Author Topic: Ran rich, rejetted, now not running?  (Read 1646 times)

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Offline n9viw

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  • Floyd, '76 CB550k
Ran rich, rejetted, now not running?
« on: June 23, 2005, 12:41:36 PM »
Oy, if it's not one thing, it's another...  ::)

Here's the bike:
'76 CB550k, 30k miles, K&N pods, 4-2 open turnouts. Was jetted to 118, now 109. (see below). Aftermarket chrome coils, stock points.
Here's the situ:
Engine was running well, but bogged at WOT due to over-large main jets. It started seeping oil, so I tucked in and found out the head wasn't properly torqued, so in between stripping and helicoiling holes, I cleaned the combustion chambers (carbon fouled), and cleaned up the casting marks in the intake and matched the ports to the manifolds.
Reinstalled and retorqued the head, making SURE to keep the cam timed properly to the crank. I reinstalled the rocker assembly and reset the valves, put the pipes back on with all new exhaust gaskets. While the carbs were off, I rejetted from 118 (#56 drill) to 109 (#57 drill).  Cleaned the carboned plugs and regapped to 0.030" (range is .028-.034", I think they had been at .025"). Put everything back together, and kicked myself raw trying to start it. Tried the elec starter, but the battery was really low (it had drained just sitting for a week with no connections on it, go figure), so it didn't help.
I charged the batt overnight, and tried it again this morning. I can't get it to start without full choke and FULL THROTTLE. When it kicks over, since it's at full throttle, it revs WAY up, but seems to be running only on the left side and just sporadically on the right. As a result, the engine is vibrating some, not happy. As soon as I back off the throttle a bit, it dies. Sided-ness running is validated by a quick thumb on the pipes- left two are hot, #4 is cool, #3 is DEAD cold.
Haven't had a chance to check the plugs, but the only things I can think of are: Improper valve clearance, bad coils, or blocked carbs. The carbs were only open long enough to swap out the jets, and nothing else was changed or adjusted. Valves were done by the book, I don't know why I'd suspect them, but I'll double-check just in case. The coils seem to have a reputation of having weak primary windings, I suppose it's possible they chose this time to give up the ghost, I'll ohm them out and report back later.
In the meantime, anyone got any suggestions of what else to check?
Thanks,
Nick

'76 Honda CB550k
'73 Honda CB750k

Offline TwoTired

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Re: Ran rich, rejetted, now not running?
« Reply #1 on: June 23, 2005, 06:39:49 PM »
The stock spark gap for the CB550 is .025.
What are your plug numbers?  Are they resistor plugs? Are you using resistor caps, too?
What are the specifications for your coils?  Primary resistance?
You still running points?
What is your voltage across the open points with ign ON?

Um, what made you think larger main jets were required?

And, please share your trick about how to make large holes smaller with a drill bit!

Are you using jet reamers or ordinary twist drills?  Are you checking holes size result with a gauge?

Did you change slow jets, or needles?

What are your air screws settings?
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline n9viw

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Re: Ran rich, rejetted, now not running?
« Reply #2 on: June 24, 2005, 08:20:29 AM »
The stock spark gap for the CB550 is .025.

According to both Haynes and the FSM, the gap range is as I noted.

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What are your plug numbers?  Are they resistor plugs? Are you using resistor caps, too?

Plugs are NGK D8EA, non-resistor plugs, resistor caps (and resistors intact).

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What are the specifications for your coils?  Primary resistance?

Specs are 5 ohms, and these measure out at 4.6 and 4.8 ohms.

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You still running points?

As I mentioned in the second line of my first post, yes, stock points.

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What is your voltage across the open points with ign ON?

Open-point on voltage is 11.8v.

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Um, what made you think larger main jets were required?

According to past experience and industry recommendations, one jet size is required for pod filters, and another for open exhaust. Stock jets are 100s, I misread the chart and drilled out too large (as noted in my first message).

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And, please share your trick about how to make large holes smaller with a drill bit!

Not JUST a drill bit... one can solder the hole in a jet shut, then re-drill the jet. I simply had a spare set of 100 jets, which I drilled to 109 (close enough to 110, two steps up for the intake/exhaust changes).

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Are you using jet reamers or ordinary twist drills?  Are you checking holes size result with a gauge?

Used both drills and reamers, and using a MIG tip gauge to verify.

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Did you change slow jets, or needles? What are your air screws settings?

Nope- 38 slows, air screws 1/2-turn out, stock needles with the clip in the middle.

Thanks for the verification, but I figured it out- it was lean and starving. It seems vinyl tubing doesn't like gasoline (causes it to kink and twist) so I switched back to rubber fuel line, and the prob went away. Acceleration is MUCH improved, and no bogging/falling on its face at WOT.
Seems I've got it!
Thanks,
Nick

'76 Honda CB550k
'73 Honda CB750k