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Running poorly after carb clean.

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SkullDanny

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Hi guys I'm new to the forum and just getting my head around it so I apologise if this is already covered.

I bought a 76 CB750 k a few months ago. I was so excited that I changed the oil out, clean up all of the electrical connections. New pugs, bulbs and cables and fired her up. She ran first kick sounded slightly clunky. I tensioned the cam chain and that was that. She ran perfect every time I fired her up. As far as I was aware she had not been run for 2 years prior to my purchase.

So.. I decided to clean the carbs. I pulled them cleaned and checked all jets, floats needles etc. everything seemed fine except a bit of crud in one of the main jets and a pilot jet ( not in the same carb ).

I fixed everything back to gather being as careful as possible.
Now she struggles to start with and without choke. Slightly better with. When she does fire the revs drop and cut out when I apply throttle. I have checked all of the boots for leaks. I can only find one screw in the side of the carbs (not the plug screw).i can't get her running long enough to do any tuning.
Thanks

Dan
 
Why would somebody clean carbs on a machine that 'ran perfect every time I fired her up' ?

Look at your work, the answer is there. What changed. Suspect the old boots.
 
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It might be if one is super sharp as to how to do it, most would tend to leave well enough alone. You of course see why now. An expert simply would take them apart again and not go back together until the fault found or enough detail inspection to ensure the problem is NOT the carbs.

Look here, the boots crack when they get old and you stretch them to get carbs in or out. Dunno how you checked for that but most just like with the carb build job do that half--ssed too. Nothing personal intended there at all, they just don't have the knack for attention to detail in that kind of work. Most for instance 'check the jets' but then completely miss that the jet is only a short part of the entire fuel pathway, that path can be a couple inches long on some. Looking at the first 50 thousandths of an inch there is NOT cleaning carbs. The ENTIRE path must be clean on idle, main and any other corollary fuel circuits in the working of carb. There's like 50 other things to be looking for besides just jets, in today's world of ethanol laced fuel simply displacing what looks like 'crud' can be flawing the carb when you fault a fuel circuit that when cleaned now has a corrosion hole in it. The floats get set and if using old parts you messed up by mixing them up if you did. Any disturbed gasket or rubber either must be primo or replaced. The carbs must be re-synced as well. What do you think you are going to 'tune'? The only thing you got there is idle speed and idle mixture, they only really affect carbs at idle, the motor should run above idle speeds even with those messed up.

It's a 4 cylinder engine, can you even tell if only one or two not working or all of them, need skills to do that. Those skills do not come with carb kits.
 
I understand that most don't check the full circuit. Non of the internarls appeared corroded.

When checking the boots I used starter fluid.

I am by no means an expert. I've had a few bikes that I have managed to improve through practice and I don't have many skills in this field yet but
 
No worries. That's the exact video that I used as reference. I have however had a revelation.
I sent my tank away for painting and have been using a mower tank that is pretty banged up but clean inside( my friend had it blasted in and out ), however the cap does not have a vent I only realised this having a good read of my shop manual. So I popped the cb cap over the filler hole on the mower and she fired up and idled, revs are sticking a little.
I also noticed that header #2 is leaking some exhaust fumes. I have only just recently installed the exhaust clamps. They weren't on the bike when it arrived.

Also I removed the air box to clean some dust out that I missed and blow out the filter, I left the velocity stack shaped boots on the carb. Could any of this lead to revs sticking.

Thanks Danny
 
Hanging rpm can be lean condition, vacuum leak, far off carb sync, binding throttle cables. sticking ignition advancer or weak advance springs can also cause a hanging rpm, have seen it several times especially on bikes that have set for a long time or with tons of miles.
 
X2, I sometimes forget the earlier ones use 4 cables, that can hang very easy. The modern dual cable setups are stronger sprung and hardly do that unless misadjusted.
 
kinks or rust or frays in the dual cable setups can cause them to stick or bind also. Seen cables get pinched in the steering lock causing binding. Also need to look at how they are routed. Its easy to get the cables routed wrong and can bind the cables when turned one direction or another.
 

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