Bertram 28 fuel burn

Classic Trade · Post by **Classic Trade** » Jun 30th, '10, 10:53

I have a 1977 Bertram Flybridge with chevy 350ci 260 horsepower engines. I burn 10 gallons of gas on starboard engine per hour and 13 gallon on port at 2850rpms. I just replaced carbs with new ones What could cause that big of a difference in fuel burn from one side to the other? I had the same fuel burn numbers before the new carbs were installed.

Thanks

Arthur

In Memory Walter K · Post by **In Memory Walter K** » Jun 30th, '10, 11:33

Logic says one carb is off. Hopefully, not the starboard. Same guy rebuilt both?

Carl · Post by **Carl** » Jun 30th, '10, 11:56

The list could get long....

-Carb could be off as Walter said

--Vacuum leak, Base or Throttle Shaft

-Ignition System

-Timing ***

Wheel Out***

Shaft Out

Alignment's Out

Tachs off

Could be any one of those of a combination...been there with each.

makomike1 · Post by **makomike1** » Jun 30th, '10, 13:44

I have 1973 28 bert with 350 crusaders 270hp. I burn around 20gal per hour 21knots @ 3200rpm. comes to about 1gal per mile. I am cruising the chesapeake bay so its brackish water, salt water like the ocean run a little slower. Mike

Carl · Post by **Carl** » Jun 30th, '10, 14:48

I thought in Salt Water you ran faster as the water is more Buoyant...

scenarioL113 · Post by **scenarioL113** » Jun 30th, '10, 22:30

I had 5.7's in my B28 and 10GPH @2800-2850 is pretty on the money.

Having a Ding in a prop or being out of alignment can surely cause a difference in fuel consumption.

Flow Scans can pick that up, but they will not diagnose the problem. They will only tell you if the problem is resolved or not.

Check the things you can check:

Timing
Tune-Up (Bad plugs????)
Fuel filters changed recently
Check the spark arrester on carb intake (clean with gum-out or something similar)
Feel for any vibrations between idle and 2800 when under way

Alignment can be checked if you know how to do it.

My engines were OFF a little shy of 1.5 GPH while cruising and I never did get it resolved. I did not go crazy over it though, I am sure if it is bothering you, you can narrow it down and get it right.

Good Luck!

Classic Trade · Post by **Classic Trade** » Jul 2nd, '10, 09:50

Thanks everyone. Both carbs are new, not rebuilt. I will try the timing first as the props were just referbished and it has new plugs and no vibration. Should I retard the timing or advance it?

scenarioL113 · Post by **scenarioL113** » Jul 2nd, '10, 10:26

Do you have a timing light that has dial for setting the timing?

If I recall correctly I had my timing set at about 12 degrees base timing and then when the engines were revved up the timing went to about 30 degrees, my numbers may be a degree or 2 off as I have not messed with then in a number of years.

You want to set the base timing enough but not too much. When the engines are hot if the base timing is too much they can or prob will be hard to crank.

If you get too much advance on the top end they will not run correctly either, you can get spark knock (I think that what its called).

I had spent a bunch of time modifying my distributer to achieve the perfect balance.

You can also power time the engines if you are not sure.

You basically set the timing but leave the locking bolt loose. Have someone drive the boat and bring the boat to a cruising speed. Then play with the timing by turning the distributer. The engines will create or lose power as you do this.

You should hear the engines sound and RPM's and a sweet spot will be found. If you have flowscans the GPM can be optimized with this as well.

I did all of these things to get my 5.7 mercruisers to where I wanted them.

Every engine is different and it is hard to say what is best for all. If you do some of the above mentioned things it will show you how some of these variables can impact performance and economy. There will be common ground that you will find and be happy with.

Leigh · Post by **Leigh** » Jul 2nd, '10, 13:10

When checking your timing, you'll want to confirm that both engines advance per the specifications as you throttle up. This can be affected by worn bushings in the distributor and also by the thunderbolt ignition amplifier being bad (the box mounted on the riser). Don't ask me how I know. Good Luck, Leigh

scenarioL113 · Post by **scenarioL113** » Jul 9th, '10, 21:43

At the very least you want FULL advance before you reach you cruising RPM. I am a little rusty but I am pretty sure you should be getting just over 30 degrees at FULL advance. Maybe even 33degrees IIRC.

Timing is very critical and make sure it is working properly.

Carl · Post by **Carl** » Jul 10th, '10, 07:36

Everyone has opinions on timing.

A boat cruising along is working those engines like a car towing a trailer up a hill.
For that reason I say go with the manufactures spec...make sure you time it at the right rpm, with engine at temp...make sure your advance works as it should...again that can be found in the manual.
Anyway that is my opinion.

A quick check as you did not mention changing Plug Wires...when its dark open the hatch and see if you can see arcing around the plug wires (Blue Glow). I have to change my wires fairly regularly ( 2-3seasons) I can hear/feel a miss now but before that I'd just peek under the hatch at night and know it was time to get a new set of wires.

Could your tacks be off, sync off? You may be pushing the engine burning more fuel just a tad more...

For me with the flow scans, I can cruise same rpm on both motors, sync shows they are right on and they sound in sync...yet one motor pulls more fuel...I can usually pull back the throttle a hair and push up the other a hair so fuel burn is pretty much the same and motors are still in snyc. and not pick up or lose speed. It really does not take much.

Hyena Love · Post by **Hyena Love** » Jul 12th, '10, 10:38

Bruce suggested to me years ago that the upside of timing games was not worth the risk. Set to Mfg'er's specs and leave it there.

scot · Post by **scot** » Jul 12th, '10, 18:45

You said both carbs are new, what carbs on on the engines? (make & model)

bob lico · Post by **bob lico** » Jul 12th, '10, 22:47

sim i will supply you with titanium and you weld and contruct two rudder boxes (open U shape) for my boat and i will install a intake system in your boat that no other boat in the world has . extremely expensive part bought dirt cheap. will increase fuel economy 20% and performance as well.

Classic Trade · Post by **Classic Trade** » Jul 13th, '10, 13:27

Scott

The carbs are Rodchester quadrajets. One other thing that was suggested to me is to swap the fuel monitors on each engine to see if it is the flow scan monitors. I will try this when I get a chance and let you know of the outcome. At least the total fuel consumption is correct.

Arthur

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