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Old 02-21-2011, 07:50 PM   #1
stuff4mason
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Lightbulb Backfire - Why?

Guys, I've changed/cleaned EVERYTHING in this G8! Have new header gasket. Muffler has no leaks. Carb is working as it should. Have correct/new plug in. No oil leaks anywhere on the engine. Air box is totally sealed as it should be. No vacume leaks. Gov is removed and running cable directly to the carb. I have 165LBS PSI. Engine is running at full potential. However, as I come down a big hill and let off the gas, I still get a minor backfire. Its fine going up the hill, or on a level surface, but going down, BANG! or bang! I don't think folks in the campground are going to appreciate this at midnight....
Any idea's??
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Old 02-21-2011, 07:55 PM   #2
rib33024
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Default Re: Backfire - Why?

Sounds like the butterfly in the carb is not closing all the way, check and see,. you might need to adjust the cable
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Old 02-21-2011, 08:02 PM   #3
smallblock450sl
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Default Re: Backfire - Why?

Quote:
Originally Posted by rib33024 View Post
Sounds like the butterfly in the carb is not closing all the way, check and see,. you might need to adjust the cable
I agree with Rib (who'd you get so smart) ...Back off the throttle stop screw all the way and make shure your accelertaor cable will alow it to close all the way and see what happens.
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Old 02-22-2011, 10:35 AM   #4
sho305
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Default Re: Backfire - Why?

I've found closing the throttle all the way can cause it, because then the idle circuit does not work. Mine has never backfired/popped. I set the idle so it idles really slow just faster than the starter. Set the idle mix as rich as you can and have it still idle for a while. If too rich sometimes it will stop idling that slow after a half minute or so. It should start better in cool weather too. It backfires because the idle is too lean, either from being too lean or throttle too far closed for some carbs. Idle mix should still be around 1.25 turns out as per factory, maybe up to 1.5 turn depending you have to fiddle with it. Get it to idle slow as you can first, then richen it a little, make sure its running faster than the starter. If you idle it fast the clutch closes on the belt, if your clutch is dry it may do it anyway stop it and pull the clutch out then idle it and they usually don't go back in at idle.
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Old 02-22-2011, 11:44 AM   #5
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Default Re: Backfire - Why?

Wow! OK.

The butterfly is closed all the way when off the pedal. I've read this several times to try to rich it up a bit. I haven't touched the mixture screw since I got it. I'll try sho's suggestion and see how she does. One other thing, there were holes in the muffler, which I thought I got all welded up a few weeks ago. But there is always that possiblity that I didn't get all the holes 100%. I am thinking I'll pull the muffler and re-weld, to ensure its 100% too.
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Old 02-22-2011, 03:35 PM   #6
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Default Re: Backfire - Why?

I took a look today. The butterfly was all the way closed. In fact, the throttle wasn't even touching the idle screw. So, I screwed it in, just enough where its touching. The mixture screw was 2 1/2 turns out. I brought that back in to 1 1/2 turns. The plug surpriselingly looked good. Just light brown. I also took the muffler off and found a pin sized hole I must have missed on my last weld job at one of the brackets. They are easy to spot, since there was a tiny bit of carbon build up around the hole. But, I also found a very minor crack between the muffler and the header. Got all that welded back up. Its snowing today and the driveway is a muddy mess, so I can't test the changes yet.

Thanks guys for your input!
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Old 02-22-2011, 03:51 PM   #7
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Default Re: Backfire - Why?

Air getting in ahead of the muffler can make some loud backfires, aside from that you just need a richer idle one way or another. See the G1 was supposed to idle and with the later G2/9 they didn't say that in the manual, but it seem to work better. If my cart is warm and I touch the pedal it will idle just above the starter, which is quite slow it barely runs really compared to say a lawnmower. Its a G9, you can hear it speed up just a little from starter rpm to running, and it does not creep unless my clutch gets dry in fact that is how I know to lube it. My clutch will fall open when I stop if it has some grease in it, it will drag the belt if dry. That is how I set the idle I start with it off and turn it up until it speeds up a little off the starter. What can happen otherwise is if someone creeps around on the starter they can kill the battery and wear the starter, if it idles then its running instead. An old guy did that I finally set his idle so he could not kill his battery, I got tired of jumping it for him.

Come on, snow is fun!
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Old 02-23-2011, 01:09 PM   #8
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Default Re: Backfire - Why?

Quote:
Originally Posted by stuff4mason View Post
I took a look today. The butterfly was all the way closed. In fact, the throttle wasn't even touching the idle screw. So, I screwed it in, just enough where its touching. The mixture screw was 2 1/2 turns out. I brought that back in to 1 1/2 turns. The plug surpriselingly looked good. Just light brown. I also took the muffler off and found a pin sized hole I must have missed on my last weld job at one of the brackets. They are easy to spot, since there was a tiny bit of carbon build up around the hole. But, I also found a very minor crack between the muffler and the header. Got all that welded back up. Its snowing today and the driveway is a muddy mess, so I can't test the changes yet.

Thanks guys for your input!
Where are you located? No snow in N Va.

Sorry--that was yesterday. Yeah, we got ice and snow.

Last edited by Dave in VA; 02-23-2011 at 01:11 PM.. Reason: can't read
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Old 02-23-2011, 01:16 PM   #9
stuff4mason
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Default Re: Backfire - Why?

Hey Dave, is that Massanutten Mountain in your Avitar?
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Old 02-23-2011, 01:23 PM   #10
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Default Re: Backfire - Why?

No, that's Buffalo Mountain, in Patrick Co. We've got a 2nd home in Carroll Co. and plan to retire there sometime....
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