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Back fire?
Posted: Thu Sep 13, 2007 7:15 pm
by todds112
Truck ran great all day up in Yellowstone. Even at the higher elevations it would pull really steep grades at about 35 MPH. Got about 15 MPG.
One issue: On the decent side of those long hills coasting (in gear, 40-35 MPH) long, it would let out a back fire or maybe two. If it did two they were spaced out a minute or so.
Scared the heck outta me. The flash was impressive in the dark. Sure don't want to start a forest fire if that happens in the back country.
Posted: Thu Sep 13, 2007 7:57 pm
by mjnims
Todd
You simply need to fix the leak in your exhaust system. The flex system from SAV works great for this. I have to admit the flames out the exhaust did look impressive, always wondered what a biker would think if it went off while he was passing.
Posted: Thu Sep 13, 2007 9:09 pm
by andy
Mike, probably a dumb question, but why would a leak in the exhaust system cause a backfire? I would think a leak wouldn't allow pressure to build up. Could you or someone else educate me about this? I read these things knowing that one day I will have the problem. I'm trying to get a clue. Thanks.
Posted: Thu Sep 13, 2007 9:22 pm
by pinzwheeling
Andy wrote:Mike, probably a dumb question, but why would a leak in the exhaust system cause a backfire? I would think a leak wouldn't allow pressure to build up. Could you or someone else educate me about this? I read these things knowing that one day I will have the problem. I'm trying to get a clue. Thanks.
I believe it's cooler air getting sucked back in when you let off of the throttle?
Posted: Thu Sep 13, 2007 9:26 pm
by todds112
mjnims wrote:Todd
You simply need to fix the leak in your exhaust system. The flex system from SAV works great for this. I have to admit the flames out the exhaust did look impressive, always wondered what a biker would think if it went off while he was passing.
Did that already, helped alot with the noise and fumes. The muffler is pretty sketchy though, guess I'll order one from Scott @ EI.
Thanks!
Posted: Thu Sep 13, 2007 9:44 pm
by mjnims
the pinz or just about any older designed engine leaves a considerable amount of unburnt gases in the exhaust system. If fresh air can get into a hot exhaust system you get a backfire. One reason for the catalytic converters and smog pump is to burn these gases off before they escape into the air. The fuel injection systems that are becoming available for the Pinz should also help with this condition.
Posted: Sat Sep 15, 2007 1:16 pm
by Twin Pinzies
I have a 710M without the flex pipe upgrade and the stock (short pipe)section keeps getting gaps/leaks forming where they fit together. While waiting for the flex pipe upgrade to be shipped to me, I have tried to band-aid that section together to keep it air tight. I have tried a mixture of muffler repair tape, bailing wire, and muffler gap filler. Now I know why the upgrade is flexable... any "repair" I do only lasts a few days before it gets vibrated apart and the gaps form again. I have found that the Pinzy exhaust system needs to be totally air tight or it backfires (under engine braking) like a rifle shot! So seal up that exhaust system kids! Oh yeah, it sounds less like a '65 VW micro bus with the leaks all sealed up!
Posted: Mon Sep 17, 2007 5:16 pm
by jpipes
Excellent info! I had been having this problem as well and had no idea why. No it's very clear and I understand what's going on. My truck is in the shop having some major upgrades and repairs done to it (long report and pics to be posted when it's all done) and I believe they are fixing the leaks in the exhaust system.