How to ajust my rpm

[sum123]

Hi, Can someone please tell me step by step how to adjust my boats erratic rpm. The carbonator is a Rochester Quadra jet AQ 260 Volvo Penta. As soon as the boat starts the rpm keep jumping from 500 to 750rpm. The timing is adjusted new sparkplugs , new spark plug wires, new rotor and cover. And can someone tell me what the 2 setting screws are for at the bottom of the carb? Thanks

 

[poppasmurff]

Re: How to ajust my rpm

Those two screws have springs on them correct? If so they will be your mixture screws.

 

[tacconelli6]

Re: How to ajust my rpm

I believe those two screws are your low idle speed and high idle speed. They adjsut your air/fuel ratio at low and top speed. try turning them all the way in or seating them, (don't crank them down too tight). Turn them both out 2 1/2 turns and start the boat, from there you can adjust them back in until you have a nice idle. I did one at a time and just smoothed it out till I had a nice idle.
Hope this helps I just went thru all this and got it figured out. If not I'm sure some one will come out w/ something more correct.

 

[a70eliminator]

Re: How to ajust my rpm

The two screws are in fact the idle mixture adjustments, but they have nothing to do with the main fuel circuit, they are only effective as idle air fuel adjustment. The above idle primary fuel circuit is effected by the needle jets and engine vacuum, if your idle is hunting around chances are you have a vacuum leak somewhere, one way to fortify the assumption is to screw those two idle mixture screws all the way in till they they lightly seat, your engine should stall out completely, if it doesn't then start looking for vacuum leak, other than that maybe your advance plate is messed up just attach a dwell meter and watch to see if the dwell is hunting around. Hoe does it run mid to WOT? Do a compression test if all else fails, you could have a valve problem causing a cylinder to be down on power.