No load RPM

[strehl]

How high of Rpm can I let the engine rev to while attached to the hose in the driveway without screwing something up? Is 5500-6000 too high?

[transomstand]

That's waaay to high for me. The conditions present in a free running engine at high rpm, as opposed to being underway on the water, are so different, I don't see any benefit to doing that.

[Jay Smith]

IMO I would'nt make it a habit of free reving an engine up without a load attached.

Jay

[strehl]

I wasn't planning on holding it there. I was just wondering if it was going to hurt it if I give it a quick shot of throttle to let it get get up to wot rpm for a spilt sec then bring it back down. I'll just have to wait until I can get out to the lake then. Thanks for the quick replies guys.


Jeff

[boilerdawg]

the first merc i eva had blew up about 2 minutes after i buzzed it.

[flabum1017]

There is no point in revving it past 1000 - 1500 with no load.... it will do more harm than good. Plus revving it that high won't tell you anything.

[pyro]

The service manuals make reference to rod/bearing/crank damage resulting from free-revving, complete with photos of the damage. The result is a "hammering" of the rod bearings against the metal surfaces, imprinting the metal. The patterns of forces of the piston against the cylinder wall are also very different in an unloaded motor than one with a constant load on it.

Why in God's name would you want to let it rev at 6000 rpm? You can set the WOT timing at cranking speed...

[strehl]

Why in God's name would you want to let it rev at 6000 rpm?



I don't know I was just wondering if I could without blowin it up.




There is no point in revving it past 1000 - 1500 with no load.... it will do more harm than good.


Mine revs to about 3500-4000 right when it starts then I pull it back. Thats the only way I can get it to catch. What am I doing wrong?

[pyro]

-Trim it down all the way, so the motor can inhale weakly atomized fuel easier.
-Pump the bulb till it's firm, then give it another firm squeeze for good measure. Sometimes this helps to force some fuel past the needles/seats.

Does your motor have chokes? or an enrichener valve? ("push key")
Either way, use it liberally. Figure out how much it needs depending on how cold it is.

You shouldn't need to give it a ton of throttle to get it to start.

Sync the carbs and check your timing...

[strehl]

-Trim it down all the way, so the motor can inhale weakly atomized fuel easier.
-Pump the bulb till it's firm, then give it another firm squeeze for good measure. Sometimes this helps to force some fuel past the needles/seats.

Does your motor have chokes? or an enrichener valve? ("push key")
Either way, use it liberally. Figure out how much it needs depending on how cold it is.

You shouldn't need to give it a ton of throttle to get it to start.

Sync the carbs and check your timing...


The engine really doesnt want to start if its trimmed all the way down. i think its from too much back pressure then.

It use to have chokes. I just changed over to the carbs I got off the blown xr4 that I got so I just changed over the the enrichment last night. I just found several broken bleed lines and a couple of my foam floats were "fuel logged" also I just replaced old reeds with boyesen so hopefully with the new carbs and fixed bleed lines it will start easier and idle lower. It wouldnt idle below 1300 in neutral before.

[j_martin]

The engine really doesnt want to start if its trimmed all the way down. i think its from too much back pressure then.

It use to have chokes. I just changed over to the carbs I got off the blown xr4 that I got so I just changed over the the enrichment last night. I just found several broken bleed lines and a couple of my foam floats were "fuel logged" also I just replaced old reeds with boyesen so hopefully with the new carbs and fixed bleed lines it will start easier and idle lower. It wouldnt idle below 1300 in neutral before.

Mine doesn't start when trimmed all the way down either. It wants to be level, which is out a bit from the stop.

All the crap you found and fixed would make it idle lousy. You probably got it fixed.

The foam floats all sunk when ethanol got in the fuel. The hard plastic floats are so reliable, nobody, including Mercury, makes replacements. It'd be worth while to find a set of 88 or later 135 carbs to get hard floats.

Rapping an old 2.0 to wot without a load is about the quickest way I know of to blow it up. Maybe in your heart you really want a 2.5.

hope it helps
John

[strehl]

Maybe in your heart you really want a 2.5


I bought an entire 89 xr4 in pieces. It has 1 bad sleeve so as I get some spare cash I'll be working on getting that back together.

I also bought 6 replacement floats via a part number someone posted on here for my old carbs but they dont fit. Would I be able to find just the bowls off of some newer carbs and fit them on my old wh6 uppers? Right now I just put on the xr4 carbs to get the ol 2.0 running. Those carbs only say WH What is the difference between the WH carbs that I now have on and the WH6 that I took off?

[strehl]

Also whats the optimum WOT RPM (under load) for one of these old 2.0?

[pyro]

Factory WOT range for these motors was usually in the 5500-6000 range. Around 6000 rpm is safe, short WOT bursts to 6500+ won't usually hurt either.

[j_martin]

I bought an entire 89 xr4 in pieces. It has 1 bad sleeve so as I get some spare cash I'll be working on getting that back together.

I also bought 6 replacement floats via a part number someone posted on here for my old carbs but they dont fit. Would I be able to find just the bowls off of some newer carbs and fit them on my old wh6 uppers? Right now I just put on the xr4 carbs to get the ol 2.0 running. Those carbs only say WH What is the difference between the WH carbs that I now have on and the WH6 that I took off?

Bingo, I figured that one out.:D

You'll love the XR4. It's a pretty snappy engine bone stock, and it will give you a bit more with the simple mods.

My XR4 carbs are WH41's could be 41a's. .074 mains, .048 idle jets. The A's have .052 idle jets (leaned out a bit.) the 41 number is imbedded somewhere in the plate numbers on the carb, I forget where.

hope it helps
John

[pyro]

I was under the impression that the motor in question was the one listed in the signature, a '78 2.0 1750, with (mismatched?) XR4 carbs. :confused:

[strehl]

I was under the impression that the motor in question was the one listed in the signature, a '78 2.0 1750, with (mismatched?) XR4 carbs. :confused:


The one thats still on the boat is the 78 2.0 1750. I bought a xr4 in pieces with a bad sleeve. I just took the carbs from the pile of parts and put them on the 2.0.

I finally got a chance to put it on the hose to try firing it up. Pumped the carbs full, turned the key on held the enrichner for 2 sec to let all air out of the lines, turned the key and she fired in about 1 sec of cranking.

Where I had everything set to barely get it to idle at 1300-1400 last year was now at 2500 so I shut it down quick lowered idle timing and adjusted throttle plates to go completely closed. Started it back up messed around with timing to see how low she'll go. Got it to idle all the way down to 4-500 rpm with only a miss everyonce in a while. But I brought the idle back up to 10-1100 rpm so once its in the water with some backpressure it should be at 8-900 rpm.

I cant believe how quick it started for the first time since last fall and how nice and consistent the idle is. Only misses every once in a great while. Now I really want to get it out on the water to finalize idle speed and see if I somehow got top end rpm up.