82 GS300L - Right-Side Drop Outs, Bogs, Stalls

[Guest]

Hi everyone,

82 GS300L; experiencing drop-outs on the exhaust, bogging and stalling.

- Bike turns over every time and starts well
- Running smoothe enough at idle, sometimes varies slightly but generally pulling the choke, gradually pushing it in, a flew blips and 5 minutes of warm up time shows positive results
- Once a get riding, I get frequent drop-outs and bogs on the right side only, sometimes resulting in the engine losing power, often wanting to die when I come to a stop or slow down
- Engine runs well at high speed

Work Done:
- I have cleaned the carbs thoroughly several times as described from some better parts of this forum
- Checked all boots for cracks, WD40 spray test with no real change in behaviour
- I have cleaned the gas tank with vinegar, hot water, heat gun, etc
- I have used half a can of Seafoam
- I have tried 87 and 89 Octane
- Vacuum hoses, fuel lines and petcock seem to be ok
- I have adjusted valves to spec
- I have done a compression test which looks ok

Carbs:
- a wide range of adjustments to pilot screws on the carbs seem to have not had major improvements on the ride; all the way in and the bike dies (as expected), all the way out and I don't notice major changes; some small ups and downs in idle and I have ridden at slight 1/4 and 1/2 turns out by degrees and no major change in behaviour
- pilot screws do seem to bottom out unevenly, as if once may have been bottomed out harder than the other, wondering if this might have an effect (???)

Any tips, ideas, advice?

Thank you!
Phil

[fbody_mike]

Set the petcock to prime, clamp the vacuum line from the right carb to the petcock shut and test again. I think your diaphragm in the petcock is torn and is adding fuel to the carb in certain situations. Its a chance and an easy test.

[philmotion]

Hi Mike,

Thank you. Haven't tried this yet. Will give it a shot and come back to you with the result. Much appreciated

[fbody_mike]

I know that the GS250 and GS300 was very similar in engine design besides displacement. But on my 250, it is very sensitive to air box leaks, from the lid to the couplings, any issue there really messed with its running, especially in the mid-range. So that is something else to look at.

[Gorminrider]

on the right side only

Because it's just one cylinder misfiring, it's unlikely the petcock is the problem. but further down, the float needle and fuel level...?

pilot screws do seem to bottom out unevenly, as if once may have been bottomed out harder than the other, wondering if this might have an effect (???)

Whatever, better take them out and see. If one has a broken tip, the missing piece is a worry... Or, if one is missing its little o-ring or whatever(but these can get left behind in the hole too)
There's a big list of things to check..BUT "the last thing you did" is often the first place to return to if the bike "changed" since doing it. At least you know that one side is "bad".

You might get a clue by looking at the spark plug. Is the bad side choking on fuel, running out of fuel, or not either? Knowing this might give you some direction.
Since it's specific to a certain rpm, that should be a clue. Unfortunately, both idle and main carb passages are involved in the mid-range.
Plugged idle and main jets (the tiny holes) are pretty common. Depending on how you cleaned the carbs, the stuff can still be coming round to foul them again.

Your bike probably has screens in the mouths of the carbs. Unlike any other on this forum...Check these.

...does goosing the throttle help? just maybe, a sticky vacuum slide or leaky "CV" diaphragm


Some ignition ideas can be crossed off the list before returning to the carbs...
Take the little round cover off. Check the mechanical advance operation. Inspect the wire going to the ignition sensors along it's length for chafe..it can be vulnerable where it goes along the engine near exhaust and into the casing...
Also the TCI box..unlikely to be the ground but maybe where that cylinder's sensor or coil wire plugs in
Swap sparkplugs with an eye to replacing them.
plug leads, checking the wiring to the coil...

[LAB3]

I'd be inclined to check the plug cap resistance, should be 5k ohms

[philmotion]

Hi Mike, tried this today but with no luck. The vacuum hose was rather hard so I swapped that out with a temp fix until later this week but it gave me a newer softer hose to work with and clamp but sadly no change.

[philmotion]

I know that the GS250 and GS300 was very similar in engine design besides displacement. But on my 250, it is very sensitive to air box leaks, from the lid to the couplings, any issue there really messed with its running, especially in the mid-range. So that is something else to look at.

Good tip on airbox. Models are almost identical. I did pull the entire box out to clean and put in a new filter but I will check again for leaks.

[philmotion]

I'd be inclined to check the plug cap resistance, should be 5k ohms

Hi Lab,

Good tip. I did check these according to the manual and they check out ok. I even flipped them today but no change. Thank you.

[philmotion]

Set the petcock to prime, clamp the vacuum line from the right carb to the petcock shut and test again. I think your diaphragm in the petcock is torn and is adding fuel to the carb in certain situations. Its a chance and an easy test.

Hi Mike, tried this today but with no luck. The vacuum hose was rather hard so I swapped that out with a temp fix until later this week but it gave me a newer softer hose to work with and clamp but sadly no change. I also double-checked the float-level again and it is set to spec but no still nothing.

[philmotion]

Because it's just one cylinder misfiring, it's unlikely the petcock is the problem. but further down, the float needle and fuel level...?

Whatever, better take them out and see. If one has a broken tip, the missing piece is a worry... Or, if one is missing its little o-ring or whatever(but these can get left behind in the hole too)
There's a big list of things to check..BUT "the last thing you did" is often the first place to return to if the bike "changed" since doing it. At least you know that one side is "bad".

You might get a clue by looking at the spark plug. Is the bad side choking on fuel, running out of fuel, or not either? Knowing this might give you some direction.
Since it's specific to a certain rpm, that should be a clue. Unfortunately, both idle and main carb passages are involved in the mid-range.
Plugged idle and main jets (the tiny holes) are pretty common. Depending on how you cleaned the carbs, the stuff can still be coming round to foul them again.

Your bike probably has screens in the mouths of the carbs. Unlike any other on this forum...Check these.

...does goosing the throttle help? just maybe, a sticky vacuum slide or leaky "CV" diaphragm


Some ignition ideas can be crossed off the list before returning to the carbs...
Take the little round cover off. Check the mechanical advance operation. Inspect the wire going to the ignition sensors along it's length for chafe..it can be vulnerable where it goes along the engine near exhaust and into the casing...
Also the TCI box..unlikely to be the ground but maybe where that cylinder's sensor or coil wire plugs in
Swap sparkplugs with an eye to replacing them.
plug leads, checking the wiring to the coil...

1. Petcock, floats and needles all seem ok to me.
2. No broken tips on pilot screws and rubber o-rings are still there but the springs aren't exactly a perfect match.
3. Jets all fine
4. Screens on the mouths of the carbs are ok; one bent some time ago but I straightened it out and seems to be fine.
5. Slides ok; diaphragms have no tears and were properly seated.
6. Electronic advance, no points; wires seem ok.
7. Swapped spark plugs, even changed them altogether as well as swapped coils left and right + measured coil resistance as per manual = all check out ok, and no change in behavior.
8. I did the ignitor test as per the manual = also ok.
9. I did check the Regulator/Rectifier which checks out to spec but oddly only when I flip the test leads and do the opposite of what the manual states for + and - with continuity and no continuity flipped but still seemingly ok. It is a new Rick's motorsports R/R from 2 years ago when a similar issue led me to find that the stock R/R was defective. I did swap it out and never had any problems until now.

Worked on it today and it strangely wasn't obviously just one side as it seemed in the past weeks; bike starts great, idles fine for a minute or two and then just dies out of nowhere. Starts again no problem and same, it dies again. When I get to riding, it has good moments and then it starts to bog in 1st and 2nd especially. I get this big drop-outs and I do indeed have to goose the throttle until it kicks back in again and I keep riding.

[Gorminrider]

Did you try turning the petcock to prime per fbody's suggestion? because, This does not say you tried "prime"....

Petcock, floats and needles all seem ok to me.

I didn't include it because he did. It's a good easy one to try. and is relevant to your symptoms, especially as it's not a one-sided problem anymore.

and I do indeed have to goose the throttle until it kicks back in again and I keep riding.

...goosing the throttle gives a vacuum burst to the petcock's diaphragm. If you find it's the petcock, at least check for a split or kinked vacuum line first.

[philmotion]

Did you try turning the petcock to prime per fbody's suggestion? because, This does not say you tried "prime"....

I didn't include it because he did. It's a good easy one to try. and is relevant to your symptoms, especially as it's not a one-sided problem anymore.


...goosing the throttle gives a vacuum burst to the petcock's diaphragm. If you find it's the petcock, at least check for a split or kinked vacuum line first.

Hi Gormin,

Good additional tips and insight, thank you. I did have it in "prime" yes.

I did also remove and take apart the petcock some weeks back and everything looked fine there as well. From what I can tell the fuel and vacuum lines look ok but the vacuum line is quite hard. I have ordered fuel and vacuum lines as replacement for this week as well as new float needles to perhaps give that a go. One needles has a very tiny almost barely noticeable ring around it so I will try to remove that from the equation as well.

[Gorminrider]

ok. ...but nothing you're buying looks to be the problem...(I buy very little until I can be sure it is the fix) So far, I only see the "goosing" as a clue and if the vacuum pulse is shaking something loose, it can be other vacuum things too.
I say "looks" because people have been known to just replace stuff that's likely and the problem is fixed. Petcocks are a good example. They are tricky brutes and hard to catch "at it". Petcock rough test is start the bike on residual bowl contents and check for fuel flow from the tap...Stuff like that. Not perfect of course. i'd use a fairly full tank of gas but Fuel pressure (gravity"column" above tap) varies as the tank empties so use the level where the bike is failing.

still,
"Floats and needles" can all be tested "in situ" with a fairly-full tank of gas on Prime.(or tip the tank to simulate a full tank) Even a little seeping shouldn't cause the bike to die. By the way, I think that with metal needle and seat, usually BOTH are replaced. Kind of like putting a new chain on a worn sprocket...but the seat might not be and you may be fine.... (The seat of a rubber-tipped needle can be much harder to replace if it all )

(Just a thought) The little ring you see can just be the needle polishing itself in the seat. ...ideally, it's a vibration as the bike uses fuel and is replenished again. The one that isn't polished as a ring might be the odd one.


Vacuum line should be fairly stiff so it can't kink...I prefer automobile-type hose versus too-thin vinyl types that can get warm,soft and even collapse with vacuum.

That you had "similar symptoms" with the old R/R might be a clue. But IME, it's unlikely to affect the bike as a running failure unless it stopped regulating and allowed the bike to run at a high, pulsing voltage...On a twin cylinder, it's very rough at low rpm and the headlight pulses too. ... but whatever , the bike can run on battery alone quite a distance, so it's easy to nail this down as a cause too.

[philmotion]

Once again, a wealth of info, thank you.

I will look into the needle and seat combo, makes sense.

I will investigate further with the petcock as well. The tank, off the bike with no vacuum or fuel line, does not leak in the "ride" position and flows freely in "prime". When you describe the rough test for the petcock with residual bowl contents, is this meant to test the vaccuum, i.e. that fuel is successfully being pulled down into the float bowls?

ok. ...but nothing you're buying looks to be the problem...(I buy very little until I can be sure it is the fix) So far, I only see the "goosing" as a clue and if the vacuum pulse is shaking something loose, it can be other vacuum things too.
I say "looks" because people have been known to just replace stuff that's likely and the problem is fixed. Petcocks are a good example. They are tricky brutes and hard to catch "at it". Petcock rough test is start the bike on residual bowl contents and check for fuel flow from the tap...Stuff like that. Not perfect of course. i'd use a fairly full tank of gas but Fuel pressure (gravity"column" above tap) varies as the tank empties so use the level where the bike is failing.

still,
"Floats and needles" can all be tested "in situ" with a fairly-full tank of gas on Prime.(or tip the tank to simulate a full tank) Even a little seeping shouldn't cause the bike to die. By the way, I think that with metal needle and seat, usually BOTH are replaced. Kind of like putting a new chain on a worn sprocket...but the seat might not be and you may be fine.... (The seat of a rubber-tipped needle can be much harder to replace if it all )

(Just a thought) The little ring you see can just be the needle polishing itself in the seat. ...ideally, it's a vibration as the bike uses fuel and is replenished again. The one that isn't polished as a ring might be the odd one.


Vacuum line should be fairly stiff so it can't kink...I prefer automobile-type hose versus too-thin vinyl types that can get warm,soft and even collapse with vacuum.

That you had "similar symptoms" with the old R/R might be a clue. But IME, it's unlikely to affect the bike as a running failure unless it stopped regulating and allowed the bike to run at a high, pulsing voltage...On a twin cylinder, it's very rough at low rpm and the headlight pulses too. ... but whatever , the bike can run on battery alone quite a distance, so it's easy to nail this down as a cause too.