my prairie back fires when i run about 50 mph and let off the throtle. it seems to happen when i reach 20 to 30 mph. you can see what mods ive done below. i also noticed around 45 to 49 mph holding it steady it seemed to surged, it was hard to hear but it was there. would this be wright where the cdi ramps down?

what do you think might be wrong?

i would like to get this resolved before i install the new dyna cdi (not here yet)

thanks for you time any help would greatly appreicated!

_________________

02 650p
nyroc muffler,6-3/8" holes
napa #7335
158f/162r jets
needles shimmed .033
epi black 2ndary spring
700p drive spring
warn 2000
plow

 

Howdy,
I had the same thing when I was adding the pipe and opening up the intake. If you look on the right side of the quad at the carbs you will see the idle mixture screws. Start turning them counterclock wise 1/4 turn at at time. After each turn run the quad and see if it doesnt get better. I think I am running mine out 3 1/2 turns. It worked on mine. Hope it works for you!! Have a goodun!!!!!

 

I would say to check the jetting. A Backfiring exhaust on decelleration typically indicates a lean condition.

 

i have adjusted my air screws while i was riding today. i was reading that i should turn them (counter clockwise) till the motor slows then turn them back till the rpms come back up.

is that wright, the proper way to do it ?

i have jeted it preaty big now. the plugs look fine, maybe one more up. but i have noticed that it runs a little faster one size down, so i might try that first. i still cant get to 63mph yet, it will only hit 59mph.

_________________
02 650p
nyroc muffler
158f/162r jets
napa #7335
needles shimmed .033
epi black 2ndary spring
700p drive spring
plow
warn 2000

 

four strokes dont have air screws they have fuel screws. you dont adjust them by turning them in and out to find peak rpm, (you do with 2 strokes) put them to factory settings then start backing them out 1/4 of a turn until the popping stops

 

Before all of the stuff already mentioned, check for exhaust leaks. Happened to me.

 

no exhaust leaks!
what about the surging?

ericruby
(factory pilot screws are 2 1/4 turns). mine was set at 2 1/2 r, 1 1/4 front. you want me to start their? im sorry air/ fuel screws, their called pilot screws buy the book.

_________________
02 650p
nyroc muffler
napa #7335
158f/162r jets
needles shimmed .033
epi black 2ndary
700p drive spring
warn 2000
plow

 

Surging problems...I had those just 2 weeks ago (mine ran good from 0 to 30ish and then would start surging from 30ish to top-speed) and completely fixed them by doing the following:

First, I dropped 2 sizes on the main jets and the surging instantly stopped...but it seemed to have lost some acceleration thruout the powerband and went 5 mph slower on top-end (made me think it was now too lean and that I needed to go up 1 size on the main jets). Next, I found a problem with the gas tank vent hose lines that sit atop my P650 fuel tank as they were moved over towards the very edge of the gas tank causeing a kink in the hose...when I moved it back into the little slots where the lines are supposed to sit, it instantly made the engine run stronger than ever.

So I think your answer is to go down on the main jets...you might try reading your plugs first to see if they are too rich OR alternatively you could try to turn on the choke while riding it to see if that helps or hurts the surging problem. If it the choke seems to make the problem get worse or you notice no change, I'm guessing you are too rich and you just need to drop a few sizes on the main jets. Also, it won't hurt to double check to make sure your vent hose lines are where they should be too.

Good luck and happy trails...[img]i/expressions/face-icon-small-smile.gif[/img]

 

mikeyboyesq
my plugs look fine. they are light tan with little little black specks. i ran 145/148 jets and did a plug check and they were bone white. ran 155/158 and they looked a little better, i had the best mph with these jets(60 mph). i might go down 1 size. mph wright now is 58-59.

i will check the breather lines today.
i will try the choke today as well.

________________
02 650p
nyroc muffler
napa #7335
158f/162r jets
epi black
700p drive spring
warn 2000
plow

 

Deerchopper,
Where is the surging occuring? If its at 30mph and up (while accelerating at WOT from a dead stop), they the problem is the main jet is too rich or too lean. If its surging soon after you are off throttle, then it might be the Needles that are too rich or too lean. If its surging right from a dead stop when you hit WOT, then you may have a problem with the pilot jet or just need to adjust the idle mixture screws.

Regardless of when it is surging, you should run it WOT until the surging starts and then hit the kill switch (while you keep thumb ON the throttle)...after it rolls to a stop and cools down, then read the plugs to see if its too rich or too lean at that throttle position.

Hope this helps. Happy trails...[img]i/expressions/face-icon-small-smile.gif[/img]