What did your bike top out at before and after the mods? Did the cam give ya anymore power or is it just clutching now that is holding the bike back? What about some head work like the 3 or 5 angle valve job, or lighter springs with polished stainless steel valves? Why don't ya get the stock carb modiifed by Ritter cycle, could he do anything for ya? I plan on purchasing another and hve followed your progress with great inticapation to see what has been working. My plan was to make a bike that would be able to beat the new Kawi that my cousin has on order. As you can see that my Honda is loaded and can do 60 mph but that is where my old HO could run it down. I've got a 33TM Mikuni with an accelerator pump carb, maybe the ticket would be stepping down to the 36TM. I know that two other guys that have this carb on the exact same bike as mine and it's too much carb for the little motor, the accelerator pump floods their engines down even when jetted lower then stock. Please carry on with this project, maybe ya should cut some weight off the big HO, racks, bumpers, or maybe replace the Headlight with the 325 expeditions' speeedo. Good luck and don't give up yet, I think everyone would like to see ya succeed!

 

If you did some airbox mods you may have opened it up to much if so the carb that the H.O. uses will not work properly put your air box back to stock and try it.

 

Fourlix, Sorry I am getting here a day late. I found out almost 20 yrs. ago that I could'nt have everything I wanted on one quad-----just ain't possible. In '85 I had a 250 Big Red for hunting and a 350x for pleasure riding. Now I have slowed down enough that a bone stock '99sp feels like a rocketship to me. I understant your frustration but if you make the Sportsman into what you want then it will be something else. I wish you the best of luck but starting with the Sp 500 platform requires a heck of a lot of hp to make it go faster. I am amazed that it runs in the same performance level as wheelers weighing more than 150lbs less and l00cc more.

 

Fourlix, Sorry I am getting here a day late. I found out almost 20 yrs. ago that I could'nt have everything I wanted on one quad-----just ain't possible. In '85 I had a 250 Big Red for hunting and a 350x for pleasure riding. Now I have slowed down enough that a bone stock '99sp feels like a rocketship to me. I understant your frustration but if you make the Sportsman into what you want then it will be something else. I wish you the best of luck but starting with the Sp 500 platform requires a heck of a lot of hp to make it go faster. I am amazed that it runs in the same performance level as wheelers weighing more than 150lbs less and l00cc more.

 

You might be right about the promise not delivered with the HO. It was just a stopgap so that Polaris would not get beaten by the Rubicon. Factories do this to get off the hook. The 500 motor is a slug and not worth the effort to do extensive head/valve work experimenting. Oh sure, we've all hear that 4-S-T has a large displacement 500, but just read what their results were with their Raptor project. It does not work.

Actually I'm glad I went thru the experience of modifying my 500 to go beyond HO performance. At least I know what makes it tick. The biggest engine performance gain was the 40mm carb. The cam and Wiseco piston sharpened it up. And yes, even the lowly IDS2 did it's job. All these components coupled together has made my "original 500HO" easily outperform the "new factory HO's". The component that really made everything work together work was the roller clutch setup. I've heard of many who can't get it to work for whatever reason and most of these folks don't even have a tach. It's not as simple as buying parts and installing. In fact, in the end it was the clutching that got us the edge. Our machine picked up 8+ mph on top end with stock gearing. By bringing the rpm's down it picked up 4mph alone. That's quite significant. It also picked up quickness that it never had. I'm reading of flyweights as low as 44gr. (Ihope that's at high altitude) It's no wonder it won't perform. You are way past the hp peak of this motor. We have a TPI Thunder Shift Kit and are runing flyweights in the mid-60's @1,000 ft. alt. and still turning 7,000 on the tach.

It took a while like it always does with all Polaris equipment, but we got what we wanted out of it. Go on further, I doubt it. I don't think this motor is worth modifying further, at least for my intended use. If I wanted 4-wd racer I wouldn't pick a Polaris. It's very reliable though. I'm happy with it. It's too bad the HO's that come from the factory don't perform as well. Fine tuning is the name of the game.

 

Regarding some models of the same ATV being faster than others has anybody checked and verified the ignition timing or the camshaft indexing?

 

>>>>>>The heart of the problem on your HO is the cylinder head. The ports are to big for the RPM's and valve size. The big ports kill VELOCITY. Port work is not really the answer either .

Wouldn't a larger carburetor further compound the problem of velocity?

Maybe a modification to the Constant Velocity carburetors vacuum plumbing would be advantageous.

 

I never tried a new 500 HO but one thing all these magazine all agree on is that the new SP 500 has more power than last years and this engine makes the heavy SP the quickest 500 utility made today.Also alot of people traded there old SP500s for the new SP 500 H.O and said there is more power,are they all lying?