Hey guys, I have a problem with my bike that I can’t quite nail down. It’s a 76 1200. S&S Super E. Teardrop air cleaner. Jets 265/68. I had a blown head gasket so I’ve had a semi top end refresh, new piston rings with a a cylinder hone, and then obviously new gaskets & a valve clean up with new seals. This was about 6 months ago. All back together and it started and ran nicely, didn’t ride it anywhere it was just stationary and I ran it for about 15 minutes. Shut it off. And have been fixing other problems, brakes etc. Then a few months later, re kick over, and now the front cylinder is puffing black smoke out the exhaust, only the front, and the plugs foul within about 4 minutes to the point of it not being able to run. Sooty plugs. Assumed really rich, when I turn the idle mixture screw all the way in the black smoke goes away and it seems to sound a better idle. The timing hasn’t been changed. I marked it years ago and it’s been running fine on that mark. Bottom end wasn’t opened during rebuild. Push rods have solid lifters. Not sure if it could be a valve problem but the push rods definitely get slackish at the bottom of the stroke if that makes sense. Plug wires and coil have been tested. Battery level stays solid. Gas filter is clean and float level working nicely with no muck in the bowel or clogged jets. Checked for manifold air leaks.

Anyone have any thoughts?

Appreciate any help.

Thanks for your time.

Arlo.

 

Go back to the carb - the needle and seat could have caught a small grain of sand - happens a lot - and is flooding the engine But i am surprised the idle mixture will cure it

you said you replaced the valve seals - and you replaced the piston rings - over rich soot and oil passing into the engine is almost the same visual

do a compression test cold - if you have the equipment a leak down test is great for singling out - need more info at this point

 

Soooo.....no break-in? 😶

 

Sounds like it don't run good enough for the break-in

 

May not have aligned the rings correctly

cam install does not have enough travel and the top retainer has crashed into the valve seal causing a direct oil feed to the engine

 

Is it possible to install the head/jug gaskets wrong blocking the oil drain hole from the top end?

 

I wonder if that would build enough pressure to blow the rocker box gasket first or the valve stem seal???

 

Thank you for all your replies. Heres an update & replies after having an evening free to tinker.
Break In - Doesn't run long enough to break in yet unfortunately.
First task completed was a intake leak check with some WD-40 and there was none to be found.
Fouled plugs within 3 minutes, sooty black.
Took the intake manifold and exhausts off, checked the push rod travel and there is confirmed no pressure holding valves open.
Watched valves open and seat by slowly turning the engine, not a noticeable amount of oil on them, not enough to foul plugs in 2 minutes anyway, not that I know what I'm talking about.
Cleaned carb out again and noticed a little bit of dirt in the air mixture screw, started and ran again and it ran for about 15 minutes without stopping itself, plugs still sooty black but didn't cut out in that time.
It seems to be missing though, like consistently on the front cylinder (one that has a consistent black smoke puff). I have changed the plugs a lot so that could rule out plugs? I have checked new plugs with an out of cylinder spark test, and they both spark, would that mean the leads are okay? Could either the leads or the coil crap out when it needs to do more work?
Anything anyone has to add would be highly appreciated in my next steps to look at.

Thank you for all your help and time.

Arlo.

 

You could have the float level too hi this causes the engine to run over rich

new plugs that foul are no good any longer - what number and type plugs are you using

with both plugs looking the same you have to back track and make sure every thing is ok in the fuel system

 

Here's a long shot. This actually happened to me a few years ago when I first got my bike.

Bike would idle fine and run good up to about 2000 rpm, then my front cylinder would start cutting out. Intermittent symptom. Drove me nuts! I finally figured out that the coil cover was vibrating enough that the sharp edge had cut thru the plug wires enough to short out. I learned what was going on while riding and reached down to make sure the plug wires were not loose on the coil. Got a nice jolt from the coil and looked down to see a spark jumping to the coil cover. Now that i think about it . . . this coincides with my need to replace the regulator. Sometimes I'm a slow learner. Anyway, I used my Dremel to take away some metal from the coil cover and haven't had that problem again.