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:Me]

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."

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[Akzle]

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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.