CB350f hits a wall at 45mph. (Solved)

Scratcher09

Scratcher09

Been Around the Block
I recently picked up this 1974 CB350F with less than 6000 miles. Starts on first kick almost every time. Problem is I can't take it past 45 or 50 mph. It feels strong until I get on the high way. In neutral I can rev it near red line and it sounds strong. But after 45 mph, the power just platues. All four cylinders are firing. I pulled the carbs and the looked to be in good shape. I didn't break down the rack. I just cleaned all the passages and jets and put them back on without changing any of the settings. Anyone have any ideas what could cause this?
 

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Re: CB350f hits a wall at 45mph

My 400f was doing this until I checked the needles. They were on the number 2 setting but should have been on 3. Changed them all and it now pulls like a truck. Might be worth checking?
 
Re: CB350f hits a wall at 45mph

check the points are not pitted or burnt and gapped correctly

and that the timing advance unit is working
 
Re: CB350f hits a wall at 45mph

Adjust your valves. Then check your compression. Then check your spark and your plugs. Then check your points. Then check your timing. If these don't get it running right, then go back to the carbs. Jets, float height, sync, needle, vacuum leaks. Running well, a 350F should hold 75-80 at 7500-8000rpm on stock sprockets.
 
Re: CB350f hits a wall at 45mph

Update--I discovered the problem was a dragging front brake caliper.
 
Re: CB350f hits a wall at 45mph

carnivorous chicken said:
Christ! A dragging brake kept you to 45 on the freeway?
Click to expand...


Doesn't take much when you're only starting with 30hp or so....
 
Re: CB350f hits a wall at 45mph

carnivorous chicken said:
true, but I would've thought there'd be insane heat or smoke or fire or something!
Click to expand...


You'd think it would be pretty easy to notice when you come to a stop as the bike would be pretty hard to push.
 
It was not easy to figure out it was the brakes because it from zero to 40 mph it felt normal. Rotor looks fine. Doesn't seem to have caused any damage. I didn't want to wait for the rebuild kit so I just dismantled and cleaned the caliper and master cylinder. It's working fine. Stops great (compared to my CL twins). I bought some dot 3 brake fluid a and noticed after the fact that it says synthetic in small writing. Is there any harm in using that? I thoroughly cleaned the system so there was not any old fluid left.
 
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