Topic: CB350f carb rot; rich mixture; pitted emulsifiers

[CurbTiger]

Questions on a CB350f.
State of tune: 10k miles, dwell equal on points, dynamic timing spot on, sync done with matched vacuum gauges, air screws 2.5 turns out, needles at middle clip, main jet o-rings good, new plugs, new fuel, "clean" carb rack, stock jetting, 23mm float height, all the floats are around 8.85 grams in weight.

Symptoms: Bike(from cold) starts easily and idles well, if a bit rough and stinky(fuel). As the engine gets closer to running temp, idle gets rougher and response to throttle off idle becomes more hesitant. Sometimes the idle stays high, as if the idle mixture is too rich. If I try for a road test, the bike bogs horribly and will hardly get out of it's own shadow. Basically unrideable.

Here's the squeeze: If I shut the fuel off and allow the bowls to empty some, the idle becomes better and throttle response is how it should be. Fuel back on, idle roughens up, back to the bogging.

Diagnosis: An over-rich situation across the board. I understand the air screws should be a max of 1.5 turns out. Increasing the float height to 23mm helped, but not enough. Maybe I should try a 25mm float height.

How endemic is carb rot on CB350f's? Three sets of carb racks; the cleaned one(on the running bike) shows serious pitting on the main jet towers and on the o.d. of the emulsion tubes. The tubes fit somewhat looser than I would expect and I'm suspicious this may be causing a rich condition. Other two racks are fuzzy with varnish/goo/ectoplasm at the end of the main jet tower and are sorta crumbly.
Back to the pitted emulsion tubes....They come out of the carb body rather easily. A slight nudge and they fall out of the carb, ie. no need to really push them from the top.

I guess this is directed towards the guru, Mr. HondaMan. Have you encountered this problem, leading to a over-rich situation? Implying, more fuel is being sucked past the top end of the emulsifier/carb body contact point.

Thanks for the help and the great resource SOHC4 is!!
NE

[scottly]

Curb, I like your style! Especially about including the float weights. Check my thread on carburetor issues. Others here have suggested a method for checking the actual fuel level in the bowl with a piece of clear plastic tubing in the drain holes, on the bike. That's what counts, not the mechanical setting.
Scott  

[HondaMan]

As long as those emulsifiers are only receiving fuel through the mainjet (and it is not leaking in past the mainjet itself), it should meter OK, despite the surface quality of the tubes. I would be more concerned about the cleanliness of the holes in the emulsifier tubes. If the holes are too small, it will aerate poorly and act rich. If they are too big, it may have an extra flat spot or two where the holes are: the upper holes are lower throttle range, and vice-versa.

Look to see if the air bleed port into the "mainjet tower" (where the emulsifier slides into place) is clean. VERY clean. If the port is even 10% blocked on the Baby Fours, it can make them run rich, as everything is so little.

With those air screws out at 2.5 turns, it would take about 5 minutes to foul the plugs black. Then you'll have to get new ones before trying anything else (or sandblast and wash the old ones), or you'll just chase your own tail.
 

[wdhewson]

I'm just re-doing my CB350F carb quartet.  One thing I don't like is the cheesey method of making sure that the chokes stay "OPEN" and the engine runs not choked.  Low pressure ball detent on carb #1,  Make sure that your choke lever is truly open and stays open.

Hondaman, is not the air screw spec 7/8ths of one turn?  And thus 2.5 turns is lean, as these screws control air.  I defer to your expertise and experience.