Cyclical "surging" on argo conquest kawisaki fd620d

[JRNICo]

Hey Guys, new here to the forums, found you from a google search. Ive got a argo conquest that sat for a while and gummed up the carb. I took the carb apart and cleaned it out, drained the tank, fresh gas, basically did a nice tune up. I got it running OK, but it has a nasty cyclical rpm surge. I took a video, maybe you could pinpoint it by just seeing the duration of the surge. Any help would be much appreciated.

[JohnF]

Howdy

Did you already find the other fd620 thread? Lot's of stuff there.

That's pretty sporadic. Were you holding the twist grip WOT? Is the choke "on/closed" or "off/open"?

In the other thread I describe how to set the low idle mixture/RPM. Do that.

My initial gut feeling is that one or all of the main fuel ports (tiny little holes on the back wall inside the carb above the throttle vale when closed) or the main circuit air jet is plugged. To me, it sounds like the main circuit isn't operating.

Clues for the above would be: When we hear the increase in RPM it is happening when the throttle valve is opening and you see a bit of fuel come out the tube that sticks into the middle if the carb. If the RPM increase is happening not because of the fuel dribble but because the air catches up (throttle will be open a bit after the dribble) then we are on the other side and the engine is trying to run too rich - this is a kinda rare type of surge because most things conspire to kill a rich engine.

Could also be a sticky anti-afterfire solenoid. (the dang thing)
Or a main jet that is severely restricted.

If it were me, I would take it apart and clean it again using a can of cleaner with the red tube and pushing everything backwards from those ports. There are ways to check the solenoid but the easiest to me is to take the top off of the carburetor and watch it - key on/key off. Then put it back together, set the low idle values, make another video and post it.

While you have it apart, check that the float is set right.

[JRNICo]

John,

Thanks for the reply with the great input. I will take the carb back apart and do a more thorough job of cleaning all those ports. In the video I probably had it about 1/4 to 1/3 throttle.

[JohnF]

... In the video I probably had it about 1/4 to 1/3 throttle.

Ah, it's trying to transition to the high idle (main) circuit and there isn't one there to catch it.

When you have the carb apart and you look down into the, uh, vertical milled tubes that feed those ports, there is a small journal that connects those vertical tubes way down at the bottom. You probably can't see it. If that's plugged it dang tough to know it. I was able to use a small diameter piece of copper wire (one strand of 22g phone wire) with a 90 degree bend in it to feel it. I could push it through the journal and see it on the other side. I would check that.

Check the solenoid. (this could be a wire connection problem too!)

[Bazooo guy]

Did you replace your fuel filter?