Topic: cb750 K3 - Help with flooding/fouling after top end rebuild

[mwiese105]

I am sure this has been covered elsewhere so you have my apologies...

Short story; just finished a top end rebuild - went fairly well. Feel good about the timing (not sure timing makes a difference in my situation). Got it all back together last night. Didn't touch the carbs during the process. I had to replace a spark plug and cap for two unrelated reasons (busted piston ring in #2 fouled the spark plug and the cable terminal on the cap broke off because I am heavy handed sometimes).

Bit of extra info; I am using these crush rings (http://www.vintagecb750.com/parts/480/18-0110.jpg). The look like multiple "washers" that are soldered together. I think they need to be replaced because the pipe flanges will not fully seat up against the cylinder head.

Upon attempting to start my bike last night (yes - choke in mind), if will not start and/or run. At times, it will rev up to 3/4k and die. I have checked the plugs and they are a little wet with what I think is gas as I do not see how oil could get in there at this time. I ended up flooding and spilling gas out of the exhaust and on the ground but only out the #2.

Any help in diagnosing would be great.

[calj737]

First order of business is to verify the fuel level in the carbs with Clear Tube method.

Second is to determine if all 4 cylinders are firing, and whether the pipes are getting equally hot.

[flybox1]

AIR, FUEL, SPARK.
Air - what filter/pods opu using, and is the flow unimpeded? 
Fuel - +1 to calj....clear tube test the carbs. be sure the fuel level is adequate.
Spark - check points gap again.  .014"
I hate those alu exhaust gaskets. Copper on my bike. 
They are a one-time use item.  They'll never seal properly if reused.

[mwiese105]

Stock air filter - was a little tight to get back but that is expected. I really don't see how there could be any blockages
Fuel level should be ok hence the flooding, right?
Pipes are NOT getting equally hot - #3 is getting hot but I can't say the same for the others. Some are straight up cold
I've verified that the coils are delivering spark on all four
I checked the gap on the plug before putting them back in but it's worth the time to double check

Question: If it was oils that is fouling the plugs then I should see that coming out of the exhaust, right? That was the behavior when the oil ring on the #2 piston ring was broken in 2 places. You think it would be even worst because if these plug were fouled with oil then it would literally be pouring in from the valve head.

[calj737]

Fuel level should be ok hence the flooding, right? Exactly wrong. Flooding is an issue of too much fuel being drawn in by vacuum and not burned.
Pipes are NOT getting equally hot - #3 is getting hot but I can't say the same for the others. Some are straight up cold Well there's another clue...
I've verified that the coils are delivering spark on all four How did you verify this? If they were sparking, the fuel would be burning and the plugs fouled from too much fuel.

Question: If it was oils that is fouling the plugs then I should see that coming out of the exhaust, right? That was the behavior when the oil ring on the #2 piston ring was broken in 2 places. You think it would be even worst because if these plug were fouled with oil then it would literally be pouring in from the valve head.

If there's oil in the plugs that is fouling them, they will be black and wet. Post pictures of your plugs.

Since you didn't touch the carbs, I'd encourage you not to presume they're good, but go back and insure they're good. It's easy and well worth it.

[flybox1]

cold cyls = no spark, or mixture is too far off for proper combustion.
Check carbs and ignition components....again.
Dont assume anything is still correct.

[mwiese105]

So I got it to start, again, and was able to get an idle! Here is my theory:

The initial fire did not have enough gas, sure. But, it was also with fresh piston rings... I wasn't able to run it long enough to get the rings to expand in heat before fouling the spark plug with oil from the crank case (not the head). So taking the plugs out and cleaning them 3-4 times did the trick.

Thoughts?

[calj737]

I think you are grasping at straws speculating as to "why" when you simply haven't done the work to prove anything. But if you're happy, then that's all that matters.

It's odd to me when someone asks for advice from people with more experience to help solve a problem then disregard it. Why not just do what you think is right then deal with the results?

Ride safely-

[mwiese105]

Why do you think I disregarded your advice? "Oil on the plugs" was the troubleshooting path I took.

[calj737]

I could explain it to you, but I can't understand it for you. So there's little point.

[mwiese105]

AIR, FUEL, SPARK.
Air - what filter/pods opu using, and is the flow unimpeded?  No - Check
Fuel - +1 to calj....clear tube test the carbs. be sure the fuel level is adequate. Check
Spark - check points gap again.  .014" Check
I hate those alu exhaust gaskets. Copper on my bike. 
They are a one-time use item.  They'll never seal properly if reused.

Thanks as this IS helpful - I have copper rings on the way. So cold starts are the issue as I can run just fine, idle @ 1-1.2k, when it's hot. Also, realized it's fuel and soot fouling the plugs, not oil. And this morning, different pipes failed to heat up making it inconsistent so there was a fuel issue.
So, flybox, correct me if I'm wrong (remember, first rebuild) but the issue is likely with the carb because now with the improved compression, the mixture is rich. Bottom line, not getting consistent combustion because the plugs are wet.

[martin99]

Got to say you should listen to these two guys - both of them. All they're trying to do is help you to achieve a baseline from which to diagnose your problem properly. Even if you can't get your head round the theory at the moment, do it anyway. Or carry on chasing your tail.

Personally I'd be taking those carbs apart, cleaning meticulously, and clear tube checking them. When you're satisfied they are good, and if the problem still exists, at least you can rule them out. Process of elimination.

[riverfever]

Got to say you should listen to these two guys - both of them. All they're trying to do is help you to achieve a baseline from which to diagnose your problem properly. Even if you can't get your head round the theory at the moment, do it anyway. Or carry on chasing your tail.

Personally I'd be taking those carbs apart, cleaning meticulously, and clear tube checking them. When you're satisfied they are good, and if the problem still exists, at least you can rule them out. Process of elimination.

Yes sir.

[flybox1]

Thanks as this IS helpful - I have copper rings on the way. So cold starts are the issue as I can run just fine, idle @ 1-1.2k, when it's hot. Also, realized it's fuel and soot fouling the plugs, not oil. And this morning, different pipes failed to heat up making it inconsistent so there was a fuel issue.
So, flybox, correct me if I'm wrong (remember, first rebuild) but the issue is likely with the carb because now with the improved compression, the mixture is rich. Bottom line, not getting consistent combustion because the plugs are wet.

Those ^^^^ tell me your air/fuel mixture is incorrect.
If the bike runs so-so when it gets hot, great....run it, get the engine hot. 
Put in a new set of plugs, and start the bike.
Let it idle (cooling fan on the engine).  No blipping of the throttle.  4-5 minutes.
Pull the plugs.  Line them up next to each other 1-2-3-4, and take one clear closeup picture of their tips/Insulators, and post the picture for us to see.