SOHC.co.uk Forums > CB500/550

Carb problems

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mhirst121:
To answer a few of the questions, I need the choke full on for a couple of kicks then I have to move it about half open to start it, otherwise it just floods. Air screws are 2 turns out and have adjusted about a sixteenth of a turn either way to get it running smooth, they are the solid type. The plugs are new NGK D7EA`s, this is the second set I have in now, others were so sooted up they arced all over the place.(have a jig to test my stationary engine magnetos on, just used these plugs to check them.) In response to Yoshi, no I have not checked the plug cap resistance but will do tomorrow. I cannot run the bike with the air filter in(new) it just puts out extremely black smoke from the pipes. The down pipes are all hot, do not have a non contact thermometer to check them, but this may tell me a bit more if I can borrow one.
Thanks again for the hints, as I said it all helps to gain a better understanding.

Cheers,
MartinH

Spitfire:
Are you running a stock air filter and stock pipes ?

Cheers

Den

Yoshi823:
I have just remembered that I had a problem many moons ago, where I had a similar problem. It was more to do with the timing than carburation. Apart from the heels of the points being worn, somehow the blue & yellow leads from the points had been swapped over. I normalised things & it ran perfectly.

Worth a try...?

mhirst121:
Right I have done some investigating this morning. I have found out that the standard jets and needles are as follows:-

Needles   272304
main jets  100
pilot jet  40

Now the other three sets of carbs I have had:-

Needles 273004
main jets  98
pilot jet  38

What I would like to know is, were the mains and needles changed to the 98 jets with slimmer needles at any time by Honda. The set of carbs I have just stripped do not look like they have ever been apart.
I only have two of the 272304 needles but plenty of the others, do you think the 272304 needles with the with the 98 jets would be ok?
Cheers
MartinH

SteveD CB500K0:
Check Mike Nixon's carb pages: http://www.motorcycleproject.com/motorcycle/text/specs.html

The 98/38 selection was used on the US (and European) CB550K which looked just like our 500/4 but with the 550 engine. We only had the CB550F and K3 here.

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