Topic: CB550 Four K3 1979

[dave500]

wow ill do 200 kays before reserve mostly.

[Cruiser]

wow ill do 200 kays before reserve mostly.

I was expecting something like that as well... But I have no idea why she's using this much fuel. She runs really well, still rich though since spark plugs are sooty (dry though). I did 45 mins of highway yesterday hoping to break down the carbon build up from the bad carb settings I had in the beginning but still, no luck.

Default settings (default airbox and carbs), 14,5mm float height, 90 main jet, mixture screw 1 turn out, jet needle 3rd groove.

Not sure what else I can try at the moment and keep it stock.

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[newday777]

[...] It goes up to 3000RPM for 20 seconds and then drops to normal idle. After that she always just starts and idles great. Is this because I don't start with the choke on? Or is this normal behavior?

It is typical behaviour for the K3.

Ummmm......
It wasn't typical when they were new. I bought one new for my 1st wife.

[Deltarider]

Something must be wrong. Is the air intake free? No obstructions like a forgotten cloth under the seat?

[Cruiser]

Something must be wrong. Is the air intake free? No obstructions like a forgotten cloth under the seat?

Free air intake, new air filter as well.

I don't think it would run well either with a clogged air intake? Unless its sucking in air from somewhere else?
All the connections are all the way in. The rubber boots between carbs/engine are still the old ones (no cracks) as well as the rubber boots between the air filter and carb. Those are also still soft. The ones between engine and carb are a bit harder though, but not cracked and completely on the carbs/engine.

[dave500]

go right over the ignition first,be sure the advancer is free to move,plug caps in resistance spec etc,dont #$%* around around with the carbs untill the ignition is 100% squared away!!

[Cruiser]

go right over the ignition first,be sure the advancer is free to move,plug caps in resistance spec etc,dont #$%* around around with the carbs untill the ignition is 100% squared away!!

I installed electronic ignition, advancer is free and works. Coils have been renewed since cyl4 was faulty and now spark way better,  new Denso spark plugs with no resistor and a 5ohm resistor cap (still original ones).

Would the caps be that big of a change?

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[Cruiser]

Would it be an option to let it idle and the spray something like starter fluid on the boots between carbs and engine to see if it leaks and if the idle changes?

Or any ways to detect air leaks better?

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[bryanj]

Yes to the spray trick but also yes to new caps as they are old, not as old as me but old.

[Cruiser]

Yes to the spray trick but also yes to new caps as they are old, not as old as me but old.

Well, I think they are the originals so pretty old.

You recommend 5ohm ones or also no resistor (the Denso spark plugs I use have no resistor)?

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[dave500]

replace those caps if they are unknown,also set the ignition with a timing light,not just static,the more advance you can run improves economy,shine the timing light on the marks,then as you slowly increase the rpm from idle watch as the advance comes in,keep increasing rpm until the advance stops advancing,hold that rpm and set the marks to that two line hash full advance mark,then ignore where the timing mark ends up at idle,ignore that F mark!

[Cruiser]

replace those caps if they are unknown,also set the ignition with a timing light,not just static,the more advance you can run improves economy,shine the timing light on the marks,then as you slowly increase the rpm from idle watch as the advance comes in,keep increasing rpm until the advance stops advancing,hold that rpm and set the marks to that two line hash full advance mark,then ignore where the timing mark ends up at idle,ignore that F mark!

Bought new caps and will probably be able to lend a strobo next week from my brother! So I'll hope to improve it with that.

I sprayed some starter fluid on the boots but no change in idle speed or sound. So that looks good. I also hear air being sucked in through the air filter so that appears to be ok.

[Cruiser]

Also did the clear tube test and clearly the levels of carb 2,3 and 4 are way too high. 1 appears to be good.

All the floats are at exactly 14,5mm however.

So this means what exactly? Floats of 2,3 and 4 are bad and taking in fuel? Or that the shutoff valve operated by the floats are not closing? Or something else?

That might explain the high fuel usage if its constantly leaking



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[Cruiser]

So I did a test with the carbs off and on the bench. Now all stopped overflowing except number 3.

I did a float test and it floats, doesnt take in fuel.

When I take the bowl off and manually set the float with my finger at the point where it should depress the little spring, it stops overflowing, like it should.

However when I place it back in the bowl, and let fuel get into the bowl, it just leaks again. Seems like the float isnt going up all the way even though in a seperate test it floats...

When I change the float height, so it should compress the pin earlier then the others, she still overfloods.

When its hanging on the carb, I can move the float freely all the way down and all the way up (up so it compresses the little spring completely)

What on earth am I missing here?! Especially since it stops flowing when I manually lift the float up to just touch the pin.


The other three are fine, just this one that won't seem to close whenever it relies on the boyancy of the float (even though it floats fine in a seperate test off the carb).

Edit: here's a video for reference

[newday777]

Definitely hanging up on you

[newday777]

There was a post last week of Hondaman??, maybe someone else, mentioning the brass on the floats needs to be checked it isn't hanging up on the posts causing the float to stick.

[Deltarider]

When maintenance is needed, cleaning the floats swivel pins is recommended*. A little naphtha or WD-40 will do. You may use one of your granddad's pipe cleaners. Do not use anything abrasive. Swivel pins are best removed by using your fingernails. If you must use pliers, I repeat must, do not pinch the pin's ends!
Is the O-ring around the float valve seat OK?
* Here's why. Although this video deals with the oldstyle carbs, the principle also applies to your PD carbs. From 17:00 - 18:20 it shows what goes on in practice.

Note how gentle the movement is and how little force is exercised. Note also the little pin at the bottom of the needle does not compress. It's only there to absorb eventual shocks. So measurements should be made with the float's tang touching that little shock absorber, but not compressing it!
Video courtesy Gruzzel

[Cruiser]

When maintenance is needed, cleaning the floats swivel pins is recommended*. A little naphtha or WD-40 will do. You may use one of your granddad's pipe cleaners. Do not use anything abrasive. Swivel pins are best removed using your fingernails. If you must use pliers, I repeat must, do not pinch the pin's ends!
Is the O-ring around the float valve seat OK?
* Here's why. Although the video deals with the oldstyle carbs, the principle applies also to your PD carbs. From 17:00 - 18:20 it shows what goes on in practice.

Note how gentle the movement is and how little force is exercised. Note also the little pin does not compress. It's only there to absorb eventual shocks. So measurements should be made with the float's tang touching that little shock absorber, but not compressing it!
Video courtesy Gruzzel

Well everytving except the floats have been renewed. After thinking long about it, the float could only be the fault.

So I submerged it again for a long time now...

Took it out and watched the fuel evaporate from it and closely look where it remains wet, if it remains wet I know there is a hole. And yes, there is a tiny crack in it. After blowing on it with compressed it, I saw it opening up. Hardly visible without blowing at it.

Weird that I saw no bubbles when I submerged it for a minute yesterday. Must be so tiny that it takes some time to fill up.

Guess I'm ordering a new one...

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[dave500]

those PD carbs suck balls man!finicky #$%*ing things!

[Cruiser]

those PD carbs suck balls man!finicky #$%*ing things!

Since I ordered new ones anyway I thought to try and repair this one with some heat. But I think this is not plastic but bakelite?

Anyway, I wouldn't trust them anymore.

Pretty sure this is where the high fuel usage comes from. Never saw a leak when I was off the bike since I always immediately close the petcock. While driving I think this must leaked into the airbox and out of the drain below it.

I hope it clarifies the fuel usage though

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[dave500]

going by your fuel consumption numbers,sure you aint blowing black smoke?
again,get that ignition squared away first,then #$%* with the carbs!

[Cruiser]

going by your fuel consumption numbers,sure you aint blowing black smoke?

95% of the time it didn't (or very little while riding). Sometimes however when I blip the gas, let it idle, blip, then it would throw some black smoke... Out of cyl3 btw

So that explains that as well.

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[dave500]

yeah ok,get on that ignition man!

[Deltarider]

I don't think the OEM floats can leak! If you cut one, you'll see they're all foam. BTW, this is explained in the video I've posted in reply #116, from 10:05 - 10:20. No cavity in yours.
Are the parts in your carbs OEM or imitations?
Do your choke flaps function as should?

[dave500]

i beg to differ delta,on my car years ago with a rochester four barrel carb,the old plastic float sank,it was as you described a sort of foam/solid thing,it sank like a stone lucky i was close to home.