Topic: CB500 problems carbs 4into1 / 4into4 experiment

[jonda500]

Hi, I have carb issues with all three of my hondas, but my attention is currently focused on the set that came with my 2nd cb500 which I sent to harisuluv to be reconditioned. When I got them back I first put them on my 1st cb500(original 4into4 exhausts) but it ran way way too rich and would only run ok for the first 20 seconds or so before blubbering so bad the plugs kept dieing requiring removal and drying before they would fire again! Hari sent me replacement needles but they made very little difference (winding the mixture screws 2 1/2 turns out did help though). So then I tried dropping the needles two positions to hondas 550Fss setting(second slot from the top) and fitting them to my 2nd cb500(fitted with 550Fss 4into1). This made not much difference (still rich as %$@#) so then I swapped out the pilot and main jets for same size (#40 & #100) oem items but again no change. Then I tried them on my 550Fss and they were even worse on this bike. Although harisuluv said "no don't do that" I today went ahead and tried leaner than correct needle heights. I did this by fitting the carbs back on my 2nd cb500, and leaving the needle clips in #4 position but installing my 4 into 4 exhausts from my 1st cb500 onto it. Took it out for about a ten mile ride and for the first time with haris carbs fitted it actually idles quite well(screws still 2 1/2 turns out) and is very responsive from idle to 1/4 throttle, but midrange feels flat and strangled (feels much more like I remember my 400-4 being with the revs very slow to climb as the tacho needle passes 5000rpm). But it does run much better than it ever did before with the haris carbs fitted - the problem now is that the last third to W.O.T. boggs down the motor unless you have it screaming! 

[jonda500]

It's hard to see in the picture but the plugs after ten miles look a little too light in colour particularly the inner (#2&3) ones and also the two inner exhaust pipes look like they will turn blue if I keep riding it like this...
  the plugs were black before the ride (and indeed have been black every time I've taken them out until now!) -so changing from the 4 into 1 exhaust system to the 4 into 4 exhausts without touching the carbs made a massive difference to the mixture! Any one have any suggestions what I should try next? - I thought maybe trying setting the needles to the middle (and leaving the 4into4's on), and then smaller pilots(#38's).
   Mean time I guess I need to conduct a WOT for 10mins up a hill then hit the kill-switch, pull over and remove the plugs for a colour check to see if the 100 mains are too small or too big!?!

[jonda500]

Still hoping for some comments, surely many of you out there have experienced carb tuning problems with these bikes?

[dave500]

whats the air filter like?how does it run with the filter removed?hows the ignition?have you got it spot on?

[jonda500]

New standard air filter, new points/condensers, new carb mounting boots, new intake manifold o rings, timing spot on checked with a timing light - centrifical advance good, valve clearances done.
   I haven't tried them with no air filters, but did try pods on them when I stuck them on my 550F as in picture.

[dave500]

whats the resistance through the plug caps?

[jonda500]

the original honda plug caps have a resistance of (ohms):

#1 - 9000, #2 - 8600, #3 - 7000, #4 - 7000

Are cap readings of 1st and 2nd cyls high enough to cause problems?

[dave500]

you may see a faint,very faint marking on the sides in ohms,if its 5k then fit new ones,fit news ones anyway if those really are the factory ones?the markings fade a lot you might need to get the light on them at just the right angle?

[jonda500]

Both my 500's have their original plug caps with no markings evident
I have spares - but only 3    -and they don't say either!
My 550 has NGK ones exactly like the top one you posted
   For eliminating my caps as being the cause of any issues I will swap with the 550 ones(after testing them)
Meanwhile I will still be trying to find new original honda ones so as to keep the original look I love!

[TwoTired]

the original honda plug caps have a resistance of (ohms):

#1 - 9000, #2 - 8600, #3 - 7000, #4 - 7000

Are cap readings of 1st and 2nd cyls high enough to cause problems?

Even with those readings, I wouldn't expect a spark issue, especially if the connections are solid.
In the US, the standard plug caps were 10K.  The original caps had no external markings for value.   Hard to believe that all four of yours are really that far off 10k.  Is their corrosion visible at the cap connection points?   
Do you have a local electrical supply that sells 10K ohm resistors?  Check your meter with one of those for calibration error.


Regarding the over rich mixture:
Have you checked the actual fuel level in each carb with the clear tube method?

Do all the spark plugs show the same deposit patterns across the bank?

What spark plugs and the numbers on them?

Do you know the numbers stamped on the slide needles?

Can you verify that the emulsion tubes are clean?  Has the needle jet been enlarged or the needles worn?

Check the air box inlet for restriction(s).

While a new air filter shouldn't cause restriction, try operating with out for a test period and note the effect.


I should ask about choke operation to verify that you know up is choke applied (on/cold start) and down is warmed up running position (off).

[dave500]

if it had 10k caps i dont think the resistance is getting less?,id say they were 5k and its going up?youve already had carbs off and on a few times over,your opersating the choke in the correct direction?lever up is choke on,down is off?what rpm range do you ride in?if your trickling around under 3500 and rarely hit 7000 its too low.

[TwoTired]

if it had 10k caps i dont think the resistance is getting less?,

High voltage circuits have unique failure modes.  Usually, the resistor element within the cap is a cylindrical stack/column of carbon.  If some of the carbon overheats with electrical current, portion of the carbon stack becomes fused, altering the resistive properties. Those fused portions allow greater continuity, and thus the resistance gets lower.  They can also become altered the other way, where portions of the carbon stack have holes blown in them.  This makes the resistance rise as the electron pathways narrow.  Blowing holes in the carbon path is sometimes the first step toward total separation or a part in the carbon stack.  Such a separation failure as this would show an open.  However, it simply adds another spark gap in the secondary circuit.  As long as there is enough voltage potential, the circuit still operates with this extra gap, until it widens beyond available voltage potential.

The sparking circuity operates quite differently in detail than the easy to understand low voltage DC on the rest of the bike.

[jonda500]

the original honda plug caps have a resistance of (ohms):

#1 - 9000, #2 - 8600, #3 - 7000, #4 - 7000

Are cap readings of 1st and 2nd cyls high enough to cause problems?

Even with those readings, I wouldn't expect a spark issue, especially if the connections are solid.
In the US, the standard plug caps were 10K.  The original caps had no external markings for value.   Hard to believe that all four of yours are really that far off 10k.  Is their corrosion visible at the cap connection points?   
Do you have a local electrical supply that sells 10K ohm resistors?  Check your meter with one of those for calibration error.


Regarding the over rich mixture:
Have you checked the actual fuel level in each carb with the clear tube method?

Do all the spark plugs show the same deposit patterns across the bank?

What spark plugs and the numbers on them?

Do you know the numbers stamped on the slide needles?

Can you verify that the emulsion tubes are clean?  Has the needle jet been enlarged or the needles worn?

Check the air box inlet for restriction(s).

While a new air filter shouldn't cause restriction, try operating with out for a test period and note the effect.


I should ask about choke operation to verify that you know up is choke applied (on/cold start) and down is warmed up running position (off).

err resistance increases with time not decreases!?
outer spark plugs are a little darker, inner exhaust pipes look to be running hotter
I will check with my clear tube although these carbs were professionally rebuilt by harisuluv
I use NGK D8EA's - I have some D7EA's but thought they would run even hotter?
I have tried both the standard original needles and new aftermarket ones from harisuluv
Carbs are reconditioned/ don't know if the needle jet has been enlarged
Pulling the air filter I think may have been great to try when bike was running RICH
I am completely familiar with the choke operation- the butterflys close when you pull the lever towards you

[dave500]

the cap can also fail inside where the contacts ride,they can fail along the first elbow inside aswell,see if yours can be unscewed(unlike your pregnant girlfriend)from the end that goes on the plug,youll find a spring and the resistor if it comes apart,check the resistor only,keep your hands off the probes,you can scratch up the contact surfaces if the resistor checks out ok.

[dave500]

put the 7s in man!i run 7s in queensland!your in act where all the worlds snow comes from.

[jonda500]

if it had 10k caps i dont think the resistance is getting less?,id say they were 5k and its going up?youve already had carbs off and on a few times over,your opersating the choke in the correct direction?lever up is choke on,down is off?what rpm range do you ride in?if your trickling around under 3500 and rarely hit 7000 its too low.

I would very rarely ride at under 3500rpm -in fact given that there's no unavoidable traffic in the way, and I'm not in a carpark or school zone, never!! - regularly take it well over 7000rpm

[dave500]

ok cool,similar threads have had riders babying these around.

[jonda500]

put the 7s in man!i run 7s in queensland!your in act where all the worlds snow comes from.

oops I didn't pay attention properly somewhere - I thought the 7 was a hotter plug that would help a rich bike?
8's are easy to buy here but I don't know where to get 7's although I have one set and two old used sets so I can try them(I was saving them for when I get one of the bikes to run right first!)

[dave500]

?i can get 7s at cheapa auto parts if you have that franchise there?any bike shop should have them?or use denso X22ES-U,dont run champion,bosch is ok but they make better alternators,starter motors and ignition modules than plugs for some reason?i think the equivalent bosch are colder?sort those caps aswell,dont do too many things at once or it gets a bit confusing,go the 7s though.

[jonda500]

ok cool,similar threads have had riders babying these around.

Back in '85 I did that for quite a few weeks when I got my 2nd bike (honda 400-4), before I realized that the real power and all the fun was to be had by keeping the revs above 7000rpm or at least 6500rpm. Years later I went through exactly the same thing with my '70 CB450DOHC!! - I didn't expect the twin to have such an impressive top end(often a bit too powerful for the poor old clutch unfortunately)

[TwoTired]

err resistance increases with time not decreases!?

This depends entirely on the resistor composition and the failure mode.

outer spark plugs are a little darker, inner exhaust pipes look to be running hotter

Did I miss the declaration of a carb vacuum sync?

I will check with my clear tube although these carbs were professionally rebuilt by harisuluv

I agree they "should" be correct.  Built by humans always means a possibility of error, or even damage in transit.  But, if we assume they are perfect, we might replace the rest of the bike a component at a time until we say "WTF"!

I use NGK D8EA's - I have some D7EA's but thought they would run even hotter?

Hotter is good for the CB550.  And that means the plug is better able to self clean off the carbon deposits.

It doesn't mean the engine runs hotter, you know.  It's just plug tip temperature of concern.

I have tried both the standard original needles and new aftermarket ones from harisuluv

Carbs are reconditioned/ don't know if the needle jet has been enlarged

So they must be perfect and beyond question?  ooook...

Pulling the air filter I think may have been great to try when bike was running RICH

The point is, why must you have the carbs tuned so far from factory specs?  You have leaned the pilot screws and needle quite a bit from factory position.  What if the cause was an air filter or other induction restriction.  Would you be happy detuning the carbs to compensate?

[jonda500]

"The point is, why must you have the carbs tuned so far from factory specs?"

This is exacly the question I am seeking an answer for in this forum! I have tried two different new air filters and new pod filters and there is definately no obstructions to the air flow. I have sprayed wd40 around all the connections between the new boots and the carbs/manifold/engine with no effect to engine idle speed.
Believe me I would love it if it would run with everything at factory spec. settings and sizes!

[dave500]

just out of interest my 550 has a first oversize bore,stock airbox and genuine filter,4-1 with a longish upswept straight through glass packed muffler and boyer electronic ignition,the inlet runners are matched to the head not ported,i run 38/100 jets,ive run this bike hard for a few years.

[jonda500]

The one thing I am pretty clear about is that fitting new genuine honda #38's (when they get here and after I put the 4 into 1 and straight through muffler back on) to compensate for the 4 into 1 is fairly likely to allow me to return the mixture screws closer to the standard 1 turn out setting. Then maybe I'll try replacing the needles for a third time (unless I get a better idea meanwhile!).

[dave500]

the book air screw setting is sort of ball park,anyones may need more or less?my are just over 2 out,say 2 and 1/8?solid screws,some are drilled and dont shut off air fully when closed,aftermarket ones are mostly drilled,a bit like tamperproof idle screws on mid 80s cars?use solid ones if you can find them or solder yours solid like this.

dont frigg around with the carbs untill the igniton is well sorted though.