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PostPosted: Mon Oct 22, 2018 7:56 am 
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On the street

Joined: Tue Jul 24, 2018 3:56 am
Posts: 10
Location: Isle of Wight UK
Country: UK
Bikes owned: 1973 GT250
Hi All, Got an issue with the right cylinder on my Gt250. It runs noticeably cooler and has a very muted exhaust note compared to the typical ping/pulse of the left side, it is also running very oily on the right side with a lot of visible oil on the exhaust baffle. In addition, whilst the left cylinder will happily idle with the right plug cap off, the right side will not idle at all on its own.
I've pursued all the normal fault finding avenues.... swapped coils/plugs and leads/condenser & points and all the wiring and connectors in between and the problem remains firmly on the right side, compression readings are fairly similar at around 120. Carbs have also been fully stripped and checked.
I'm starting to consider the possibility of crank seals being the possible cause, so any help hints or advice would be much appreciated before I get the spanners out!


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PostPosted: Mon Oct 22, 2018 8:29 am 
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Expert racer

Joined: Mon Dec 01, 2008 2:52 am
Posts: 1159
Location: Manchester, UK
Hi, is the right-side exhaust baffle clear, and is the actual exhaust itself free of carbon and crud?

If I remember right, the pipes on GT250s are one piece with the header welded to the main body of the exhaust. On the GT380 triples which have a similar one-piece pipe, you get a ring of carbon/crud build up where the header is welded to the exhaust. This acts like a restrictor washer.

The only way to get rid is to remove the pipe and poke something flexible but strong down the header, like one of those springy drain-clearing snakes you can get from DIY shops. Banging the seams of the silencer with a rubber mallet also helps loosen built-up crud, which you can tip out of the pipe.

Give that a go before looking at seals, etc.

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1976 GT380 - wounded by me, and sold on
2006 SV650S. It's got cams, and valves, and stuff


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PostPosted: Mon Oct 22, 2018 10:50 am 
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To the on ramp
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Joined: Mon Jun 12, 2017 12:01 pm
Posts: 222
Location: Galveston County, Tx.
Country: USA
Bikes owned: '75 T500M since '93 Ridden it over 100,000 mi
Tapnell wrote:
.........I've pursued all the normal fault finding avenues....
Except the first thing that should be checked BEFORE ANY type of troubleshooting.....the battery.....even if it is brand new. Maybe you have checked it and just not mentioned it. I'm not saying that's the problem but a lot easier to eliminate that first as the problem. Charge the battery to 13.00 V (surface charge will eventually dissipate and should hold at 12.6 if a flooded type battery. That reading should hold overnight with the battery at rest and not connected to anything if the battery is good. A good quality mini battery hydrometer for testing each cell is also a nice tool to have.

Good Luck


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PostPosted: Mon Oct 22, 2018 11:54 am 
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Moto GP
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Joined: Mon Dec 13, 2010 4:32 pm
Posts: 3260
Location: southwestern Pennsylvania
Country: USA
Bikes owned: 69 T350 thru 75 GT750
After you address the issues Craig380 & dorT500 mentioned, you need to balance the carbs.

Sync the carb slides so they reach the top of the carb inlet at the same throttle opening.
Then balance the idle rpm when running on one cylinder. With the right cap off, see what rpm it idles at. Then with the left cap off, adjust the right carb idle to get the same rpm. Then with both caps on, adjust both carbs the same amount to get a good idle rpm.

If this solve the problem, you might need to tweak the adjustment after the bike has been run for some miles to clear out the right cylinder.

I had a similar problem with the GT380 cafe build. Doing this made a big difference -- much more than I would have expected.

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BAS (Bike Acquisition Syndrome) - too many bikes but have room for more

Suzuki:
GT750 2x75
GT550 72 project & 75
GT380 72
T500 73 project
T350 69, 71 & 72 project
T250 72
Honda 85 CB650SC & 86 CB700SC
09 Triumph Bonneville SE


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PostPosted: Tue Oct 23, 2018 1:17 pm 
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On the street

Joined: Tue Jul 24, 2018 3:56 am
Posts: 10
Location: Isle of Wight UK
Country: UK
Bikes owned: 1973 GT250
Many thanks for all your replies,..... I did replace the battery hoping it might resolve the problem but it remains. I have also synchronised the carbs but only by watching the slides not by rpm on each cylinder ( Ill give that a try!). As for the exhausts, the baffles are clear but I haven't checked for any restriction below the headers, although that wouldn't explain all the oil in both the far end and that running out of the header/barrel gasket! The quest continues.........


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PostPosted: Wed Oct 24, 2018 6:47 am 
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To the on ramp

Joined: Fri Aug 11, 2017 7:09 am
Posts: 290
Country: england
Bikes owned: several gt250 ramairs
hi mate, first thing to know would be, what model of gt250 is it? the ramair models and the later 250a had different oil feeds to the crank main bearings. on the earlier model the middle bearing was fed by the gearbox. on the later model the right hand bearing was fed by the gearbox. need to know which before i can help you further.
also, if you've got oil leaking at the exhaust flange then either the gasket is knackered and/or the castellated ring isn't tight enough. slacken the back nuts off [where the rear footrests are], then tighten the rings up with a 'c' spanner - fully. then retighten the rear nuts up. :D model first, and we'll go from there :D
cheers, dd.

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GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
GT285 road registered. Overbored - 58mm and TS125 +2 pistons fitted.
GT10 road registered. '65 T10 engine, GT250 frame.


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PostPosted: Wed Oct 24, 2018 9:36 am 
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To the on ramp
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Joined: Mon Jun 12, 2017 12:01 pm
Posts: 222
Location: Galveston County, Tx.
Country: USA
Bikes owned: '75 T500M since '93 Ridden it over 100,000 mi
Hello, Tapnell,

Do you have a multimeter?

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PostPosted: Mon Nov 05, 2018 6:25 am 
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On the street

Joined: Tue Jul 24, 2018 3:56 am
Posts: 10
Location: Isle of Wight UK
Country: UK
Bikes owned: 1973 GT250
Thanks for your reply dollydog haven’t been able to get on the site due some bandwidth issue so apologies for the late reply. It’s a 1973 250k. As for the header leak, I’ve so far been unable to get a decent flush fit between the header stub and the pipe flange. Tried filing the footrest mount to allow a bit more adjustment but it almost seems like the engine needs tilting backwards to get the two surfaces parallel.


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PostPosted: Mon Nov 05, 2018 6:29 am 
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On the street

Joined: Tue Jul 24, 2018 3:56 am
Posts: 10
Location: Isle of Wight UK
Country: UK
Bikes owned: 1973 GT250
Hi dorT500, yes I do have a multimeter :up:


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