FrenchRIverMorgan
Recruit
- Joined
- Jul 30, 2020
- Messages
- 2
Hey Guys.
First off let me apologise in advance for the wall of text but I just want to give as much info as possible about what steps Ive taken so far, so I can save us all some time.
I'm kind of lost and would be really appreciative of some help. Im not bad with a wrench but I've never dealt with carbs before.
I have a 17 foot Legend dual sport with the Mercury(yamaha) on the back. We are the second owners of the boat. We have had the boat trouble free for 10 years up until now.
So a few weeks ago I was out on the water. First trip of the season after boat was stored all winter. I was WOT when the motor instantly lost power and the boat fell off plane. There was no prior indication of trouble brewing. It was like a snap of the fingers - no power) I limped it to the marina, the motor running very rough, where I trailer it and brought it home.
I suspected I was down a cylinder.
My limited diagnosis so far:
1) My first step was to start pulling plug wires while it was idling and listen for reduced speed in the motor. 1,2 and 3 all created a noticeable drop in RPM.
Cylinder 4 does not.
AT THIS POINT IM FOCUSING ON EVERYTHING RELATED TO #4 (Please tell me if that's faulty logic).
2) I pull plug to inspect. No water. It's a bit black. They are a few years old. I swap it for the plug in cyl 2 and retest.
The trouble remains with cyl 4.
3) Next thought wascoils. This motor has the type of coil packs the run two plugs per coil. So 4 spark plugs, but only two packs.
I interchanged the two coil packs as their part numbers don't differ, and retest.
The trouble remains with cylinder 4.
4) Now I'm worried. I buy a compression gauge. I run the motor out of gas, then I pull all the plugs. I move the throttle to wide open(as per service manual). proceed to take readings.
I have 180psi across all 4 cylinders (service manual says 160 minimum, 180 max).
5) When I crank the engine and hold the plug to the block I have spark
I changed all the plugs anyways and gapped them as per service manual.
No Change
The inline fuel filter hasn't been changed in a few years, but just for fun, I have bypassed it for the purpose of troubleshooting.
Here's where I start to need some help......
I pulled the intake/carb pack off the motor and removed carb 4. Upon disassembly, I think Inside looked pretty clean? No yellow tarnishing. No debris. bowl is clean. Float moved freely. I pulled a small brass tube with tiny holes in the end of it, that seems to go from the float bowl into the venturi. It seemed clean and unobstructed. The choke valve and throttle valve move freely.
I reassembled and NO CHANGE
I'm kind of stumped at this point
INTERESTING NOTE:
After all this I had the throttle partly open at about 2k rpm and I banged on the fuel pump (Mechanical one attached to the head) with a wrench and the motor spun up to about 5k rpm and stayed there until I moved the throttle back to normal. While engine was idling, I went and pulled the wire off plug 4 and there was no change in idle.
First off let me apologise in advance for the wall of text but I just want to give as much info as possible about what steps Ive taken so far, so I can save us all some time.
I'm kind of lost and would be really appreciative of some help. Im not bad with a wrench but I've never dealt with carbs before.
I have a 17 foot Legend dual sport with the Mercury(yamaha) on the back. We are the second owners of the boat. We have had the boat trouble free for 10 years up until now.
So a few weeks ago I was out on the water. First trip of the season after boat was stored all winter. I was WOT when the motor instantly lost power and the boat fell off plane. There was no prior indication of trouble brewing. It was like a snap of the fingers - no power) I limped it to the marina, the motor running very rough, where I trailer it and brought it home.
I suspected I was down a cylinder.
My limited diagnosis so far:
1) My first step was to start pulling plug wires while it was idling and listen for reduced speed in the motor. 1,2 and 3 all created a noticeable drop in RPM.
Cylinder 4 does not.
AT THIS POINT IM FOCUSING ON EVERYTHING RELATED TO #4 (Please tell me if that's faulty logic).
2) I pull plug to inspect. No water. It's a bit black. They are a few years old. I swap it for the plug in cyl 2 and retest.
The trouble remains with cyl 4.
3) Next thought wascoils. This motor has the type of coil packs the run two plugs per coil. So 4 spark plugs, but only two packs.
I interchanged the two coil packs as their part numbers don't differ, and retest.
The trouble remains with cylinder 4.
4) Now I'm worried. I buy a compression gauge. I run the motor out of gas, then I pull all the plugs. I move the throttle to wide open(as per service manual). proceed to take readings.
I have 180psi across all 4 cylinders (service manual says 160 minimum, 180 max).
5) When I crank the engine and hold the plug to the block I have spark
I changed all the plugs anyways and gapped them as per service manual.
No Change
The inline fuel filter hasn't been changed in a few years, but just for fun, I have bypassed it for the purpose of troubleshooting.
Here's where I start to need some help......
I pulled the intake/carb pack off the motor and removed carb 4. Upon disassembly, I think Inside looked pretty clean? No yellow tarnishing. No debris. bowl is clean. Float moved freely. I pulled a small brass tube with tiny holes in the end of it, that seems to go from the float bowl into the venturi. It seemed clean and unobstructed. The choke valve and throttle valve move freely.
I reassembled and NO CHANGE
I'm kind of stumped at this point
INTERESTING NOTE:
After all this I had the throttle partly open at about 2k rpm and I banged on the fuel pump (Mechanical one attached to the head) with a wrench and the motor spun up to about 5k rpm and stayed there until I moved the throttle back to normal. While engine was idling, I went and pulled the wire off plug 4 and there was no change in idle.