1987 Mercruiser 260 Lacking Power and knocking only under load

j1musser

Cadet
Joined
Sep 2, 2012
Messages
6
Hello,

Purchased an 87' Searay Weekender 230 with Merc 260 and Alpha One. Ran and started when I got it but just to be safe we rebuilt outdrive and did bellows, gimbal bearing, alignment, distributor cap and rotor, sensor inside distirbutor, fuel/water separator, and drained 30 gallons of orange gas. refilled fresh gas and dropped her in. adjusted idle to about 750. temp stays at 150 deg. oil pressure about 60psi i believe.

Trip#1- Started up and idled out of river to lake. As soon as gave it gas it seemed as if really dogging/ lacking power. Wouldnt get up on plane. Knocking/rattle above 2800-3k rpms. Did not like sound so came back in. Runs well at all RPM's at dock just not under load. Checked plugs and looked good. Dbl checked plugs on distributor all lined up. Old prop was beat so put on buddies spare.

Trip #2- Idled out and hit gas and she took right off. rattle still above 3200ish rpm's. planed and doin low 30mph around 3k rpm.assumed bad prop/ spun hub. still unsure of knock. ran below knock rpms and trolled then ran in fine. put on brand new prop.

trip#3- idled out hit gas, same as 1st trip. no balls and wouldnt plane. went out to fish at 10 mph and trolled fine. changed all plugs(all looked good), changed oil -valvoline 40sae, added qt marvel oil w/ oil, cleaned fuel line screen next to carb.

trip 4- ran maybe a touch better. still getting knock under load. got up on plane and did about 20-25 at 3k rpms but had to work trim and boat to plane.

So it runs great til under load at higher rpms, but yet ran pretty good the one time? The boat was slipped last year so i know it ran some at least. Trying to out what direction to go next. Check timing? Replace carb. Any thoughts and please let me know if more info needed.

Thanks,

Jarod
 

series60

Chief Petty Officer
Joined
Jan 4, 2010
Messages
420
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Hello,

Purchased an 87' Searay Weekender 230 with Merc 260 and Alpha One. Ran and started when I got it but just to be safe we rebuilt outdrive and did bellows, gimbal bearing, alignment, distributor cap and rotor, sensor inside distirbutor, fuel/water separator, and drained 30 gallons of orange gas. refilled fresh gas and dropped her in. adjusted idle to about 750. temp stays at 150 deg. oil pressure about 60psi i believe.

Trip#1- Started up and idled out of river to lake. As soon as gave it gas it seemed as if really dogging/ lacking power. Wouldnt get up on plane. Knocking/rattle above 2800-3k rpms. Did not like sound so came back in. Runs well at all RPM's at dock just not under load. Checked plugs and looked good. Dbl checked plugs on distributor all lined up. Old prop was beat so put on buddies spare.

Trip #2- Idled out and hit gas and she took right off. rattle still above 3200ish rpm's. planed and doin low 30mph around 3k rpm.assumed bad prop/ spun hub. still unsure of knock. ran below knock rpms and trolled then ran in fine. put on brand new prop.

trip#3- idled out hit gas, same as 1st trip. no balls and wouldnt plane. went out to fish at 10 mph and trolled fine. changed all plugs(all looked good), changed oil -valvoline 40sae, added qt marvel oil w/ oil, cleaned fuel line screen next to carb.

trip 4- ran maybe a touch better. still getting knock under load. got up on plane and did about 20-25 at 3k rpms but had to work trim and boat to plane.

So it runs great til under load at higher rpms, but yet ran pretty good the one time? The boat was slipped last year so i know it ran some at least. Trying to out what direction to go next. Check timing? Replace carb. Any thoughts and please let me know if more info needed.

Thanks,

Jarod

The same orange gas was in the carb also. It has probably left residue in there and gummed up the jets and orifices. Now that is has run some new gas through it the alcohol could have loosened up some varnish in the carb. Consider a carb rebuild using GOOD parts dip and high pressure air hose after the dip.

I can't hear the knocking/rattle from here so I have to guess it might be a timing issue.
 
Joined
Jun 17, 2012
Messages
940
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

For sure check the timing - that knocking/ rattling sound is a pre-ignition symptom. Could destroy the engine if not corrected:eek:
 

j1musser

Cadet
Joined
Sep 2, 2012
Messages
6
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Thanks guys. I will work on checking timing this weekend. I dont have the experience to rebuild carb so I am kicking around idea of buying new for not much more than a rebuild. Good friend has much more experience and has been very helpful so far. Appreciate all ur help and time. Will keep updated. :cool:
 

j1musser

Cadet
Joined
Sep 2, 2012
Messages
6
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Tucked away for the winter and had the carb rebuilt. Finally Spring in Michigan. Launched today and got it started, adjusted idle. Ran great at dock then took out to pier heads. Same exact symptoms - no power to get on plane, knocking at higher rpm. Returned to dock and checked the timing. It was set at 25deg at idle. We adjusted the distributor and did not have a chance to get back out to the lake. I really hope this was the problem! Find out this week when I get back out there. Thanks for your help!
 

NHGuy

Captain
Joined
May 21, 2009
Messages
3,631
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Well, that's an obvious thing, hope it solves your issue. I was worried that you might have had too tall a prop that wouldn't run to correct rpms. But hopefully the timing will be your solution! Now when you get out there next you want to get to 4500 or 4600 rpm at wide open throttle.
 

akorcovelos

Petty Officer 1st Class
Joined
Jun 17, 2006
Messages
242
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

WAY too much initial timing, should be 8 deg at 700 rpm.
 

j1musser

Cadet
Joined
Sep 2, 2012
Messages
6
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Thanks guys. Find out soon. The timing plate tab thingy had white paint slopped on it, so im guessing someone messed with before.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Sounds like someone looked at the advance curve, saw the MAXIMUM advance was 25 degrees and set the INITIAL advance at that... :facepalm:
 

akorcovelos

Petty Officer 1st Class
Joined
Jun 17, 2006
Messages
242
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

If someone messed with the timing tab I would suggest verifying that it is the correct tab since there were a couple versions made for different years. Would also be a good idea to get a dial back timing light and set the initial timing to 8* @700rpm, then take it out and run it up to 3k rpm under load and see what timing is. Should be all in by 3,000ish rpm so you should see total timing at around 32*. The TBIV control box handles the advance, so the additional 24-28* advance should be automatic.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

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j1musser

Cadet
Joined
Sep 2, 2012
Messages
6
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Thanks for the support guys. We did have a dial back timer. Set at 8* at idle which was about 750 rpm on external tach. Weather is terrible here so maybe this weekend we can get out and run it. Hour drive to boat, half hour to lake half hour back, hour drive home makes for tough during school week. Thanks!
 

j1musser

Cadet
Joined
Sep 2, 2012
Messages
6
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Well all I can say is WOW! After adjusting the timing she ran awesome. Only ran for short time but got up and went, no knocking. I cant say enough for the help gentlemen. VERY GREATLY APPRECIATED!!!! :) I had no idea timing could make such a change. Will be testing a few other items when time and conditions allow.
THANK YOU!!
 

tazrig

Lieutenant Commander
Joined
Dec 20, 2012
Messages
1,752
Re: 1987 Mercruiser 260 Lacking Power and knocking only under load

Well all I can say is WOW! I had no idea timing could make such a change.

Where do you think the expression: "timing is everything" came from??? :laugh:;)
 
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