1973 Mercury 1500, Intermittent no power.

[Overpoweredpony]

Hey everyone, I have a 73 1500 i picked up reasonably cheap for my 17.6 champion bass boat.
When i got the motor it sat for awhile so i put some new plugs in it cleaned and rebuilt the carbs with new floats, did a link and sync and all seemed ok. starts and idles great on the muffs

I took it down to the river today and did a holeshot and ran great! I cruised around for about 10 minutes, stopped, and tried it again and all it did was bog, It would barely turn 1.8k rpm's. So i stopped let it idle for a bit tried it again, boom shoots out of the water and ran great again. through out the day it just kept doing it, sometimes had to try several times before it would come up on plane. When it bogs it seems like its loading up. when it was bogging i used an oil can with some 50:1 premix in it and it would die.

I checked compression before i bought it and they are 115lbs 1-6. Reeds seem ok as there is no gas spitting out of the carbs. The plugs don't look bad, I messed with the idle-air screws for a good amount of time and got no where, The wiring harness is kinda blah but i did tape it up, distributor wires are ok, plug wires are ok, I cleaned the cap and rotor, I looked at the fuel pumps and the diaphragms are not cracked.
The fuel lines are kinda dry rotted but not leaking, but can they suck air in? is there enough vacuum for that? Fuel filters are clean. I feel like i have just about checked everything, Anyone have any ideas?!?!? Any help would be greatly appreciated!!!

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

The more i keep thinking of it i keep thinking its a fuel problem. I decided to take the fuel pumps back apart. Behind the diaphragm its wet with fuel. Is this normal? I wasn't sure if it would make it down there from the crankcase or not. I guess i could go ahead and just buy the kits, they are fairly cheap

 

[Chris1956]

Re: 1973 Mercury 1500, Intermittent no power.

I would not think fuel from the crankcase would make it to the fuel pumps. I would install the rebuild kits.

 

[Faztbullet]

Re: 1973 Mercury 1500, Intermittent no power.

Yes, the backside of the diaphrams will be wet on the triangle fuel pumps as crankcase pressure/vacuum directly off transfer ports is what drives them. Install the new kits anyway as the diaphrams stretch and cause lower fuel pressure. Also check your distributor as if the dist.cap has the breather hoses these can cause distributer to rotate slowly and cause a bog as will a overgreased distributor

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

I don's see a breather hose on the distributor, But it does seem to have a lot of grease on it as its coming out on the sides.. Is there any specific way to clean it out?
I will be putting in the new pumps tonight also.

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

Alright i put the new pumps in and cleaned what i could on the distributor and still does it.
Humor me here, i know this distributor is a mechanical advance but is it possible for it not to advance when turned? Can or will the trigger do this? I'm starting to lean towards possibly a weak spark. I honestly think i have ran out of options.

 

[Faztbullet]

Re: 1973 Mercury 1500, Intermittent no power.

That ignition system either works or it dont, if the trigger is slow to rotate the engine gets fuel before spark advance. Do a decarbon with some Powertune and recheck compression with a different guage as 115 is low for that engine. Factory was 145-155psi new as it has high dome pistons. I myself do/will not work on them if compression is below 120 psi.....

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

i guess i can give that a shot and pray for the best. It just seems kinda odd to be intermittent. but who knows! Thanks for the info!

 

[CharlieB]

Re: 1973 Mercury 1500, Intermittent no power.

Idle mixture is CRITICAL for crisp acceleration.

You recently cleaned and readjusted the carbs. But you adjusted the idle mixture while on the hose, NOT while in the water. There is a big difference in exhaust back-pressure caused by the water colummn once launched.

While ON the water and IN Forward gear, readjust idle mixture to BEST idle speed, then further richen the mixture to provide the additional fuel necessary for acceleration. The actual amount varies with each boat/motor/load combination but further opening the idle mixture screws 1/8 turn CCW should get you very close.

Try your holeshot, any hesitation/bog proves a need for even more idle fuel. Open each another screwdriver blade width and retest. Repeat to perfection.

Serious increased load such as pulling up a skier or tuber can requeire even more idle fuel.

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

I performed the decarb lastnight, and i must say i was very impressed with it. I used my compression tester from work instead of one i had at home and all are reading between 130-135. after i did it i changed plugs and tried it, and yes it's still there.

I have adjusted the idle/air screws numerous times on the water charlieb, from 1 3/4 all the way to 2 3/4.. it's honestly been driving me up a wall as i am a mechanic. Nothing like not being able to fix something lol. Anyone have any other suggestions? Thanks for the input

 

[Chris1956]

Re: 1973 Mercury 1500, Intermittent no power.

OK, how about doing a link and synch on that motor. Carbs should just start to open at 4-6* BTDC(this is called idle pickup timing). Max spark advance is 21* BTDC. idle RPM is anything under 900RPM, in the water, as slow as you can get it to run.

Idle pickup timing is set by rotating the brass collar on the midsection of the distributor. it is held by two stainless steel bolts w/ 5/16" heads. Max spark advance, throttle stop and idle stop are set using the set screws in the plate above the distributor.

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

I'll try a link and sync again tonight when i get home. The way i did it was is i removed all the plugs besides #1. and grounded the rest together, and just had someone crank it as i used the timing light. Is this way ok? I also made sure my pointer was correct. Thanks a lot for commenting and giving me some info! It's greatly appreciated!

 

[Chris1956]

Re: 1973 Mercury 1500, Intermittent no power.

Pony, that is the way to do it.

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

Hey everyone! back with an update! I replaced the fuel pumps, fuel lines, fuel filter, spark plugs and did another link and sync. I finally got some extra time to try it out today and it was great for the first 10 minutes or so. I fired it up on the trailer let it warm up and it idled great and everything, Gave it some throttle and was very responsive. So i let it loose and headed up river and it ran great,It was running at 5400rpm's and ran like a top. Headed back to the ramp to pick up my friend. As i was backing up from the ramp and then shifted it into neutral i could tell it was going to act up, It just seemed like it was going to load up and bog and it sure did. Stuck around 1800-2.4k rpm's. from neutral to full throttle it seems like it will run great then around 2.4kish falls flat on it's face. I finally was able to get it up on plane and i ran it for 10 minutes or so to get a good plug reading and here is what i got. 1-5 look pretty good, they have a good carbon trace. now 6 still looks like a brand new plug. I came home and decided to pull the powerhead to check the crank seal pulled the bearing cap off and the crank is scored some where the seal rides.
I guess it makes some sense it acts the most when backing up as it forces water up through the exhaust. I guess a new sleeve and seals should do the trick. the question i have is about the seals. There is an older boat shop here outside of town and this guy said to put three seals in it and pack is full of grease, I call another and they say to do two like what is in it. Is there a downside to either one of these? I'd rather not pull it off again, damn thing is heavy! Here is a pic of the plugs. The one on the left is what 1-4 look like. the one on the right is 5-6, 5 is the bottom, 6 is the top. Thanks for the help everyone!

 

[Overpoweredpony]

Re: 1973 Mercury 1500, Intermittent no power.

Does anyone know where i can find a new speedi sleeve? Seems kinda hard to find

 

[CharlieB]

Re: 1973 Mercury 1500, Intermittent no power.

Any bearing/seal supply should either have it or be able to get it. You need to give them the O.D. of whatever you are installing it on.

I've often had to fab an installer tube/driver to use sleeves one axles. P.I.T.A. but without them we'd be screwed.

 

[Chris1956]

Re: 1973 Mercury 1500, Intermittent no power.

Use the three seals