I bought a 1998 21' Reinell Coho that has a 98 Mercruiser 5.7 Liter V8 250 HP motor with the Thunderbolt V ignition and 2bbl carburetor. The thing ran beautifully the first several times I used the boat. It cruised with no odd noises and top speed on calm water was 48 mph according to the GPS. Plenty of power, idled perfect.. started easy.
One morning when it was a little cooler outside I decided to do the motor a favor and gave it an extra pump on the throttle. Needless to say bad idea..it wouldn't start and would diesel after turning off the key. Eventually it started but I had clearly flooded the motor. Could smell fuel and it would aspirate fuel through the carb. After getting it started it ran fine... Went out on the water and it ran fine. Next cold start.. same thing.. hard starting. I figured i had fouled a plug so I pulled the #1 plug and took it to Napa and spent $87 on NGK iridium plugs matching the plug I had removed. (should have checked the manual). When I put the new plugs in I had a friend (mechanic) who was helping me. (yes I can change plugs but change 4 or 5 of those bastards and you'll let your friend help if he's willing with the remaining plugs). Pulled the rest of the old plugs and they were all some autolite brand.. apparently he only had 1 NGK. My friend when putting one in said oh I think I owe you a plug.. I may have cracked the porcelain. He then told me that it was good to go and he hadn't.. I should have verified but I didn't.
After changing the plugs it started easy and ran smooth. Took it out on the water and it ran fine... I do think that it wouldn't reach the RPM it should have on the top end but I blamed it on the water and the tides.
Today I took the boat out.. started harder than the last time but still not bad. Idled fine.. maybe a little rougher than normal. Cruised about 15 miles at about 3500 RPM and was hearing this sound. It sounded like a rattle but to me it sounded like a higher pitched rattle like maybe a spark issue.. like it wasn't timed right or something... Went back lifted motor cover while we were cruising along trying to find where came from.. hoping it was a vibration.. pushed on a few things etc.. walked back up took the helm and could feel the motor struggling.. I started to slow slightly and it fell on its face and started running horribly. Came down to an idle and clearly not running on all cylinders..
Limped home and pulled the plugs and sure enough... porcelain was cracked on the #4 hole. Spark plug electrode strap looked like it had broken off or melted. Figured I had found my problem so I went and bought all new plugs that are recommended for this particular engine.. (not iridium). Decided while I was at it I would change the cap and rotor and the coil (i guess i felt like I had an extra $80). Figured it would run like a champ... put it all back together.. started it up and it ran like crap still. Put a timing light on it and it looks like it's horribly advanced at idle..
My buddy got it to where it ran smooth (it would die if you even came close to 10 deg btdc). Started easy.. ran smooth.. sounded good.. I figured hmmm maybe the cylinder had been loaded up with fuel and it just cleaned itself out..
We took it out on the water and you could hear that awful noise at high rpm again. He adjusted the distributor under load and underway at about 4,000 rpm (which is about all I could reach) and got rid of that annoying sound... came back down to idle and boom... ran rough and almost died... gave it some more gas to try to get back up and it would barely run.. like it was not firing on all cylinders again..
Any help is greatly appreciated! I'm confused as all hell.. I did an OHM check on the plug wires and they all seem to be higher than normal.. As an example the #4 wire was about 14.1k ohms..
Right now I'm thinking everything from fuel issue (carb, vent) to ignition module, knock module, timing chain jumped a tooth, stuck valve.. junk motor.. have no idea.. It's all just confusing to me right now!
One morning when it was a little cooler outside I decided to do the motor a favor and gave it an extra pump on the throttle. Needless to say bad idea..it wouldn't start and would diesel after turning off the key. Eventually it started but I had clearly flooded the motor. Could smell fuel and it would aspirate fuel through the carb. After getting it started it ran fine... Went out on the water and it ran fine. Next cold start.. same thing.. hard starting. I figured i had fouled a plug so I pulled the #1 plug and took it to Napa and spent $87 on NGK iridium plugs matching the plug I had removed. (should have checked the manual). When I put the new plugs in I had a friend (mechanic) who was helping me. (yes I can change plugs but change 4 or 5 of those bastards and you'll let your friend help if he's willing with the remaining plugs). Pulled the rest of the old plugs and they were all some autolite brand.. apparently he only had 1 NGK. My friend when putting one in said oh I think I owe you a plug.. I may have cracked the porcelain. He then told me that it was good to go and he hadn't.. I should have verified but I didn't.
After changing the plugs it started easy and ran smooth. Took it out on the water and it ran fine... I do think that it wouldn't reach the RPM it should have on the top end but I blamed it on the water and the tides.
Today I took the boat out.. started harder than the last time but still not bad. Idled fine.. maybe a little rougher than normal. Cruised about 15 miles at about 3500 RPM and was hearing this sound. It sounded like a rattle but to me it sounded like a higher pitched rattle like maybe a spark issue.. like it wasn't timed right or something... Went back lifted motor cover while we were cruising along trying to find where came from.. hoping it was a vibration.. pushed on a few things etc.. walked back up took the helm and could feel the motor struggling.. I started to slow slightly and it fell on its face and started running horribly. Came down to an idle and clearly not running on all cylinders..
Limped home and pulled the plugs and sure enough... porcelain was cracked on the #4 hole. Spark plug electrode strap looked like it had broken off or melted. Figured I had found my problem so I went and bought all new plugs that are recommended for this particular engine.. (not iridium). Decided while I was at it I would change the cap and rotor and the coil (i guess i felt like I had an extra $80). Figured it would run like a champ... put it all back together.. started it up and it ran like crap still. Put a timing light on it and it looks like it's horribly advanced at idle..
My buddy got it to where it ran smooth (it would die if you even came close to 10 deg btdc). Started easy.. ran smooth.. sounded good.. I figured hmmm maybe the cylinder had been loaded up with fuel and it just cleaned itself out..
We took it out on the water and you could hear that awful noise at high rpm again. He adjusted the distributor under load and underway at about 4,000 rpm (which is about all I could reach) and got rid of that annoying sound... came back down to idle and boom... ran rough and almost died... gave it some more gas to try to get back up and it would barely run.. like it was not firing on all cylinders again..
Any help is greatly appreciated! I'm confused as all hell.. I did an OHM check on the plug wires and they all seem to be higher than normal.. As an example the #4 wire was about 14.1k ohms..
Right now I'm thinking everything from fuel issue (carb, vent) to ignition module, knock module, timing chain jumped a tooth, stuck valve.. junk motor.. have no idea.. It's all just confusing to me right now!