Gt750 Middle cylinder smoking

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Janv750
Posts: 10
Joined: Sat Oct 14, 2017 5:12 pm
Location: South Africa

Gt750 Middle cylinder smoking

Post by Janv750 »

Hi. My name is Jan. I am based in South Africa and own 4 old British bikes. I bought a 76 GT 750 a week ago. Rode one 40 years ago and just had to have one again. The plugs are a bit oily especially the centre one. The centre exhausts smokes quite a bit on start up and remains smoking throughout the ride. The performance is good and the bike starts immediately. I tuned the oil pump down a bit and the left and right plugs are now burning brown with very little traces of oil. The centre plug is still sooty. Any advice is appreciated.
Thank you for allowing me on the forum.
Roger Ackery
Posts: 3693
Joined: Wed Jul 20, 2011 3:40 am
Location: Sydney NSW Australia

Re: Gt750 Middle cylinder smoking

Post by Roger Ackery »

Welcome Jan,I'm in Sydney (Australia)
I have a 1976A model for over 15 years now & think I've finally got her running nicely :P
Do you have a workshop service manual for the bike ? There is a lot of info on the Internet.
The vacuum carbruettors work slightly different than most,screwing the air screw out actually riches the mixture & in makes it leaner,
3 quarters of a turn of the screw is the factory setting recommend,but not that critical.I'd fit 3 new plugs (NGKB8ES) & see how the bike performs,do you know what's in the oil tank ?
Might be an idea to get fresh 2 stroke oil.
if the bike has been stood for awhile could explain the smoking ?I don't think there is a crankshaft oil seal problem with any luck ;)
No doubt others on "here" will add some advice
Cheers.
Roger
GT750A.
Janv750
Posts: 10
Joined: Sat Oct 14, 2017 5:12 pm
Location: South Africa

Re: Gt750 Middle cylinder smoking

Post by Janv750 »

Thank you very much. Will do as you suggested
barney01
Posts: 3118
Joined: Wed Sep 26, 2012 7:33 pm
Location: Prestatyn.Wales

Re: Gt750 Middle cylinder smoking

Post by barney01 »

Hi Jan and welcome to the forum. A plug fouling up and excess smoking can be caused by many things. As Roger says a bike that has been laid up for years may have a lot of oil and water build up in the exhaust's usually caused by continually starting the engine without riding it. A good hard ride will eventually sort that! If the middle cylinder is not firing correctly for example bad ignition timing or wrong carb setting causing over fuelling then oil will foul the plug and spit into the exhaust. Another possible fault could be the SRIS valve sticking open causing that cylinder to over oil. Try checking all these and come back.
Why not put some pictures of your bike up? We all like looking at bikes...
NO SMOKE .......NO POKE
Janv750
Posts: 10
Joined: Sat Oct 14, 2017 5:12 pm
Location: South Africa

Re: Gt750 Middle cylinder smoking

Post by Janv750 »

Thank you for making me feel welcome and your response. Will do as you suggest and post again with photos. Appreciate your help
Janv750
Posts: 10
Joined: Sat Oct 14, 2017 5:12 pm
Location: South Africa

Re: Gt750 Middle cylinder smoking

Post by Janv750 »

Hi Guys. I replaced the 2 stroke and transmission oil and fitted new plugs. The outer carbs' pilot screws were 2 turns out and the middle one 2.5 turns. I set them all to 1 turn out and there is hardly any smoke. The spark plug tips burns a light gray colour. Is this correct or what would be the ideal plug colour? Thank you for the advice.
User avatar
slosher
Posts: 901
Joined: Fri Sep 23, 2011 6:55 pm
Location: Walsall,Black Country

Re: Gt750 Middle cylinder smoking

Post by slosher »

Hi Jan,welcome mate ideally your plugs need to be showing light brownish colour,if i where you i would try Pilot Air screws 1.25 turns out or even 1.5 to start with IMO always go a tadge rich with strokers,unless your racing it :)

Cheers Dave
GT750L
GT550L
TL1000 97s
T140V
Loctite Trained Engineer :lol:(since having the Bonnie)
User avatar
Alan H
Posts: 12104
Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: Gt750 Middle cylinder smoking

Post by Alan H »

Welcome Jan, nice intro.
I worked in South Africa some years ago - stayed in Florida Park in Roodepoort near Jo' burg and worked quite a lot in Germiston. Managed to do some Scuba diving a few times at Sodwana Beach and Umhlanga area as well!
Took the better half to Capetown and travelled the Winelands and the Garden route for a holiday a few years ago too. Nice place.

Now the problems you have. Are you anywhere near Jo'burg or elsewhere on the high veldt?
The higher altitude will make the engine/carbs slightly weak and you may need to keep an eye on this until you have a few decent runs on the bike to get it all clear. That 'may' be the issue with plug colours. What plugs are you using by the way?
Proof that four strokes are over complicated
Janv750
Posts: 10
Joined: Sat Oct 14, 2017 5:12 pm
Location: South Africa

Re: Gt750 Middle cylinder smoking

Post by Janv750 »

Hi Guys
Thank you for the welcome. I live in Vereeniging near Johannesburg which is at higher altitude. Will turn the pilot screws out and check again. Alan I holiday just north of Umhlanga. I am using NGK BH8ES plugs. An oil leak at the gear indicator switch has returned, will attend to it today as well. Do you perhaps know where I can import parts from? Is e-bay ok with our postal problems? Courier costs are very expensive. Need a seat cover and some odds and ends.

Thank you for the chats it helps tremendously.
Roger Ackery
Posts: 3693
Joined: Wed Jul 20, 2011 3:40 am
Location: Sydney NSW Australia

Re: Gt750 Middle cylinder smoking

Post by Roger Ackery »

HI,I have being getting my parts from Germany for a long time now, email gtreiner1@aol.com no Web Site, but will happily email you a parts list.
lots of suppliers on the NET of cause :) All the best with the bike,please keep us informed with your progress :)
Cheers.
Roger
GT750A.
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