Slight sputtering

At 60mph, 4k rpm. Throttle set to maintain 60. It runs fine just below, and above that particular throttle setting. I have to keep giving just a little more throttle to make it run smooth, but then that makes it gain speed.

If I let off just a hair, it runs smooth but it starts losing speed. I have checked valves, cleaned the lower ends of the carbs, diaphragms are all good. Is this an emulsion tube issue?


Any ideas?

Thanks guys,

Rich

 

I think it may be an emulsion tube cloggage. My 750 was put on a Dyno and theres a huge dip in power at the mid range, was put down to clogged emulsion tubes and gives exactly the same horrid, seems like it's only running on 3 cylinders running at about them speeds.

 

Ok, thanks bro.

Any other thoughts?

 

You ought to be aable to look at the Plugs and determine whats happening.

If you get lean in Mid-range ... Its because the Emulsion Tubes are clogged and you are not drawing-up enough Fuel ...

OR, ... And this is a New one I encountered just this week while tuning the 900.

Your inline Fuel Filter needs to be installed in a Vertical Configuration to allow Fuek to "Fall" into it without causing the Bubble in the Fuel Filter to impair the Fuel Flow.

That, plus you might need to have the Pilot Mixture Screws bumped Out, like as much as the width of a DIME!
Almost not moving it at all. But nudged a bit toward Rich.

Listen for the "Pop-pop, pop-pop-poppidy-pop" in the exhaust note at
3,000 rpm.
Tweak the Pilot Screws to make the "Poppidy's" smooth-out.

 

Oh, I have my inline filter vertical... Interesting thought...
All four plugs have WHITE ceramic insulators....

My mixture screws are at about 1 1/2 to 1 3/4 turns out. Is that too lean for 4700 ft.