wont go over 2400RPM on water

[tengals123]

I have completed the 'sync and link' adjusted everything out of water and adjust idle in water. Runs fine and smooth, very happy. Now, big problem when I give it the gas, I go to full throttle and it only does 10mph at 2400rmps.<br />What have i done wrong!!!<br />merc 68 1000<br />Please help.<br /><br />Thanks in advance <br /><br />cheers

 

[AndyL]

Re: wont go over 2400RPM on water

Just my guess that you have missed out a linkage. DO all the carb butterflies open when you open the throttle?, does the spark advance move correctly when you advance the throttle?. <br /><br />If that all looks OK check the compression and sparks.

 

[tengals123]

Re: wont go over 2400RPM on water

Thanks for the post AndyL,<br />carbs open full. spark advance moves correctly.<br />I shall check spark tomorrow. Compression is fine.<br />Anyone else?<br /><br />cheers

 

[MortenH]

Re: wont go over 2400RPM on water

Have you checked fuel line, primer bulb, tank vent etc? <br /><br />-M-

 

[tengals123]

Re: wont go over 2400RPM on water

yep, no problems there.<br /><br /><br />cheers

 

[lark2004]

Re: wont go over 2400RPM on water

when you rebuilt the engine, did you rebuild the carbs, with new gaskets, needle and seat, etc...?<br /><br />p.s. you know it's just murphy's law, since you launched yours before boomyal!

 

[tengals123]

Re: wont go over 2400RPM on water

yeah, i rebuilt the carbs with full kits, floats, needles and seats.<br />'is boom punishing me????' <br /><br />I guess it has to be spark,timing or idle screws???<br />So my question to all is, if my timing is out for some reason is this a common symptom?<br />Also if it's a spark is this the symptom, same goes for idle screw?<br /><br />Anyone?<br /><br /><br />cheers

 

[lark2004]

Re: wont go over 2400RPM on water

not sure of the specifics on the mercs. but a basic of any ignition is the need for a good spark. Can yours jump a 10mm gap on each plug lead?<br /><br />one other thought, do the carbs have a high speed needle?

 

[tengals123]

Re: wont go over 2400RPM on water

not sure on the high speed needle. I one I ordered looked the same as the ones I pulled out, so they should be fine. I have not checked for spark yet, but I believe spark my be my issue. I have noticed something scince all the rebuilding was done. A grey gunk comming from the prop exhaust. I know this is un-burnt fuel mixture, but is it possible that it's happening now because I am not firing on one or more pipes?<br /><br /><br />cheers

 

[AndyL]

Re: wont go over 2400RPM on water

Maybe a silly idea but with the plugs removed and the engine in gear can you rotate the propeller. Just wondering if something gone tight in the drive line. If not it looks by your point that unburnt fuel leaking out the exhaust that it is not really firing on all 6 properly. Strange why it seems to run OK up to 2400rpm. Above that does it run rough or does it just not get beyond that rpm level. Will it run above 2400 out of gear. Have you tried manually lifting the butterflies at the engine? Can you borrow a seperate fuel tank and line from someone so that you can eliminate bad fuel or problem between your fuel tank and the engine.

 

[lark2004]

Re: wont go over 2400RPM on water

check the plugs when you pull em out. If any aren't firing, they will be all wet with fuel.<br /><br />The reason for jumping a large gap, is that if it can't, It will fail to jump the correct under compression. your's may be border line, and the faster it tries to fire(as rpm's go up) it is getting it to a point where it fails completely.<br /><br />Maybe.

 

[tengals123]

Re: wont go over 2400RPM on water

AndyL, At full WOT it does NOT get above 2400RPM. at that speed it seems to run fine. I have not checked RPM's in neutral, but i will for a split second tomorrow just to see it it gets to 3000 or so (just for a second!) <br />Butterfies are fully open at WOT, spark advance is at the stop screw. I have an external tank, and may check it but pumping the primer bulb didnt help so i don't think that's the issue.<br /><br />Lark, i'll check the sparks and gaps tomorrow.<br />I want this fixed <br />other than that she running great.<br /><br /><br />cheers

 

[Clams Canino]

Re: wont go over 2400RPM on water

Could it be overpropped for the boat? Checking in neutral will accomplish little. Did it have a better WOT before you tuned it, or is this motor / boat combo a new config to you?<br /><br />-W

 

[tengals123]

Re: wont go over 2400RPM on water

clams, no i have had this boat/motor for a few seasons now. WOT previously was quite good, between 4900-5100RPM.<br /><br />cheers

 

[tengals123]

Re: wont go over 2400RPM on water

BTW its a 14,1/4 by 17' prop.<br /><br />cheers

 

[Clams Canino]

Re: wont go over 2400RPM on water

Was it OK before tuning it - or did you tune it to hopefully fix the problem?<br /><br />-W

 

[tengals123]

Re: wont go over 2400RPM on water

After pulling the carbs, i actually never run it before doing link and sync. I did them both together.<br /><br />cheers

 

[Laotzu]

Re: wont go over 2400RPM on water

Not sure how many carbs a 6 cyl has, but my 50hp 3 cyl has 3 and did exactly the same thing. Purred like a kitten but wouldn't go more than 2800rpm under load. My problem was varnish gunk in one of the carbs blocking the jet, so it was running on 2 cyl. Cleaned out and now runs good.Since you rebuilt everything(no offence) but maybe you didn't put the carbs back together correcly.<br /><br />Try pulling the plugs after a run. If firing correctly, they should have a tan/grey color residue on the electrodes.<br /><br />Jerry

 

[tengals123]

Re: wont go over 2400RPM on water

ok little update. I checked all cyls. for spark at idle and wot, I have spark on all 6.<br /><br />cheers

 

[tengals123]

Re: wont go over 2400RPM on water

More updates. I re timed the motor, I rechecked everything, I re adjusted the idle screws, primary pick-up, spark advance and throttle stop.<br />It seems to be running nice. I have a idle rmp of about 850 and in gear about 750. No sign of the motor dying. Using a bin full of water as load for a split second i gave it some gas, well what do you know, well over 4000rpms. because I don't want to ruin the motor, I din't push any further. It was enough for me to say, 'maybe' ive fixed the problem.<br /><br />Note, after re-adjusting everything from idle to WOT it seems this is how it goes.<br />Neutral -----> start to open throttle.<br />20% hits primary pick up ( 4deg BTDC),<br />40% spark advace is at it's max stop ( 35deg BTDC)<br />40% butterflies open right up to full WOT<br />so my 'splits' so to speak are 20-40-40<br /><br />What i did notice before i re-adjusted everithing was my 'splits' were like,<br />10,70,20<br /><br />so im sure ive worked somethings out.<br /><br />Does this make any sense?<br />I just hope im on the right track, I feel alot more confident.<br /><br /><br />cheers