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PostPosted: Sun Sep 13, 2020 8:35 am 
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Still in the Driveway

Joined: Mon Aug 24, 2020 4:00 pm
Posts: 6
Country: Canada
Suzuki 2-Strokes: 1977 GT750
Attachment:
77 GT750.jpg

Good Morning
My name is Marvin , live in Winnipeg Canada. Have never owned a 2 stroke before but I purchased a 1977 GT750 a few weeks ago and have been working on it when I have time but have some issues and was hoping to get some help. Anyway, the carbs apparently were cleaned and I had the bike running and took it for a few short test runs and it seemed low on power and slow to accelerate but not terrible. Then it started to backfire and stall but would start again but now its fairly hard to start. Plugs are new and don't look bad. It won't start with the choke when cold or hot, the choke has to be off. I'm wondering if a combination of timing and carburator issues ? It seems like more exhaust pressure out of the right exhaust pipe then the left but compression is L 129,C 135,R 129. Also,I have to crank it over with the kick starter but a strange thing is the electric starter spins the crank on the points side but not the engine ? Does that mean the starter clutch is kaput ? Anyway, any help on this old machine would be much appreciated !
Best Regards,
Marvin


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PostPosted: Sun Sep 13, 2020 8:59 am 
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Expert racer

Joined: Mon Dec 01, 2008 2:52 am
Posts: 1234
Location: Manchester, UK
The triples are ALL cold-blooded, and should always need the choke to start from cold unless the ambient temperatures are 80F and above. So I'd suspect a carb problem, perhaps the choke plungers are sticking part open. Give the bike a good basic service (point gaps, ignition timing etc) and double-check the carbs are as they should be.

All the manuals are here: https://www.oldjapanesebikes.com/mraxl_ ... /index.php

I can't help with the starter motor issue but someone will be along soon to help with that.

_________________
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 Sep 13, 2020 10:42 am 
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To the on ramp

Joined: Sat Sep 05, 2015 3:14 pm
Posts: 297
Location: southeast pa
Country: us
Suzuki 2-Strokes: GT
When you say the starter spins the points side,but not the engine, is it spinning the points cam?
If it spins the points cam but not the engine, it could be a sheared key on crank shaft for starter clutch. If this key shears it will throw off points cam alignment, causing timing to move.

_________________
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe


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PostPosted: Mon Sep 14, 2020 12:52 pm 
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Still in the Driveway

Joined: Mon Aug 24, 2020 4:00 pm
Posts: 6
Country: Canada
Suzuki 2-Strokes: 1977 GT750
Craig380 wrote:
The triples are ALL cold-blooded, and should always need the choke to start from cold unless the ambient temperatures are 80F and above. So I'd suspect a carb problem, perhaps the choke plungers are sticking part open. Give the bike a good basic service (point gaps, ignition timing etc) and double-check the carbs are as they should be.

All the manuals are here: https://www.oldjapanesebikes.com/mraxl_ ... /index.php" onclick="window.open(this.href);return false;

I can't help with the starter motor issue but someone will be along soon to help with that.


Ok,Thanks Craig380. The PO said the carbs had been cleaned recently but hard to say how good of a job was done.


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PostPosted: Mon Sep 14, 2020 12:58 pm 
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Still in the Driveway

Joined: Mon Aug 24, 2020 4:00 pm
Posts: 6
Country: Canada
Suzuki 2-Strokes: 1977 GT750
karl pa wrote:
When you say the starter spins the points side,but not the engine, is it spinning the points cam?
If it spins the points cam but not the engine, it could be a sheared key on crank shaft for starter clutch. If this key shears it will throw off points cam alignment, causing timing to move.


Yes, spins the points cam. If the key is sheared then I assume a fairly big job fixing it ?
Thanks karl pa


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PostPosted: Mon Sep 14, 2020 2:26 pm 
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To the on ramp

Joined: Sat Sep 05, 2015 3:14 pm
Posts: 297
Location: southeast pa
Country: us
Suzuki 2-Strokes: GT
Not to big a job, you need to remove left cover,to do this I removed points plate and hung down out of way,if like mine the idler gear shaft came with cover and I had to figure out how everything was to go back together,this is where Alpha Sports parts diagrams come in handy. then remove starter clutch from crank.
While in there you can check condition of the nylon water pump gear.
The starter clutch has a pin that fits into a slot in points cam shaft, with a sheared key your timing is no longer attached to crankshaft and will be floating all over and needs fixed before you worry to much about other things.

_________________
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe


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PostPosted: Mon Sep 14, 2020 3:18 pm 
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Still in the Driveway

Joined: Mon Aug 24, 2020 4:00 pm
Posts: 6
Country: Canada
Suzuki 2-Strokes: 1977 GT750
karl pa wrote:
Not to big a job, you need to remove left cover,to do this I removed points plate and hung down out of way,if like mine the idler gear shaft came with cover and I had to figure out how everything was to go back together,this is where Alpha Sports parts diagrams come in handy. then remove starter clutch from crank.
While in there you can check condition of the nylon water pump gear.
The starter clutch has a pin that fits into a slot in points cam shaft, with a sheared key your timing is no longer attached to crankshaft and will be floating all over and needs fixed before you worry to much about other things.


I took it apart and yes the key was sheared, the shaft is grooved up a bit but not too bad. I don't know how it even ran like that . Checked the nylon water pump gear and it has a big crack in it. Is this something that after cleaning loctite 495 or similar glue can fix ?


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PostPosted: Tue Sep 15, 2020 2:36 pm 
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To the on ramp

Joined: Sat Sep 05, 2015 3:14 pm
Posts: 297
Location: southeast pa
Country: us
Suzuki 2-Strokes: GT
Marvin wrote:
Checked the nylon water pump gear and it has a big crack in it. Is this something that after cleaning loctite 495 or similar glue can fix ?

Sorry I really don't have an answer to that. I would think it should help, I seen somewhere someone used metal to reinforce the gear but can't remember.
My one had a crack when I was in there, that's been several years ago. I hope I don't jinx myself. Now you have me wondering. :shock:

_________________
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe


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