Tried all suggestions and it still won't start.

[Oldmerc75]

Hi everyone. You're my last hope.

For 3 years I've been restoring my old sailboat. Finally ready to sail and I pulled the outboard, a 1971 Mercury 75 (7.5 hp) out of the garage and tried to start it. No luck. Understandable. It's been sitting up for three years. Saving you the boredom of the problems I've discovered and repaired I'll list the items I've checked and / or replaced. All of this has been done under the guidance of the SELOC repair manual and reading many internet posts for help.

1. Checked compression: It's the same on both cylinders depending on how hard I pull the starter rope. About 60-70 PSI. The manual said it's more important that it's even than an actual pressure being a hand start.

2. Rebuilt Carb: Tore it down, replaced all gaskets, the needle, float. Re adjusted everything to manual specs, cleaned every inch of it.

3. Replaced many frayed wires: Over time they seem to have deteriorated.

4. Replaced plugs and plug wires.

5. Made sure gas was brand new and mixed properly.

On to the issues. After doing all of that I CAN NOT get the motor to start. I have verified good spark with a spark tester. When I pull the plugs they are dry. That's where I'm stumped. I have checked the carb since rebuild. The float bowl is filling and staying full of fuel after pumping it up. After several pulls of the rope, gas is dripping from the barrel of the carb. It seems as if the powerhead isn't pulling the gas to the pistons. I took a teaspoon of gas / oil mixture and poured it directly into the spark plug holes. After a few pulls it would fire for one pop, a little smoke would come from the exhaust and that was it. That verified I am getting spark but not gas. Other than a clogged carb, which I have verified it is not, what could stop the gas from getting to the cylinders?

I am open to ANY suggestions you guys can offer. Please end this frustration for me!

Thanks for any help offered.

 

[steelespike]

Re: Tried all suggestions and it still won't start.

When primed you should get more than a pop.Should run for a few seconds.
Put some fuel in a squeeze bottle or pump oiler with the choke open very carefully squirt into the carb throat should fire and run a few seconds.
Are the plug wires on the right plugs?Did you confirm all passages and jets are clear in the carb?Nice blue spark with an audable snap?

 

[Laddies]

Re: Tried all suggestions and it still won't start.

It's a common problem for the insulator blocks on the point studs to crack and cause the engines to not run but still have spark. At times the will backfire of kick but seldom run.

 

[JB]

Re: Tried all suggestions and it still won't start.

Do "Outboard won't start" in the Engine FAQs, OldMerc.

Let us know what you find.

 

[jerryjerry05]

Re: Tried all suggestions and it still won't start.

If the compression is really 60-70 and the guage is good.Pour some oil in both cylinders while the motor is tilted up.Then do another compression test and see if there is a difference from the first reading.Post your results.Jerry

 

[Oldmerc75]

Re: Tried all suggestions and it still won't start.

Thanks for all of the quick replies everyone.

To answer the plug questions. I am sure the correct plug wires are on the right plugs. These plugs are gapless ones. I'm unaware how I might test the spark the traditional way (Holding against a ground and watching). I did purchase a spark tester that goes inline with plug wires and it's lighting up bright.

The points could very well be a problem. This motor was rebuilt before I acquired it and the points were new then. My understanding is the motor has about 20 hrs or so on it since the rebuild. When I was rewiring I pulled the points and inspected them. The surfaces are not flat. They are quite uneven. When reinstalling I was able to gap them correctly (.20) with no issues. I didn't notice any cracks but I wasn't thinking of looking for cracks. It was more of a cursory inspection. I will pull them and take another look. Could they be causing a weak spark? Would a weak spark still burn the fuel but not enough to push the piston down causing the plugs to still be dry after several pulls?

The carb is as clean as could be. Like I said, I rebuilt it about two weeks ago and cleaned every passage it contained. I have verified the float bowl is filling and staying full. The needle had to be readjusted after rebuild because the new one was slightly longer than the old one but I have double checked that adjustment 5 times already.

I will try the compression test suggested as soon as possible. It may be a week or so before I can get out and work on it with all of the Holiday activities I have planned currently. As soon as I do I will post the results.

Thanks again everyone for the help!

 

[sdsaw]

Re: Tried all suggestions and it still won't start.

I might be talking out of my a** but here it goes
To me, it seems that the motor is not drawing the fuel in.
Have the reed valves been looked at and functioning properly?
And I thought, but may be incorrect that old mercs have issues with the crank cases leaking in the seams and not having good vacuum to draw the fuel in.

Just an idea, Scott

 

[JB]

Re: Tried all suggestions and it still won't start.

Your compression is plenty good enough and has nothing to do with your non-starting problem.

What you need is logical troubleshooting before you start replacing or overhauling stuff that probably ain' broke.

Replacing or rebuilding parts is the most used, most expensive and least effective troubleshooting method known to man. I might add that it is the method most likely to introduce new problems.

Let us know what you find doing "Outboard won't start".

 

[sschefer]

Re: Tried all suggestions and it still won't start.

I might be talking out of my a** but here it goes
To me, it seems that the motor is not drawing the fuel in.
Have the reed valves been looked at and functioning properly?
And I thought, but may be incorrect that old mercs have issues with the crank cases leaking in the seams and not having good vacuum to draw the fuel in.

Just an idea, Scott

Scott, that would be my guess too. If the crankshaft seals dried out and cracked during storage he might not have enough vaccum to pull or push fuel into the cylinder.

I haven't seen anyone mentioning the fact that testing compression at the spark plug hole is actually a secondary test. The primary compression test is to fill the block with 5lb's of air pressure and make sure that it holds. It requires block plates that most folks don't have so I guess that's why.