Topic: CB550: Flat spot better but still poor mileage. STILL RICH :( See page 4

[TwoTired]

That chart you posted helps too as it's the only one I've seen that has the needele clip position.

That chart is from a Honda shop booklet for their Mechanics.  I have a Jpeg for the outer cover.  But, I can't find where I put it right now.

Next up are fresh plugs and see how todays changes work. I can honestly feel a difference. I think......and please correct me if I'm going the wrong way.....that if I'm still on the edge of too rich, I'll lower the needle one clip. For all I know, these carbs are stock and unaltered, but I have NOT pulled the needles to verify this yet.

That,   ...er...  does put them in the unknown category.

What are your thoughts on that suggestion about RAISING the needle and using a smaller main? Is that for the other carbs where the clip isn't already on the 4th position?

The 069a carbs for the F have a smaller main and a lowered needle.  They have a 4 into 1 with a muffler more quiet than the early 4 into 4, which likely means a higher muffler pressure level profile.

I don't believe in changing the main to compensate a midrange mixture issue.  (Other people do, though. So, if you design by committee, do pursue that.)

IMO, the main should be the easiest to select, providing you have a test track.  Warm up the motor, install fresh clean plugs, start up, and immediately wail on the throttle in the various gears at WOT and keep it there for 30 secs. to a minute.  (You can add weight to the bike for a closer to worst case power maker.)
Pull in the clutch and hit the kill switch simultaneously and come to a stop.  Pull out each plug and read the deposits.  Compare to the chart here:
http://www.dansmc.com/Spark_Plugs/Spark_Plugs_catalog.html

You can do the equivalent on a Dyno, and they'll also supply a fuel map for the entire range of engine operation (including WOT) under load conditions.  All it takes is money.

[Scott S]

 I'm leaning towards raising the clip and leaving the main alone.

 Will any of the things I'm doing help my mileage? 28mpg just seems poor to me. I am VERY rich on the jetting right now, though.
 I'm hoping fresh plugs, the timing bump and raising the clip will help not only the performance but the mileage, too.

[HondaMan]

I'm leaning towards raising the clip and leaving the main alone.

 Will any of the things I'm doing help my mileage? 28mpg just seems poor to me. I am VERY rich on the jetting right now, though.
 I'm hoping fresh plugs, the timing bump and raising the clip will help not only the performance but the mileage, too.

Raising the clip will reduce fuel consumption, for sure. Advanced timing can help, too.

[Scott S]

 Advancing the timing did seem to help. It's very cold and I just made a few runs up and down the main road. A longer test drive is in the wings.
 I'm sure some fresh plugs won't hurt, either.

[Scott S]

 I know that I have some tuning and trial and error ahead of me. I know I have to R&R the carbs at LEAST one more time. That said, I'd like some suggestions.

 My options:

A) Raise the clip and lower the needle.
B) Go smaller on the main (from a 100 to a 90).
C) Do both A and B.
D) Try a smaller slow jet. Keihin drops from a 38 to a 35.
E) All of the above.

 My initial thought was to just lower the needle. My Dad (who is my wrenching partner in the garage) wants to do it all. I, personally, don't think the slow jet needs changed. My problem is in the 1/4 to 1/2 throttle range, hence changing the needle.
 I'm VERY rich. I'm not having any trouble on the top end, so should I go to a smaller main and risk leaning it too much? Again, right now I am VERY rich.....my plugs aren't just sooty, they're FURRY with carbon!

[grcamna2]

Sounds like you're in for some trial and error.

I had the flat spot after putting everything together, pretty noticeable. I still do now but ever so slightly and not all the time. The hesitation only comes after cruising steady at ~4000 rpms for any length of time. But I've gotten used to it so what I do is close the throttle slightly before accelerating and no more hesitation. I think it's a nature of the 74 - 76 CB550 beast.

You might try and pull your carbs again and go through them. One more cleaning and checking everything won't hurt. Put everything back to stock. Then test ride. If it still persists and your plugs show rich condition them move your needles down one notch. test ride and recheck. it took me a few times but my plugs look perfect, the bike starts immediately even after sitting a while, and has plenty of power through the rpm range.

+1 on going completely through them and double checking everything  internally;have you replaced all the o-rings ? I've had similar problems on different bikes when the needle valve seat o-rings leaked just enough to make it run rich.

[seanbarney41]

I know it can be a pita pulling those carbs multiple times but you really need to only make one change at a time...otherwise you will not know what did what

[Scott S]

 Grcamna2, the O-rings have been changed. I cleaned the carbs once myself. There is a local carb guy just down the street from me. He cleaned them again, changed the o-rings, set the floats, etc.

Sean, I'm personally leaning towards just doing the clip and see if that helps.

[phil71]

Again, right now I am VERY rich.....

then you should just buy a new bike!

[Scott S]

Again, right now I am VERY rich.....

then you should just buy a new bike!

 Nyuck, nyuck, nyuck!

[TwoTired]

A') Verify that existing parts, specifically needle and jet, meet Honda or Keihin specification.
A) Raise the clip and lower the needle. Perhaps After finding out what it is clipped at now  Some "rebuilders" think that middle clip is "normal". I'd guess, from input given here, that this will aid you plug soot issue and fuel mileage.  But, if the needle taper is wrong, then some part of the throttle range will become too lean and even "hesitant".  Also, expect to undo/redo  the air screw setting changes you've already made.
B) Go smaller on the main (from a 100 to a 90). I can't imagine this is the proper answer unless you also narrow the inlet air passage opening and/or use an exhaust system equivalent to what the 77-78 CB550Ks had.
C) Do both A and B.  You intend to fix one thing and break another so the overall outcome is certain to require another change cycle?
D) Try a smaller slow jet. Keihin drops from a 38 to a 35. You can do this without removing carbs from the bike.  Do the plugs soot simply letting the bike idle?
E) All of the above.  (you mean flail? - then add F)
F) Run around waving arms overhead with a horrified look on your face.    

[Scott S]

 Hehe....I guess that's a 'round about way of saying try the needle clip first? I will be sure to check the #'s on it when I get in there.

 Everyone says you can do the jets on the bike, but it's just about as fast for me to pull the carbs!

[TwoTired]

Hehe....I guess that's a 'round about way of saying try the needle clip first? I will be sure to check the #'s on it when I get in there.

Best check for wear and alterations, as well.

Everyone says you can do the jets on the bike, but it's just about as fast for me to pull the carbs!

I worry about damage to the carb couplers with repeated bank removal/installation.  But, if you have all new boots and couplers, it's probably not too bad.
I know *I* can change jets faster than the additional work of removing the whole bank first.  After you get the carbs out the jet change operation is the same time sink as on the bike, and you still have to get them back in and adjust cables and such.

But you, or your dad, is doing the work.  So, it is your option to choose.

Cheers,

[Scott S]

 Have you tried changing the clips on the bike? How big of a job is that, compared to on the bench?
 (Oh, and we work as a team in the garage, so we'll both be doing it)

[TwoTired]

Have you tried changing the clips on the bike? How big of a job is that, compared to on the bench?

I have changed the slide needle clip positions while the carbs are on the bike.  Somewhat of a challenge and a very slender shaft cross point driver is nearly essential.
It's a lengthy procedure to describe.  (I think I did post some time back)  But, not long to perform (4 times, though).  And, you will need to vacuum balance the carbs afterward in any case.

Cheers,

[Scott S]

 I know there's no magic bullet, no secret combination...but IF this were your bike and IF the clip is indeed in the 4th position (from the top), and IF everything else is in good shape with no undue wear.....would you try raising it just one clip to start?

[TwoTired]

If the clip is in the correct position, and the needle is stock unaltered, I'd then measure the Jet opening for the needle.
In short, if the carbs are set up in stock config, I'd look for reasons why your carbs don't behave like every other set of 550K carbs in the world.

In other words, if I found one of the forks bent, I would not simply bend the other one to match.

If your example carbs in perceived original setup configuration do not operate the same as the majority population of like examples, then something is wrong with them to cause unexpected behavior.  I would try and find out what about them is different than when they left the factory, as it is unlikely that when new the bike sooted up spark plugs regularly.  What is different about your bike that requires a change to the stock config?
The alternative, as I see it, is to keep tweaking randomly until it is acceptable, or you get tired of fiddling with it.

Understand that mine is an engineer's approach.  I need to know why it works or not.  And, I'm not happy tweaking things I don't understand until it appears to work.  Mechanics just replace and tweak until the complaints stop for that example, and don't care about why.
I don't have enough information about your carb set to make an informed decision.  I don't have test data about wide open throttle mixture, I don't have information about throttle response from off idle.  Only a general complaint about fouling plugs and poor mileage, for which I speculate an issue with the throttle valve.  But, I can only speculate, the machine's tech has to find the aberration.  Once that is found and firm decision can be made about correction or change direction.

At this point, if you cannot find a reason why your carbs don't behave as predicted, and you want the most expedient way of getting the bike operating as you like, then get a different carb set.

I should have asked this earlier, I suppose.  But, was the float height checked, and the fuel levels in the bowls verified?  If the fuel levels were too high excess droplets would make the operation too rich and yield similar symptoms as you describe.  Were the float valves replaced with aftermarket?  Reading some of Hondaman's recent posts about the spring pin strength, altering those springs would require a change to the stock float height measurement.  It makes perfect sense, to me.

Cheers,

[bwaller]

I don't mean to harp, we're all on your side. I agree with the above again...about float height. I know the carb expert down the street set them, but you need to know for sure they are set correctly. This is step one before you start changing jets or other settings. One logical step at a time.

Good Luck

[Scott S]

 Changed the plugs and pulled the carbs this morning. I'm only on the first carb, but going by appearances, these thhings haven't been monkeyed with. The lock washers on the slides, screw heads, etc. all look virgin to me.

 The clip IS on the 4th notch from the top. The # on the slide appears to be 272301. That might be a 4 on the end, but I'm pretty sure it's a 1.

EDIT: Or maybe it is a 4....so hard to read those tiny numbers. There seems to be a small line at the end, making it look like maybe it is a 4. So, 272304...which would be stock.


 The slide is a Keihin slide and it is marked 2.5 and 103. I did not pull the emulsion tubes, but I'd bet my lunch money that I was the first person to go this deep into these carbs.

[Scott S]

WOW! What a difference! It no longer loads up below 4K rpm. In fact, I let it get as low as ~2400 rpm a couple of times when waiting on traffic to make a turn in front of me and was actually able to roll back on it w/o a stumble or cough.
 EASILY pulls away cleanly in the 3,000-4,000 rpm range now. Pulls much cleaner when rolling off and back on the throttle. Still plenty of power on the top end.

 The plugs (well, the #4 plug, which is the only one I pulled) look very nice. A nice tan color on the electrode and the insulator.

 Very happy about this one so far. I can wait for a warmer day to really put some miles on it and see how she behaves. And to check the mileage again.

 I did set the air screws back to 1.5 turns and will do a little tweaking on them again next time, too.

[Scott S]

 UPDATE:

 While the bike runs much better and the flat spot or loading up is all but gone, the mileage is still very poor and a plug chop shows the bike to still be a little rich.
 I'm now getting ~30 mpg with a best ever of 33 mpg. I recently took a 260 mile round trip of mostly highway and backroad riding in 5th gear at ~50-60 mph. Mileage was 30 mpg on three fill ups.

 -I'm considering a smaller main, as that is where I was on these rides....about 3/4 throttle, which puts me in that transition area between the needle taper and the main jet.

 -I've read a little about some emulsion tube mods in the "Thoughts of HondaMan", but I'm not really sure what that's all about. Since I'm no longer chasing a performance issue (flat spot or stumble, etc.) but a mileage issue, is this something I should consider?

 -Should I leave the main alone at the stock 100 and lower the needle one more clip?

 -So far, I'm having a tough time finding a main jet smaller than a 98. Source for some 90 mains? I also need to find or borrow a jet tool and measure the main jets in the small, off chance that someone has drilled mine out.

-Considered a sprocket change to lower the RPM's and help mileage, but this won't cure the rich condition.

 Thoughts? Especially on the next step as far as main jet or needle clip changes and the emulsifier mods.

[grcamna2]

UPDATE:

 While the bike runs much better and the flat spot or loading up is all but gone, the mileage is still very poor and a plug chop shows the bike to still be a little rich.
 I'm now getting ~30 mpg with a best ever of 33 mpg. I recently took a 260 mile round trip of mostly highway and backroad riding in 5th gear at ~50-60 mph. Mileage was 30 mpg on three fill ups.

 -I'm considering a smaller main, as that is where I was on these rides....about 3/4 throttle, which puts me in that transition area between the needle taper and the main jet.

 -I've read a little about some emulsion tube mods in the "Thoughts of HondaMan", but I'm not really sure what that's all about. Since I'm no longer chasing a performance issue (flat spot or stumble, etc.) but a mileage issue, is this something I should consider?

 -Should I leave the main alone at the stock 100 and lower the needle one more clip?

 -So far, I'm having a tough time finding a main jet smaller than a 98. Source for some 90 mains? I also need to find or borrow a jet tool and measure the main jets in the small, off chance that someone has drilled mine out.

-Considered a sprocket change to lower the RPM's and help mileage, but this won't cure the rich condition.

 Thoughts? Especially on the next step as far as main jet or needle clip changes and the emulsifier mods.

+1  I agree for you to check the actual MJ hole to see if it is what is stamped on it.

[Duanob]

I would try lowering the needles one position first. It doesn't cost anything and you can do it with the carbs on the bike. If that doesn't fix it then try modifying jet sizes. Remember, baby steps. It doesn't take much change in thses carbs to really make a big difference.

[Scott S]

 I've already lowered the needle once. Doing it again is OK, I guess?

[Scott S]

 Bump....any more thoughts? Main or needle again?