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Needle valve settings

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  • Needle valve settings

    Model cars have two needle valves, one for high speed and one for low. Thats because they have to be able to engage the brake and stop and also start the race from a standing stop. So they need more control over their engines. Model boats (not all) have just one needle valve to contend with. Thats because most model boaters are in competition and race each other. They dont give a flying flip about going anything other that wide open. For them its the thrill of victory and the agony of defeat. They are therefore the ones that run 65% nitro and are always looking for the perfect needle valve setting, which is fleeting at best.For the rest of us who just go out on the weekend and just tool around the lake we are not so worried about it. With changes in atmospheric pressure , oxygen content, and variations in fuel chemistry from ounce to ounce, its one of those things that Dave Merriman would classify as a fools errand. And the smaller the displacment of the engine the worse the problem is. For the most user friendly setup stick with 20 to 25% nitro. More later.
    Last edited by greenman407; 04-30-2010, 01:50 PM.

  • #2
    When buying fuel stay with the low nitro mix. Also stay away from the race formula. In it they cut back on the oil. They sacrifice engine protection for speed. As far as needle valve settings go, start with the factory recommended settings and go from there. That setting is going to be on the rich side. Thats good because you want the engine set rich to begin with in order to break a new engine in anyway. When you start the engine up before putting it in the water the engine is going to be running rich, that is a given, because a marine engine with no load on it is going to run rich. When you throw it in the water and the load is applied to the prop , now the engine will instantly lean out by virtue of the applied load. After you have run a couple of tanks of fuel through it you can slowly start to lean it out. Take note of the sounds that the engine makes and the way it behaves. Many people make the mistake of trying to set the needle valve on land. They rev up the engine and if it doesnt clean out and rev quickly they start leaning. By the time it hits the water its now way too lean and it runs poorly and before too long the piston and sleeve are toast. Get it in the water first and listen. A rich engine is going to miss and have no power and generally act lazy. In contrast to that a lean engine(not too lean)will scat like a scalded dog for a half a lap and then start to slow. Get it out of the water and turn the needle out(counterclockwise)an 1/8th of a turn and try it again. The good thing is that once youve got it close, everytime you go out it will still be close and you can make additional adjustments then.
    Last edited by greenman407; 04-30-2010, 01:39 PM.


    • #3
      All of the above info is true and correct unless you are starting out with too big a propeller. It is better to run a propeller thats a size too small than one thats too big. If your prop is too big then no matter what you do the engine will not respond because it is out of its power band. Also your fuel must be fresh. If youve left the cap off of it or store it in a fuel bottle without a completely sealing cap its probably no good. Try to store it in a cool, dark , dry place. Any fuel left over after a year should be discarded as the alchohol slowly evaperates and the fuel will lose its punch. Patience is needed when setting up a boat and the needle valve is no different. Take your time. Your efforts will be rewarded if you do.


      • #4
        By observing the glow plug element after each run you can also get a clue as to how your needle is set. If the element is pushed up inside the opening then its probably running too rich. If its mishappen and distorted and it looks like someone has grabbed it with a pair of needle nose pliers and tried to pull it out then its probably running too lean. A perfectly set needle setting will appear as a brand new plug, just a little duller in shine. I have seen plugs that look perfect and you test them before you put them in and you cant get that engine to fire to save your life. Change the plug and it will instantly start. So dont be afraid to change the plug if you start having trouble. For this reason you should keep some extra on hand.