1970 165 hp mercruiser-trouble keeping high rpms

[falcon_lake_texas]

hello all,
i would like to take a second to say thank you to everyone that has helped me in the past.

i finally got the boat in the water this last weekend for the first time this year. the problem is it doesn't get past 2k rpms before it starts dying down. it runs great at 2k rpms but when i give it full throttle, it starts to die. it has a new carb and new wires, and everthing else that a tune up consist of. can anyone tell me whats going on. once again thanks for your time

 

[Don S]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

List of possible causes of low WOT.
The fuel system test in item 3 below would be the place to start looking.

Engine Won't Reach Operating RPM. Check

• Fuel condition. Type and Octane possibly old fuel
• Propeller pitch or diameter, damaged blades
• Restricted fuel pickup tube or anti siphon valve Fuel System Test
• Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
• Marine growth on hull and outdrive
• Wrong gear ratio in outdrive
• Restricted carburetor air intake (clogged flame arrestor)
• Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
• Poor cylinder compression Compression Test
• Carburetor defective, or wrong type.
• Fuel pump pressure and vacuum
• Boat overloaded, improperly loaded, or improperly trimmed.
• Engine Overheating
• Engine timing and ignition system operation
• Remote control cables and linkage for proper travel to open throttle plates fully.

 

[Don S]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

One other thing, since you said you did a tuneup. Assuming you have points, put on a dwell meter and see what the dwell does when you get to the dead spot at 2000 rpm.

 

[ziggy]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

i finally got the boat in the water this last weekend for the first time this year.

so you had no issue last year it sounds like? if so. my first thought would be something that you've touched between then and now. like the tune up or the carb.

it has a new carb and new wires, and everthing else that a tune up consist of.

so is the tune up part set to specs. ie. dwell, then timeing. plug gap correct? plug wires in proper places?

is the carb. new? or rebuilt from an aftermarket? i've heard of carbs. being remanufactured and not working correctly.....

use dons's list. it's a good one. check ea. item off after ya check it..... yer problem surely lies within that list i'd think..... my comment is obviously within the list. just trying to narrow it down a little.... like i said, if it ran good last year and not now.... i'd suspect myself in error for the tune up and carb. replacement first.....then move to other items on the list if i didn't find the cause..... ya might look in yer oem service manual too. it has a trouble shooting guide in it..... dons's list covers it pretty much though.....

 

[Bt Doctur]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

Try running off a remote tank , fuelpump getting weak?

 

[hoot]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

i have an older boat also, 1978, with points, carb, etc. had a similar problem with the rpms dropping at wide open throttle. replaced the ignition coil and haven't had the problem again.

 

[starsnstripers]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

Yep this is the right place to get answers. Good list of ideas there. I like that list Don. Weak coil / fuel pump is a good place to check. A remote fuel tank might do too. I was thinking maybe that antisyphon valve may be weak if there's one on it. It may be closing prematurely. Good luck with that, Let us know what you find.

 

[Windykid]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

Tank Vent?

 

[JerryKinney]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

This may not be the same problem, but.
I bought a 1970 mercruiser 302 Ford.
Runs OK, with slight vibration, up to 2600 rpm, then its
like putting it into neutral. When you lower the rpm it takes
off again. Can only do about 9 mph.
Acts like something is slipping.

 

[JustJason]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

JerryKinney... start your own thread for your own problem... Your much more likely to get answers that way.
Best,
Jason

 

[starsnstripers]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

Oh one thought! Check the advance in dist. springs/weights make sure their fully operational. possible sticking from winter sitting. good luck BTW. Nice list Don

 

[soler]

Re: 1970 165 hp mercruiser-trouble keeping high rpms

Ignition Coil. I've had this happen on two boats. And I knew a guy that got a car that was only 4 or 5 years old at the time. He paid $300 for the car because it wouldn't run. He put a coil on it and away he went.

I spent a weekend at Lake Havasu (memorial day weekend) several years ago. Friend had a boat, wouldn't go very fast. We essentially did a compete engine tune up. Everything on the top of that motor was either new or rebuilt when we got thru (except the coil). New plugs. New wires. Rebuilt the carb. Replace points, condenser, etc. New fuel pump. Let's see, what else is up there. Anyway, it was getting spark but we didn't have the meter to show how much. Well, long story short, when he got home his dad looked at it, put a new coil on it ($10, by the way), and it ran like a top.

SOLER