Topic: In search of the SOHC Holy Grail

[Bodain]

Well it's almost Christmas and typically I take a few weeks off of work. This year is no exception.
One of my favorite pass times is tinkering with the old 1795 CB550. I've had the bike for about 6 months now.
I've put much work and $ into it. I'm long past the point were I could ever resell it for what I have in it.
It's a money trap. Much like my boat used to be.

Why do I spend so much time fiddling with it? It represents something from 1975 that was unattainable at that time.
I can have many things now that I couldn't have back then.I have no really good reason for even owning it other
than I like to tinker. As far as motorcycles go. I demand far more of my everyday rider than this old Honda can
every provide. Still, the old Honda is one of my favorite pass times. I may never even register and inspect it. I tinker,
then drive it around the neighborhood. The heavy road work is reserved for the Kawasaki ZRX ...

Now to the Holy Grail. The Honda runs basically fine. Yes it has pods. Yes I've rejetted. Still like many old Honda's
when you start it up, it will PFFF, PFFF out of the number two and three carbs. I've learned to live with it.
It seems to happen primarily when it's warming up. This happens very infrequently when the bike it warm.
Number two is the worst. Number 3, not near as freqent as number two. One and four never do it.
There has been a good amount of discussion on the isssue in this forum.

The resolution to this is my Holy Grail..........

I started the elusive search once again, starting yesterday. I'm sitting in the garage and pondering the problem.
My intention is to try and get the problem to move to cylinder 1. If this happens I will know the answer.

I'm thinking ignition.....
I switch spark plug cabs with 1 and 2. I'm looking for it to move.  No change..
The bike does appear to run fine, still the wires and caps are original and old.
I'm down at the local motorcycle shop. For $21.00 I purchase 4 ft. Solid wire and four caps.
Installed at the house and fire it up. No change.   

I swap plugs 1 and 2.. No change
Hmmm....

I pull the coils to clean all connections. Many are rusting.
No change...

I'm back into the timing and points. I generally screw all the timing and 2 hours later get it all good again.
No change.

Now I'm looking for Intake and or exhaust leaks.. I become suspicous of those old rubber boots on
the intake. I swap 1 and 2... I would love to see this problem move to cylinder 1. It doesn't..

I can detect no intake or exhaust leaks...

I'm back on carbs. I pull the carbs and decide to go fishing..

I swap mains, pilot, floats and bowls with 1 and 2.

Again no change. The Pff, Pff continues on number 2.

I retire from the quest for now. Once again the Grail eludes me.

Reflection.......

It has to be a sticking valve that loosens as the engine warms.

[mcpuffett]

that's half the fun of these old bikes the tinkering   mick.

[TwoTired]

It has to be a sticking valve that loosens as the engine warms.

Could be.
 Have you tried synching the carbs?

Do all the carbs have identical parts?
Are the orings all new?

[TwoTired]

One of my favorite pass times is tinkering with the old 1795 CB550. I've had the bike for about 6 months now.

I want one of these 1795 models.  Pilgrim model 

This from a man who spells Guido  "Gweedo". 

[Gordon]

This from a man who spells Guido  "Gweedo". 

The fact that you remember that is either impressive or depressing, can't figure out which.

[DiscoEd]

I want one of these 1795 models.  Pilgrim model 

Here is a Kawasaki version of what you're looking for.

Apparently these were fabricated at about the same time the Chinese were dropping circular stones with big holes in the middle of them off the western coast of the Americas.

-DiscoEd

[DiscoEd]

Recently recovered during an excavation at the base of Mt. Fuji, the CB001...

[KB02]

Are you sure if the points timing is spot on for both the 1&4 module and the 2&3 module? I had to adjust mine individually rather than the whole plate.

Have you checked your compression lately?

[Bodain]

I see you guys are tuning into my typo... <GRIN>  1795

Engine has brand new piston and rings with less than 100 miles on them. Compression is not an issue.

TooTired questions about the carb sync was interesting. In my mechanical mind. I fail to see how syncing would improve
this situation.

Fact... I had totally disassembled the carbs months ago to rebuild them. Never did a sync.
Well I have the Motion Pro unit that has never been used. Silly me!  So I did it last night. 1 and 4 were pulling much more vaccum than 2 and 3.
Task completed.. Now I needed to wait until the engine cooled down to see if this made any improvment.

Fired it up this morning... Hmmm...  It appears to be better. I still have the familar PFF,PFF out of number two, but
it appears to be less freqent.

I must be getting closer to the Grail.

[eldar]

Have you done a low speed idle mix with a dwell meter?  you said you did timing but did you clean the points at all?
What s with the 1795 bit??

[TwoTired]

I fail to see how syncing would improve this situation.

Fact... I had totally disassembled the carbs months ago to rebuild them.

When you rebuilt the carbs, did you replace the old, hard orings?  Particularly the ones on each main jet?  Leakage here can upset fuel metering over the entire throttle setting range.

Because of the four individual carbs, the cylinders try to behave as four individual engines.  The carb slide position would determine the firing speed of each cylinder if they weren't linked together with a common crankshaft.
Let's say number 2 had a slide position of 900 RPM and the rest had a slide position of 1100 RPM.  The resultant actual RPM might be 1050 RPM, with #2 hardly contributing and getting a lean mixture for that RPM.  A slight backfire through the carbs could result from a lean mixture.

During cold warm up, do the head pipe temps come up evenly?  If not, which ones take longer?

Can you equate the presense of the PFT with choke operation?  And, are you certain that each choke butterfly is in an equivalent position with the others over the entire application range?

What is your air bleed setting?  Are these the same across the bank?   Float levels?  Slide needles: size, shape, and position?

I think if you want all four cylinders to behave the same, you have to be certain all four carbs are behaving the same.

Cheers,

[ken74-550K0]

My 1974 CB 550 does the exact same thing.  I just rebuilt the carbs and synched - it does it less, but it still does it.  My next try will be doing a very fine adjustment on the air/fuel mixture screw.  However, this will likely have to wait until the weather get's a bit warmer.  I don't know why - but the sticking valve theory seems very plausible.

The Keyster rebuild kits came with new main jets, needles, main jet o rings.  These items were of course replaced in the course of the rebuild.  The only major difference with my bike is that it's running with velocity stacks.

[Bodain]

I spent a bit of time with it again today....

Zoned in on the points. I wanted to be certain point timing was dead nuts on.
Gapped and cleaned points, again.   No change.
I reversed the condensor set. Hoping to observe a move to 1 and 4. No change.

I played with the air adjusting screws today. Normally 1.5 turns out.
Set them at .5, 1.0, and 2 turns out.   No change.
Tried leaving 1 and 4 at 1.5 turns then only alter 2 and 3.  No change

I guess even after the carb sync last night. It's about the same as it always was.

All components in the carbs were replaced with the Keyster kit. Which by the way. I will probably never buy again.
The float bowl rubber o-riing have grown at least 20%. I've read elsewhere the quality control on the Keystar
kits are so bad they should be avoided.

The ideal situation here would be to have a set of carbs on another 550 that didn't do it.
That should tell a real interesting story, but it's not available. Ya can't really swap individual carbs.

The PFFF, PFFF only happens at idle. Not under RPM. I could leave it alone and it would be fine,
but I've taken this on as a personal challenge. Someone will eventually come up with resolution
to this since so many of the old CB's seem to do it.

I'm just about totally convinced it's not carbs or ignition.

When I had it bored and installed the new pistons and rings, I checked the valves for leakage.
I put a small amount of acetone on top of the valves at intake and exhaust. Looking for leakage.
I found none, so I did nothing to the valves.

I think the head will be coming off one more time the day after Christmas.

[TwoTired]

Could you have bent a valve when you put the cam cover back on?  If you didn't back out the adjusters and/or were extra careful during installation, the adjusters miss the top of the valve stem and push them sideways.

Just a thought...

[HondaMan]

Things that make ratty idle:

#1: float bowl level. The adjustment of the idle bleed screw will not cure this one. One low float will cause that cylinder to barely run. Don't overlook the "air equalizer" tubes, the ones that vent the bowls. If one is pinched shut or plugged, that float level will always be low. Pulling off the hoses to check is a good start, but run with them attached to prevent fires from splashiong fuel on rough roads.

#2: If all else fails, swap the coil wires and the points wires, 1-4 to 2-3 and vice versa. (I have seen one side weak on too many Honda dual coils.) See if the problem follows the coil.

#3: you've done this one: bad plug.

#4: carbon buildup on the intake valve guide and stem. When the assembly warms up and the guide opens up, the thing runs OK. Try running BG44K (1 ounce per tank of fuel) for a while, or pull the head to check it out.

#5: this is often overlooked: valve clearances. The exhaust should be .003" unless you wind it up a lot or have low-restriction exhausts, then it should be .004". Intakes should be .003" (yeah, I know, Honda says .002", but that's good for noise reduction, not RPM), especially if you are running velocity stacks or a K & N intake filter.