1973 CB450 Twin Honda stalls

[KingCustomCyc...]

Good evening, my CB450 accelerates at redline in each gear to about 70, begins missing, and then settles in at 50 mph and is smooth again. I cannot accelerate again until the bike has been below 50 awhile, then I can go again until it misses and decels to 50. I have cleaned and tested the fuel petcock, tank, and carbs, new sparkplugs, starts and runs perfect. I have been a mechanic for 35 years and this one has me stumped. Thanks all!

[finpos]

Two things you've not mentioned - Fuel breather (which will be built into the fuel cap) and the condenser. Also try different coils if you have some spare.

Not dropped a cylinder when it's lost power has it??

f.

[Shreddie]

It does sound like a fuelling problem to me. Hows the fuel filter?

[prawny1]

Is your advance unit working as it should? (assuming it has mechanical advance.
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hellkat wrote:

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[KingCustomCyc...]

Wouldn't rev to redline with advance stuck, coil would not fail and then begin working consistently, fuel tank vent is fine as the petcock drains as new. I am leaning toward a plugged bowl vent on one carb. after sleeping on it. Thanks guys, other ideas welcome.

[paddlesat16]

Give the points the once over, might need re-gapping or replacing, and check the timing hasn't slipped.
Check out https://www.hondatwins.net loads of info available here for cb450 etc
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I once saw a bloke shagging a donkey.... in Saudi arabia. Theory Test Passed 26/10/09 Mod 1 Passed 26/4/10, Mod 2 Passed 7/6/10 Current Bikes Suzuki GSX1400 K5, Aprillia Pegaso 650, Suzuki DR350T.

[KingCustomCyc...]

OK guys, still have the problem and nothing you have offered, except the plugged tank vent, could even be possible. All other responses would have different symptoms than I described. Either I didn't get the description very clear or I am getting all the common problems and solutions. This is uncommon or it would have not stumped this aerospace mechanic and inspector/college professor. I will let you know what I find.

[N cee thirty]

eugh hate points

try the condenser,when mine went it did all sorts
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[Casper]

I had this problem with an old GPz550. Turned out to be no air getting into the tank. stick the tank key in the lock if you have a spare and take it for a fast ride. When it starts to die open the cap and if it starts to run fine straight away you know your problem.

[Vincent]

[gfiandy]

Definately sounds like fuel starvation. If its not an air lock as suggested, could you have a fuel line that is collapsing?

I guess you have already checked that there are not blocked fuel filters. I don't know this bike but mine had some sneaky whitches hat filters just next to the carbs that blocked casing slow fuel delivery.

Regards,
Andrew
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ANDY

[Odie]

The diaphrams are split in the carbs, common problem from when i had one (years ago!)
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