Topic: Do I have a vacuum leak, or . . . ?

[Honda-Rog]

Yeah, needles were all set to 4th clip from the top, as I've done the new ones.

It had occurred to me to overprice, not sure that would work. Anyway at this rate I'll be fixing it for years 

[Vinhead1957]

Did you check the advance springs ?    Could be advancing early

[Honda-Rog]

Update: Had trouble getting the bike to start up firing on all four yesterday.  I now think there may be an electrical problem on #2 cylinder, which seems to be running cooler than the rest. Could be loose connection, dodgy plug cap or coil, etc. I now have new air filter as well as refurbished carbs and new plugs.

Is anyone else as bored with this thread as I am? I think I won't post again until the problem is solved - sure the rest of you have more interesting lives to live over there . . .

[dave500]

re read posts 5/13 and 22.

[Honda-Rog]

Cheers Dave500, I did check the caps and resistance on each was only slightly over 5K, so I think they're fine.

However I did find a bad LT connection on one coil, repaired but have yet to road test.

I will also be rechecking points gaps and then timing, which is currently spot on.

FWIW I now believe that the carbs are fine, and the problem is probably somewhere in the ignition side.

Appreciate your help.

Rog

[Honda-Rog]

Bad LT connection repaired, but made no difference. Then I found it ! - one wire from the HM unit to the points was chafing against the nut on the end of the crankshaft, inside the points cover - the insulation was gone and the wire was clearly contacting the earthed metal. So I replaced the entire wire, roadtested, and - no difference!

It does seem that at least one cylinder is not firing at idle. Anyone ablke to pinpoint the likely cause, given that I've completely overhauled the carbs with new jets etc.as well as carb cleaning? Could it even be a faulty coil - they were replaced last year?

I've regapped the points, and today I'll recheck the timing with static and strobe. I'll also regap the valve clearances, and retension the cambelt. Then I'll set all the air screws to 1.5 turns, and resync the carbs.

Then I'll get my bicycle out and ride off the stress!! Anyone want to buy a nice CB500 . . .

[dave500]

what coils are they?check the continuity of the primary and secondry on them.

[Honda-Rog]

Done that Dave, thanks, it had occurred to me there could be a problem, but all OK. I'm now resetting valve clearances as per manual, followed by static then strobe timing.

But not tonight - watching the soccer World Cup, Germany v Argentina, live on TV over here, and not to be missed  .

[dave500]

what ohm coils are they3? 5?,tried bypassing the relays?

[Honda-Rog]

OK, so I reset the points, and the valve clearances, and the timing, having done everything else previously alluded to.

And - it works!  For the first time in 5 years this bike drives as it should, with smooth power through all the gears up to the red line, and idles more or less - needs minor tweaks to air screws, and I'm now sure my vacuum gauges are not too accurate. But there's none of the wildly variable idle, no cutting out, and my life is now stress-free (lies, all lies).   

Many thanks to everyone who's contributed to keeping my life long and happy.

(Thinks) now, how to avoid selling it - priced at £5000 (c.$8500), that should do it . . . 

[Honda-Rog]

Once again I'm premature in my pronouncements - when will I ever learn!

Idle is better, although far from good; sometimes it's clearly only idling on three cylinders, and doesn't easily pickup the 4th when I rev it. Still drives pretty well. I found a suspect LT connection on the relevant coil and fixed that, no difference. Seems like No.2, which at idle is not getting as hot as the others (touching the pipes - ouch).

Changing the air screw settings doesn't make any difference, richer or leaner. I had them out to almost 3 turns at one point.

Going to pull the carbs again, and give #2 a real good look and another clean. I did notice one occasion when the overflow tube spouted forth fuel, once I'd turned off the engine. So maybe a sticking slide or float valve, or a tiny piece of dirt in my clean carbs?

Questions:-

Can a coil malfunction on only one circuit?
If carbs have been thoroughly cleaned, and new jets etc. fitted throughout, what else could go wrong with them?

What else could cause one cylinder not to fire at idle?

Why is the UK still in the EU? (rhetorical)

Thanks to all, once again.

[dave500]

so what ohms did you read through the coils?

[Honda-Rog]

One was 16K+. the other 17K+ - is that too high? I read somewhere that 15K was about right. Plug caps were all less than 10% over the 5K.

Have now widened plug gap to the upper end (0.27"), seems a little better idling in the workshop. Also made another attempt at vac. sync, seems more consistent.

Road test soon, will report back.

Reading this thread - http://forums.sohc4.net/index.php?topic=139148.0 - looks very similar. Hoping we may find the solution soon.

[dave500]

what about the primary side resistance?!

[Honda-Rog]

Haven't checked that yet, but rechecked all float levels yesterday. As somebody pointed out elsewhere, the comparative levels when the spring is compressed is important, and I could see variations. So I set them as close to 22mm as possible, whilst keeping them all level on compression (i.e. when the float bowls are full). The idle is now a little more robust and less likely to surge or break down, but still not steady enough.

Pulled the plugs after a 5 minute idle, and all were black, two more than other, so adjusted the airscrews outwards.

Still concerned that one coil might be less than good - any thoughts on the secondary resistances of 16k+ and 17k+? Plug caps are all 5k to 5.5k.

You said earlier that using resistor caps AND plugs was not a good idea, does this reduce the spark too much? I have DR8ES with SD and XD05 caps. Would the bike idle better with DR7 or D& plugs?

[dave500]

use d7ea,dont let it idle for bloody five minutes!