When the boat 'bogs-down' after throttling why does it pick-up if you run it lean for a period of time. Are we simply clearing excessive fuel which has
slowed the combustion down? Does running lean increase the exhaust gas temperature which affects the tuned pipe dynamics changing the effective' pipe
length (i.e longer).
Understanding Throttling
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 toadtoad |
Understanding Throttling |
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Posts: 8 (06/23/09 08:49:20) |
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HendricX |
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Posts: 67 (06/23/09 12:42:17) |
What you describe is due to .. too rich on the low needle.
Than you have a bad "transition" from low rev's to high rev's . (drowning the engine with fuel) As you wrote , leaning the high needle helps to get rid off the abundance of fuel. So go leaner on the low-needle , if corectly adjusted , you should be able to throttle down for 10 sec. and when trottling up the engine must accelerate without hesitation. |
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Dave Marles |
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Posts: 916 (06/23/09 23:32:01) |
Running lean effectively shortens the pipe by increasing EGT and so thats not what allows the motor to pickup again. When the motor is 'bogged down'
the pipe cools and effectively lengthens the pipe length which may help the pickup but I think the real issue is that the motor has flooded with fuel during
throttling and going lean on the radio needle helps to clear the motor of the excess fuel.
The throttling metering on most 21 carbs is extremely difficult to get perfect on critically setup 21 motors. Lengthening the pipe will help somewhat but then speed is lost. Reducing oil content also helps but then engine life is shortened. High compression ratios and close squish clearances make the biggest difference once the carb is set up for best throttling.
Dave
Tuning software
Last Edited By: Dave Marles
06/26/09 22:32:10.
Edited 1 times.
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