Topic: Another Carburetor Topic

[Sporkfly]

The "missing" brass fitting is the needle jet orifice at the end of the emulsion tube.

These tubes should all seat o the same depth.   You'll have to take them apart again to determine why they aren't the same length or what is blocking them from a proper seating position.

Really stupid question on the topic of emulsion tubes, I'm a noob with carbs... The PO had them screwed out a couple of turns, is that normal or should I seat them all the way back in? Would that be contributing to my non-revving state?

[TwoTired]

ok , i just found what part you speak of.
anyone with some 78 550 carbs lying around?

You may have assembled the parts wrong.  The needle jet can be inserted backwards, which would account for your change in height or "missing" issue.  Take it apart again and make sure the jet is inserted with the long length (away from the step) toward the carb throat.

[TwoTired]

Really stupid question on the topic of emulsion tubes, I'm a noob with carbs... The PO had them screwed out a couple of turns, is that normal or should I seat them all the way back in? Would that be contributing to my non-revving state?

I know of no valid reason the main jet or the emulsion tubes would be purposely left loose.  I've never tried running that way so I can't say that's causing the symptom you describe.  You are in the best position to tell us.  And, assembling the carb the correct way certainly can't hurt anything.

Cheers,

[pablo78cb550]

ok , i just found what part you speak of.
anyone with some 78 550 carbs lying around?

You may have assembled the parts wrong.  The needle jet can be inserted backwards, which would account for your change in height or "missing" issue.  Take it apart again and make sure the jet is inserted with the long length (away from the step) toward the carb throat.

i looked and compared, they are definitely missing. PO probably rebuild and forgot to reinstall them and sold them to me. they had been siting for a while i just notice them gone while tracking down my non running issues.

[Sporkfly]

I have the carbs so clean I could put soup in the bowls and chow down, everything in the carbs is as clean as I can get them without superhuman-carb-cleaning capabilities.

My conclusion? Valves. I'm getting popping on the third cylinder. The plug looked alright, close to optimal, but a little rich. So, am I looking at tearing my top end apart again? I took it for a run and I couldn't get her up past 3-3.5k rpm but every now and then it would feel like it wanted to kick up higher (and would, that's when it was hitting the 3.5k).

[TwoTired]

I would do a compression check before tearing it appart.

[Sporkfly]

Compression is equal and to spec all the way across. Looks like I'm going to work out a manometer and another new battery and run some more tests on the charging system.

One quirk though... I was having an issue figuring out the throttle stop so the slides open further than they should... When I had it full open or anywhere near it the compression gauge would just jump up and down and not hold anywhere. When I say full open I mean I did not open it all the way due to the slides not stopping properly.

So I'm guessing my bench sync might not have been accurate enough.

EDIT: Just opened up my regulator... The point on the top was touching. My manual says 0.3 mm gap on 'points' so I'm guessing it wasn't supposed to be touching like that? Anyway, I adjusted the upper and lower points to 0.3mm and now my fuse isn't getting hot and neither is my alternator cover (was getting warm just having the key on before). Lights seem a bit brighter too. Guessing that's a good thing .

STILL can't get it above 3k rpm. Back to the carbs I guess.

[Sporkfly]

[youtube=425,350]http://www.youtube.com/watch?v=N5i5MNzWAsQ[/youtube]

The sound quality is awful and I doubt it will help any near the end you can hear it bogged and nearly died but when I let off it went back to idle just fine. Through most of that I eased on all the way up to WOT. I had one dead cylinder during this, and it seems like I get a dead cylinder after anything I change. It's not usually the same one, this time it was #2, it's been #3 and #4, but never #1. After that test there #1 was a lot hotter than the rest.

[TwoTired]

My first observation is that you have the wrong tach.  Possibly from a 750.  And, it is wildly inaccurate for use on a 550.
Beware you can easily exceed red line without ever knowing it using that tach.

Given that the tach is lying and the sound quality isn't much to brag about, and I can't see what you are doing to the throttle or the choke...

 


Cheers,

[Sporkfly]

 

Didn't even notice it was the wrong tach! Thanks for pointing it out, mate!

http://cgi.ebay.com/ebaymotors/75-HONDA-CB550-CB-550-GAUGES-SPEEDOMETER-SPEEDO-TACH_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQcategoryZ50463QQihZ002QQitemZ120273096459QQrdZ1QQsspagenameZWD1V

Guess I should pick that one up, yeah? Aside from that I wonder if there's a way I can figure out the difference between the two for the time being What I find strange is when it's idling (and it sounds like a healthy idle) that it's idling at 1k according to the tach, if I turn the idle screw out any further it dies.

Anyway, I'll take another quick clip so you can see what's going on with my throttle. I had the choke all the way in as the bike was warmed up. Also I'll get a shot of my speedo so you can tell me that it's the wrong one as well If it is, maybe I wasn't going 45, maybe I was going loads faster (and the engine too) than I realized. Still doesn't explain bogging down above 1/4-1/2 throttle.

[TwoTired]

It's been a long time since I had a 750 tach on my 550.  But, if memory serves 6000 was as high as it would go.  I'm not exactly sure was kept the engine from winding up to destruction.  Valve float, points float??  Tough little engine, that...

[Sporkfly]

Well, update. I took it out on the road today for a little test run. I've got no power. Seems to rev fine in neutral and parked, and going by your analysis of the tach I can rev it up to 5k on the 750 tach so I assume that I'm getting pretty nice revs. However, as soon as I had it on the road I couldn't get it above 3-4k when it was in gear... On the way to my buddy's house I had her up to 60 on the highway. In 5th. The tach was reading 4k.  Here and there the engine would surge a bit, but I didn't feel it in the acceleration and I couldn't get it above 60.

On the way back it was a different story, I couldn't get it above 40. Also it was surging a bit more, but again I didn't feel it in the acceleration/speed. Little to no acceleration or power, was unable to get it past 3k on the tach. When I pulled into the garage I was able to rev it up without a problem in neutral.

Ho hum.

[Sporkfly]

So, fuel delivery or timing from what I can gather, correct? I know the timing is on. I set the point gap and have the circuit breaking DEAD ON at the T mark, I set it with my multimeter.

So it's a question of fuel, and I want to say lean? I have pod filters on there now, but stock exhaust so I wasn't expecting much for having to rejet (found a few sites that said 550s and smaller SOHC4s usually don't need rejetting with pods and no exhaust change?). I adjusted the fuel screws out, but maybe not enough?

[TwoTired]

Assuming that all the tuneup items and the compression are good, you've been mislead about the PODs making no difference.
They present little restriction to incoming air flow and this reduces the throat vacuum in the carbs.  The throat vacuum is what pulls fuel through the various fuel metering orifices in the carbs.
The Pods are starving your engine for fuel, in this case.

You can check your spark plugs for combustion deposits, but I'm guessing you won't find any, as there isn't any excess to deposit during combustion.

You can verify the lean condition by applying some choke when your engine power runs out.  A little choke will add to the throat vacuum and force more fuel to draw through the metering devices.  However, that will also limit power at high RPM due to the added inlet restriction of the choke butterflies blocking the carb inlet.  So, it is a diagnostic tool, not a cure for the condition.

The "fuel screws" you mention, are called Idle Mixture Screws (IMS).  The IMS primarily effects mixture settings at throttle positions below 1/8.  It has a very small range of authority, and does very little for mixtures when the throttle is opened above 1/8 of a twist.  The slide needles control mixture in the 1/4 to 3/4 throttle position and the main jet determines mixtures at 3/4 to WOT.

You should tell us what sites said PODS didn't effect carb jetting, so we may place them on the list of sites to avoid.

Cheers,

[Sporkfly]

I'll take a look at the list of sites on here (I believe it was listed on sites to buy from in the thread here).

Anyway, I opened my carbs again and decided to check my needles. I assumed they were at the stock 3 setting, but when I opened them up they were at the second notch. Ouch. I think that was my problem, I set them at the 4th notch to compensate for the pods (good move? maybe?) I haven't tested it out yet, but later today I'll give another update. If this proves helpful I'll look into new jets. One size up would probably be good running stock exhaust? The stock jets on these carbs are #90 (according to fiche), I only seem to be finding #105 screw ins (on Z1).

[deerslayer]

I don't claim to be an expert on this type of motorcycle but from the symptoms you describe I think you are on the right track pursuing lean running conditions. either inadequate fuel flow or too much air.

You mentioned your ignition timing is spot on. Have you confirmed your valve timing? Not sure how this could be off unless something was disassembled (or the chain jumped) but if I had been chasing this problem as long as you have it is something I would check. Sometimes if your valve timing is off it will also give low compression readings on the gauge but the running problems you are describing are causing me to suspect it. (did the engine ever operate correctly since you've had it?)

For those few that may be reading this that don't know what I mean by valve timing, it refers to the relationship of the camshaft rotation to the crankshaft rotation. This is established during engine assembly by aligning the sprockets/gears for whatever means turns the cam on a particular engine. (a chain in this case) If it is even one tooth off it will cause some major issues as the valves are not opening or closing at the correct time and can cause a severe power loss.

[Sporkfly]

Valve timing is spot on as well. I think I've got it figured out at this point, I need bigger main jets now because up to 3/4 throttle I have excellent response. After 3/4 throttle where the main jets kick in (that would be correct, yes?) I start to bog so now I have to get some new jets or take a tiny drill bit to my current ones (a horrible idea if you ask me due to any angle on the bit causing differences between the jets).

Now I get to work on my charging system and order some bigger jets .

[deerslayer]

I just removed a set of pod filters from a CB750k3 that was running lean in the midrange. I could get it to respond well if I put the choke on about 3/4 of the way. It would then rev up fine until more toward the top end and if I opened the choke fully at that point it would rev up more yet.

I went back to the airbox and everything was fine. I had never run the bike with the airbox. (and subsequently found out the previous owner hadn't either.) When I got the bike the carbs, filter box, pods and a bunch of other stuff was in a box. (you know, the proverbial basket case). When I assembled the bike we put the pods on it never suspecting that they could be responsible for the poor running. I have only driven it about 500 miles over the past two years since I was concerned by the lean running. Glad I found this forum and found out what the likely problem was.

Now with the airbox on it's all good. Haven't had a chance to drive it any distance but confident that was the sum of the trouble.

[dusterdude]

oh yea,pods will give you one hell of a high speed lean surge,ask me how i know.

[dusterdude]

btw,one way to check,pull your choke closed a bit and see if it picks up

[Sporkfly]

oh yea,pods will give you one hell of a high speed lean surge,ask me how i know.

How do you know?

For now the needle adjustment (I can't figure out WHY they were at the second notch, running the stock airbox was giving me problems even :\) made a pretty significant difference. Still needs work, but I know what's wrong now, anyway . Ah, persistence, that's what keeps these old bikes on the road when it comes down to it!

Back to that charging system 

[deerslayer]

I just removed a set of pod filters from a CB750k3 that was running lean in the midrange.

Now with the airbox on it's all good. Haven't had a chance to drive it any distance but confident that was the sum of the trouble.

...
Well, I was able to give the bike a good ride today (about 25 miles) and confirmed that it is running great. So the pods were definitely the issue. I am interested in economy more than power at this point so not interested in re-jetting. Has more power as is than what I need...