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750 Katana running rich on number 4 cylinder only... help

  • Thread starter Thread starter Scott
  • Start date Start date
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Scott

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This is a real saga I bought the bike about 8 weeks ago it's jap import gsx 750 katana with about 15000 miles on the clock. It was running very rich
From the outset so I stripped down the carbs and adjusted the float hights cleaned all the jets etc . This cured the rich problem on all but the number 4 cylinder the down pipe cooler than the other 3 and there is a smell of unburnt fuel from the exhuast on the left hand muffler.

So idecided to go for a full overhaul I replaced needle valves and seats, jet needles, mixture srew orings and swapped the needle jets on 1 and 4 to see if the problem moved. It did not move and the rich number 4 pot remains.

I notice that when I adjust the mixture screw when at tick over on 1,2 and 3 there is change in pitch as you would expect but the mixture screw on 4 seams to have no effect.

Please help I am stumped.

Scott.
 
I'd start by checking cylinder compression. Also check the spark plug wire, and the connector at the end. Swap plug connectors with another cylinder and see what happens.
 
I have already tryed swapping the plug caps and HT leads but to no effect.

I guess if it had been running rich for a long time before I bought it there could be some wear on the rings. Would this cause the rich number 4 cylinder?

If this is the case do you think there is a chance that fuel may be making it to the crank case?

Does anyone have any experience with this problem?
 
A rich condition can make the mixture screw not operate as it should.
It could be an intake valve opening too long or other problem, but you may just need a carb vacuum synch.
Too much vacuum at #4 as compared to the others will create a rich mixture. When you hook up the tool the initial level read should be significantly higher than the others. If it's not, it's not vacuum related.
Of course, the valve clearances should be set BEFORE the carbs are synched.
 
I've never worked with buckets and shims before my last in line four was CB400 four which had these handy wee holes that allowed you to adjust the tapets using a feeler gauge and a spaner.

Does anyone know where I can get a step by step guide to adjusting the the valve clearances?
 
Scott said:
I've never worked with buckets and shims before my last in line four was CB400 four which had these handy wee holes that allowed you to adjust the tapets using a feeler gauge and a spaner.

Does anyone know where I can get a step by step guide to adjusting the the valve clearances?
Click to expand...
I'm sure someone here has the same valve adjustment procedure as your model. Make a new topic specifically asking for this info if you need to. Be sure to follow the factory procedure EXACTLY though. Many people take what they see as a short cut and measure with the cam lobe always pointing up. Even though the manual may tell you the measurement can be taken in this position, you'll get inaccurate results if you crank away and make every measurement with the lobe straight up. Once you see the quicker, simpler, factory method, you'll know what I mean.
I can give you the info for my '79 1000 and similar, but I believe your model has the screwdriver type adjustable clearances?? If not, let me know and I'll type it out.
Adjusting the clearances on any model is an easy enough job. There are some tips to help you though. You'll need a special tool to change out the shims too if your model is like mine. The tool can be found for about $30 new.
 
An 83 Katana 750 is screw and locknut valve adjustment NOT bucket and shim, adjust the clearences and then balance the carbs witha vacuum balancer, you will then have a far clearer picture of where the problem lies.
Dink
 
I still say check cylinder compression first. No amount of valve and carburetor adjustment will help low compression.
 
Well I did a compression test and the suspect number 4 cylinder was just 60 PSI and when I added a litttle oil to the cylinder the compression went up to about 100.
So it looks like a strip down and at best new rings. It's a real disapointment because it has only done 23,000 km and I had hoped it would not be a compression problem but when I bought the bike it was running very rich due to poorly adjusted float hight and a dodgy needle valve and that wont have helped as it would have been washing all the oil from the bores.

I guess with 23 year old bikes it's as much about the milage they haven't done as it is the milage they have done.

Thanks for all the help.


Scott.
 
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