Author Topic: Carb clarification & jet source (Read 2751 times)

Nortstudio · « **on:** April 14, 2011, 08:51:56 PM »

1976 CB550K. Stock air box with UNI filter. 4-1 exhaust. 087a carbs.

I have always had a slight hesitation since putting the 4-1 exhaust on, in the 1/8 - 1/4 range (roughly) and have figured I might need a bump in the slow jet. Lately, it has seemed like the hesitation is closer to just off idle up to 1/4 throttle or so. Maybe a move of the needle clip position as well???

My carbs are stock jets now (slow=38), so I have a couple questions: if I were to try to go up in size, how many sizes would be safe? 1 size up to 40, or jump to 42? any thoughts on needle clip position?

Also, any suggestions of where to buy jets that are of solid quality? I don't want to go round and round, only to realize the QC was so low that the sizes from jet to jet are off.

Thanks in advance,

Scott

TwoTired · « **Reply #1 on:** April 14, 2011, 10:14:50 PM »

I wouldn't go more than 40.

But, have you tried simply turning the Air bleeds inward an 1/8 turn or so?

dave500 · « **Reply #2 on:** April 15, 2011, 03:08:52 AM »

even try running the ignition one or two degrees advanced,wont have to fiddle with jetting.

Nortstudio · « **Reply #3 on:** April 15, 2011, 04:16:46 AM »

I have messed with the air bleed screws quite a bit, and it never got rid of it.

As far as advancing the ignition, I had a hell of a time just getting it to be correct the first time (finally got it thanks to TwoTired's how-to for running out of room), so the idea of trying to mess with that makes me even more nervous.

I'm not sure I understand how advancing it would effect the spot in question, and not the rest of the throttle positions???

Thanks guys!

Nortstudio · « **Reply #4 on:** April 15, 2011, 06:40:35 AM »

I am planning on doing another full clean of the carbs. Since I was messing with the air bleed screws so much last fall, is it preferable to put them back to stock position when I put the whole thing back together, before doing the sync?

Sorry if this is obvious, but I have never seen the air screws mentioned in relation to the sync.

Also, I never have issue with the throttle positions past about 1/4, maybe a little more, so if I were to try a rejet, it would really only need to be slow jet, correct? No need to mess with the main jets? I think this is what I have cobbled together from the graph....

TwoTired · « **Reply #5 on:** April 15, 2011, 10:56:25 AM »

How fast and far are you twisting the throttle when you experience the problem hesitation?

Do you have any general observations about spark plug deposits?

If you have a timing light, you might check that the timing is still in correct position.

Does the hesitation improve when partial choke is applied? If not, a slow jet change isn't going to help.
In other words, does fuel enrichment indeed solve the hesitation issue?
(Beware that partial choke is not the answer, just a test. Choke plate closure will mess with high RPM operation.)

Cheers,

Nortstudio · « **Reply #6 on:** April 15, 2011, 03:36:20 PM »

The hesitation happens when I am slowly pulling through (closest to 1/8-1/4 best as I can tell), but if I move faster through it, I really don't notice it that much. It's when I'm following a car, having to hang in traffic, if that make sense. I do SO much of my riding at slow speeds, and this seems to be a place in the throttle throw that I live in often (figures). It only lasts if I hang in that throttle position for a few moments.

I feel like it was better when I first completed all the tune-up procedures (sans sync) but it could have been "wanting" to feel better. It definitely wasn't gone, but it has come back more pronounced again.

I will test the timing again as soon as I get a chance. I have not messed with the choke at all - should have thought about that.

Thanks TT. I know I'm not being very scientific here. I will get back on this, with a more thorough mind, next time I'm able to ride/test it.

TwoTired · « **Reply #7 on:** April 15, 2011, 04:21:28 PM »

Do make note the RPMs and throttle position where the issue occurs.

I wonder if it is an 087 issue. These were the last carbs used before the PDs were put in place.
The 087 was essentially the same as the 022a carbs. But, clearly something was different to earn a different set up number.

Just speculation, but I wonder if the EPA made Honda do something inside these carbs, before the PD's characteristics were mandated, in order to reduce low speed emissions?

I couldn't find anything different in my 087 set. But, I suspect they had been opened up before I got them. Stripped bowl screws are kinda a giveaway.

Which reminds me to ask. Are all the carb bowl mount screws the same size on your set?

Cheers,

Nortstudio · « **Reply #8 on:** April 15, 2011, 04:43:15 PM »

Sorry, I can give the RPMs now. That's all I noticed at first until I was schooled on the whole throttle position deal. I thought RPMs were not the thing to look for.

It's at 3000 RPM. Almost on the nose. It's always been that way. Just a bit of hesitation/burbling that disappears the minute I flick thru it.

Are you asking about the 4 screws that hold the float bowls on? If so, I think they are all the same.

TwoTired · « **Reply #9 on:** April 15, 2011, 05:29:25 PM »

I need both RPMs AND throttle position.

My 087s have larger screws in two positions; for the bowls on the front for the two outer carbs. You know the ones easiest the get way too much torque on if the bowls gaskets are leaking.

It was symetrical, so it made me wonder if the factory did that for some unknown reason. They are the only 087 carbs I've seen. I made extensive measurements to both my 087 set and an 022a set that I KNOW were in stock configuration and could find no difference between them. I feel confident now that someone just stuffed 022a parts in the carb bodies stamped 087. So, the correct internals of the 087 are still a mystery to me.

If you are going back into the carbs, do you want to make measurements while you are in there?

Cheers,

Nortstudio · « **Reply #10 on:** April 15, 2011, 06:21:13 PM »

I will definitely take measurements for anything you think would be helpful. It's all so new to me that any little of info will be helpful.

For the record, I am almost positive all the screws are the same size. I'm going from memory here, and wasn't looking for it - but the one time I tried to get my bowls off while on the bike, there were NONE that had any better torque. They all sucked

I decided then and there that I would forever more, man up and take the damn things off if I'm having an issue.

I have a rack that will hopefully be coming my way soon, and they may be the 022s. That way I would have the 2 side by side for comparison.

The issue I'm having is definitely at about 3000 RPM and somewhere between 1/8 to 1/4 throttle. I think this latest thing is just off throttle - and is gunk related? It's a new thing - and came after some wavy traffic in manhattan. About an hours worth, twice in one day.

Does heat contribute to strange reaction?

I don't want to confuse the issue here. The 3000 RPM hesitation has been happening forever, but this new one just happened yesterday, and I haven't been back on the bike to see if it's still happening.

TwoTired · « **Reply #11 on:** April 15, 2011, 06:24:25 PM »

Are you putting any additives in your gas?

Nortstudio · « **Reply #12 on:** April 15, 2011, 06:33:11 PM »

I was, but stopped not long ago. I had tried the small amount of Sta-Bil prescribed on their bottle - for each fill up. Mostly did it through the winter - when I had no idea whether I would be snowed in for two weeks a day after a fill up.

I stopped that a while back, maybe 3 tank fills ago.

I know you posted to my mention of MPG awhile back. I took you advice and kept track of the mileage between reserve to reserve. Pretty darn close, because I was within a mile of a gas station both times. It hit 75 miles exactly.

I know that's problaby too little, but when I tell you that I do most of my driving at 5 MPH, I'm not exagerating. It's pitiful around here.

Sadly, Brooklyn is not the paradise I had hoped for when I was young, dreaming of owning a street bike....

TwoTired · « **Reply #13 on:** April 15, 2011, 06:48:10 PM »

Wow, that's a lot of low speed. Do you get above 5000 rpm much? Do the carbs get pretty warm?

I'm wondering if the gas is evaporating and leaving deposits at the transition point between carb throat and fuel sources. Like where it enters the carbs or where it feeds the emulsion tubes (mixes with air at that point).

If you are goin in, check it out. Maybe you need some kind of fuel additive as a "cleaner"?

I'll dig up my spreadsheet where I wrote all the measurements I made in the carbs. (been a couple years or five.)
When you getting into the carbs?

Nortstudio · « **Reply #14 on:** April 15, 2011, 06:59:01 PM »

I know! I'm no speed demon, but this much low speed is really a drag. I don't do a ton of 5000RPM, but try to keep it up towards 4k if possible. Unfortunately, often that's not possible when surrounded by 30 yellow cabs.

I get some times outside of the city when the weather gets nice, but since the fall it's been all city riding. the bike does get hot (I can feel it on my legs - specifically my ankles) but I've never checked the carbs specifically.

Do you suggest a certain "cleaner?" Based on the way things have been going, I'm thinking something along the lines of napalm!

I'm waiting to hear back on this other set of carbs before I dig in, unless it takes too long to hear back, and the inerds are clogged. That would mean middle of next week.

What exact measurements would you be looking for?

Nortstudio · « **Reply #15 on:** April 17, 2011, 07:06:30 AM »

So I just had to make a quick run to the bank. No time for any real tests, but being sunday morning in Brooklyn, the hipsters are all sleeping this early (before 1pm really), so I was able to freely use the street for some slow riding, without the threat of being hit by any cabs.

The very low throttle issue I was having the other day is gone. I still had a bit of hesitation in the typical area (1/8-1/4 throttle, 3k RPM) but not too exaggerated.

It really makes me wonder if heat/high temps from running that long on slow traffic has something to do with it.

I also noticed that the heatitation at 3k is much les pronounced if I am shifting/throttling quickly, right up through the gears (because for the first time in a while, there were not 28 cars in front of me!).

Hmmmm......

TwoTired · « **Reply #16 on:** April 17, 2011, 10:39:05 AM »

Do you recall if the hesitation is simply a lack of power that suddenly comes back cleanly, or does the power come back with a burble, sputter before it evens out?

Heating the carbs/fuel, does effect the burn rate and propensity to ignite.

I don't usually say this for the 550 but, if your ride routine mostly has the engine running on the hot side, maybe you are better off with D8EA plugs? If your bike is like mine, you'll hate the warm up transition at the beginning of the ride, though.

These are the measurements I took for my carbs. I've done 627B, 069a, and 087a, but haven't gotten to 022a yet.
Slow jet
Main jet
Jet Needle and taper (Throttle valve) clip position
Jet needle number
Jet needle OAL
Jet needle diameter at tip
Jet needle diameter at 1cm
Jet needle diameter at 2cm
Jet needle diameter at 3cm
Jet needle diameter at 4cm
Jet needle diameter at 5cm
Needle jet orifice
Needle jet Air bleeds (Number and holes size.)
Air screw opening (air Bleed)
Air screw type (hollow tip/ solid tip
Main Air jet
Slow air jet
Float Height

May need to add the hole size and count for the slow jet emulsion tube, too.
(I think stock Honda is uniform in thus regard. But, replacement types may no be.)

Cheers,

Nortstudio · « **Reply #17 on:** April 17, 2011, 11:27:08 AM »

I would say that when I was having the really bad (possibly heat related) issue the oter day, it was sorta lurching, so I'd say coming back with a burble. it felt like something was stuck in the carb, and then would come loose, and again, and again... I know that's not what was happening, but that's what I remember thinking.

The old 3k issue seemed to be a cleaner transition back to normal. It's closer to what I've seen people describe when talking about the typical hesitation with these bikes. A slight lack of linear power once I hit a certain spot, and then it passes thru it as I continue the throttle pull.

I will measure those carbs as soon as I have a second this week - I am really curious to see if there is some type of crud in there making waves....

I do have a set of those plugs I could try, to see if it effected my slow, traffic laden nightmare rides. Not excited for a worse warm up period, but I'd rather it give me a hassle on the curb than in the middle of manhattan....

TwoTired · « **Reply #18 on:** April 17, 2011, 11:42:51 AM »

I'll just add that recovery from hesitation with a burble, to me, means the engine had an over rich event that would not support combustion (yielding power).

Conversely, if it recovers from hesitation cleanly, like someone just turned it back on, it is recovering from a too lean to support combustion event.

This assumes spark and engine mechanicals are in good shape, of course.

Maybe this will help with your diagnosis, and corrective approach?

I colder plug should take heat from the combustion chamber and put it into the head/fins. So, if combustion conditions are being effected by heat colder plugs should lower it somewhat. It's a tough call because the cooling fins need the hot air it heats, replaced with cooler air, in order to keep pulling heat from the head (which is where the spark plug places it). In all cases, heat flows in a conductive path from warm to colder areas at a rate relative the differential between the two.

Maybe I'm getting too far into heat transfer dynamics (which can be a science discipline all unto itself).

Cheers,

Nortstudio · « **Reply #19 on:** April 17, 2011, 11:55:32 AM »

Indeed, a discipline I do not have

.

But the explanation makes sense to me, and should help in a diagnosis. I am due to make the same exact trek next week, and will try a few of the things we have discussed here, and be better at keeping track of the changes/effects.

I wish I could be more scientific about my description of te burble vs smoother transition, and maybe I will be, after it happens again.

Thanks for all the help TT.

Deltarider · « **Reply #20 on:** April 17, 2011, 01:30:55 PM »

Quote

The 087 was essentially the same as the 022a carbs. But, clearly something was different to earn a different set up number.

Originally the 087A carbs shared the same jets with the 022A and the needle set with the 022A, the 627B and 649A. Clip position may differ however. But... the air screw is definitely different. The 087A share that one with the 069A carbs, where as the 022A share the airscrew with the ones in the 627B and 649A carbs. Hence the difference in set up numbers.

Nortstudio · « **Reply #21 on:** April 17, 2011, 02:26:30 PM »

What exactly are the differences between the air screws?

TwoTired · « **Reply #22 on:** April 17, 2011, 02:45:22 PM »

The 069a carb had air screws with solid tips. The 627B and the 022A air screws were hollow tipped and cross drilled.

My 087a carbs have the hollow tipped and cross drilled air screws. But, I cannot verify they are original.

Cheers,

Nortstudio · « **Reply #23 on:** April 17, 2011, 02:51:08 PM »

Ok, so I will be getting the other set of carbs shortly (yes!). I have to find out though, whether they are 022a, which I think they are.

If I end up using the 022a on my '76 550k, will this difference in air screw effect it functioning properly on my bike. I was hoping to make a perfect set between the two (minus the air screws obviously).

There is an issue with my 087 with the tube/cylinder that holds the main jet, has damage. I figured if they were almost identical - I would swap to the 022a and use whatever I needed from my 087 to augment what might be missing.

Could this work ok?

TwoTired · « **Reply #24 on:** April 17, 2011, 03:02:05 PM »

Ok, more to consider.
The 022a air screws have a 12 degree taper, and the 069a air screws have an 18 degree taper angle.

I haven't measured the *seat* taper angle in the body of these two carbs and I'm not exactly sure how.
I just thought it best to keep the proper air screw type with the carb body it came with.

Again, my 087a carb set could have had anything done to them. So, I may never know if the seats in the carb body changed with the air bleed screw type.

Caertainly, if you change the internal parts on any of these carbs, the stamp on the outside is meaningless for all future considerations.

Cheers,

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Author Topic: Carb clarification & jet source (Read 2751 times)