Topic: general power question

[nashport_native]

how much "pull" should a 10k (just rolled to 10k) mile 78 750 have? mine seams to run out of steam at around 6k.

I just think it should rev to the red line, but im afraid to try because at 6k it just seams to quit pulling.

the Bike is stone stock, I gave it a tune up at 9100 miles, (oil, filters, plugs)

any Ideas?

[TwoTired]

A tuneup should include points dressing/replacement, gap and  spark timing.
Also the valve clearance should be checked/adjusted.
 
Did the dealer sell you resistor plugs?
Do you know the brand and numbers?
When you look at the spark plug deposits, what do you see?
Do the exhaust head pipes feel of equal temp?

Cheers,

[nashport_native]

yes I bought the plugs from my local dealer and they are a resistor plug. but I didnt check the points. or valves.  How often should the valves be adjusted?

[Bob Wessner]

they are a resistor plug

Don't know if this will solve your problem, but they should be non-resistor plugs. The plug caps have resistors in them already, so this could be causing a weak spark. I made this mistake once and did notice an improvement when I switched to the correct plug.

[TwoTired]

Do yourself a favor.  Track down and install NGK D8EA spark plugs for your machine, non-resistor.  Or, change all your spark plug caps to 0 ohm type.

The tuneup maintenance interval is 3000 miles or 6 mos. whichever occurs first for all tuneup items.  Oil is every 1500 miles or 3 mos., according to my 77 CB750F Owner's manual.

Cheers,

[Buffo]

my 1978 CB750K8 pulls like a $50.00 Hook......er, well you know. At 5000rpm my bike turns into Mr. hyde.

you should have lots o power at 6000

[nashport_native]

im gonna look into the plugs first. See what happens after that. im hoping its somthing dumb like that.

[endobendo]

Just for clarification:  You said you put on new filters with the tuneup.  Do you mean an oil and an air filter or did you modify the stock air intake with pod style filters?  Any modifications to the airbox or even a non oiled K&N filter can greatly change running characteristics.  The bike I bought from a guy fell on its face at 6k and it was all because of pod filters without rejetting.  Lack of power at high rpms could be a lack of fuel.

[nashport_native]

I ment oil and stock air filter. I know that even putting in a drop in k&n you should rejet.....no I have done nothing to the engine It is as it was when it left honda in 78.

[hymodyne]

would the D8EA work on a 500 as well? currently I'm running D7EA.

hym

[TwoTired]

D8EA will fit and fire in the CB500.  But, they are a colder plug, meaning they wick away heat from the combustion area faster than the D7EAs do.  This is appropriate for the higher mass of the CB750 engine that more easily retains combustion heat.  But, the CB500/550 doesn't really benefit from this unless you are running at high power settings for long durations in hot weather.
The D8EA in the CB500 will essentially lower the combustion temps.  Carbon fouling may become a problem as the temp may not get high enough to "self-clean".
I have also found in my Cb550s that operation during warm up is very poor.
Cheers,