backfiring after carb rebuild


Information and questions on GL1000 Goldwings (1975-1979)
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RBGERSON
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Motorcycle: 98 SE GL 1500
had every year from 75 to 83

backfiring after carb rebuild

Postby RBGERSON » Sat Sep 07, 2013 4:57 pm



79 gl1000 with points

Working on a bike for another guy..he bought Randakk's rebuild kit and new seats and float needles from K&L..carbs cleaned all jets spotless, floats set to 21mm, no extra fuel in the plenum idles nicely at 950-1000, revs up well too while sitting ..sycned close to perfect.

Now when I take it out for a test ride..major backfiring out the 1/3 side on acceleration/load..pop-pop-BANG-BANG..fairly regular not just a few here and there. So what could cause this. I'm thinking out of time, hanging valve, belt off a tooth+, crud keeping the valve open a bit, air cut-off o ring not seated properly???..definitely out the exhaust..not back up the intakes.

I switched the plug wires and she won't start..she backfires and putters but no real start up..switched them back and she fired right up..a couple small back fires and then smooth at idle and everything up to 5,000 rpm's..while sitting. Took her out again for a quick ride around the block..less backfiring but still there especially on acceleration 1/3 side mostly..while running at a constant speed she runs fairly smooth with an occasional backfire..if I crank the throttle she bucks and backfires.

could this be carb related???

I am still thinking valve or timing/points issues but since the carbs are the only thing recently worked on????? Not sure how it ran before the carb job I will have to ask.

What would be YOUR 1st guess..???


HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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portugeezer
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Re: backfiring after carb rebuild

Postby portugeezer » Sun Sep 08, 2013 9:09 am

Sounds like one carb is getting too much fuel. I had trouble when I didn't change the float needles. One of the little plungers was stuck. Put in a new needle reset the floats and everything worked perfectly. I'm not the expert by any means. Just my two cents!

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dingdong
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Re: backfiring after carb rebuild

Postby dingdong » Mon Sep 09, 2013 7:19 am

My initial thoughts are that the carbs are too lean. You might look around for a vacuum leak on that side.
Tom

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virgilmobile
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Re: backfiring after carb rebuild

Postby virgilmobile » Mon Sep 09, 2013 7:27 am

Backfiring in the exhaust is rich.
In the intake is lean.
If it didn't do that before the carb repairs,the problem is in the carb.
A sticking float or slide.
Poorly set fuel level.
The float must just rest on the needle and be exactly the same measurement front to back,side to side.

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RBGERSON
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Motorcycle: 98 SE GL 1500
had every year from 75 to 83

Re: backfiring after carb rebuild

Postby RBGERSON » Tue Sep 10, 2013 7:11 am

I'll pull the carbs again!! and check the floats and slides..I did bench the float needles seal and no fuel came up and out of the jets while on the bench test..but probably not as much pressure as when the pump is running.
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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virgilmobile
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Re: backfiring after carb rebuild

Postby virgilmobile » Tue Sep 10, 2013 7:36 am

Tell ya what....Before you pull the carbs,stick a inspection mirror in the bottom of the plenum box and,with a flashlight,look at the slide position...All should be at the bottom.Start the bike and snap the throttle once for each carb...Watch the slide action.Each one should bounce bout half way up and settle right back down....

As far as the float level....This is difficult but possible...Start the bike,run it for several seconds to fill the carbs...Turn off the fuel...Drain each carb while on the bike....measure the amount of gas in each carb...It's a quick tell of how there set....

I fashioned some aluminum foil to go under the carb and funnel the gas out to the container

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RBGERSON
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Joined: Tue Mar 09, 2010 7:57 am
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had every year from 75 to 83

Re: backfiring after carb rebuild

Postby RBGERSON » Tue Sep 10, 2013 8:07 am

I'll both ideas a try..mirrors and slide pop..I think I'll try to screw some clear tubing into the carb drains and see how high the gas goes with the bike on level ground and standing straight up like it was on the road.
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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virgilmobile
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82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: backfiring after carb rebuild

Postby virgilmobile » Tue Sep 10, 2013 9:04 am

Just to verify things.Start the bike from cold.Keep it at a idle for 6 seconds.
Shut it down and lightly tap each exhaust header.All 4 pipes should be equally warm.

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virgilmobile
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Re: backfiring after carb rebuild

Postby virgilmobile » Tue Sep 10, 2013 9:12 am

Also because you don't really know the history first hand,assume nothing.
The carb rebuild can be just fine and now that the engine is getting the proper fuel its not burning it right.
Don't spend a lot of time agonizing over them.
If the slides work and the fuel levels are the same move on to the points and timing belts.
Are you good at setting the points by the "split the difference" method.??
Precise ignition timing is critical on the point system,as well as dwell angle.The must be the same for each bank.

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virgilmobile
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78 GL1000
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83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: backfiring after carb rebuild

Postby virgilmobile » Tue Sep 10, 2013 9:18 am

One other tidbit of info.The air cutoff valve.
It is a automatic fuel control valve. It allows more fuel/air to enter the system during heavy deceleration only.

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RBGERSON
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had every year from 75 to 83

Re: backfiring after carb rebuild

Postby RBGERSON » Tue Sep 10, 2013 1:34 pm

OK.. I pulled the carbs rechecked all the floats..straightened tangs on 1 & 3 and reset 1 and 3 floats, cleaned the slides, tubes and carb walls again. From what I could see..not easy to see in the carbs with mirror..It looks like the slides are working..so I took her for a ride..gas pouring out of #1 now??? was #4 which I changed out the float needle seat. So out they came pulled #1 bowl looking very closely I noticed the o ring seemed to be pinched, a piece shaved up..pulled the seat..replaced the o ring..reset the float..will take her out again.

Note I am riding w/o air box and I have the lid up so I can see into the air box as she runs..let's hope no major backfires ..with flames out the intakes I could loose my eyebrows!!!

Wish me luck..
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

User avatar
RBGERSON
Posts: 2612
Joined: Tue Mar 09, 2010 7:57 am
Location: SCOTTSDALE, AZ
Motorcycle: 98 SE GL 1500
had every year from 75 to 83

Re: backfiring after carb rebuild

Postby RBGERSON » Tue Sep 10, 2013 3:35 pm

Well, I am back still have my eyebrows BUT!!! ##!!@@@##%%% I finally realized the 1 and 3 headers are not hot IE not firing consistently..so fuel builds up and when it does fire BOOMM~!!!!

Fine at idle where 2-4 can carry the engine nicely but under load runs like crap. Accelerating aggravates the problem..so now to tell the owner of his new issues.

Ps..like Randall's says check everything else first before you crack the carbs..lesson learned. Don't take on a rebuild w/o including $$$ for valves, timing, compression check etc. or say I'll rebuild but won't guarantee it will fix your problem.
HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB

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virgilmobile
Posts: 7647
Joined: Sun Sep 19, 2010 5:39 pm
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Previously owned
78 GL1000
81 GL1100
82 GL1100 I
83 GL1100 I
83 GL1100 standard
84 GL 1200 I

Re: backfiring after carb rebuild

Postby virgilmobile » Tue Sep 10, 2013 5:18 pm

At least you identified that there was a underlying problem not related to the carbs.
It still could be as easy as point settings.
After that is valve adjustments.
Truthfully,they need to be done anyways.Its just a few more hours.
Keep us posted.

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RBGERSON
Posts: 2612
Joined: Tue Mar 09, 2010 7:57 am
Location: SCOTTSDALE, AZ
Motorcycle: 98 SE GL 1500
had every year from 75 to 83

Re: backfiring after carb rebuild

Postby RBGERSON » Mon Sep 23, 2013 7:58 am

Ok, I should have checked this first but figure no one could ride around with the bike running so badly and not notice..anyway 1-3 wires were backwards..to start with.


HAD LOTS OF GOLDWING 75-83
NOW INTO 1500'S..RIDING A 1998 SE

FAIR WINDS,
RB


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