Twin idles smooth for minutes, but when revved to 6000RPM drops pops and dies.

1976 KZ750 Twin

Worked fine for 7000 miles. The other day, I tried to pull out of an intersection with the tach going to a normal 6000 for me, but this time when revs dropped, the bike started running on one cylinder. I rode all the way home with 375cc's worth of power. The next day, I put a new plug in and it ran well, but then right as I revved it a couple times, it coughed and stumbled then finally died. It also seems to switch cylinders, not dependent on which plug wire is on the plug.

If idle circuit was dirty, then why would the bike idle great until revved above 5500RPM? Could it be the coil? It has taken the bike 7000miles.

If there were vacuum leaks, debris in carbs, wrong float level, wrong fuel level, then why did the problem appear out of nowhere?

This bike ran great for 7000 miles before it made a pop noise on an acceleration, and has never been the same since then....

Thanks for any advice given.

Charles

Looks like a fuel starvation Problem like a vaccum in the fuel tank (clooged cap vent). Try to test drive with the tank cap open.

Do you have a fuel filter ? In line or in the tank ?
Is your fuel contaminated ?
Sounds like a fuel starvation problem as already mentioned
Dave

Could also be a bad electrical connection somewhere. The high revs might vibrate a switch contact loose then it makes and breaks while idling.

Alright, I will check each of the things mentioned!

It has the little in tank filter nubs. I figured running alternate filters might make fuel flow too slow.

Before it dies, there is popping and crackling out the exhaust.

I would think the fuel would "catch back up " in the bowls if I kept it idling but it never does.

6,000 rpm to pull away from an intersection?

One strange thing...

When I open the enrichener just a little, the bike revs through the whole range fine and does not stumble. So lets say it was lean?

But it will idle smooth and not miss a beat, and headers dont get really hot. As soon as I rev it, it changes personality.

6000RPMs.... I like to live in the fast lane like the Eagles...

If you have been pulling away from a dead stop at 6,000 rpm I'm not really surprised the bike is now running poorly. Why would you want to do that? Ed

I go up to 6000 in first gear! Not start at 6000 in first gear...hahahaha....my tire tread would be long gone if I was doing that.

I am sorry but organizing my thoughts for others to understand is tough for me so I can see how that would be misinterpreted.

The bike works again!

Thank you all for your answers. It helped me get past the initial frustration of a non working bike.

The pilot had a tiny piece of leaf in it and on top of that, the route from bowl to main to pilot also had some dirt build up.

Should I get in line fuel filters? Will they impede the flow of fuel?

An inline filter is a good idea. As long as you buy one designed for gravity-feed motorcycle application, it will flow just fine. I recommend the Golan micro-mini. It is more expensive that the plastic disposable ones, but it is unaffected by ethanol and filters much finer debris. Yes, every year or two it is a good idea to open it up and clean the filter screen, but that requires very little more effort than replacing the cheaper ones every year.
Again, be sure whatever you use, it is designed foe a system with no fuel pump. Filters designed for pressurized systems typically have a paper element, which will saturate with fuel and stop flowing if there is no pump. Yes, I have that t-shirt.

Edit: I see that it is called the Super Mini at Denis Kirk.
www.denniskirk.com/snowmobile/golan-prod...ontent=Golan+Filters

Here is a direct link to Golan

golanproducts.com/product-category/filters/super-mini-filters/

Awesome! Thanks again for all the help, I really appreciate it. I will get those filters.