Replacement engine from Rapidomarine...

[John_S]

Re: Replacement engine from Rapidomarine...

Can we get clarification on the ignition system? It now sounds like you have a points system, but prior posts indicated a V6 module that would indicate a T4 ignition. Possibly mis-matched ignition components, using a resister wire coil with T4?


You mention pushing the carb AV either way didn't make a diference. Even if it didn't increase, I'd expect it to fall on its face by opening the AV.

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

You mention pushing the carb AV either way didn't make a diference. Even if it didn't increase, I'd expect it to fall on its face by opening the AV.[/QUOTE]

Good point..was wondering about that also. If opening the air valve didn't make any difference, were the secondaries opening? Is the throttle linkage grossly mis-adjusted?

 

[CharlieB]

Re: Replacement engine from Rapidomarine...

It would be a LOT quicker, and easier to do a spark gap test then a cyl leak down test.

Remember, the coil wire gets used for EVERY pulse while individual plug wires only get THEIR pulse. I've seen far more bad coil wires than plug wires.

Marine/industrial motors often use stainless core wires instead of carbon core with a single stainless strand. The reason being, when, not if, when the carbon core arcs a gap (burns) as the gap enlarges, it also burns, melts, creating a gap in the stainless winding, thus an air gap begins to grow INSIDE the sheath, unknown and unseen, adding resistance to that wire, until it begins to fail to carry the load, cyl's begin to misfire, limiting RPM.

I'd be willing to bet your leak down tests will be fine.

 

[choochooharley]

Re: Replacement engine from Rapidomarine...

I agree check the spark.

 

[CharlieB]

Re: Replacement engine from Rapidomarine...

Still curious exactly WHAT spark plugs are you using and HOW MUCH gap? If over .032 then regap and retest.

Pictures of them showing their burn/color could also be helpful.

When manually opening/closing the A/V on a Q-jet makes NO difference in the operation of the motor then you can be SURE that it is NOT a carb problem limiting the motor.


Either a weak ignition or an exhaust restriction is the problem. Closer inspection and testing will reveal the truth.



You stated that you ran a wire from side to side thru the Y-pipe to check for a dropped rag, but did you pull the outdrive and LOOK?

Also double check the exhaust passages thru the upper and lower gear boxes to be CERTAIN there is nothing that isn't supposed to be there, i.e., the neighbors cat, mouse nest, etc.

 

[Aloysius]

Re: Replacement engine from Rapidomarine...

Is the polarity on the coil correct? Negative to the distributor?

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

I am ready to revive this thread, the snow is gone and have been mulling this damn boat over in my mind all effen winter. I have new ign wires, coil and fuel pump to install. I also have had the thoughts of what if the carb were leaking, dumping too much fuel right about 28k rpm, making it too rich, I.e., choking it... I saw this as the oil quickly was fouled with little time on it-this of course could also be blowby, but, there is no evidence of this at the valve cover vents. I will remove the carb and check for leaks on the bench, yet again. If anyone has more to add, please feel free.
Many thanks from this overworked, underpaid boat mechanic..
Keno

 

[leo319]

Re: Replacement engine from Rapidomarine...

ordering a 4.3 long block this week from rapido... Oh so much work ahead of me....

 

[Normspeed]

Re: Replacement engine from Rapidomarine...

This is probably so far off as to be stupid but I had a similar problem with my 86 4.3 OMC (stringer). It ran perfect right up to planing rpms, then would not rev up enough to get up and go. I'm only tossing this out because so many things have been checked already. Mine turned out to be simple. The OMC has a "shift interrupter" designed to reduce rpms at the moment you shift from neutral to forward or reverse. It causes a brief interruption to the ignition to drop the rpms, for a smooth shift. Mine was improperly adjusted and was interrupting the ignition as the throttle was advanced in forward gear. I sorted that out and the problem never occurred again. Sorry if this is just useless info. I don't know if your mercruiser has such a gadget. Probably not, but after reading all these posts I see no one brought it up.
I feel your pain.

 

[FreeBeeTony]

Re: Replacement engine from Rapidomarine...

Any news here?

Was the problem ever resolved?

 

[Kevoz]

Re: Replacement engine from Rapidomarine...

No, the problem has not been resolved. Last week I replaced the fuel pump, removed the carb, sealed the fuel bowls in it and rebuilt it yet again and also replaced the ignition coil. Took it to the lake last Friday and now it idles ever so smoothly and could only muster up 2600-2700 revs on the water. I left the spark arrestor in place while trying to get the boat to plane and sprayed starting fluid into it, the engine fell flat on its face when I did this....so, I guess its not a fuel problem. I have since spoken with a certified Mercruiser mechanic who also spoke with his daily boat mechanic co-workers and they all went straight to the high compression as the culprit. He also suggested replacing the ignition module, but, I have seen full advance and it has not missed once. I did some research on high compression problems and one of them was a rpm ceiling being a problem in some engines with high compression. It was also suggested that I get a prop with less pitch as to spin the engine faster on the water. I have all but given up and will be calling Raul at Rapidomarine tomorrow, I am sure he will be a big help...
I am just about to say it has beaten me.
cheers,
Kevoz

 

[alilley]

Re: Replacement engine from Rapidomarine...

this is just a thought here as i am by far no master mechanic.
i just finished readding this hole thread fropm start to finish. in a nut shell the boat ran fine just sprayed oil out which caused the engine swap. once you got the new crate engine in you pulled the lifters out of the old motor and put them in the new one cuz they was roller lifters correct? did you happen to double check to make sure they was the same legnth? if the roller lifters are shorter then the valves would open all the way not allowing proper air fuel in or out causing loss of power. i can see how it would spin right up on the muffs as it would take a hole lot less power there as it is not pushing a boat gear and water.

what about as mentioned before what about checking the outdrive portion of the exhaust for blockage?? i once had a dirt bike (grant it it was a 2 strok but princapulls are the same air goes in and it has to come out ) that i bought for like 50 bucks guy said it dont rev up i took it home fired it up. sure enough it would hit one rpm and hold it. pulled the exhaust off and it would rev up. talked to dad to see what to try and he took the torch stuck it in the muffl;e and let it sit for like 45 min and burned out all the old carbon. mran like a top till i sold it....man i miss that bike

 

[Fish Foot]

Re: Replacement engine from Rapidomarine...

How did the call to Raul at Rapidomarine go?

I know your confidant about the rocker arms but I would still try the ones that came with the motor incase something is getting missed here. Another rocker arm swap would be a cake walk after what you have been through. Also I'm going to post a link that tells how to adjust valves on a chevy smallblock step by step. Good Luck!



http://www.classiccarauto.com/impala/how_to/adjust_valves.shtml