Mercruiser 260 prevortec

[prockvoan]

OK guys,this one is killing me.RH rotation engine.Now the problem: It will not run pass 2500 rpms under load.Had changed out plugs (set at .35),new wires,coil,cap,fuel filter,new carb,fuel tank clean and everything else vent hose!Timing is set at 8 drg BTDC,check it at 3000 rpms and is at around 27 drg.Checked to see if the secondarys are opening,they are.Ran a compression check,all cyl are running 147 to 150 psi.After changing everything,it ran fine for a short run,next day,back to the 2500 deal,check it out again,still doing it.Any help?this engine has about 110 hours on it.

 

[Galloping Ghost]

Re: Mercruiser 260 prevortec

just a few little ideas, as i am having problems of an almost similar nature. did you remember to tighten the distributor, and double check the timing? do you have points? gap ok? do you have the proper prop? sometimes in rougher water it will not plane and the load will be too great if you have the wrong prop. correct plugs?<br />your problem seems to be ok then it goes bad correct?

 

[prockvoan]

Re: Mercruiser 260 prevortec

Just the one time the problem went away.Yes i had check everything 4 times over,don't have points,have thunderbolt IV.

 

[xltier]

Re: Mercruiser 260 prevortec

did u check for good fuel flow.possibly corrosion in the drain back valve coming out of the tank.got me once.hth

 

[Wart T]

Re: Mercruiser 260 prevortec

Check shutters and throttle position.

 

[prockvoan]

Re: Mercruiser 260 prevortec

Fuel flow is good,the primarys and secondarys are opening as needed.Looks as if to much fuel is going in.

 

[prockvoan]

Re: Mercruiser 260 prevortec

Still working on this one!

 

[bobmoore]

Re: Mercruiser 260 prevortec

sounds like the wrong prop

 

[bobmoore]

Re: Mercruiser 260 prevortec

ok i didn,t notice where you said it did run fine for a short time , make sure the choke is working ok,and that is not closing on you under load

 

[navigator336]

Re: Mercruiser 260 prevortec

It could be a bad pick-up in the distributor. I believe there is a method for testing it, but I don't know it. Somebody on the board here will.

 

[highaltitude]

Re: Mercruiser 260 prevortec

a timing light will tell you if you are getting a good spark throughout the rpm range.

 

[prockvoan]

Re: Mercruiser 260 prevortec

Yes,I had put a timing light on it at the landing.8 drg at 900 rpms and 28 drg at 3000 rpms.It will not make full rpms under load.Same prop as before,twin engines,inboard.Carb has been checked out,swaped from other engine,duel tanks,swap them out.One thing I didn't try is do a vacuum check,which I will do tomorrow after I get off of work tonight.Got to drive 200 miles were I more my boat.

 

[prockvoan]

Re: Mercruiser 260 prevortec

Well guys,after this weekend,and running that dam engine,looks like I have a burnt or sticking valve on #7 cyl.To hell with it.Had just replace the port engine not a month ago.Planning on dry docking my boat Labor day weekend.<br /> Wasn't able to get ahold on a vacuum gauge,but I will before dry docking her.

 

[prockvoan]

Re: Mercruiser 260 prevortec

Dry dock my boat,ran a vacuum check.What a suprise!Vacuum is reading around 16".After checking,looks like I have to much oil in the engine.I will change it out,clean the spark plugs and retime the engine,hopping it will be ok.Question is,were did the extra oil come from?Only thing I can thing of is that some how gas pass thru the engine.

 

[Don S]

Re: Mercruiser 260 prevortec

Do a compression test while you have the plugs out, I could answer a lot of questions.<br />And read this service bulletin.<br /> Service Bulletin 97-25

 

[prockvoan]

Re: Mercruiser 260 prevortec

Thanks Don,I did a compression test.Found all cyl are with in 150 psi.This engine has around 110 hours on it.What I found before was the intake manifold was leaking.Went in and replace it.At idle it runs fine,as rpms pick up,I hear a miss in the engine(at around 2500 to 3000 rpms) when the boat is in netruel.<br />Were are you getting those service bulletins at?

 

[elpaso]

Re: Mercruiser 260 prevortec

http://boatfix.com/

 

[tryan]

Re: Mercruiser 260 prevortec

looks as if to much fuel is going in and too much oil in the engine....sounds like a hung float. maybe? is it a quadrajet? holley?<br /><br />my brother built a 502 with a holley double pumper this past winter. the carb was used. the center hung float had a weak tab and flooded the motor at initial start up. we changed to a newer style float with a reinforced tab. the carb was still puking fuel into the intake. one of the air bleeds had clogged which allowed the engine vacuum to pull straight fuel (instead of a fuel/air mix) thru the progression port.

 

[prockvoan]

Re: Mercruiser 260 prevortec

I had replace the carb after this problem started.In infact,I went thru 2 carbs.I might of had high oil level at the time of changing them out.<br />There is a web sight that shows what a vacuum gauge does when you have high oil level or rings going bad and I have a match to the T.I will look it up in post it here.

 

[tryan]

Re: Mercruiser 260 prevortec

do you think you timing chain may have jumped a tooth?