Topic: Quick brainstorm

[jessezm]

Oh, and I do plan on taking your other advice, though, and swapping out jets and needles among the carb bodies, that may be more practical for me than trying to measure openings...

[grcamna2]

Honda has a special tool called a "jet cleaner"(I have one and I can get you the O.E. part # if you like)and it has the size of the jets marked on each corresponding wire jet "gauge"...the tool really is nice and makes sizing the jets you have a little easier;it's basically a wire gauge w/ jet #'s printed for each of the wire gauges all the way down to the# 35 pilot jet.

[TwoTired]

For the Keihin jets, the number corresponds to a metric diameter. Ie. a #100 jet is 1mm in diameter,  #105 is 1.05 mm, and a #90 is 0.90mm, etc.

If a jet has been altered you can tell by using the shanks of drill bits, in go/no go fashion, to get a pretty good feel for the jet being somewhat near spec.  High precision is nice, but probably only necessary if you're reaming jets to a larger size.

You don't even need metric dill bits.  A dimension is a dimension be in the metric, fractional, or inch units.  The web is rife with unit converters.

Cheers,

[jessezm]

Reviving this thread for more thoughts...   I did some more tuning work and I have since swapped the needles with another set of Honda needles I had.  Needles are now shimmed one half-step richer than stock and I installed all new 98 main jets.  Carbs are re-synchronized and dead-on.  I also made some drain plugs with nipples and clear tubes with my new (to me) drill press, and verified that fuel levels are in fact equal between #1 and # 4 carbs.

Wide-open throttle chop still shows a slightly leaner #4 cylinder.

I ordered new o-rings for the carb manifolds, thinking I may have a tiny air leak there, but I'm not sure where else to go with this.   It's not so lean-looking at this point that I'm too worried about it, but still would prefer to be able to determine and correct the issue...  Thoughts?

[TwoTired]

Have you verified the vacuum test tool accuracy/calibration?  There are four, of course.  Supply the same vacuum source to all four, and verify they all read the same.  (I have a mity vac and a 5 gang aquarium manifold for this purpose.)  I had a sticking gauge once and it screwed up the vacuum sync.  The bald spot from the head scratching has filled back in nicely, thank you.

Emulsion tube differences:  The number and size of the cross drilled holes, impact air emulsion and therefore fuel mixture.  The main/throttle valve delivery circuit has an emulsion tube.  And, the pilot jet has an emulsion tube as part of it.  Corrosion can effect these as well as acidic or basic cleaning solutions.

Have you checked the air jets for alteration or damage?  There are two in each carb body.  I once found a set where one had been removed.

If you have 4 individual filters, how can you be certain that each presents the same pressure drop across each filter membrane?
Perhaps you can move them from one to another position to see if the symptom follows the filter.

Is the compression equal among cylinders?