped in a new set of plugs yesterday, warmed it up and took off on a little tour with it yesterday. Sled run good again out of the shoot, I'm seeing about 7500 RPM peak, I'm thinking that should be higher but I don't know for sure.

The sled seems to struggle around that 6500 RPM mark even if it can hit 7500 RPM.

I didn't get a chance to do a compression test but I might still do that for peace of mind.

The exhaust bellows are clean and dry of any oil...... good tip though.

I couldn't find a fuel filter on that thing to save my life ( could it be in the tank? ), so if that is the case then the carbs ( and the fuel pump ) should be torn apart and checked for sure, probably my next step......

FYI: If I can get the sled to hit 7500 RPM, it will hold it for as long as I want.

If that isn't it, I'm almost thinking the clutching is off on this sled, when I was cruising along at 6000 RPM or so ( no speedo ) it's just like the sled was pulsing like it would shift to a higher gear and then back again ( RPMs wouldn't change much ), it wasn't a steady cruising speed like you normally see. If I couldn't get past 6500 RPM, I could back out of the throttle and punch it again and it would climb past 6500, sometimes very easily and I could hold it wide open and it would stay there. Maybe we have a weak primary spring or too heavy of weights in there, the sled doesn't seem very ' snappy ' but that's coming from someone that's driven a 800cc or higher for the past 10 years.

This just reminds me why I NEVER suggest anyone buy used race sleds!!!

I've got a buddy that might stop by and take it for a spin, he use to race a few sleds back in his day, both Polaris's and Cats maybe he can shed some light on a possible issue.

Keep the ideas coming guys, I'm always open to suggestions.

Thanks

Mike

[Surface Tension]

"Or possibly a crack or leak on the pulse hose for the fuel pump?"

Yes, I meant that under air leak but could have been more specific.

Trace the hose from the fuel pump to the crank. Check for bad clamp or cracked hose.

[Surface Tension]

If its running/pushing it with the fuel level low on the bowl at higher RPMs your going to notice that on the plugs as a lean condition. So what did the plugs look like?

Check them immediately after it bogs. Also water in the gas will do about the same thing as far as the bog at higher RPMs.

[Meat-Run]

I think you're getting close, I think it might be springs or water in gas tank.

MR

[Surface Tension]

You have to start somewhere on the diagnoses and I stated what I thought given the info.

Its also a good place to start because if I am right you don't want to be driving it under a lean condition.

[MN Mike]

Plugs look good, cookie brown.

Will look for water.

Thanks!

[leech~~]

It's been pretty warm and humid the last few days. You said it starts out ok but starts acting up after a while "warmed up" Has he had and ran this when it was really cold and did it do it then? I'm still thinking fuel issues and carb float as ST suggested. If it was the clutch and you run at an even & higher speed the weights and springs would really have to be pretty screwed up to keep kicking in and out at a higher even speed?