1974 Mercruiser Died/initailly was rough idle

[orthoguy]

I'm sorry if this answer was posted elsewhere, but I have been searching the forums and couldn't find my specific answer...so here it goes:

I recently bought a 1974 SeaRay with a straight 6 Mercruiser 165 HP, the guy said it started idling rough last time he had it out.

OK, I get the boat home and it was hard to start without applying 1/2 to 3/4 throttle. I got it running but could not return it to neutral without it dying. It would only stay running above 1500 RPM's I ran some seafoam through it with no change. I replaced the plugs...which the old ones looked good. The spark plug wires are newer and it looks like there is a new distributor cap on it. After replacing the plugs and it still won't idle correctly without dying, I decided to take off the carb and rebuild it. As I was starting to disassemble the linkage and fuel lines, I noticed that one of the idle mixture screws looked like it was screwed in too far, so I tried screwing it in to see where it was set at and I only could turn it in 1/4 of a turn....so, I set both of the idle mixture screws out 1 1/2 turns reassembled the fuel lines and tried to fire it up....It started IN NEUTRAL with the tap of the key! I ran it until it was warm and it was smooth as silk, never stumbled once.

I take it on her maiden voyage today and after idiling out to the lake for 20 minutes, it is running nice and smooth! I start to take off and now it stumbled at 2000 RPM and above, cuts out until I back off the throttle then runs smooth again. I slowly advance the throttle and get it up to 2000 RPM and it ran fine...try and throttle beyond 2000 RPM and it dies altogether...Now I have the complete opposite problem, now it idles but won't run above idle. OK, so I run it around the lake for about 45 minutes at 1500-2000 RPM the warmer the engine is getting the more it starts running rough and dropping in RPM's that it will run at and finally dies at ANY RPM! I have to re-start it several times to get back to the boat launch never getting above 800 RPM's and never could keep it running for more than 3 seconds finally dying 200FT from the ramp and now will not start at all and the engine is hot and the temp gauge is just shy of leaving the Green range and entering Red...so I have to paddle this heavy boat the rest of the way in!

I have read about electrical issues and carb issues both having similar conditions as mine, but have no clue where to start. I see that the carb is getting gas, but I didn't get it taken apart to inspect the float and so forth. Why would it all of a sudden run fine after I fixed the idle, now die out on me? Is it a temperature issue? Fuel? Points? Carb?

Help....I appreciate it!

Mike

 

[achris]

Re: 1974 Mercruiser Died/initailly was rough idle

One of the things that most 'automotive' mechanics miss on I/Os is the exhaust manifold and exhaust elbow... They are something you just don't see on a car engine... My first check would be to pull the elbow off and have a look inside the exhaust manifold for water... You see water, that's bad, and would account for the problems you are having... If the elbow is more than about 6 years old I would view it suspiciously... The same for the manifold if it's 10+ years... Also do a compression test... And check the engine oil... if the manifold or elbow is leaking water, then there is a good chance the water has made its way into the oil....

Chris.........

 

[DutchMerc]

Re: 1974 Mercruiser Died/initailly was rough idle

Firts, find out if this is a temperature problem. When you start the next day, does it start again? Seems like it ran better when cold, and the warmer it got , the worst...I'd say this is a problem is in the ignition/distributor. This is the part wich reacts the most on temperature-changes. Did the motor run on all cilinders?

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

One of the things that most 'automotive' mechanics miss on I/Os is the exhaust manifold and exhaust elbow... They are something you just don't see on a car engine... My first check would be to pull the elbow off and have a look inside the exhaust manifold for water... You see water, that's bad, and would account for the problems you are having... If the elbow is more than about 6 years old I would view it suspiciously... The same for the manifold if it's 10+ years... Also do a compression test... And check the engine oil... if the manifold or elbow is leaking water, then there is a good chance the water has made its way into the oil....

Chris.........

No water in the oil

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

Firts, find out if this is a temperature problem. When you start the next day, does it start again? Seems like it ran better when cold, and the warmer it got , the worst...I'd say this is a problem is in the ignition/distributor. This is the part wich reacts the most on temperature-changes. Did the motor run on all cilinders?

I will start the boat again this morning and see. When I got it home I was too upset and put the cover on it and went inside

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

OK, engine will not start this morning...it did for a brief period, but only a very rough idle @ 600 RPM, apply any throttle and it kills. So now I am back to square 1.

Distributor cap & rotor look good, there were some metal shaving type particles on the points though. By the way, how do you set the dwell if there is no window in the distributor cap?

 

[ziggy]

Re: 1974 Mercruiser Died/initailly was rough idle

have ya done any tune up to it. not just looking at them, replace them. dist. cap, rotor, plugs, points, fuel filters (at the fuel pump + at the carb), dwell and time it. to set dwell. i just take the cap and rotor off. hook up my dwell meter, then with a remote starter switch, i crank it over and set the dwell. double check after ya get it set.

as suggested before, do a compression test too. gotta have something to work with for it to run right.....

so you didn't do a carb. rebuild? could be it does need to be gone through, but eliminate the electrics first.... if ya do a carb. rebuild, do soak it, wash it and air dry all parts with compressed air and set up per the merc. service manual...

ya might check yer manifold and riser too per achris's statement. as old as they are, they are likely in need of replacement if they are the originals.......

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

***UPDATE***

Well, I think the problem is solved.

Here are the repairs I performed:

First, I removed the distributor cap to check the points, they looked tarnished and burnt and the wire to the condensor was pinched completely flat. I replaced the points, condensor, rotor & cap & got the boat to at least fire, but still would not run. Next, checked the fuel delivery, pressure was good but filters look clogged. Finally I removed the carb to rebuild it...That was the main culprit! Float bowl was 1/2 filled with crystalized chunks! Upon cleaning I found most all the jets and passage ways were clogged. Float was set stationary...needle valve was OK, but float still would not move up nor down. So, fresh rebuild, new float (other one had a dent in it) I replaced the fuel pump filter, carb filter and installed a fuel/water separator filter. It started right up! Runs very smooth, but still have to put it in the water for a trial run.

As long as I was at it, I also replaced the coil & installed new plug wires. I attempted to set the timing, but for the life of me & with asststance from a neighbor we could not locate the timing marks with the light! I cleaned the notch in the pulley and applied a fresh dab of white paint on it, but to no avail! I loosened the distributor and rotated it in an attempt to bring the timing mark into view....still nothing! I backed the throttle down to 600 & 500 rpm and still nothing! So I had to try and set the distributor back in it's original position, rotating it until the engine smoothed out.

Other than that, I am good to go for my 2nd sea trial.

BTW, does this engine have a slight stumble at idle? It idles really nice, just an ocasional stumble (both before and after I adjusted the dist.) Bump the RPM'S to 1000 & above the stumble completely goes away.

I will report back after my test run.

Thanks for your tips!

Mike

 

[ziggy]

Re: 1974 Mercruiser Died/initailly was rough idle

so did ya get the dwell set to 31-34*?

if ya can't find the timing mark, ya can't time it. if ya can't time it, it won't run proper.....

i've read, thought about it, and believe it. an engine can be set to have a different spark plug for number one. as long as the distributor wires are run in the proper firing order using that plug as number one. perhaps ya can remove all the plugs, bring the timing mark on the harmonic balancer around to where it's coming up to 0. see where the rotor is pointing to. this may be number one. needs to be on a compression stroke for the cyl. in question for it to be regarded as number one i'd think...... if this is the case. it may be why ya ain't seeing the timing mark. ya most likely have it clipped to #1. move the inductive timing light lead to appropriate cyl. and ya should see the mark......

no it shouldn't have a stumble.... did ya soak the carb. in cleaner, soap and water it cleaner yet + air dry with compressed air thru all the small passages in the carb?

do time it at idle (650-700). much above idle and the distributor adv. weights will start advancing the timing for you...

another thought. bring the timing mark heading towards 0. be sure #1 is on a compression stroke. bring the mark up to 0 and the rotor should be pointing to #1. if it ain't, make it so and retime it......

it's just a thought... and if any of the gurus think i'm full of it. please chime in and set this feller stright..... i'd hate to miss lead someone.....

glad to hear yer making headway on it.... cool....

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

so did ya get the dwell set to 31-34*?

if ya can't find the timing mark, ya can't time it. if ya can't time it, it won't run proper.....

i've read, thought about it, and believe it. an engine can be set to have a different spark plug for number one. as long as the distributor wires are run in the proper firing order using that plug as number one. perhaps ya can remove all the plugs, bring the timing mark on the harmonic balancer around to where it's coming up to 0. see where the rotor is pointing to. this may be number one. needs to be on a compression stroke for the cyl. in question for it to be regarded as number one i'd think...... if this is the case. it may be why ya ain't seeing the timing mark. ya most likely have it clipped to #1. move the inductive timing light lead to appropriate cyl. and ya should see the mark......

no it shouldn't have a stumble.... did ya soak the carb. in cleaner, soap and water it cleaner yet + air dry with compressed air thru all the small passages in the carb?

do time it at idle (650-700). much above idle and the distributor adv. weights will start advancing the timing for you...

another thought. bring the timing mark heading towards 0. be sure #1 is on a compression stroke. bring the mark up to 0 and the rotor should be pointing to #1. if it ain't, make it so and retime it......

it's just a thought... and if any of the gurus think i'm full of it. please chime in and set this feller stright..... i'd hate to miss lead someone.....

glad to hear yer making headway on it.... cool....

There is no place to set the dwell...no screw. I aksed a mechanic at the local Marine shop and he stated to gap the points that's all. Yes, carb soaked for 3 days, throughly cleaned then finally compressed air was shot through all the passage ways-jets....the carb is good to go. I tried what you suggested and even moved the timing light conductor to a different plug (the first plug at either end of the block) Very strange! I tried every idle point from 900 all the way down to 500.

I may have to readjust the idle mixture screws one more time and try and smooth it out a little bit more....a couple boating neighbors say it sounds great, but I think it's stubling a little bit.....

 

[achris]

Re: 1974 Mercruiser Died/initailly was rough idle

....

it's just a thought... and if any of you think i'm full of it. please chime in ....

Yeah Ziggy, ya full of it ... But ya right again

I set dwell on those engines by removing all the plugs, leaving the dissy cap off and spinning it on the starter and reading the dwell meter...Then just adjust the points gap to get the dwell right... easy... What is dwell if it isn't the time the points are closed with respect to the time they are open...

Chris......

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

Yeah Ziggy, ya full of it ... But ya right again

I set dwell on those engines by removing all the plugs, leaving the dissy cap off and spinning it on the starter and reading the dwell meter...Then just adjust the points gap to get the dwell right... easy... What is dwell if it isn't the time the points are closed with respect to the time they are open...

Chris......

Going to have to get a dwell meter....I see how you guys are setting them now. I was used to setting them through a window in the dist. cap.

 

[Fishermark]

Re: 1974 Mercruiser Died/initailly was rough idle

Now what you haven't addressed is the overheating. Before you take it on another sea trial, you need to find out why it is overheating. The manifold and riser was mentioned as an obvious place to look - but I'm surprised no one has asked if you changed / checked your impeller. Have you? Have you ever run it (even to see if it will start) without having water flowing to the outdrive via a set of muffs? Check your water pump in the outdrive - THAT'S the place to start looking for your overheat problem.

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

Ever try and purchase a dwell meter in 2008? LOL! They all looked at me like I was from another planet!

But I found one and the dwell was at 32-34

Going for a test run.......

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

Now what you haven't addressed is the overheating. Before you take it on another sea trial, you need to find out why it is overheating. The manifold and riser was mentioned as an obvious place to look - but I'm surprised no one has asked if you changed / checked your impeller. Have you? Have you ever run it (even to see if it will start) without having water flowing to the outdrive via a set of muffs? Check your water pump in the outdrive - THAT'S the place to start looking for your overheat problem.

The boat is running on the extremely low side of the temp gauge with muffs, we will see what temp it runs at on the lake....I think the reason the temp rose so high when the engine failed, is because I kept starting it and slamming it in gear for 1 second to keep the boat in a forward motion and the impeller didn't have a chance to pull in enough water to cool.

However, before I use the boat next year I plan on installing a new impeller anyway to be on the safe side.

Thanks!

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

BTW, the reason the engine was stumbling was because of too low of an idle. When I hooked up the Dwell/Tach meter the RPM's were at 400, but the boat RPM guage read 800, so I feel the Dwell/Tach was probably more acurate and set it with that....no more stumble.

 

[chiefalen]

Re: 1974 Mercruiser Died/initailly was rough idle

You didn't overheat at all, the second time out?

Impeller change, t-stat changed, And if it don't fix it riser and manifold pulled to see whats what.

Don't try to hide things from us cause your only hurting yourself. You will on here asking how to change out a head gasket.

Oh 650-700 is where your supposed to idle shifting at 800 you'll be asking what to do about new gears or a clutch dog.

I have mine set at 600 but thats a different story. Gauges on boats are notoriously wrong.

Supposed to set idle in water in gear 650-700.
Good luck!

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

You didn't overheat at all, the second time out?

Impeller change, t-stat changed, And if it don't fix it riser and manifold pulled to see whats what.

Don't try to hide things from us cause your only hurting yourself. You will on here asking how to change out a head gasket.

Oh 650-700 is where your supposed to idle shifting at 800 you'll be asking what to do about new gears or a clutch dog.

I have mine set at 600 but thats a different story. Gauges on boats are notoriously wrong.

Supposed to set idle in water in gear 650-700.
Good luck!

Why would I hide anything from you? I didn't take it out on a second run during my previous posts, just the 1 time.

 

[orthoguy]

Re: 1974 Mercruiser Died/initailly was rough idle

***TEST RUN COMPLETE***

OK, I just got back from the test run after all my repairs were completed.

Engine is running in the middle of the Green according to the temp gauge on the boat...didn't even stray much above 3/4 while idiling this time and actually dropped to about 1/4 while at WOT. Engine ran smooth and strong at every RPM, no hesitation nothing, just very very smooth! I slowly brought it up to plane, then did a few hard acceleration runs, it ran flawless on every test. I ran it for about 1 hour variating the RPM's and running WOT and then finally idiling..."0" problems. I do think the RPM's may be a little high at WOT, the boat Tach was reading over 4500, but this is also the same Tach that showed my idle to be higer than it was until I hooked up the dwell meter and found it to be much lower. I think I am going to back down my inital idle just a tad even though it shifted smoothly into forward and reverse, it just seems a bit high right now.

Going to move on to the impeller now, (for peace of mind) and so I will know the age of all the parts on the boat.

I want to thank each and every one of you for ALL your input, I deeply appreciate it!!!!!!

BTW, the intakes look good...I think they were replaced at some point, what you can see of the gaskets look newer.

Thanks again!

Mike

 

[achris]

Re: 1974 Mercruiser Died/initailly was rough idle

I just love a happy ending