165 inline6 only gets 2000 rpm stringer drive

[cmorr176]

hello, i have a 1973 grady with an inline 6 -165hp. 250 mercruiser being pushed by an omc stringer electric shift. i can only get 1800-2000 rpm when under load. at the dock she will rev.3500+.i have put on rebuilt carb,new fuel lines changed filters, new points,plugs ,wires,cap,rotor.i thought the might be a fuel restriction so i ran from a 6 gal tank. same problem.i have a new coil ready to go on but i don't think it is an electrical problem.my next idea is to change fuel pump. i have taken linkage off when under way and operated carb by hand, still no improvement.. adjusted distributor and checked timing all ok....could it be motor is shot? ball gears? anything i missed?

 

[ziggy]

Re: 165 inline6 only gets 2000 rpm stringer drive

could it be motor is shot?

have ya done a compression test? seems like that might be a logical next step.

 

[imported_TheMan]

Re: 165 inline6 only gets 2000 rpm stringer drive

This is going to sound stupid, but my clymer manual had my distributor post order diagram wrong..

I'd suggest following the advice I got:
Make sure all the cylinders are firing by carefully removing the spark plug wire while the engine is operating. If the cylinders are working properly, the idle RPMs should drop about the same for each cylinder and you will hear an audible difference as you remove each spark plug.

 

[Haut Medoc]

Re: 165 inline6 only gets 2000 rpm stringer drive

I'm pretty sure that a GM I-6 is 1-5-3-6-2-4, & has been that for pretty much forever.....
Do the compression test, & a vacuum test.....
That is where I would start......JK

 

[ziggy]

Re: 165 inline6 only gets 2000 rpm stringer drive

& a vacuum test

good idea HM. a vac test can tell ya a lot too.. easy to do on a il6 too as the vac. port is right on top of the manifold....if ya get any descrepencies ya can follow up with an air leak test to further isolate the issue......it's time for some diagnoisin i'd think. throwin parts at it is hit and miss at best + ya could further add to yer problems with the R&Ring of parts, then haveing multipule problems to isolate......find out what works right, eliminate it, and move on to the next test to find what aint workin right.....

but my clymer manual had my distributor post order diagram wrong..

ut oh, time for dons to post his outhouse pic.... speakin of dons. he's got this post that lists things that could be wrong for not being able to reach wot. i can't find it. darn search function..heres a few of them that i had written down...
fuel type or octane, maybe old fuel
wrong propeller or damaged blades
restricted fuel pickup in tank or anitsiphon valve
to much oil in crankcase causeing aireated oil
marine growth on hull and drive
wrong vertical drive gear ratio.
operating at high altitude
flame arrestor clogged
restricted exhaust outlets in engine, transom bracket or drive
carb size and type correct for engine
fuel pump pressure and vacuum
boat overloaded, or loaded improper, or trimmed wrong
engine overheat
engine timeing and ign syst operation, tune up
remote control cables and linkage for proper travel. throttle plates opening completely
thanks to dons for this list. it seemed pertanet for this post

 

[cmorr176]

Re: 165 inline6 only gets 2000 rpm stringer drive

thanks to all who replied i will do compression and vac test next. all other causes have been ruled out.

 

[ParallaxBill]

Re: 165 inline6 only gets 2000 rpm stringer drive

You mention not getting much rpms but how does it idle and run in general? Start up okay, stall, bust up under load or just no rpms with everything else just fine? Engine noises?

We need more symptoms.


My outdrive is Mercruiser but I have a perfectly good running 73 165 and know the engine, carb, ignition well.

Just trying to help.

 

[cmorr176]

Re: 165 inline6 only gets 2000 rpm stringer drive

You mention not getting much rpms but how does it idle and run in general? Start up okay, stall, bust up under load or just no rpms with everything else just fine? Engine noises?

We need more symptoms.


My outdrive is Mercruiser but I have a perfectly good running 73 165 and know the engine, carb, ignition well.

Just trying to help.

 

[cmorr176]

Re: 165 inline6 only gets 2000 rpm stringer drive

the motor starts and runs fine..just seems like it is running on 3 or 4 cylinders.also does it need a vacuum line? none was hooked up from carb when i got the boat

 

[ParallaxBill]

Re: 165 inline6 only gets 2000 rpm stringer drive

There's no vacuum lines on mine nor provision for one. You might have a plug in the intake in which you can rig a vacuum connector to do a vacuum test.

Does it seem to be running on 3 or 4 cylinders at idle or just under a load? Mine idles real smooth and quiet, your's should too if all 6 are firing properly.
Mine didn't when I first bought it but a change of plugs and distributor re-indexing (for proper timing) got it all straightened out. Plugs were two numbers too cold.
My wires, cap and rotor button were all new. I'm also running a Pertronics electronic ignition. No points or condenser.

What plugs are you running, and what is your static timing at or below 600 rpm? Should be 6 degrees BTDC.

 

[ParallaxBill]

Re: 165 inline6 only gets 2000 rpm stringer drive

Getting any blue or black smoke in the exhaust? Is your spark arrestor black or full of soot? If so, could be an overly rich condition.

 

[ziggy]

Re: 165 inline6 only gets 2000 rpm stringer drive

.just seems like it is running on 3 or 4 cylinders

mine ran just fine on 4 cyl. too. a little ruff, but it ran, i could even get wot. not to bad. a compression test reveled #1 to be at 60psi and #2 at <90psi. that is not in spec.the rest at 120-140psi. that is in spec. a air leak test reveled air leaking between #1 & #2 spark plug holes. blowed head gasket was my diagnoisis. removed the head to revel a crack in the front of my block, inside the front port head bolt hole. end of that block.
i aint sayin that's what ya got. but ya need to get onto the basics right now. ya've throwed parts at it and it aint helped it seems. start with the basics. work up from there. especialy if ya've throwed parts at it to no avail. if ya need help with doin a compression test, ask. i'm sure anyone here would like to help ya out. same with the vacuum test. there are charts to help you interpert the vac. test availble on line. ya do need to have the tools though. they are readily available. i got mine at sears....these are pretty basic engines to work on. and are not terribly intimidateing. do you have any service manual? it really helps to read about the marine systems.....
one of the things i aint hip to though is this omc drive with a merc engine. i guess i assume omc used the il6 too and since there aint much differences in il6's. a merc one is what ya ended up with in a R&R situation....
as for the vac. lines. i don't have any vac. hooked up to my carb. dont think thats the way it is. there is a port on top of the manifold. my 72 il6 had it pluged off. my 75 il6 has it routed to a oem vac. gage on the dash........let's see some compression #'s and go from there.........hope ya have better luck than i had with my cracked block.........

 

[Boatist]

Re: 165 inline6 only gets 2000 rpm stringer drive

You could have saved a lot of money if you started with a compression check. Do the compression check first.

If you think it is running on 3 or 4 cylinders then it should idle real rough. Pull off one plug wire at a time. If you find one that makes no difference then check the stark. If you have good spark then check the fireing order. Pull the plug and see what it looks like, that should give you a good clue of what wrong. If all the cylinders are working then likely not as engine problem.

Check the growth on the hull. Is the hull clean?
What is the condition of the prop?
Is the hull and flotation full of water?
Have you added any weight to the Hull? Extra motor, live well, or Hardtop?
Are you sure you have the right amount of oil in the Engine?
Have you checked the Oil in the upper and lower units? Have you checked the oil in the intermediant unit?
Is the engine running cold or hot?
Have you added anything that creats more drag like trim tabs or a big transducer?
At 2000 RPMS is the boat even getting on plane and has it always been hard to get on plane with the power you have.

Have you changed the prop to a higher pitch or more blades?

I know a lot of questions but if the compression is good and it not missing on a clyinder or two, the timing is right and the plug look good then likely external to the engine.