No hole shot, breaking up top end

[mnmfors]

Hello everyone! I have a 1977 150 hp Mercury inline six I need help tuning. I have been working on this engine for some time now off and on. It is mounted on an older 17ft. Glassstream bass boat. <br /><br />I Bought this engine with no spark but 150lbs +-2lbs. compression each cyl. <br /><br />I changed the switchbox and distributor. (type 2 ignition with trigger in distributor) Timed it according to my manual (seloc). <br /><br />Rechecked compression warm, still 150lbs. <br /><br />I cleaned and sealed all electrical connections, grounds. <br /><br />Carbs were leaking so I cleaned them real good, reinstalled, adjusted according to my manual.<br /><br />I installed a hot foot.<br /><br />Changed lower unit oil to sythetic (no water in old oil). Unit shifts normally with no load (in yard) Engine starts and runs beautiful. Engine cools excellent. Keeps battery charged.<br /><br />Guy I bought it from said he had it rebuilt and he had lightweight racing pistons put in it, but I cant be sure. <br /><br />It has a racing lower unit (low water pick-up) <br /><br />The exhaust is run out of the mid section, sounds real good <br /><br />First of all, I know that my prop is wrong. My engine came with a 15x24 chopper. I have no hole shot, takes 4-5 seconds to get on a plane (about 20 mph). I have to lift the prop halfway out of the water to keep it from stalling, then lower it down with a small amount of throttle. Anyone have a suggestion of where to start? Maybe a 14x21? I had a 1985 90hp with a SS 14x19 on this same boat that worked real well. The 90hp ran 5500 WOT.<br /><br />Secondly, I am "Breaking Up" after 4500-4600. I know my WOT should be at least 5200 for sure. It acts like it is running out of gas. I hit my choke (enrichner valve), did not help. I didnt run it long like that so I didnt damage the motor if it is a fuel problem. Or maybe I made an error when I timed it. Any suggestions would be appreciated.<br /><br />Another thing is someone for some reason took off the mechanincal fuel pumps and it now has an electic fuel pump. I am a little suspicious of this pump but it seems to feed the carbs fine. <br /><br />Thanks in advance for any help.

 

[ZmOz]

Re: No hole shot, breaking up top end

I just recently had a problem with the same engine, wouldn't go above 1200 RPMs under load. I rebuilt the fuel pump and decarbed the engine...now it runs great.

 

[The Marine Doctor]

Re: No hole shot, breaking up top end

Recheck your timing. Look for damage to #3cyl.<br />Trying a different pitch prop might be a good idea as well.<br /><br />TMD

 

[mnmfors]

Re: No hole shot, breaking up top end

Thanks for the suggestions, at least I know I am on the right track. <br /><br />I guess I will recheck the timing and compression. <br /><br />I am still wondering about that fuel pump is adequate. Has anyone else used these elec fuel pumps in place of a mechanical pump?

 

[mnmfors]

Re: No hole shot, breaking up top end

Ok, plenty of compression in each cyl. so I did no damage as of yet. <br /><br />I do believe that my timing is way off. I am having problems setting the timing. When I set the timing after changing the distributor, I had help, from someone I thought was knowledgeable. <br /><br />I check the timing in the yard and it shows 21 deg before top dead center. I looked in my book and it should be 6 degrees btdc at idle. 21 deg max spark. <br /><br />I tripple checked to be sure I installed the belt with the distributor in the correct position. Engine idles perfect in this position. I moved the distributor over both ways two teeth (one at a time) and the engine ran rougher each time. I moved the belt/dist back to original position, and it idles fine again.<br /><br />I dont know who worked on this engine before me, so I thought someone may have the flywheel on wrong (this flywheel separates without actually pulling it) I moved it over one set of bolts and then it is way off mark.<br /><br />I have read through the timing section in my manual at least 20 times, and still cant come up with the solution. <br /><br />Another thing, I cant get the idle below 1500 rpm. This is in the yard, not the water, so maybe this is ok.