Topic: I give up.....

[Lostboy Steve]

So after a whole bunch of time screwing around with these 77 carbs, I am completely out of my mind with tuning. Heres what I got. Stock carbs, 110 mains 40 slows, pods and a really free flowing exhaust. Timing is stock by the book and plugs are new / gapped. Think starts up on one kick, runs and drives awesome. I setup my sync gauges and started to play with the adjustment screws. Right off the bat at 1500rpm number two is sitting in the middle of the red "late valve timing" area. After setting everything the best that I could every gauge read the same. (Middle of the red "late valve timing".) So now it runs about the same but I still get strange idle issues. It idles normal then it goes high and then it goes low almost stalling. Its not really a normal surging issue because it takes about 20 -30 seconds in between high and low. Again other than that it runs well. Now I wonder if the carbs are messed up. When I got the bike the carbs were 100% seized. And the three toothed hillbilly that i bought it from tried to free them up (I think) by prying on the slides, I'm thinking the number 2 carb may have been forcefully, inadvertently adjusted? The plug chop shows a very rich condition. I just don't know what to do. Its driving me nuts.

[KingCustomCycles.com]

Forcing the carb slides will bend the tab that the pick-up uses and throw the length way off.  That should adjust out with the sync. though.  I am leaning towards leaking intake valve or valves by what you describe. I just did the heads on my 69 with a fresh valve grind and seals.  Went from a 3000 rpm hanging idle with sudden drop and stall to perfect idle and smooth power.  I have yet to synch as things are fresh and I am actually satisfied with it the way it is. Compression test is in order.

[Lostboy Steve]

WILL DO! Thank you King! If a valve job is in order new timing chain as well? Engine has about 9k on it.

[KingCustomCycles.com]

It should not need a chain with that mileage. 

[Johnny5]

From experience, I can tell you that your carb settings are lean for that bike. Try 130 mains and the needle in the richest setting, fuel screw out 2 turns and go from there.

[flybox1]

did you sync your carb sync gauges(to carb #2) prior to sync'ing your carbs?
...or at least check to see they were/are all pulling the same vacuum to begin with? 

[Lostboy Steve]

Yes i synced to number 2 and i assure you johnny its super rich right now i mean terrible you smell like #$%* standing next to it rich.


Sent from my iPhone using Tapatalk

[Lostboy Steve]

Anyway im doing a compression / leakdown test sometime this week and will post that once completed.


Sent from my iPhone using Tapatalk

[Lostboy Steve]

King, do you think its necessary to grind them? Or just a good solid lapping? This engine did sit for 20 years maybe some rusting around the open valves and seats caused gaps in the sealing surfaces. I wish I had a bore-scope.

[Johnny5]

Yes i synced to number 2 and i assure you johnny its super rich right now i mean terrible you smell like #$%* standing next to it rich.


Sent from my iPhone using Tapatalk

Wow, almost seems impossible with running 110's. Were they drilled out? Maybe your floats are set too high and drowning the engine?

[Coyote13]

Make sure your fuel line is not being blocked by anything.  RPM's, for whatever reason, fluctuate A LOT when you're running out of gas.  Check your lines and filters if you've got em.  Hopefully for you it's something that simple.

[KingCustomCycles.com]

If you do get in to the valves, and I would exhaust all other possibilities first, you will want to replace the valve guide seals, which means valves out, and you can take a look then.  If the seats are in good condition, as well as the valve sealing surface, a lapping may be all that is needed.  If the guides are worn, they need to be replaced or those seals won't last long.  Like I said, check what others have mentioned above and do a compression test.  I do know that the real culprit behind many of the posts on this board regarding tuning, and hanging idle issues, is valves not sealing. 

[Lostboy Steve]

No filter on the line, only a 6 by 1/4in line connected to a clean tank with brand new petcock and screen. Floats are fine.  The jets I ordered from honda. The way King said his bike ran before the head work is almost exactly what mine is doing. Plus I have to think that when an engine sits for 20 years at least a few valves are left open and that mixed with the mice living in the airbox,means theres mouse piss and other moisture getting in there and rusting the then shiny valve seating areas. I bet the valve's / seats are #$%*ed.

[Johnny5]

No filter on the line, only a 6 by 1/4in line connected to a clean tank with brand new petcock and screen. Floats are fine.  The jets I ordered from honda. The way King said his bike ran before the head work is almost exactly what mine is doing. Plus I have to think that when an engine sits for 20 years at least a few valves are left open and that mixed with the mice living in the airbox,means theres mouse piss and other moisture getting in there and rusting the then shiny valve seating areas. I bet the valve's / seats are #$%*ed.

Oh, you have a CB550, I thought you had a Cb750. Nevermind what I said about the jetting and carb stuff.

[Lostboy Steve]

No filter on the line, only a 6 by 1/4in line connected to a clean tank with brand new petcock and screen. Floats are fine.  The jets I ordered from honda. The way King said his bike ran before the head work is almost exactly what mine is doing. Plus I have to think that when an engine sits for 20 years at least a few valves are left open and that mixed with the mice living in the airbox,means theres mouse piss and other moisture getting in there and rusting the then shiny valve seating areas. I bet the valve's / seats are #$%*ed.

Oh, you have a CB550, I thought you had a Cb750. Nevermind what I said about the jetting and carb stuff.

lol I was gonna say 130 seemed a bit large.

[Lostboy Steve]

Heres what I got:
Cylinder 1,2,3 120psi
Cylinder 4 80psi 10% leak-down.

Theres my problem! Time to pull the head!

[Lostboy Steve]

Oh and I almost forgot!!!! KING was right on the money! Intake valve is leaking, I could hear the air from the leak-down test through the air filter but not the exhaust.