245hp 20ft IMP can't get on plane... Few questions

[jstcrzyengh]

Hello everyone,<br /><br />Great site I have really enjoyed reading everything and have picked up a few ideas on what could be my problem, but I wanted to see what everyone else thinks.<br /><br />The boat is a 1971 IMP 20ft Cuddy Cabin. It has a OMC electric drive outdrive and a Chevy 350, I assume from the same year, but I am not sure.<br /><br />While taking the boat out yesterday after $2,300 worth of new outdrive repairs which included a new Forward spring, new reverse magnet, new tilt motor, new shift cable, new wiring, and new warm up lever for the shifter, (I just purchased the boat ugh!) we could not get the boat on plane. At WOT it would maybe do 15 KNTS. It was a true dog. Before I start ripping things apart to figure it out let me give you some of the first observations. <br /><br />1. The tachometer would only go up to 1500 RPM, the engine sounded higher, but the Tach wouldnt show it. Now out of the water at home on the trailer with little to no strain on the engine we can get it to 3200 RPM no problem.<br /><br />2. I noticed it appears to be a VERY small leak from the right side of one of the manifolds that drips onto the spark wires, now it idles just fine, I am not noticing any stumbling like it is not getting spark... But would rather let everyone know that upfront.<br /><br />3. The distributer cap is loose. The Engine cover can easily knock it off. Now while that will kill the engine, putting it back on it fires right up, but I am thinking that this could have something to do with it. The Distributer is a mallory Distributer. I believe it is a electronic ignition upgrade distributer.<br /><br />4. Fuel, it had some fuel sitting in there for at least 4 months, from what I am told anyway. Could be bad, but not sure. <br /><br />Here is my course of action, but it just doesnt seem to be what the problem could be, but I am use to rebuilding cars, not boats per say.<br /><br />Rebuild the carb, I believe it is a 2bbl Holley. I would like to upgrade to a 4bbl soon. Replace all the spark plugs and spark plug wires. Change oil and filter out to mobil 1. Change out the fuel filter. Run the starbrite fuel treatment. Possibly install a new distributer. Any other ideas for the lack of speed? The boat weighs in at around 2800lbs dry. We had 20gallons of fuel, and I even tried moving the guys upfront but it did no good. Any ideas to do as well? I would like to do everything all at once.<br /><br />James

 

[moderator1]

Re: 245hp 20ft IMP can't get on plane... Few questions

Moving to I/O questions.

 

[tommays]

Re: 245hp 20ft IMP can't get on plane... Few questions

i guess that you did not try out the boat on the water before you bought it<br /><br />you are starting out with so many things wrong it is to hard to guess<br /> <br />but start with the ingition system the cap should not come lose<br /><br />the water leak is a big deal and you should find the cause before you do any more major work<br /><br />tommays

 

[jstcrzyengh]

Re: 245hp 20ft IMP can't get on plane... Few questions

Hi Tommays,<br /><br />Unfortunately it was a buy in with a buddy of mine and he backed out and it's kind of a mess. We got the boat for a pretty good deal, but true we got sucked into a lot of problems. Is there something you would check on first? For some reason it seems to be more of a problem under load. The engine was recently rebuilt and sounds strong. I am just looking for some kind of game plan to really go out and counter this thing. With that engine I would think that this boat should get up no problem. A couple of different people have told me 35knts wouldnt be a problem at WOT. Any ideas?

 

[POINTER94]

Re: 245hp 20ft IMP can't get on plane... Few questions

No good answers here but 35knts sounds about right maybe a tad more. Did you do a compression test on all the cylinders? Sounds like concentrating on the distributor is the right first step. They typically don't go bad on a boat but do a continuity test on the plug wires and check the coil to make sure you are getting a good spark. Is there excessive exhaust smoke? How do the plugs look? Try strobing the engine to make sure the tach is accurate. (you should be making better than 4300rpms) Is the prop in good shape and of appropriate size and pitch?<br /><br />Just some idea's, good luck. The weight to horsepower on your boat is just fine and you should not have any problems planning out. Yes a four barrel will give you a boost.

 

[Bondo]

Re: 245hp 20ft IMP can't get on plane... Few questions

Ayah,<br />I think if you proceed along the lines you state,<br />And,<br />Follow up with Pointer's Ing.Checks,+ Compression Test,.. You Should be making the required Horsepower.....<br /><br />After that,<br />It's on to the Prop,+ drive.....

 

[highaltitude]

Re: 245hp 20ft IMP can't get on plane... Few questions

what pitch prop are you using? i would start checking the simplest and cheapest things first.

 

[jstcrzyengh]

Re: 245hp 20ft IMP can't get on plane... Few questions

Well, <br /><br />Tomorrow I am going to go down and do a compression test. I believe the previous owner converted to Electronic ignition, so I will try replacing the cap and rotor, if original than change out the points. I will also do a complete tune up. Oil, plugs, plug wires, etc... Someone I spoke to said that the carb could have some issues, but I didnt notice any surging. It just felt like the power wasnt being produced or just couldnt move the boat. Another thing is if we dropped from "WOT" to idle, the engine died. I just had over $2300 done to the drive and it should have no issues, hopefully anyway. I had the reverse magnet changed, and the forward spring changed. Along with a new throttle cable, however I was having this problem prior to taking it in. Quick question for you guys. I have a shortblock that I built, that by all standards is a marine shortblock. It is a completely forged and blueprinted bottom end. My buddy said it should drop right in since all of the mounting points were the same, but he didnt know if the outdrive hooked up to a flywheelor to the crank directly. I would like to just go with a new motor, some vortec heads and be done with it...<br /><br /><br />I have heard good things about the Holley 4160... I wonder if that is a straight swap.

 

[Wart T]

Re: 245hp 20ft IMP can't get on plane... Few questions

Hull might be saturated. Like they said simple things first. Prop? Tune up? Compression test? Exhaust shutters?

 

[Jdeagro]

Re: 245hp 20ft IMP can't get on plane... Few questions

You said that the motor would wind up to 3200 RPM on the trailer. it should go easily to 5000 RMs.<br /><br />Look at the ignition system, get the correct specs. Look at the fuel system. You are not performing under a load - either ignition or fuel. I would start with ignition.