Topic: Carb conundrum continues...

[SamP]

After a bench sync I'm having what I consider to be some damn stubborn carbs.
Pertinent details: 1977 cb550k, stock airbox, foam filter, idle screws 1.5 out, 100 mains, 45 idles, 4 into one mac exhaust.
So I thought the carbs would be pretty close to balanced after a decent bench sync. I connected my manometer to dial in the carbs with a good vacuum sync and I'm still having the same issue right off the bat. Long story short, #2 pulls such a strong vacuum and #4 pulls virtually nothing. No amount of adjustment either way affects the vacuum from a visible, liquid-in-bottle point of view.
Since #2 is the baseline carb to balance the others off of, I cannot do anything to tweak it. After a bit of tweaking #1 and #3, I was able to get them stable (no major up or down on the level in the bottle), however either #2 has such a strong vacuum or #4 has a negative vacuum that after 30 seconds of idling the bottle on #4 empties. Extreme adjustments to #4 either bottoms out and raises the needles on the other 3 carbs, which sends RPMs up very quickly, or, in the other direction, it stalls out.

I took this video before I had evened out #1 and #3 (1-1.5 turns counterclockwise), but the same thing seems to happen with #2, but much more violently since it's the only one that seems to have excessive pull. I know I will need to change them back (i.e. equal vacuum as #2), but I really wanted to demonstrate that adjustments DO have an impact on the other carbs, just not #4.
And the ultimate question is - WHY NOT?
For what it's worth, I did notice that bottoming out the slide in #4 did cool the cylinder - the pipe on #4 cooled off when I had bottomed it out. Upon lifting it the pipe heated back up, as if to indicate the adjustment was having an impact on the amount of fuel getting to the chamber - just not the vacuum.
Any thoughts here? I am completely stumped.

[harisuluv]

.... where did the liquid go?  Unconventional setup you have there.  Looks like even the lines directly hooking up to the vacuum port connectors have liquid residue...

[flybox1]

gatorade does not work well as a vacuum gauge fluid 
all the bottles, and lines, and t connectors....dang.  too many variables for me.
i'll stick with my cheap@$$ dial gauges 
sorry I can t help.  good luck with your carb tuning.

[Don R]

Have you checked compression? Valves set right? Does it act up with a stock filter? I know, possibly redundant questions.

[SamP]

But - it's got electrolytes! 

Kidding aside, I know it's not perfect but there are no leaks. 4 bottles daisy-chained 1-2-3-4-1 with antifreeze (wanted something with higher viscosity, but didn't have anything else on hand). The vacuum pulls air up, which raises the fluid level in the bottle. There's a line for each bottle to each carb, and a separate line between bottles. That way the lines are separated from risking fluid intake into the cylinder - even if all the fluid goes to one bottle, it isn't high enough to get into the carb line. Also, bottles are glass so they don't fluctuate from the pressure (tried it with plastic bottles and that was a complete failure as they inflated and deflated with pressure). Like below, but x4.



I would get some dial gauges, but I can't rationalize shelling out $70 to use a tool once and then (ideally) never again. However, if everyone is of the opinion that it's the manometer that is the weak link, I will break down and purchase one. I seriously don't think it is though, since the adjustment screw on #4  doesn't change anything vacuum-wise.

Have you checked compression? Valves set right? Does it act up with a stock filter? I know, possibly redundant questions.

Compression is all good - between 120-125 psi across all 4. Fresh off a bottom end rebuild, so rings are fresh, cylinders honed, new resistor caps and plugs, valves to spec. Don't have a paper filter, but that would affect all 4 carbs, not just one.

[Don R]

 True on the all 4 carbs. sometimes a seemingly unrelated change will show something unexpected. doubt it this time. Sounds like you did your due dilligence. So, you think it's something in the odd carb?

[HondaMan]

But - it's got electrolytes! 

Kidding aside, I know it's not perfect but there are no leaks. 4 bottles daisy-chained 1-2-3-4-1 with antifreeze (wanted something with higher viscosity, but didn't have anything else on hand). The vacuum pulls air up, which raises the fluid level in the bottle. There's a line for each bottle to each carb, and a separate line between bottles. That way the lines are separated from risking fluid intake into the cylinder - even if all the fluid goes to one bottle, it isn't high enough to get into the carb line. Also, bottles are glass so they don't fluctuate from the pressure (tried it with plastic bottles and that was a complete failure as they inflated and deflated with pressure). Like below, but x4.



I would get some dial gauges, but I can't rationalize shelling out $70 to use a tool once and then (ideally) never again. However, if everyone is of the opinion that it's the manometer that is the weak link, I will break down and purchase one. I seriously don't think it is though, since the adjustment screw on #4  doesn't change anything vacuum-wise.

Have you checked compression? Valves set right? Does it act up with a stock filter? I know, possibly redundant questions.

Compression is all good - between 120-125 psi across all 4. Fresh off a bottom end rebuild, so rings are fresh, cylinders honed, new resistor caps and plugs, valves to spec. Don't have a paper filter, but that would affect all 4 carbs, not just one.

Why does this make me want some cherry coke?

[HondaMan]

Sam:
Did you replace the old O-rings in those castings where they bolt the carbs to the head? They wear out (and leak vacuum in about 10,000 miles from the engine heat. It is the very same O-ring as is used in the valve caps.

[Shane72]

If there's one thing carburetors have taught me, it's to not over-think them.

Did it idle/run well either before or after the initial bench sync?

Are you performing this test to isolate a definite tuning issue from before, or since the latest sync?

Have the carbs been disassembled, cleaned, and re-assembled with known-good jets and leak-free boots?

There are more questions, but this is where I'd start.

My brother once had convinced himself that the new parts/jets he had purchased were perfect in every way (and that the problem lay somewhere else), until I made him hold each one up next to the stock ones for comparison--they were shorter, and had fewer holes for emulsification.

Clean stock ones back in--problem solved.

With a good bench sync and known-good parts, I've only had to make the smallest of later adjustments, if at all.

All the best,

Shane

[seanbarney41]

Are you sure all four cylinders are firing?   Doesn't sound like it in the video...

[SamP]

True on the all 4 carbs. sometimes a seemingly unrelated change will show something unexpected. doubt it this time. Sounds like you did your due dilligence. So, you think it's something in the odd carb?

I don't know what else it could be. When I bought it she ran super rough on idle, so I know the PO futzed with a lot of stuff and messed it up, but man - i did everything short of dipping them (which they didn't need, from the looks of it), corrected the inverted floats, and put the right jets in, mixture screw to spec, everything. Just made sure all passages were clean and still this issue. I was going through some old threads and the only potential thing that it could be would be a bent valve. But since compression is all good and I don't have any coughing or spitting, that doesn't seem like it could be the problem with no vacuum/pull on cylinder #4.

Sam:
Did you replace the old O-rings in those castings where they bolt the carbs to the head? They wear out (and leak vacuum in about 10,000 miles from the engine heat. It is the very same O-ring as is used in the valve caps.

Yeah, when I did the first top end a year ago I replaced all the O-rings, including those under the intake ports. They're fresh.

If there's one thing carburetors have taught me, it's to not over-think them.

Did it idle/run well either before or after the initial bench sync?

Are you performing this test to isolate a definite tuning issue from before, or since the latest sync?

Have the carbs been disassembled, cleaned, and re-assembled with known-good jets and leak-free boots?

There are more questions, but this is where I'd start.

My brother once had convinced himself that the new parts/jets he had purchased were perfect in every way (and that the problem lay somewhere else), until I made him hold each one up next to the stock ones for comparison--they were shorter, and had fewer holes for emulsification.

Clean stock ones back in--problem solved.

With a good bench sync and known-good parts, I've only had to make the smallest of later adjustments, if at all.

All the best,

Shane

It idled like crap before, after the bench sync it was ok, save for the complete lack or vacuum on #4. I didn't ride it after the bench sync, since I wanted to vac sync them first.
I'm currently trying to isolate tuning issue that has existed since purchase 1.5 years ago. Top/bottom ends rebuilt, finally at the carbs stage.
Carbs have been removed and cleaned, but not removed from linkages. Known, good jets are installed, as are new boots. Clamps could be replaced, but boots are tight enough that they shouldn't be the issue (famous last words). They're tight.

Are you sure all four cylinders are firing?   Doesn't sound like it in the video...

All four pipes are hot. Engine sounds uneven because I'd been messing with the adjuster screws.
This is how she sounded before the bench sync:

[dave500]

go right over your ignition first,be sure its all spot on,use a strobe and square it all away first,measured the caps resistance?

[SamP]

Static timed the points, gap is to spec. Don't have a strobe, but can buy one. Wouldn't timing affect 1 AND 4, not just 4?

New 5k caps on new plugs.

[Maurice]

You need to remove the cap from carb #2, or your results will be funky.

[SamP]

You need to remove the cap from carb #2, or your results will be funky.

Won't that completely eliminate the vacuum from #2? I thought the point was to balance the pull across all 4 evenly.

They're PD46 carbs, for what it's worth.

The more I think on it, the more I come to the conclusion that I either have a vacuum leak on the intake manifold on #4 (hence no vacuum), or a problem with the actual carb body on one of the deeper passages I can't get to (blocking air/mixture somehow? End result being no ability to pull anything through the carb. Valve issues shouldn't completely eliminate the vacuum, so I'm left with a leak or a bad carb.

[Maurice]

No, you have to remove the cap so you can compare apples to apples. #2 will pull a decent vacuum and the others less, you'll never get them balanced.

PD carbs, I have 2 bikes with those.

You could have a vacuum leak. Sound on your video is not great, I seem to hear a bit of exhaust leak if anything.

Do address issues one at a time. Take that cap off and move from there.

[DaveBarbier]

You need to remove the cap from carb #2, or your results will be funky.

Saw that too. Was going to comment on it.

Sam, have you actually sprayed carb cleaner or similar to check for air leaks? Sometimes, at least in the manifold, I've found that the new o-rings I've gotten are a tad smaller in diameter than they should be. It felt like they installed normally but after I took them off again one was pinched against the head and ripped.

Did you install the slides the right way? Cutout facing the air box. I only mention that because nothing keeps it from being installed improperly other than the user.

Just to completely rule out your manometer can you borrow someone else's? What's your location? Maybe someone on the forum can swing by.

I don't really know too much, but it seems like an air leak would also lead to high hanging RPMs and I don't see that in your video.

I had a really stubborn carb issue (PD46C) that I couldn't figure out and then I noticed that the PO drill out the idle jets to over double the size. Instead of a 42 it looked like a 100.


---
1978 Honda CB550K

[SamP]

You need to remove the cap from carb #2, or your results will be funky.

Saw that too. Was going to comment on it.

Sam, have you actually sprayed carb cleaner or similar to check for air leaks? Sometimes, at least in the manifold, I've found that the new o-rings I've gotten are a tad smaller in diameter than they should be. It felt like they installed normally but after I took them off again one was pinched against the head and ripped.

Did you install the slides the right way? Cutout facing the air box. I only mention that because nothing keeps it from being installed improperly other than the user.

Just to completely rule out your manometer can you borrow someone else's? What's your location? Maybe someone on the forum can swing by.

I don't really know too much, but it seems like an air leak would also lead to high hanging RPMs and I don't see that in your video.

I had a really stubborn carb issue (PD46C) that I couldn't figure out and then I noticed that the PO drill out the idle jets to over double the size. Instead of a 42 it looked like a 100.


---
1978 Honda CB550K

I haven't sprayed yet, but I will try with some liquid wrench next time. The fact that I was using new o rings and tightened them up has stopped me from suspecting that. Certainly nothing to gloss over with a loss of vacuum.

It's been a while since I had the slides out, but I vaguely recall them only being able to fit in the body if installed in one direction.

I'd love to borrow someone else's manometer, but don't know anyone that has one to lend. I've linked them up so that the bottle that is on 4 was on 1, but still it's the same issue on 4. But if anyone is in the central Virginia area (Charlottesville) and wants to lend it, I'd happily accept.

The only other potential issue was a minor ding in the upper seat of the idle jet on 4. Posted pics on another thread, I'll see if it's on my phone still.

No, you have to remove the cap so you can compare apples to apples. #2 will pull a decent vacuum and the others less, you'll never get them balanced.

PD carbs, I have 2 bikes with those.

You could have a vacuum leak. Sound on your video is not great, I seem to hear a bit of exhaust leak if anything.

Do address issues one at a time. Take that cap off and move from there.

I didn't see anywhere else that I was supposed to have #4 disconnected. Other videos of 550 syncs show all for connected, and since it has a port to connect it I figured it was supposed to be linked in with the others.

[SamP]

You could have a vacuum leak. Sound on your video is not great, I seem to hear a bit of exhaust leak if anything.

Exhaust is torqued on there. The hiss is from the breather. I admit, it does sound loud

Also, here's a pic of the pilot jet seat on 4.

[Maurice]

#4 disconnected? I wonder where you got that from...

No, you simply have to remove the carb top from #2 carb body, just like the other ones. Number 5 here:



Just do that before anything else and report back.

[SamP]

Sorry, I misspoke. I meant carb #2 disconnected during a vacuum sync.
 I see what you're saying now. No, the top was installed. This needs to be removed during a sync? If so, that might be my problem.

[DaveBarbier]

It's been a while since I had the slides out, but I vaguely recall them only being able to fit in the body if installed in one direction.

Since you've got, I think, the PD46A carbs then you might be right. The PD46C's can go in either direction if I'm not mistaken.

Yes, as Maurice said remove the top cap on all 4 carbs. The slides don't provide a perfectly air tight seal so having the cap on top of #2 would/could slightly increase vacuum on that one throwing off results.


---
1978 Honda CB550K

[madmtnmotors]

the top was installed. This needs to be removed during a sync?

Yes. All 4 carbs should be operated under the same conditions.

[SamP]

It's been a while since I had the slides out, but I vaguely recall them only being able to fit in the body if installed in one direction.

Since you've got, I think, the PD46A carbs then you might be right. The PD46C's can go in either direction if I'm not mistaken.

Yes, as Maurice said remove the top cap on all 4 carbs. The slides don't provide a perfectly air tight seal so having the cap on top of #2 would/could slightly increase vacuum on that one throwing off results.


---
1978 Honda CB550K

This is exactly what I was looking for - the not exactly obvious upon initial inspection thing I was missing. But reflecting on it further, of course that will increase its vacuum over the others. I'll have time to try again Thursday and I'll report back.

[SamP]

Well, removed the top from the #2 carb and tried to sync again. The vacuum was much more balanced overall, not nearly as much pull from #2. Much more even, but adjustments on #4 still don't do much, if anything, and #3 pulls hard despite adjustments to it. I got them somewhere that was somewhat stable, but it still stalls out, high hanging idle after throttle blips, and sounds like crap at 1000-1100 rpm idle. I don't know how else to to describe it, but as the idle gets lower, the engine sounds like it's limping. It also sounds like there's a hiss that seems to be coming from cylinder 4, but I've removed the intake and exhaust tappet covers and it doesn't seem to be coming up through there, nor is there spitting or coughing back into that carb. Could a bent valve/valve leak be indicative of my symptoms here? Or do I just need to take another methodical crack at tuning?

Thinking I might have to break down and get a real set of gauges, even though I don't have that kinda money to shell out right now. Anyone got one to sell, or willing to lend? I'd gladly reimburse for shipping and then some.