Topic: Help tuning carbs on a '77 cb750

[77cb750]

Hi, I need some help tuning the carbs on a '77 cb750 I just got. When I got it the only way it would run is if I had the choke on, this is even after it was warmed up. I did some reading and learned about the needle jet height. I tore apart my carbs and found the needle clip was all the way at the top, way too lean. So I have moved it down to the middle position. The bike runs better and will run without the choke but pops and spits at anything above idle and is very low on power. Am I still too lean? I would think so and I may try and bring the clip down one more notch. I should say that this bike has a 4-1 header and pod filters. I also have the stock 115 main jet. Can anyone offer some help? I am going to check the timing this weekend also, and it does have a Dyna electronic ignition already. HELP??

[77cb750]

bump

[jdpas29]

have someone synch the carbs before you go too far into the clip adjusting.  you may need your float height adjusted and your timing/firing may be a little off.

the pods and the 4-1 are going to speed air through the system faster than the stock setup so the bike will tend to run lean as is.  my bike is the same way.

[750goes]

Have you given the carbies a general clean as well, some of the poor idling coughing etc, can be quite easily caused by some blocked jets, or sediment being stirred up via fuel tank, float bowls etc..

You need - clean fuel, clean fuel lines, clean filter (if one is installed), clean carbies, ... then start making a few adjustments,
slowly slowly catchy monkey.

what model carburretors are on the bike?
what are the idle jet size ?
have you done anything else apart from adjusting needle clip position ??
what condition were the float bowls??? lots of sediment/varnish???

nearly everyone on this site has been there (some many times) done that ,, it gets better ,,,

[damn_yankee]

Are you sure your pilot jets are clean? I was able to place a small piece of wire (from a lamp cord) up the jet all the way so it was visible in the butterfly throttle opening.

[750goes]

any updates from the weekend

[eurban]

The previous poster's comments about the idle jets is a wise one.  Trying to tune your carbs before you have established that the carbs are properly cleaned and functioning is a waste of time!  Assuming that your carbs are the problem and that you have the stock acel pump carbs then you should certainly make sure that all is clean, adjusted and  particularly that those pressed in idle jets are clean.  Pull them out gently and run a strand of copper wire thru them.  These #35 jets are a bit lean to start with on a poded bike so any obstruction will mess things up.  Also you should confirm that the acelerator pump is functioning.  You can do this with your carbs on / off  (for off you would have to provide some fuel to the carbs and operate the throttle wheel by hand) the bike by removing the filters and blipping the throttle and seeing if you get a squirt from the brass nozzle located at the back of each carb.  The pump may take some priming if fuel has been drained from its resevoir (under carb #2)  In general its a good idea to make sure everything is up to snuff with the entire machine  before you spend time "tuning" your carbs.  FYI, you should be happy that your 77 carbs needles are adjustable.  The 78s came with non adjustable ones