Topic: YACI (Yet Another Carb Issue!) CB500K1

[AndyH]

After cleaning the carbs and replacing the aftermarket jets/needle with Keihin originals, I then bench synced using the method espoused by TwoTired and many others (back off the idle screw completely, then set using light gap.)

I selected carb #2 as master and calibrated the Motion Pro sync tool on this carb.  The motor was previously warmed up and was running OK but somewhat "rough".  The idle screw was adjusted out to get near 1000rpm.
Initial indications showed #4 out by quite a bit.  Anyway, after some adjusting across #1,3 and 4 I the idle could not be reduced below ~2200rpm (idle screw not contacting the throttle bar).  I did not adjust #2 as it was the master.

As per the 3000 service .....timing, tappets and cam chain adjusts have been specced.

Jet needle is at 4th position from top, air screws at 2 turns out.  (DeltaRider I'm setting this bike up to US specs!  )

What is my next troubleshooting step folks? 

[Deltarider]

Either airleaks or idle set too lean (try 1¹/₂ turn out), unless your ign. timing is not correct and/or advancer is not working right. Does it pick up right and do rpm fall snap to 2200 immediately after rev. or with some delay?
Did you consult the Honda Shop Manual and - the in this site missing! - p.8 in particular?

[AndyH]

Either airleaks or idle set too lean (try 1¹/₂ turn out), unless your ign. timing is not correct and/or advancer is not working right. Does it pick up right and do rpm fall snap to 2200 immediately after rev. or with some delay?
Did you consult the Honda Shop Manual and - the in this site missing! - p.8 in particular?

Tried 1.5 turns out but minimal change.  Seems to snap back OK....I'm starting to suspect an air leak somewhere, but I'll do some more checks.

I have the shop manual, but page 8 assumes gauges....I'm using a Motion Pro fluid gauge where the important parameter is calibrating the fluid columns on the "master" such that they are ~ equal.  There is NO specific vacuum amount.

[dave500]

youull have to set the bench sync again,you have the "master"one set too high,wind it down first so the throttle bar goes back to idle position more.

[AndyH]

youull have to set the bench sync again,you have the "master"one set too high,wind it down first so the throttle bar goes back to idle position more.

Hi Dave, yep I realised what I'd done wrong and have reset the carbs.  I also found my static timing was incorrect.   I followed timing instructions for points, NOT electronic ignition...timing was retarded several degrees.   Fixed.
That'll learn me to RTFM properly next time!!

Carbs will go back in tomorrow.

[dave500]

well done,get hold of a timing light and set the timing dynamicly,shine the light on the marks and slowly increase rpm watching the advance take place until it stops advancing,this will be about 3000 rpm and the full advance marks should be at the index mark,if not adjust the timing until they are,forget where the marks end up at idle rpm,youll be riding the bike over 3000 rpm anyway and itll always be running at full advance,unlike a slower 5500 rpm car that pretty much uses advance through most of its rpm range these bikes rev easy to 8/9000 and 3000 is just their starting point!

[AndyH]

Once I get things reciprocating, I'll do the dynamic timing check Dave. 

[dave500]

consider the advance more of a retarding device!it lets you start the engine easy then once fired up it advances to the running position,in the old days it was all done manually for the very same reason.

[Deltarider]

consider the advance more of a retarding device!it lets you start the engine easy then once fired up it advances to the running position,in the old days it was all done manually for the very same reason.

Dave is right with this. Static timing is only to start with. Timing at full advance is where it matters.  BTW, like others I have good results with a few degrees extra advance. I keep it just outside (right side) of the two full advance marks. Results in a livelier, more responsive motor. 

[BomberMann650]

consider the advance more of a retarding device!it lets you start the engine easy then once fired up it advances to the running position,in the old days it was all done manually for the very same reason.

Dave is right with this. Static timing is only to start with. Timing at full advance is where it matters.  BTW, like others I have good results with a few degrees extra advance. I keep it just outside (right side) of the two full advance marks. Results in a livelier, more responsive motor.

With or without indexing the cam timing degree?

[dave500]

leave the stock cam as it is,you can run a few degrees past the factory full advance so long as you have good fuel and an ear for detonation,ignore those idle "F' marks,you gotta use a timing light and set it using the full advance method,if you have electronic ignition this is where you will pick up some free performance,the balance between having two set of points being exactly timed and staying that way leaves too much for error and they never hold perfect,100 billion vehicles with electronic ignitions cant be wrong?

[AndyH]

Back on-topic  , carbs are back in the bike.  All Keihin brass except for the float valve & needle.
#40 slow, #100 main, IMS 1½ turns out, jet needle 3rd groove as a starting point.   My exhaust is a 4 into 1 (I think Delkevic, dunno how to confirm?) but I'm saving my shekels for a repro 4 into 4 from a bloke in Preston, VIC, Australia.
https://www.ebay.com.au/itm/Honda-CB500-Four-CB550-Four-Mufflers-Exhaust-System-Reproduction-/182588936538

Other commitments today have precluded me firing up the bike but I'll do so tomorrow.

Stay tuned....

[Deltarider]

Back on-topic  , carbs are back in the bike.  All Keihin brass except for the float valve & needle.
#40 slow, #100 main, IMS 1½ turns out, jet needle 3rd groove as a starting point.   My exhaust is a 4 into 1 (I think Delkevic, dunno how to confirm?) but I'm saving my shekels for a repro 4 into 4 from a bloke in Preston, VIC, Australia.
https://www.ebay.com.au/itm/Honda-CB500-Four-CB550-Four-Mufflers-Exhaust-System-Reproduction-/182588936538

Other commitments today have precluded me firing up the bike but I'll do so tomorrow.

Stay tuned....

Not to sidetrack, but let us try to call things by their proper name. This is a public space and I hate to see incorrect info echoed and echoed over again. Now Andy H knows this ofcourse but ignorant readers might get the wrong idea here. Oldstyle Keihin carbs like the 627B had airscrews that metered air to the slow jet. The term IMS or pilot screw (Hondaspeak) we reserve for the screw engineside that meters the already mixed, aerated fuel. The latter is found on the PD carbs that for instance the CB500/550K3 models had. Airscrews and pilot screws just don't do the same thing! More in:
https://www.4shared.com/office/jC4Zzkqhce/Honda_Motorcycle_Carburetor_In.html
Stay tuned.