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Smoking coming from engine?

  • Thread starter Thread starter TheNewGuy
  • Start date Start date
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TheNewGuy

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Bought a 1977 Gs750 last week. Has 19,200 miles.Rode it 15 miles home. Bike was smoking out of the engine. Ran poorly and didn't want to rev above 5k. Anyone ever heard of this? Could it be a head gasket or bigger problems? I changed the oil,plugs and cleaned the carbs. Probably should have addressed the smoke first. Going to do a compression test tomorrow. Any help would be appreciated.

Thanks
 
TheNewGuy said:
Bought a 1977 Gs750 last week. Has 19,200 miles.Rode it 15 miles home. Bike was smoking out of the engine. Ran poorly and didn't want to rev above 5k. Anyone ever heard of this? Could it be a head gasket or bigger problems? I changed the oil,plugs and cleaned the carbs. Probably should have addressed the smoke first. Going to do a compression test tomorrow. Any help would be appreciated.

Thanks
Click to expand...
Where is the smoke coming from?
 
"smoking out of the engine" you'll have to be a bit more specific than that. Was it smoke coming out of the exhaust pipes or was smoke actually coming from the engine area? was the smoke blue or white? the compression numbers will good to see. These bikes are pretty easy to work on no matter what the issue. Welcome to the forum.
 
It's not coming out the exhaust but the engine it self. I'm having trouble pin pointing the exact location it's coming from. The smoke is not blue.
 
Last edited:
azr said:
"smoking out of the engine" you'll have to be a bit more specific than that. Was it smoke coming out of the exhaust pipes or was smoke actually coming from the engine area? was the smoke blue or white? the compression numbers will good to see. These bikes are pretty easy to work on no matter what the issue. Welcome to the forum.
Click to expand...
I thought about asking what color, but there should be no way of getting white smoke from an air cooled engine.
 
Oil leak then. You'll have to clean off the engine first to figure out where it's coming from. Could be as simple as a valve cover gasket or as bad as a base or head gasket leak. All are fixable. Clean the engine and start hunting, should be easy to find. If it's a tinny leak and hard to find some people clean then use some baking soda in the area they think it's coming from and start the bike up for a short time, minutes, and then look at the powder.
 
TheNewGuy said:
It's not coming out the exhaust but the engine it self. I'm having trouble pin pointing the exact location it's coming from. The smoke is white colored.
Click to expand...
I'm not sure how your getting white smoke. it should have a blueish tint. White smoke is usually steam coming from a coolant leak into the cylinder. You have an air cooled engine with no water or coolant. Is the smoke coming from the breather on top of the engine. There is suppose top be a hose running from there to the airbox behind the carbs.
 
Sometimes people think their bike is 'smoking' from the pipes but then you start asking questions and they say it's 'white smoke' and it turns out they have been running their bike too long in the driveway idling and it's simply the water building up in pipes causing steam.
 
First off this forum is awesome. Thanks to all for the quick replies. I will post the compression numbers tomorrow and clean the engine and really take a close look for the source of the smoke.
 
azr said:
Sometimes people think their bike is 'smoking' from the pipes but then you start asking questions and they say it's 'white smoke' and it turns out they have been running their bike too long in the driveway idling and it's simply the water building up in pipes causing steam.
Click to expand...
Gotcha. I didn't think about that much condensation building up in exhaust outside of Florida.
 
gsrick said:
I'm not sure how your getting white smoke. it should have a blueish tint. White smoke is usually steam coming from a coolant leak into the cylinder. You have an air cooled engine with no water or coolant. Is the smoke coming from the breather on top of the engine. There is suppose top be a hose running from there to the airbox behind the carbs.
Click to expand...

I have the hose to the air box hooked up. I'll take a real close look at the color of the smoke tomorrow. Thanks for the info.
 
A couple other things to consider while diagnosing. Is your "smoke" happening as soon as you start the bike? While warming up? After sitting in the driveway for 15 minutes? After coming in from a hard run?

Where are you seeing the "smoke"? From the top of the engine? From the front? From behind the cylinders? From the bottom?

.
 
Well it doesn't look good. Compression test says:
Cyl 1- 90
Cyl 2- 80
Cyl 3- 80
Cyl 4- 90

Plugs are black and dark. The engine is smoking after being ridden around the block. Still can't tell where from. From the valve cover to the air box im seeing smoke. Thoughts on where to go from here are greatly appreciated.
 
TheNewGuy said:
Well it doesn't look good. Compression test says:
Cyl 1- 90
Cyl 2- 80
Cyl 3- 80
Cyl 4- 90

Plugs are black and dark. The engine is smoking after being ridden around the block. Still can't tell where from. From the valve cover to the air box im seeing smoke. Thoughts on where to go from here are greatly appreciated.
Click to expand...
Not the greatest numbers, but each cylinder is within 10-15% of each other and that is good news. Did you hold the throttle wide open while doing the tests? You can also do a leak down test to see where you're loosing compression. If it is the rings, which could be the cause of the smoke, you'll be able to hear the air escaping in the crankcase by listening in the oil fill hole. If it is the valves you'll hear the air leaking out of the air box or exhaust pipes. I don't remember if you said if you adjusted the valves or not.
 
As Rick says, the numbers are not all that bad, but a little background is necessary. Did you do the test before or after the trip around the block? It should be done on a warm engine. Was the throttle held wide open? Were ALL the plugs out? Have the valves been adjusted?

.
 
Steve said:
As Rick says, the numbers are not all that bad, but a little background is necessary. Did you do the test before or after the trip around the block? It should be done on a warm engine. Was the throttle held wide open? Were ALL the plugs out? Have the valves been adjusted?

.
Click to expand...

I did the test after riding the bike around and held the throttle open during the test. I have Not adjusted the valves yet. All the plugs were out during the test.
 
Ran the leak down test:
Cyl 1- getting pressure through oil fill hole
Cyl 2- getting pressure through oil fill hole
Cyl 3- leaking through carb and exhaust pipe
Cyl 4- leaking through exhaust pipe

Not sure where to go from here. New engine? Full rebuild. Just rebuild the head? I think my rings are bad on one and two though
 
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