About to burn this bike to the ground

[jthomasbtm]

I built this 1976 cb750. Can't figure it out. Running keihin carbs, pod filters, straight pipes, dyna coils and electronic ignition. Fully rebuilt engine. The bike will start up and idle fine, but as soon as it's given throttle it cuts, misses and dies out. I've tried everything the Clymer says and can't figure it out. I need to get this thing on the road. Any advice is greatly appreciated.

https://youtu.be/xFr9U9nX6tE

There's a video of it being a shit bag. Tell me what you guys l think or what to try.

[jthomasbtm]

By the way I suspect it's a carb issue but I've tried everything I know. I'll pay someone in as much beer as you want if you can come make this run. Literally cases upon cases upon cases.

[Guest]

Sounds like it is idled really high, do you have the choke out or in?

[JuanCarlito]

I feel your pain! Maybe we can burn our bikes together?

[jthomasbtm]

Choke was out when it started then I pused it off.

[Freewheeler]

It sounds nice, there's a lot of power there - can't be a lot wrong.

Sounds like fuel starvation to me, i.e. kinked fuel line or maybe a blockage in the fuel cap breather.

What sort of condition is the fuel tap in, is there good fuel flow from it? is the bowl at the bottom of the tap fuel of rust?

Or have you tried all of the above already?

Nick

[gs650]

What size jets are you using? From what I've been reading and experiencing, its really hard to get them to run right with pod filters. Sounds like yours is running out of gas but with the stock jetting it will not run right with the pods. Velocity stacks are supposed to be much better than pods but I haven't tried them yet.

[deathmetaldan]

its for sure a fuel/air thing. Its always a fucking cunt, especially when you do pods and pipes at the same time and have no baseline of how far up you have to go.

[Freewheeler]

its for sure a fuel/air thing. Its always a fucking cunt, especially when you do pods and pipes at the same time and have no baseline of how far up you have to go.

Indeed. What baseline did you work against or was it running ok with the same setup before you rebuilt the bike?

It it was running ok before using the same setup then something has been misplaced during reassembly - as I say, kinked hose, sediment in the tank stirred up during reassembly, idle screw settings for instance.

If its a brand new setup then its a tuning issue and you would need to get some guidance on what pipes, filters and jets will work well together.

The other thought I had was that my old Honda 4 did used to take a while to warm up and would die if taken off the choke too quickly.

Just a few thoughts that might not be in your manual.

Nick

[jthomasbtm]

Steady fuel flow from the tank to the carbs. I pulled the plugs last night after this was posted and they were fouled completley black so I'm assuming too much fuel.

[jthomasbtm]

I can't remember exactly what size jets I'm running, but I'll check it out. I thought it was a jetting issue but don't know what size to run or a good place to get them from.

[jthomasbtm]

I had the motor running in the stock frame/setup for about a day and then pulled the motor so I don't really have a base to go off of. I know it's something with fuel and air delivery/mixture but not sure how to go about getting it set right. It'll fire right up but when I put it in gear and try to pull out it sputters out. Carbs are my worst nightmare on any bike.

[gs650]

There is lots of info on tuning for pods on the SOHC forum. Your bike has a different style of carbs than my bike but from what I found out 2 sizes bigger on the pilot jet and 3 sizes bigger on the main jet will get you close.

[mcclane]

You Must der the needles in the sliders higher; and check the high of the float gauge

[Freewheeler]

Steady fuel flow from the tank to the carbs. I pulled the plugs last night after this was posted and they were fouled completley black so I'm assuming too much fuel.

It's starting to sound like that isn't it?

That's a good point made about the float height as well - also worth checking the floats aren't ruptured or split and do actually float.

Also, it would be really helpful to make notes on jet sizes, number of turns on idle screws and such and how it ran with those settings - I always found it so much easier to refer back to notes that relying upon my memory.

Don't worry, we will get you there

Nick