Topic: '74 350f running rich

[davis96]

Hey guys,
   
     Believe me I have searched to exhaustion. Here's my problem:

     The bike is a '74 CB350F, 20,xxx miles, craigslist special.. Ive been trying to get it to run as good as possible the last month or so, but at the moment I am running very rich (gas coming out of the muffler while running). Here's the pertinant info:
         
     The Bike:
          -good compression (so I'm told, havent checked for myself)
          -MAC 4-into-1 installed by the PO
          -starts and idles/revs fine with clean plugs, plugs foul out quickly (black sooty appearance, sometimes wet with gas), gas comes out of the exhaust (i dont actually ride the bike other than test runs around the block.. but i know its running really rich)
          -starts easily without any choke
          -clean tank
     
      What I've done:
          -stock airbox, brand new filter
          -carbs pulled, disassembled, cleaned (emulsion tubes were caked with #$%*, all passages are clean now)
          -bench sync
          -floats are set to spec
          -new fuel lines, fuel filter
          -valve tappet clearances set
          -static timing done, advanced a touch
          -set the points gap, sanded them down a
          -airscrews set 1.5 turns out
          -didnt mess with the needle height while cleaning
          -oil change tomorrow morning

So my theory is that clogged emulsion tubes were acting to lean out a rich mixture made by the aftermarket 4-1 exhaust, and after cleaning them up, the richness was made worse. (i could be wrong, I've read many threads , stating various opinions on how fuel mixture is affected by aftermarket exhaust).

So my question is what options do  I have as far as leaning out my mixture? I'd rather not go out too far with the airscrews. Could I set the needles up another notch? two? Another thing I thought could work would be to go with pod filters in leiu of the stock airbox to lean it out.

Thanks in advance!
Davis

[wdhewson]

That amount of richness means floats aren't stopping flow and flooding is occurring.  Also,  make sure the chokes are open.

What type of o-rings did you fit to the valve bodies and main jets?

[davis96]

That amount of richness means floats aren't stopping flow and flooding is occurring.  Also,  make sure the chokes are open.

What type of o-rings did you fit to the valve bodies and main jets?

The choke is open. The floats are the correct height and the valves are seating properly (I say this because the bowls are not overflowing/leaking.. And they arent overflowing into to the airbow or anything.

I am using the original o-rings, they look fine and were not dried out. I did have to replace the #1 main jet o-ring (I used a generic rubber o-ring, which I know youre going to say isn't the 'right' thing to do, and that this o-ring may be eaten away by the fuel... I realize this, but I'm not worried because this would occur somewhere down the road, not 2 weeks after being exposed to gasoline) and besides, the #1 cylinder isn't behaving differently than the others, according to the deposits on the plugs, which indicate that the #4 cylinder is the worst off.

[davis96]

No ideas? maybe a hotter sparkplug? I dont really know, my manual is fairly worthless as far as this sort of thing goes.

[camelman]

That o-ring could have been eaten right away.  Sorry to say, but a rubber that is only formulated to seal against water is not going to last in gasoline.  It will turn to black ink in no time flat.

Camelman

[Cormac]

try setting your floats LOW, like really low, just to eliminate them as the culprit. And a jet change is probably much cheaper than pods. You could just run sans filters to check, wouldn't recommend it normally, but around the block twice would give you an idea...

[HondanutRider]

Check the needle valve pistons to make sure they are all facing the correct way - i.e. with the lower notch facing the inlet side of the carb.

[davis96]

Check the needle valve pistons to make sure they are all facing the correct way - i.e. with the lower notch facing the inlet side of the carb.

When I pulled the slides, i made extra sure to keep them in the correct order.. and since these slides can only go in one way (because of the protrusions in the shaft where the slide goes), i am pretty sure theyre in there correctly

[HondanutRider]

When I pulled the slides, i made extra sure to keep them in the correct order.. and since these slides can only go in one way (because of the protrusions in the shaft where the slide goes), i am pretty sure theyre in there correctly

OK....if you say so.

[davis96]

Update:

I took off the airbox and rubber manifold thing to see how it would run, and sure enough, it runs much better with zero gas coming from the exhaust... I found that it ran the best with the choke on less than 1/4... (if I run pods on it, I think the filter element could create close to that amount of air restriction.. so thats good).

I'll keep you posted

Thanks!

[wdhewson]

It would have to be a grossly clogged air cleaner to make things run that rich.  Sometimes an air cleaner is clogged with both dirt and bugs and microbes that are living on the oil and dirt.  These microbes put down a slime that really plugs things.  Don

[davis96]

Well it was a brand new filter... I'm thinking the exhaust caused the richness, but it wasnt noticable until i cleaned out all the gunk in the carbs which was leaning out the mixture.

[HondanutRider]

With the air filter and its box off, did you peer down the carb inlets to SEE that the notches on the slides are facing that way?

[davis96]

Check the needle valve pistons to make sure they are all facing the correct way - i.e. with the lower notch facing the inlet side of the carb.

My slides have one side notched and one un-notched (flat)... the notched side is the choke side (inlet). This would be opposite of what you said. However, looking at the carb diagrams I have, it looks like I am correct (the notch should be on the inlet side). So I guess it is possible that I mixed up 1/2 and 3/4 when I reassembled them, but the diagram seems to suggest I was right? Can I get a definitive answer on this? thanks!

And it seems to me that If I were to move the lower, un-notched side to the intake side, that would make me run even more rich 

[davis96]

Another update:

I pulled the carbs today and found two interesting things that I hope might help explain my problem:

The slow jet for carb #1, when I looked through it, was clear BUT it had TWO holes in it (talking about the main hole, where theres supposed to be only one)... This cylinder was the one whos plug would be the most fouled after running the motor. So I switched the jet with the #2 slow jet, and cleaned the plugs and ran it again, and sure enough, now #2 was getting blacker than #1.

I started pulling the bowls, got #1  off, everything looked in order (aside from the 2 holes in the idle jet).. got to #2 and 3, and the idle jets were just sitting there, not screwed in to their holes, just lying there not doing anything... is this a common problem with these motors? Its seems reallly strange to me that the jets I screwed in myself (pretty tight I thought) would just fall out... upon screwing them back in, they went in with no problem and felt snug, so I think ill rule out that the threads are jacked up or something...

Ive ordered a replacement slow jet and i'll install it soon and let you know how it goes.. but could these idle jet snafu's even be the cause of my running rich? Now that I think about it, the only time i checked to see if gas was coming out of the exhaust was when it was idleing..

Also, anyone want to chime in on the correct position of the slides? moon-shaped notch on the intake side or on the engine side?

Thanks guys!

[HondanutRider]

Those slow jets definitely need to be screwed into their carb bodies, or without them seated the mixture will be way rich.  They also have the central hole down the middle of the tube, as well as two sets of holes in the body of the tube itself that go completely through to each side (of the tube).  All holes need to be clean and clear of any obstruction.

Regarding the notch on the slides:  it DEFINITELY goes on the side of the carb facing the choke butterfly or the inlet side of the carb.  The other flat side faces the motor.  If it is reversed, you get poor running and I believe a rich condition.  It can be reversed if the wrong slide is installed in the wrong carb body.

[davis96]

Those slow jets definitely need to be screwed into their carb bodies, or without them seated the mixture will be way rich.  They also have the central hole down the middle of the tube, as well as two sets of holes in the body of the tube itself that go completely through to each side (of the tube).  All holes need to be clean and clear of any obstruction.

Regarding the notch on the slides:  it DEFINITELY goes on the side of the carb facing the choke butterfly or the inlet side of the carb.  The other flat side faces the motor.  If it is reversed, you get poor running and I believe a rich condition.  It can be reversed if the wrong slide is installed in the wrong carb body.

Ok, the slow jets are re-installed now.. How can I keep them from falling out again? also, if you say the notched side is on the intake side and the flat side is on the engine side, then my slides were correct... I'm hoping it was the idle jets falling out that were causing the overly-rich conditions!

[HondanutRider]

Ok, the slow jets are re-installed now.. How can I keep them from falling out again? also, if you say the notched side is on the intake side and the flat side is on the engine side, then my slides were correct... I'm hoping it was the idle jets falling out that were causing the overly-rich conditions!

I've never had screwed-in jets fall out like that...maybe I tighten them more; although, I have seen reports of others having the same problem.  Be careful not to over-tighten as the threads may be stripped - and that would be disastrous.  Likely this is what caused your overly-rich condition.

Good to hear that you've confirmed your slides are in the correct direction.  That's an easy mistake that is often made the first time someone tears into these carbs.  Years ago my son cleaned-up my CB77 and got them switched.  It ran terrible until his old man figured it out.

[flybox1]

your slow jets shouldnt fall out unless the threads on the carb body are stripped. this would be bad. finger tight and a slight turn is all you should need to secure them in place. 

i bet its condensation coming out of your pipe....
if you've just been idling, and its been cold/damp outside, i would guess you're not getting hot enough to burn all that condensation off.  ride.  get it really hot.  then see if it clears up.

your floats could be set high (lower mm #), allowing gas into the system, causing a rich mixture, and NOT overflow out your tubes.  if you have the carbs off, recheck 24mm's.
what are your needle positions?

[davis96]

your slow jets shouldnt fall out unless the threads on the carb body are stripped. this would be bad. finger tight and a slight turn is all you should need to secure them in place. 

i bet its condensation coming out of your pipe....
if you've just been idling, and its been cold/damp outside, i would guess you're not getting hot enough to burn all that condensation off.  ride.  get it really hot.  then see if it clears up.

your floats could be set high (lower mm #), allowing gas into the system, causing a rich mixture, and NOT overflow out your tubes.  if you have the carbs off, recheck 24mm's.
what are your needle positions?

The stuff coming out of the muffler was definately gas, I smell-checked it.

From what I can tell, the threads for the slow jet werent stripped. when I screwed them back in they fit snugly and didnt want to fall out..

I set my floats according to the manual, but I may re-set them to 24mm just to see... Oh and I didnt change the needle position, so its whatever the PO had them set at (stock position I'm sure).

Think I should move them up?

[fletcha221]

Davis,

Good lord man. My suggestion is to return everything to stock. Get back to a baseline and go from there. Air screws, float height, etc. What size jets are you currently running? (will be stamped on the side)

If you have gas in your exhaust, it would at some point ignite. My guess is some richness mixed with condensation, not pure gas.

If, it was pure gas, your floats are way way way to high, and the flange on the floats isnt hitting the pin (to shut off more fuel)......It's just highly unlikely.

Did those parts get there yet?

[fletcha221]

Also,

If you adjust the needle up, she's going to run even richer.

[MADCB400F]

Mornin, one thing to remember, there are two hole that appear to for the slow jets in the carb body, make sure you are using the one that is threaded. The other thing would be the air screw. It should be .75 turns out. Good luck.

[davis96]

Davis,

Good lord man. My suggestion is to return everything to stock. Get back to a baseline and go from there. Air screws, float height, etc. What size jets are you currently running? (will be stamped on the side)

If you have gas in your exhaust, it would at some point ignite. My guess is some richness mixed with condensation, not pure gas.

If, it was pure gas, your floats are way way way to high, and the flange on the floats isnt hitting the pin (to shut off more fuel)......It's just highly unlikely.

Did those parts get there yet?

hah yea man youre tellin me. So far everything has been set to stock as a starting point. the only things ive changed is i turned the air screws about an extra 1/2 turn out, which helped.


I'll check the mail in a few when I get home!

[davis96]

Ok guys heres an update:

I dont want to jinx it, bbuutttt the bike is running pretty good right now. Heres what ended up working for me:

          -I needed more airflow so I made my own filtered velocity stacks using the little factory velocity stacks from the airbox, fine mesh on the carb side, snugly fit, and held in even more securely by the carb pushing against it. Then I cut out foam filter material to fit the flared end, it cant get sucked in because of the mesh, and a piece of saftey wire keeps it from falling out.

          -I also took some wise advice and set my float height lower than the manual says (24mm)

with those two things done, it runs nicely. Once I replace that holy slow jet, and install my new points and condensers (thanks fletcha) and reset the timing, it should be running like a top