81 gs250t

[Mainezuki]

Here is my 81 gs250t rat cafe, built it last winter, it runs great but tops out @  5.5k rpm, 55mph, is this normal? Is there a way to increase this, I've looked for rear sprockets but non seem to exist is there a way to increase rpm range 

[gs7_11]

Yes, 55mph is normal with that exhaust and filters.

[wraith]

Yep, had one years ago mover got more that 55-60mph ended up putting the 400cc motor in it, much more fun.

Welcome to OSS.

[gs7_11]

Seriously, if it'll only do 55mph, 5500rpm in top, you've clearly got an issue. Should pull it's own standard gearing to 70-80mph even with a tired engine.

The carburation is likely to be all over the place with that set up, but even if all you've done is up the main jet, that should be good enough for full throttle, but being CV carbs you might not get out of a mid range flat spot if it's too bad.

Changing the gearing to suit your new, crippled, power output isn't the way ahead!

Edited December 9, 2019 by gs7_11

[Gixer1460]

9 hours ago, gs7_11 said:

The carburetion is likely to be all over the place with that set up, but even if all you've done is up the main jet, that should be good enough for full throttle, but being CV carbs you might not get out of a mid range flat spot if it's too bad.

Changing the gearing to suit your new, crippled, power output isn't the way ahead!

Agreed - cv's won't tend to pull through the mid-range if the jetting ain't right. It's unlikely a jet kit will be available, so a Dyno session may be the solution or you'll be forever fiddling with them!

[TonyC]

Have you checked the carb diaphragms? If they're split, the main jets won't open fully.

[bluedog59]

I suspect those exhausts will also be helping in screwing everything up as well. 

[Mainezuki]

Ive been through dozens of main and idle jets configurations needle positions ext, it start beautifully and runs perfect right to 55k rpm, and it's like hitting a wall, seems a couple of you say it's normal and a couple say it's not, guess I'll just keep tinkering, can anyone tell me For Sure what the redline was when factory new, and just an fyi it only has 12k miles on the odometer. 

[jensvonbustenskjold]

If it's hitting a wall at 5500 rpm at neutral, or any other gear, then it sounds like electronics issue. Ignition would be my primary suspect.

According this site you should reach 13 000rpm. And 90 mph.

https://www.motorcyclespecs.co.za/model/suzu/suzuki_gs250t 80.htm

 

Forgive me, but I don't know this bike, but in Norway there was different types of power restrictions for different licenses for motorcycles. Could it be manually restricted to achieve a top speed limitor or HP limitor, somehow, back in the 80s?

Just thinking out loud 

 

[Gixer1460]

1 hour ago, jensvonbustenskjold said:

According this site you should reach 13 000rpm. And 90 mph.

https://www.motorcyclespecs.co.za/model/suzu/suzuki_gs250t 80.htm

I think i'd take that with a large pinch of salt! Other sites / reviews quote a believable 10k redline

[gs7_11]

Of course it's not normal. 

You appear to still have the standard clocks......The red line is on the tacho, no?

10k sounds about right. It won't pull that in top, possibly, but should get close. Mine would do 80+ in top, given enough run up.

[jensvonbustenskjold]

1 hour ago, Gixer1460 said:

I think i'd take that with a large pinch of salt! Other sites / reviews quote a believable 10k redline

Oh yes indeed  I just wanted to help finding some more answers. IMO the 5500 rpm sounded a bit of the chart. 

[gsx]

Had one years ago with filters and pipe , would hit 95 with larger gear box sprocket .

Think the thing your missing is an air corrector kit which tap into the back of the carb , ledar used to do them and I believe they are back in production .

Have a word with grumpy 1260

[wraith]

When I was dispatched riding had a 250 was great around town but go on a motorway and it got imbarrasing, when it took what seemed like all day to overtake a hgv  I think the best I got out of it was 65mph and top gear had no pull.

Got a 400 engine and carbs and it would do 110mph all day  never got to know why the 250 had no top end even a wet dream had better top end but the 250 would rev to the red line in all but top gear, 4th gear would get there but slow, always seemed like top gear was just a overdrive gear.

[Rich]

I had a 250E slabside, same engine I believe, and it would hold 75mph all day and maybe touch 80mph with a tailwind. That was on standard carb settings, airbox & filter and twin exhausts with collector box. A 2-1 exhaust put a noticeable hole in the midrange but it still pulled through it and on to 75-ish. I would be looking at your filter - jetting - exhaust set-up.

[Mainezuki]

Awesome thanks for all the good info, now I have some things to work on over the winter, if I have time lol, got a 79 gs550 coming soon and may focus on that lol.

[bluedog59]

I would suggest you get this bike running right before you start the next project. There is far more to building a project than making it look cool. Finish it, learn from it and apply it to the next. No point in a string of pretty bikes that done run right.

[inazumarob]

I had a GS250T back in 1985, it had a pair of short slashcut exhausts on it as original exhaust had holes in. Mine had standard jetting and gearing and topped out showing 92mph on clock. CV carbs do not like foam air filters as they work on pressure differential between airbox and air basically when engine running. I would put airbox on and check valve clearances as well. Clearances are tiny on the GS from memory, about 2 thou I think. 

[johnr]

have you checked that the auto advance retard bobweights on the ignition rotor are moving freely? it may be seized, not uncommon on an engine with mechanical advance and retard.