New to me gt750a

Post your Kettle problems here and cures
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: New to me gt750a

Post by teazer »

Holes in the diaphragm will stop them from lifting.

If possible, check the FUEL level. I have a spare adapter you can have for a small fee. PM me if you are interested.

A simple check with the carbs is to blow air into the air filter side at the top and they should rise at more or less the same rate. You can also raise them and let them drop to see if they drop at more or less the same rate.

Did you check FLOW through the jets and drillings in the carbs? Start with the main jets because it's easy to see what's going on. I use a can of WD40 because it's less hazardous than carb cleaner. Spray through one main jet and then repeat on the other two. The flow should all look about the same. The idea is to try on one jet and then repeat on the other two for comparison. Don't try to do all the jets/holes on one carb and them move to the next carb.
Include the air jets (both sides of the carb) and the drillings in the float bowls and carb body. Don't forget the starter jets in the float bowls. http://pinkpossum.com/GT750/carb/BS40carbs.htm for pictures of the passages.

While you are busy spraying noxious liquids all over the place, check the bottom of each of the choke plungers. They harden with age and then fail to seal properly. The "rubber" insert should be reasonably soft to seal properly. I had one bike that one cylinder was really cool and after checking everything several times, I finally replaced the plungers and problem fixed.
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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 »

canaletto5 wrote: Thu Mar 25, 2021 8:48 am Is the vacuum pipe from the tap to the carbs ok? No kinks or splits? If you leave the tap on Prime, do you still get the same problem?
Yea same problem with prime position
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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 »

teazer wrote: Thu Mar 25, 2021 2:51 pm Holes in the diaphragm will stop them from lifting.

If possible, check the FUEL level. I have a spare adapter you can have for a small fee. PM me if you are interested.

A simple check with the carbs is to blow air into the air filter side at the top and they should rise at more or less the same rate. You can also raise them and let them drop to see if they drop at more or less the same rate.

Did you check FLOW through the jets and drillings in the carbs? Start with the main jets because it's easy to see what's going on. I use a can of WD40 because it's less hazardous than carb cleaner. Spray through one main jet and then repeat on the other two. The flow should all look about the same. The idea is to try on one jet and then repeat on the other two for comparison. Don't try to do all the jets/holes on one carb and them move to the next carb.
Include the air jets (both sides of the carb) and the drillings in the float bowls and carb body. Don't forget the starter jets in the float bowls. http://pinkpossum.com/GT750/carb/BS40carbs.htm for pictures of the passages.

While you are busy spraying noxious liquids all over the place, check the bottom of each of the choke plungers. They harden with age and then fail to seal properly. The "rubber" insert should be reasonably soft to seal properly. I had one bike that one cylinder was really cool and after checking everything several times, I finally replaced the plungers and problem fixed.
Will check the float height. 27.6mm ?
Should be what 2mm below the seam ?
teazer
Posts: 1035
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: New to me gt750a

Post by teazer »

Fuel level 2mm to 3mm below the gasket surface is a good place to start.

Setting float height is a good place to start and get them close enough to fine tune but not accurate enough for troubleshooting.

Do you have an adapter to screw in place of the drain bolt?
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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 »

teazer wrote: Fri Mar 26, 2021 12:10 am Fuel level 2mm to 3mm below the gasket surface is a good place to start.

Setting float height is a good place to start and get them close enough to fine tune but not accurate enough for troubleshooting.

Do you have an adapter to screw in place of the drain bolt?
Thank you teazer for the info.
i generally aim for 2mm below the seam for the 4 strokes i work on.
I didnt have an adaptor, but i figured since the bike was running really good in the midrange, float height cant be too far off.
Checked the usual float height, and was right at 27.6, may be .2 either way.
Didnt change it. Original floats and seat.
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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 »

Put it all back together, i did match the throttle plate opening on all 3. But my vaccum sync was a touch different.
May be i will go back and do a vaccum sync again.
But the problem has been solved. Can anyone guess ?

1 slide diaphragm was less than perfect. Upon closer examination, that slide would drop down far quicker than the other 2.
Had a spare carb bank, switched that out, confirmed the rate of drop was uniform across all three.
Did not find anything else wrong anywhere. Thats all she needed.

No wonder i kept getting pulsing when it was trying to go full throttle, as one cylinder wasnt going full throttle on slide, and leaning out.
Hope this helps someone in the future.

Cant believe i missed that originally.
Didnt even need to take the carbs off or take apart. But its a good thing i guess, that now i know everything inside is perfectly clear.
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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 »

Since manually evening the carbs, i can see that once warm, it wants a little more revs at take off.
All screws are at 3/4, but seems like vaccum sync will do it the trick it needs. As i didnt have this problem earlier.

Also, a good thing, that the intake manifolds i sofetened last year, were still as soft, and taking off and on was a breeze.
5 mins to take off, and 5 to put back. Cable undoing and reinstall was probably the hardest part.

Thank you guys for all the help.

Now will do the sync, and then the front end will come off.
New bearing races, and fork seals, and see whats up with the brakes.
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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 »

When i got the bike, the needles were at 2 from top, any one knows why would they be at 2 ?
fuel mileage perhaps ?
it has stock 45 pilots.
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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 »

Anyone using tapered steering bearings ?
Which ones do you recommend ?
I am not a fan of allballs, but thats me.
Anyone has used sss250 out of japan ?
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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 »

So now that the bike starts idles and runs good, i decided to take it for a short ride, 10 miles, since i was itching for it before pulling the front end apart for service.
The bike takes a while for the temp needle to start moving, it moved after about 3 mins of gentle riding, and around 3 mins of idling before starting to ride.
But then the needle keeps climbing and doesnt stop.
Luckily, i got to where i was going, but the needle was at 3/4 mark.
I parked and once back, around 10 mins, it had come down to 1/4 mark, strange. I felt the radiator, was warm but not excessively hot.
So i headed back, keeping an eye on the guage.
Needle started climbing again. Once i got back, while hot and engine stopped, needle reading 3/4, i pushed that red plunger, and nothing, no pressure.
I took the cap off carefully, and coolant was there. I felt the temperature of the coolant, i could put my finger in and wasnt hot, it was warm.

No coolant flush has been done, i will do that.

Is there a way i can verify flow ?
Thermostat housing i will take apart. Cylinder head was hot to touch, didnt have a gauge, cant tell how much, but was hot.

Thermostat feels closed once started, and does open up as i can tell the top rad hose neck starts warming up.
Radiator fins are clear, and no fluid is leaking.

Can these impellars corrode away over years of storage ?
I do not want to take the water pump out, if i dont have to.
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