Topic: 1975 CB550F Lacks power! HELP I AM DESPERATE!!

[ACVWguy]

Alright don't laugh. I found the problem but it was a serious noob overlook by me.

This morning, after losing just about all hope and wasting 3 hours sitting in the forums reading other peoples problems and trying to piece together mine, I went out to the garage.

I started the bike - one kick - instantly fired up and idled good. I took it for a ride and tested out the throttle. Still bogged whenever I passed 1/4 throttle - I can only assume that this is the point that the main circuit starts to open.

I went home and did a little experiment. I took out the air filter. I drove without the air filter. The bike ran lean at idle and had very little power, but began to open up when I passed maybe 3,000rpm. When I pulled the throttle past 1/4, It didn't bog, it took off and actually had "some" power.... but not much. More than with the filter at least.

I came back home and pulled a spark plug. It was white again? So I finally got it to run lean? Alright, so If the bike runs painfully rich with the filter on and very lean without, I needed to find some sort of "middle-ground" restriction to make the bike run correctly. So, I took out the filter retainer spring and duct taped the filter so there is a gap of about a centimeter between the filter and the airbox. I then took it for a ride.... and it ran AWESOME!!! Seriously like a banshee.

I pulled the gas up to 1/4 throttle and the bike ran normally. I then pulled the throttle up to 3/4-full throttle and the thing pulled like a freight train!! Pulled right past 5000rpm without a hiccup and pulled to 9000rpm smoothly and consistently. Every shift. I got it to pull to 100mph on a long abandoned road - previously it wouldn't even pass 55 unless i was going downhill.

I drove back home and pulled a spark plug (the same as last time). It was tan-white and clean!
So, the verdict?

I need a new air filter. That is all. My old filter (the original - 36 years and 6800miles on it - didn't look very dirty) was restricting enough that it caused the bike to run way to rich when the main fuel circuit was opened. Awesome. All of this work and heartache just for a measly air filter Oh well, at least its cheap enough could be alot worse!

[Tugboat]

Man that totally makes me smile. Seriously - that's something I would do. Been watching this all day and glad this story has a happy ending!

[TwoTired]

I need a new air filter. That is all. My old filter (the original - 36 years and 6800miles on it - didn't look very dirty) was restricting enough that it caused the bike to run way to rich when the main fuel circuit was opened. Awesome. All of this work and heartache just for a measly air filter

I've been telling people for years that the paper filters are only used for one year max, whether they look dirty or not.  Wet paper won't hold its shape.  And, paper absorbs the humidity in the air, so it slowly collapses all the pores that is has and develops a "choking" effect.

Check out the Honda maintenance schedule.  6 months OR 3000 miles-clean, 12 months OR 6000 miles -replace.

Personally, I think that costs too much to replace yearly.  Much cheaper to use the UNI NU-4055 filter and just clean it periodically. IMO

I thought you told us earlier in the thread that you ran without the filter and it behaved the same way?  Maybe I was confused with another post thread?

Glad you got your bike fixed.  But, you may want to return all the carb's setting to stock position, (after trying to re-tune them to a clogged air filter).

Cheers,

[ACVWguy]

I just ordered the UNI-4055 based on your advice in another thread, TwoTired.

And yes I did say that it ran the same, but now that I think about it I probably just said that because it still ran like crap. I admit it and I'm over it

I set up the carbs to stock position in the first place, other than the air screw adjustment ( as close as I can with non-stock carbs) - I'm not one to tweak settings to compensate for a problem like so many....

Anyways, thanks to everyone who helped me out! And I apologize to all those who were following this thread hoping for some sort of climactic ending

[Spanner 1]

Wow ... the very first response 53 responses ago asked 'did you replace the filter' but was ignored/ deemed too easy a fix.... see ! ya never know  ( Sorry couldn't resist ! ).

[dave500]

how many times have carbs been removed over and over and it turns out to be something else,now go and ride it,,those new plug caps still wouldnt go astray.

[papp101]

I love happy endings.

[BudgetBiker]

Last post 2011?
Well here goes. Lets see if anyone still reads this.
I have the same issue with minor differences.
Did much of the same maintenance and rebuild.
I get to 60mph in 4th and go to 5th and it struggles to stay at 60mph.
I have pods because original had them and no full box replacement kit at a reasonable price.

Now I have 40 pilot and 110 main as per classic octane recommendation or what he uses with pods on his Youtube channel. Plugs are looking a bit black so im thinking too rich but im at 1 1/4 turns with same problem.

I suspect the timing is off. I discovered recently it has a Dyna S coil replacement for the points. Im going to spend a few hours today smoking ribs and working on Black Beauty and see if i can't make progress. 

This bike was severely neglected and i have replaced a lot of parts and it was dropped at some point. No major damage but it took out the speedo. So i have a cognito now. Hoping to get this fixed today.