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Discussion Starter · #1 ·
Got this as a project bike. I rebuilt the carbs, new fork oil seals and brakes. Top speed on a good day is about 65 mph. Build details:

Compression 165-170 psi in each of the two cylinders
stock sized 105 main jets but aftermarket ones
new plugs and new coils
new points; timing is right on
Original chain/sprocket ratios
15w-40 oil
New tires, stock size
new stock air filters
What else is there to make it faster? Redline is 10,500 and it will barely rev over 9000. I think if the rings were bad that it'd smoke and have bad compression. Some people are claiming 95 mph. I'd be happy to hit 75. Thanks for your advice.
 

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Did you verify that you are getting full timing advance over 3,000 RPM? If not check that, as the mechanical advance mechanism is known to get tired and a little sticky. Usually solved by disassembly and cleaning if the advance cam is in good shape.
 

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Check the voltage at the coils at idle and at 3000 rpm or higher. It should be within one volt of battery voltage.

Clean connections in the headlight bucket, clean kill switch contacts, check and clean key switch and connector to switch. Check ground wires/connections.

Timing set with a timing light? Makes a difference. I have always found issues with the mechanical advance mechanism and all have required cleaning and lube at the least.

Have the throttle cables been checked for fully opening, check for smooth operation of the throttle, I clean and polish the bore for smooth operation and full lift by the diaphragm.
 

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Discussion Starter · #6 ·
The electrical connections seems to be good but I can double check. I checked the timing with a strobe at idle and above 3000. It is right on. I replaced the throttle cables and both sides open all the way. It's possible that one side is doing more of the work and I'm not sure how to synchronize them. People seem to use vacuum gauges but if there's a discrepancy, I'm not sure how to adjust.
 

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are your brakes dragging?
did you install the wheels correctly (brake plate properly aligned)?
as stated above, ignition advancer functioning properly?
firing on both cylinders (both headers same temp)
cam timing correct (cam at either 12 o'clock or 6 o'clock when crank is exactly at LT)
clutch slipping?
 

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balance the carbs, my 450 was a dog until I properly balanced them.
 

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Discussion Starter · #9 ·
are your brakes dragging?
The wheels turn freely.
did you install the wheels correctly (brake plate properly aligned)?
Wheels are installed correctly.
as stated above, ignition advancer functioning properly?
Used the strobe and the marks are right on
firing on both cylinders (both headers same temp)
Both cylinders are firing but I suspect one might be weaker. I'm not sure how to synchronize the carbs.
cam timing correct (cam at either 12 o'clock or 6 o'clock when crank is exactly at LT)
I don't know about the cam but I doubt it's off since it hasn't been manipulated.
clutch slipping?
Clutch is not slipping.
I'll check the exhaust temperatures. Thanks for the feedback.
 

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Discussion Starter · #10 ·
Do you know how to balance the ones on the CB350? I've seen videos where they measure with a vacuum gauge but then I'm uncertain about how to make the adjustments.
 

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Loosen or remove both throttle cables at carbs.
If yours has vacuum ports, you connect a manometer to the left and right carb vacuum ports.
With the bike warm you adjust the idle screws until both carbs show the same on the manometer and the idle speed is correct.
Adjust throttle cables.
using the adjust at the handgrip, bring RPM's up to about 3000 and adjust throttle cables at the carbs until manometer shows carbs are even.

I kept this generic since I don't have info on a 350.

My 500T has vacuum ports, my 450K6 didn't. I thought long on hard after reading another member had drilled his heads and added vacuum ports. I finally did drill my head and add vacuum ports, after adjusting them it was like a completely different bike with a lot more power.

By the Honda FSM, with no vacuum ports, the 450 is balanced by putting your thumbs over the exhaust outlets and adjusting the carbs until the exhaust felt even. The most ridiculous thing I had ever read.
 

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the guitar wire method is extra work and not needed...it's better to use the same method but without the string; just do the same thing with the idle screw stop with the butterfly fully closed.

difference being that base idle will be a tad high using the guitar string and a tad low without.

problem with the string is; if you adjust idle screws with it too high then you may need to readjust throttle cables again afterwards to get proper 1mm slack at the hand grip.

the procedures are otherwise correct
 

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The way we did it when they were new was to back off both idle screws until the throttle plates are completely closed, then adjust the lower cables so both throttle shafts move at the same time when the throttle is opened. You can reach one hand in there, fingers touching both throttle shafts, and feel for movement when working the throttle with the other hand. With the cables adjusted, run both idle screws in evenly until it will idle. 95 mph isn't out of reason for a good running 350, check for fuel delivery issues(petcock flow, float level, main jet). Check the mufflers for mouse nests or other obstructions. Pull the tops off the carbs and check for pinholes in the diaphragms.
 
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