chevyv8nut,

Here's a few things to investigate &/or retune...


If stock cylinder / piston, its PSI should be "fresh" at 120, normal between 100 to 85. If 85, then start saving the dollars to rebuild the top end. Anything under 65 is a hit / miss if it will run at all. The reason isn't the PSI but the dramatic reduction in the stock carb's "impulse". For a normal running Polaris 90, it should be between 90 to 100.

Do check the spark plug color in all throttle ranges. Specifically in the idle, 1/2, 3/4 and WOT range. The plug color MUST BE slight black to beer bottle brown. Beer bottle brown is the best. If "jet black" (like a witches hat), then the carb is way too rich. If white specs or white tip, then its too lean (too hot). If white, immediately stop driving it. Re-set the carb until slight black to beer bottle brown is obtained.

If you do decide to install a new top end (re: block, piston, rings), I'd recommend you purchase a pre-bundled Top End kit. Some folks buy the piece parts and bore out the factory block. For me, I find it's best to buy a complete kit. Depending on the kit you do purchase (for example 53mm kit), it will probably have a range of 140-150 PSI. Thus, even more power. If wondering, I obtained our 53mm kit from Billy Holt at WRH Racing. Instant 150 PSI since day one.

As a suggestion, do contact the person you bought the performance parts from. If they value their reputation, they will review how you installed their parts, review the spark plug color (for jetting) and suggest other changes that may need to be done.

For the Pred-90's 16mm factory carb with performance pipe, higher RPM engine and opened air intake system, many recommend removing the 16mm carb and replace with a 20mm carb. The 20mm carb is made for higher RPM engines (compared to the 16mm carb) and is much easier to change its jetting. Yes, some folks can stablize the jetting on a 16mm carb but if you live in a changing climate like me, installing a 20mm carb is much less hassle. While chatting to your performance pipe seller, ask them about a 20mm carb upgrade. With your new performance parts and climate changes, a 20mm carb upgrade might be worth it as well....

Also, check for a stuck roller in your current configuration. A stuck roller won't allow the CVT system to "open up" (sort of speaking). The engine will rev but the CVT system can barely pull up a normal hill.


Hope this helps as well....

.

 

I agree Spike, if I had to do it all over again I would go with the big bore kit.

 

IMO:: I feel the home-brew pipe may be the problem.
Some times you hit it, sometimes not. [img]i/expressions/face-icon-small-sad.gif[/img]
If your not a high tech-read up-over achiever, prolly not. [img]i/expressions/face-icon-small-smile.gif[/img]
I can do loads on motors and all but I'd never try making a pipe after reading up on all the measurements and such.
Try a pipe made for the machine before scapping it.
FYI: to do a compression check you hold the throttle open and crank till it don't increase in pressure. Usually only a few seconds of cranking. Kick cranking may produce compression faster.

 

.

Also, do inter-swap your "stock" rollers and clutch springs with your new "peformance" rollers and clutch springs. A while ago, I remember reading a post from someone stating his stock rollers worked much better with his new clutch spring. Much better then the performance rollers. Also, do check the proper "rate" of clutch spring from your pipe seller. Sometimes, the correct rollers but wrong spring is sometimes sent to the customer by mistake.

Thanks to someone on this forum, I'm running the stock rollers, RFC "light weight" Clutch and provided clutch spring on our Pred-90. The performance gains is better then stock - especially with power sprockets. Like many, I had to swap in / out several times to determine "the best combination" for our power wants.

Hope this helps as well....

.

 

After reading this entire thread again, I would agree with LT80.

Re-install the factory pipe (with CVT changes, CDI changes) and stock carb. Do a baseline and get its spark plug to slight black to beer bottle brown. Beer bottle brown is the best. Do a little race and see how she goes. Then, install your custom pipe. Re-tune the factory carb and do another speed test. In other words, do a before and after baseline. That will help eliminate a problem part - like your home grown pipe.

If its worst then pure stock, re-focus on the CVT changes. Get that pinned down.

Once you get the proper pipe and CT changes nailed down, then do tweaking on the air filter system.

Little steps at a time....

.

 

Hi, I am not saying this is your problem, but my daughter's quad lost power last year and it ended up being a stuck ring. It might be something for you to check. Good Luck!

 

Why are you not asking the pipe mfgr what is wrong? Something is jacked up there. A good head will help as will the correct clutching mods which obviously the pipe mfgr didnt get you. You can get a new much better head for a little bit more than having the head shaved and it will have a screwed up chamber/squish. For $30-$100 you can get a new good one. You said you went up a little on the jet size what does that mean? Are you in the 80 range or 120 or 180 range on jetting. That'll help us help you.

 

thank you all for you input. I think I will look into a top end kit for this thing. the compression does seem a little low to me. I will put a new post in after I have done more changes.

 

fastestdad: read his 2nd post. It explains how he made a CR80 pipe for it.
After reading that, tell me it's not the pipe. [img]i/expressions/face-icon-small-smile.gif[/img]

 

So what happen when you put the stock pipe back on. Did it run better.