Topic: Syncing Carbs with bad coil?

[mmmpeanutbutter]

I'm riding a 77 CB400f.

I took my bike in the other day to get an oil change and have my carbs synced (since I just finished a complete overhaul with new carb kits).

So I brought it in and showed back up at the end of the day.  He tells me that there are problems.  One of my exhaust flanges is loose so I'm getting leaking.  o - k.  Not too concerned. 

But the bike isn't running right.  He sprays the water on the pipes and it seems that pipe 2 isn't hot.  We pull the cap and check for a spark.  Nothing.  We take off the tank and fiddle around with it and it works.  It is a bad wire (cause 3 was working no problem)(and the wires are hard-wired to the coil).  So I left the place and took it home nice and easy (on 3 cylinders).

I went to a salvage yard yesterday and paid too much for a coil, got it installed and I'm up and running.


My question is... can you properly sync a set of carbs if one of the plugs isn't even firing?  My gut is saying no, but I'm also new to all this.  I have a feeling that the bike still isn't running the greatest.

[Raul CB750K1]

I would say you can, because the sync just takes into account the vaccuum pressure, and that's independend from what the cylinder do with the mixture (burn it or waste it), but I guess some more knowledgeable people will be able to give a more informed opinion.


Raul

[jsaab2748]

I'd say no because the three running cylinders are being adjusted to compensate for, or, carry the "weight" of the dead cylinder. Even when syncing carbs on an otherwise healthy engine, adjusting one carb will almost always affect one or more of the others, requiring them to be furthur
tuned till a balance is reached by all. Have your carbs resynced now that you're hitting on all 4.
Once it's right, it'll bring a smile to your face

[Bob Wessner]

I agree. Sometimes trying to sync the carbs is a bit like chasing your tail because of the interaction. 

[Bodain]

Could you sync carbs if only two cylinders were firing? Could you do it if only one was firing?

I'm confused... You have a four cylinder engine. Only 3 cylinders are firing and you need a mechanic to tell you this?
My 550 would indeed run on 3 cylinders. It was very noticible. No power, No idle. Syncing carbs would be impossible.

[mmmpeanutbutter]

Does anybody know for sure?

Should I call the guy and bring it back for re-syncing? (and make him do it for free?)  I'm sort of considering just bringing it someplace else.  I wasn't super confident with the fact that he even did anything.  Argh.

Dentists, car mechanics and bike mechanics...  never think I can trust any of them.

[Gordon]

Carb sync is always the last thing you do after a full tune-up.  That would include getting all four cylinders to fire first. 

[jsaab2748]

Carb sync is always the last thing you do after a full tune-up.  That would include getting all four cylinders to fire first. 

Amen Sir! And maybe change your oil in case there's a lot of raw fuel from the dead cylinder now diluting
the oil as well. P.S. Some auto mechanics are really nice guys, honest!