Topic: CB550F #1 plug fouling

[jimbir]

I own a '76 CB550F. All stock except for Uni pod filters. Compression runs 105 to 115 psi consistently in all cylinders. Spark coils have been tested and are ok. New wires and 5K caps have been installed. Running NGK D7EA plugs in cyl's 2, 3, and 4 and a D6EA in cyl 1. Have cranked the engine with the plugs laying on the head and the spark looks to have the same intensity on all plugs. I have meticulously cleaned and adjusted the carbs and have the needles set at the #2 notch down from the top. The bike runs beautifully but, after 70 - 100 miles the #1 plug is completely fouled with a dry black carbon powder causing a misfire at idle and while starting fron a stop. Cyl's 2, 3, and 4 show similar fouling on the base of the plug body however, the ceramic is a light tan color.

In another thread about this subject, was the following link.

http://www.sohc4.net/index.php?title=CB550#Tech_Info

I opened it and eventually drilled down to this link.

http://www.sohc4.net/index.php?q=content/cb500550-carb-id-and-specs

On this page the main jet number for the 550F is #98. I don't remember exactly, But I'm sure my mains are at least 110 or even 115 certainly not 98. Could this be a cause for the fouling?

This post describes the condition of the fuel and ignition systems on the bike and the problem I'm having. I have two other points I'd like some thoughts on which I'll address in a follow-up post.

Thank's, Jim

[TwoTired]

#98 mains are stock and correct for a 550F with the stock exhaust and air filter arrangement.
It won't be correct for an engine with a more open exhaust and a change of air filter.  In fact none, of the book value settings will apply when induction and exhaust mods made to the stock engine.

The fact that all the cylinders are not showing the same deposits is the first problem to solve, way before fine tuning.

Something is different between cylinders or carbs across the bank and that is the first thing to discover.  Having the right bits cleaned and the part equal in all carbs must be verified.  Are all the orings inside been renewned, and are you certain the main jet is properly retained in it's proper place in the carb?
You are NOT going to solve this problem by running different heat range plugs in different cylinders.
Have the carbs ever been vacuum synced?

I don't see why your mains need to be that big, unless the exhaust is way open, perhaps.
On K bikes with more open exhaust, the slide needle is clipped in the 4th position, and they use #100 mains.  They may use a different slide needle profile, as well. (does according to the Carb FAQ chart.)

There is also no information that the parts inside the carb are from Hinda or aftermarket, with aftermarket bits being suspect for part uniformity.

As a W.A.G., I'd guess someone tried to overcome the lean midrange by over compensating the mains and that the oring for the main on the fouling cylinder is leaking.
Or, someone crudely drilled out the existing jets in the carbs.

These are things I would check as steps toward solving the problem.  Clearly more, and accurate, information is needed.

Cheers,

[jimbir]

Thanks for the reply

About carbs...
New orings and seals last summer. Not vac sync'd but bench sync'd to +/- .003". No reason to believe internal aftermarket parts installed. Neither the Jets or the emulsion tubes have been drilled and all are the size stamped on them. They are installed per the manual. When you say' needle is clipped in the 4th position' is that the top notch on the needle (all the way down)? I've been told to check the part of the carb body containing the main jet/emulsion tube assembly for cracks. Have you ever seen this?

The exhaust is stock 4 to 1 with all baffles in place.

[TwoTired]

When you say' needle is clipped in the 4th position' is that the top notch on the needle (all the way down)?

The needles have five grooves, and the top of the needle is opposite the pointy end.  Groove number is counted from the top.

I've been told to check the part of the carb body containing the main jet/emulsion tube assembly for cracks. Have you ever seen this?

I've not seen cracks.  But certainly, abuse can make it so.  I have seen corrosion prevent proper main jet seal.

Bench sync is not a proper substitute for vacuum sync.  It just get you close.  Further, the vacuum reading is another info source for possible cylinder problems/mechanical health.

Cheers,

[jimbir]

Thanks for the replies. As soon as I psych myself up to tearing into the carbs I'll get back you with the results.

[jimbir]

Raining and cool here today. Took the bowl off the #1 carb and pulled the main jet. It's a #98 and it looks like the PO pulled it out with a pipe wrench. I want to get four new ones and headed to cycle-re-cycle. they've discontinued them. Got any ideas where to get them? Part number is SKU 99202 602 0980, Honda code is 0331595.

Thanks again, Jim

[TwoTired]

The jet outside can be knurled without effecting function.  It's the orifice that does the work.  And as long as that, and the oring can seal between the carb body and the jet groove, full function can be achieved.

Change them if you want to.  But, be aware that it may not actually fix anything but cosmetics. (Depending on how bad the jet was abused, of course.)

Cheers,

[jimbir]

Found jets on ebay. Will replace old ones and while in there will look at the seats to make sure they're not corroded. Will have a careful look for any place gas could be leaking past the control circuits in the carb.

Jim

[jimbir]

Replaced the main jets with new ones. Close inspection showed side wall of seat to be very badly corroded in #1 carb and less so in other 3. Pulled emulsion tubes to make working room. Cleaned seats using #600 emery cloth wrapped around a dowel followed by crocus cloth. Oring groove in old jets was also corroded. Replaced jets. Put it all back together and it idles much better then before and the # 1 plug is running cleaner.

Thanks for the help, Jim

[steam-powered man]

hijack!

am working thru a similar situation, and followed all avenues that have been suggested in various posts i have seen regarding one cyl running rich.  prob carb is #4. 

carbs cleaned and benched synch'd, new plugs, replaced #4 resist cap w/new NGK 5 ohm (previously had huge number of 80.2, not 5 ohm), valve adj re-checked, set timing at "F", dwell set at .016 because i ran out of plate adjustment, verified advance is working using timing light, relative compression is good, cam chain tensioner re-checked ok, re-set this float from 16mm to 14.5mm, re-checked this emulsion tube (still perfectly clean), adjusting air mix screw has no effect.  not sure what i am missing but i'd next like to check the "side wall of the seat" for corrosion/wear. 

can someone point me in the right direction to find an exploded view of the pd-46a carb showing interior components?  need to find this "seat", and which "o"-rings are you referring to?  many thanks!
bobp
   

77cb550k w/pd46a carbs, oem 4/4, pods
mains - 105
slows - 42
clip pos is 4th down from top
needle is e2350f
floats set to 14.5mm
air screws on #1 - #3 is 2t out.  plugs look nearly perfect
air screw on #4 is now 1t out, still very sooty

bike idles fine at 2000, all pipes evenly hot, plugs have identical spark when viewed in darkened "shop", pulls very strong to 8000, no steady-throttle hesitation anywhere, no popping on decel, pretty quick little bike.  thx!
bobp       

[jimbir]

The first thing you should do is clean the #4 plug. Then, adjust the air screw on the #4 carb to at least 2 turns out. Turning this screw out increases the air in the idle circuit. The way you have it set (1T out) creates a rich mixture which may account for the sooty plug. I'm attaching an exploded view of a typical carb and a sheet of specifications for the carbs used on the '69 - '83 Honda's. If you had the the emulsion tube out, then you would have had to remove the main jet.You, therefore know what it is.The oring I refer to is the one around that jet and they slide into what I call the seat. Again, I think your biggest problem right now is the air screw adjustment.

Jim

[steam-powered man]

i started at 2T out and found the rich #4 plug.  i read some time ago in the FAQ that if the airscrew is on the engine side, out = richer.  on my carbs the airscrew is on the engine side, so out only 1T should be leaner.

i do see the "o"-ring now, my carbs are a bit different from the pic, no "o"-ring.     

i've been cleaning the plugs before each test (really thought i had it when i found the faulty plug cap).  many thx for the pic.
bobp  

[jimbir]

OK, we do have different models and yours is probably a lot different.