Carb Rebuilds vs. EFI Upgrade

[Gerard Hebert]

I am new to boating and purchased a '98 SCR 3700 with carbed 7.4L engines in July.

Based on my searches here, the topic of swapping out carbs for aftermarket EFI systems seems to come up every few years. My apologies if I have missed a more recent thread. Please feel free to refer to it here.

My boat is having issues and I need to decide next steps. It takes approximately 30 seconds (3 tries of 10 seconds) to start each engine at the beginning of the weekend and there is a very strong smell of gas after shutting them down.

Rebuilding the carbs would be the cheapest solution, but Holley's Sniper systems look very appealing. It would likely eliminate both issues with the added benefit of improved fuel economy.

Two questions:
1) What do people do these days: rebuild the carbs, replace the carbs, or install EFI?
2) The WOT speed of this boat is just over 26 knots. Is that to be expected?

[Patrick Bodkin]

I can't comment on what your WOT speed "should be" for your 37 foot model. All I know is that my 2008 2900 SE with EFI got up to 48 MPH on its sea trial prior to my recent purchase. I'm sure that my boat, at 10,000 #'s without passengers or fuel/water, weighs considerably less than yours. It is powered by 2 x 5.0 L 260 hp Mercs.

[jrsick]

Sorry to answer your question with a question, but some more info would be helpful. Have you done a tune up: wires, plugs, caps, rotors? Also taking a look at the condition of your plugs and the inside of your distributor cap would give good info. Sometimes starting problems and fuel odors are caused by poor ignition.
What is your WOT, and what size prop are you running?
Since boat is new to you, you probably don't know the history of the carbs. If tune up doesn't fix your problem then I would recommend rebuilding the carbs. Get the boat in good running condition then decide if you need EFI. My limited experience comparing carb with EFI is that EFI is more responsive at low rpm, but I can't tell any difference beyond that.
This being your first boat, you may want to try something different in the future. EFI is a significant investment for a 22 year old boat.
Keep us updated on your progress.

[shrew]

Originally Posted by Gerard Hebert

My boat is having issues and I need to decide next steps. It takes approximately 30 seconds (3 tries of 10 seconds) to start each engine at the beginning of the weekend and there is a very strong smell of gas after shutting them down.

What is your starting sequence? IT should be:

1) Put the engine in neutral (If there is a single shifter/throttle lever)
2) Pump the throttle 3 times.
3) Advance the throttle slightly and turn key
(You may need to slowly advance the thottle a bit more until she catches and starts, at which point, bring the throttle back to idle)

Originally Posted by Gerard Hebert

Two questions:
1) What do people do these days: rebuild the carbs, replace the carbs, or install EFI?

Rebuild carbs or repower. Converting from carb to fuel injection is a significant project

Originally Posted by Gerard Hebert

2) The WOT speed of this boat is just over 26 knots. Is that to be expected?

Engines are measured by max RPM. Most Mercruiser inboards should be able to reach 4400-4800. (Newer HO models are a bit higher)

The top speed isn't really relevant because there are too many variables that impact it (wind, current, tide, load, and sea state). That is why you don't really see speed in real world statistics.

[Gerard Hebert]

A lot of good comments and questions.

WOT is 4400RPM.
No idea about the props other than the fact that they have 4 blades.

Starting sequence:
In July when I bought the boat it was 'turn a key and start an engine'.
Two months later, its half-throttle-and-back but always at idle when turning the key. Rinse and repeat. I will try full throttle and back next time.

Ignition:
No, I have not checked the ignition components because I never noticed the smell until after the engines were shut off, but that could easily be a timing thing. Every time I back this thing into a slip, I feel like the guy who has to land the plane because the pilots died. Not much else gets my attention until the ropes are tied.

It is true that I do not know the history of the engines. The best plan is probably to replace all of the ignition components and get the carbs rebuilt. The PO provided a box of parts that included new wires and plugs.

Thanks.

[shrew]

Originally Posted by Gerard Hebert

Starting sequence:
In July when I bought the boat it was 'turn a key and start an engine'.
Two months later, its half-throttle-and-back but always at idle when turning the key. Rinse and repeat. I will try full throttle and back next time.

I'm not sure you need to go to full throttle. I used to pump mine about 50-60% three times. then back to zero and then a slight advance, then start. That seemed to be enough.

[Gerard Hebert]

Originally Posted by shrew

I'm not sure you need to go to full throttle. I used to pump mine about 50-60% three times. then back to zero and then a slight advance, then start. That seemed to be enough.

Thanks for clarifying.