Topic: Carb conundrum continues...

[Maurice]

I could ship you my gauges if you promise not to break them.

That motor sounds awful, or hopefully it's the youtube compression. Your issue could be bent valve stem, yes. But first double-check valve clearances, almost sounds like they are too tight. When that's the case they will leak but not through the cover, through intake/exhaust. And sound just like this.

Pay special attention to the page in the manual that shows what valves to adjust on which TDC, it's easy to confuse.

[SamP]

I may have adjusted them a bit on the tight side - pretty sure I did, since I wanted to prevent clatter and needing to readjust later on. I will go back and double check either this afternoon or this weekend, depending on how much time I have. The engine sounds decent, I think it's a combination of the mic on my phone and the youtube compression. Sound-wise the only thing I'm noticing is that hiss around cylinder 4. Gas leak from one of the (brand new) pucks? Incorrect torque?

Interesting thing happened, I went to record the hiss and fired her back up. She ran smoothly, no high hanging idle, no sputtering, until I realized I hadn't turned the gas on, and it was only running on what was in the bowls. Turned it on and it started getting all whacked out again.

I appreciate the offer on the gauges, Maurice. I'll check back once I check my clearances and see how it runs after that. Definitely promise not to break them.

[Maurice]

Clatter to an extent is normal on these engines. "Angry sewing machine" is how I heard it described once and that is spot on.

Too tight clearance and you will burn that valve so watch out.

One thing at a time...

[SamP]

Got time to take the tappet covers off and check the clearances. All were within spec. Didn't seem overly tight.

What's next? How should I check for a bent valve? Compression test? Or try syncing again with the proper gauges?
My only misgiving about the manometer being inaccurate is the fact that adjustments on carb #4 don't produce any change in vacuum, and only increase revs or cause a stall out.

[seanbarney41]

whoaaa...those clearances look pretty huge when you shake the tappet to check for tdc!  You need to bend those feeler gauges at about a 45 degree angle about a half inch from the tip so that they are sliding in perpendicular to the valve, I like to loosen the tappet up a lot. put the feeler gauge in there, and snug the tappet down gently.  Then you can get a good feel with the gauges.  Keep the gauge in there when you tighten the lock nut and make sure you get the same feel afterwards.  ...and just to confirm, you are using .002 inches intake, .003 exhaust?

[harisuluv]

If it hasn't been mentioned yet have you checked for vacuum leaks? 

In your last video I can see that the #4 air intake is not on properly.  There is a raised line that is the halfway mark and has a corresponding groove in the rubber.

[SamP]

...and just to confirm, you are using .002 inches intake, .003 exhaust?

Yup, going by the specs in Clymer's. When I initially set the clearances that's how I did it (loosen them up then tighten them down. The free play is really more side-to-side than up-and-down), but I'll loosen and re-tighten them to make sure they're spec.

If it hasn't been mentioned yet have you checked for vacuum leaks? 

In your last video I can see that the #4 air intake is not on properly.  There is a raised line that is the halfway mark and has a corresponding groove in the rubber.

I checked for leaks on the intake manifold, but not where the carb connects in. When I installed the boots and carbs, everything was as tight as could be (short of pushing the bike over to get those stubborn things on) but I will take a look and test for leaks on the carb-boot connection.

[thrutheframe]

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.

I'd have a hard time justifying chasing my tail for hours to save $70.00.  And someone already asked but... Where did the fluid go?  Sucked into your intake and bypassing your rings in turn contaminating your oil?

Spend the $70.00.  You'll be glad you did.

[SamP]

I'd have a hard time justifying chasing my tail for hours to save $70.00.  And someone already asked but... Where did the fluid go?  Sucked into your intake and bypassing your rings in turn contaminating your oil?

Spend the $70.00.  You'll be glad you did.

The fluid is contained within the 4 bottles.  It gets pulled up and out, into another bottle with stronger vacuum. Only way it could go into the engine is if all the fluid goes into one bottle to reach the line to the carb, and I purposely filled them up so that there's not enough liquid to get there.

Maurice has offered to lend me his, but I'm going to try another valve clearance before I resort to that, just to see if that helps balancing.

[martin99]

Never removed the cap from #2 before on my 750s with PD carbs, but after reading this it seems to make sense so I will do in the future. Learned something again (or maybe I'm getting so old I learnt it before but forgot? ).

Sam, I appreciate money may be tight but the gauges are a must-have tool IMO. And unless you expect to do less than 3k in your ownership, you'll be using them more than once and they will be available for your next bike too

[SamP]

Update on the carbs -
It's been a long winter, and spring has called for more garden work, which cut into my tinkering time.
Broke down and bought a sync for the carbs. Finally got them tuned with a professional, legitimate, functional piece of tech. They ran nice but...
I went to take her for a ride and all sorts of weird stuff was happening. It kept stalling out while coasting through turns, pulling in the clutch to roast through. I noticed that angling the bike in different positions seems to affect the idle, and under no circumstances could I get a stable idle. Sometimes it would stall out, so I'd crank in the idle adjustment screw. Then it'd get nasty hanging idles, so I'd screw it back out.
Decided to take a video when I forgot to turn on the gas. It ran fine until the gas was opened. Then it started sputtering and stalling out. Happened to look back at the airbox manifold to see gas leaking from the drain outlet (the part connected to the carbs, not the box). The float bowls are getting so full that they are literally overflowing, and leaking back into the airbox. I unscrewed all the clamps on the airbox side and checked them, and sure enough, each was wet.
So now I know where I need to look, but I'm confused as to why that would be the case. I set all the floats to spec (14.5 cm, I believe? That or 12, can't recall), installed new float needles, and the pins are all brand new, so they shouldn't be getting stuck open. Only thing not replaced are the floats. They all looked to be in near mint condition, no gouges, mars, dings or corrosion. Can the floats themselves go bad if there is no visible deterioration? Or should I just set the float height lower in the bowl to compensate for whatever is happening?

[flybox1]

Update on the carbs -
It's been a long winter, and spring has called for more garden work, which cut into my tinkering time.
Broke down and bought a sync for the carbs. Finally got them tuned with a professional, legitimate, functional piece of tech. They ran nice but...
I went to take her for a ride and all sorts of weird stuff was happening. It kept stalling out while coasting through turns, pulling in the clutch to roast through. I noticed that angling the bike in different positions seems to affect the idle, and under no circumstances could I get a stable idle. Sometimes it would stall out, so I'd crank in the idle adjustment screw. Then it'd get nasty hanging idles, so I'd screw it back out.
Decided to take a video when I forgot to turn on the gas. It ran fine until the gas was opened. Then it started sputtering and stalling out. Happened to look back at the airbox manifold to see gas leaking from the drain outlet (the part connected to the carbs, not the box). The float bowls are getting so full that they are literally overflowing, and leaking back into the airbox. I unscrewed all the clamps on the airbox side and checked them, and sure enough, each was wet.
So now I know where I need to look, but I'm confused as to why that would be the case. I set all the floats to spec (14.5 cm, I believe? That or 12, can't recall), installed new float needles, and the pins are all brand new, so they shouldn't be getting stuck open. Only thing not replaced are the floats. They all looked to be in near mint condition, no gouges, mars, dings or corrosion. Can the floats themselves go bad if there is no visible deterioration? Or should I just set the float height lower in the bowl to compensate for whatever is happening?

Thats it right there.

Proper fuel level in your carb bowl is the goal.  Re-read this last statement
That goal is 3-4mm below the carb bowl gasket seam.  Your floats are fine.  just verify they are not twisted in relation to each other, and they pivot nicely on their post pins.

It is common for NEW float needles to 'look' the same as OEM, but minute differences can make your perfect float height off enough to make fuel incorrect.
internal pin height, internal spring strength, etc...are off enough to change  your fuel level and have your bike behave like you've described.
14.5mm is your stating point for float height, but you need to verify your fuel level is correct when your float valves close.
The only way to check this is with the clear tube method.
this diagram is not specifically for our bikes, but it is a good representation of the test.  if you have PD carbs, this clear tube will fit on your overflow tube nipple.  its an easy test to perform.

[dusterdude]

Also,make sure your floats arent hanging up on your bowl gaskets

[SamP]

Thats it right there.

Proper fuel level in your carb bowl is the goal.  Re-read this last statement
That goal is 3-4mm below the carb bowl gasket seam.  Your floats are fine.  just verify they are not twisted in relation to each other, and they pivot nicely on their post pins.

It is common for NEW float needles to 'look' the same as OEM, but minute differences can make your perfect float height off enough to make fuel incorrect.
internal pin height, internal spring strength, etc...are off enough to change  your fuel level and have your bike behave like you've described.
14.5mm is your stating point for float height, but you need to verify your fuel level is correct when your float valves close.
The only way to check this is with the clear tube method.
this diagram is not specifically for our bikes, but it is a good representation of the test.  if you have PD carbs, this clear tube will fit on your overflow tube nipple.  its an easy test to perform.

I had a chance to attach clear tubing to the drain valve and measured each one. They were all about level with the throat of the carb, which explains the backflow. It also explains why I was able to start up the bike cold without any choke - already running way too rich (you would think that should've been diagnostically significant in my head, right?).

Went ahead and removed the float bowls and lowered the floats one at a time, checking each time I made an adjustment and got the first 3 down to about 3-5 mm below the gasket seal. Then, for whatever reason, when I went to adjust number 2, all hell broke loose. Made the adjustment, reinstalled it, opened the gas and the float bowl drain screw and gas shot up to the level in the tank. Made NO sense. Tried lowering it more, same thing. Tried replacing the float needle with an older one I had for backup and it still went super high (may or may no have been the same height, all I saw was the gas charge up the line before I cut it off).

Then I measured the OTHER carbs to see what they were doing and then they were back to their original problem height, level with the throat.

For curiosity's sake I went ahead and ran her for a bit. Needed choke to start (good sign), and wasn't nearly as easy to start as before (also good I think), but ran. Got the idle adjusted and it didn't sputter out and stall like it was wont to do before, and no hanging idle on throttle blips. All good signs, but damned if I couldn't get the gas at the level it should be.

Gonna try again tomorrow when I have more light. Anything you all think I should look at while I'm down there?  Or is it all a lost cause until I get a new set of needles and/or seats?

[SamP]

Well, I think I got it. After playing with it all morning to no avail, I removed the whole rack, cleaned each float needle seat, and replaced the needles with the older ones. I noticed that the spring was much softer on the older needles, and that probably helped contribute to it shutting off the gas and seating properly.
Once I did that, made sure the gas was all level in each carb (at least below the throat), I reinstalled the rack and started her right up. Needed choke still, but the was no risk or stalling once it got warmed up. Took her for a ride and noticed that there was no tendency to stall out while coasting through turns, and in fact, only stalled once when I came to a stop (but I think that is more sticky new clutch discs than anything else). No hanging idle, no runaway idle, just nice and even.
Gonna keep an eye on the gas level for future reference. This has been a huge PITA trying to solve.

[flybox1]

Good work! 
fuel usually shoots up the clear tube if you have a float stuck in the down position.
I usually keep a rubber mallet handy to give the rack a of carbs a nudge as the bowls fill.
it knocks the floats free and fuel gets shut off right away as they rise.

[mystic_1]

How clean is your gas tank? 

When I reassembled my carbs last fall with all new internal parts and what I thought was a nice clean tank, I had an overflow condition on #3.  Found one tiny little piece of junk stuck in the float needle seat itself, wedged into the feed hole so it wasn't apparent when I dropped the float and needle. 

Pulling junk into the carbs would explain some of your symptoms.  Does your bike have a petcock strainer?  If so clean and inspect it.  If not, stick your fuel line into a clear container and run a little gas with the petcock set to reserve.  Check for debris.  The reserve position of the petcock draws from the bottom of the tank so any debris should be apparent.

The stiffer pins on the float needles shouldn't be a problem, but differences in taper angles or orifice sizes could explain the problem too.  It sounds like you're swapping new needles into old seats?  That can be a problem, they are usually considered a matched set and in fact I avoid even moving float needles from one carb to another even if I KNOW they're identical, especially with the metal-tipped needles.

mystic_1

[SamP]

How clean is your gas tank? 

When I reassembled my carbs last fall with all new internal parts and what I thought was a nice clean tank, I had an overflow condition on #3.  Found one tiny little piece of junk stuck in the float needle seat itself, wedged into the feed hole so it wasn't apparent when I dropped the float and needle. 

Pulling junk into the carbs would explain some of your symptoms.  Does your bike have a petcock strainer?  If so clean and inspect it.  If not, stick your fuel line into a clear container and run a little gas with the petcock set to reserve.  Check for debris.  The reserve position of the petcock draws from the bottom of the tank so any debris should be apparent.

The stiffer pins on the float needles shouldn't be a problem, but differences in taper angles or orifice sizes could explain the problem too.  It sounds like you're swapping new needles into old seats?  That can be a problem, they are usually considered a matched set and in fact I avoid even moving float needles from one carb to another even if I KNOW they're identical, especially with the metal-tipped needles.

mystic_1

Tank was cleaned and coated immediately after buying the bike. I could tell that was one of the first things. It also needed a new petcock, and with that a new fuel strainer.

The float needles were, by all appearances, completely identical. but I know there could've been some microscopic differences in taper or something. The tip was soft but not squishy, and the spring being stiffer on the new ones was the only difference I could find. With the older, softer springs I think the needle has more time to adjust and properly shut off the gas by setting in the seat correctly, but that's just a guess. Float needle seats are old, from my research it looks like that can't be replaced. All I know is that the fuel doesn't shoot up to the height of the tank like it did before, so I'm happy with that.

[mystic_1]

Huh weird, if I'm reading it right the parts list says "16011-329-004 Valve Set, Float" and I'm seeing both needles and seats in the pics:





Looks like the needle seats are held in with a little clamp and screw?



Anyway the proof is in the pudding as you say, and definitely keep an eye on those fuel levels.  Glad you got it sorted!

mystic_1

[SamP]

Yeah, I couldn't see any logical way to pull the seat out, and it doesn't look like there was a way to push it out from the other side since it links to the fuel line.

Plus it was confusing when I tried sourcing parts. Being the PD carbs, all my searches either had different compatible years or models, but not 77 for the K model. Those that did only had the float needle, no seat.

Maybe someone that has successfully changed the seats on PD46a carbs could shed some light on the matter. If I ever need to change them out in the future it'd be nice to know how.

[flybox1]

seat taper wont matter if you use the viton-tipped float needles.
16011-382-004
http://4into1.com/replica-keihin-float-needle-rubber-viton-tip-honda-cm200t-cb400t-cx500-cb550-cb750/

[harisuluv]

Don't think the metal, rubber tipped valves are interchangeable

[seanbarney41]

Last time I bought needles from Honda, I got rubber tipped...they sealed fine in my 750k1 carbs but lowered the fuel level in the bowl.  I was too lazy to re-adjust so I put the worn originals back which will seep and cause overflows if I leave the petcock on and the engine off.  They work fine with the engine running.


...forgot we were talking about PD's here, I am thinking, but not sure, that the PD's use the same needle's?

[flybox1]

Yes, the PD float valve part number is the same for the 550k in this thread, and my 750k8 PD 42b's..
I listed it above...