Low RPM at full throttle???

[margaritaman]

I had the same problem once and I would get full rpm if someone pumps the bulb on the fuel line. It had a pin hole and was sucking in air so fuel was not getting into the carbs. The bulb was brand new and had a pin hole in it.

[curtiscapk]

Nice margarita I forgot about the bulb....

[wed]

You might want to check the fuel line under full throttle to make sure it has not collapsed. I would look at the plugs...if it is running lean they may indicate some erosion (burning) of the plug surface which is very damaging to the cylinder, pistons, etc. Just something to consider.

[slowdog]

I had the same on my boat found a sticking float on the lowed carb. I had the carbs off about 15 times befor we found it .

[GregD]

I had similar problems with my 1995 Mercury/Mariner 40 hp (4 cylinder) two stroke several weeks ago. First problem the motor shut down and would not start, my son changed the power pack and also noticed the voltage regulator was burned. After changing these two items we put it back in the water and it would only run about 3600 rpms. He cleaned the carbs, put it back in the water, 3600 rpms. He changed the "trigger" (?) and now it runs perfect, 5600 rpms.

[GreenGolfBall]

Ok so we checked the coil packs...they seem to be fine. Spark plugs...still good. Fuel tank fitting...good. Looks like we're going to be rebuilding all 3 carbs. I like the stuck float idea...we'll check that when we rebuild. And also we'll be checking the voltage regulator. What is the "trigger"? Those are both great ideas and next in line for checking. I guess that saying is right "the happiest days are the day you buy your boat and the day you sell your boat!" Thanks everyone.

[Parasympathetic]

Methinks it's the carb also, but all of the above should be checked anyway. In my old boat, the alcohol gas had left a concrete like substance coating all inside the carb and had clogged the jets so that it would only run under 3000 rpm.

If yours is not too far gone, this may save you a carb rebuild. You could try spraying some Seafoam into carb with high idle for about 5 minutes. Then spray very fast and heavy till the engine dies. Wait 5 minutes and then start engine again.

[GregD]

http://www.outboardignition.com/

[BassFrequency]

take the plugs out, clean em off best you can, put them back, start the motor and rev it up. take the plugs out again and see if any appear darker or different than the others. good way to see if all your plugs are firing. sounds kinda like your lacking from one cylinder.

[Steveclv]

Take a timing light with you and check that the ignition advance system is working correctly.

It doesn't sound like carbs to me but ignition timing - carbs would cause a stutter or bad running - ignition timing plate being stuck would simply cause the engine to be down on power as it would not be getting enough advance - so your 60hp motor would only be producing say 35hp - so it would not be able to spin the prop which was set up for a 60hp.

Get the advance curve specs, remove the cover, connect the timing light to number 1 cylinder and start her up and check the timing at the engine speeds that the specs call for. If it's not advancing enough then your timing plate is stuck/corroded.

[LTB Racing]

This is a fuel issue (or lack of)w the carbs....if the motor is picking up RPM when you press in the key and dump fuel in through the enrichment valve then it is starving for fuel. ....and because you have to have fuel in the carbs in order to have fuel in the enrichment valve more than likely its not a fuel pump issue... Always start with your basics ie spark, fuel, compression but when a motor w/ these symptoms picks up RPM when u hit the enrichment circuit(choke) its usually a dead give away that its a fuel problem.

[Steveclv]

This is a fuel issue (or lack of)w the carbs....if the motor is picking up RPM when you press in the key and dump fuel in through the enrichment valve then it is starving for fuel. ....and because you have to have fuel in the carbs in order to have fuel in the enrichment valve more than likely its not a fuel pump issue... Always start with your basics ie spark, fuel, compression but when a motor w/ these symptoms picks up RPM when u hit the enrichment circuit(choke) its usually a dead give away that its a fuel problem.

You are right, sorry I missed his second post with that information about the choke effect.

When you close the choke, it pushes a plate across the carb openings and this then increases the engine vacuum in the carb causing it to suck in a lot more fuel. This gives the fuel delivery system (fuel pump, hoses, tank pickup) an easier time so that any leak is 'masked' for a couple of seconds because the engine is sucking much harder.

Of course, choking the hot, running motor is going to cause it to stutter pretty quickly.

It could still be the diaphragm in the fuel pump that has a pinhole or as another poster suggested, a pinhole in the primer bulb or a leaking connector, or dirt in the needle valve or a bad carb gasket but I'm with you now that it's fuel related.

[GreenGolfBall]

yeah, we've already changed the fuel line, checked the fuel pick up from the tank, and rebuilt the fuel pump. It still runs the same, so I ordered 3 complete carb rebuild kits. Should be here this week. Lets keep our fingers crossed. I'll keep you guys posted. Thanks.

[tkrein]

do a compression check. since that is an easy one to rule out.

[GreenGolfBall]

I'm 99% sure that compression is good. I accidently knocked one of the plug wires off once when I was putting the engine cover back on and boy it rode different!!! But i'll try it before we rebuild the carbs.