1975 115hp Merc Hard starting

[utfyrfytr]

I have a 1975 115hp Merc that is hard to start. I have to choke it constantly and it still takes 10-15 attempts. I have the cold idle lever up 3/4 to full and on full choke the entire time. Even after running for 15-20 minutes if we shut it down and fish for 20-30 minutes in order to start it I have to give it full choke and make 5-6 attempts to get it running. The fuel system is all new from the tank to the motor. I have an electric fuel pump and also the OEM mechanical pump which has a new diaphragm. I just got it out of the shop for this very issue and I would take it back if it wasn't for the fact it is 75 miles away. It makes for a 300 mile trip to the shop. We don't have anyone else around who works on these old engines anymore. The plugs are new and I went through the carbs last winter. Spark is also good to each plug. Compression is 120 120 118 115 112 118. Any thoughts?

 

[Chris1956]

Those motors need the engine to crank a certain speed (say 300 RPM) to have sufficient air flow to choke up. I would make sure the battery cables are clean and intact, so the starter gets all the juice it wants. Obviously the battery needs to be good as well. The choke shutters are closing all the way?

Run your fingers over the battery cables. Feel for any bumps, which indicate corrosion. It can happen under the insulation.

 

[utfyrfytr]

Thanks Chris, I was wondering about the cranking speed, although it sounds good, but it seems strange to me that you would have to continue choking the motor even after it is warmed up and only sat for say 20-30 minutes while fishing. Never the less at this point I will try anything. I will also check the choke shutters and make sure they are closing sufficiently. I appreciate you sharing your knowledge.

 

[Chris1956]

You should not need to choke the motor after it has run and sat for 20-30 minutes. Are your carbs clean, the floats are good and adjusted properly?

Do you seen any fuel on the water when cranking?

 

[utfyrfytr]

Carbs are clean, I went through them last winter. I did not check the floats or the adjustment on them. I have not seen any fuel in the water. What should the floats be set at and how do I adjust that? Another problem I have after running and engine is up to temp is it does not want to idle very well. Seems like a lack of fuel to me. The idle adjustment is set at approx. 1 1/8 turns out.Thanks

 

[444]

I would pull the carbs and set the floats, idle screws and do a proper link and sync as per the service manual then retry. Sounds like a fueling problem. Why do you have an electric fuel pump on there? I hope that's not putting out too much pressure and pushing past the needle and seat. Mine's almost as old, a 1978 and it runs well with a factor fuel pump and a good fuel primer bulb.

 

[Chris1956]

The original floats were foam, and tended to dissolve in the current gasoline/ alcohol mix. I recommend replacement to the white hard plastic floats. Also, check to make sure the little springs are intact in the float tops.

To set the float height, invert the carb cover. Bend the lower lever until the top lever is parallel with the edge of the carb cover. Turn cover right side up. Bend lower lever until distance between levers is 1/4".

If the inlet needles and seats are the original nylon and brass/rubber, I would replace them. Newer inlet needles are SS with neoprene tips. Seats are all brass.

Replace gaskets as well. Your motor should have a banjo filter under a cap on the carb cover. Make sure it is clean.

Lose the electric fuel pump as well. It could confuse your issue.

 

[utfyrfytr]

444, Thanks for your input. A mechanic suggested the electric fuel pump because I am pulling fuel from a bow tank that is approx 25' from the motor. I have run the motor with the elec pump and also without and it doesn't seem to make any difference. I usually only use the electric to initially push fuel to the motor and then shut it off. I don't have a primer bulb in the fuel system at all. That wouldn't make a difference would it? I don't have a timing light to do a linc and sync. I could get one if you think that is really necessary. Any other thoughts, keep them coming, I'm open to about anything.

 

[utfyrfytr]

Chris, I put in new needle and seats last fall, the floats are the hard plastic and springs are in tact. I don't recall if I measured the float height or not but I will today. I can remove the elec. fuel pump but like I told 444, I have run both with and without and it doesn't seem to change anything.

 

[merc_man]

How is the compression for your motor?

 

[utfyrfytr]

merc-man, compression is: 120 120 118 115 112 118, thanks for weighing in.

 

[utfyrfytr]

Ok, just finished going through the carbs and setting the float heights and drop. Man what a job to pull the carbs on that thing. Everything seemed fine, nothing out of sorts where I could say that I have found the problem. I'm going to put them back on and button her up and give it a try. I'll pull the electric fuel pump off if there is no improvement and see what that does. Thanks everyone for your ideas but keep thinking, I don't believe we have found the problem yet.

 

[merc_man]

What about hooking up a small boat motor gas can near back of boat temporarily just to rule out its not a distance isue for the fuel to travle.

 

[jimmbo]

Are the choke plates closing against the carb throats, or is there a gap? Does your engine have choke shutters on all 3 carbs, or just the top 2. Are you trying to start the engine when it is down fully, or partially lowered?
The symptoms you describe do sound like low fuel level, usually from a float set too low.
It doesn't seem like the electric fuel pump is an issue, except for a fire hazard if one of the carbs is flooding and the engine stalls and isn't restarted soon. Usually electric pumps put out too much pressure and overload the float/inlet resulting in flooding

 

[utfyrfytr]

Welcome Jimmbo, I had to come in out of the sun for a few minutes before I go and finish up and give the old girl a try. I'll answer your questions while I'm here. 1) there is about a 1/16" in gap between the choke plate and the carb throat. 2) choke shutters on two of the three. 3) Engine is in the full down position. 4) electric fuel pump is low pressure, I have shut off valves between the pump and the engine and I try to remember to shut it off as soon as the engine starts. If there is a float set too low it is less than a 1/16" because I just finished rechecking them this afternoon.

 

[utfyrfytr]

Merc-man, I did that when I first mounted the engine early this spring and it was the same issue. This engine is on a 1968 Crestliner that I have been redoing for the past couple of years. I hooked it up to a nurse tank before I had the fuel tank set fuel pump installed and lines ran.

 

[utfyrfytr]

I finished putting things back together last night and the motor started on the first try. I got up this AM and with it sitting all night it started on the first try again and seemed to me to idle smoother also. I wish I could give you an answer as to why it runs better but I don't know, I found nothing that I can say was the reason for it to be hard starting. I can say that the choke plates would not close when I first put it back together because I had the lock nut to tight on the middle carb but I didn't pay attention to how tight it was when I removed it so I can't say that was a problem from before. Anyway I can't wait to get it out next week and see how it runs on the water. Thanks for everyone's input and suggestions.