How to adjust throttle positioning?

[JonnyQuest]

Hi gang,
After replacing the carb, fuel pump, and installing a racor separator, the old Atomic 4 runs super well. The throttle however is not set properly for the new carb. Here is how it currently responds:

-full throttle is at 12 o'clock position (this used to reduce rpms and stall out the engine before my carb etc replacement).
-Idle is somewhere around 2 o'clock--very short range of normal operation, I expect. Anything past 2 o'clock will reduce rpms below 700 and stall out the engine.

How should the throttle range normally be for me?

Also, I can't find any info on how to adjust the throttle positioning, can ya'll shed light here for me?

Thanks for the suggestions,

Jonny Quest

 

[Bill Roosa]

Carb basics

There should be 80-85 degrees of angle that the throttle turns through from WOT to idle. At WOT the butterfly valve should be parallel with the air flow, at idle the butterfly should be almost shut. You need to get this right first or the rest of the adjustments will just be a waste of time. Take the throttle cable off and see if the butterfly will operate through something like 90 degrees.

The 20 degrees has me worried that there is either some choke linkage that is getting in the way or something is jammed.

 

[JonnyQuest]

Thanks Bill, I'll check on that hopefully tomorrow. I seem to recall that when I was installing the brand new carb that the butterfly valve actuated fully--I'll make sure though. At least I'll have that straight before fiddling with the cable linkage.

--of course I don't know yet how to adjust the cable linkage ...is that difficult?

 

[Bill Roosa]

Throttle cable link adjusting

No, it is quite easy. Depends on the actual set up but I've seen with just one screw clamping the cable. Not very seaworthy but it is what it is
Perhaps now is the time to get a picture?

 

[JonnyQuest]

Re: Throttle cable link adjusting

I'll snap some shots today if I make it to the boat to confirm the carb butterfly valve action.

Thanks Bill.

 

[kenn]

Like Bill says, the throttle needs to be set and checked by itself (disconnected from the throttle cable) first. In addition to checking the range of motion of the throttle arm, the idle needs to be set to the desired rpm, so that the engine canot be stalled out by too low a throttle position.

Once the above is done, that's the time to connect the throttle linkage. I have a hard time imagining how the linkage + cable is putting all 80 degrees of throttle motion into just 20 or 25 degrees of remote lever arc. It could be that the cable was attached to a point too close to the pivot of the carb throttle arm...?

On most throttle levers and cables I've seen, the coarse throttle lever positioning is done by how the cable is installed, and if necessary by repositioning the linkage arm at the remote lever. Fine adjustment is done by turning the cable ends back and forth on the threaded rod ends of the cable.