Carb jet sizes

[neat street]

Hi All
I am looking for new main jets for my CB750F1 (1976) The standard is 105, and looking to go down to 100. E-bay and the like do have loads of jets for the Keihin carbs, but not specific to each carb type, so do not know which to order? any help would be gratefully received.
Thanks
John

[mick]

Hi John why do you want to go smaller?  what issues are you having if any ? cheers Mick.

[neat street]

Hi Mick
Still running a little rich, so going down a size should solve the problem?? The only other thing I thought of was the oil breather tube putting too much in the air filter box (If this is the case, not sure what to look at next)?
Many thanks for your reply
John

[hairygit]

If it's running rich on 105's you really should be looking elsewhere for the problem, air filter, float levels etc

[mick]

Hi John what symptoms are making you think its running rich? do you know what you carb needle clip is set on?, mine was doing the same mine was stumbling at low revs /throttle, I dropped my needle by one setting to weaken it up and it seems to have done the trick  cheers Mick.

[neat street]

Hi Mick
I have replaced all the jets (same as was on the carbs std setup) but plugs are coking up, it doesn't appear to be oily, new air filter etc, I also dropped the needle down one, when she runs, she runs well, but does hesitate a little in mid range (similar problem to Billy`s)
Sorry I haven't been on and replied earlier, working in Germany for a few days.
Many thanks
John

[mick]

Hi John I've just had a similar thing with my bike, I have a F1 engine, carbs & airbox in my KO frame, running 4 into 4 pipes HM341'S, genuine Honda air filter,

my bike was stumbling and running rich, my needle clip was in the middle one and I raised the clip one notch lowering the needle and weakening it up ,

105 main jet and 40 pilot jet float height 26mm, it now runs a lot better  ,  I did 100 miles on it today and its running the best it ever has no stumbling and

pulls like a train,  cheers Mick. 

[K2-K6]

John, have you got any current compression test readings to see what general engine health is like?

[neat street]

Thanks for your reply's, I thought that raising the clip (lowering the needle) would make it richer? so I lowered it by one (from the centre), maybe I should re set to lower the needle and try that first? I haven't got a compression test kit at the mo, but maybe could borrow one and see how that goes as well. I have just put in some higher heat range plugs to see how they work. I will keep you posted, but may take a week or so to get back to you.
Thanks again for your help and advise, always appreciated.
John

[neat street]

Thanks again, Odd job, I will check out the jets for the 500, but first will lift the clip up one above the centre and re balance the carbs before I change the jets
Thanks again to the knowledge you all pass on.
John

[Bryanj]

I think yours are the screw in type whilst the 500 has push in, Sirius in canada sell "Sets" of jets in assorted sizes

[neat street]

Thank you all for your help, Adjusted the needle and now runs a lot better with no coking! This has now created another issue, as well as one that I had before, but not mentioned maybe you can help please?? (new problem) When I let go of the throttle, the engine takes its time to slow down? I am thinking this would mean re-setting the idle jets (set at about 1 3/4 to 2 turns out at present),(old problem) and when starting from cold I have to re-set the engine speed (Increase the speed by the adjusting thumb screw, (1500 revs) when it gets warm/hot it then revs at 3000 so have to adjust again. Any ideas, apart from that, its running well.
Thanks again for your help and input.
John

[MarkCR750]

I read a while back that "hanging" revs , i.e. when you shut the throttle it takes time for the revs to drop means it's running lean.

PS anyone needing jets might want to try NRP (nrp.carbs.co.uk) Tel 0161 832 8646, I bought a set of mains from them today, £4.24 each, that's half the David Silver price, also they are carb specialists and can offer advice.

[SteveD CB500K0]

Mark, can you post this in "Recommended Sources for Parts..."

It will be safe there (but disappear down the list on here)

Steve

[MarkCR750]

Done, titled "carburettor specialist, jet supplier".