2003 prairie 650 popping and backfiring - Kawasaki ATV Forum
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post #1 of 9 Old 05-10-2019, 09:59 AM Thread Starter
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2003 prairie 650 popping and backfiring

Hello I have a customer with a 03 650 that I have serviced a couple of times. I am a golf cart shop but work on some 4 wheelers as well. Any how the story is he was just out riding and it started loosing power and running bad.

I checked the gas for water and cleaned the carb bowls. All is good. Adjusted the valves intake.005 exhaust.008 they were super close but needed a little adjusting, and replaced the plugs. The motor is still popping through the carbs and back firing. Did a compression check front cylinder is 47 lbs and the rear is 50lbs, This was with a slightly warm motor I believe this is on the low side of the specs???

any thoughts would be greatly appreciated.
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post #2 of 9 Old 05-10-2019, 11:06 AM
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Check the fuel pressure and volume, then the valve timing as well as battery voltage...all can cause this. Yes, the compression is getting there but as I recall op-range is 33-66+ lbs so it still has a ways to go.

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post #3 of 9 Old 05-10-2019, 12:41 PM
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Also be aware that I believe that this year prairie had an electric fuel pump in the gas tank - So fuel pressure and volume is key, and there is aftermarket rebuild kits for the electric pump assembly.
If I am wrong, then there would be a vacuum style pump which uses the cylinder head vacuum to actuate the pump from both front and rear cylinders.

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post #4 of 9 Old 05-11-2019, 07:03 AM
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These motors will pop through the carbs if the air filter box is not installed in it's entirety.
Check to be sure it's not in "limp mode". The sure sign is that it WON'T shift into 4wd while slowly driving along.

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post #5 of 9 Old 05-14-2019, 08:54 AM Thread Starter
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Ok so checked fuel pressure today, I do have the electric pump in the tank. Gauge is in 2lb increments. I could not really see much of a reading but the needle did move off 0, maybe 2 lbs max. What should it be on this? I figure with carbs it cant be much...

And yes the air box is fully installed and sealed well. I have not checked valve timing yet but if the fuel pressure is even close to correct I will go that direction.
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post #6 of 9 Old 05-15-2019, 05:18 AM
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Check intake boots for cracks.

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post #7 of 9 Old 05-15-2019, 02:25 PM
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Quote:
Originally Posted by NovaKaw650 View Post
These motors will pop through the carbs if the air filter box is not installed in it's entirety.
Check to be sure it's not in "limp mode". The sure sign is that it WON'T shift into 4wd while slowly driving along.
And? ^^^

2002 698 Prairie
VFJ 11.5:1 coated pistons
FST Stage II Cams
Fundy Performance Porting, 1mm milled off heads
Kibblewhite valves
Crossover intakes
Modded airbox
Full Muzzy
Custom machined stock weights
VFJ Springs
DynaTek CDI
Other weird stuff

2011 Stratos 186XT Bass Boat
Mercury Optimax 115hp
Minn Kota 70lb 24v trolling motor
Lowrance HDS 10 Electronics
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post #8 of 9 Old 05-16-2019, 10:57 AM Thread Starter
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Got the 4 wheeler jacked up and on stands, ran in gear 3-5 mph shifts in and out of 4wd. Sprayed intake boots with brake clean while running with no changes in motor.

Someone mentioned valve timing earlier, I know when I did the valves at TDC the lifters had play in them as they should. Is it possible I could have a sheared key way? Or would that make the valves far off enough to see?
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post #9 of 9 Old 05-17-2019, 01:37 AM
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Quote:
Originally Posted by jskent View Post
Got the 4 wheeler jacked up and on stands, ran in gear 3-5 mph shifts in and out of 4wd. Sprayed intake boots with brake clean while running with no changes in motor.

Someone mentioned valve timing earlier, I know when I did the valves at TDC the lifters had play in them as they should. Is it possible I could have a sheared key way? Or would that make the valves far off enough to see?
The flywheel has nothing to do with cam timing.

2002 698 Prairie
VFJ 11.5:1 coated pistons
FST Stage II Cams
Fundy Performance Porting, 1mm milled off heads
Kibblewhite valves
Crossover intakes
Modded airbox
Full Muzzy
Custom machined stock weights
VFJ Springs
DynaTek CDI
Other weird stuff

2011 Stratos 186XT Bass Boat
Mercury Optimax 115hp
Minn Kota 70lb 24v trolling motor
Lowrance HDS 10 Electronics
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