what prop for my omc 4.3 cobra

[bigbo27]

Re: what prop for my omc 4.3 cobra

get hte extra prop this saturday hope its a good match & as far as getting my current prop reconditioned I think i will just buy a new do to the fact that the marina charges just a few dollars less than getting a new one

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

bought the 1986 sea ray 4.3 cobra engine good needs a starter & outdrive good gave 250 for the whole boat used the prop on mine hope it works well try to let you know tommorow

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

Had the boat out today with the trial prop. It got up on plane much better the gps speed was 36 mph & rpm was at 3300. The prop i had was a 14.5 x 19 the trial prop is a 15 x 17 how can i get the rpms up going to hook up an aftermarket tach & see how close they are . Any help would be helpfull thank you. Had about 7 people on board

 

[john cole]

Re: what prop for my omc 4.3 cobra

Yes definitly get a different tach hooked up, something isn't right. if your rpms are the same with the smaller pitch prop your speed should be less, but your saying the speed and rpm's where the same with both props?

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

yes they were the same but i had 2 people the last time 8 yesterday plus went from the 14.5 x 19 to a 15 x 17 which i was told would equal out ( no gain).also added hydo-foils i think thats what they are called (fins bolted on each side of the lower).Does the extra weight make a huge diff. on the rpms I was thinking it would be working harder so the speed would be down & rpms up becaause of the extra work the engine is doing.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

well hooked a different tach up better water conditions & the specs were 3700 rpm @ 35-36 mph got the rpm's up but do I still need more?

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

Help I really dont know where to go from here . From everything I have read on here i should atleast be at 4200 rpm which is the recommended rpm. What do you think Plz need some advice.

 

[john cole]

Re: what prop for my omc 4.3 cobra

i would check and see if your throttle really is opening the carb wide open. diconnect you cable from the carb and work it by hand to be sure the throttle plates are opening all the way, then reconnect and re check them using the throttle handle (engine off) adjust if needed, and re check your timing.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

I have done this but I'll re check it . It may be a day or so to get this done do to my work but I really do Thank you for your advice with this i will post my results asap

 

[john cole]

Re: what prop for my omc 4.3 cobra

You also need to make sure you timing is set for WOT not idle, it will make a big difference too. this is where the timing light with an advance feature on it will help. if you are still lagging on rpm's sound like you will need to to check the compression in the cylinders.

 

[bigbo27]

Re: what prop for my omc 4.3 cobra

not sure what the timing should be set at the manual says 1 btdc at rpm but it dont say at what rpm what do you recommend & how to go about it if not at idle (in water,in gear)