Topic: #2 and #3 Running Rough

[Freebirdbeachbum]

I wouldn’t think they’d be related but after installing new 4:4 exhaust, it appears #2 and #3 aren’t running smoothly, almost like they are somewhat fuel starved. I believe it’s numbers 2 and 3 as those headers don’t seem to be as hot as #1 and #4.

I’ve taken two test rides and the problem starts and stops and starts again.

Ideas?

[TwoTired]

2&3 operate on the same coil, point set and condenser. So check ‘em.

What do the spark plug deposits tell you?

Cheers,

[Deltarider]

Was installing a new exhaust system the only thing you've carried out, or have you done maintenance? For instance, have plugcaps been removed?
Have the headers been properly mounted with new gaskets? Any new sounds (like ticking) there?
A check of the 2+3 ignition would include:
Are plugcaps firmly connected to their wires and are resistances correct?
In case you have the stock ignition, it wouldn't harm to have a look at the ign plate to check for possible arcing of the 2+3 breakerpoints which would indicate a faulty condenser. This vid may be helpful.

At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner

[Freebirdbeachbum]

Was installing a new exhaust system the only thing you've carried out, or have you done maintenance? For instance, have plugcaps been removed?
Have the headers been properly mounted with new gaskets? Any new sounds (like ticking) there?
A check of the 2+3 ignition would include:
Are plugcaps firmly connected to their wires and are resistances correct?
In case you have the stock ignition, it wouldn't harm to have a look at the ign plate to check for possible arcing of the 2+3 breakerpoints which would indicate a faulty condenser. This vid may be helpful.

At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner

I’m not seeing anything like that. Do condensers that are “bad” work sometimes and other times not?
Are there any other systems that serve only 2-3 or 1-4 besides the ignition system?

[newday777]

Was installing a new exhaust system the only thing you've carried out, or have you done maintenance? For instance, have plugcaps been removed?
Have the headers been properly mounted with new gaskets? Any new sounds (like ticking) there?
A check of the 2+3 ignition would include:
Are plugcaps firmly connected to their wires and are resistances correct?
In case you have the stock ignition, it wouldn't harm to have a look at the ign plate to check for possible arcing of the 2+3 breakerpoints which would indicate a faulty condenser. This vid may be helpful.

At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner

I’m not seeing anything like that. Do condensers that are “bad” work sometimes and other times not?
Are there any other systems that serve only 2-3 or 1-4 besides the ignition system?

That's a good video example.

A loose barrel connectors could give that occasionally cutting out and going back on.

[Deltarider]

Freebird, you haven't answered my question.

[Freebirdbeachbum]

Freebird, you haven't answered my question.

Sorry. No other maintenance was done. Only exhaust replacement with new gaskets. No new noises.

[Freebirdbeachbum]

Turns out it was the 1-4 condenser.  I replaced the condensers recently from a tune-up kit and it seems this one failed so I’ve now ordered some Toyo brand.

Thanks all.

[Deltarider]

Strange, although I have seen it before. Someone had the 1+4 breakerpoints doing the 2+3 coil, since his advancer had accidentely been reassembled a 180^o wrong.

[Freebirdbeachbum]

It's funny that I deduced it was 2-3 because the 2-3 headers didnt seem to be as hot as the 1-4 based on my spraying some water on each of them. The water on 1-4 evaporated instantaneously while the water on 2-3 lingered a fraction longer.

I was so focused on 2-3 that I didnt notice that the 1-4 points were the ones arcing excessively. The 2-3 points and condenser were fine.

I gapped them and set the ignition timing and it's running great now. Is there a better 70s era bike than the CB750?

Thanks again all.

[Kevnz]

. Is there a better 70s era bike than the CB750?

Yes, the CB500

[Freebirdbeachbum]

. Is there a better 70s era bike than the CB750?

Yes, the CB500

the 750 is at least 1.5 times better than the 500. 

[Kevnz]

How good must a Harley then be? 2.4?

[TwoTired]

. Is there a better 70s era bike than the CB750?

Yes, the CB500

the 750 is at least 1.5 times better than the 500. 

If not accounting for weight and higher Center of gravity. :-)

Cheers,