Topic: Low Power Across the Board

[Farley121]

  Hi All,

Sorry if this sounds all too familiar, but I didn't find exactly what I wanted using the search function.

I have recently resurrected my 78 CB550K after 15 years of storage.  I did the usual cleaning/tune up.  Rebuilt the carbs, did the valve clearance, timing, new plugs and oil.  I had to replace my much coveted 4/4 exhaust with the Mac 4/1 as well.

When it was last on the road, it had pod filters with the stock exhaust, now pods with the Mac.  I rejetted to 105 mains and an extra 1/4 turn out on the mixture screw. 

Now when I start it, I don't need choke and the power is uniformly low across the rev range.  I pulled the plugs and they are black and sooty but dry.  I have to feather the clutch to get moving, but once at cruising speed, it runs fairly smooth with no popping, burbling or surging.

The carbs also leak.  Everytime I take them out and reclean them, a different carb leaks.  I have tried both 12.5mm and 14 mm float heights to no avail.  It would appear that it is getting too much gas at all times as well as overfilling the bowls.  All I have to say is WTF?

[Farley121]

Bump

[RJ CB450]

Could it be that your floats arent seating,  easy to check by holding float closed and seeing if they are leaking.  In addition, verify timing as well.  It could be off a bit?

The exhaust plus pods might just not have proper dynamics together.  While you are getting air and fuel, it could just be really bad circulation resulting in a poorer flame front.  It isnt just how much air and fuel, but how it is mixed together.

[TwoTired]

Start with a the 3K tune up schedule.

Check the spark advance is working.

Try new spark plugs to see if that, at least temporarily, fixes the problem.  Too rich fouls spark, poor spark makes engine run worse, which will continue until mixture and spark is corrected.


Oh, and "pods" is not a specification.  It's a general style.  You don't tune engines to a style.  You tune them to a specification.
4into1 with or without a muffler and baffles?

[iron_worker]

Usually I would expect pods to run lean unless they have a super restrictive filter on them or something?

IW

[RJ CB450]

Just a thought in regards to above and last comment.  Could me mac exhaust has improved scavenging, etc and now carbs just in general working better if whole map is rich.

[TwoTired]

Just a thought in regards to above and last comment.  Could me mac exhaust has improved scavenging, etc and now carbs just in general working better if whole map is rich.

The 4 into 1 concept only improves scavenging in the upper power band.  And even then it only works if the pipe diameter and length is properly tuned for that narrow power band, usually at or near red line or the peak of the power curve.

All all other rpms, like idle or cruise power, the reflected pulses from the 4 into 1 make scavenging and tuning issues worse, as the pulses don't aid the extraction, they fight/spoil any smooth outflow at the exhaust valve.

I don't believe there was any pipe diameter or length tuning for any MAC system.  It is for looks only and a cheap replacement for whatever fell out of favor of the owner.

[RJ CB450]

The 4 into 1 concept only improves scavenging in the upper power band.  And even then it only works if the pipe diameter and length is properly tuned for that narrow power band, usually at or near red line or the peak of the power curve.

All all other rpms, like idle or cruise power, the reflected pulses from the 4 into 1 make scavenging and tuning issues worse, as the pulses don't aid the extraction, they fight/spoil any smooth outflow at the exhaust valve.

I don't believe there was any pipe diameter or length tuning for any MAC system.  It is for looks only and a cheap replacement for whatever fell out of favor of the owner.

Makes me glad I salvage the OEM header pipes...

How about sound.  Usually can hear or feel if it is a mix issue?

[Farley121]

  Thanks Guys,

As it turned out, my fuel line was disintegrating and the rubber bits were causing the float needles not to seat.  I've since determined that coils/wires are in need of replacement so Ive ordered the Dyna S ignition kit with the coils and wires.  I had intended to replace the ignition at a later date but figured I would just get it all at once.

Thanks again for the replies.