OMC 4.3 No Power

[mohogg]

Hey guys<br /><br />I've got a OMC 4.3 1986 with the rochester 2bbl carb. Is it just a pipe dream to want to hit 40mph. Its in a 17 ft starcraft bowrider. I've got a manual and rebuilt the carb. Set the timing the best I could and it won't idle at 550 -600 like it should. What about point gap? what if its off by .01? Vacuum leak? The boat runs smooth and hits 4400 rpms. I have a 14 1/2 x 19 prop and I cant get above 28 mph with just me in it . ive also tried a 17p prop but still same speeds just better hole shot. HELP!!!

 

[tmclendon]

Re: OMC 4.3 No Power

40 Should be no problem with that combo. I have a 16.5'-3.8L that does over 50 with a 19" prop. Something ain't right. Check the compression and make sure you don't have a dead cylinder. You might have to get professional help with this one.<br /><br />Good Luck!<br /><br />Tom

 

[Lark40]

Re: OMC 4.3 No Power

At 4400 rpm's, you engine is in it's top range, which is 4400-4600.<br /><br />I have the same engine, it is rated at 170 hp.<br /><br />My 22' aluminum cuddy cabin hits 39 mph at 4500 rpm using either the 17" prop. That has been measured with multiple GPSs.<br /><br />So, something is wrong, but it may not be the engine. Does the boat have barnacles or some other hull problems?

 

[mohogg]

Re: OMC 4.3 No Power

No hull problems. She was as clean as a whistle when I put it in two weeks ago. I've been getting the same speeds all along. The boat is new to me this year I bought it used and fixed it up. The motor runs as smooth as can be but I'll check the cylinders for compresion just to make sure. I did the carb myself and the points so I am most suspisious of them. Thanks i'll keep you informed.

 

[DJ]

Re: OMC 4.3 No Power

mohog,<br /><br />If you're hitting 4400 rpm's. with that prop., your speedometer is lying to you. As they frequently do. The math doesn't add up.<br /><br />Check it with GPS.

 

[mohogg]

Re: OMC 4.3 No Power

UPDATE...... OK guys here is the deal. I had the point gap way to big. I check the dwell it was fine set the gap right and hooked the dwell/tach meter up to test the rpms. I am now geting obout 36 mph with 3900 rpms out of the 19 pitch prop and about 33 mph and 3900 rpms out of a 17 pitch prop. So I am doing better. I still want to get to mid 40's. any sugestions on gaining speed without lowering the rpms? I need to be around 4200 - 4600. Thanks for your replies.

 

[akriverrat]

Re: OMC 4.3 No Power

sounds like something stopping engine from going over 3900 rpm. or, more likely, the tach is telling you lies.

 

[cbr9rr]

Re: OMC 4.3 No Power

I agree with you, with a 4.3l and a 17ft. boat you should be hitting at least the mid 40's. My 19ft. Chaparral bowrider with a 4.3 hits 45-47mph with a 21 pitch Lazer 2 prop. Did you set your timing properly? I think a good starting point is 8-deg on a 4.3L. Check your compression, replace plugs and wires. Is your throttle cable opening up your carb all the way. Have you played with your trim on your outdrive? That's the only way I can get my boat over 40!! Hope this gives you a few things to look at.