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PostPosted: Sat Oct 20, 2018 1:05 pm 
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To the on ramp

Joined: Fri Aug 11, 2017 7:09 am
Posts: 466
Country: england
Suzuki 2-Strokes: several gt250 ramairs
as most will know, i've built a full size suzuki gt350 engine - based on a pair of 64mm pistons from a ts185 and 54 stroke, giving me roughly 347cc, the same as the rd350. engine starts first kick every time, hot or cold, but putting my hand behind any of the silencers and blipping the throttle leaves my hand with a big patch of mixture on it - obviously running a tad rich :D i used the rd350 carb jets as my baseline [carbs are my worse nightmare], so i've got a pair of standard gt250a carbs, vm28's, 130 main jets and #30 pilot [was going to use #25], needle in middle position, 2.5 cutaway on the slides. where the hell do i start? main jets? needle height? i really am crap when it comes to carb tuning, so any help with this would be gratefully accepted :) i know my way round carbs, but that's about it. i just need somewhere to start. btw, plugs are ngk b7's, air filters are k&n type, which will be replaced when my airbox rubber and filter get here. exhaust system is standard gt250. removed the plugs and there's a tiny blob of oil on the outer electrode, that's all. also once warm and the choke off, it will happily tick over :D any help out there please?
cheers, dd.

_________________
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: Sat Oct 20, 2018 8:17 pm 
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Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 6087
Location: Illinois
Start by setting fuel level on both sides to 3mm below the gasket surface +/- 1mm.

Then get it to idle. I'd start with #27.5. Adjust the air screws and see where that takes you. Once the idle is good, you need to get the main jet sorted and after that you can mess with needles and needle jets. That way round because the main jet doesn't really come in until about 3/4 throttle at full load. Then teh needle and jet modulate it below 3/4 when they are the restriction.

And raw fuel doesn't necessarily mean that the mixture is rich. I know that sounds odd, but we have had situations where there is a lot of unburned fuel but air to fuel rations looked OK because there was fuel not being burned. The right amount of fuel was burned but because droplets were too large, the raw HC levels were high.

On a piston ported motor use a Primary type needle jet from the so called Dave F or Dale A mod.


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PostPosted: Sun Oct 21, 2018 12:35 am 
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Expert racer

Joined: Mon Dec 01, 2008 2:52 am
Posts: 1224
Location: Manchester, UK
The carb, jet & needle specs for the various years of T350 are here, which might give you a baseline: http://www.ozebook.com/compendium/techb ... %206-9.pdf" onclick="window.open(this.href);return false;

The later models ran a 32mm carb but you may well be able to get the 28mm jobs to work.

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1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed


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PostPosted: Sun Oct 21, 2018 2:07 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2350
Location: The Republic of South Yorkshire
Country: England
Suzuki 2-Strokes: 2 x GT550s GT750, T200, TC200
I had similar with the GT750 until I fitted an in-line tap from the tank. Always parked the bike on the centre stand in the garage but always had 'spitting' out of the tail pipes, so the (new) fuel tap just leaked. I may fit another someday, but £100 for another possibly leaky diaphragm tap isn't happening anytime soon.
Problem you also have Ade, is not being able to take it out and actually clear the engine and exhausts yet.
Starting on choke then running in the shed will never clear it. Maybe take the exhausts off and hang them to drain?
Even then the baffles will be clagged up somewhat, so you may have to get them out and dry them too.
If you have a leaky tap, you have the chance of hydraulic lock and a bent rod, I don't think you need that at this stage.

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Think of how stupid the average person is, then realise that half of them are more stupid than that.


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PostPosted: Sun Oct 21, 2018 5:10 am 
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To the on ramp

Joined: Fri Aug 11, 2017 7:09 am
Posts: 466
Country: england
Suzuki 2-Strokes: several gt250 ramairs
thanks for the info everybody :D i'll go through them one at a time and see what happens.
i left the bike for 24 hours, fuel turned off, til this morning and think i found something that might be a problem. left hand fuel line was full to the top, but the right hand was nearly empty. proves the tap isn't leaking, but something is inside the right carb, and the right side chucked a load of mixture out of the silencer when i first fired it up yesterday. what would it be leaking past to empty the fuel line? if it was the float needle, surely the fuel would have come out of the overflow, not gone into the engine? but everywhere is dry. strange.
unfortunately, i've got no #27.5 pilots, but i do have some #25's, so i'll try them until the 27.5's arrive. while sorting through my carb spares i found a bag marked gt350 and 130 main jets :( hmm, they were supposed to be in it, so when i've finished stripping the carbs down i'll check just what the hell mains i've got in it.
another question. i've noticed that some pilot jets have more holes than others. does this make a difference? the ones i'm going to fit have 4 holes. anyway, onwards and upwards, and i'll edit this post with what i find in the carbs :D stupid boy :D
cheers, dd.
time to kick oneself in the nuts and shout rude words out. measure twice, cut once. should have listened to my own advice. right, the first thing wrong was the carbs had 112.5 mains in [for a 250a], so i changed them for a pair of 130's. #30 pilot jets, i've changed them for a pair of #25's. the float height on the left carb was 13.5mm as accurate as a steel ruler can be, which was right. the right carb it was 17, which most definitely is wrong, so adjusted down to 13.5mm. when i pulled the fuel lines off they were both empty - i thought one was full - so fuel is going into the engine somehow overnight. put new float needles and seats in, so hopefully that will cure that. just finishing rebuilding and fitting them, then i'm gonna take the plugs out and kick the engine over a few times before i put the tank back on. one thing to check is that the overflows are clear. if they are blocked it would obviously stop the carbs flooding - in theory. back later when everything is done.

_________________
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: Mon Oct 22, 2018 2:57 pm 
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To the on ramp

Joined: Fri Aug 11, 2017 7:09 am
Posts: 466
Country: england
Suzuki 2-Strokes: several gt250 ramairs
much better :D warmed it up and ticks over nicely, albeit a bit high. only blipping it to about third throttle, but sounds crisp - or as crisp as it can do with standard silencers on it :D onlyy thing that's bugging me atm is, although the right silencer is virtually clear of smoke, the left is smoking rather a lot. perhaps there's still oil in there? but i ran it for at least 5 minutes and it never got any better, surely it should have cleared it by then? took the plugs out and the right is a grey colour, but the left looks like brand new. will post a photo of them tomorrow. thanks again.
cheers, dd.

_________________
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: Tue Oct 23, 2018 4:15 am 
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To the on ramp

Joined: Fri Aug 11, 2017 7:09 am
Posts: 466
Country: england
Suzuki 2-Strokes: several gt250 ramairs
photo of the plugs after a good 5 minutes of running, just blipping the throttle up to about 3500 revs. plug on the right is out of the right pot and is a nice grey colour, but plug on the left looks like new - but that's the pot that's smoking a lot. i was expecting it to be oily, but it's as clean as a new pin :D
cheers, dd.
Image

_________________
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: Tue Oct 23, 2018 6:29 am 
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World Superbike
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2350
Location: The Republic of South Yorkshire
Country: England
Suzuki 2-Strokes: 2 x GT550s GT750, T200, TC200
Try a 1 grade hotter plug in the oily side to see if that clears it. Just don't run on it (natch!)

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Think of how stupid the average person is, then realise that half of them are more stupid than that.


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