Mercruiser 260 engine problems

"Having spent weeks getting my

"Having spent weeks getting my starborad engine running properly the port engine has started playing up. This engine had rebuilt heads ten years ago but has not run since except for the odd fire up. During the last three months recomissioning the boat it has always started easily and run smoothly throughout the rpm range. Oil pressure, temperature and vacuum have always been good. We took the boat out this weekend (first really good run) and both engines ran well at about 3000 rpm. When approacing the anchorage at maybe 1500 to 2000 rpm the port engine was "cycling", dropping 1000rpm and then going back up. The vacuum gauge was also cycling between maybe 15 and 5 ins. When we came back today the engine was a little hard to start necause of the cycling, it would rev up and then stall. Once it got warm it ran ok,but still cycling. We came home at 1500 rpm and once in the harbour moved her up to 2000rpm. This was followed by intermittent "popping" which I presume was backfiring. Any ideas on what the problem might be?

thanks"

"A number of boaters this year

"A number of boaters this year have had the same experience you have described. Change fuel filters. If one is a separator, dump it into a glass jar and look at its content."

"Thanks Guy, I pulled the filt

"Thanks Guy, I pulled the filter/seperator and dumped the fuel. It was clean, no water and no contamination. I started the engine, with some difficulty. It would start and then die as the rpm cycled. When it did run I let it warm up and at 1500rpm the tach would cycle from 1500-1100 RPM and the vacuum gauge from 13-10 ins. The engine was running with 19 ins of vacuum before this problem developed. I noticed that there was a "clicking" sound coming from the engine and it appeared to be coming from the top end but not sure. Would appreciate any suggestions."

"It still sounds like a fuel i

"It still sounds like a fuel issue. If you have a mechanical fuel pump there is a filter inside the dome. Does adjusting the mixture make the engine run better, worse or no difference? If no difference then the idle circuits are plugged. Does the accellerator pump produce strong fuel sprays? Carb may need rebuilding if it has been a few years.

Dump the fuel from the filter/separator and fill it w/SEAFOAM and run the engine for 3-4 mins. Shut it off and let it sit for a day. Then start it up and see if the SEA FOAM cleaned any dirty circuits in the carb.

Check the carb base nuts for tightness. W/engine running spray some carb cleaner around the base gasket and the intake manifold gasket. If the RPMs rise quickly you found a vacuum leak.

Backfiring can be a lean mixture, burned valve or cross firing of plug wires. The wires should be routed parallel and not criss-crossed. Check the engine timing at idle in case it is off a little.

Top engine noise could be a lifter, sticky valve, loose valvetrain part. Try a pint of SEAFOAM in the oil and see if it quiets down."

"Guy, just thought I would let

"Guy, just thought I would let you know the story on this one. As the season was pretty well shot I did not rush to fix this but when I did I followed your suggestions without success. A compression test came up with about 150 psi all around except #4 which was 200 psi! I pulled the valve cover and noticed that the rocker arm stud on #4 intake was about 1/4 inch longer than all the others. The rocker probably had about that in clearance so there was my "ticking" noise. Turns out these studs are not threaded but a push fit in the head. I tapped out the hole with a 5/16 14 tap and fitted a threaded stud, adjusted the valve clearance and she now runs like a top! The tap and stud came to $10.47 so I am a happy camper. Thank you for your responses, much appreciated."

Good for you.

Good for you.

Good work. I had a Pontiac eng

Good work. I had a Pontiac engine with the same issue. The stud pulled out due to a siezed rocker arm. Cause was low oil pressure from a bad pump. I'm sure you checked the ball and rocker before re-assembly. Keep an eye/ear on that engine
Chris

"Thanks guys, I will certainly

"Thanks guys, I will certainly keep an eye on things. This happened after the boats first hard run in over ten years so I am hoping it was "one of those things". Oil pressure is good and both engines are now running fine although I have not put them under load yet. I will just run the engines for twenty minutes or so once a month and look forward to next season. Lots of winter projects on the boat to keep me busy! Thanks again.

Mike"