backfire idle hang and bog

barkerman77

barkerman77

Member
Joined
Nov 7, 2013
Messages
156
Age
32
Location
Madoc, Ontario, Canada
Recently I blew a belt on my 02 viper and I put a brand new Yamaha belt on it. I noticed my idle went for a shit. DIDNT like to stay idling. Its like the belts catching. Only idles at about 1400ish. If I set the idle up higher it won't stay up it always comes back down. When it comes down it let's out one little pop/backfire. I figured it was the cracked manifold that was letting fresh air into the unburnt fuel in the expansion chamber. I took it off and tig welded it back up all nice. Still does it. If I'm riding then let it coast down to a stop it always pops coming back down at about 2500 then it drops off to 1400. I have cleaned the carbs a few times. I have checked the boots there alright. Anyone have any ideas? The sled has 17000 km on it I believe its original pistons. 110psi in each hole. I'm stumped. It also bogs it I punch it from dead stop. If I feather out its fine and dandy. And its great everywhere else mid and top end.
 

super1c said:
Carbs sound dirty.
Click to expand...

x2
You noted the carbs have been cleaned a few times, when was the last time? They should be cleaned and inspected at the start of riding every season with this ethanol gas, some people clean them multiple times a season.
 
Sprayed carb clean/brake clean in & out of all internal passageways and blew out with compressed air to make sure they were clear? Checked and clean tophat filters on inlet seat?

Do the plugs look good, and consistent among all 3? Piston domes look good/good wash when looking down the plug hole? Any chance you have or can get ahold of an inspection camera to take a good look?

17000km, has it had new rings? If not, you may be on borrowed time especially if you don't know the history of the engine.

I didn't catch it before, but 110psi compression "in each hole" is not correct for a stock Viper, PTO side should be 10%-ish less than other 2. Do you have stock, unmodified head?

Do the carbs have stock pilot jets and main jets? Have the needles been raised to clip position 3.25?
 
Sorry it has ten less on pto side. I'm sure its all stock all the jets are spotless. I'm getting a camera from a buddy of mine I'll post some pictures. Maybe a video of what it's doing.

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When the belt let go, did the motor overrev? Maybe causing internal damage?

Is the new belt riding high in the secondary, may need to remove a washer or two to drop the belt.

I've found that backing my fuel screws out 1/4 -1/2 turn cured any idle hang I've had.
 
Belt DIDNT completely let go I was trying to see where it was setting in the secondary and blew the top section of ribs off it. I think I'm gonna pull washers on the secondary. See from there. Still doesn't explain the backfire.

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Have you ever replaced your plug caps? I just replaced mine with the NGK's and it comes down to an idle much smoother, along with a nice steady idle. I had other problems thou that might have played a role before.
 
Never have. I've heard the NGK caps were bad because they had a resistor in them. At least that's what I heard from a fellow sledder with an srx.

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You have to get the ones that ohm out same as stock caps. I think it was 5 ohms. They are the all rubber caps, not the hard plastic ones.

Check yours first to see if they are even bad, but with those miles, I'm betting they're out of spec. They do make a difference.
 
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Just an update here I pulled the washers from the secondary and it seems better with the idle. It still seems boggy until its warmed right up. As for the miss I DIDNT check ohms but I wiggled them around with it running. The miss seems to go away once its warm. Would it be a fuel pump diaphragm?

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I had the backfire and idle hang, no bog though. Turned out it was a combination of a bad header-to-pipe gasket and chipped reeds. The reeds are between the carbs and the crank. 4 bolts hold each reed cage.
 
I had a bullring gasket and also had cracked manifold. I just fixed both of them. Still does it. I know where they are just DIDNT know what to look for other than obvious problems like chips or cracks. Is there anything else I should look for. I'm going on a big trip this weekend I'll look when I get back

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