#1 running rich: checklist please?

[bdento59]

Hi all,

I'm running out of things to check to find the cause of my #1 plug showing so black and rich. The other five plugs show normal burn, and the bike runs strong and starts well. Valve lashes are all in spec, warm compression values are all 140-155 PSIG, carbs were recently rebuilt and bench tested negative for leaky float valves and cracked overflow tubes, and positive for proper accel pump action. Pilot screws on carbs #2-#6 are set at 1.25 - 1.5 turns out, but even at 0.5 turns out on #1, she still shows rich and black after very few hundred miles. Float heights are set at 18mm. Stock jet needles, no shims, #98 mains. Double checked that the air cutoff circuit on #1 is clean, but I replaced the o-ring under the diaphragm cap with a solid rubber plug just to rule this out. Coils test OK (and #6 plug is burning normally anyway), wires are good and plugs were new, running stock airbox with K&N filter, stock exhaust. There's probably more, but can y'all just tell me what you'd check in this situation and I then I'll whittle down the list based on what I've already tried. TIA.

[alimey4u2]

Looks like you have all the bases covered Bill. Forgive me if this is obvious to you. If the plug shows it being soft black soot ( easily wiped off) it is rich combustion. Black but not easily wiped off is oil contamination. If soft & sooty, check the jets are seated properly, check that there are no restrictions in the header ( wild cards I know but all I can come up with right now I'm afraid.) If not "soft & sooty", look at leaking valve guide seals.
Personally I like to find what range is giving the problem. Idle, mid range or WFO by holding the throttle in that fixed range & then checking.

[bdento59]

Looks like you have all the bases covered Bill. Forgive me if this is obvious to you. If the plug shows it being soft black soot ( easily wiped off) it is rich combustion. Black but not easily wiped off is oil contamination.

Thanks alimey, it appears to be rich, not oil fouling. The bike "does" need new valve stem seals, as it smokes a bit on starting after sitting overnight (just like my '68 camaro used to do). Having said that, the #6 cylinder, not #1, is the worst offender in that regard, based on the appearance of the exhaust port with the header off (oily black), and yet the #6 plug shows normal. Since the worst cylinder wrt valve stem seals shows a relatively normal plug, I tend to think that even if the #1 cylinder has the same problem, the majority of the depositis have to be coming from some other root cause. Make sense?

[alimey4u2]

I tend to think that even if the #1 cylinder has the same problem, the majority of the depositis have to be coming from some other root cause. Make sense?

Your analogy does make sense Bill...
OK jets.... Given their age, there is a possibility that jets have been enlarged due to overzealous cleaning, also needles may be worn. How can you tell ? If you switched components & the problem followed, the components are at fault. If the problem didn't follow.....you guessed it, time to rethink....
You can check jets with a chemical lab pipette, timing the displacement of a liquid using a stop watch. Needles would require dial calipers & micrometer....

OH, I just had another thought, # 1 vacuum slide sticking on return ??

[bdento59]

...there is a possibility that jets have been enlarged due to overzealous cleaning, also needles may be worn.

Alimey, The needles show no signs of wear under magnification, but the pressed in pilot jets are suspect, I agree. I am planning to address this over the winter, hopefully with some expert guidance from local carbmeister Mr. McMunn.

[alimey4u2]

Bill, I'm sure the others will contribute in time. If I think of something else I'll contribute...Please keep us up to date as to your findings....

[bdento59]

Please keep us up to date as to your findings....

Will do, thanks mate.

[cbx6ss]

Bill I promised you pix of stock needle and Stage 1 some time ago. Here it is. The bottom (with clip) is DJ Stage 1, and the top is the stock needle.



/r
Brad

[bdento59]

Bill I promised you pix of stock needle and Stage 1 some time ago. Here it is. Brad

Thanks mate, confirmed, the stock ones are the ones I have. Now if I could just solve the problem of the #1 carb (only) running rich....

[alimey4u2]

Put a clear plastic tube on the carb drain on # 1, open the drain valve & see where the real float level is being maitained

[bdento59]

Put a clear plastic tube on the carb drain on # 1, open the drain valve & see where the real float level is being maitained

Hi Alimey, Been there, done that, on and off the bike. Not the problem, as I set the floats at 18 vs 15.5mm just to be sure the last time they were off.

[alimey4u2]

Wild card here, measure the piston hieght at top dead center on 1 & compare it to # 6... Compression values say they are the same... but ?

[bdento59]

Wild card here, measure the piston hieght at top dead center on 1 & compare it to # 6... Compression values say they are the same... but ?

Where are you going with this... bent rod a la hydrolock?

[alimey4u2]

Where are you going with this... bent rod a la hydrolock?

Yes but as I said, a wild card... then the compression tests "may" disprove it. My theory being the lower compression resulting in a less efficient burn. Easy check though & one to tick off....

[bdento59]

Well, I pulled my carb rack again this weekend to see if I could make any progress
on my #1 rich condition. As Dave McMunn and I had surmised, the pilot jet orifice is
larger than it should be. Using the K&L indexed carb wire set, I determined
that the third smallest (0.018") wire will pass the orifice tightly. I
checked the #2 carb next to it for reference, and it will only pass the
smallest wire (0.012"). Doesn't sound like much, but when calculating for
orifice diameter, that means that the #1 pilot jet is ~124% larger than it
should be (2.54 x 10**-4 vs 1.13 x 10**-4).

If I understand jet size numbers correctly (which I probably don't), the #35
pilot is a 0.35mm hole (or 0.0138"). So it follows that an 0.018" hole
correlates to ~0.457mm or a #45 idle jet. No wonder it's running rich.

I drilled the pilot with a 3/32 drill, tapped with a 3mm tap and pulled it
out as per Dave's excellent write-up. I'll index the rest of the idle jets this week so
I know how many are oversize. My guess is that #4 and maybe #5 are large as
well, based on the appearance of the plugs.

So the good news is that I'm probably on my way to getting these carbs
running correctly.

The bad news is that Sirius Consolidated Inc. is still backordered on the
friction fit #35's, so I'm screwed until they come in. I sure wish someone had some of these press fit jets squirreled away....