GT550M Carb Problem

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Syd
Posts: 311
Joined: Tue Aug 16, 2011 11:25 pm

GT550M Carb Problem

Post by Syd »

We finally got my restored 75 GT550M fired up today and she sounds really great and runs smoothly, however I have a problem with the LH and centre carbs leaking petrol freely from the bottom carb bowl overflow tubes and also from the top overflow tube next to the centre carb. When the engine stops, the petrol stops flowing out of both the LH & centre carb overflow tubes. The RH carb is fine with no leaks at all. All of the carbs have been cleaned and fitted with new Mikuni jets etc and the float height levels set at 24.25mm and rechecked again.

We tried tapping the carb bowls that were leaking with the engine running to see if this helped, however this did not help at all. I have had the odd problem in the past with carbs leaking out of overflow tubes on old classic 2 strokes but never with petrol flowing out of the tubes like this. Is 24.25 the correct float height for the 75 GT550M? My service manual is a copy of an original, however sometimes these old manuals can have errors. If anyone has any ideas for me to try, that would be appreciated. On a side note, I noticed that the top overflow tube is next to the LH and centre carbs but not on the RH carb, is this correct?
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GT550.jpg
barney01
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Joined: Wed Sep 26, 2012 7:33 pm
Location: Prestatyn.Wales

Re: GT550M Carb Problem

Post by barney01 »

Hi Syd
This carb manual
http://www.3cyl.com/mraxl/gt/manuals/su ... /cover.htm
Says float height should be 25.75 . 25.25 is for j/k models this means there is too much fuel in the bowls and could be the problem.
It goes without saying that overflow tubes are flowing because the petrol is not switching off at the level it is supposed to. Usually caused by sticking float or punctured float sinking. Are the float needles clean as it's possible a small piece of debris can prevent the valve from sealing
NO SMOKE .......NO POKE
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Alan H
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Location: Wombwell, Republic of South Yorkshire

Re: GT550M Carb Problem

Post by Alan H »

Dud floats, leaky float valves or incorrectly set float levels.
Proof that four strokes are over complicated
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Syd
Posts: 311
Joined: Tue Aug 16, 2011 11:25 pm

Re: GT550M Carb Problem

Post by Syd »

Thanks for your comments gents - there seems to be a lot of really conflicting Suzuki info out there. My manual has the float height at 24.25 as shown on the attached photo and in digging deeper, the Suzuki 75 GT550 M spec below says 25.8 - see attached link. Seems obvious what the problem is and how to fix it. I will also double check to see if the floats are sticking or dud.

https://www.oldjapanesebikes.com/mraxl_ ... les/page-9

Top overflow tubes question - I noticed that there is a top overflow tube on the LH and centre carbs but not on the RH carb, is this correct?
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550pg041.jpg
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PaulD738
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Location: Warrington Cheshire

Re: GT550M Carb Problem

Post by PaulD738 »

I don’t know about the 550 but are you sure they aren’t the choke tubes?
They're rubbish them Jap bikes lad they won't last five minutes! you want to get yourself a nice Royal Enfield!
A quote from my old dad 8-)

I started out with nothing and I’ve got most of it left!
barney01
Posts: 3118
Joined: Wed Sep 26, 2012 7:33 pm
Location: Prestatyn.Wales

Re: GT550M Carb Problem

Post by barney01 »

Syd as Paul says the right carb on the gang setup has no choke it is fed by the left and centre starter circuit. Are you missing tubes that connect them together
I see there is an air vent tube too
https://www.partzilla.com/catalog/suzuk ... tor-gt55ol
NO SMOKE .......NO POKE
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Syd
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Re: GT550M Carb Problem

Post by Syd »

Sorry about the delay in getting back - I found the problem which is he RH carb float (LH float in the attached pic) as it was hanging down way too low in the bowl which resulted in the valve needle partially dropping down and most likely jamming the float. While I checked the float heights on each carb, I didn’t check each float position and how they moved up and down in the bowl when sitting in the normal position. This resulted in petrol coming out of the bottom of the float bowl tubes and also out of the top tubes which are ganged together. All the float heights seem to be correct at around 25.75. I have ordered a new carb float to fix the problem.

My earlier question about the top overflow tubes can be seem in the photo as the white plastic tee fitting is attached to the LH & centre carbs and not the RH carb which I assume is all correct? - just hope not too much fuel got past the carbs if fuel was coming out of the top overflow tubes when this happened.
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yeadon_m
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Location: Canterbury Kent

Re: GT550M Carb Problem

Post by yeadon_m »

Syd,
Super orange GT550M! a credit to you. The white plastic T pieces link each adjacent pair of carbs, hence for a triple, there are but two links and drain hoses. You're OK as shown, same as my 550B carbs. I agree with Alan on possible causes.
Cheers,
Mike
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