Mercruiser 165 upgrade to Throtle Body injection

[Ike-110722]

My 1972 Sea Ray has a Mercruiser 165 (GM 250). I had the Rochester 2GV carb rebuilt 4 years ago, but it still has some problems with flat spots and stalling, all of which I am familiar with and can work around by playing the throttle. But it is getting worse and I have been looking at replacements. (this is the OEM carb and is 44 years old) Of course I can just buy a new carb and drop it on and problem be gone. However, I got to overthinking this as I am wont to do (I'm an engineer, LOL), and was looking at throttle body fuel injection. The throttle bodies are cheap, but the rest of the package isn't.

Have any of you done this on an old inboard engine. If so how complex is it? If so does it significantly improve the engine performance? I am not as interested in HP improvement as in smooth running without flat spots, stalling etc. Of course better fuel consumption would always be welcome.

Any constructive thoughts on this would be welcome.

 

[Scott Danforth]

I would say you never did have the carb done right 4 years ago. The flat spots and hesitation and stalling is dirt in the carb. The cost of a brand new carb will be about 20% of a marine rated fuel injection system for your 44 year old motor, then again, a good cleaning and carb kit is $50

 

[alldodge]

Have not heard of anyone doing it, but it could be done I'm sure. Need an ECM and software to program it. Then install an O2 sensors in the exhaust to make sure you don't run it to lean/rich, and the equipment to read the sensors. Should upgrade to electronic ignition so the ECM can tell how many times the plugs are firing, and temp sensors to tell it what the motor temp is.

Most engine builders agree, a carb will give a motor more top end (WOT) rpm power over EFI, but the power is slight. Throttle response is better with EFI but this to is minimal, and a more even fuel burn.

In short, don't see a great benefit over carb, and I am a pro EFI person

 

[Bondo]

(I'm an engineer, LOL),

Ayuh,..... 'n that's a Good thing,.... You'll be engineerin' the whole thing by yerself,....

I've never seen any attempts at it,....

 

[Ike-110722]

"I would say you never did have the carb done right 4 years ago. The flat spots and hesitation and stalling is dirt in the carb"

I thought so too. However I have cleaned it several times and tuned it each time. (haven't done a tune up yet this year but I'll get to that) One carb guy I talked to said that the shaft on the valves may be worn. Could be. I probably will just buy a new one. Sierra makes an identical replacement, but I may go with a Holley instead. Some of these 165's had a Holley and I am told they ran a lot better than the Rochester.

Yep, we engineers have a bad habit of over engineering things, simplify, simplify. KISS. It sounds like a lot of work for little benefit. (I'm retired and I hate having to actually work. LOL)

 

[Scott Danforth]

"I would say you never did have the carb done right 4 years ago. The flat spots and hesitation and stalling is dirt in the carb"

I thought so too. However I have cleaned it several times and tuned it each time. (haven't done a tune up yet this year but I'll get to that) One carb guy I talked to said that the shaft on the valves may be worn. Could be. I probably will just buy a new one. Sierra makes an identical replacement, but I may go with a Holley instead. Some of these 165's had a Holley and I am told they ran a lot better than the Rochester.

Yep, we engineers have a bad habit of over engineering things, simplify, simplify. KISS. It sounds like a lot of work for little benefit. (I'm retired and I hate having to actually work. LOL)

Sleek for yourself. A good engineer knows when to repair something, when to replace something, and when to design something new

 

[Ike-110722]

I am speaking for myself. You are absolutely right. Most of the engineers I have had the privilege to work with over many many years were very good, very professional and excellent engineers. However there were a few......... Anyway. This was just an exercise in over thinking on my part and I was just casting about to see if any one had ever tried this. I posted the same question on several other forums and they consensus seems to be it isn't worth the effort and expense.

 

[thumpar]

If you want EFI get a V8 that has it already. The cost will be about the same and the headaches will be less.