backfire
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From: pontotoc county mississippi
backfire
i replaced the front rocker box gaskets not to long ago because of leaks. i also had a problem with a high idle after riding and when i would cut the engine off like at the gas station for a fill up and start back i would get a loud pop right before it started. i replaced the back rocker box gaskets friday and while i had it all apart i changed the intake gaskets and the gasket between the carb and the filter housing. i got it put back together and got my oil leaks fixed but still got the pop when starting with the engine hot. i tried to make sure i got the intake seals on right. the guy that bought it new had the dealer work on the carb right after buying it and the dealer had changed jet and put on a set of s.e. pipes. it has a purple spot right near the end of the pipe, i dont know if that was there before the carb work or if it formed after. do you think the popping is still a intake leak or something on the inside of the carb. if you can tell me how to check for a intake leak. bike is a stock 1998 except for the different jet and s.e. pipes. thanks toccopola
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From: pontotoc county mississippi
it feels like its coming from up front. i took the air filter off and still can't tell but it dont sound like its coming out the exhaust. i sprayed wd40 on the intake flanges with it running and it didnt change the idle any. the engine ran smooth and had very good response when you hit the throttle before while riding but after i unhooked it from the intake and layed it up on the front cylinder on its side while replacing the rear rocker gaskets. now it does not open up with a fast response it kinda feels like my old tractor when some trash gets on the needle.
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Joined: Dec 2005
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From: NC USA
I've had them do that on startup. A "pop" like that is from a cylinder (or both) running way too hot. It fires steaming fuel when both valves are open on the in-between part of the stroke. That's why it doesn't sound like a back fire or back thru the carb. Kinda both at the same time.
That comes from a vacuum leak most often.
Did you get the hose to the VOES reconnected when you had it off last time? Did you disconnect either wire to the VOES, if so are your sure they are hooked up now? Is the choke cable going all the way back in? The **** will stick out about 1/16" at the cable nut when it's all the way closed.
I read your other thread and sounds like you installed the manifold correctly. What can easily happen when you pull a carb off for something else, is the grommet will stay put (but not really) and doesn't seal when you put it all back together. Or, if you pull the carb away from the manifold any amount to meet up with the air cleaner back plate on re-assembly, it'll pull the grommet enough to cause a leak. Not enough you can tell, but enough to cause a leak there. Finding a leak with the usual methods is a hit or miss at best. If you definitely find one, it's usually running so bad it won't hardly start anyway.
Always make sure the grommet is bottomed out on the manifold. And always put the back plate on the carb before you start pushing it into the manifold grommet. And a thin smear of grease on the inside of the grommet where the carb fits is always a good thing to do.
So, if you're sure the VOES hose is in good shape and connected and the wires going to it also, I'd say pull the carb and check the grommet and/or replace it with genuine HD (they are a tick thicker and hold up better / let you pull the carb more times without needing replacement). Let us know if that fixes it.
That comes from a vacuum leak most often.
Did you get the hose to the VOES reconnected when you had it off last time? Did you disconnect either wire to the VOES, if so are your sure they are hooked up now? Is the choke cable going all the way back in? The **** will stick out about 1/16" at the cable nut when it's all the way closed.
I read your other thread and sounds like you installed the manifold correctly. What can easily happen when you pull a carb off for something else, is the grommet will stay put (but not really) and doesn't seal when you put it all back together. Or, if you pull the carb away from the manifold any amount to meet up with the air cleaner back plate on re-assembly, it'll pull the grommet enough to cause a leak. Not enough you can tell, but enough to cause a leak there. Finding a leak with the usual methods is a hit or miss at best. If you definitely find one, it's usually running so bad it won't hardly start anyway.
Always make sure the grommet is bottomed out on the manifold. And always put the back plate on the carb before you start pushing it into the manifold grommet. And a thin smear of grease on the inside of the grommet where the carb fits is always a good thing to do.
So, if you're sure the VOES hose is in good shape and connected and the wires going to it also, I'd say pull the carb and check the grommet and/or replace it with genuine HD (they are a tick thicker and hold up better / let you pull the carb more times without needing replacement). Let us know if that fixes it.
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From: pontotoc county mississippi
i replaced the seal on the manifold where the carb goes back on. the kit had all the parts, intake seals and carb rebuild parts. i didnt unplug any wires(but will check to make sure they didnt come loose) but i did put the carb back on before i put the back plate on. i will go back and redo that along with a thin coat of grease on the seal. i think i got the hose hooked back correct but will check that and make sure it hasnt got a bad spot. the engine starts perfect from cold with no popping only pops when it hot and thats if you start it right back up. it doesnt pop or backfire when you decelerate . whatever is making it pop like you said with the steaming fuel was a problem before i ever owned the bike because it done it right after i got it on the restart after my first fillup. i had in my mind that it was the carb leaking some fuel into the intake after it was shut off. after the engine cools off it doesnt do it just when hot. going to go back and check everything. thanks for helping
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From: pontotoc county mississippi
i still got a manifold leak. i pulled the manifold back off replaced the seals again and replaced vac lines. put it all back together and still had a leak. i bought a reconditioned manifold that has been glass beaded off ebay. it came with the seals that have the extra inside lip. put it all back on and it almost fixed my problem pop(it went from a pop to a thud) and when i sprayed a little carb cleaner it still causes the engine to idle up. i had bought a extra set of seals so i went back and put them on and i checked the flanges to make sure they were good and flat(they are) i got it put back together and still have a leak. thinking about buying a new set of flanges just to make sure there not the problem.
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Joined: Apr 2016
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From: Long Island
When I had a problem on my old Honda 4- carb, I used a light smear of clear silicone.It cured that problem.
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Like I said, hit or miss when using traditional methods of checking for an intake leak. Problem is, if any mist gets sucked into the carb, it'll give you false positive. Best to do the spray or propane check with the air cleaner on or have someone hold a cardboard tube against the carb while spraying.
You mentioned a dealer installed pipes and changed a jet? Do you have the part number of the jet they installed. I'm asking for wondering if they changed the main or idle jet. I'll bet it was a main. And did you by chance look at the bottom of the carb to see if the idle mixture screw plug has been removed?
For the moment, let's assume you did get it sealed good and look to a few other things that will cause it to run hot inside the cylinders. I'm in bit of a hurry but I'll be back this evening and try to offer more info/help.
DO NOT put any sealer anywhere on the intake/carb, please, please, please - do not....
You mentioned a dealer installed pipes and changed a jet? Do you have the part number of the jet they installed. I'm asking for wondering if they changed the main or idle jet. I'll bet it was a main. And did you by chance look at the bottom of the carb to see if the idle mixture screw plug has been removed?
For the moment, let's assume you did get it sealed good and look to a few other things that will cause it to run hot inside the cylinders. I'm in bit of a hurry but I'll be back this evening and try to offer more info/help.
DO NOT put any sealer anywhere on the intake/carb, please, please, please - do not....
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From: pontotoc county mississippi
the plug had been removed, just put one in. now its raining like it never has. the service records and the pink copy from the dealer shows where they used .45 883/12 jets that was in 1998 when they put the se pipes on. then in 2017 it was back at the shop for surging at cruising speed, it states that the carb was cleaned re jetted and dynod but does not state which jet was used. so i have no id what its jetted to now. i hope that plug was all the problem. will let you know when the road dries up.
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