Just took a trip of about 48 miles around trip...One engine ( 1984 Crusader CH270) used 32 gal and the other (1984 Crusader CH270) used 52 gal...Tachs both read 2300 RPMs and equal...I was towing my 12 AB Inflable boat with a 40hp Yamaha and cruising about 8.5 knots..Any ideas on why the big difference?
Fuel useage
- Thread starter Jimmy B
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So exact same engines but one used 1.625 times more fuel? So if your tach is to be believed, then one of your engines is receiving a lot more fuel than the other. I would think the likely place to look after all the usual tune up items, is the carburator.
Certainly running on a external 2 gallon tank with a watch with a shop tach could easily confirm the rate the engines are pulling fuel. Once you do that, a carb switch would isolate it to the carb if that were the cause.
--Rick
Certainly running on a external 2 gallon tank with a watch with a shop tach could easily confirm the rate the engines are pulling fuel. Once you do that, a carb switch would isolate it to the carb if that were the cause.
--Rick
Generator Fuel? Are the engines carb or fuel injected, if FI does the return go to a single tank? I doubt it was burned, if the rpm were off that much you would have been steering into the dead engine and if the engine speed was the same it would have been so rich it wouldn't have burned.
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My 270's use different amounts also. I think it is because 1 engine is counter rotating. I’m also convinced that I sometimes don’t get both tanks filled to the same level. But I’m never off as much as you.
Also, that seems like a lot of fuel to burn for 48 miles. I did a recent trip of the same distance and speed as yours but at lower rpm of 1600 – 1800 and I burned 23 gallons total but I realize there are a lot variables.
Good luck
Niles
Also, that seems like a lot of fuel to burn for 48 miles. I did a recent trip of the same distance and speed as yours but at lower rpm of 1600 – 1800 and I burned 23 gallons total but I realize there are a lot variables.
Good luck
Niles
Both engines are using the Rochester QJ...The engine that burned 52 gal has a new rebuilt carb on it...My boat has aways seemed to get about .8 mpg, The engine (32 gals useage) is the one that seemed different..(1.5 mpg) I have never got that kind of mileage..
It just like one engine wasn't working hard at all...
It just like one engine wasn't working hard at all...
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I bet that engine voted for Obama!
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Agree with Gregory S. Either run at hull speed, around 6.5 knots or get up on a decent plane. Anything inbetween is a huge waste of fuel. At hull speed, you could probably make that same trip on 40 gallons (assuming all is right with your engines).
Get vacuum gauges for each engine. That way, keeping equal readings, your throttles are opening the same and running the same load. RPM doesn't tell you anything but the RPM. You need to know the load on the engines.
Props are another thing to look at. Sometimes a gear change with larger diameter and pitched props turning slower is more efficient for 2 reasons. Most props are more efficient turning slower and the engine has less load...which translates to less throttle.
Props are another thing to look at. Sometimes a gear change with larger diameter and pitched props turning slower is more efficient for 2 reasons. Most props are more efficient turning slower and the engine has less load...which translates to less throttle.
Whenever I hear about that great a discrepency, my 1st thought is always that there are 2 tanks but the crossover valve is left open . Since fuel will tend to draw from the path of least resistance, it may not be that the engines themselves are burning vastly different amounts of fuel, just that one tank, pickup, A/S valve, filter, line, etc., is harder to draw from than the other to some degree. If there is a crossover valve & it's open, I suggest you close it.
Thanks for all the good things to check...Just remember I was towing a 12 AB inflatable center console with a 40 hp Yamaha...My flowscan computer said I was burning 12gph on the starb eng and 9 gph on the port eng. I'm leaning toward my tach being out of cal. The boat ran great and started and idled fine.(No black smoke)
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When was the last time the props were scanned?
One way to determine if one engine is turning more rpm’s than the other is take a run on smooth water, no wind, no current (if you can) and no auto and watch your gps and see if your direction drifts one way or the other. My boat has 4 tachs on it and they all say something different. I use the synchronizer to set my rpm's and it tracks pretty straight so I don't pay much attention to the tachs other than to get it close.
Good luck
Niles
One way to determine if one engine is turning more rpm’s than the other is take a run on smooth water, no wind, no current (if you can) and no auto and watch your gps and see if your direction drifts one way or the other. My boat has 4 tachs on it and they all say something different. I use the synchronizer to set my rpm's and it tracks pretty straight so I don't pay much attention to the tachs other than to get it close.
Good luck
Niles
Was your original observation of 32 gal burned by one engine and 52 gal burned by the other based on the Floscan totalizer display only, or by gallons actually pumped to fully refill each tank at the end of the trip?
Particularly at low speeds over long time as when trolling, FloScans can sometimes be inaccurate , or the sensors can give inaccurate readings of actual fuel flow if air is entrained in the flow( filter gasket, loose clamp, spongy fuel line..) or trapped by the sensor if the fuel line is not kept uphill to the engine.
An inexpensive photo tach is one of many ways to get a reality check of your tachometers' accuracy. http://www.harborfreight.com/digital-photo-sensor-tachometer-66632.html