cb350 lost power on highway

[space pup]

so i was riding my cb350 on the highway the other day at about 75mph when it lost a bunch of power and i couldn't keep it above about 50mph. so i get off at the nearest exit and it regained power. tried the highway again and same problem. get off and its fine. finally one last time on the highway, this time i keep it below 70mph and it runs without issue.

i recently added inline fuel filters, but i don't think thats the problem.

other things i have remarked on: i can never get it to start with choke on. which suggests that its running rich. but when i follow the carb tuning steps in my clymer manual, i end up with it running sounding fine at 1100rpm and it never starts with choke on.

i wonder if there might be an issue with air leakage somewhere, given that the rubber collars between the engine and th carbs are 40 years old.

what else could possible cause this behaviour?

 

[g-machine]

I would check your charging system just for safe measure.....

 

[space pup]

charging is fine. i've had that problem before!

 

[Big R]

Sounds like a fuel flow problem- clogged tank vent, fuel filters (I know, but it's worth double checking), pinched fuel line, etc.

 

[cleeuw]

I had this exact problem with my CB400 twin. I checked the plugs and my right cylinder was lean. What was happening is that the float was not adjusted properly so at high speed I was draining fuel faster than it could re-fill (which is why I never had the problem at low speeds either). I adjusted the float valve, cleaned the carbs and it works fine now, though I might take the jets up a size to keep it a bit on the rich side.

If you read the thread I had on it there's plenty of experiences with it (check out Maritime's story).

http://www.dotheton.com/forum/index.php?topic=27549.new;topicseen#new

 

[Maritime]

Yep, lean is bad! But sounds like a float or fuel starvation issue for sure. As you pull off teh fuel catches up and then you get the power back.

 

[space pup]

hmmmm, i'll try pulling the filters first, since i just added them. clearly they restrict fuel flow a bit, due to their nature and design.

 

[bendoug]

I had a problem similar to this on my 750. Turned out one of the floats was stuck open

 

[bendoug]

I mean the float was stuck in the up position, so that would be closed. Sorry

 

[space pup]

Yup, it was a partially blocked petcock! Such simple things sometimes!

 

[bendoug]

Good deal, glad you figured it out.