Carb Back Fire

[BreadMan]

I just bought a '99 500 Sportsman. It did not run. The seller said
"It needs new lifters! The shop said it would be $1500"
Being well above the mechanical average I picked it up for $200. I got it started and it runs, but has a lot of popping comming from the air box. I understand this may be a common problem for these motors...Can anyone who has been through this tell me how much of a pain in the butt it will be as well as an estimate on parts costs? Do I have to pull the engine?
It's not a bad looking machine...I may sell it "AS IS"

[1of7627]

These are overhead cam engines and don't have lifters, per se. Without seeing it, my guess is the cam and rockers are worn out and you have a burned valve due to inadequate clearance. The cost would be as estimated for new parts and if you took it to a shop. But, you could do better if you were able to find a decent complete used head and a shop manual. You don't have to pull the engine, but plan on lengthy disassembly. Good luck. - MarkC

[4getful2]

I'd try adjusting the valve clearance first,along with cam-lobe inspection and verifying cam timing,compression test, then a thorough carb. cleaning.
It sounds like it either valves are out of adjustment,or it's not getting enough fuel.

[Diesel man 03]

Most likely the cam is worn, common problem with that year machine.

[Russ C]

cam worn, get a cam and rocker arm for the exhaust, 400 bucks in parts and some time in the garage 9 ft/lbs of torque on the rocker arm bolts and 6 on the cam sprocket bolts, just did one last week

[BreadMan]

Thanks for the info. I will let you know how it goes!

[BreadMan]

After reading all of the info, I wondered...If the cam and rockers/lifters are worn...the valves would not open totally. Could this cause a burned valve? Why would valves that were not opening all the way cause it to pop back through the air box?

[1of7627]

Originally Posted by BreadMan

After reading all of the info, I wondered...If the cam and rockers/lifters are worn...the valves would not open totally. Could this cause a burned valve? Why would valves that were not opening all the way cause it to pop back through the air box?

These engines lose valve lash with wear and seat recession, so the problem is that the valves don't close completely. This will cause them to burn over time and underlines the importance of keeping them in adjustment. - MarkC

[Bamper]

+1 for worn exhaust lobe, my 96 would do the same thing pop back through the carb once you gave it any gas, but would idle great. I think the reason it pops back out the carb is it isn't letting all the ignited gases out the exhaust because it wont hold the exhaust valve open long enough. The next cycle after the exhaust stroke is the intake so it could be the pressure still in the combustion chamber expelling the rest of the gases when the intake valve opens.

[BreadMan]

That makes sense! Mine does the same thing...idles fine, but pops when you add throttle. Did your '96 have burned valves? Did you change the cam chain? If so, how do you get a new chain around the crank shaft? I guess I should have asked 1st if you did the work yourself? Thanks!