Topic: Need helping with starting problem

[Lordzacharious]

I had a 78 CB750K sorta fall into my possession not too long ago. Currently Im facing the same aggravating issue and I cant seem to sort it out.

I cant get it to start and run. The odd thing is really when I try to start it, it wont even attempt to do so with the idle screw contacting the linkage...

Ive cleaned the carbs thoroughly several times, replaced the float valves, and did an accelerator pump rebuild including verifying it was function by making sure it was pumping gas through the tubes in the carb bodies.

Ive set the float levels (dry) according to specs Ive seen on here.

I had synched them previously when I was able to get it running previously using one of those 4 vacuum guage tools

Replaced the condensers, and have adjusted point gaps. Valves were adjusted.

Bike is stock, 4-4 exhaust is on, airbox is on with new filter.

Gas tank is on.

Starts and runs shortly with starting fluid.

Not really sure what to do now? Maybe I need to verify fuel level by doing a wet test? Doing so on the bike doesnt show anything out of the ordinary, but its not level with the bike on the side stand and all.

Does have spark, new plugs showing what seems like a good blue spark as well.

Any help is greatly appreciated.

[robvangulik]

Running on starter fluid means all it lacks is fuel, so give it some.
You wrote the acc. pump is working, twist the throttle a couple of times and start it up!

[Lordzacharious]

Eh, I've tried that a number of times. I pulled the carbs off today and inspected the slides. It appears they are pretty out of synch. Adjusted the idle screw to let a paper clip under the #2 carb and the rest of the carbs are closed, not allowing the same paper clip to pass under any of the others. Now I'm wondering why I was able to adjust synch with a nanometer and have it read synched on that, but be so far off on the bench.

[Patrick]

I think you've found the problem yourself. Go back and bench synch the carbs so they all close at the same time. Then open them just a hair with your throttle screw and go from there.

If you synch a hot bike - particularly if you don't have a fan on the engine, that number 2 cylinder will drag all the rest up to the idle it wants. That works when the engine is hot. But once you turn it off all three other carbs closed down. So you are starting it on one.

Re-synch and try again. I think the results will be much better.

Patrick

[BobR]

  I doubt synch has anything to do with it. As mentioned it seems starved for gas . I'd verify the bowls are full with a clear tube check -if you haven't already. Bob

[Patrick]

I think more specifically, Bob, is a lack of explosions inside the cylinders. I am not sure we have enough information yet to determine if it's a lack of fuel or a lack of air. He said the slides on three carbs were closed. Unless he was twisting the throttle when he was trying to start it, those carbs were getting no air.

So Lord Z, were you holding the throttle open as you tried to start it?

[BobR]

I think more specifically, Bob, is a lack of explosions inside the cylinders. I am not sure we have enough information yet to determine if it's a lack of fuel or a lack of air. He said the slides on three carbs were closed. Unless he was twisting the throttle when he was trying to start it, those carbs were getting no air.

So Lord Z, were you holding the throttle open as you tried to start it?

  Well he said he couldn't get it to start and run- except with ether. I dont know about the 78 carbs but my K4 just isnt that finicky. Just sayin -as they say. Bob

[Patrick]

Yeah, whatever, Bob.

Lord Z, since you have the carbs on the bench anyway, I suggest you bench synch them before you re-install them. If it starts, it starts. If not, you needed to do it anyway.

Patrick