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Volvo 74 carb tuning

tollywally

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"I have a big block chevy with

"I have a big block chevy with a Holley 4011 carb. I run this motor in a 28 ft. Tollycraft. I generally cruise it at 2800-3000 rpms at roughly 12 knots burning 10 gal/hr hour measured with a fuel flowmeter. I run it usually just before the secondaries kick in. Frankly much faster and it gets too noisy. I also fish with it, trolling just at idle.

Since higher performance is not my goal any tips on carb tuning for better milage and if possible slower trolling speeds?"
 
"Charlie:

You are running t


"Charlie:

You are running that boat at the worst possible speed for gas mileage: hanging on a plane. It's also the noisiest speed since the engine is lugging like crazy. (I see people do this all the time.) If the boat won't plane out and THEN hold a plane at this engine speed, then the prop is off a bunch, the hull is encrusted with growth, or the engine is way out of tune (or needs a rebuild). It's Tolley, man! They aren't slow hulled boats.

On the lower speed for trolling, don't laugh but how about adding an outboard? Several friends of mine have done this for fishing--and one guy has a 32 footer! He rigged up the boat's steering to turn the outboard, and says he gets fantasic gas mileage compared to running the inboard. I've also heard of people using a large electric outboard while letting the inboard idle in neutral, charging the batteries.

Jeff"
 
"Charlie replied by email, I b

"Charlie replied by email, I believe he thought he was replying to the board... so I will post his reply here:
<blockquote><hr size=0><!-quote-!><font size=1>quote:</font>

Thanks for the input Jeff,
Actually I've studied the fuel burn issue quite a bit. I have a flow meter and a gps so I can crunch the numbers fairly easily.

Revolutions speed consumption knots/gallon cost/knot cost/hour
2200 8.7 6.8 1.28 $ 2.15 $ 18.70
2500 10.5 7.8 1.35 $ 2.04 $ 21.45
2800 12.8 9.8 1.31 $ 2.11 $ 26.95
3000 14.5 11 1.32 $ 2.09 $ 30.25
3200 17.2 13 1.32 $ 2.08 $ 35.75
3500 20.1 16.5 1.22 $ 2.26 $ 45.38
2400 10.4 7.8 1.33 $ 2.06 $ 21.45


This was the results from todays trials. I replaced the original spring in the diaphram that controls the secondaries on my carb today. It appears to be working a bit smoother than the past. I've just started to fool with trhe carb. I'm hoping to be able to improve my milage some by playing with the jets and power valves.

I'm trying to keep from putting a kicker on my boat. Two reasons why I'm against a kicker, 1. I don't want to maintain another motor, 2. I just don't like the looks, kind of silly but...

Any input you might have would be greatly appreciated.

Thanks
Charlie
<!-/quote-!><hr size=0></blockquote>"
 
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