Topic: Keeps fouling #4 plug -(problem solved )

[matt mattison]

The bike is a 1975 CB550F. It seems to foul the #4 plug in the low to mid range area of RPM'S . The carbs have been disassembled, dipped, scrubbed and blown out with compressed air, all o-rings were replaced, jets replaced, emulsion tubes cleaned, etc. the needles are all in the same position and all parts seemed to be within spec. Ignition wise, I replaced the caps, clipped the wire ends, new plugs, hondaman ignition,new points, engine timed with a strobe. Valves adjusted to spec per manual.I even swapped the #1 and #4 wire to see if the problem will move, it don't. I currently run a 4to1 MotoGPWerks pipe, and velocity stacks. I performed both compression and leak down tests, both checked out very good. The engine only has 5000 original miles on it. I had to tweak the jetting obviously with the intake and exhaust changes, but 1,2&3 all run well and the plug readings are a light tan. NGK D7EA plugs used.The #4 carb was gone over several times already. I also changed the intake o-rings, and checked for vacuum leaks. Currently I'm waiting for new Honda intake boots and clamps to come in .I'm changing them for the sake of changing them at this point, I figured it won't hurt. The old boots actually still seemed pliable. All valve stem seals were recently changed as well.  Any suggestions at this point will be appreciated.

[ekpent]

Do you try and clean and resuse the old plug or are you changing it out with a good new one.? If using a new one how long does it usually last. Must be running rich at that cylinder.

[matt mattison]

Done both, new plugs and cleaned. Plugs usually lasts about 15 min

[lucky]

How many miles are on the bike?

[matt mattison]

Miles in the engine 5000. Tuned up this April . It had this condition since i put it on the road. I have been just managing the situation since April .

[Gordon]

Have you compared the amount of fuel in the float bowls with the petcock shut off?

[matt mattison]

Yes, they are all equal. I drained each bowl into a measuring cup. I even lowered the fuel level via float adjustment . Had the same result.

[Red Good]

Switch the needle from your #4 to your #1 and see if the problem follows . Had a set once that the po had used sand paper to remove the varnish on the needles .

[ekpent]

No expert on the 550's though I bought a 500 earlier this year. Wondering if your mains are held on by those leaf springs and if you have them all. Maybe a main jet fell out. ?  Just fishin probably. A good picture of your fouled plug would be interesting to see if it is dry or more oily. Could indicate fuel or oil fouling. Does that cylinder smoke at all be it black or blue ?  Have you compared the exhaust head pipe temp with a wet rag to that one compared to the known good with a non fouled plug ?

[matt mattison]

No expert on the 550's though I bought a 500 earlier this year. Wondering if your mains are held on by those leaf springs and if you have them all. Maybe a main jet fell out. ?  Just fishin probably. A good picture of your fouled plug would be interesting to see if it is dry or more oily. Could indicate fuel or oil fouling. Does that cylinder smoke at all be it black or blue ?  Have you compared the exhaust head pipe temp with a wet rag to that one compared to the known good with a non fouled plug ?

I have all the MJ leaf springs installed, and the jets are installed correctly. The fouled plug is a dry black color. There is not really any smoke, black or blue. The engine don't use much oil either. Yes, I did compare the head pipe temp. The offending cylinder (#4) is only warm, never hot , like the others .  I'm still holding a little hope out that I got a vac leak at an the intake boot. I really couldn't detect a leak while the engine was running. The new intake boots and clamps should be in this week. Red Good also had a good suggestion to swap the needles around. I might give that a shot as well since I have the carbs off right now .

[matt mattison]

I just compared my #1 carb and #4 carb needles and emulsion tubes. It seems as if the #4 ( which has been fouling the plugs) has a little more wear in the way the needle fits into the emulsion tube as compared to #1. It's not detactable by the eye, but by fitting the two together. It seemed unlikely to me at first because the engine had low miles on it, or so I think. I need to find a new/different 069A emulsion tube to try out.

[ekpent]

Fingers crossed that it may be your problem as you have done some good troubleshooting so far. Is it a big hassle changing those on those carbs as maybe a switcharoo over to number 1 may be in order to see if the problem follows along.

[matt mattison]

Fingers crossed that it may be your problem as you have done some good troubleshooting so far. Is it a big hassle changing those on those carbs as maybe a switcharoo over to number 1 may be in order to see if the problem follows along.

LOL. it's no more a hassle than everything else has been so far. So I guess I will be swapping the needles and emulsion tubes around. If the problem moves, I need to find new emulsion tube for 069A carbs. I might be better off just converting to 022a needles and emulsion tubes, as these are more readily available.

[Duanob]

They are a wear-able item although slowly. I think you can still buy replacement needles and emulsion tubes. Or buy donor carbs from a low mile bike for spares.

[mrrch]

You could also try swapping the plugs wires around on #1 & #4 to see if the problem changes to #1 ( #1 & #4 fire at the same time like the 750's don't they?)

[matt mattison]

I turned out to be the needle jet (emulsion tube after all) . I bought one set of K needle and jet . Unfortunately, it's very hard to find a F model needle and jet so I had to settle for the K. The bike runs much better, but I just have some minor tuning issues to deal with now in that carb, no big deal really. Since the original F needle was good, I might experiment putting that needle in the K needle jet and see what happens.

[bwaller]

Congratulations on you finding the problem. It seems incredible that one needle jet/jet needle combination be worn out in a bank of four carbs, but regardless....job well done.

We can appreciate the fact that these fine brass parts will wear. I"ll bet though most 40yr old carbs have never had these parts changed, still people struggle to get engines to run correctly or produce advertised gas mileage.

I bought a set (unseen)of supposed low mileage smoothbores for my racebike that were completely worn out. An obvious case of no filtration. I'm happy with the carbs, but it cost me a fortune to get them sorted.