Correct oil to gas ratio?

I've been having problems with my new engine sagging at mid throttle,and stalling allot. It seems to run well the first 2 minutes,then it starts to have problems running. I mix the fuel at a ratio of 32:1 as per the boat manual instructions. On another forum I've read that a correct mixture of oil to gas would be 16:1 (8oz. of oil per gallon)Could I be running my mixture too lean,and causing these problems? I'm new to gas engines,and just figured that the manual was correct. RR

If your running a stock engine? .... IMO 32:1 is fine so long as you keep needles on carb set right and not running lean.

If boat does a lap or two before is sags off, I would think you are too lean on carb setting.

* First off richen the HIGH needle @ 1/8 turn CCW at a time until engine starts too blubber or you get a speed loss. If a richer setting cures the sagging power, your good too go.

If when you are running at slower speeds on water and you suddenly open the throttle ... If engine take a big gasp and hesitates before taking off? low needle needs to be opened up slightly as well. If engine sputters and sounds like its choking, it is already too rich.

:woohoo: LOW needle is closest to engine, HIGH needle near intake bell.

*** I would for sake of general safety run a richer gas/oil mix at @ 16:1 or 20:1
Thats 7-8 ounces oil per gallon.

Thanks,Scott! I'll mix up some fuel using 8 ounces of oil per gallon. The motyor is stock,but seems (to me) to run a little hotter than it should. Ron

Many years ago Mike Hoffmeister did some dyno tests and found that a higher oil content improved power, probably because it improved the piston seal. We confirmed this on several engines. Even 10:1 may still help. The difference isn't much, but it's measurable.

Lohring Miller

I'd love to see this same test with data for 32:1 AND 16:1 for comparison.

Several years ago a manufacturer of large (100 cc+) 2-stroke engines for airplanes did a similar comparison. He used 50:1 (recommended by oil vendor) and also 25:1 ratios. He found that the big air cooled engines ran hotter with more oil and produced less power. But these engines only turn ~7,000 rpm and do not see the loads of a boat engine

But at some point there must be a power loss since oil takes the place of fuel, and the more oil, the less fuel there is to burn to produce power. I wonder how high the oil must be before power starts to drop off??

I've lost the data for Zenoah oil tests when we changed computers on our dyno. With the higher oil mixtures we just richen the needle slightly. In small engines, factors like piston seal and ring friction overshadow many other factors. Quickdraw was able to improve power during the development of our SAW engines by changing the hone pattern on the cylinder.

Lohring Miller

Thanks for the great info on this!

I Was running 7-8:1 in my J&G 25.6. Now I was told to run 10:1 and have run a couple of gallons through it. There seems to me that there is a tone difference in the sound of the motor??? I am also getting a lot of oil out the end of the muffler...is that oil pluging up the muffler??

Piratefish

Piratefish wrote:

Thanks for the great info on this!

I Was running 7-8:1 in my J&G 25.6. Now I was told to run 10:1 and have run a couple of gallons through it. There seems to me that there is a tone difference in the sound of the motor??? I am also getting a lot of oil out the end of the muffler...is that oil pluging up the muffler??

Piratefish

Nope, just passing threw :blink:

I think I may be having the same problem. I had my first run today with the new boat. It seemed to run just fine for 2-5 minutes, then it seemed to loose throttle response. Eventually it would sit and idle fine but would bog down and die when hitting the throttle. The carb appears to be getting fuel. Wasn't sure if the carb was dirty or carb seetings need to be adjusted. After reading the post, maybe it's the gas mixture. I mix it at 32:1 as well. Engine is the Zenoah26.

illiniboater wrote:

I think I may be having the same problem. I had my first run today with the new boat. It seemed to run just fine for 2-5 minutes, then it seemed to loose throttle response. Eventually it would sit and idle fine but would bog down and die when hitting the throttle. The carb appears to be getting fuel. Wasn't sure if the carb was dirty or carb seetings need to be adjusted. After reading the post, maybe it's the gas mixture. I mix it at 32:1 as well. Engine is the Zenoah26.

Richen up the LOW a tad, same with the HIGH.

* As engine heats up is does require a tad more fuel.

You could also have air bubbles getting into fuel line and into the carb, that REALLY mess's up how the carb works !!