Parts interchangability ???

[Luckymann77]

Was at the parts counter at Bass Pro Shop recently to purchase a fuel pump rebuild kit for my 1977 Merc 1150 and the guy mentioned that the "newer square pump" worked much better than the "old style" pump that I was rebuilding...

Is there any truth to that statement and are there other "newer" versions of other parts that "work" better ???
IE: carbs, electrical components or such...

Wondering how many members that would benefit from this parts interchangibility info...me included !!!

Thoughts Guys ???

God Bless,
Luckymann77

 

[MH Hawker]

Re: Parts interchangability ???

A lot of the merc parts and used on several motors and yes depending on exactly what motor, improvement are made to them. For instance that fuel pump may be used on ever thing from a 9.9 through a 100 HP and it may of had problems on a 100 hp and it was changed and as long as it fits its no big thing.

 

[Luckymann77]

Re: Parts interchangability ???

Thanks for the reply MH Hawker.

Does anyone have first, or even second hand experience with "newer" style fuel pumps specifically?
Do they actually work better, more reliable, better the engine performance???
I'm considering purchasing a used one and rebuilding it, if it makes a difference of course...

I also wonder if the later model carbs are interchangeable and not as finicky on again, the I6 models or do the differences in ignition systems not allow for such a swap???

Is there a knowledge base somewhere or will some more of the Sages of this forum please chime in...

Thanks,
Luckymann77

 

[jimmbo]

Re: Parts interchangability ???

Never swapped fuel pumps so I have no comment regarding them. Swapping to Late model carbs has a few issues, First in 1982 merc started prop rating the motors, so your 115 is a lot different than a post 1981 115 and the carbs are not calibrated the same, Second around merc late 1983 merc stopped putting chokes on the carbs and started using a fuel enrichment system to dump fuel directly into the transfer port to get more fuel for cold starts. I don't recall if the choke system can be added to the newer carbs

 

[Luckymann77]

Re: Parts interchangability ???

jimmbo,
Thanks for the info...
Guess that rules out the carb swap for sure...

Still wondering about the fuel pump swap though...
Just get the feeling that it is the weak link in the fuel system and would really like to know from someone somewhere if it would be a beneficial swap....

Luckymann77

 

[jimmbo]

Re: Parts interchangability ???

Does your engine have the 2 fuel pumps in series on the starboard side of the engine, on the transfer passage covers or just a single pump, mounted on the lower cowl or sometimes on the crankcase?

 

[Chris1956]

Re: Parts interchangability ???

Jimbo, He likely has the single "figure-8" shaped fuel pump. They are barely adequate to the task. I suppose if he could get another pump with two pulse lines, that he could mount somewhere, a swap may work.

Lucky, The pulse lines cannot leak air, if the pump is to work properly. Also, they often have springs inside them to keep the lines from collapsing. Make sure they are all in good shape. Go to a 3/8" fuel line, as that will help. Remove the quick connect and connect boat tank directly to fuel pump.

 

[Luckymann77]

Re: Parts interchangability ???

Thanks Guys for the responses...
As Chris has surmised...

The dreaded "figure-8"...lol !

So, I'll need a pump with 2 pulse lines...
I hadn't thought of that side of the pump...better inspect those lines as ASAP.

Also, the rebuild kit that I got didn't have replacement check valves and the bulb feels kinda squirelly when pumped up...
Hence the "weak link" feeling I'm getting from the pump...

Hmmm, thanks guys...
Wheels are turning a bit better now...

Luckymann77

 

[Luckymann77]

Re: Parts interchangability ???

Well I looked again at the square "newer style" pump on ebay and it appears to have only a single pulse line on it...

Unless there is some way to combine the two pulse lines off the engine that makes sense then I'm done with this idea...

Luckymann77

 

[Chris1956]

Re: Parts interchangability ???

Some of those square pumps bolt to the crankcase, covering a hole in the crankcase. This hole substitutes for the 2nd pulse line.

 

[Luckymann77]

Re: Parts interchangability ???

I saw that and wondered if that was possible...

So slap on some fittings and a piece of hose ???

Thinkin I'm going to try it...

Any thoughts about a low pressure electric pump being feasible/better ???

 

[wired247]

Re: Parts interchangability ???

I saw that and wondered if that was possible...

So slap on some fittings and a piece of hose ???

Thinkin I'm going to try it...

Any thoughts about a low pressure electric pump being feasible/better ???

The electric pump would work but a lot of people don't like electrics on 2 strokes out on the water unless you run a kill switch attached to a sensor showing that the engine is running. With a 4 stroke its easy to rig off the oil pressure. 2 strokes are different as there is no oil pressure. An engine fire with a 2 stroke could ruin your day if the fuel keeps pumping into the fire. There is a VW knock sensor that allows you to safely wire in a electric pump by killing the circuit if it doesnt sense the engine running.

 

[Luckymann77]

Re: Parts interchangability ???

Ok,
Dumb question now...
What VW sensor is that???
And,
Couldn't an electric pump just be wired to the ignition switch ???
That would nullify the need for the priming bulb too...true ???
Another weak link...
Or would that not be Coast Guard Approved...
AKA dangerous also ???

Seems simple enough to me or am I in left field???
I could care less about keeping it "stock"...

The electric pump just seems like a sure fire cure all...
And cheaper, less finicky, and way better performance to boot.

Luckymann77

 

[wired247]

Re: Parts interchangability ???

Ok,
Dumb question now...
What VW sensor is that???
And,
Couldn't an electric pump just be wired to the ignition switch ???
That would nullify the need for the priming bulb too...true ???
Another weak link...
Or would that not be Coast Guard Approved...
AKA dangerous also ???

Seems simple enough to me or am I in left field???
I could care less about keeping it "stock"...

The electric pump just seems like a sure fire cure all...
And cheaper, less finicky, and way better performance to boot.

Luckymann77

Wiring fuel pumps , or anything else with a large inductive load , directly into the ignition switch is not generally accepted good practice in cars or boats. You'll fry the switch and wiring. You could run the switch through the relay with a safety interlock of some sort such as the VW 321 906 059 G relay. It needs pulsed excitation from the ignition circuit to remain closed. Or a tunable knock sensor. You can rig your wiring however you like to rig stuff but ideally you'd want the pump to shut off on its own if the engine isnt running .

 

[Luckymann77]

Re: Parts interchangability ???

Ok,
Didn't realize they would draw that much current to need a relay but that figures...
Hope I didn't sound nieve...

So this VW part is a "relay"...
And it will shut off the pump when the engine is off...
Even when the ignition switch is still on???

Just want to make sure I understand this correctly...

If so, that's pretty cool...
But adds additional cost too.
Quick look shows them at $24 plus shipping/tax...

Still like this idea though...

Luckymann77

 

[ajgraz]

Re: Parts interchangability ???

You might try getting the parts to do the double triangle-shaped pump previously mentioned. Seems to me you'd need a replacement lower transfer cover (p/n 62978), two triangle-shaped pumps (p/n 55156Ax) and the associated fuel lines / fittings.

These are a slightly older pump set up for your motor, but those pumps are bulletproof. Typical case of manufacturer fixed something that wasn't broken.

 

[wired247]

Re: Parts interchangability ???

Ok,
Didn't realize they would draw that much current to need a relay but that figures...
Hope I didn't sound nieve...

So this VW part is a "relay"...
And it will shut off the pump when the engine is off...
Even when the ignition switch is still on???

Just want to make sure I understand this correctly...

If so, that's pretty cool...
But adds additional cost too.
Quick look shows them at $24 plus shipping/tax...

Still like this idea though...

Luckymann77

Yes, The VW relay has a lead going to it that senses ignition pulses and de-energizes the relays coil if none are present. You can use a $5 auxiliary relay and a momentary switch to prime the system or just turn the motor over a few times to prime the carbs.


With electric fuel pumps, the ideal setup is a return flow mounted either on the tank or a the motor with a return line running to the tank. That way you can be very consistent with the main line fuel pressure. On low pressure systems such as mercury's they are very sensitive to fuel pressure changes and G forces in the fuel lines. A lot of problems with engines dying on sudden stops can be traced to fuel pressure spikes.