Topic: Where's the power?

[rokusek]

Just finished rebuilding a '73 cb350f...hard tail and 18" apes (only cause I've never seen anyone do it...) Going down the road and she seams to struggle doing 45mph, feels like I'm dragging a giant anchor and it's slow to take off. I know it's not a big bike but it should have some sunk to it...so what can be causing this? Do the carbs need more work...will a different sprocket fix it...

[Markcb750]

Timing advance, float height, plugged emulsion tubes, plugged orifice, running with open carbs and headers causing it to be too lean.

Butthoonose, the experts who know without seeing  will arrive shortly.

[Don R]

Well, lets go out on a limb here and ask the usual, what kind of air filter you have? (Then you say pods or stacks and we say OMG, that'll never work) Seriously though,  if you take off the stock filter box major rejetting is in order.

[dave500]

with ape hangers the wind drag will slow a 350 four up.

[thep1pe]

with ape hangers the wind drag will slow a 350 four up.

Plus the Ape will weigh way more

[70CB750]

How well do wheels spin, or better - are you brakes dragging?

[rokusek]

Thanks for the replies all...I think the carbs need more work cause it's running lean, the spark plugs are really black. This sucks cause I had a shop sync them for me last year cause carbs are my downfall.

The exhaust isn't plugged up as I am running open pipes with no baffles.

Because the way the bike is set up and the Indiana laws regarding apes, the bars are right at shoulder height. So really not much drag is created.

[thep1pe]

If the plugs are black it's running too rich.

[Muckinfuss]

or wet black ....   oil fouling causing poor combustion

[Bodi]

What about the air cleaner?
These carbs are pretty easy to set up with the stock airbox, filter, and exhaust - assuming the carbs are cleaned well. Open pipes will present tuning issues, not too severe: usually just a main jet change and needle height change. Pods plus open pipes is a serious challenge to tune with decent results!
Mis-adjusted ignition timing can really destroy performance, I would check that first.
You should be able to go highway speed sitting upright on a 350-Four, it will work hard uphill or into a headwind though! I wouldn't go on a cross country trip though: although a 350-Four in good condition would be able to do it I would be in bad shape from the vibration and wind.

[TwoTired]

What is your engine RPM at 45 MPH?

Don't expect much from throttle twist alone.  Small engines need lot's of downshifting to make them scoot.   I think this engine needs 4000 rpm to get into any sort of power production band.  If your gearing is near stock, expect to downshift a gear or three in a quick passing maneuver.


Black plug indicate a rich mixture.    I'll ask if you can verify full closure and opening of the choke butterflies.

Sooty plugs by them selves can rob power from misfires.  But the cause of sooty plugs is from too much fuel delivery.  You have to fix both issues simultaneously.

Float height?  Does your engine sit level while running?

[rokusek]

Not sure what the RPM is, I don't have the tach on it anymore...been riding so long don't need it anymore...the carbs fully open and close...I don't have the stock air box, I switched to pods...yes the engine sits level...if I can't get it running better I'll just sell it, too much time in it already, I've got a xs650 I've got to get started on

[eastyork1977]

What Markcb750 said! Timing and float height. If you have a big power bog, and your plugs are fouled, I'm gonna go out on a limb and say your running too rich.

I would raise your float heights to specified millimetre and while you're at it, I would check the jets for blockages just in case. When you're adjusting the float heights, make sure they all match exactly. Will help your idle even out.