1971 mercury 650 4cyl not getting above 1900rpm

[fullthrottle]

Hi there, i have a 1971 mercury 650 4cyl wich is only getting 1900 rpms on the lake, now it seems like it kicks in fine but tops out at 1900rpms and 12mph. It runs great, no hesitation, sputtering or anything. I replaced the plugs, didn't help, did compression test all were spot on, spark is good, checked all the fuel lines and the fuel filter, all seem fine. I tore everything apart thinking maybe the carbs were just gummed up, they looked great, cleaned them anyway, put everything back together and fired it up, ran the same, in the driveway if i try to rev it up in neutral it sounds like it's trying to hold itself back from revving up. also when i look at the plugs from running it on the lake, and at the house they were oily, not a mixing issue because i thought that right away and filled a new tank and ran it, same thing happened. Also looked at the diaphram in the fuel pump and the check valves, looked allright. anybody with any info on this would be greatly appreciated, thank you

 

[Jake.]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

Have you checked to make sure your carb butterflies are all fully open at WOT?

 

[fullthrottle]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

yes they are fully open at wide open

 

[CharlieB]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

Distributor?
Is it turn all the way to the full advance stop?
Sticking or binding, limiting advance will not accelerate.

Also check spark on each cyl again with an inductive timing light while the condition occurs, a poor wire or cap may be shorting to ground under load when spark voltage rises far higher than it is at idle.

A failing timing light should prove a shorted wire, cap, etc.

 

[fullthrottle]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

allright i fired her up and pulled each spark plug cap, the #2 cylinder did not change the idle when i pulled it off, but i did check for spark, its getting spark but not firing??? also when i pulled the #1 plug the engine died. #3 and #4 both changed the idle if this helps. any ideas of what i should do next

 

[CharlieB]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

Distributor model?

4 carbs?

Spark test each plug wire to be sure all 4 will arc hot blue across a 7/16 inch gap. If any fail, find out why, bad wire, terminal, or distributor cap.

Pulling the plug wire from #1 kills the motor but 3 & 4 just make a noticabale change in idle indicates the carbs are out of synch.

Check here to see if your service manual is still available

http://forums.iboats.com/showthread.php?t=309079

Study the section on synchronizing the carbs and linking the throttle to the ignition timing, follow the directions to the letter.

 

[fullthrottle]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

It has 2 carbs, not sure on the distributor

 

[194269]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

Run a compression check, the #'s should be between 110 an130 with a 10% variance. Also check to see if engine has the proper ign. timing.

 

[fullthrottle]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

Run a compression check, the #'s should be between 110 an130 with a 10% variance. Also check to see if engine has the proper ign. timing.

the motor ran great last year when i put it away, if i haven't messed with any of the timing shoulden't it be the same? not sure i dont know much about outboards. i did do a compression check by myself, but i only turned it over for 4 seconds on each cylinder they were all spot on 90, tonight i took the cap off the distributor, alittle bit of crud on the points cleaned them off, tried it again and same thing

 

[fullthrottle]

Re: 1971 mercury 650 4cyl not getting above 1900rpm

Distributor model?

4 carbs?

Spark test each plug wire to be sure all 4 will arc hot blue across a 7/16 inch gap. If any fail, find out why, bad wire, terminal, or distributor cap.

Pulling the plug wire from #1 kills the motor but 3 & 4 just make a noticabale change in idle indicates the carbs are out of synch.

Check here to see if your service manual is still available

http://forums.iboats.com/showthread.php?t=309079

Study the section on synchronizing the carbs and linking the throttle to the ignition timing, follow the directions to the letter.

I did check it again and it would stay running pulling all 1,3,4 plugs with a change, but #2 did not change