1975 mercruiser 140 i/o carb prob

[patrick882]

i just rebuilt my carb on my 1975 mercruiser 140 and now when i turn it over it wont even attempt to crank unless i have throttle wide open and it will try to sputter and crank but wont at all what it the problem please help thinking may be something to do with stat choke adjustment should i be able to open the top flap on the carb when not running

 

[Don S]

Re: 1975 mercruiser 140 i/o carb prob

Cranking, to us, means the engine is turning over with the starter. Not running, just turning over.

Starting, on the other hand, means the engine will keep going when the starter stops.

NOW, do you have a cranking or starting problem?

Do you have bright blue spark that will jump a half inch? Bet not, bet it's yellow and might jump 1/4" maybe a little more.

When was the last full tune up? and compression check? Fuel filter change etc.?

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

it was running last weekend just when i get up bout half throttle it would surge and bog down but when i let off the throttle it would be fine and it would idle fine so i rebuilt the carb now it wont START and while i am CRANKING it will only sputter and try to fire when the throttle is wide open

 

[Bondo]

Re: 1975 mercruiser 140 i/o carb prob

i just rebuilt my carb on my 1975 mercruiser 140

Ayuh,..........

You did Something Wrong,.......Probably otta go back,+ Try again,....
The Details are Very Important....

help thinking may be something to do with stat choke adjustment should i be able to open the top flap on the carb when not running

The Choke Flap should be closed til it Fires Up.....(Starts)

Btw,.......

Welcome Aboard to the forums here at iboats.com............

And,... See if you can find some periods,+ commas,+ whatnot,......
ContinuoussentencesareHardtoreadforsomeofuswitholdeyesparagraphshelptoo.........

 

[starsnstripers]

Re: 1975 mercruiser 140 i/o carb prob

Patrick, sounds like the fuel pump needs to be tested either it was getting weak and finally quit or you may have a fuel blockage, filter? I'd check to see if the carb is getting the right amount of fuel, pressure test.

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

what about the auto choke.. how far are you supposed to turn that cover b/c im thinking that is the problem and also the two air needles what is the adjustment on those... i just replace the gas tank with a plastic one.. also i put a inline fuel filter that was twice the size of the old one could that be part of the problem please help want to go fishin this weekend

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

it has a mechanical pump would i be better off using an electric pump.. if so what size should i use it has a rochester 2 barrel

 

[Don S]

Re: 1975 mercruiser 140 i/o carb prob

NO, you wouldn't be better off with an electric fuel pump. Did you check the fuel pressure on your existing pump, and don't start fixing and replacing things until you are sure they are the problem.
Do you have an OEM service manual? If not, then that is probably the first thing you need to get.

 

[starsnstripers]

Re: 1975 mercruiser 140 i/o carb prob

First things first > determine that it is pump failer. A mechanical pump is fine as long as it's marine and installed correctly. Besides an electic pump is more expensive from what iv'e seen. Dont want to go buying parts if their ok! (test it)

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

no i havent checked the pressure would the oversize filter have anything to do with it and does anyone know how to set the auto choke by turning the stat cover on the side of the carb how do you do it

 

[Don S]

Re: 1975 mercruiser 140 i/o carb prob

Is there gas in the tank, the new lines and new filter up to the pump? No fuel, and it won't pump. Or you could have an air leak in the new stuff that won't allow fuel to the fuel pump.

DO YOU HAVE A SERVICE MANUAL ????

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

yes new tank and lines and filter but like i said the filter i put on it is twice the size of the one i took off(in-line see thru type) also had wiring problem when first got the boat... had to wire the coil to the battery thru a switch because would not stay running after i let go of the key but that seems to be doing fine it was ok idling just when im going for a few minutes it would surge up and down and bog down but never cut off i would back off the throttle and it would be fine

 

[Don S]

Re: 1975 mercruiser 140 i/o carb prob

2 questions.

1. DO YOU HAVE A SERVICE MANUAL?????

2, DO you have blue spark that will jump 1/2" ??????

Water seperating fuel filters are used on 3.0L (140's) all the time

 

[starsnstripers]

Re: 1975 mercruiser 140 i/o carb prob

Well, could be burning out the points(if it has points) bypassing the ign. switch. back to what i said determine if the carb is getting the proper amount of fuel to it. If it is i'd start checking ignition stuff.

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

no i dont have a service manual they do no good for me have had haynes manuals and things dont have much use for them and where am i supposed to look for this spark

 

[starsnstripers]

Re: 1975 mercruiser 140 i/o carb prob

Mercruiser manuals will explain these procedures(checking spark,fuel,etc.) I think you either need one or a friend that has a little mechanical knowledge on these simple tests. You should get the ignition switch fixed first because there is a resistence wire there that you have prob. bypassed and burnt your points. Do you know if you have points or electronic? 1975 are prob. points unless it got changed over.

 

[Bt Doctur]

Re: 1975 mercruiser 140 i/o carb prob

Not to sound rude but if you don`t know where to check for spark you do NEED some sort of manual.If you want an answer to your questions we will try our best but, if you have no clue of what were saying to you .then what??????????
What you describe sounds like a fuel delivery issue.did you prime the complete fuel system? is it airtight from the pump to the tank? inline car filters are a no-no in boats especially if you installed it on the pressure side of the pump.
But then again it just might be the "thing-of-a jig" thats causing your trouble.
as far as the choke is concerned, a starting point is to close it untill a 1/8 th inch drill bit is holding the choke plate open when the motor is cold.just loosen the 3 screws and rotate the housing.

 

[patrick882]

Re: 1975 mercruiser 140 i/o carb prob

if i convert it to electronic ignition will that hurt the coil or can i buy one of those resistors to put inline with that wire

 

[Don S]

Re: 1975 mercruiser 140 i/o carb prob

All you want is an EZ Button, so here it is.

You don't install something completely different to fix something. Find the problem. not try electric fuel pump, electronic distributor etc.

Now, if you want to fix your engine, then it's going to take some work, some testing, An OEM SERVICE MANUAL so you can read and see what we are talking about, and how to do simple tests.
Sounds to me like you have a lot of issues both electrical and fuel that need to be fixed properly. Right now, you have so much wrong it's almost impossible to say what is wrong.

 

[starsnstripers]

Re: 1975 mercruiser 140 i/o carb prob

You need to do the troubleshooting before buying or upgrading systems. You haven't determined what you need yet. I'd suggest 1) fix ignition switch 2) check fuel pressure to carb. 3) check spark from ignition/ponts, replace points their cheap ( upgrade to electronic after)