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bogging and backfiring

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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Hi all, I am new to the forum and new to my GS450 bike. The previous owner abandoned the bike and has left it for me and my fraternity brothers to use. I have not spoken to him recently and thus do not know what year it is. I do know that it has CV type carbs. I have done a full cleaning on the carb. It has very good spark (new plugs too) and compression and always starts on the first try. Here are the problems: It backfires, mostly when letting off of the throttle, at all rpms. Also, it idles fine (except for the backfiring) and runs great at high rpms (cruising on the highway) but bogs alot between 1000 and 3000 rpms. To get around this I have to get it up to 3k rpms before taking off (if I let off the throttle and try to give it more gas again it bogs). Sometimes when I rev the engine it will "stick" at 3k rpms but will come back to idle if I rev it up to about 5k or 6k rpms (the throttle cable is not sticking, I quadruple checked it). I have checked the floats and the needles are not sticking, and the bowls are getting plenty of gas. Another thing to note is that I have drilled the (air screw?) plugs out, but have not yet tried adjusting them as I do not know if this is the problem. Everything on the motor is stock. I have spent 2 weeks trying to get her to run right but the low rpm range just plain sucks. Any help would be greatly appreciated as I am at a loss as to what is the next step in diagnosing these problems. Thanks in advance for any replys.

Chris
 
Re: bogging and backfiring

The symptoms you describe would be the result of an induction tube leak on the induction tubes between the carbs and the cylinder head.
Doe your engine have "spigots" on the cylinder head and use round sections of "hose" to connect the head to the carbs, or does your engine use a flanged end induction tube? If a flanged tube, then there is a groove in the flange for an "O" ring seal and that sealing ring is probably dried out and cracked.

Earl



biznaller said:
Hi all, I am new to the forum and new to my GS450 bike. The previous owner abandoned the bike and has left it for me and my fraternity brothers to use. I have not spoken to him recently and thus do not know what year it is. I do know that it has CV type carbs. I have done a full cleaning on the carb. It has very good spark (new plugs too) and compression and always starts on the first try. Here are the problems: It backfires, mostly when letting off of the throttle, at all rpms. Also, it idles fine (except for the backfiring) and runs great at high rpms (cruising on the highway) but bogs alot between 1000 and 3000 rpms. To get around this I have to get it up to 3k rpms before taking off (if I let off the throttle and try to give it more gas again it bogs). Sometimes when I rev the engine it will "stick" at 3k rpms but will come back to idle if I rev it up to about 5k or 6k rpms (the throttle cable is not sticking, I quadruple checked it). I have checked the floats and the needles are not sticking, and the bowls are getting plenty of gas. Another thing to note is that I have drilled the (air screw?) plugs out, but have not yet tried adjusting them as I do not know if this is the problem. Everything on the motor is stock. I have spent 2 weeks trying to get her to run right but the low rpm range just plain sucks. Any help would be greatly appreciated as I am at a loss as to what is the next step in diagnosing these problems. Thanks in advance for any replys.

Chris
Click to expand...
 
bogging and backfiring

I don't really understand how to tell what kind of induction tubes I have. There are 2 screws holding the tube to the jug and the tubes go out to the carbs, when I put the carbs in there is a groove on the carbs that the tubes snug into, there is a clamp on each carb side of the tubes. I synced the carbs today and got it to stop reving itself up and sticking at 3k rpms, but anything from idle to 2.5k is bogging. As a test i sprayed some starter fluid around where the induction tubes meet the jug and it didn't rev up. I was reading some other posts about similar problems and some have said airscrew adjustment but my plugs are a nice brown and others have said that some air pilot jet may need to be adjusted but my carbs have no such jet. Anyone have any ideas, I am baffled. I guess if its the only option I'll have to check out the seal from the tubes to the jug.
 
Biz,

Earl is talking about this O-ring (red arrow)

486754cylhead.gif
 
Hey Earl,

Sorry about that......but just had too darn many people always confused about what o-rings you meant :) :) :) :) :) :)

As many times as it comes up, hell......it should be right under the "Carb Cleanup Series".
 
Hey, I ws serious. You saved me many paragraphs of written explanation.
I'll take all the help I can get. ehehe thanks again

Earl


frosty5011 said:
Hey Earl,

Sorry about that......but just had too darn many people always confused about what o-rings you meant :) :) :) :) :) :)

As many times as it comes up, hell......it should be right under the "Carb Cleanup Series".
Click to expand...
 
bogging and backfiring

Thanks for the info, I had checked out from some other posts what those O rings were and how to check for a bad one (gap in the ring). Took the bike out today and rode her around for about an hour. I noticed a fuel smell, but no gas is leaking from the float overflow tubes and the plugs are not fouled. Am I supposed to be smelling a little gas, could it just be the exhaust?. Just thought I'd let you guys know cuz I never noticed it before. After my finals I'm gonna pull those flanges off and check those O rings. Another thing to note is that the clamps from the carb to induction tube seem like they bottom out before they really start squeezing the tube to the carb, how tight are these things supposed to be? Thanks guys

Chris
 
I have a friend who's GS850 had a crack in one of the induction boots, and it would spray gas out of it, and onto his leg. I imagine a bad o-ring could do the same thing.
 
Re: bogging and backfiring

Chris, considering the age of your bike and the probability those "O" rings have never been replaced, I think it would be a good idea to Bite The Bullet, and spend the big bucks for new ones. Two "O" rings should grand total out at about $2.50, and you will no longer have to wonder. :-) :-)

If youre smelling gas, there are only a couple possibilities. Leaking petcock, leaking or loose fuel line, leaking float valve seals. floats set to too high a level and the overflow tubes dripping. Bike stored in a hot place and fumes leaking from the gas tank vent.

Earl


biznaller said:
Thanks for the info, I had checked out from some other posts what those O rings were and how to check for a bad one (gap in the ring). Took the bike out today and rode her around for about an hour. I noticed a fuel smell, but no gas is leaking from the float overflow tubes and the plugs are not fouled. Am I supposed to be smelling a little gas, could it just be the exhaust?. Just thought I'd let you guys know cuz I never noticed it before. After my finals I'm gonna pull those flanges off and check those O rings. Another thing to note is that the clamps from the carb to induction tube seem like they bottom out before they really start squeezing the tube to the carb, how tight are these things supposed to be? Thanks guys

Chris
Click to expand...
 
bogging and backfiring

I found a site that has lots of parts for gs450's (including those orings at 5 bucks a set) but I have no idea what year or specific model it is. Does anyone know how to identify the bike? The only things I found were on a plate on the motor "GS450 113309". Thanks

Chris
 
Chris / Biz,

You don't have any mfg date stamped up front on the frame anywhere? How about paperwork with the bike?
 
bike identification

bike identification

No paperwork as of yet (gotta wait till my bro mails it to me). Where abouts on the frame should I be looking, should I pull the gas tank off?

Chris
 
Usually there's a plate riveted/attached up on the frame, in the front, by the steering stem.....with all the appropriate info on it (behind the headlight).
 
identification

identification

Thanks for the tip, found out she's an '80.

Chris
 
bogging and backfiring

Ok guys, so I installed new "O" rings on the induction tubes (the old ones were flat and there was gas under them), and got tighter clamps on em, but the bogging and backfiring persists. Still no idea whats causing the problem. Anyone got any ideas?

Chris
 
Chris,

Don't really know what to tell you. Any idea when carbs were cleaned last? Are you running bike with or without fuel filter?........Doesn't take much to start clogging jets. You said you checked floats.......so, we know that they're not stuck, but how about the float heighth? The backfiring during the letting go of the gas could also be due to leak in the exhaust system (perhaps where the pipes attach to the headers).

If it were my bike, I would probably give the carbs a good cleaning. While I had them off, I would have checked/replaced the o-rings under manifold (which you already did). Then during reassembly/reattachment, I would ensure good fuel flow to the carbs (making sure that there are no crimped fuel lines and/or vent lines). Then, after running - I'd check plug colors to see whether mixture screws need any adjustment. If all that didn't work, then I'd start looking at the electrical system.

Wishing you the best of luck, hopefully someone else will have more insight.
 
Re: bogging and backfiring

What color is the center ceramic on your spark plugs ? If you are running lean, it will be very light, if rich, it will be much darker. Which is it?
When you are riding the bike, what rpm does this symptom start at and what rpm does it end at? Do you have the stock aircleaner box (with lid) and element in the box? Do you have stock exhaust pipes? Do you know what your idle air screw and fuel pilot screws are set to?

Now that we have the "O" ring question solved (the first step) I need to know what the situation is with the air intakes on both sides of the carbs (the airbox and exhaust system) Thats why my further questions. Everything works together as a system and you cannot step into the middle without knowing what is happening at both ends.

Earl





biznaller said:
Ok guys, so I installed new "O" rings on the induction tubes (the old ones were flat and there was gas under them), and got tighter clamps on em, but the bogging and backfiring persists. Still no idea whats causing the problem. Anyone got any ideas?

Chris
Click to expand...
 
bogging and backfiring

The carbs were cleaned about 2 weeks ago, and its behavior hasn't changed since then. No fuel filter (just the one in the tank). Dunno about the float height, I have no specs as far as that goes, but there is no fuel coming out of the overflow tubes. The exhaust is pretty blown out, each pipe has a hole near the end, the manifold side seems fine, bolts are nice and tight. Mixture screws are at factory setting, and fuel is flowing to the carbs (petcock is operating properly). Spark plugs are very light brown. The bike idles fine at 1k RPM, any additional throttle makes it bog down. I quick flick of the throttle then letting go will increase the RPM's to about 1750-2000 RPM, if I hit the throttle right when it peaks at 1750-2000 RPM, it will rev up like normal. The bog is much worse when the engine is under load (in gear). The air box is stock but has no filter. I have put foam in there to see if it helped but had no effect. As I said before, the bike runs great once I get it opened up but low RPM's are just bogging. Thanks for any help fellas.
 
Chris,

Again, I'm just guessing here, but trying to get a GS engine running perfect without a proper air filter can be a very tricky affair.
 
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