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Mercruiser 260

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54_corvette

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"1983 Mercruiser 260 with less

"1983 Mercruiser 260 with less than 600hrs, heads re-done, new carb, new plugs. Starts and revs fine but no power under load. Vacuum gauge reads 12-15 ins at 1000rpm idle. Any ideas? thanks"
 
"Mistake in firing order, stic

"Mistake in firing order, sticky/stuck advance mechanism in distributor, wrong carb, fuel pump, plugged fuel filter, sticky anti siphon valve in tank...... idle seems too high."
 
"Vacuum gauge reads 12-15

"Vacuum gauge reads 12-15 ins at 1000rpm idle." Try a 650 RPMs and see what the vacuum reads.

As Robert said "sticky/stuck advance mechanism in distributor"; good place to start. Might also check the timing after setting the idle.
 
"Thank you for the responses.

"Thank you for the responses. Firing order is correct, I checked that. fuel filter is new, maybe five hours on it. Carb is good, replaced port and starboard and port engine is running fine. These are the original tachs so not sure of accuracy. I will put the timing light on which has a digital readout and adjust to 650rpms and then check the vacuum. How do I check the advance mechanism? thanks again, we are supposed to be going on our first big cruise this weekend so "no pressure"!"
 
"How do I check the advanc

"How do I check the advance mechanism?"

Remove the cover plate that holds the points/condenser. If there is heavy rust spray it w/WD-40 and blow dry w/comp. air. Weights should move. Check both springs; may be broken.

"...no power under load."

If the RPMs go up w/increased throttle but there is no power; try another prop.
 
"There are no weights or sprin

"There are no weights or springs, this is a Thunderbolt ignition. Checked timing and it is bang on. Chris Craft tachs are accurate and the engine will idle at 650 but not happy. I took the following vacuum readings:

650 rpm 15 ins
1000 15
1500 17
2000 18
2500 17
3000 15
3500 7
4000 7

When I got to the top end of the test the engine died right down to 1000 rpm and 0 ins of vacuum after a few seconds it cycled back up to 2500 and 12ins then it would do the same thing without any throttle adjustment. So am I right in saying this is a fuel and not a spark problem? The tank did have some old fuel but I put 40 gallons of fresh in each tank last weekend and the port engine is running fine. Any help would be appreciated."
 
"I did not adjust anything, ju

"I did not adjust anything, just slapped them on and away they went. Both engines were running fine at the end of last season. The engine starts up with no problem. If this is a fuel supply problem could the "cycling" of the RPM be the foat chamber filling with fuel and then emptying, fuel supply not keeping up with the demand?"
 
The vacuum needle was steady o

The vacuum needle was steady on each RPM reading. When we got to the higher range (no load) the RPM dropped right down to below 1000 and the vacuum dropped to zero. It then went back up to 2500 RPM and 12 ins. I cannot explain why this happened after I had gone through the RPM build up other than maybe the engine got warmer?
 
W/steady vacuum readings your

W/steady vacuum readings your engine isn't the problem; JMHO

"...no power under load."

"If the RPMs go up w/increased throttle but there is no power; try another prop."
 
"sounds like you are running o

"sounds like you are running out of fuel

swap fuel pumps and see if the problem transferes,

swap fuel lines from the fuel tanks and see if the problem transferes.

swap carbs and see if the problem transferes.

not much else to say at this point....."
 
"Thank you guys, I do not thin

"Thank you guys, I do not think it is the prop as this does not explain the cycling with no load. Fuel is probably the way this looks, I will take a look tomorrow and let you know what I find, thanks again!"
 
"Hi, I need to find out how th

"Hi, I need to find out how the wirers go on a 1994 5.7L. The wire harness is from a 1987 omc.as that is what is on my 1987 bayliner engine that is blown. The old onwer took some wires off an I dont no were they go.I could use a digram of it.thanks for any help I can get.George"
 
"Okay, so I switched the carbs

"Okay, so I switched the carbs no change, I switched the fuel pumps, no change. the two gas tanks feed into a Y connector and supply both engines, so nothing to switch there. When I pulled the carb there looked to be droplets of water on the intake manifold?? I pumped some fuel into a jar, no water in it. I pulled the fuel/water seperator and dumped it, no water but the top of the seperator canister was rusted (installed less than a year ago and maybe 5-10hrs running time. I also noted a lot of sediment. I cut open the old seperator and there was lots of sediment and again evidence of some rust. Put everything back together, fired up the engine and no change. A little harder to restart this time and the engine would "lock up" like the ignition was too advanced but I had checked that and it was correct. Yes, I cleaned the filter in the carb, a little sediment but not much. Any more ideas?? thanks"
 
The concensus seems to be that

The concensus seems to be that the problem is fuel related. All of the key fuel parts were just swapped w/o any change. Perhaps it's time to swap ignition amplifier modules. Look at the condition of the optic trigger senser under the rotor. If it's rusted then the fine wires can be corroded and cracking under vibration. It the optic sensor is moved then the timing must be checked.
 
"Guy, I agree don't know w

"Guy, I agree don't know what else to look at fuel wise. I did have the cap off and under the rotor was what looked like 1/4 ins dia., very fine wire brush looking up at me and yes it was rusty. Is this what you are talking about and would this explain the symptoms if it is ng? Do I just replace this? thanks"
 
That's it. A closer look

That's it. A closer look when removed will show the damaged hair like bare wires. Retime the engine when done. New models are plastic.
 
"Thanks Guy, the parts places

"Thanks Guy, the parts places are all closed today so I thought, before I part with some cash, I might switch distributors and check out the theory. Can I switch them between a lh and rh rotation engine, is there any difference and would you recommend changing both sensors?"
 
""I might switch distribut

""I might switch distributors...Can I switch them between a lh and rh rotation engine, is there any difference..."

I don't know.

"...and would you recommend changing both sensors?"

Yes, if they are corroded; going to fail anyway; when?"
 
only difference between RH and

only difference between RH and LH is the firing order is reversed. that's why they have the second set of numbers on the cap.
 
"Okay, so I replaced the senso

"Okay, so I replaced the sensor and restarted the engine. No change, hard to start and when it did start it ran lumpy with the RPM cycling up and down. I thought I would let it run for a while and see what happened, it smoothed out and was running pretty good at about 2000 rpm. I thought I would check the timing and while getting this organized noticed some steam coming from the top of the engine. I removed the air cleaner/flame arrester and found a mess of light brown goop bubbling nicely on top of the intake manifold on the left hand bank. switched off, checked the water level, way down, pulled the dipstck, light brown goop, kind of like Jello pudding. So all I can think now is to pull that head and take a look. Any ideas how I clean out the engine to get rid of the goop, it is everywhere!"
 
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