Riddle me this experts. This is a new to me boat and I don't have much history.
My boat will not exceed 2800rpm after its been run a day or so, I've seen it plane out and do 32mph. Judging by my calibrated ear the 32mph day was around 3800-4000rpm, but I don't have empirical data to back that up as the tach/rpm gauge was left at home for this quick run post headgasket replacement, then later that day, wouldn't exceed 21mph, then the next day wouldn't get over 17mph.
1990 20' Renken MBJ (pretty much the standard 90's open bow I/O 7 passenger boat)
1989 Mercruiser 3.0
Mercruiser 2bbl carb
Alpha 1 drive
14.5" x 19 pitch prop (dinged)
Compression is a bit weak in 1 hole, thinking its gummed up due to a previously blown headgasket (now fixed). Seafoam jumped up compression 10psi in that hole.
Either way it is 145-90-125-150.
Before headgasket: 135-40-50-140, so we are moving in the right direction. Post head gasket (driveway check) it was 135-80-120-145.
Carb has been gone through; twice. Everything but jets and power valve actuator rod/spring has been replaced.
New fuel pump (Not pumping sometime after winter)
New fuel lines from tank to new water/fuel separator system (4hr on it), and back to fuel pump.
New plugs, new points (Timing is 6BTDC and dwell is 32), new cap/rotor/etc. We've validated timing advances up as rpm increases.
New coil (proper spec) All new parts are marine parts when called for. Also new NGK plugs didn't make a difference.
Plugs are showing white (lean) and with my experience, if it is a lack of fuel, that would be the only thing stopping it from reving up. Now with the inconsistency, I think that there is junk in the fuel tank. Tonight we are going to go out with a 5 gallon external tank and see if it runs off that. If it does, that answers our question and the tank has to come out
. I am assuming however that it won't solve it as this boat isn't playing ball nicely.
Now I do know the compression is low in 1 hole, but it should still rev out to proper wot RPM.
Plus the fact that one day it does 2x the speed of the next day, tells me something is messed up.
In order:
Previous owner:
Fall 2011 -Put away, planed and got to 36mph with 5 people in it.
Spring 2012 -Carb was pulled for rebuild after no start condition.
-No fuel at carb, replaced fuel pump
-No spark, replaced coil, distributor cap/rotor/points.
-Put on lake, wouldn't plane and stalled out.
I took over possession of project to fix/purchase from previous owner (frustrated brother in-law).
Drained fuel and put in new fuel, installed water/fuel separator system.
We set points, pulled down carb to validate everything and it wouldn't get over 16mph, one time we trimmed the heck out of it and after taking hard corner after hard corner (small lake) got it to 29mph, never to be repeated.
Came back and compression tested it, determined blown head gasket.
Replaced head gasket, took out on lake, 32mph out of the gate but still seemed a bit off.
Pulled off test lake to put on big lake, turd doesn't get over 21mph.
Pulled plugs, fouled, did compression test, higher than post head gasket (seafoam is clearing up valve seats we are thinking). Replaced plugs.
Put back on lake next morning, doesn't get over 17mph now.
MPH is with calibrated GPS, rpm is from digital tach/timing light.
Where would you go from here, assuming the tank test tonight doesn't work?
My boat will not exceed 2800rpm after its been run a day or so, I've seen it plane out and do 32mph. Judging by my calibrated ear the 32mph day was around 3800-4000rpm, but I don't have empirical data to back that up as the tach/rpm gauge was left at home for this quick run post headgasket replacement, then later that day, wouldn't exceed 21mph, then the next day wouldn't get over 17mph.
1990 20' Renken MBJ (pretty much the standard 90's open bow I/O 7 passenger boat)
1989 Mercruiser 3.0
Mercruiser 2bbl carb
Alpha 1 drive
14.5" x 19 pitch prop (dinged)
Compression is a bit weak in 1 hole, thinking its gummed up due to a previously blown headgasket (now fixed). Seafoam jumped up compression 10psi in that hole.
Either way it is 145-90-125-150.
Before headgasket: 135-40-50-140, so we are moving in the right direction. Post head gasket (driveway check) it was 135-80-120-145.
Carb has been gone through; twice. Everything but jets and power valve actuator rod/spring has been replaced.
New fuel pump (Not pumping sometime after winter)
New fuel lines from tank to new water/fuel separator system (4hr on it), and back to fuel pump.
New plugs, new points (Timing is 6BTDC and dwell is 32), new cap/rotor/etc. We've validated timing advances up as rpm increases.
New coil (proper spec) All new parts are marine parts when called for. Also new NGK plugs didn't make a difference.
Plugs are showing white (lean) and with my experience, if it is a lack of fuel, that would be the only thing stopping it from reving up. Now with the inconsistency, I think that there is junk in the fuel tank. Tonight we are going to go out with a 5 gallon external tank and see if it runs off that. If it does, that answers our question and the tank has to come out
. I am assuming however that it won't solve it as this boat isn't playing ball nicely.Now I do know the compression is low in 1 hole, but it should still rev out to proper wot RPM.
Plus the fact that one day it does 2x the speed of the next day, tells me something is messed up.
In order:
Previous owner:
Fall 2011 -Put away, planed and got to 36mph with 5 people in it.
Spring 2012 -Carb was pulled for rebuild after no start condition.
-No fuel at carb, replaced fuel pump
-No spark, replaced coil, distributor cap/rotor/points.
-Put on lake, wouldn't plane and stalled out.
I took over possession of project to fix/purchase from previous owner (frustrated brother in-law).
Drained fuel and put in new fuel, installed water/fuel separator system.
We set points, pulled down carb to validate everything and it wouldn't get over 16mph, one time we trimmed the heck out of it and after taking hard corner after hard corner (small lake) got it to 29mph, never to be repeated.
Came back and compression tested it, determined blown head gasket.
Replaced head gasket, took out on lake, 32mph out of the gate but still seemed a bit off.
Pulled off test lake to put on big lake, turd doesn't get over 21mph.
Pulled plugs, fouled, did compression test, higher than post head gasket (seafoam is clearing up valve seats we are thinking). Replaced plugs.
Put back on lake next morning, doesn't get over 17mph now.
MPH is with calibrated GPS, rpm is from digital tach/timing light.
Where would you go from here, assuming the tank test tonight doesn't work?
