carburetor help on a fd620

[Bazooo guy]

Hopefully the Denver guys get them from NY.

Holy crap I thought Nick was in Buffalo New York (elevation less than 1000 ft)
Denver is much higher and could be 5000 +. Sorry bout that

[JohnF]

Maybe you can disconnect the governor linkage temporarily and see if the surging goes away.

There really isn't a super easy way to do that.

Holy crap I thought Nick was in Buffalo New York (elevation less than 1000 ft)
Denver is much higher and could be 5000 +. Sorry bout that

LOL - yeah, he is in NY (as far as I know). I shopped kawasaki parts here in my neck of the woods - Denver. Didn't matter who - it takes 2 weeks. If the Denver guys get parts from NY then the parts are already closer for Nick. I would just buy these from an Argo dealer.

[jessieherrera]

Hello,
If it ran fine until the problem then you most likely don't need to do anything more than make sure the carburetor is thoroughly clean and that everything is tightened properly. The problem most likely is that the needle and seat are not closing fully, your float may not be adjusted correctly or faulty. Put the float in a liquid filled bucket (preferablly a thin liquid such as gas or solvent) and see if it floats. Check for heavyness due to entering liquid. The only other thing I can think of is to make sure that oil from the crankcase is getting into the intake by way of a breather or PCV valve. If you have a PCV valve it may be faulty. Over filling the oil or excessive pressure in the crankcase can force oil into you intake system. If you have a seperate oil source such as an oil tank that supplies the motor apart from the trans you may have a poor seal at the crank. This causes the oil from the engine to be sucked into the crankcase and be forced into the intake. This will manifest itself in the engine oil tank being low often without any visible signs of leakage.
Good luck.

[jessieherrera]

Hello,
If you didn't have this problem before with the same setup it is probably not a mixture issue assuming that you cleaned it thoroughly and tightened everything up like the jets. It may be a float or needle and seat problem.
Check for the proper float adjustment and make sure that it's not leaking. Place the float into a bucket or container of thin liquid sauch as gas or solvent. See if it floats or gains any weight due to leakage.
Check your needle and seat for any dirt or residue that can cause it to stay open. You may also have an excessive amount of pressure coming from your fuel pump if so equipped. If it is gas then you may want to put in a generic pressure regulator between your fuel pump and carb.
Another thing to consider is that it may be oil that is causing the problem. Check to see if it is getting oil into the intake from a breather or PCV valve. If you have a PCV valve it may be faulty.
If not and you suspect excessive pressure from the crankcase it may be forcing oil up from the trans. If you have a seperate oil tank for the engine which is apart from the trans check to see if you are losing oil excessively from your engine tank. A bad or poor seal at the crank will draw oil from your tank into the crankcase and force it up into your intake.
Good luck.

[JohnF]

SixGunNick,

There are two seals on the butterfly valve axles. If your mechanic didn't remove these before the dunk tank then they are probably ruined. If the seal on the throttle butterfly (and less so the one on the choke) leaks significantly then it would exacerbate a lean condition and contribute to surging. They are small and since there isn't a carburetor kit for this carburetor (to have replacements for all the things you screw up in the dunk tank), unless you know they are there it is easy to ruin them.

A float issue keeps popping up. jessieherrea does bring up the point that our fuel delivery test does ignore the float valve assembly.
The fuel level in the bowl does not affect the fuel flow in the main (or pilot) circuit (to any appreciable degree) in this carburetor*. It does, like I hinted at earlier, affect the accelerator pump function - but we aren't there yet.
(*Okay, as long as there is always fuel in the bowl and the fuel delivery can maintain a static level.)
Failures that then can affect us are:
1. Valve never closes - fuel will spill out the vent holes in the top; I imagine you would have noticed this.
2. Valve never opens - engine starves and dies - no surge - dies - and you would be complaining that it doesn't start.
3. Valve is constricted (contaminated/dirty) - fuel delivery cannot meet fuel demand. What you would notice is that it starts great, you go WOT and it runs great... for a few seconds, maybe 30. Then it either dies (really slow valve) or you get a sporadic surge that doesn't get very near high idle RPM.
4. Something is sticky inside so that the valve stays closed until just before starvation and then the valve stays open until the bowl is full again (cycle) - this would be a very very long surge cycle; you wouldn't even call it a surge. To get a feel for how long it takes to get to the near starvation point with a full bowl: unplug the fuel pump, start the engine, go WOT, and wait. It will be seconds.

Where I think we are and why I think we are on this track:
1. We have adjusted the pilot mixture.
2. We have adjusted the pilot RPM.
3. We are adjusting the main mixture. (Kawasaki calls this high idle)
4. We may adjust the high idle RPM. (this may include governor tweeking)
5. We may adjust the accelerator pump function.

Why mixture?:
1. the surge is short cycle (maybe 1 or 2 second???)
2. the surge is "higher" in the RPM band.
3. we eliminated fuel delivery problem. (Well, mostly, see above.)
4. we know it is sporting a too lean jet for the elevation per the jetting chart.
5. It runs better when conditions provide a higher density altitude and in fact the problem didn't present until a lower density altitude.
[in edit] 6. And this is exactly how a properly running fd620d would balance this condition. (I could explain the dynamics...)

I am assuming:
1. carb is clean. (this should be everyones first line if attack for all carb issues and SixGunNick believes it to be true.)
2. given that I believe the mixture is lean, the surging means that the governor is working properly.
3. that I understood the description of the condition through text in a forum from a person I do not know from half way across a continent.
4. properly running engine.
5. a properly operating carburetor. (all seals are doing there job and there are no "extra-design" holes as was found already. If air leaks between the pilot circuit and the main circuit it will run lean - for example.)

Anyway, check those two seals. I bought new ones and replaced them and just now considered what would happen if someone didn't know.

Oh shoot! I meant to tell you to google "fd620 92093" and that would lead you to the parts blowup of that carb. 92093 (and 92093A) is the part identification for the seal.

[Bazooo guy]

I thought we were at replacing the missing spring and link rod that looked like a coat hanger.
And what happened to the fuel pump test?

Can we hold the governor shaft or disconnect it and see if it keeps surging?

[SixGunNick]

Hey guys believe it not I think it is fixed , I finally got to mess with it last night and it was the link next to the carb I had to bend it a couple different times and readjust the idle and air and there is no surging it must of had way too much play and I didn't know enough to to that had to be perfect.I am takin it out for a ride this weekend so hopefully it holds up.Thankyou everyone for helping me figure this out
Nick

[JohnF]

I thought we were at replacing the missing spring and link rod that looked like a coat hanger.
And what happened to the fuel pump test?

Can we hold the governor shaft or disconnect it and see if it keeps surging?

Yeah, you can do that but it is harder than you might think. That governor is very persistent. It would be easier if you disconnected the throttle link and manipulated that.

And it is extremely probable that the surge would stop because conditions to cause a surge sans governor are pretty rare involving coupling of the air/fuel inertia and combustion (rpm). (assuming everything else is working, like the ignition system - which, of course, may be where you were headed.)

... and it was the link next to the carb I had to bend it a couple different times and readjust the idle and air and there is no surging ...

Cool, but you don't get off that easy Now we have to figure out why.
You didn't happen to take a picture of the rod before and after?

Knowing the geometry of the control tabs I can't imagine rod shape causing anything except perhaps hanging up on something and I'll group that with "slop" which is coming up.

Slop would act like that old worn out steering on Grandpa's pickup truck. When you drive you feel like you are herding the truck down the road. In this case the governor would be hunting the RPM.

If we assume this and also assume that the slop isn't too much (because too much would be obviously annoying I think) then we ought to see if we can distinguish this kind of surge.

Assume for all cases that the twist grip is held at full throttle.

Fuel delivery surge would be caused by fuel supply not meeting demand. I would expect this surge to happen at lower RPM - but the closer the fuel delivery gets to being able to meet the demand the longer the surge duration and higher the RPM. Also sporadic as this would likely not be dynamically stable. (Actually, it would probably sound like a surge in a surge as there are two functions competing here.)

Mixture surge due lean condition would be dynamically stable - almost a perfectly rhythmic smooth sound that crosses the RPM half way mark. Can't exactly predict the pulse width - probably like 2 to 4 seconds.

Slop - I would expect this one to be fairly high frequency and definitely in the high RPM range. Probably a stable surge if the slop has no stickiness to it.

Remember, we are helping everyone who reads this thread with a surge problem for as long as this thread lives.

So Nick, did any of that sound like your surge?

Did you replace the spring too? That could help in this situation - it would act to bias the throttle decision (always pull the truck left...) which doesn't remove the slop but does remove the hunting. , maybe that's the real reason for that spring. It's still annoying when removing the carburetor.

And I'll be honest here, You said it didn't have power. I have a hard time imagining a condition where slop would have a dramatic effect on power unless the slop was so much that you could actually see the governor arm move while the throttle plate did not.

Was it <warmer/lower barometric pressure/higher humidity/combination> yesterday?

When we know that works we can talk about the next two adjustments. (You'll need a tachometer for setting the high idle.)

[Bazooo guy]

I would take it for a drive and see how it runs.
When you get back check the plugs and see if they look fouled.

If the rod was bent and the wrong length the revs would be limited to a lower rpm and the governor would fight with any throttle advance.

[JohnF]

:
If the rod was bent and the wrong length the revs would be limited to a lower rpm and the governor would fight with any throttle advance.

I'll have to think about this. I might even have to make me a short rod to see it. (down side to being a scientist )

The governors job is to pull against the throttle cable spring to limit RPM. It doesn't advance RPM.
I think a too short link rod would show as a reduced high idle RPM. Basically, RPM wouldn't get high enough for the governor to kick in.

[SixGunNick]

Not sure but I took it down the driveway a few times and back and it seems ok the surging came when I would throttle up at all so bad that I would have no power to turn at all because it would cut out so much I could barely turn (loss of power) and I couldn't really enjoy driving it at all now it seems to throttle up fine and I can also hold it at high rpm and it runs steady I can also turn with no hesitation
I will also replace the spring as soon as I can find one

[Bazooo guy]

In my eyes the governor link pushes back against the throttle when the revs go up and the spring pulls the throttle back to idle but I'm not looking at the carb and don't have one.
Remember the two stroke lawnboy mowers that would surge all the time with no throttle control.
Most of the problems were with the governor adjustment,link,or spring

[JohnF]

In my eyes the governor link pushes back against the throttle when the revs go up and the spring pulls the throttle back to idle but I'm not looking at the carb and don't have one.

This engine has a centrifugal governor that operates a shaft coming up out of the engine. Attached to this shaft is an arm - kinda long, maybe 8 inches - that has, on the other end, a direct link to the throttle valve in the carburetor. The throttle position is set at the point where the (governor spring pressure + governor shaft pressure) = (throttle spring pressure). In the low RPM range governor shaft pressure doesn't play. Pretty much all engine RPM governors work in this sort of proportional control configuration. Wonky springs that don't have a constant rate can wreak havoc with this balance. Engines with a really wide RPM range can be super sensitive to throttle position - enough to exacerbate every condition.

So, throttle spring pulls to open the throttle and the governor acts to close it. For an engine with a set RPM the throttle spring pressure is set and for these machines the throttle spring pressure is controlled by the twist grip.

[Bazooo guy]

So, throttle spring pulls to open the throttle

Did they set it up that way in case the spring fails? And if it gets weak or stretches the throttle would be sluggish or not open.
My throttle return spring pulls the throttle closed and the cable connects to a brake type lever on the right stick.

[JohnF]

Did they set it up that way in case the spring fails?

It's a spring between you and the throttle valve so that the governor has precedence over you. I have noticed that the governor spring is a stouter wire than the throttle spring. This could be for the purpose you mention. In fact it probably biases most every spring failure towards lesser RPM. Hey, neat! I purchased a tachometer and found that at WOT it ran at 3400RPM and the means to adjust this was already at the stop. So I had to embark on tweeking the governor arm on its shaft - an insanely sensitive adjustment - and it took me a couple hours to get it done. I probably should have just ordered new springs. It would have been, to my best estimate, a zillion times easier if it worked.

And if it gets weak or stretches the throttle would be sluggish or not open.

Yep. But let's say both the throttle and the governor spring are weak. Very weak, like short bits of rubber band. In this case I would expect surging, probably wild and dramatic, because the balance of spring pressure acts to attenuate (like a shock absorber) the governor arm. This would be a sort of extreme in the wonky spring scenario and the surging shape would be anyone's guess.

My throttle return spring pulls the throttle closed and the cable connects to a brake type lever on the right stick.

I forgot about the throttle return spring. On the conquest it has no part in throttle valve positioning. It's really just a part of the twist grip and cable - the driver input piece.
If the throttle return spring is a part of the valve positioning, then it adds to, and maybe even is, the governor spring in the function I gave above; assuming there is a governor.