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Backfiring, with LOTS of detail... Help please.

  • Thread starter Thread starter Skyboy8950
  • Start date Start date
S

Skyboy8950

Guest
So here is my backstory:

I bought a 82 850G from someone who rode it for 7 years on long trips. He sold it to me running pretty well. I went to go do a carb cleaning because he said he just ran an additive through there every few gas tanks. I also did a valve adjustment. Here is what I found:


  • Floats were improperly adjusted. Measured to the top of the float, not the step down.
  • Valves were way out. At least 4 of them were .1 to .15 too tight.
  • Synchronized with Morgan Carbtune (edit)
So I corrected those. Took it for a spin and it started backfiring through the carbs. I noticed it would do this occasionally before hand, but was doing it more so now. I took it home, started it up one morning and looked at the carbs. Poofs of smoke were coming out of the cracked intake boots. This is what I did then:


  • Replaced intake boots and o-rings.
Put everything back together and went for a 200 mile ride. Along the ride, in 4th and 5th gear while cruising, cylinder #1 would go in and out. I could tell it was this one because I felt the carb backfiring (because it does it through the carb) and when I stopped, #1 pipe was not as hot as the others.


  • Today, I was tinkering. I took carb #1 apart, cleaned it again, and put it back in.
  • I check the valve clearances, and they were good.
  • I took the airbox apart, replaced some weather stripping because the foam on the sides was half gone. (one thing to note here is that my breather hose is cracked and not currently hooked up. There is tape over the hole into the airbox.)
  • I lightly oiled my filter (it was dry).
  • I adjusted the mixture screws to 3 turns out, not 2.5.
  • I moved the breather hose on the right side of the airbox from the first hole in the bottom to the hole above it to the top (don't know if that is correct).
  • Turned the air filter upside down (or rightside up, don't know...) so that that "bucket" is facing up.
Now the bike runs better, but still backfires into the airbox and lags in 4th and 5th gear cruising only. I really don't know what else to do. I won't tell you what I think anymore because I don't know. PLEASE HELP!!!:-k:-k:-k
 
Last edited:
I think, based on my limited knowlege, you are overly RICH. Generally, popping thru the pipes is a sign of a lean condition, backfiring thru the carbs/airbox/pods is a rich condition. Opening those screws more has richened your mix, go back to TWO turns out, and try again. ALSO, did you SYNC the carbs after you had them apart and cleaned them? This is a necessary step, and the bike will not run smoothly if this has not been done.
 
Some thoughts..
1. How do the plugs look?
2. Did you vacuum sync the carbs?
3. When was the last time the plugs, wires and caps were replaced?
4. Did you check the boots between the carbs and the airbox with some
carb cleaner or wd40 to see if the idle changes?
5. When you cleaned the carbs did you take them apart, clean them and reassemble with new o-rings, gaskets..etc.
6. #1 cylinder cutting out could be carb related..is the pipe hot at idle?
7. What voltage are you getting at your coils?

Its been my experience that when these bikes don't run right it's because some maintenance issue(s) has not been performed. I can't tell you how many posts I've read on this forum where a guy will take a bike that has been sitting for 20 years, try and ride it and then wonder why the bike runs like crap. Even buying a bike from someone and you don't know the maintenance history is questionable. I'm not comfortable until I check each system out myself no matter what the PO claims to have been done.
 
almarconi said:
Some thoughts..
1. How do the plugs look?
2. Did you vacuum sync the carbs?
3. When was the last time the plugs, wires and caps were replaced?
4. Did you check the boots between the carbs and the airbox with some
carb cleaner or wd40 to see if the idle changes?
5. When you cleaned the carbs did you take them apart, clean them and reassemble with new o-rings, gaskets..etc.
6. #1 cylinder cutting out could be carb related..is the pipe hot at idle?
7. What voltage are you getting at your coils?

Its been my experience that when these bikes don't run right it's because some maintenance issue(s) has not been performed. I can't tell you how many posts I've read on this forum where a guy will take a bike that has been sitting for 20 years, try and ride it and then wonder why the bike runs like crap. Even buying a bike from someone and you don't know the maintenance history is questionable. I'm not comfortable until I check each system out myself no matter what the PO claims to have been done.
Click to expand...



  1. Plugs look white/light brown
  2. Vacuum synched with Morgan Carbtune after carb cleaning.
  3. Plugs new, wires and caps unknown.
  4. No, but I did a visual inspection and they are good with no cracks and still rubbery.
  5. Yes
  6. Yes, it gets hot. When I said it was not as hot as the others, i should have said it is still very hot.
  7. Unknown.
Thanks for the help. I really appreciate it. I hope this information helps.
 
p_s said:
Compression? Cam timing?
Click to expand...

Compression is 120 in first cyl. Cam timing, I have not touched... but runs pretty well considering the problems currently. I can pretty much rule that out.
 
Still think you're rich... Displays some of the problems (not the popping, but the needle lag at cruise speeds) as my bike is SOMEWHAT displaying, and i KNOW i am rich on that. Give the screws a full turn back and see what happens. Not tough to do. you've done your valves, youve sealed the intake, youve cleaned the carbs, and synced them. You're not far off...
 
Did you check all the vacuum hoses on the bike to make sure all are present and that there are no leaks?

As a check of the ignition system did you check the vacuum advance, I know on my KZ that this part requires periodic maintenance/cleaning. The part advances the timing above I believe 3k rpm, this will cause driveability issues if it is sticking. I would change the plug wires and caps since you don't know when it was done.

Check the voltage at the coils. Weak spark will cause problems. You want to see battery voltages at the coils. You may want to consider the coil mod if your voltages are below normal.

Check the carb boots with the cleaner to see if the idle changes when you spray the boots.
 
almarconi said:
Wouldn't the plugs be sooty/black rather than white or tan??
Click to expand...
not necessarily. Depends on how much time he spends in that RPM range. If its fine everywhere else, they will clean up. My plugs dont display a real rich look either, but running i can tell it is in a given throttle range. Mine are tanish, with just a slight touch of white/grey. At this point, if it is running well in other areas and otherwise, plugs are not going to give a good reading unless he is doing plug chops designed to show whats going on in a specific area of the throttle range. running around, in and out of the different circuits will not reveal much on the plugs. My suggestion was simple. If it doesnt work, then he knows that there is something else amiss. But, if its bone stock, 3 turns out seems a bit excessive. My 1100G runs about 2.25 to 2.5 turns out, and like i said, i KNOW im a little rich.
 
Rich... Maybe. That could be right and I will try it. It is a simple task.

As for vacuum lines. I only know of one vacuum line on a GS and that is to the petcock. That is working fine.

Also, the wires cannot be changed as they are hardwired to the coils. The caps can be, but compared to my last gs, they are looking good.

Thank you so far for the help. Definitely new ideas to me.
 
almarconi said:
Did you check all the vacuum hoses on the bike to make sure all are present and that there are no leaks?

As a check of the ignition system did you check the vacuum advance, I know on my KZ that this part requires periodic maintenance/cleaning. The part advances the timing above I believe 3k rpm, this will cause driveability issues if it is sticking. I would change the plug wires and caps since you don't know when it was done.

Check the voltage at the coils. Weak spark will cause problems. You want to see battery voltages at the coils. You may want to consider the coil mod if your voltages are below normal.

Check the carb boots with the cleaner to see if the idle changes when you spray the boots.
Click to expand...
Pretty sure, and i may be wrong, but all GSs had MECHANICAL advances. My 82 1100G doesnt have a vaccum line for anything except the petcock, and essentially its the same bike as his, with a bigger bore. I do agree with testing your plug wires, and caps. Might help to unscrew the caps, and trim back some of the wire, to expose FRESH wire and then rescrew the caps, since you have stock coils.
 
TheCafeKid said:
Pretty sure, and i may be wrong, but all GSs had MECHANICAL advances.
Click to expand...
Somewhere about '82 or '83 the ignition advance was built into the ignitor.

I see suggestions every once in a while on the board for somebody to get a Dyna system, but they also have to look up an advance mechanism for an older bike. :-k
 
I did unscrew the cap and replace it. I think it may have helped temporarily, but then the problem continued. I never thought of trimming the wire...
 
What I meant to say was the advance mechanism..I believe it is mechanical. It advances the engine timing as the engine RPM increases. They require periodic maintenance.

Maybe vent lines would have been a better term than vacuum lines..you know the line that hook up to the air box from the top of the engine..it has to do with emissions. The point I was trying to make is to make sure all the tubing was present and in good shape. This line was missing on my 750L when I bought it.

You can add new wires to your coils..NGK makes splices for this purpose. You can check the caps with an VOM to make sure you are getting the proper resistance.
 
I think I remember you saying that your intake boot o-rings were a little tight and you had to stretch them to get them on? Prolly wrong model and maybe replace with the right ones? Just wondering if you fixed that.
 
Diaphragms looked great. I did check for holes or tears and their was nothing.

The o-ring on the boots were small. They ended up being able to be stretched and are currently installed.
 
Just a thought. The air filter should be lightly oiled - and they do mean lightly. I thought I had gotten most of the oil out of mine, but the bike ran lousy until I took the filter back out and squeezed the life out of it, removing as much oil as possible. The filter still needs to be porous enough to let lots of air thru.
 
flyingace said:
Just a thought. The air filter should be lightly oiled - and they do mean lightly. I thought I had gotten most of the oil out of mine, but the bike ran lousy until I took the filter back out and squeezed the life out of it, removing as much oil as possible. The filter still needs to be porous enough to let lots of air thru.
Click to expand...


What I did with my filter, because I didn't know, is put about two tablespoons of engine oil in my hands and rubbed it in. There is definitely not enough oil to squeeze out, but just damp.

Since we are talking about the filter, how does it sit in the box. It is just a foam filter. There is no housing like shown in my manual. Which way is it supposed to sit?

What is the breather hose for on the left side of the airbox for? How is the hose supposed to hook up?
 
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