Suzuki GN250 '94 bogging out at higher RPM, speed?

[Suture]

Well hello there Kiwi's from the coldness of Denmark

In my efforts to troubleshoot a Suzuki GN250 from 1994, it seems New Zealand is the place for 250's.

Soo, here's hoping you guys can help me out :)

I currently have a GN250 that seems to bog out at higher speeds. 45-50mph (70-80kmh) and it will start bogging and behaving badly, as if I was releasing the throttle for 0.5-1 sec and engaging it again. This happens mainly in 4th and 5th gear. If I max the throttle in 4th gear, it will bog out a little but once it reaches above 7k RPM (or so) it will behave better and won't bog out. If I swap to 5th and the RPM's drop a bit it goes back to bogging constantly and I won't get above 55mph at best. It will also backfire if I max it out in 4th gear then release the throttle and let the RPMs drop down.

For the odd parts :

I had a mechanic clean and adjust the carburetor, change the sparkplug and the clutch plates. I've also changed the airfilter, oil and oilfilter. No difference.

Once, when the problem first started, it would die if I let it idle even for a few seconds. This lasted a day or two, after that it idles but around 1k RPM til after 20 min of riding.

And the strangest part is, after it starts bogging out, I can stop for 20-30 seconds and just let it idle (either in gear or neutral) and give it gas every now and then to prevent it from stalling. When I set off again, it won't bog out for a decent amount of time. As an example :

Today it started (2 attempts, with choke on, usually starts on 1). I set off, goes fine for about 5 minutes, I hit the higher speed in 4th gear and feel it's starting to bog out slightly. I swap to 5th and it starts bogging out a lot. I park it on the side for roughly 1-2 minutes (took off gloves, checked phone) and it was in neutral. I then set off again on the motorway, gently increasing the throttle and changing gears. I hit 70mph(112kmh) in 5th and there were no problems at all for 15 min or so.

Help :/

[Akzle]

tl:dr.

Its a gn.
"higher" speed is only relative to a gn (or harley)'s lower speed. Both are fucken slow.

Sell it and buy a busa.

[Akzle]

tl:r

carb choon. Main jet and or needle. And air leaks. All the air leaks.

[husaberg]

Well hello there Kiwi's from the coldness of Denmark

In my efforts to troubleshoot a Suzuki GN250 from 1994, it seems New Zealand is the place for 250's.

Soo, here's hoping you guys can help me out :)

I currently have a GN250 that seems to bog out at higher speeds. 45-50mph (70-80kmh) and it will start bogging and behaving badly, as if I was releasing the throttle for 0.5-1 sec and engaging it again. This happens mainly in 4th and 5th gear. If I max the throttle in 4th gear, it will bog out a little but once it reaches above 7k RPM (or so) it will behave better and won't bog out. If I swap to 5th and the RPM's drop a bit it goes back to bogging constantly and I won't get above 55mph at best. It will also backfire if I max it out in 4th gear then release the throttle and let the RPMs drop down.

For the odd parts :

I had a mechanic clean and adjust the carburetor, change the sparkplug and the clutch plates. I've also changed the airfilter, oil and oilfilter. No difference.

Once, when the problem first started, it would die if I let it idle even for a few seconds. This lasted a day or two, after that it idles but around 1k RPM til after 20 min of riding.

And the strangest part is, after it starts bogging out, I can stop for 20-30 seconds and just let it idle (either in gear or neutral) and give it gas every now and then to prevent it from stalling. When I set off again, it won't bog out for a decent amount of time. As an example :

Today it started (2 attempts, with choke on, usually starts on 1). I set off, goes fine for about 5 minutes, I hit the higher speed in 4th gear and feel it's starting to bog out slightly. I swap to 5th and it starts bogging out a lot. I park it on the side for roughly 1-2 minutes (took off gloves, checked phone) and it was in neutral. I then set off again on the motorway, gently increasing the throttle and changing gears. I hit 70mph(112kmh) in 5th and there were no problems at all for 15 min or so.

Help :/


Check the air entry on the fuel tank, then check the fuel flow out of the tank (not sure if Suzuki still fit the silly diaphragm tap) but take out the petcock and check the filter on the entry (if it has one).

[Suture]

tl:dr.

Its a gn.
"higher" speed is only relative to a gn (or harley)'s lower speed. Both are fucken slow.

Sell it and buy a busa.

You don't drive a Hayabusa in winter in Denmark. This is my winterbike and 80mph is just fine for higher speed in this climate.

[Suture]

tl:r

carb choon. Main jet and or needle. And air leaks. All the air leaks.

I'll try to check for airleaks after work. The mechanic had a look at it and his idea was the carbs were working fine but it could be an ignition issue?

[Suture]

Check the air entry on the fuel tank, then check the fuel flow out of the tank (not sure if Suzuki still fit the silly diaphragm tap) but take out the petcock and check the filter on the entry (if it has one).

Pardon the newbie question, but wouldn't the fuel flow cause the same issue irrelevant of speed and RPMs in that case? I'll happily check the it after work. From what I could see it doesn't have a fuelfilter tho :/

[Akzle]

Pardon the newbie question, but wouldn't the fuel flow cause the same issue irrelevant of speed and RPMs in that case? I'll happily check the it after work. From what I could see it doesn't have a fuelfilter tho :/

no, vacuum changes through the revs. Its less at w.o.t. so a restricted vent will affect its sucking powah.

I have a tendency not to trust "mechanics."

an ignition problem (coil) will usually present when hot. You can check for arcing by running it in a dark garage and looking for sparks.

[nodrog]

is there nobody in Denmark that can help?

[old rig]

is there nobody in Denmark that can help?
They don't speak English over there he dose look at his post all in English 😲

Sent from my SM-G900I using Tapatalk

[husaberg]

Pardon the newbie question, but wouldn't the fuel flow cause the same issue irrelevant of speed and RPMs in that case? I'll happily check the it after work. From what I could see it doesn't have a fuelfilter tho :/

Fuel flow with a blocked or partially blocked air intake on the filler cap (breather ) is intermittent normally runs fine for 5-10 minutes then the symptoms start and magically disappear (when the cap is opened to check the fuel level (for a while.)
The filter on the petcock intake (if it has one buried in the tank) is dependant on a number of factors including fuel head (level) and the amount sloshing happening In the tank.

[Katman]

I have a tendency not to trust "mechanics."

:weep:

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:weep:

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[Akzle]

:weep:

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:weep:

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bro. I'v got this gsx thats running rough... Fix it oi.

[haydes55]

Ride around with the fuel cap slightly open.

[Suture]

no, vacuum changes through the revs. Its less at w.o.t. so a restricted vent will affect its sucking powah.

I have a tendency not to trust "mechanics."

an ignition problem (coil) will usually present when hot. You can check for arcing by running it in a dark garage and looking for sparks.

No fuel filter, I checked all the hoses and couldn't see anything that looked cracked or worn. Sadly here it gets pitch black around the time I finish work so can't disassemble anything until the weekend. It does "run" better when it's colder outside, if that makes sense.

[Suture]

is there nobody in Denmark that can help?

Not anyone trustworthy. The mechanics here are overpriced to the point where diagnosing this issue alone would cost more than the actual bike did. As a benchmark, cleaning and adjusting the carb, changing clutch plates, checking the breaks and changing oil+filter as well as airfilter would cost 900$ here as a package deal.

[Suture]

Fuel flow with a blocked or partially blocked air intake on the filler cap (breather ) is intermittent normally runs fine for 5-10 minutes then the symptoms start and magically disappear (when the cap is opened to check the fuel level (for a while.)
The filter on the petcock intake (if it has one buried in the tank) is dependant on a number of factors including fuel head (level) and the amount sloshing happening In the tank.

Ah, so if I do what haydes55 suggested and drive around with the fuel cap slightly opened, this would diagnose the above? If it works it's the air intake and if it still an issue it's the fuel delivery (petcock, hoses, filter) or possibly the ignition system?

I'll have to check it tomorrow morning because for some reason the evening gets colder and the problem doesn't really present itself as much then, if at all. I suppose it does point to your suggestion as cold generally means less expanding of parts which could cause a blockage?

[husaberg]

Ah, so if I do what haydes55 suggested and drive around with the fuel cap slightly opened, this would diagnose the above? If it works it's the air intake and if it still an issue it's the fuel delivery (petcock, hoses, filter) or possibly the ignition system?

I'll have to check it tomorrow morning because for some reason the evening gets colder and the problem doesn't really present itself as much then, if at all. I suppose it does point to your suggestion as cold generally means less expanding of parts which could cause a blockage?
yes it could. A decent mechanic should be able to sort what the likely cause is in a few minutes
Not really anything to do with expanding parts, the bits are blocked or not
Note the colder weather =better running, maybe points to the mixture being overly rich at the moment , so check the air filter and the carb flat level as well.

[sidecar bob]

Not anyone trustworthy. The mechanics here are overpriced to the point where diagnosing this issue alone would cost more than the actual bike did. As a benchmark, cleaning and adjusting the carb, changing clutch plates, checking the breaks and changing oil+filter as well as airfilter would cost 900$ here as a package deal.

Sounds like I need to move to Denmark. Are there many BMW cars over there?

[husaberg]

Sounds like I need to move to Denmark. Are there many BMW cars over there?

That's rotten, I always suspected something was rotten in Denmark.................

[Laava]

That's rotten, I always suspected something was rotten in Denmark.................

Just the state. The rest of it should be sweet.

[husaberg]

Just the state. The rest of it should be sweet.

Alas I knew you so well, (that I knew you were going to say that)

[Jamesdsm]

It's bloody cold in Denmark at times, I'd adjust the idle to sit around 1500, see if that works for ya. As for the power loss, there's a bunch of things it could be, mostly been covered by previous posters

[Suture]

Sounds like I need to move to Denmark. Are there many BMW cars over there?

I suppose there are a few, but their drivers don't exactly have the greatest reputation :P

[Suture]

yes it could. A decent mechanic should be able to sort what the likely cause is in a few minutes
Not really anything to do with expanding parts, the bits are blocked or not
Note the colder weather =better running, maybe points to the mixture being overly rich at the moment , so check the air filter and the carb flat level as well.

Unfortunately the weather has been around -3 to 5 degrees. After I checked the cables the issue hasn't occurred at all so can't really say what helped and what didn't. I'm hoping you were spot on, and it was just a blockage that released :)

[Suture]

It's bloody cold in Denmark at times, I'd adjust the idle to sit around 1500, see if that works for ya. As for the power loss, there's a bunch of things it could be, mostly been covered by previous posters

The idle is set to 13-1400 from the visit to the mechanic. It doesn't start 100% as it used to (required throttle) , but when it's warm it idles perfectly. I'm hoping the previous posters were right in that it was a blockage, because I haven't experienced the issue again. And yeah, it's friggin cold :P I have heated handles and heated gloves and my fingers still get a bit chilly if I drive above the speed limit :P