03 f7 efi backfire and power loss

[jonesin]

Last night my 03 F7 EFI backfired once as I took off, it seemed to run just fine, revd up to 8200 rmp and normal speed but then all of a sudden it seemed to lay down, just loose power and run about 50.
I could slow down or stop then take off and it would go just fine then lay down again.
Any ideas?
I replaced the coil last year...
Thanks

 

[raceinsnow]

Exhaust valve cables or exhaust valve motor. The cables chafe and hang upon the inside then the engine will go into limp mode.

 

[jonesin]

i've only had this a little over a year and havent ever cleaned exhaust valves, i guess that its time to give it a try....
anything to be afraid of besides dropping carbon down the cylinder?...

 

[raceinsnow]

The exhaust valves on the cat motors don't seem to gum up that bad, I am not saying don't clean them but I think you have another problem. If the exhaust valve cables have not been changed yet I would start there first.

 

[mezz]

I would tend to agree with that statement as I have checked mine every year & after 4200 miles so far, I have not had to clean them yet. I can't say that it's the oil (Cat Synthetic) or not riding it too slow, they have no build up on them. Simple to check, can't hurt anything, but, more than likely another issue going on. How may miles on it, perhaps time for rings.-Mezz

 

[rtrypwr]

Friend of mine has an '03 Firecat F7, probably 10k miles on it. It was rebuilt at about 6k, last year same thing happened. Ran well all day, after about an hour of playing and landing hard a few times his started hitting a wall. Got back and cleaned the exhaust valves and ran fine the next day.

Another guy I ride with has an '05 F7 and it backfires at least once a day while riding, because he doesn't allow it to idle a bit before shutting it down. Let it idle for 30 seconds before you hit the kill switch and see if the backfiring continues...

 

[jonesin]

thanks guys, i hope to ride sat and see if it happens again

it only backfired one time, i was idling and adjusting my face mask and when i pinned it to catch up with the group it went pow! but only once
the odd thing is it only seems to go limp when im hard on it and not right away and sometimes not at all.... i didnt notice it in the fields and drifts but it was late at night and we just happened to be passing by within a couple miles of home so i just peeled off the group and took some fields home

i do let the idle drop before shutting it off and preach the same to my kids, my wife blew up the muffler on my lawn mower not doing that, (i think it was on purpose, she hasnt used it since)

it does have 7k on it but the motor was tested at the end of the season last year and compression was good, i'm going to see about getting a tester and doing that also...

thanks again!

 

[raceinsnow]

One more thing I can add is , I was talking with my F7 riding friends and they said that their sleds would back fire when they used 87 octane fuel. When they filled back up with premium fuel the back fire went away.

 

[jonesin]

it has only backfired the one time
i changed plugs and added sea foam sat then rode around the house for almost an hour
it still happens but its always when im going wide open and at about 70mph, even when i would let off the throttle and burp it or what ever it wouldnt regain power but as soon as i would slow down at the end of the field or whatever and nail it again it would be just fine
it would not happen every time either, just once in a while.... weird

 

[jonesin]

ezra nailed it

ezra told me to check the clutch and sure enough it had a cam busted off
thanks ezra and all who offered ideas!