Idle, mixture, and backfiring on decel after carbs were "balanced"

[Guest]

Hey everyone.

Been riding my gs650GL for a little while now (2 months). Rode it up to Santa Cruz from San Luis Obispo (about 180 miles) and it ran like a champ, despite the 20-40mph gusty X-winds...

I noticed on the trip, and around town that when I decelerate, especially when the bike isn;t completely warm, I get some minor backfires. Most of them are pops, never a real BLAM.

It also smells a little rich after starting and with the choke off.

The last thing I noticed is that my idle dropped too low when it rained. Too low as in I had it die on me after shutting off the choke and worried it would die for the rest of the ride. I had to give it gas when I took off from my first stop.

Does that sound like the carbs are set too rich to you guys too, or is it a good idea to keep them pretty rich in the event of hot weather or hard riding? The temp dropped from mid-80's to mid-50's when it rained, but I don't know if this is a reasonable change.

I had a shop diagnose engine noise (loose cam chain) and balance the carbs, but they seem too rich to me now.

Feedback from the experienced would be great.
William

[kwi0102]

Not that I have a buch of experience, but it sounds like you're running a little lean ???
Have you checked the plugs ??? There are some great visual picture references for spark plug conditions ... A pretty clean & white insulator might indicate a lean combustion.
Maybe start with all the air box stuff (new seals & gaskets), plus intake O-rings (BassCliffs site is a great place for this info http://members.dslextreme.com/users/bikecliff/ ).

Good luck ... Maybe someone with a bit more experience may shed some light ...

[WilliamGLX81]

Anybody else?
I'm fighting off a sinus infection, so I'm pretty sluggish. I might pull the plugs though, they started bogging on me at high revs 2 nights back.... >.<

If it turns out the carbs are rich, how am I going to change that? Smaller jets? Adjusting the flow-balancing screws? If I adjust the screws, I bet I'm going to lose the balancing, right? Or is the syncing simply adjusting them all to the same throttle opening? I thought it was synching the vacuum flow on them all.

They did do something to the carbs because it ran a lot better when I got it back than it had before I took it in.

I'll check the plugs either today or friday, since I plan to ride to Santa Cruz to visit family this weekend. Can't have it bogging on me on the highway.

Is there a rev limiter on the bikes, or is will it just rev higher till it comes apart? My tach stopped working... either the cable broke or the sender in the head is toast. Got a number of things to check.

[rustybronco]

Hey everyone.

Been riding my gs650GL for a little while now (2 months). Rode it up to Santa Cruz from San Luis Obispo (about 180 miles) and it ran like a champ


It also smells a little rich after starting and with the choke off.

The last thing I noticed is that my idle dropped too low when it rained. Too low as in I had it die on me after shutting off the choke and worried it would die for the rest of the ride. I had to give it gas when I took off from my first stop.

I had a shop diagnose engine noise (loose cam chain) and balance the carbs, but they seem too rich to me now.

If you eyes and nose tell you they're running rich, listen to them, they probably are...

did the shop adjust the idle mixture screws when the carbs were balanced making them too rich at idle?

and, most likely, you will have to something more to your carbs, as in clean and adjust them properly.

[Dave8338]

It does sound rich and NO, there is no rev limiter (unless you count your right hand). Also when the temps drop, the bike will tend to run leaner, not richer. Can you tell if the backfire is through the carbs or the exhaust? Often times an exhaust leak will cause a backfire on decel. Also, it sounds like you had it running better BEFORE you took it to a shop. True? The plugs will be black if it is running rich. White if lean.

Stock exhaust and air box?

[spyug]

Popping on deceleration is a sure sign of air infiltration on the exhaust side. Are your pipes on tight and are there gaskets in place? It can also occur at the joint between downpipe and the muffler or at the cross over tube if fitted. Rust holes in the undersides of pipes even as small as a pin hole can cause this. Also look for black exhaust marks near any joints as this could show leakage.

The carbs could be set a bit rich but unless the jets have been changed up that would be limited. You may notice a bit of smell at start up but that would go away as it warms up (if indeed there is a bit of lean condition also present to balance things out). Reading the plugs may not tell you much unless they are light tan to white indicating overlean.

Usually if the bike is rich you will notice gas smells when idling at stops and even sometimes when riding along. In addition gas mileage will be poor.

Have a look for any indication of air leaks and eliminate any. Your popping should stop.

cheers,
Spyug

[WilliamGLX81]

Thanks for the replies.

Uh.... yeah, maybe it's time to get that muffler welded on finally....

Until then, I'll presume it's that. I got the bike with a broken exhaust stud and a ruined header on the #1 (from left while seated) cylinder. Replaced it with a nice shiny one, but I have yet to get it welded on. It's in place, but not sealed.

The bike felt a whole ton better after I took it to the shop and got it back. Power delivery was irregular before I took it in and it felt like power was uneven between cylinders.

That's right, it should be leaner when cold. Maybe the exhaust just tends to hang around a little longer, or I leave it on choke longer to warm it up.


I can smell gas at some stop lights. Not infrequently. If I change the idle air screws, am I going to un-balance the carbs? AFAIK adjusting the idle mixture is all I can do, and tuning the carbs requires different jet sizes past that.


The carbs had to be completely disassembled and cleaned before the bike would idle off choke. Very thoroughly cleaned and checked. A few o-rings could do with replacing, but they're not 100% shot.


I should get my tach working again with a new cable. Then I'll know if it's just a misperception that it's bogged out at 6k or if I really am running it pretty high.
Is there a speed beyond which it just won't rev any higher? Or is something wrong if I can't rev it to destructive speeds.... lol.

[spyug]

[QUOTE) If I change the idle air screws, am I going to un-balance the carbs? AFAIK adjusting the idle mixture is all I can do, and tuning the carbs requires different jet sizes past that.
[/QUOTE]

I'm not sure what you are asking /saying. Setting the mixture screws is the first step in balancing the carbs. Generally, the screws are best set at 2.5 turns out for optimum idle. That's to say the screws are turned in all the way until bottomed out then backed out the 2.5. They should be set the same. Setting them to different levels will throw the balance off.

To balance the carbs you will need a manometer (vacuum guage) which will be attached to the ports on the intake manifolds of the head. There is a set screw with lock nut on the connectors between the carbs. Loosening off the locknut allows the set screw to be turned in and out. With the engine running and manometer attached the screw is turned in or out until the manometer shows the carbs drawing the same level of vacuum. The carbs are then "balanced"

Jets have nothing to do with carb balancing unless one carb carries significantly different jets than the others.

You mention that the o-rings could stand to be changed but haven't been. I would suggest that you do this as they may appear ok but aren't providing a good seal. Any air getting in where its not wanted will cause issues.

Hopefully this helps abit and your getting to the bottom of it.

Good luck,
spyug