HELP!
On-going running issues are taking the joy out of my bass boat. I can't go to lakes that are so large that I can't get back on the electric trolling motor. Fishing the river is out of the question.
1979 Champion Pro-style bass boat, 16'10"
1978 Mercury V-1500, 150 HP. (Label on front cover says "1978 M-1500")
The motor starts easily. Idles nicely. When it wants to, it comes out of the hole strongly. When IT wants to. It always runs great "on the hose."
The trouble is that it seems to be flooding or missing when idling in the water. When it is revved up without the prop engaged, it puffs smoke out of the exhaust. When you engange the prop and power up, it bogs down and "loads up," seeming to run on only 4 cylinders. It's rough, like a miss, but reminds me of an old 2-stroke motorcycle I had when its carburetor bowls were over-filling.
With the motor trimmed up to where it is level, it idles smoothly, and is less likely to bog down. However, if the power comes on, the boat seems to want to stand straight up on its tail. Can't do that.
When it's trimmed down for a proper nose-down attitude, it is tipped downward in the back. Seems almost extreme to the eye, but that's the way the whole system was designed, and that's how the boat comes out of the hole cleanly. Anyway, it's in this position where it bogs the worst.
Also, if it gets up to speed, it's not steady. Max power seems to cut in and out. On for 5 seconds, off for 5 or 10. Sometimes won't come up to full speed for a mile or so, then power comes in for a couple miles, then drops off again.
Last evening, I took the covers off, and removed the air box, so the carburetors were open to the air. I wanted to watch to be sure the chokes were staying fully open, and look for signs of over-fueling in the throats. Without the air box in place, it idled better. And, every time power was applied, it acted like it wanted to bog at first, then power came up. The boat came up on plane faster than it ever has. The crazy thing without the air box is that it never bogged down (slightly at first throttle-up) or failed to come strongly out of the hole.
Early on, I was told that it was probably the fuel pump. If I reached back and gave the priming bulb a couple of squeezes, sometimes the power would come on. At that time, you could make the thing drip fuel using the primer. So I rebuilt the carbs and the fuel pump. The priming bulb now pumps up tight. No drips. Squeezing the priming bulb while it's bogging down has no affect, and the bulb is tight, meaning the carbs are full and the float needles are working.
I have long suspected that the problem could be that the carbs are allowing fuel to run "downhill" into the motor when it's trimmed down and idling. But I have no way to know that. I have also suspected the ignition system, as it is old and I have had to make some repairs that I knew it needed.
Everything I have done seems to "help a little." But still the problem remains. Here's what I have done, roughly in order over the last three seasons. Everything is guided by the official Mercury shop manual for this motor.
-- Replaced the spark plugs. NGK BU8H. Closest replacement to the original surface-discharge plugs.
-- Replaced the head and cover gaskets, to repair a water leak at the top of one head. Fully de-carboned the heads and piston tops. Compression on all 6 cylinders is 105 to 115 psi. Replaced the totally inoperative thermostats at the same time.
-- Rebuilt the carburetors. Took them off a second time to double-check the floats. These carbs are completely unadjustable except for idle speed, and the float levels are exactly as specified. Applying pressure with the priming bulb shows no float needle leakage. Only way to adjust mixtures is to replace jets, if you can get them at all.
-- Rebuilt the fuel pump.
-- Replaced the O-ring on the gas cap that was letting rain water get into the fuel tank. Tank vent is free and open.
-- Experimented with fuel filters. Settled on a low-restriction glass unit that lets you see the screen and any water or other contaminates that may be in the fuel.
-- Replaced one igniton box that went bad.
-- Adjusted ignition timing.
-- Plugged six holes in the exhaust box (and the outer cover around it) that a previous owner had drilled. I guess he thought (wrongly!) that reducing back pressure would make more power. Or maybe he just wanted the noise. All I know is, this quieted it down to a pleasant level. PLUS this made it idle within specs for the first time since I got it.
-- Adjusted ignition timing.
-- Replaced the second ignition box this spring. This finally and completely solved hard starting issues that it used to have.
-- Experimented with plug wires, replacing the stock solid-wire cables with high-performance helical-wound wire-core suppressor wires. (Leftover pieces from my car project.) No difference. Put the old wires back on, with new rubber boots and silicone dielectric grease.
-- Replaced spark plugs with NGK BP8H-N-10. This is a "conventional" extended tip "V-Power" spark plug. This extends the spark out into better contact with the air/fuel mixture. (Yes, I measured for clearance. Way more than enough.) I figure with unleaded gas and modern full-synthetic oil, fouling should not be an issue. (That's what surface-discharge plugs are for). Same heat range as original. 0.040" gap. The surface gap on the original plugs measures 0.060", and that smooth round surface is horrible for initiating a spark.
NOTE about the spark plugs: These plugs made a major improvement in idle quality and in top-end power. I was concerned that my prop pitch was a step too high. Not any more! However, they did not solve the main problem.
About the only thing I have not done is replace the coils. However, they all test within specs. But I also know they are 33 years old. A tech at Mallory igntion confirmed for me that coils can "get old" yet still test within specs. But I think this may apply more to the top-end on-off power feeling, more than the low-end bog. I'm slow to do this because the budget won't take the hit right now. Best price I have found is about $25 each.
So... I'm going to check the ignition timing one more time. The original movable marker is missing from the top housing. But I used a white wax pencil to mark its correct position. I use an electronic timing light and electronic test tach to set the timing. The timing adjustment is fully mechanical, tied to throttle position. I have a feeling it will still be on spec from the last time.
Please, I am very open to suggestions. As I said, having this problem makes the motor so undependable that it's taking the joy out of boating. Can't fish large lakes. Can't fish anything with a strong current. One good thing about our flooding this year, I guess. I wouldn't be going after Missouri River catfish even if the motor was perfect. Too much debris floating downstream.
The ultimate solution would be to replace the motor with a fuel-injected unit. But wow! For the price of even a used one, I'd be just as well to spend a little more at Bass Pro and get that new Nitro X-5 I've been eyeing. The budget definitely won't absorb a replacement motor or new boat!
On-going running issues are taking the joy out of my bass boat. I can't go to lakes that are so large that I can't get back on the electric trolling motor. Fishing the river is out of the question.
1979 Champion Pro-style bass boat, 16'10"
1978 Mercury V-1500, 150 HP. (Label on front cover says "1978 M-1500")
The motor starts easily. Idles nicely. When it wants to, it comes out of the hole strongly. When IT wants to. It always runs great "on the hose."
The trouble is that it seems to be flooding or missing when idling in the water. When it is revved up without the prop engaged, it puffs smoke out of the exhaust. When you engange the prop and power up, it bogs down and "loads up," seeming to run on only 4 cylinders. It's rough, like a miss, but reminds me of an old 2-stroke motorcycle I had when its carburetor bowls were over-filling.
With the motor trimmed up to where it is level, it idles smoothly, and is less likely to bog down. However, if the power comes on, the boat seems to want to stand straight up on its tail. Can't do that.
When it's trimmed down for a proper nose-down attitude, it is tipped downward in the back. Seems almost extreme to the eye, but that's the way the whole system was designed, and that's how the boat comes out of the hole cleanly. Anyway, it's in this position where it bogs the worst.
Also, if it gets up to speed, it's not steady. Max power seems to cut in and out. On for 5 seconds, off for 5 or 10. Sometimes won't come up to full speed for a mile or so, then power comes in for a couple miles, then drops off again.
Last evening, I took the covers off, and removed the air box, so the carburetors were open to the air. I wanted to watch to be sure the chokes were staying fully open, and look for signs of over-fueling in the throats. Without the air box in place, it idled better. And, every time power was applied, it acted like it wanted to bog at first, then power came up. The boat came up on plane faster than it ever has. The crazy thing without the air box is that it never bogged down (slightly at first throttle-up) or failed to come strongly out of the hole.
Early on, I was told that it was probably the fuel pump. If I reached back and gave the priming bulb a couple of squeezes, sometimes the power would come on. At that time, you could make the thing drip fuel using the primer. So I rebuilt the carbs and the fuel pump. The priming bulb now pumps up tight. No drips. Squeezing the priming bulb while it's bogging down has no affect, and the bulb is tight, meaning the carbs are full and the float needles are working.
I have long suspected that the problem could be that the carbs are allowing fuel to run "downhill" into the motor when it's trimmed down and idling. But I have no way to know that. I have also suspected the ignition system, as it is old and I have had to make some repairs that I knew it needed.
Everything I have done seems to "help a little." But still the problem remains. Here's what I have done, roughly in order over the last three seasons. Everything is guided by the official Mercury shop manual for this motor.
-- Replaced the spark plugs. NGK BU8H. Closest replacement to the original surface-discharge plugs.
-- Replaced the head and cover gaskets, to repair a water leak at the top of one head. Fully de-carboned the heads and piston tops. Compression on all 6 cylinders is 105 to 115 psi. Replaced the totally inoperative thermostats at the same time.
-- Rebuilt the carburetors. Took them off a second time to double-check the floats. These carbs are completely unadjustable except for idle speed, and the float levels are exactly as specified. Applying pressure with the priming bulb shows no float needle leakage. Only way to adjust mixtures is to replace jets, if you can get them at all.
-- Rebuilt the fuel pump.
-- Replaced the O-ring on the gas cap that was letting rain water get into the fuel tank. Tank vent is free and open.
-- Experimented with fuel filters. Settled on a low-restriction glass unit that lets you see the screen and any water or other contaminates that may be in the fuel.
-- Replaced one igniton box that went bad.
-- Adjusted ignition timing.
-- Plugged six holes in the exhaust box (and the outer cover around it) that a previous owner had drilled. I guess he thought (wrongly!) that reducing back pressure would make more power. Or maybe he just wanted the noise. All I know is, this quieted it down to a pleasant level. PLUS this made it idle within specs for the first time since I got it.
-- Adjusted ignition timing.
-- Replaced the second ignition box this spring. This finally and completely solved hard starting issues that it used to have.
-- Experimented with plug wires, replacing the stock solid-wire cables with high-performance helical-wound wire-core suppressor wires. (Leftover pieces from my car project.) No difference. Put the old wires back on, with new rubber boots and silicone dielectric grease.
-- Replaced spark plugs with NGK BP8H-N-10. This is a "conventional" extended tip "V-Power" spark plug. This extends the spark out into better contact with the air/fuel mixture. (Yes, I measured for clearance. Way more than enough.) I figure with unleaded gas and modern full-synthetic oil, fouling should not be an issue. (That's what surface-discharge plugs are for). Same heat range as original. 0.040" gap. The surface gap on the original plugs measures 0.060", and that smooth round surface is horrible for initiating a spark.
NOTE about the spark plugs: These plugs made a major improvement in idle quality and in top-end power. I was concerned that my prop pitch was a step too high. Not any more! However, they did not solve the main problem.
About the only thing I have not done is replace the coils. However, they all test within specs. But I also know they are 33 years old. A tech at Mallory igntion confirmed for me that coils can "get old" yet still test within specs. But I think this may apply more to the top-end on-off power feeling, more than the low-end bog. I'm slow to do this because the budget won't take the hit right now. Best price I have found is about $25 each.
So... I'm going to check the ignition timing one more time. The original movable marker is missing from the top housing. But I used a white wax pencil to mark its correct position. I use an electronic timing light and electronic test tach to set the timing. The timing adjustment is fully mechanical, tied to throttle position. I have a feeling it will still be on spec from the last time.
Please, I am very open to suggestions. As I said, having this problem makes the motor so undependable that it's taking the joy out of boating. Can't fish large lakes. Can't fish anything with a strong current. One good thing about our flooding this year, I guess. I wouldn't be going after Missouri River catfish even if the motor was perfect. Too much debris floating downstream.
The ultimate solution would be to replace the motor with a fuel-injected unit. But wow! For the price of even a used one, I'd be just as well to spend a little more at Bass Pro and get that new Nitro X-5 I've been eyeing. The budget definitely won't absorb a replacement motor or new boat!