Hot weather needle settings

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The basic changes for summer in hot and humid places like Huntsville AL are:
1. Prop down
2. Pipe out
3. Lean down

If you have a gauge like a Kestral you can look at the "water grains" when readings get above 100 performance goes south fast. I've been at Huntsville when the WGs reached 120.
Water grains is the amount of moisture in the air, IE Anything below 50 is dry, above 50 is wet and above 100 is really bad.
 
how much lean down, I know thats a big open question but on a WT-257 are we talking 1/8 in? 1/2 in? I cant get a good reading on my plug and my engines are down 1-2k rpm.
 
timothy johnson said:
Pipe adjustment should be 1/4 inch. Trial and error on the needle. WT-257 ??
There is much more that will come with experience.
You don't provide the boat, engine, fuel and location.
Click to expand...
the engines are 4-5 different cylinders heads swapped out to trial and error different porting theories. hulls are cats and hydros. location is 599ft above sea level. I set pipes by feel of where they make peak power in the throttle range for a given prop and cylinder heads exhaust port duration.

as it stands the engines are making peak RPM on my makeshift redneck dyno with 1-1/4 out. they are wanting MORE fuel in the heat for some reason to make peak rpm (~20k range). any more lean and they struggle to make it over 17.5k, even with lighter load prop it simply will not spin beyond that.

fuel is basic pump 10% ethanol with 8oz of super techniplate + 2 oz of benol.
 
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On my 257s, high speed needle is normally about 1 to 1 1/8" out
Went to the nationals in Georgia and the humidity was thick.
My high speed needle wound up at 7/8"
Didn't touch my low speed at 2"
Yes, also had to go down 1 prop size and 1/4" longer on my pipe length
 
Dave Gilles said:
the engines are 4-5 different cylinders heads swapped out to trial and error different porting theories. hulls are cats and hydros. location is 599ft above sea level. I set pipes by feel of where they make peak power in the throttle range for a given prop and cylinder heads exhaust port duration.

as it stands the engines are making peak RPM on my makeshift redneck dyno with 1-1/4 out. they are wanting MORE fuel in the heat for some reason to make peak rpm (~20k range). any more lean and they struggle to make it over 17.5k, even with lighter load prop it simply will not spin beyond that.

fuel is basic pump 10% ethanol with 8oz of super techniplate + 2 oz of benol.
Click to expand...
On your dyno, what are you using for load?....brake dyno?....inertial dyno?.....the real time dynamic on the water is entirely different (loading). And moving air around carb.

Tim's advice, above, is how we approach air density, temp, and jetting regarding loading and engine performance.

By the way, Super Techniplate has 20%-25% BeNOL blended in.
 
Timbo Whalen said:
On your dyno, what are you using for load?....brake dyno?....inertial dyno?.....the real time dynamic on the water is entirely different (loading). And moving air around carb.

Tim's advice, above, is how we approach air density, temp, and jetting regarding loading and engine performance.

By the way, Super Techniplate has 20%-25% BeNOL blended in.
Click to expand...
with very thick bearing grease on a super long shaft. Its really a jig with a tach its not a dyno. I had 2 extra ounces of castor because A. Ive burned cylinders before and not exactly sure what caused it, and B Im testing leaner conditions at high RPM and high heat.
 
Dave Gilles said:
with very thick bearing grease on a super long shaft. Its really a jig with a tach its not a dyno. I had 2 extra ounces of castor because A. Ive burned cylinders before and not exactly sure what caused it, and B Im testing leaner conditions at high RPM and high heat.
Click to expand...
Well, you need data ....EGT is good start. Sounds like your 'burning cylinders' due to lean fuel/air ratio, not a lubrication issue.
R/C marine engines need to be setup and tuned on the water....that's the load, and if jetting is too lean under load, well, the engine burns down. Prop dia/pitch, strut depth affects load, too.
Generally, poorer air quality dictates less jet, longer pipe....good air quality wants shorter pipe, more jet, with all other things being equal.
Between 13.0:1 and 14.7:1 is near the ideal stoichiometric fuel/air ratio for a 2 stroke running on gasoline.
20-25:1 fuel/oil ratio.
 
Timbo Whalen said:
Well, you need data ....EGT is good start. Sounds like your 'burning cylinders' due to lean fuel/air ratio, not a lubrication issue.
R/C marine engines need to be setup and tuned on the water....that's the load, and if jetting is too lean under load, well, the engine burns down. Prop dia/pitch, strut depth affects load, too.
Generally, poorer air quality dictates less jet, longer pipe....good air quality wants shorter pipe, more jet, with all other things being equal.
Between 13.0:1 and 14.7:1 is near the ideal stoichiometric fuel/air ratio for a 2 stroke running on gasoline.
20-25:1 fuel/oil ratio.
Click to expand...
I burned a cylinder last fall with 1-1/8 out and 55 degree air temps. Is that too lean? Im pretty sure it was the oil amount and type cause Ive never had a problem since switching to a high castor mix. it was on like 25:1 with yamalube. I thought it could have also been over-cooling at the header block causing the cylinder to go out of round, all scoring is on the exhaust side. water temps were pretty darn cold that day maybe late november.
 
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Dave Gilles said:
I burned a cylinder last fall with 1-1/8 out and 55 degree air temps. Is that too lean? Im pretty sure it was the oil amount and type cause Ive never had a problem since switching to a high castor mix. it was on like 25:1 with yamalube. I thought it could have also been over-cooling at the header block causing the cylinder to go out of round, all scoring is on the exhaust side. water temps were pretty darn cold that day maybe late november.
Click to expand...
Yeah, wish I could have a definitive answer for you, but I don't....maybe come up with a means to get exh gas temp reading....that would tell you a lot.

I don't know if Futaba has a probe and function for that, or not. I do know Eagle Tree used to offer the ability to monitor a few functions.

Terry Keeley, I believe, did a dyno build and threaded it here and had the ability to monitor those different functions. It's all relative. He and Lohring Miller both are quite adept at these things, and I think Lohring has a lot of experience with the gas engines in our hobby.

Give this thread a study, also search for Lohring's content here. I believe he's even written some articles for NAMBA's International Propwash paper's technical section.

https://www.intlwaters.com/threads/run-in-stand-dyno-build.78248/

Send Lohring Miller a PM here and he can probably send you to the appropriate NAMBA Propwash technical article, or offer some guidance for you.

Check this article out by Lohring, too-

https://www.modelgasboats.com/magazine/tech-articles-mainmenu-608/547-gasoline

Hope all this helps!
 
timothy johnson said:
The basic changes for summer in hot and humid places like Huntsville AL are:
1. Prop down
2. Pipe out
3. Lean down

If you have a gauge like a Kestral you can look at the "water grains" when readings get above 100 performance goes south fast. I've been at Huntsville when the WGs reached 120.
Water grains is the amount of moisture in the air, IE Anything below 50 is dry, above 50 is wet and above 100 is really bad.
Click to expand...
Huntsville is the only place I have ever run a boat (here in Aus or the 3 or 4 I have done in the USA) where it performed TOTALLY different to at any other lake I have ever run or raced at. This was in May, so it was pretty hot and sticky...but I have run in hot and sticky before, that lake was different for me that's for sure!

sorry, bit off topic :)
 
A cable with grease will not be consistant or repeatable. You would be better off turning airplane props. With Lohrings help, I built an inertia dyno and have been working on some ideas. Mostly pipes. I settled on porting some time ago. I prefer to work on set up rather than chasing the last bit of hp.
Weather plays a big role in performance. Download the Airlab app. Keep notes of how your engine performs in different weather conditions. Every set up will react a bit differently. Gas is very forgiving on mixture most of the time. Severe weather swings can give you fits though. I mainly change prop load to account for changes during the day.
 

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