75 GT550M Oil Pump Setting?

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

75 GT550M Oil Pump Setting?

Post by Syd »

My oil pump is set up correctly as per the service manual on my 75 GT550M with the line on the oil pump lever aligned with the line mark on post when the mark on the carb slide is correctly aligned with the top of the hole on the carb, however the bike just puts out too much smoke. The engine has been completely overhauled and the bike runs really well. The oil pump seals and orings were also replaced during the restoration and new Siris valves fitted.

I have just adjusted the oil pump lever mark approx 3-4mm down (see attached photo) to lower the oil pump output when the carb slide mark is aligned with the hole. Before I take the bike for a ride, I would be keen to know if any anyone tried this adjustment on a GT550 oil pump and found that this has helped reduced the amount of smoke?
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Oil Pump Lever.jpeg
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Alan H
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Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: 75 GT550M Oil Pump Setting?

Post by Alan H »

Mine are set standard Syd. What oil are you using? I use Rockoil semi synth now Putoline stopped doing TT light semi synth. These bikes do like a regular decent fast run to get rid of the crud though.
Proof that four strokes are over complicated
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Syd
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Joined: Tue Aug 16, 2011 11:25 pm

Re: 75 GT550M Oil Pump Setting?

Post by Syd »

Hi Alan, I am using CASTROL ACTIV 2T MOTORCYCLE 2 STROKE OIL - not sure if this is available in the UK? I agree with your comment about a good run, however these oil pumps do seem to deliver more oil compared to what is required, therefore the idea to reducing the flow slightly seems like a good idea. Would be keen to hear if anyone has tried this before?
asco58
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Location: London

Re: 75 GT550M Oil Pump Setting?

Post by asco58 »

I had an issue with the bike smoking heavily at idle some time ago after a rebuild as well. The main cause of the problem was the cam at the top of the oil pump being in the wrong position. Might be worth looking into that if you haven't already as once I corrected that the heavy smoke at idle changed to a bit of smoke when cold and then a light haze when warm with more smoke under acceleration. For reference, I'm using Comma SAE30 2 stroke mineral oil. Ash
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Syd
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Joined: Tue Aug 16, 2011 11:25 pm

Re: 75 GT550M Oil Pump Setting?

Post by Syd »

Great info, thanks. I'll check that out but I'm 100% sure the cam is correct, however no harm in another check. If its all fine, what are your thoughts on adjusting the arm a few mm as shown in my photo?
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canaletto5
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Location: Derbyshire

Re: 75 GT550M Oil Pump Setting?

Post by canaletto5 »

I wouldn't recommend it Syd. Too much oil is better than not enough, you could risk seizing a bearing. Check your air/fuel mix to see if it is running rich (black sooty plug etc) or try a different low smoke 2 stroke mixer oil
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