1980 GS 450 BOGGING, LOSING POWER, MAKING LOW RUMBLE and STALLING

[William P. Guff]

Hmmm your initial description of the symptoms definitely sounded like mine on one cylinder, but the further descriptions make it sound less like that now...

When it starts happening, have you tried popping your fuel cap off to see if that fixes it?

What Skreemer is saying is that if there is no vent for the fuel tank, as it starts using the fuel it needs to replace the volume with air. If that can't happen, then the fuel stops flowing because it essentially creates a vacuum that holds the fuel in the fuel tank, just like if you try to pour water out of a container that has no vent in it...

You know I had noticed something whenever I got on my bike. I'd warm it up on choke while it was still on center stand. Then I'd get on it and rock the bike down to go.

And I would notice a hissing, vaccumy sound from the gas cap.

You think that might be a factor. Should I try to start the bike with the cap off?

I only have one key to the ignition, so taking the cap after starting is not an option.

[William P. Guff]

But again how many things could cause that sound ,(BRRGGGHHHHUUH), and instant, but fleeting, loss of throttle?
lots of things can cause that. Lots and lots. I think the folks here doing a great job of blasting the birds out of the air, but somebody- you or your mechanic-has to start plucking them. I bet your mechanic groans when you show up.

I appreciate all the help. And you are right, my mechanic is not too thrilled when I call. But I'm writing down the stuff you tell me. Thanks again.

[William P. Guff]

I see the Champion decal- what kind/brand of spark plugs are you running?

I have NGK spark plugs. And the small red stickers on the tank edge say NGK spark plugs. I bought Champion plugs locally but have not used them....yet.

They are in the tool roll on the bike. I have heard that Suzuki bikes run better on NGK. But after the NGK die, I'm replacing them with Champions.

[William P. Guff]

Progress Perhaps?

Well today I took off the gas cap and started the bike, as I read that it may be a vacuum type problem.

When the bike started I did not have to choke it, because it was so hot out.

So when the bike stared I noticed a bunch of tiny bubbles moving in the gas, like ooooooooooooooooooooooo I mean literally about the size of the o's you see to the left.

They stopped in about 30 or so seconds, and there was just a vibrating wave of gas moving like normal.

I left it on centerstand and took it from 1st all the way to 6th with no problems or bog sounds.

I turned the bike off put the gas cap back on. Then I got on the bike as both pipes were hot as hell, and went about 3/4 mile to the store, and I GUNNED IT at one light to silence some cigar chomping guy in a souped up Miata....... and NO PROBLEMS.

Went into the store and got back out. Took the gas cap off, put it back on and went.

But at one stop light it did the bog...but only briefly and threw me back up to speed. Then I went to another place stopped went in and out, to no problems.

Then I went home ate, and went on the highway where it gave me problems before.

I went gingerly at first, but on the way back I blasted past this young punk in a green Acura integra, with the fart beetle sounding upgrade engine...left him in the dust went all the way to 6th gear....NO PROBLEMS or bogging.

But then I got back into town after that full blast and the RPMs dropped again at one light, sending me into a panic because these young women were looking at me and the bike the stop light.

I was like "oh great. This is bad PR if this damn thing stalls"

It began to make the loud bog, but I managed to pull out of it. And again at the next stoplight I tried to beat this guy off the line to get ahead of the closed lane.

I got to third and the BOG agaain! But I still managed to keep the RPMs up enough to avoid stall.

I retreated to another avenue where the bike returned to normal RPM and made it home.

But Im thinking the problem is related to putting the bike up on centerstand and then knocking it down to the tires causing some kind of pressure thing to affect flow.

Anybody have any ideas? I think I can at least run errands safely if I routinely start the bike without the gas cap on. But thats only a temp fix.

[Gorminrider]

The "hissy vacuumy" sound is ok. That means your vent is ok.
Reason is, if you lay your bike down, gas will not come flooding out the cap,and make a nasty scene, because it's a "leak" just big enough for air to account for gas going into carbs...

it'd be interesting to know what you did here:
"It began to make the loud bog, but I managed to pull out of it"

and be careful .Girls don't want the bodily fluids of dead guys.
The guy on the vespa will pick them up while they're gawking at your accident scene....

[William P. Guff]

it'd be interesting to know what you did here:
"It began to make the loud bog, but I managed to pull out of it

I pulled in the clutch and kept the throttle and rpm's up. A delicate balancing act. If I didn't the bike would stall.

And when engaging the clutch, the bike would move, but sluggish at very high rpm. Suddenly it would get back to normal throttle, and I could operate it at regular shifting.


Today though I did the same thing as yesterday. But I limited my shifting not going beyond 4th.

I was able to get around with no problems until I tried to pass a truck.

This truck coincidentally happened to be my ex girlfriends Dads truck. Its a truck that I hadn't seen in years.

I consider the truck as a steed, and them as people, that I really would prefer to avoid. Not that they're bad people, its just to avoid the coincidental awkward run in.

Human nature.

So of course the bogging happened as soon I went to 5th gear for the first time all day, and tried to get past them. Thus sending me swiftly to a side street where the bike toiled to get me home.

The good thing was that because I couldn't pass the truck, they might not have seen me. So maybe I should thank the bog......

......this time.

Obviously it is a change to a certain gear that makes it happen. Last time it was 3rd gear.

Now its 5th.

And I was able to get around for 2 days without too many bogging instances. But the COUNTDOWN has begun.

Last time it was a few days living with the bog....but pretty soon when I started the bike the bog happened and I couldn't get out of the parking lot.

So the sequence begins again. Soon the bike will not go anywhere. After the football game was over I got on my bike and a block later it was bogging.

Any remedies? A cure all?

Or a procedure that might make it run regardless if the bog is not precisely identified.

Sort of like when a computer gets a virus and the whole thing is wiped and re installed?

[William P. Guff]

Well today I tried the same procedure that I tried the first time this happened.

Today,though, the results looked promising.

I unscrewed the carb bowls, and drained the gas in them. I then added to the gas tank the Star Tron additive that my mechanic gave me the last time this happened.

So I tried to start the bike after this and no luck. After about 25 or so no starts, I began to adjust the idle screw. Then it started.

I took it around the block but the bogging wasn't quite resolved. Plus the rpms were not stable and immedialey dropped to stall as soon as I loosed throttle.

So I pulled in the lot and put it on center stand and proceeded to loudly take it through all speeds trying to force the gas and Star Tron through.

The pipes began smoking from chain lube drippings, so I just parked it for a few hours.

I then came back out and tried to start the bike several times. Each time adjusting the idle screw until the rpms stabilized and the bike actually idled.

I took it around the block and immediately noticed that the Star Tronwas doing what it was supposed to do and I felt that the bike was actually running well.

I then took it on the hi way for about 1/4 mile and it did ok until I turned off to turn around. I put it in 2nd and it bogged for a second, but it went right away.

So tomorrow I hope it can get me around town. Ill post results hoping someone will give me advice based on the symptoms that Im describing.

[Big Rich]

I'd like to point out: it's not a problem with what gear the transmission is in. Transmission problems are completely different than what you are describing. The engine itself is working just as hard at 4000 rpm in 3rd gear as it is at 4000 rpm in 6th gear (relatively).

What size jets are in your carbs now? Any shims under the needle clip? Air / fuel mixture screw still at the stock setting? Float height set to the stock setting?

What all this boils down to is this: somebody has to work on your bike. It is almost 34 years old now. If you don't want to work on it, and your mechanic doesn't want to be bothered with it, then you should probably sell it to somebody who is willing to do the work to keep it on the road.

[pete]

Things I can think of that could be disturbed by some additive to the fuel and draining the float bowls...

- Rust in the tank.
- Inline fuel filter between tank and carbs that isn't flowing properly.
- Faulty fuel tap/petcock that isn't flowing properly.
- Improperly cleaned carb's, or carbs being fouled after being cleaned by rusty/dirty tank or bad fuel.

Also, when you drain your float bowls, you will need to prime your carbs before trying to start the first time, otherwise you will experience what you did where it will take a long time to be able to fire up. Priming the carbs lets fuel into the float bowls without needing the vacuum to open the fuel tap.

Your fuel tap will either have a PRI position or it will have no PRI position but a brass flat head screw beside the tap. If you have the screw, turn counter clockwise a couple of turns to open it up, wait 30 seconds, then tighten it gently again. Carb's primed.

I will also give Rich's comments a +1 on this... either find a good mechanic who likes working on these old bikes and has the patience for it, or learn to do it yourself, or get a different bike.

Most mechanics won't be interested unless they've been working on these for many years and like the older bikes.

Most people on this forum have learnt to wrench themselves, even if (like me) they are not mechanically minded and have never done so before...

[Gorminrider]

pulled in the clutch and kept the throttle and rpm's up. A delicate balancing act. If I didn't the bike would stall.

see, to me, this sounds like a cylinder has dropped out...

And when engaging the clutch, the bike would move, but sluggish at very high rpm. Suddenly it would get back to normal throttle, and I could operate it at regular shifting.

and this sounds like it kicked back in. But I'm just a brain-in-a- bottle on the internet with no fingers to feel or eyes to see what you are.

I hear what you're saying about the gear-shifting causing it...I am thinking though that it's not the gears themselves(or, I hope not!)- I'm thinking it's the change of throttle during the shift....and that's about the carbs,or even the spark...perhaps the spark advance mechanism is sticking- it's rev-dependent and it getting stuck would lose power. It's easy to inspect, too.

[esmithers]

Sounds to me that you have coils or coil that is breaking down (thermal) i have had this happen before and it makes diagnosing problems a hassle look into getting some decent used or new coils and see how the bike runs. I would also look at changing the plug wires and cleaning up the contacts in the plug boots

[William P. Guff]

Sounds to me that you have coils or coil that is breaking down (thermal) i have had this happen before and it makes diagnosing problems a hassle look into getting some decent used or new coils and see how the bike runs. I would also look at changing the plug wires and cleaning up the contacts in the plug boots

Thanks for all the suggestions. I'm taking it all into consideration. But today I took the bike out for about a 8 mile ride. Maybe 4 miles to destination parked, then 4 miles back.

I never took the bike beyond 4th gear though, and it got me where I needed to go.

Now my mechanic really doesn't have a problem working on the bike. And he does specialize in older Suzukis and Japanese bikes. He does have a lot of other responsibilities, though, as he runs the state MSF course.

So again thanks for the suggestions. Ill print this page out and give it to him when I get the bike serviced next.

[esmithers]

Did you make any improvements on the bike on getting it to run correctly and stop bogging down