Topic: 1975 CB750F Idle Problems

[DuckFan]

Hey all,

I rebuilt the carbs on my bike (Tons of corrosion in the float bowls!) using an ultrasonic cleaner with good results. I replaced all of the jets, gaskets, ect. When I put them on the bike, it ran ok but still felt a little off. I decided to change the oil as the last bit of maintenance and the oil REEKED of gas. It was almost as thin as water. I filled it with new SAE 30 oil and fired it up. It ran well for about a minute and now will barely hold idle.

Any ideas?

[Jerry Rxman Griffin aka MuthaF'er]

1) turn off the petcock when not riding
2) check your float levels and ability to move properly
3) check your float valve to be sure it shuts off the flow
4) then worry about the idle

[DuckFan]

Thanks for your reply!
1) Haven't done any riding on it yet, but it's always off when not in use
2) Floats moved properly and were within the normal range for height
3) The float valves were replaced, but I am unsure how to check that they actually shut off flow
4) This is where I'm stuck. My guess at the moment is that the difference in oil viscosity altered how easily the pistons move and now I need a higher idle to compensate for the increased work? But I feel like "Just turn up the idle" doesn't solve the problem, it only masks it.

As always, any help if much appreciated!

[DuckFan]

Update:
The bike starts and runs well, but only for ~15sec before the RPM's drop and it dies unless I keep on the throttle. My plan was to check my spark plugs next and see if they elude to anything. Anyone have any ideas?

[DuckFan]

Another Update:

So I got the bike to idle well at 1700 RPM, and then realized my choke was engaged. When I disengaged the choke, the idle shot up toward 6000 RPM until I shut it off. I turned down the idle screw to 1700 RPM where it held for a few seconds before dying. Engaging the choke caused the idle to increase to 3000 RPM as expected. I leaned out the air screw until it would hold idle but now it has almost no response when I open up the throttle. I checked the spark plugs and they are covered in carbon so nothing is making sense right now.

Seriously, does anyone have any ideas?

[DuckFan]

Well you've all been so helpful thus far but what the hell, another update:
I replaced the spark plugs which were black and sooty with new NGK D8EA's. As a result,  my idle got worse! I believe it's running rich because any throttle after starting almost kills it. But at the same time, it needs throttle to run beyond the initial start. I'm stumped.