Dark exhaust

Q

quadracer351

Coast to Coast
Have my 74cb750 bored out to 811, right now I have 110 jets in the carb and getting dark exhaust. It's not every dark but certainly noticeable. The motor is bored out to 811, because of the Pistons I had to have a thicker head gasket made its
.070mm thick, with pods and 4 into 1 exhaust. Too cold in the garage right now so I'll be doing a compression test tomorrow when it's warmer. I'm hoping the gasket isn't too thick, the motor is a fresh rebuild and I'm sure the rings aren't fully seated yet, also thinking the slow jet and needle will have to be changed/adjusted?

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150 is a good result if cold.

What do you mean by dark exhaust? Smoke? What color?
 
SONIC. said:
150 is a good result if cold.

What do you mean by dark exhaust? Smoke? What color?
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Light black. Plugs are also oily. At this point I'm hoping its just a carb/timing issue. I knew the carbs would need to be adjusted after the pods, bore and exhast. I also static timed the dyna coils but I can't get my timing light to work on this system for some reason.
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quadracer351 said:
Light black. Plugs are also oily. At this point I'm hoping its just a carb/timing issue. I knew the carbs would need to be adjusted after the pods, bore and exhast. I also static timed the dyna coils but I can't get my timing light to work on this system for some reason.
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Are you advancing the cam when you static time the Dyna? Or are you using point with Dyna coils.
 
irk miller said:
Are you advancing the cam when you static time the Dyna? Or are you using point with Dyna coils.
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No its a whole new dyna S system, got rid of the points. Again I don't know why I can't get my timing strobe to work with it, it's a brand new light. It was timed as instructed with the spark fully advanced.

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How long have those plugs been in? They are really oily. Did you replace the valve stem oil seals when the top was off?
 
They're really oily, or they're carbon coated and covered in fuel. How often does oil burn dark? It's usually white.
 
That's a lot of unburned oil. Plugs can only burn off oil and fuel if they get up to operating temperatures. If the plugs are old, they should be replaced. If they are fresh, there's a lot of oil around - maybe from the rebuild - or from seals or rings not bedded in and the bike hasn't been run hard enough to heat the plugs or to burn off any surplus oil.

It's not a jetting issue that causes that - unless the mains are so huge that the motor cannot get up to temperature. At this time of year it's hard to run a bike hard enough to get it working properly - except on a dyno. Good time to strap it to a dyno and see what's up.
 
teazer said:
How long have those plugs been in? They are really oily. Did you replace the valve stem oil seals when the top was off?
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Plugs are brand new. Forget the band off hand but there one of the better ones for this bike, I'll look and get the name tomorrow.
Tim said:
What if any work was done on the cylinder head?
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Just polished, there was interference with the new Pistons before I got the thicker gasket so I just polished them to get rid of the very small marks the Pistons made during that contact.
teazer said:
That's a lot of unburned oil. Plugs can only burn off oil and fuel if they get up to operating temperatures. If the plugs are old, they should be replaced. If they are fresh, there's a lot of oil around - maybe from the rebuild - or from seals or rings not bedded in and the bike hasn't been run hard enough to heat the plugs or to burn off any surplus oil.

It's not a jetting issue that causes that - unless the mains are so huge that the motor cannot get up to temperature. At this time of year it's hard to run a bike hard enough to get it working properly - except on a dyno. Good time to strap it to a dyno and see what's up.
Click to expand...
I'm in New York and its very cold right now and the motor hasn't been ran long enough to break in also haven't gotten the timing light I have to work with the bike so I'm hoping its also just a little out of synch. I did get one or two backfires when starting it up.

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Sorry guys closed on my first home this week and have been tied up with that. The plugs I have in now are Denso X24ES-U which from what I heard are one of the better ones to use. That's what's in right now. I also have NGK D8EA sitting around that can go in. Any thoughts?

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