Number Four Cylinder Won't Start!!

Hey all,

A little bit of back story:
So a few weeks back, I noticed I had quite a bit of backfiring under deceleration, so I decided I'd up the size of the pilot jets to attempt to get rid of this problem. When I took the carbs off to change the jets, I took the carbs almost completely apart (with a friend who knows what he's doing) and I gave them a real good clean, and we played with the float bowls a tad (one was bent and at a different level then the rest of them). They weren't too dirty to begin with either. However, when I reassembled everything, my bike had a real tough time starting. 2 of the cylinders (I believe 2 and 4) wouldn't start, only 1 and 3 were getting warm. I tried to troubleshoot, and after no results, I took the carbs off and replaced the original jets and reassembled everything again, keeping everything clean and tidy in the process.

Now, I when I try to start from cold (with choke on), cylinders 1 and 2 fire immediately, while cylinder 3 will start to get warm after a short while, and cylinder 4 won't fire! The cylinders that aren't firing fully have wet spark plugs when I pull them out, and they all seem to be slightly on the darker, richer burning side. I have tried switching spark plugs around, but the problem remains the same.

I realize this might be a carb issue, and might have to take them completely apart again, but I was just wondering if anyone has any ideas that might be different than that -- maybe an adjustment that I need to make that I don't know about or that I may have knocked out of wack when working.

Thanks in advance for all who take the time to help a fella out!

- Mike

How old is the wires? Maybe need some new wire at the end. Nip a 1/4" off the end and screw the connector for the plug back on. Is the plug connecter good? Check the fuel levels of the carbs with the clear tube? Ohm out the coils?

What type and year is your bike?

@bluej58 I can't believe I forgot to even say what bike it is! I guess I was up too late haha
It's a 1977 kz650B1. I picked it up from brooklyn back in July, but it seems to have been kept in pretty good condition.

Thanks!

@azman857 The wires could very well be the original wires. Good idea getting a fresh connection. The plug connectors look like they're in pretty good condition, but maybe there is something loose or messing with the connection somewhere in the wire/lead.
I've heard of the clear tube trick. I should get some and see if my levels are the same, maybe when we messed with the floats, it did more harm than good.

I'll let you know what I find! Thanks!

You had some backfire on deceleration so you pulled the carbs apart and changed jets, bent the float tangs, etc., and now the bike runs poorly. It seems pretty obvious to me that whatever you did to the carbs affected how the bike runs.

Even before you messed with the carbs There's no reason that the carbs would cause backfiring unless something was changed from stock. Does the bike have the stock airbox and air filter installed?

You said you bent the float tangs - did you do a clear tube test or did you just eyeball it?

No offense intended, but it sounds like your friend "who knows what he's doing" did not know what he was doing. Otherwise the bike should not be running so poorly. It's been known to happen more than once that a friend may mean well as he screws up something on your bike. Is there a motorcycle shop close enough to you that you can get the bike to it? Ed

When was the last time the valves were adjusted?
Steve

@steve I have no idea when the last time they were adjusted. I'm guessing I should probably do that, huh? I'll look into that and see what I can do. Thanks man!

Those carbs are pretty straigt forward I'm not sure which one you have, I think the 77 had a air screw on the side of the carb housing.
Can you take a pic?
Chances are all the O rings need to be replaced, but don't buy the kits that want to sell you new pilot jets or air/fuel screws they are junk, most likely the old ones just need a good cleaning.
Like they say, it's good to check the valves and get a new cam cover gasket.
If you don't have a shop manual here's the pdf for the 77 kz650 b1
www.kzrider.com/modules/ServiceManuals/K...Service%20Manual.pdf

Sounds like your ride needs a no hold barred, no step missed, tune up. carbs cleaned and adjusted, points/ignition set/timed, valves adjusted, carbs balanced. shoot, do an oil change while your tools are out, drive chain clean and adjust. show your ride some love.

Thank you all for you responses! Turns out my floats were WAY off, so I got my tape measure out at set them to 7/8'' (or 22mm)... bada bing it runs great. Still some a little backfire, but I'm not TOO worried about it right now. And hey, maybe a little backfire in deceleration is normal.

Thanks!

If you have popping on deceleration it can very often be a leak at the exhaust manifold or aftermarket open exhausts, either way keep your friend away from it.