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post #1 of (permalink) Old 01-13-2006, 02:33 AM Thread Starter
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Problems after adding a pipe upgrade....

For Luix4.

Note: I tried to send you a PM (to the PM you sent me) but it appears your PM function is turned off. Thus, a reply via open forum....

Your question to me: I bought my daughter a pipe for her Predator 90 for Christmas. I got it from xxxx a local guy who makes pipes for ATV's. I also have one on my 400 EX and it works great. The problem is that once he put the pipe on the Pred-90, it has absolutely no bottom end. We do most of our riding in the dunes sothis is a big problem.


Many say that when someone adds a pipe, they "should" also install a clutch kit. Especialy for soft sand conditions. A clutch kit (combination of different size rollers and different size clutch springs) allows the CVT system to rev higher before engaging, and revs higher at slower ground speeds. Same feeling as driving a car with automatic tranny in 3rd gear, instead of OD gear. Higher revs = more power and momentium up/down sand hills.

Many also say when more airflow can flow through a performance pipe, (and higher rev engine via clutch mods), one should also upgrade its air filter. Thus, reduce airflow bottlenecks in the front and back end (sort of speaking). Some install K&N Filter, some install unifilter and some install open foam filter. Others, like myself, install a bigger snorkel pipe on the factory air box. If you install an aftermarket air filter or modify the factory air box, carb jetting must be done inside the factory 16mm carb. The factory main jet is 82.5. If you go above 90 main jet in the factory Pred-90 16mm carb, you must "drill out" the hole behind the main jet. A special bit size must be used. For K&N & uni filter, some run up to 120-130 Main jet size. Many of the carb experts recommend that if jetting above 90, it would be best to replace the factory 16mm carb with a 20mm carb. The 20mm has a much better "impulse pull" for higher RPMs, takes more altitude changes and takes more weather temp changes. In other words, much less adjusting after you get its base set. If you install a 20mm carb, one needs to install a 20mm carb to engine intake and a new 20mm gas cable. If you install a larger snorkel on the factory air box, your jetting will increase to 87.5 or 90. Being under 90, no carb drilling is required. Yet, some air flow improvement is obtained - not as good as 3rd party air filter replacement but it works for us. For a picture of our modified snorkel (to keep our costs down), surf:

If your young rider drives above 3/4 throttle NOW, making it rev higher via clutch upgrade will make it have slower ground speed. Thus, an upgraded CDI (one that is NOT Rev restricted) must also be installed to allow it to have the same (and a little more) ground speed.

For parts and validation of the above, contact:
Billy at
Rich at
Ed at
Brad at

Hope this helps....

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post #2 of (permalink) Old 01-13-2006, 11:53 AM
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Re: Problems after adding a pipe upgrade....

Spike thanks for the advise, I talked to Ed at Lucky 7 and he is sending me the necessary parts for a cluth tune, CDI Box, and Uni Air Filter. As far as the jetting, I also talked with someone at Hetrick's and they said that they do make jets larger than 90 for the 16 mm carb. I hope that the stuff arrives this weekend. Thanks for your reply.
post #3 of (permalink) Old 01-13-2006, 09:20 PM Thread Starter
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Re: Problems after adding a pipe upgrade....


Soft sand riding with lots of dust????

If you can, install some flex hose (can be solid, plastic or even an old vacuum cleaner hose) from the carb to the front hood area. Then, install the 3rd party air filter in the center of the front hood area. For a picture, surf:

If any dealer has such a bolt on product, please post their contact details. Sure would be nice if there was a bolt on product (like the above) for the Pred-90 16mm carb.

Once the air filter is "in place" and before you start jetting your carb, oil down an old sock and slip it over the air filter. This old sock will trap majority of dust before it hits the 3rd parth open air filter. When that old sock gets too dirty, simply throw it away and slide over another oiled down sock. This extra cover protection will save mega time and cost in cleaning your unifilter.

Glad the folks could help.

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post #4 of (permalink) Old 01-13-2006, 09:36 PM Thread Starter
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Re: Problems after adding a pipe upgrade....


Yes, many do make larger then 90 Main Jets for the Pred-90. If you find NO jetting difference between 95 and 110 (or anything above 90), then the hole behind the Main jet must be drilled out. There's a special drill bit size - if drilling needs to be done. Also, you may have to drill the float needle hole a little larger as well. If it feels like its running out of gas when going above 3/4 throttle, then this small "factory hole" (behind the float needle) is the problem.

As many will vouch, the 18mm is much easier to re-jet for performance mods that demand more air / gas flow. I've been told many times over that 20 mm carbs are even "more easier" to re-jet. The 16mm carb can be a pain to set and stablize when going above 90 main jet size. Some can it but many can't. Especially when going above 110+ Main jet size.

Something to keep in mini while jetting your 16mm carb.

Glad I can help - some how....

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