'89 OMC 4.3 Liter RPM's

[Liquid_force]

Hi - 1st post - I'll try to keep it short.<br /><br />Just bought an '89 sunbird with a 4.3 OMC. It starts and runs fine - very smooth. However, at full throttle it "feels" like it's running at 3/4 throttle and it tops out at 4100 rpm and about 36 mph. I have spent a lot of time around other 4.3's (an '88 and a '94) in similar sized boats and they seemed MUCH more powerful (50+ mph and more low end acceleration). <br />The carb has recently been overhauled - is there a fuel adjustment that I can make? Or could it be a prop issue? Does anyone know the max recommended RPM on the 4.3 OMC's?<br />The way it's running I think it would be pretty difficult to get a heavy slalom skier out of the water.

 

[tmclendon]

Re: '89 OMC 4.3 Liter RPM's

RPMs should be 4200-4600. If I had to guess I'd say look for a vacuum leak in the carb.<br />Tom

 

[Lark40]

Re: '89 OMC 4.3 Liter RPM's

Also, 4400-4800 rpm if you have the 4-bbl carb.

 

[Liquid_force]

Re: '89 OMC 4.3 Liter RPM's

I will definitely look around for a vacuum leak. I'm looking for the typical 1/4" hose hanging loose, correct?

 

[Boatin Bob]

Re: '89 OMC 4.3 Liter RPM's

If you didn't do the carb make sure it has the right gasket on the manifold and it's torqued down all the way, make sure the throttle cable is allowing the carb to open up all the way. The prop pitch might be too big as well, smaller pitch will bring your RPM's up and give a better hole shot.

 

[shussh]

Re: '89 OMC 4.3 Liter RPM's

Hello--<br />I have the same exact problem with an 88' 21 Sunbird with a 4.3 OMC. It runs perfectly smooth... but I just dont get the RPM's Im running a 17 pitch prop. I posted the same problem last week. I havent tried any of the suggestions. Please let me know what happens and what corrects your problem.<br /><br />Thanks,<br /><br />Ron<br />shussh1@yahoo.com

 

[tpatwil]

Re: '89 OMC 4.3 Liter RPM's

I have the 84 3.8L (similar to your 4.3)<br />Addeed Edelbrock Marine 4BBL intake, and carb<br />now about 200 hp<br />Replaced the points with a Pertronix unit- new hot marine coil.seemed to help RPMS<br />HAd to add a "FIX" to keep the OMC ESA module working with the Pertronix<br />Remember<br />Boat loading and prop pitch and abient temperature all affect rpm

 

[tmclendon]

Re: '89 OMC 4.3 Liter RPM's

Hey Tim how did you get the alternator to fit? I did the same mod to my '83 3.8L-4 Barrel (Edelbrock #2111 and a Holley 450 Marine carb) and the new manifold relocated the thermostat housing a bit to the right, just enough to block the alternator. I had to put the stock intake back on, just curious as to if you ran into this problem and how you solved it. Drove me crazy. Finally sold the Edelbrock intake on e-bay last week...<br /><br />Tom

 

[Liquid_force]

Re: '89 OMC 4.3 Liter RPM's

Prop is the correct (specified) size, and the throttle cable seems to be opening the carb fully.<br /><br />How would I know if the carb gasket is correct?

 

[tpatwil]

Re: '89 OMC 4.3 Liter RPM's

Had to fab a new alternator bracket that <br />allowed the alternator to pivot around the stock pivot point, up & away to clear the thermostat.<br />How does you 3.8L run with the new carb?<br />I have the pertronix conversion on mu dist. and am<br />adding the "diode fix" this weekend.<br /><br />TIM

 

[tmclendon]

Re: '89 OMC 4.3 Liter RPM's

I couldn't swing the alternator up any further as it hit the engine cover. It was a comedy of errors, like most of my projects!<br /><br />Anyway I haven't run it yet with the carb, I managed to mess up the ignition while working on the manifold so it's in the shop now. Turned out I had shorted the condenser to the dist. housing. Like I said, it was a comedy! I'm hoping it will run as well as it used to. How much extra speed did the new carb/manifold get you?<br /><br />Tom