dead spot

[searaymerc]

I have a 86 searay with a 120 hp I have a dead spot about mid throttle but passed that it seems to run fine at wot carb has been rebuilt new accelerator pump. If you push the throttle hard thru it, it dies but if you push it slow you can get passed it to wot. Any ideas idle s fine,timing set 8 degrees btdc.runs fine at wot

 

[alldodge]

I have a 86 searay with a 120 hp I have a dead spot about mid throttle but passed that it seems to run fine at wot carb has been rebuilt new accelerator pump. If you push the throttle hard thru it, it dies but if you push it slow you can get passed it to wot. Any ideas idle s fine,timing set 8 degrees btdc.runs fine at wot

It's still in the carb. Either your accelerator pump is not giving you a full stroke if you have a Merc carb
http://www.mercruiserparts.com/Show...&inbr=963&bnbr=140&bdesc=CARBURETOR+(MERCARB)

Or if you have the Rochester carb it's also not getting a full stoke or the check ball (item 12) on the bottom may not be sealing properly
http://www.mercruiserparts.com/Show...nbr=963&bnbr=130&bdesc=CARBURETOR+(ROCHESTER)

 

[searaymerc]

Thanks I guess I'll tear the carb down again to see what's happening if it's the check ball can you just change the check ball or do you have to change the whole accelerator pump

 

[alldodge]

Thanks I guess I'll tear the carb down again to see what's happening if it's the check ball can you just change the check ball or do you have to change the whole accelerator pump

Before you tear down check to see if your getting a constant stream of gas as you push the throttle forward. If not the accelerator pump and or check ball is the most likely issue (If you have the Rochester carb). If you have a Rochester carb and the check ball is there, check the sealing surface for crud or burs. Finding the same size ball if it is missing would be hard, I would then suggest buying a rebuilt carb and turn yours in as core.

When you rebuilt the carb did you replace the accelerator pump seals, or just get the carb kit without one?

 

[searaymerc]

I just bought the kit and I don't think it had one did I need to get one for it even tho it wasn't in the kit

 

[nazmen1]

I have had the same problem with my Mercruiser 4.3L with a 2 barrel Merc carb.

There is an excellent post from many years back.

Do an Advanced Search using the title "Flat Spot @ 1/2 throttle Merc 3.0 Alpha 1 drive" which gives enough explanation of the types of things it could be.

Mike

 

[searaymerc]

Thanks nazmen1 I'll definitely try looking that up