Topic: Honda CB750 K4

[Dammerung]

Im so glad I joined this forum. A big shout out to Wrenchmuch I want to thank everyone for their time and advise. Luckily for me wrenchmuch lives close to me and he helped me with my carbs. Cyl4 had a bent float holder and the float height was out of tune completely. The throttle valve holders were bent out of shape. He had spare 110 mains which we switched for my 120s. Left the idle at 40 for now. I put the carbs back on my bike and it started with no choke and all 4 cyl seem to be nice and warm now. Power output is good but since i took the throttle cables off i dont know if i put them back in right.

I still have a lot of carbon deposit especially in cylinder 4. Wrenchmuch gave me good advise and told me to start with a fresh battery and plugs and move on from there. My ignition coil and wiring harness is about 40 years old as well. That is what I will get at one by one.

Once again thank you Wrenchmuch
PS you have a wonderful family Made me miss mine so very much!

[Dammerung]

I have the one very similar to yours all done by PO. 4-2 exhaust. When i took the carbs apart i think the mains were 120 and the idle was 40. Im not sure abt the idle size but im sure the mains were 120.

I have the exact same symptoms as yours. You know i havent had it on the road yet. Just start up and drive around the parking lot IT EATS GAS RIGHT UP!!! I HAD TO FILL THE TANK TWICE ALREADY :O:O:O
aas for the spark plugs, cyl 4 gets crazy sooty from clean in 2 minutes of start.

So you think its best i run 105mains and 35 idle? Im using NGK D8EA sparks as well. I have stock air box and PODs, i dont want to change to PODs as i like the older look but will do if it means better performance.

Personally I would stick with the stock airbox.  There are many opinions on pods vs stock airbox, but that is mine fwiw.  It is my recollection that #110 main is stock on the '74 and #40 is the stock idle jet.  According to Hondaman all came from the factory jetted rich - see this thread for a collectoin of the writings of Hondaman as gathered into one thread by forum member SteveD CB500F (thanks Steve!):

http://forums.sohc4.net/index.php?topic=7401.0
In particular, this:
4. Jetting. ALL of the inline fours came rich from the factory. At sea level, we started with a 10 size less than what it came with.

I am probably running a tad lean with my combination.  My recommendation would be to switch to #105 mains with fresh plugs and ride a bit then check your plugs to see how they look.  If you still have problems then maybe change the idle jets.  Most people don't recommend the idle jet change I did.  Use it at your own discretion.

Plug #1 afer thousands of miles including long trips and riding to work and back, plus lots of sitting unused:

I got 110 and 40  in right now and previously had 120 and 40. the carbs seem good now. I will probably adjust the air mixture a bit more and see if that helps as well. For now i think i need to go step by step. Wrenchmuch is going to teach me a thing or two in the summer to come. Im hoping to get a new wiring harness, new ignition coils boots and timing. I am not sure but quite positive i have weak spark.

[phil71]

WOW, that is a great story!

[Dammerung]

WOW, that is a great story!

Yes it is He is so helpful and patient. Explained things to me twice if needed. He is going to show me how to adjust valve timing and help put together the Dyna S system for ignition in place of points.