Carb problems

[mhirst121]

Well I have spent the best part of two weeks trying all manner of things to sort out my carbs. Eventually thought I had them sussed, but as usual, they were just not playing ball. Can anyone tell me which notch(from the top) the slider needles should be in. The bike is very hard to start and when running there are clouds of black smoke coming from the exhaust. The float heights have been checked at least twenty times, so I am pretty sure they are correct. The jets are all correct(new), the only possible fault I can see is the bottom edge of the carb body is corroded where the main jet fits in showing part of the `o`ring. Would this give the problem of rich running? Honestly, I am getting sick to death of this lot, they have been on and off so often that I can whistle and they jump out and onto the bench!!!!
Any help greatfully accepted, otherwise I think I will need to try another set of carbs 

Cheers,
MartinH

[Bryanj]

If bike is standard clip should be in middle notch and yes if the "O" ring is leaking the cylinder in question will run very rich

[mhirst121]

Thanks Bryan, will check the needles, I think the ones in mine are set higher up. The problem with the `o` rings will be another challenge.

Cheers,
MartinH

[Seamus]

Would it be possible to build up the corroded area with some epoxy compound?

[Bryanj]

Yes you can "glue" the main jets in as long as you never want them out again and you use petrol proof epoxy---not all are especially with today's unleaded fuels.

One thing to check is the emulsion tube above the main jet as sometimes the cross holes get furred up, this can be a sod to remove as you have to push down from inside the throttle body WITHOUT damaging the needle jet at the top

[Yoshi823]

Can carb cleaner be sprayed from the air jets through to the mouth of each carb?
Is the small washer & minute 'O' ring on each airscrew in place?
Can you squirt carb cleaner from the primary jet through to the mouth of the carb?
Which spark plug is the most fouled up? If one is worse than the others it may be a bad spark plug.Are the spark plugs the correct type (D7EA) for the bike?

The needle clip position won't have as much effect on starting as the air screw & primary, so concentrate in this area.

[mhirst121]

Well just to update you, I have bought and fit another set of carbs and the bike runs much better. With the old carbs the plugs were all black and sooty, they are much better with the new ones
While stripping the other sets of carbs the pilot jets were all 38`s, would these have been fit when a four into one exhaust is used, only ask as out of four sets of carbs only one set had 40`s in?? Will the bike run leaner with the original exhausts on, at the moment I have the four into one on till I get things sorted, don`t want to blue my new pipes if possible.

Cheers for now, and thanks for the assistance again,

MartinH

[mhirst121]

Well I have had a play around with the carbs again today. All the plugs seem to be as black as each other and carb cleaner comes out of all the right places. The tickover is much better but I was getting it really bogging down at around half throttle. I pulled the choke on at this point and it just made it worse. So its obviously too rich so I checked the needles, they were in the second from top, I have now moved them to the top groove. Have not had a chance to give it a good run, only noticed the problem with bogging down when I went for the mot.
If it is no better with the needles in this position, am I correct in thinking I need to go down a jet size and move the needles back up??? Slowly learning alot about these carbs, which I suppose its what its all about

Cheers,
MartinH

[Yoshi823]

I know this sounds daft, but which position of the choke lever are you using to start the bike...up at the 3 o/c or down at the 6 o/c position...?

Also, how many turns out are you adjusting the air screws...? Are the tips of the air screws clean? Have you tried new NGK D7EA plugs? Do all of the plug caps measure about 5000 ohms?

[notobikeparkingtax]

What state is the air filter in and what happens if you run the bike with it removed ?

Are all exhaust downpipes getting equally hot ?

[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.