week 4 of fault finding so could do with some supportive words and suggestions to get my MC18 MK1 to run properly.

She ran well before I got the engine rebuild - crank bearings were on their way out. Got her back together but she does not run properly. She has a TA12A carb with 130 main jets (128 is std), 38 Pilot, air screws 2 1/8 out, float 13mm, NGK B8ECS plug. Same setup she had before the rebuild.

Symptoms: she starts cold without choke first kick, revs to 5000 for a min or two until she settles to ~1800. She accelerates upto about 4000 in any gear, stuttering around the 5000 rev mark. Increasing the throttle slightly gets her to move slowly to 6000. When rolling off the throttle she holds at 3000 for 10 sec until she settles back to 1800.

What have I done so far:
- cleaned carbs, replaced slow jets and main jets, measured float, reseated air screw
- bought a new battery, checked voltage at 13.3V off and 14.35-14.40V running
- checked the RC valve – they switch on at 2000 and off at 3000 rpm so indicate normal operation
- checked all solenoids visually
- plugs seems slightly rich (albeit no real riding to date so)
- checked tank breather to make sure it was not blocked
- replaced the tap and filter and checked the fuel lines
- swapped the coils with a new set

Current conclusions:
Looks to me that its electrical - I do have a spare PGM CDI so my next action was to swap that to see if that makes any difference.

Before I do that any other suggestions? She does smoke considerably more on the front than the top cylinder. However, she only had a heat cycle and 4 times around the block with several idle sessions so not sure that this is an issue. Tx

Start with the easy stuff. What you are describing sounds like bike could be running grossly lean.

I would start by looking for and air leak someplace. Did you do a leak down test to make sure the crank seals really are OK, even if new. Check that the carb boots are not leaking as well.

Did you set the mixture screw on carbs, does bike respond to a change in mixture screw adjustment, if it's not responding, that's sign that air getting in someplace else, or pilot jet clogged, but you said you cleaned them, so air leak possible.

How about the rate of fuel coming from gas tank, make sure it flows good. Check that screen isn't clogged causing fuel to just dribble into carbs. You did say you changed tap, but it's easy enough to confirm fuel is actually flowing good.

No harm in checking the ignition, but it's probably the least likely cause if bike is running to 6k rpm. If you have a timing light you could put it on there to confirm ignition is firing when you Rev it.

I would not draw any conclusions from the plugs until you have it fully running. If you are using oil injection, the oil is getting in there regardless of what's going on and could mislead you a bit.

Keep a close eye on the temp as you are running it. If you have an IR temp Guage (point and shoot) you should measure the temps of each cylinder at the exhaust pipe near head. Both cylinders should be fairly close in temp after bike is warmed up. If one pipe significantly hotter, that is gonna be the one running lean. But don't be tricked cause if both cylinders close in temp they could both be lean.

It might take some time, but you will get it sorted. And you'll feel good when you do.

thanks - good further suggestions - will draw up a list and recheck everything incl the points you made.

Sounds like you've either damaged a crank seal during reassembly, or there's an air leak around the inlet, as Eric says.

Often, a simple (albeit rather crude) way to check, is to spray a little carb cleaner behind the flywheel and the inlet manifold when the motor's running. If you notice a sudden change in RPM, that's your leak. The inlet rubbers can crack due to age, and also the manifolds have been known to warp over time. I wouldn't use any sealant on the inlet manifolds, but a little grease can help it seal against the reed cages for testing purposes.

It's very rare for a 1988 centre seal to leak, but it could be possible if the crank wasn't accurately measured, or you've pinched it during the rebuild, but the symptoms sound pretty classic. If you have no joy with the above test, it's possible it could be internal, so again, as Eric says, you need a leak down test.
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Andy.
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Tx Andy - I will go through the list of actions over the Xmas period - will keep you posted

Update - cleaned the carbs again and swapped all jets. Found a small tear in the air solenoid tube. Started her up and still the same - she struggles returning to idle. I then checked the exhausts and the bottom cylinder was hand warm whereas the top was too hot to touch. I checked the spark and she has a good spark but still misfires on the bottom cylinder. Also noticed petrol and oil being thrown out of the exhaust of the bottom cylinder.

Next step is swapping the coils (albeit both are new and had used them in the bike before the rebuild). If that is not changing anything then I will swap the PGM CDI.

Any other suggestions?

Update 2 - Swapped the carbs, swapped the coils, swapped the plugs and still when she runs poorly on the bottom - she starts well, when idling i cannot touch the top exhausts - the bottom is still only hand warm. She splatters petrol and oil out and whereas the top cylinder smokes blue the bottom is white and thick. I rechecked the spark and it looks fine to me. A bit clueless to what do now - any inspiration welcome !

Time to try Andy's suggestion to spray carb cleaner behind the flywheel to see if left crank seal is bad. The white smoke could indicate water getting into head which could be due to bad head casket.

I know it’s a newly built engine but have you done a compression test on both cylinders?

I just remembered, you said lower cylinder is the one with white smoke running cool. The lower cylinder is on right side so spraying carb cleaner on left side might not help if left seal is ok and issue is with center and / or right seal. But can't hurt to try. Pull plug on right side and have a look at it after running. Try a compression check which you can do without too much tearing down. Then consider leak down. Also check if water level in radiator has gone way down too.

White smoke would normally indicate burning transmission oil. Possibly the RHS crank seal has been pinched.
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Andy.
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There must be an electric gremlin somewhere. I checked all connectors and reseated all and once I did she started at first kick and after a short idle I was not able to touch the exhaust of the bottom cylinder and now the top cylinder exhaust is hand warm. So the problem moved from the bottom to the top cylinder so it must be an electric issue.

Then is tied all connectors with a flat screwdriver. Whist doing that I accidentally shorted the battery tripping the main fuse. After that I now don’t get a spark nor the power valve motor resets - have I fried my CDI?

It sounds like you might have.