View Full Version : Twin Engine Fuel Cosumption Difference
12-15-2003, 09:02 PM
" I have a 1989 Tiara 3100 with twinCrusader 454's, 725 hrs. My port enigne has consistently burned 25 percent more fuel than the starboard. I have owned the boat for 4 years. I do not have synchrnizers, nor fuel consumption gages. I have twin fuel tanks, each feeds a separate engine. The by-pass hose is closed.
I have had the following done in an effort to find the problem.
Compression checked (with 10 psi on all cylinders)
New Rochester Quadra-Jets installed
New Fuel Pumps
Props have been tuned
New plugs, new ignition wires.
I have breakerless ignition, so there are no points to change or set.
Props are 18x23. They are typically 18x21 for this set-up. The starboard engine reaches 4100 rpm wide open. The port only makes it to 3850 rpm.
There does not appear to be a problem with the running gear. When in nuetral, I can turn the prop shaft by hand more easily on the port engine than than the starboard.
There are no signs of fuel leaking.
The port engine does seem to show more exhaust than the starboard.
Although I would expect some slight difference in fuel consumption, this seems to be more than reasonable.
does anyone have any experience with this, or have a suggestion. The local marine mechanic has virtually given up. "
12-16-2003, 02:58 PM
"Roger, a frustrating problem for sure. It sounds like you have hit the major checkpoints, but I'm going to focus on "timing checked". Does this mean setting the initial advance only? Or have you checked that full advance is shown on the port engine? Moreover, are the ignition advance curves roughly the same?
The reason I'm asking is the advance weight and spring assemblies in older distributors can corrode or just wear out. The effect is usually to retard full advance, with the engine unable to reach full power.
Do you have to advance the port throttle more than the starboard to keep them synch'd as engine speed increases? That would be a tip. Have your mechanic lightly lube and check the advance weights, springs and pivots for proper operation, and maybe plot an advance curve for each engine for comparison.
12-16-2003, 07:47 PM
Thanks for the reply................
While I do have some mechaincal aptitude, ingition timing is probably my weakest point. The machanics came on board early in the process and "checked" the timing, so I took their word for it, whatever that is worth.
I do in fact have to advance the port throttle further to keep it up to the same rpm's as the starboard. Does this add more credence to your timing philosophy? Would this also result in not obtaining the same top RPM? "
12-17-2003, 10:14 AM
"Yep, that would do it. It would also account for being able to see the exhaust fumes from the port engine since combustion is incomplete at higher RPM's. Don't run too much with this condition as it can overheat your exhaust valves, manifolds, etc.
Your mechanic should understand my comments about checking the advance weights and using a timing light to determine an advance curve. If he doesn't, find another one that does. I can't guarantee that this is the problem, but the symptoms sure sound like it.
01-18-2004, 02:00 PM
I have a 1989 34' Luhrs with Crusader 454's. I have the same problem but with my starboard engine burning more fuel. I have a twinscan floscan and both engines burn about the same fuel up to about 3000 RPM. then the secondaries open and my port engine will burn about 16GPH and the starboard burns about 20GPH. I also thought it might be timing and took out my prestolite distributors and replaced them with Delco HEI marine distributors. It didn't seem to make alot of difference. Let me know if you come up with something but I think it might just be the characteristics of the individual engines.
05-04-2004, 10:10 PM
" My 1982 Tiara 3100 w/Crusader 270's suffers from the spark advance problem on the port engine, too.
I've tried to buy centrifugal advance springs for my prestolite distributors but can't find a source.
Does anyone know where I can get some? "
03-06-2006, 01:58 PM
"***** ****** ***** 667 ("")"
07-24-2008, 03:08 PM
"If you have the Mallory YL distributor (like I do on my '85 Crusader 270's), you can get springs from SummitRacing.com part # 29015."
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