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Joe's 1976 CB400f


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Took this for first ride in 2 years.

Starts and idles like a champ. Can even kick start it from cold, could never do that before.

However, it doesn't seem to rev/make power above 6 grand when under load? wai dis? Help.

Plugs look good, electrode has a nice milo tinge to it. No popping or anything. So pretty sure it aint lean. Could it be timing? Cam timing even?

 

Anyway. Pics (for a change)

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Nice and steady idle:

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Any suggestions as to why it not rev out under load (revs out with no load, but sluggishly)

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Will check timing when i next get a chance. 2 sets of points had tippled the complexity... haha

 

Wonder if its not advancing or something. Seems a bit retarded. puhu.

Engine feels sluggish when opening it up. Kinda on par with a triumph tc 6. hah. Far from the 1hp per 10cc beast it should be...

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Im not sure what points are in it at the moment. I have a new set with condensers to put in it aswell. But i suspect it may be one of the cheap and nastys.

 

Havn't done a full throttle chop. Could be leaning out at top end. Could try pop the #98 jets in it and see if its more responsive. If so, then it must be the main jets. Currently has #80s.

 

Could there be anything else in the carbs that could make it run ham? float heights? i set them to factory 21mm but it chooched out overflows on side stand. So i dropped them to 23mm. Stopped fuel going out the overflows. but maybe not enough in bowls? i don't know how bigger effect that has on running...

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A lower fuel level in the bowl can cause a lean condition. 

Are the pilot jets factory size? A combo of these things can make the midrange/transition between jets, lean.

How did it rev when at factory float height?

After it bogs, do the revs rise a bit when closing the throttle?

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Will have a try next sunny day.

 

Although my mudguard bracket was rubbing on tyre. So i had to take it off. But the bracket also hols on the brake caliper mount. No riding till i sort that. 1st world problems.

 

Its not like it bogs or anything. It just wont rev. hah. It just runs out of huff. Doesnt make a difference what position the throttle is in. It just wont go and faster.

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It could be the advancer on the end of the cam, Mine was stuck and caused the exact issue you are having.

 

Hmm, will look at ignition tonight. It seems like it could be something like that eh. Except mine is on end of crank.

 

But symptoms are very reminiscent of a car with too much retard. So it could very well not be advancing.

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  • 1 year later...

So yeah, Had an epiphany. 

It dawned on me that it could possibly be a blocked exhaust header....

k1012336.jpg

 

Popped the old exhaust back on. And hey presto. 10 grand all day!

Closer investigation of the old exhaust showed that they have an inner and an outer, and the inner had crushed in and was blocking the offending cylinder 98%.

Another cylinder was about 50% blocked.

 

So spent last weekend prepping it for a WOF and taking it for a hoon. Runs super happy. Does good burnouts too....

 

So yeah, wof this weekend then ride the shit out of it for summer. So much more pep than my GP125. haha

 

The dumb thing is i wont be able to run the sweet pipes.

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