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Engine basics => Engine set up tips => Topic started by: frank mccune on April 05, 2019, 06:22:44 PM
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Hello:
I have a very nice custom made needle valve and venturi that I can not adjust to get it the engine to run rich. I can turn the needle until it falls out but it will not go rich. It is stuck in a very fast two cycle and this engine is designed to 424. I have cleaned all parts of the nva and it appears to be very clean and is passing fuel and air. The only thing that I can think of is to either drill out the hole where the needle seats the flow of fuel or thin the needle itself.
The engine is a first flip starter but it will only run wide open.
Any suggestions or comments?
TIA,
Frank
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After sleeping on this problem for a night, I will bet that the venturi is too large! Will try a smaller one today. Will post results latter.
Frank
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You might be able to increase the draw a little by putting some fine screening over the venturi.
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https://stunthanger.com/smf/engine-set-up-tips/insert-into-an-fp-40-venturi/msg548951/#msg548951
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Frank,
Three options to try before pulling the whole thing apart. One, make a wood shim to slide into the back half of the venturi, this will reduce the choke size and give you an idea if the venturi is too large. Second is to try muffler pressure. You did not say what the engine is but it sounds like a more current design. Some of them with the big venturi's like higher rpm to effectively increase the pumping/suction and need pressure to run slower. One last thing would be to change the plug, sometimes a plug can just cause what you describe even in a Fox 35.
Best, DennisT
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Hello:
I have a very nice custom made needle valve and venturi that I can not adjust to get it the engine to run rich. I can turn the needle until it falls out but it will not go rich. It is stuck in a very fast two cycle and this engine is designed to 424. I have cleaned all parts of the nva and it appears to be very clean and is passing fuel and air. The only thing that I can think of is to either drill out the hole where the needle seats the flow of fuel or thin the needle itself.
The engine is a first flip starter but it will only run wide open.
Any suggestions or comments?
TIA,
Frank
If it is a custom made Needle assembly, it is maybe not made properly and that could be your problem, The other thing that is making it hard to help you is your not telling much information, you should post what engine this is, what size the venturi/restrictor is, what is the diameter of the spraybar etc... and any info on the custom needle
Randy
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Hi Randy:
Since our conversation this morning, I got the engines out to a test stand and was very pleased as to what I discovered! All the HP .40 engines started with one flip and the needle valves worked the way that they were designed. It had nothing to do with the tanks venturm or nva. After thinking about for a few minutes, I asked myself what was changed from yesterday to today? The only variable was the fuel. I was using fuel mixed last Summer and was 10% nitro, 11% synthetic oil, 10% castor oil and the remainder alcohol. The fuel that I mixed yesterday was no nitro, 20% synthetic oil and the remainder alcohol. I mixed this fuel to be run in my Gardner p&c as recommend by Mr. Gardner. I will mix other fuel for my other HP .40, ST etc. engines. This mix will be 5% nitro 22-22 oil and the remainder alcohol.
Perhaps the old fuel went "bad" over the Winter. How, I have no idea.
You were really correct re. the size of the holes in the venturm.
Thanks for all of the help,
Frank McCune
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The only variable was the fuel. I was using fuel mixed last Summer and was 10% nitro, 11% synthetic oil, 10% castor oil and the remainder alcohol. The fuel that I mixed yesterday was no nitro, 20% synthetic oil and the remainder alcohol. I mixed this fuel to be run in my Gardner p&c as recommend by Mr. Gardner. I will mix other fuel for my other HP .40, ST etc. engines. This mix will be 5% nitro 22-22 oil and the remainder alcohol.
Perhaps the old fuel went "bad" over the Winter. How, I have no idea.
Or, the thinner and less viscous all-synthetic fuel would flow enough to work, and the castor oil fuel would not. What was the temperature?
Brett
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60 Degrees F