New to me gt750a

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Salmanz8
Posts: 65
Joined: Tue Mar 16, 2021 4:39 am
Location: Edmonton AB Canada

New to me gt750a

Post by Salmanz8 »

Hello all

Thanks for giving the time to read this, here goes;

I recently acquired a 76 gt750a with 26k miles.
All original, but had sat for over a decade.
When i got the bike, it was a non runner, anytime the starter was turned it was dripping oil from the left header clamp.
Was not hydrolocked.

I have been restoring cb750’s and z1’s, for over a decade and am pretty particular about stuff, and having no known history, i wanted to get the bike running before doing other things of maintenance.
So the carbs came off, and cleaned. Ultrasonically as well as manually. Intake boots were softened.
Air cleaner was replaced with a nos one, old one had perished.
Air screws at 3/4 turn and she fired up.
Then snow came and it sat all winter.
I didnt change or measure the float height, why, i do not remember, or if i did i dont remember that either.
Jets were correct. Needle clip was in 2, which i changed to 4, remeber seeing that somewhere for updated carbs. These are the cv carbs.

Fast forward this early spring. I had to move the bike to my warehouse where my shop is, i decided to ride it there.
The bike runs good, but bogs at 5k in top gear, and starts heating up.

I have decided to work on this now, so heres the list;

Points service and check timing.
It already has new plugs b8es
And check float height.

Plugs do not look lean at all, and the bike has had baffles cleaned and wrapping removed.
I synced the carbs yesterday, with vaccum guages, and that has made it smoother obviously, but still when she fires it struggles to run on left cylinder till warm. And smokes a bit out the other three pipes. Even after, smoke is more from the other three than the left. Sris pipes are connected.

What are the standard baseline settings for these carbs ?
Anything out of the ordinary i should look for ?
I know that the points are worn, and i will adjust for now, replace with electronic afterwards.

Coolant flush perhaps ?

This is a new to me bike, and i am eager to learn.
I have worked on h1’s and rd400’s but no gt750’s.
I want to put this bike into service and be able to ride the highways. Compression though not measured, but appears good.
No oil in the oil pump area, and after nee crush washers the exhausts no longer drip. Left pipe isn’t as oily as the other three.
teazer
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Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: New to me gt750a

Post by teazer »

Welcome.

After the usual deep cleaning and replacing consumables including tires, I would clean and check the points and set the FUEL levels in the carbs. It's more accurate than setting float levels.

With the carbs off to do that, I would do both a compression test and leakdown test. On a 4 stroke I use 100psi for leakdown, but on a two stroke you cannot exceed 10psi or the seals will blow. Crank seals tend to harden and stick to the crankshaft and tear, but a leakdown test on each cylinder will show if they are leaking.

The left struggling to fire may be a partially blocked starting jet. http://pinkpossum.com/GT750/carb/BS40carbs.htm for everything you want to know about those carbs but were afraid to ask.

With the carbs off, check the short "hoses" linking them. and check the pilot bleed outlets close to the throttle valve.
Lots of owners keep the points and if you want to do that, make sure they are clean, gapped and timed correctly. Personally, I always throw them out and fit an electronic ignition. I like the Accent system. It's easy to fit and reliable. For timing, Suzuki uses a propeller which is located by the peg and has a fair amount of side to side play, but is more or less OK for such a big softie that isn't very particular about timing being spot on.
asco58
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Location: London

Re: New to me gt750a

Post by asco58 »

Hi there,

I had a similar issue but it was on my GT550. My points plate was badly corroded after siting exposed for decades (I presume) and It had affected the screws which hold the points in. My bike never ran properly on the right cylinder. Every time I set the points with the dial gauge to Suzuki's spec, after running the engine, it appeared to have moved a bit on the right cylinder's points. The insulators which touch the cam were also worn a bit and I had just cleaned and rebuilt the carbs and the engine with a rebuilt crank and re-bored cylinders so that ruled out compression and fuelling for me. It could be worth checking that the screws/threads are not stripped or damaged.

In the end, after a couple of months of checking the carbs wiring and coils and adjusting the points to no success, I also went for the Accent electronic ignition system which was very easy to install and configure. It's also very compact as it doesn't have a box to hide anywhere. After changing to the Accent system, my engine fires on all three cylinders.

I can't say exactly what your problem might be but ensure your wiring, coils, plug caps and carbs and compression are ok and the correct specs and then you'll know if the problem with the points.
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Salmanz8
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Joined: Tue Mar 16, 2021 4:39 am
Location: Edmonton AB Canada

Re: New to me gt750a

Post by Salmanz8 »

Thanks for the replies fellas.

Carbs i am pretty sure are super clean. I can always go ahead and reclean them if need be.
After the sync, once its warm its running good in the low end and midrange. It falls on its face when the throttle is wide open.
When i was putting the carbs together, i made sure not to disturb the existing float height because i didnt have the info at the time.
Secondly, the points do look worn. I can see the heals are worn and sort of falling apart. So more than likely the timing is less than perfect.
My guess is, its either the float height is incorrect, which shouldnt cause that drastic of a difference unless its very low.
Or its the timing causing all the grief.
Considering that the plugs were completely worn and had an insanely wide gap when i replaced them, coupled with the clearly falling apart points, i am hoping timing will resolve the issue.
The bike starts and idles like perfection.
No air leaks, no hanging revs.
I have gone ahead and ordered accent ignition, for the same reasons as above. Lack of box and cleaner.
I like points, but when it comes to point replacement on any bike, i’d much rather go to electronic ignition. Lets start with that.

Since the bike seems to heat up a little under load, i am contributing it to inconsistent timing at higher revs.
When i strobed it at idle, it doesnt seem too far off, but wierd things happen at higher revs. Incorrect gaps, points float ..

What is the float height supposed to be ?
Mixture screw at 3/4 turn out ?
Needle clip in 4 ?

Please add anything i’ve missed
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Salmanz8
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Location: Edmonton AB Canada

Re: New to me gt750a

Post by Salmanz8 »

Checked the timing today with a strobe, since i had forgotten since last time, it is perfect as per the suzuki pointer.
Even if the pointer is off a little, it wouldnt be too far off.
Even though i had gone ahead and ordered an accent ignition, but this bike starts and idles absolutely perfect.

The only concern i have is, why does it fall on its face at higher revs in top gear. 70-75mph in top gear and it goes booooaaaah on full throttle.
I should probably take the carbs off again, check the floats and main passages in the bowl ?
Anything else i should be looking for ?

Unless all the main passages are blocked, which seems unlikely, i do not quite understand.
It does want to overheat if you push it with wide throttle. which would kinda be with fuel starvation.
I do not think its the seals, since there are no other symptoms. Runs smooth all the way there and then falls on its face.
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Salmanz8
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Location: Edmonton AB Canada

Re: New to me gt750a

Post by Salmanz8 »

Another thing i noticed.
Runs great in low end and midrange.
Right around 3/4 throttle, starts to bog. Closing the throttle a little makes it start accelerating again.
But heres the weird thing, it pulses as it tries to accelerate.
As if, fuel is coming and then not.
Right around then the temp starts rising a little beyond half way.

My guess is, its definitely the main circuit.
Definitely, leaning out with throttle wide open.
Genuine to the bike main jets.
Float height doesn't affect main circuit too crazy, correct ?
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Salmanz8
Posts: 65
Joined: Tue Mar 16, 2021 4:39 am
Location: Edmonton AB Canada

Re: New to me gt750a

Post by Salmanz8 »

If there is crap in the bowl, i might be the unluckiest person out there, that the pilot is fine but the main got clogged. Lol
( tank was cleaned and derusted, but there is a possibility that something made its way down past the petcock screen, and in the bowls. There was some particulate in the sediment bowl )
Last edited by Salmanz8 on Wed Mar 24, 2021 9:06 am, edited 1 time in total.
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canaletto5
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Re: New to me gt750a

Post by canaletto5 »

Are you running with a stock airbox and clean filter? Kev
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Salmanz8
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Location: Edmonton AB Canada

Re: New to me gt750a

Post by Salmanz8 »

canaletto5 wrote: Wed Mar 24, 2021 8:40 am Are you running with a stock airbox and clean filter? Kev
Yes sir, airbox and a nos airfilter.
Other than WOT, it runs pretty close to perfect
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canaletto5
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Re: New to me gt750a

Post by canaletto5 »

What condition are the plugs in? are they showing rich or lean if you pull them immediately after a blast of WOT?
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