Topic: cb750k6 Rich in 1 and 4.

[ntm1974]

bike is a 76 cb750k.

Things done so far:
New boots from airbox to carbs.
Float height set with "stackpipe" while each carb was on the bike to about 2 or 3 mm below the top of the bowl.
New points with Hondaman ignition.  Dwell and timing set. (dwell 48) timing set with gun
Carbs bench synched then synced with vacuum gauges.
Cleaned carbs.  Soaked and  Sprayed carb cleaner in every orfice.
New plugs and set valve clearances.
***Replaced coil with a "new to me" ebay coil.
New plug caps.
Drilled emulsifier tubes .039
New metal clamps for boots from head to carbs (the rubber still seemed pretty good and when I spray starter fluid in the boots it has no effect on the engine)
Needles in the carbs are all set the same height.  Air screw is 1.25 out for 2-3 and 2.75 out for 1-4.  I am affraid to go out any further although turning it out did help lean it out some.

Plug chop at 1/8-1/4 throttle always yields plugs that look pretty good on 2-3 but are rich on 1-4.  I feel like it might be ignition related but I feel like I have my bases pretty well covered unless my old coil and the ebay coil I got are both bad?  The spark looks good.  The bike runs pretty well.  If I am in slow traffic at 1/8 throttle for a long time, it will feel like it bogs in that range but only slightly.  The idle is rock steady unless I run it hard and then come to a stop, then the idle seems to be elevated.  The engine "pops" as though it is hot if I run it hard and then stop also (I'm  not sure if that is a problem or common with these bikes as my 03 919 does the same thing everytime I park it.)  I am pretty much at a loss for what else I should do and would appreciate any help you can throw my way.

Thanks for looking.

[Spanner 1]

Thanks for the list of what you have done to your bike....... rich on 1 and 4 would beg a coil/spark explaination  maybe. Howabout one bad plugcap = misfire on 1 and 4 = rich ( unburned fuel ) looking plugs . Misfire in the 'drop-out' sense that is , where plugs don't fire everytime.
Try putting your 'old' plugcaps back on 1 and 4, see what happens............

[JDWells]

Also you could drop the needle down 1 and that would give you a lot more play with the air screw. As long as you are actually getting spark on all 4 I wouldn't think it's an ignition problem. Did the coils you got come off a CB? They might not hit hard enough.

[ntm1974]

Also you could drop the needle down 1 and that would give you a lot more play with the air screw. As long as you are actually getting spark on all 4 I wouldn't think it's an ignition problem. Did the coils you got come off a CB? They might not hit hard enough.

The coil came off a cb750.  I am thinking about just biting the bullet and going to a dyna coil but I'd hate to drop that kind of money and have it be something else.  Is it kosher to have different needle settings on each individual carbs? 

[Spanner 1]

Not the coil,... coil =go or no go IMO..... change/swap point condensor... don't discount plugcaps too.
Different needle settings on each carb only if you have different carbs on each cyl. or grossly malajusted carb settings......

[JDWells]

Yeah each cyclinder has it's own carb so it's ok to have different settings. The bike is old so the cyclinders and combustion chambers are worn slightly different. The exhaust shape and length is slightly different. That means the carbs might be slightly different.

Not the coil,... coil =go or no go IMO..... change/swap point condensor... don't discount plugcaps too.
Different needle settings on each carb only if you have different carbs on each cyl. or grossly malajusted carb settings......

If the coil is off a smaller bike (550 or 350) it might not generate enough voltage to make a strong enough spark but you said it's off a 750 so that's fine. Definitely check the plug caps. Resistor type right? Make sure to check those stupid little resistors.

[ntm1974]

Not the coil,... coil =go or no go IMO..... change/swap point condensor... don't discount plugcaps too.
Different needle settings on each carb only if you have different carbs on each cyl. or grossly malajusted carb settings......

I don't have the condensors connected because of the hondaman ignition.  I took them out of the equation for now (one less thing.)  I just pulled the new NKG caps and all read nearly the same resistance and continuity. (close to 1670 continuity and 4.89 ohm's)

Also, would the needle height factor into the equation at 1/8 to 1/4 throttle?  Would I lower the needle to lean out the mixture in 1-4 or raise it in 2-3 to richen them up and then move to hotter plugs?

Spanner, when you say different carbs on each cylinder.....what do you mean exactly?

[Spanner 1]

My point was that you would never have to go with different  needle heights to accomodate varying compression rates in the 4 cyls..... I think were back to carb venting in the carb upper body ( yeah there are vents there that will effect fuel level in the carb, even with perfect fuel/ float level  are they clear/proven ?

[ntm1974]

My point was that you would never have to go with different  needle heights to accomodate varying compression rates in the 4 cyls..... I think were back to carb venting in the carb upper body ( yeah there are vents there that will effect fuel level in the carb, even with perfect fuel/ float level  are they clear/proven ?

When you say "carb upper body:" Do you mean where the slides are?  I know there is a gasket of some kind there but I haven't really gotten to involved with that portion of the carb outside of bench and vacuum synching.  After needle height and slide height, what else should I be looking at in the upper body of the carb to be sure they are "clear/proven?"

Thanks for the replies.

[Spanner 1]

If you look at the upper part of your carbs you will see a rubber tube between 1 and 2 carb and 3 and 4 carb. This is a vent/balance pipe and leads carb bowl 'air'to athmosphere thru' a small opening in the carb body ( above where the jets screw in). There should be a vent hose from #2 carb and #3 carb( right side on 2, left side on 3 viewed from airbox side ). Also is  each bowl vent tube clear ?, some times one or two can be blocked by road dirt at the end where they hang down by the swingarm. 

[ntm1974]

Went into the garage today and it smelled like gas.  Sure enough, I had gas coming out of the #4 carb overflow tube.  I drained the bowl and got ready to check the height with a stack pipe.  As I was doing this, # 3 started to leak.  I tapped on the bowl and got it to stop.

My petcock doesn't totally shut off the gas.  A drop or 2 a minute comes out but this hasn't been a problem in the past because the floats stopped the gas.

The funny thing is that the level looks good when I check it with the stack pipe in all of the bowls yet they seem to leak intermittently.

The floats move freely up and down but could they be taking on gas?  When I pull them, they don't feel heavy.

Could it be the K&L needle jets that the P.O put in?

I already have a K&N in line fuel filter in addition to the petcock filter.

Any ideas on how to proceed?

Thanks

[JDWells]

If they're leaking it's because they're overfilling and the only way they can overfill is if the floats and float needles aren't holding it back. If the floats aren't taking on fuel then the only thing is the float needles. This is pretty common. The float pushes up on the needles enough but the needles aren't sealing with the seats.
http://media.photobucket.com/image/recent/Dalhan/FloatNeedleSeat.jpg
If you look at this pic the place that the arrow is pointing a lot of times gets ridges so it won't make a good seal. That's most likely your problem. Even if it's not ridges there, the float or float needle are the only things that can allow overflow. Period. Don't get discouraged with carbs. They take time to understand. They're really easy and really complicated at the same time. lol
If you can post some close ups of the internals of the carbs that are problematic. That might help and I'll keep my eye on this. Good luck!

[ntm1974]

So it sounds like I should start with the needle jet and then go from there.

Thanks for the replies.   I'll give that a whirl and see what happens.

[Spanner 1]

O.K. your problem is your petcock..... if your petcock will allow gas to flow very slowly when off, the small amound of gas entering the bowls will 'fool' the valve and it will not close tight in it's seat....
it needs a good flow of gas to 'bump' the float up and shut the valve........
A toilet tank is very like your float bowl and if you turn the water down to a trickle often the tank will overfill because the valve won't be seated with any force by the too slowly rising float 
You might ask, 'but when I get home from a ride and I turn the gas off the bowls are already full, so why should it happen ? '. The gas slowly evaporates from the bowls allowing the float to drop/valve open and accept the trickle of gas ....

[ntm1974]

O.K. your problem is your petcock..... if your petcock will allow gas to flow very slowly when off, the small amound of gas entering the bowls will 'fool' the valve and it will not close tight in it's seat....
it needs a good flow of gas to 'bump' the float up and shut the valve........
A toilet tank is very like your float bowl and if you turn the water down to a trickle often the tank will overfill because the valve won't be seated with any force by the too slowly rising float 
You might ask, 'but when I get home from a ride and I turn the gas off the bowls are already full, so why should it happen ? '. The gas slowly evaporates from the bowls allowing the float to drop/valve open and accept the trickle of gas ....

Spanner,

That makes sense but would the petcock affect 1-4 being rich or only gas coming out of the bowls after the bike sits for a while?

The gas flows well from the petcock when it is turned on.

Also, in hondaman's book, he recommends running some flexible mechanics wire through the air jet to clear it out.  Anyone try this?  What size wire did you use?

Thanks again.

[Spanner 1]

1 and 4 valves are not closing tight, obviously as they leak while bike is stopped and would also 'leak' while riding; i.e. not shutting-off when the bowl is full allowing a higher fuel level in the bowls = rich running on those cyls. Fix the leaking valves and you have fixed the rich problem IMO.
Not sure about HM's wire trick, but carb cleaner seem to work good shot thru' the emulsion air passage.

[slowjo]

Sounds about the same problem I'm having. One question, why are you not using the condensers? I purchased one of Hondmans ignitions over winter. Did is miss the step in the instructions to delete the condensers?

[ntm1974]

Sounds about the same problem I'm having. One question, why are you not using the condensers? I purchased one of Hondmans ignitions over winter. Did is miss the step in the instructions to delete the condensers?

Hondaman can answer better than me but in the directions I got, he said that the condensers can help on older bikes but are not needed.  I am going to buy new condensers but I disconnected them for the sake of removing one variable from the equation until I get this issue sorted out.