1975 Mercury 165 6cyl HELP

[azazel182]

I have a 75 Mercury 165 inline 6 Chevy engine and have a few problems and questions. FIrst question which should be easy is How far is this thing suppoed to trim down? All the way trimmed down Prop is completely horizonal. Don't really care for this because it is in an 18ft boat that is pretty heavy and sits pretty deep in the water. Anybody know?

Next problem. Ran it this weekend. Saturday it ran ok but would not go past 3000 rpm. Sunday started to run like crap and not wanting to run at all. Fuel fuel pump, filter, and carb rebuild. 100% gasoline so no ethanol. I do believe it still has points and condenser so I will be changing to electronic ignition. I have changed plugs, rotor, cap, wires and plugs. WHen I punch it the vacuum gauge goes down to zero but at an idle it has good vacuum (in the green). When you punch it it hessitates then takes off. I tried adjusting the carb and no matter how much I adjusted it lean or rich it did not make much difference I just could not get it right.

Can anybody help me? I do not have the money to take it in but am very mechanically inclined.

 

[Bt Doctur]

Re: 1975 Mercury 165 6cyl HELP

An 18 ft should NOT sit that deep or be that heavy. Give or take a few degrees ,horiz is fairly close for those cylinders. They don`t "tuck in" like Alpha`s. Points ign systems work just fine on the 6, good for atleast 5000rpm.
Max rpm is based on available horsepower , outdrive gear ratio, propeller pitch. Vac. gauge is reading correctly.Have you checked the timing?
Try adjusting the points at .018(matchbook), try 6 deg. BTDC for a starting point.

 

[system-f]

Re: 1975 Mercury 165 6cyl HELP

My pre-alpha trims down to level too...going to fix with trim tabs which it needs anyways.

Just checking, but are you 100% sure about the carb rebuid? Mine was done by someone else and the accel pump was not working and float set way too high. The thing would not accelerate unless you did it very slowly and ran SUPER rich. Also compression check? When I got the boat the valve seals were leaking and the headgasket blown plus a warped head. I have tons of pictures of the carb rebuild and head gasket repair if you want them.

 

[azazel182]

Re: 1975 Mercury 165 6cyl HELP

I was thinking wrong. It is when I take off the damn thing really rares up. I already have the electronic ignition kit so I am going to go ahead and install it and check my timing and go from there. It would be nice it it is just an ignition problem. I will check sompression and what not. I checked my oil and there isn't any water in the oil but that doesn't mean anything. Engine runs good and cool. WIll let you know.

 

[Apollo75]

Re: 1975 Mercury 165 6cyl HELP

Hello;

I would start by checking the prop pitch --- if too much prop pitch slow time to plane and lower WOT rpm.

Sounds like you have done a lot of work --- I would recommend a spin on fuel filter is you do not already have one. Also, check the distributor advance weights in the original distributor and make sure they are free and lubed. Also, make sure the lobe cam under the point rubbing block is lubed with a little grease as they will wear fast if dry.

I installed a pair of standard old plane / trim tabs on the back of my boat for the same flare up / nose up problem ---- work great, I can get on plane in about 3-seconds with much less flare up now and stay there down to 2000-rpms.

Best of luck

OFM

______________________________________
"If the boat is not sinking or on fire ---- Relax."

 

[ziggy]

Re: 1975 Mercury 165 6cyl HELP

looks like every ones got some good suggestions. only thing i'll add is there are at least two pretty good places to get list of trouble shooting improper wot. one would be the service manual. there's a trouble shooting guide in it. the other is in the adults only sticky. this one. http://forums.iboats.com/showthread.php?t=295070
bet if ya go through that list. and really check them out. you'll find the problem. it seems like a pretty good list to me anyways...

only other thing i can think of is that i'd not R&R to yer electronic ign. till ya find out what the problem is. if ya put that on. and it isn't the problem. you'll not know if its right or not and ya may end up battleing two different problems. the existing one + do you have the electonic ign. done right. fwiw. there's nothing wrong with points either. they work fine if set up proper. on mine i get 4300 rpm w/points type ign. system. so they can work proper..

as for your trim. i think my 1 drive tucks in some. below horizontal. pushing the bow down..

 

[azazel182]

Re: 1975 Mercury 165 6cyl HELP

I am new to boats but you guys have helped me figure out what is wrong. I hooked the hose up to my boat and started it up. Revved it up out of water and guess what I get full rpms. I must have hte wrong pro on it. I pulled up the part number and I have a 14" prop with a pitch of 23. I am new to this so hang with me but the boat shop here said I need a 14" prop with 19 pitch. DOes this sound right? Right now I am pulling 3000rpm ish and take a little while to get on top of the water with it trimmed all the way down. They also soold me the dolefin or however it is spelled to put on it to get it out of the water faster. Let me know if this prop set up sounds good. Thanks!

 

[Bronc Rider]

Re: 1975 Mercury 165 6cyl HELP

Do you know your gear ratio? For a straight six it does sound like too much prop. I used to have a Merc 165 (I6 not I4) and I think I was running a SS prop 14.25x19 pitch on a 1.65 gear ratio (I might remember wrong).
BTW, you should never rev up your engine while on the muffs. The hose usually cannot provide enough water to cool properly. Without a load the engine will easily rev up to its recommended WOT. Even if it?s not running correctly.

 

[ziggy]

Re: 1975 Mercury 165 6cyl HELP

agree w/Bronc Rider,
i could barely turn a 21p aluminum that came with my boat. got a 19p alum. now and works well.
ya should search hydrofoil here on iboats then search smart tabs. you'll likely get lots of bummer comments on the hydrofoil (doelfin) and lots of i sure like my smart tabs comments. my last boat had a hydrofoil. i ditched it after i hit something on the river and it broke my hydrofoil + my anti vent plate on my drive. look into props first and be able to achieve the high side of wot with whatever prop, then if need be your foil or tabs.. (if ya got questions about props go over to the prop forum, some great info and fellas that are way hip to helping ya pick a prop for you)

beware of ss too. your drive has an oring slot in the lower drive shaft. 1 drives like to break at that slot with a prop strike. ss isn't to forgiving, alum. might break the prop prior to the drive shaft. i fig. it gives ya the best chance anyways. i've also read that a prop strike, alum or ss can break the lower drive shaft at the oring slot too. your call....

yep, reving her up on the muffs proves nothing + is damaging to the engine.

 

[Bronc Rider]

Re: 1975 Mercury 165 6cyl HELP

beware of ss too. your drive has an oring slot in the lower drive shaft. 1 drives like to break at that slot with a prop strike. ss isn't to forgiving, alum. might break the prop prior to the drive shaft. i fig. it gives ya the best chance anyways. i've also read that a prop strike, alum or ss can break the lower drive shaft at the oring slot too. your call....

I sold the boat that had the Merc 165 without a working drive for the reasons you state. I also think an aluminum prop would have matched my set up better, I used to turn 4100 WOT rpm. With an aluminum prop I bet I could have hit the recommended 4300 rpm's and stay at the same pitch.

 

[azazel182]

Re: 1975 Mercury 165 6cyl HELP

I just revved it up for a second to see if it was the prop. SOunds like a plan. I will get another 14" prop but with a pitch of 19 and try that out. I planned on getting aluminum because I can get them for $75 and the boat is not a show boat! Thanks for the help guys.

 

[azazel182]

Re: 1975 Mercury 165 6cyl HELP

Well the verdict is in. I put a new carb on it because the old one was deteriorating. The aluminum began flaking inside the caarb so I repolaced it and installed an electic choke. Installed the electronic ignition and a new 19 pitch prop. Took it to the lake this last weekend and loved it. Boat jumps right out of the water and runs around 3700rpm and sounds great and runs better than it ever has. I will never go back to points and condenser. Pull towables very easily and loses next to no speed in decent turns. It is like a whole new boat. Thanks guys. I appreciate the help. Not all of us can afford a nice new boat. I had a 2002 Galaxie in 2002 and loved it but came accross hard times and had to sell it. Now I have 3 kids and love going to the lake. The only payment I have is a house payment and didn't want another payment so picked this thing up cheap and have been tinkering on it.