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Excessive fuel consumption

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markhopkins1

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"84 Silverton 34C with twin 27

"84 Silverton 34C with twin 270 carbuerated Crusaders. Starboard motor burns twice as much fuel as port. Last trip, 100 gals port and 50 starboard. When operating at same revs, starboard throttle lever is more forward than port, but not sure if this is just becuase of linkage slop. Slight ticking in starboard motor, but power is good and compression is perfect on all cylinders. Starboard prop redone before we bought it, but not port. If out of balance, could it make that much difference? Any additional ideas why fuel consumption is so high on starboard motor? Thanks!"
 
I'd be looking at a spark

I'd be looking at a spark plug that shows signs of no spark either due to bad plug or possible bad wire as well as trying to figure out ticking.
 
"It sounds like a noisy lifter

"It sounds like a noisy lifter...was planning to adjust to see if it fixes the tick. Plugs are new and gapped correctly. Easy enough to check for bad wire, but why would a bad one double fuel consumption for that engine?? Someone else suggested wires might not be going to right cylinders, but the engine starts and runs fine with plenty of power.}"
 
"If one cylinder on starboard

"If one cylinder on starboard engine isn't firing, would it sound noticeably rough at idle or under power? And would I have to give starboard more throttle to get the same revs as port?"
 
"I've lost one cylinder an

"I've lost one cylinder and it caused a 10 to 15% jump in consumption on the flowscan. If you indeed have a 100% delta, that's big. Does WOT indicate about the same RPM on each? Swap carbs port to stb. after that."
 
"Mark:

Is this new or just

"Mark:

Is this new or just noticed?

Dave's suggestions are prudent first steps. It is possible the prop was reworked but with less pitch; the WOT test will yield insight there.

I doubt the prop is out of balance. When that occurs, the vibration is usually quite noticeable and no sane individual continues to operate with the throttle off idle.

Before you swap carbs, give the 'bad' one a good visual inspection and get a wiff of the exhaust, too. if it is flooding, the exhaust should smell rich. One can usually see any excess fuel in the carb's throat, too.

I've had plug wires go bad and a 20% increase in fuel consumption was noted, not 100%. Checking the wires would be good, too. Also, check the timing advance function, especially if the distributors have the weight and spring mmechanism."
 
"Thanks, guys. I will investi

"Thanks, guys. I will investigate plugs and wires first. Then will check carb situation more thoroughly. I think revs matched at WOT, but I am not 100% sure...it's been a few months since she was in the water. Last trip was 6 hrs in bad weather and brutal seas, so I was distracted from diagnostics! Have not checked timing advance, so will do that also when I do complete tune-up in the Spring. Thanks for the advice. Glad nobody suggested props...didn't really want to pull them to have them scanned and balanced!"
 
"By the way, I called a mechan

"By the way, I called a mechanic at a Silverton dealer today with the same question. He suggested that it might have nothing to do with consumption, but maybe a result of an anti-siphon valve if it is so equipped. Apparently, equipped this way, both engines can draw off either tank...and the starboard tank might be the one of least resistance. I thought port/starboard engines drew fuel from their respective tanks."
 
"If the rpm at WOT don't m

"If the rpm at WOT don't match w/i 100 rpm, I'd have the props scanned. If the previous owner had them propscanned and the stbd prop rework was NOT at a propscan shop, i'd consider taking it to one.

Best way to determine the fuel routing is to explore it and make a diagram for the logbook. The "better" setups have valves so you can dictate which source feeds which engine. If needed, it isn't that hard to modify."
 
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