76 GL1000 misfiring/ backfiring issue

467 Views 23 Replies 6 Participants Last post by Bryanlj, 3 d ago

alobos05

Discussion Starter · 15 d ago

Hello everyone, I got this bike back in Feb and took it to a "mechanic" for a general check up and he screwed it up and i have spent the past months with the help of fellow members getting it back to where it was when i got the bike. you can follow my last thread to get caught up on what was wrong with the bike.

fast forward to now and the bike does run as i took it for a quick ride around the block yesterday and it rides. not clean but rides. the issue is that i have from the right side some backfire/misfire coming from the exhaust and you can see from the clip i attached that the back pressure is much less on the right side. one more thing to note is that if i cold start the bike with full choke it will not start the bike, i have remove choke, crank a few times and it will start then i can pull choke and keep it at 3k rpms.

any advice wold be greatly appreciated as i cannot wait to finally take this beast for a ride with my lady.

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GL1000 backfiring while idle

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1 - 20 of 24 Posts

DaveO430

· #2 · 15 d ago

Have you adjusted the mixture screws on the side of the carbs? The initial setting is 2 turns out from seated.

alobos05

Discussion Starter · #3 · 14 d ago

DaveO430 said:
Have you adjusted the mixture screws on the side of the carbs? The initial setting is 2 turns out from seated.

are you talking about these guys?

Light Gas Auto part Nut Engineering

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DaveO430

· #4 · 14 d ago

Yes, that one. Screw them in until they stop (don't force it) the back out 2 full turns. If everything is right in the carbs that is usually good enough.

alobos05

Discussion Starter · #5 · 14 d ago

DaveO430 said:
Yes, that one. Screw them in until they stop (don't force it) the back out 2 full turns. If everything is right in the carbs that is usually good enough.

Ill take a look at them tonight. hopefully this clears it up a bit as im dying to really drive this thing

alobos05

Discussion Starter · #6 · 11 d ago

so i adjusted the idle screws and it did make the cold start that much better. crank on the first try and was able to do it with full choke at 3K. once it settled to idle the popping fromthe exahust began again. I took it for a spin arouind the block and the fuel delivery does seem better since it does not feel that it is bogging but the backfire was still present even through the gears. i definitely feel that the bike is just a few steps away from being able to hit the road.

DaveO430

· #7 · 11 d ago

So, what's the status of the carbs? Have they been worked on? I think it's probably still too lean, could be float levels, vacuum leak or clogged fuel passages.

alobos05

Discussion Starter · #8 · 11 d ago

according to the PO the carbs were taken apart back in June 2021

DaveO430

· #9 · 11 d ago

alobos05 said:
according to the PO the carbs were taken apart back in June 2021

That doesn't mean much.

alobos05

Discussion Starter · #10 · 11 d ago

yeah, i was assuming that the next step was to go ahead and pull the carbs and rebuild it

Shelby-right

· #11 · 11 d ago

If you think it's on 3 to 3 ½ cylinders , get it all warm , and those screws you set at 2 turns out , try one at a time and bottom the screw out the cylinder that it makes no difference is your problem . You can blast out idle circuit in situ , just warm up rubber elbow and wiggle rubber off that one bad carbie , remove that mixture screw and squit and blow until good stream of fluid comes out brass discharge tube , you can also clean out the air bleed jet remove the brass elbow they come out ok and make sure its clean . This worked fantastic on my GL1000, Cheers .

rayworx

· #12 · 9 d ago

Have you verified that the engine is sound?
First thing is a compression AND a leakdown
test. Wide open throttle compression should be about 170psi and leakdown less than 10%. Could be something minor like a tight valve adjustment or something more serious but the engine needs to be eliminated first.

alobos05

Discussion Starter · #13 · 9 d ago

rayworx said:
Have you verified that the engine is sound?
First thing is a compression AND a leakdown
test. Wide open throttle compression should be about 170psi and leakdown less than 10%. Could be something minor like a tight valve adjustment or something more serious but the engine needs to be eliminated first.

So this mechanic i had taken it to when I got it gave me results of 120 for 1,2,3 and 115 on 4 on the compression test. I will do one myself as that guy sucked anyways. But from what I understood, a very low compression would take really long to start and would feel power restricted. Bike starts normally and power delivery is good up to 50 since I’ve only recently take it around the block only. I’ve also read about gl1000s that have no problem running on 120 compression. I never thought it could be compression since it does start up fine and runs with power

DaveO430

· #14 · 9 d ago

120 or so is probably what you would get with a cold engine and closed throttle.

Reactions: 1

Shelby-right

· #15 · 9 d ago (Edited)

I have and old 49 matchless 500 , it ran ok , pulled ok , but leaked oil , when I pulled the head off , to my amazement the piston was ½ down at TDC , wrong piston , I calculated the comp at 4.1:1 , I'm looking forward to the new compression .

Reactions: 2

alobos05

Discussion Starter · #16 · 9 d ago

DaveO430 said:
120 or so is probably what you would get with a cold engine and closed throttle.

I’ll be checking it this coming week so nice I do my own compression test at closed and open

rayworx

· #17 · 5 d ago

alobos05 said:
So this mechanic i had taken it to when I got it gave me results of 120 for 1,2,3 and 115 on 4 on the compression test. I will do one myself as that guy sucked anyways. But from what I understood, a very low compression would take really long to start and would feel power restricted. Bike starts normally and power delivery is good up to 50 since I’ve only recently take it around the block only. I’ve also read about gl1000s that have no problem running on 120 compression. I never thought it could be compression since it does start up fine and runs with power

rayworx

· #18 · 5 d ago

rayworx said:
If the 120 psi compression is WOT then there’s a problem. Wide Open Throttle should be known by anyone that calls themselves a ‘mechanic’! These kind of test results (confusion) is why I prefer a leakdown test when diagnosing engine problems

icechopper

· #19 · 4 d ago

Shelby-right said:
I have and old 49 matchless 500 , it ran ok , pulled ok , but leaked oil , when I pulled the head off , to my amazement the piston was ½ down at TDC , wrong piston , I calculated the comp at 4.1:1 , I'm looking forward to the new compression .

I'll just bet you'll be real happy with the pull after the right piston is installed but it will most certainly still leak oil. That's just what they do.

alobos05

Discussion Starter · #20 · 4 d ago

i am going to be doing the compression test this weekend but i had a question regarding the carbs. im most likely going to be oulling the carbs, since they will be pulled is it necessary to replace all components or just rubber pieces? or since i have the carbs pulled just go ahead and replace everything anyways?

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