1980 GS750 Smokes on Hot Days

[ericeder141]

Hello Everyone,
I have a 1980 GS 750 that I pretty much completely brought back to life and she has been running great, but now that it is Summer on hot days and long rides she tends to "fart out" some blue smoke when I come to a red light or a stop sign. My first thought was it was the piston rings or a head gasket but with 170 psi coming from each cylinder I am kind of puzzled. In the fall or spring with temps in the 50s and 60s she runs like a champ but on 90 degree days she shows her age. Any insight on what I can do to solve the problem? The smoke really has no effect of the ride but its more of just them smell and the sight that annoy me.

Thank you and stay safe on the road

 

[Guest]

Hello Everyone,
I have a 1980 GS 750 that I pretty much completely brought back to life and she has been running great, but now that it is Summer on hot days and long rides she tends to "fart out" some blue smoke when I come to a red light or a stop sign. My first thought was it was the piston rings or a head gasket but with 170 psi coming from each cylinder I am kind of puzzled. In the fall or spring with temps in the 50s and 60s she runs like a champ but on 90 degree days she shows her age. Any insight on what I can do to solve the problem? The smoke really has no effect of the ride but its more of just them smell and the sight that annoy me.

Thank you and stay safe on the road

I have the same bike and in 34 years and 57,000 miles nary a sign of any blue smoke on hot days here and I'm talking about 100+ days.

Has your bike been sitting idle for any length of time? Have the carbs been serviced any? When was the last time the valves have been adjusted? When was the last oil change and the type of oil you are using? Is the oil level at the full market in the window? One thing that could be going bad are the valve seals, though usually it would smoke more then just a puff at off idle. Check your spark plugs and see which cylinder(s) it is coming from. The plug may show a little oil fouling, then again could be burned off once you get up to speed.

Where bouts are you located?

 

[ericeder141]

Bike has between 16-18k miles, only reason for the guess estimate is because I took the stock speedo off for a sleeker look. Valves were just done by a Pro, I am running standard mid grade 10-40 motor oil, but am going to switch to high grade Motorex 10-60 this weekend in hopes that the higher heat resistance will help. I usually run oil 3/4 of the way up on the sight glass when motor is warm. I was told that when the valves were adjusted the new valve guides were put in, but wishing I did that job myself so I know it is true. I am going to tinker around with her and check the plugs to see if any of them have excess oil build up on them.

On side note, when bike is also hot... and I mean hot like from a long highway ride @80mph or sitting in traffic for a awhile... sometimes I have a hard time when I shut it off and try starting it right back up. sounds like the battery is weakend by the heat, Any insight would help... the two problems maybe linked...

I am in NJ

 

[tkent02]

I was told that when the valves we adjusted the new valve guides were put in, but wishing I did that job myself so I know it is true.

Did you pay big bucks to have the head removed and replaced?

If not he didn't change any valve guides.

 

[Larry D]

Did you pay big bucks to have the head removed and replaced?

If not he didn't change any valve guides.

....and if the valve guides were replaced....the rings and a cylinder honing should've been done. At least if it were mine, it would've been done. The top-end would've been off anyway and as long as you're in there.....

I'd be a bit concerned, the 2nd generation 750's are prone to top-end oiling problems. Some of them will take the abuse and run forever...others suffer from top-end oil starvation and.....well.....become locked up, toasty critters......Don't ask me how I know.

 

[Guest]

Bike has between 16-18k miles, only reason for the guess estimate is because I took the stock speedo off for a sleeker look. Valves we just done by a Pro, I am running standard mid grade 10-40 motor oil, but am going to switch to high grade Motorex 10-60 this weekend in hopes that the higher heat resistance will help. I usually run oil 3/4 of the way up on the sight glass when motor is warm. I was told that when the valves we adjusted the new valve guides were put in, but wishing I did that job myself so I know it is true. I am going to tinker around with her and check the plugs to see if any of them have excess oil build up on them.

On side note, when bike is also hot... and I mean hot like from a long highway ride @80mph or sitting in traffic for a awhile... sometimes I have a hard time when I shut it off and try starting it right back up. sounds like the battery is weakend by the heat, Any insight would help... the two problems maybe linked...

Define Pro? Motorex 10-60>? Do they even make something like that? Most here use Shell Rotella diesel oil 10w-40, has all the goodies you need for a bike, either the conventional or the syn.

Exactly what is your bike doing when shut off and trying to restart? Sounds like some other issues going on there. Even in 100+ heat and flying through the White Sands Missile range (56 miles or so) in that heat at around 80, my bike will shut down easy and starts right up without any choke at all.

You kind need to start the beginning and tell us what all has been done to the bike and when and by who.

 

[eil]

I am running standard mid grade 10-40 motor oil, but am going to switch to high grade Motorex 10-60 this weekend in hopes that the higher heat resistance will help. I usually run oil 3/4 of the way up on the sight glass when motor is warm.

Everything you've mentioned there has me deeply concerned...

1) By "standard mide grade 10-40", do you mean automobile oil? If so, that stuff is not good for your transmission or clutch. Get expensive motorcycle-specific oil, or cheap Shell Rotella 15-40 (either conventional or synthetic is fine).

2) I would not switch to 10-60. Not only will it not help, is it not the correct oil for this engine.

3) That's not the procedure for checking your oil. The correct procedure is to put the bike on its center stand on a very level surface when the engine is cold. Start it up, let it run for just a few moments. (10-15 seconds max.) Shut it down. Wait 60 seconds. If the oil level is under the top of the sight glass, add some and repeat. If it is above, drain some and repeat. See the factory service manual for details.

None of these will fix the poof of smoke you're seeing on hot days, but they are things you probably want to keep in mind.

 

[ericeder141]

By pro I mean he is a retired Certified A tech from a local bike shop who does nothing but rebuild old goldwings, GS's, BSA's, Nortons etc.

As for the oil I have been using the standard oem Suzuki Motor 10-40 but I see no harm in switching to a semi-synthic 10w60 even though its $15 a liter (but hey good oil saves lives).

As for the starting issue, on a cold start bike literally fires up, can be sitting over night or over a month and withing 2-3 cranks she purrs like a kitten. Now come a hard day of long riding and traffic lights if I shut her off to check my phone for a minute or stop to fill her, when I re-start it she cranks over but its almost like it has a weak crank. On one occasion it was eaiser to just roll her down a little hill to jump start her, but lets say if I do the same ride then go somewhere and grab a bite to eat and she cools down for 20-30 mins i get back on her and she sarts right back up with no hesistation.

So like i said maybe the 2 problems are linked. Can the coils be getting so hot that it cause the bike to not want to start? Or can the motor be getting so hot that it heats up the starter motor so much that it weaking the connection in the acutal starter? My intial thought is that the heat from the head is causing it to expand so slightly that it allows tiny particles of oil to pass though the rings causing the richness. Also while being so hot when trying to start it the compression is ever so lower becase the head has expanded... anyways this is why god created Forums lol

Sorry for any mis-spellings... been staring at this screen way to long today.

 

[Weeksz]

I've had that issue with the bike not wanting to start after I've pumped gas or stopped for a couple minutes as well. I'm not sure of a solution but just so you know you're not the only one. Not sure what the cause either because I did have a new battery.

 

[Crankthat]

My guess would be a bad exhaust valve.
I would not ride it until you get it fixed.
If the cap cracks and pieces falls in the cylinder it will destroy the piston and wall.
You will be lucky if this has not already started.

Your engine is running real hot and that would be the problem with starting.
The starter cannot take the heat.
The heat is slowly deteriorating it.
Eventually it will not work at all.

If you continue to ride it like this it will cost you more money in the end.