Backfire / Rich condition after sealing airbox. Airscrews?

[uudfourty]

81 GS550
This weekend:

Sealed airbox with foam weatherstripping. Maybe a how-to for the newbies later.

Cleaned and lightly oiled the filter.

Changed intake boot O-rings. (they weren't cracked or leaking, but I didn't know their condition. Peace of mind.)

Replaced all connections on R/R with spades and, when I felt like it was necessary, solder.

Same thing with Dyna S connections.

Put vent hoses on carbs so I could pull the old "blow in the vent" trick instead of using ether until I get my valve shims from z1. (Whoever it was that suggested drilling a wee hole in the side of the airbox and sealing it with a wood screw to give quick ether access... brilliant!)

Replaced Clutch cable

That's all that changed.

Took it for a ride to see what difference was made-- now I have a backfire. It's not necessarily on acceleration, and not necessarily on deceleration (after I've been hauling ass, then let off the throttle, let it coast a bit, then when I first open it up again: a single BOOP from the left hand pipe.Then and only then, and not every time.)


Plugs look like I've been running rich, but that was going on before the adventures in airbox sealing.

Question 1: Will simply adjusting the air screws to a more lean setting fix this.

Question 2: I'll be changing some valve shims then proper synchronizing the carbs in about a week . If I adjust the screws now, will I have to adjust them again later or will it not make any difference?

Question 3: Since I've sealed the airbox, whenever I start it, it surges to about 3.5k RPM right off the bat, then settles back down to 15k or 18k in about 2 seconds. I don't touch the throttle when starting, and it's warm enough that I haven't needed a choke for the last month. Normal? Poltergeist? Leftover cocaine?

Question 4: On the bottom of the airbox is a nipple for a vent. Is it imperative that there be anything hooked to this, or is this just to keep... I dunno, air from leaking on my boots?

Thanks in advance for your sagacious wisdom. Free half a pitcher of Lonestar (Guinness, PBR, St. Arold's Amber, Iced Tea, Lemonade, Water or Colt 45) for whoever answers all 4 first.

GO!


P.S. Airscrews currently at 2 from seated. Except for frozen #4, which remains where it will forever remain.

 

[uudfourty]

bump-a-rump

 

[Guest]

i'll have the iced tea, thank you :-D

1 adjust the shims
2 set the pilot mixture screws as per highest rpm method (see basscliff website)
3 sync the carbs

tell us the results


nothing need be hooked up to the airbox vent

 

[chuckycheese]

Carbs

Carbs

I think your problems are TOTALLY within the carbs..,not the airbox, not the air filter, not the intake boots, not in the R/R and not in the clutch cable .....only in the carbs.

These bikes are tough; they will run fairly well with air leaks, dirty air cleaners, crappy gas and all kinds of other stuff, but the carbs are totally unforgiving. They need to be jetted correctly and they need to be clean and clear.

 

[TheCafeKid]

Correct. Messing with your carbs now, before your valves are adjusted is an exercise in futility. When your valves are properly adjusted, things will change pretty drasticly. Adjust, then start messing with the carbs.

In your situation, given that this rich condition cropped up AFTER you went to sealing the intake boots (if you werent sure of condition, i would bet they had at least a small leak) and sealed up the airbox. Likely what has happened here is that the carbs have been tinkered with to get it running with the leaky intake system. Now that you've plugged all that up, they are rich. Once your valves are adjusted, i would suggest turning your adjustment screws all the way in till LIGHTLY seated, then back out 1.5 turns, if that seems lean, try 2 turns. Considering, at this point, you are now dealing with a STOCK bike (ie, propperly sealed airbox, valves within factory spec, intake boots sealed) you SHOULD be just about golden with this adjustment, UNLESS someone has futzed around with the float levels in the carbs. If, after changing your airscrews, you still seem rich, i would turn my attention to the float levels. Let us know how it goes.

 

[uudfourty]

Thanks guys. Pretty much what I figured, but wanted to check.

Though it may backfire, it idles, starts and runs better now.

i'll have the iced tea, thank you :-D

I'll just mail you a tea bag. I dunno when I'm going to be in NZ again. :-D

 

[Zooks]

He only answered 3.

I can answer all 4

1. Dunno
2. Dunno
3. Dunno
4. Not sure

 

[chuckycheese]

Leak

Leak

When I bought my GS1100, the bike was in really great shape but it had some issues. All 4 of the intake boots were split, 2 or them were split more than 1/4 of the way around. In spite of that, the bike ran surprisingly well.

I've done a whole bunch of stuff to it including putting on new boots and rebuilding the carbs and it runs like new. But, I was impressed with how well it ran even with problems. I think the reason was because the carbs were clean and in pretty good shape. I agree with Cafekid about adjusting your valves....it's quite important.

 

[catbed]

1. yes
2. possibly, and most likely
3. rich condition, fixed with mixture screw.
4. there should be a long hose with a pinched end, lets fluid out, but not air in.

 

[Guest]

zooks, mate you never fail to give me a good laugh!!!

keep em comming :-D

He only answered 3.

I can answer all 4

1. Dunno
2. Dunno
3. Dunno
4. Not sure

 

[uudfourty]

He only answered 3.

I can answer all 4

1. Dunno
2. Dunno
3. Dunno
4. Not sure

Well, fine. Fosters for you, Lipton for psy, I'll have what's left.

4. there should be a long hose with a pinched end, lets fluid out, but not air in.

I'd guess that a chunk of hose with a bolt stuck in the end of it as a plug would do the trick. If I've got fluids in there, the machine will let me know.

Thanks y'all.

 

[Dogma]

Question 4: On the bottom of the airbox is a nipple for a vent. Is it imperative that there be anything hooked to this, or is this just to keep... I dunno, air from leaking on my boots?

On mine this tube exists for when you follow the factory service manual instructions for oiling the air filter. I didn't use a 200 ton press to get the excess oil out, so it went through this tube on it's way to the center stand and then the garage floor the next day. Anything excess that got through the crankcase vent without being ingested by the intake would theoretically flow out this tube as well.

 

[uudfourty]

Alright, I've got the valve clearances all at .05mm or more.

I've got the mixture screw on #1 cylinder screwed all the way in, and I am still running lean on that cylinder.

Fire is strong, and I didn't have this problem before sealing the air box.

The float levels were checked 2 years ago when I first got this thing to run.
Dyna S, Green Dyna Coils, Clean and slightly oiled air filter....

Remember... everything was A-OK before I sealed the air box.

Soo..... what gives? Any ideas?



I'm reading the plug to come to this conclusion. It's not reading like I'm getting oil in my cylinder and burning that up, and it's not smoking, but it is still freaking backfiring like the original post.

I'll try to synchronize the carbs tonight, as I've still got a slow-to-warm #2 cylinder.


Will carbs out of synch give me backfire after sealing the airbox?

 

[82Shafty]

I pulled the air filter out of mine to see if it would no longer pop and the bike came alive... Filter was over oiled.

I cleaned filter, lightly oiled and the bike runs great!

My valves were just checked/adj, new orings on boot and inbetween carbs, carbs dipped, synch'd idle adj, new NGK boots, coil relay mod, you name it brother I did it.

 

[uudfourty]

GREAT!

Bike ran really erratically on the way home.

Got home, went to synchronize the carbs.

Now it's all screwed up.

I bet I couldn't ride around the block if I felt like it.


Is there some kind of zero point for the idle synch?

 

[bwringer]

I've got the mixture screw on #1 cylinder screwed all the way in, and I am still running lean on that cylinder.

Um... yer backwards there -- OUT is rich, IN is lean.


Also, were the carbs rejetted before you got the bike? The only way to know is to look at the mains, pilots, and needles and compare these to what they should be stock. This info is normally on the microfiche in the descriptions of the parts -- it'll say something like "JET MAIN 110" or whatever.

 

[bwringer]

Is there some kind of zero point for the idle synch?

Yes -- look up "bench sync". It's what you do when reassembling carbs to get the sync in the ballpark so you can start the bike.

However, synchronization will not cause or fix the symptoms you are having. It has nothing to do with mixture -- it simply means fine-tuning the linkages between the carbs so that the throttles all open at exactly the same time. A bike will actually run and ride fine even if it's badly out of sync, but it will sound and feel a lot smoother, especially at idle, when you take care of this last step.

You need to back up and verify whether or not you have stock jetting, since you returned to stock intake and (I think) stock exhaust.

It would also be an EXCELLENT idea to completely disassemble and clean the carbs and replace all the o-rings per the Carb Cleanup Series. In fact, farting around further without doing this is pretty pointless. Since you hadn't removed the plugs over the mixture screws before now, I bet you tried to get away without this.

There's therefore no way to know how elderly the o-rings in the carbs are. The tiny o-ring around the idle mixture screw in particular will create all sorts of problems when it deteriorates.

Finally, if the carbs have been rebuilt with kits, this may be causing some of the problems. Carb kits are well-known to include shoddy out-of-spec imitation parts, and if the jets have been replaced with shonky kit parts, there's no way to tell what's really in there, and they definitely won't work right (Guess how I know this? Go on, guess.).

Carb kits are a complete waste of money -- all you need to rebuild is a $15 o-ring kit from our pal Robert Barr ( http://cycleorings.com ) and possibly float bowl gaskets, which are about $3 - $4 each.

 

[Steve]

Alright, I've got the valve clearances all at .05mm or more.
"or more"? Hopefully not much more than .09mm, specs call for a max of .08mm.

I've got the mixture screw on #1 cylinder screwed all the way in, and I am still running lean on that cylinder.
That would be NO surprise. Turning IN leans it out, turning OUT richens. Try 1.5 turns, since your original post said you were at 2 turns.

Fire is strong, and I didn't have this problem before sealing the air box.

The float levels were checked 2 years ago when I first got this thing to run.
Levels checked 2 years ago? Why not more recently?

Dyna S, Green Dyna Coils, Clean and slightly oiled air filter....

Remember... everything was A-OK before I sealed the air box.
Apparently things were adjusted to compensate for the air leaks. Sealing the leaks is now making it a bit rich.

Soo..... what gives? Any ideas?
Another common cause of backfiring is leaking exhaust gaskets. The clamps might be a bit loose or the gasket itself might be faulty. Be careful, those clamp bolts are VERY prone to breaking off. :shock:

I'm reading the plug to come to this conclusion. It's not reading like I'm getting oil in my cylinder and burning that up, and it's not smoking, but it is still freaking backfiring like the original post.

I'll try to synchronize the carbs tonight, as I've still got a slow-to-warm #2 cylinder.
One cylinder that is slow to warm could be out-of-sync or might have dirty pilot jets. Check again after the sync to see if it warms quicker.

Will carbs out of synch give me backfire after sealing the airbox?
Carbs out of sync should not cause backfiring. What they will do is cause rough idling and ragged response just off-idle. You will also notice a buzziness in the handlebars due to uneven firing pulses. I know you don't have one, but the 1000s and 1100s seem to be more sensitive to carb balance to run smoothly at speed.

 

[uudfourty]

I mistyped: The mixture screw is all the way in and it's still too rich. My bad.

Got the synchronization squared away and leveled out. It does run much better since I adjusted the valves and whatnot...

But it still idles weird, so apparently not all is well in the state of Denmark.

I'll have to go back and re-set to the highest speed method I suppose, but If number 1 carb is still way to rich (sorry again) with the screw all the way in, what's that indicative of?

And... somehow.... the backfiring is gone.

It wasn't gone after I adjusted the valves, went away last night after I leveled off the vacuum on the carbs...

Hang on a second while I go get another job.