2002 MCM 5.0L with Thunderbolt V Ignition stalling at idle

[watered_down]

I have a 21' 2002 Crownline (bowrider) with a 5.0L 305 engine (SN# 0M076339) and alpha one outdrive that I purchased 3 years ago. It has a 187 hours on it and has been a great boat. I've had it out a number of times this year, and it's run perfectly... until Saturday. I hadn't had it out for three weeks, and from the time of launching it Saturday, the boat would stall anytime the rpms were down. So, I can throttle it to get it started, but as soon I try and put it in gear, I have to keep the engine revved as much as possible. Once I get it into gear, as long as I have it throttled it runs great, but as soon as I stop and idle, it runs for a few seconds and stalls. The engine has a carburetor, so I don't believe it is related to the IAC valve on the MPI engines that is often posted about.

Given that it's running fine at higher rpms, I don't think this is related to ignition, and my best guess at this point is that it's related to something in the carb (idle jet?). However, I'm hesitant to pull it apart if I don't need to. To this point, I've I checked the distributor cap, and while there was some buildup (which I scraped clean), it didn't make a difference. I'm not surprised because I don't think it's related to the distributor/coil/spark plugs given it seems to run fine at higher rpms. Fuel is new (I've refilled the tank 3-4 times in the last two months). Fuel lines and filter were replaced last year as a preventative measure, and I have a new fuel filter on it (changed again Saturday at the lake just in case). If this were a fuel issue before the carb, I don't think it would run well at high rpms. The fuel filter at the carb looks great overall. I also don't think it's an air issue as I removed the spark arrestor just in case it was dirtier than it looked and problem was the same.

Is cleaning/rebuilding the carburetor the next step or is there something else this might be that I'm missing? Am I incorrect about the distributor/coil/wires? Should they be suspect? I haven't replaced them since I bought it, so it's probably good to do anyway. Any thoughts would be much appreciated.

 

[Scott Danforth]

Check you lower shift cable adjustment. Has your distibutor trigger been upgraded to the new 3-wire versions

Your boat probably sat for many years. It should have close to 1000 hours on it.

 

[watered_down]

Thanks for the quick reply. I had checked the shift cables last year and they were fine but I'll check them again tonight. As for the distributor trigger, it's the old 2-wire version. I'll check it as well and will look for a replacement. Any thoughts on why you'd think of these two things? I just want to understand the connection as I wouldn't have thought of them immediately.

With respect to the distributor, given the age of the boat, I've had it on my list to replace the plugs, distributor and coil. Any recommendations on brands that you'd suggest, especially for the distributor assembly?

As for the hours on the boat, it had 80 when I bought it from the second owner. It had been stored inside the entire time and was in immaculate condition. I knew I'd have to replace some seals and other things because it hadn't been used much. I had watched for over a year and definitely scored. Our family has enjoyed every minute on it.

 

[achris]

..With respect to the distributor, given the age of the boat, I've had it on my list to replace the plugs, distributor and coil....

Plugs, definitely, and I'd probably spring for a new set of silicon plug leads too. But coil and distributor, why? You have a Thunderbolt V distributor, about the best marine ignition system available (short of going full MPI) you're not going to get any better... I have a friend with a couple of 1984 engines running that same distributor, with about 3,000 hours on them. Still in perfect condition. We did replace the sensors on both engines because one was stalling at idle (the exposed solder connections were very badly corroded). And the coil, for every coil that was replaced because it needed to be, about a million were replaced needlessly... If you have that much money to throw away, please let me have your email address and I'll give you my bank account numbers and you can deposit it directly to me....

Chris....

 

[watered_down]

Thanks Chris. Good to know. I enjoy working on my boat, but it's a lot more stressful when it's down and we don't get to the lake unless I get it fixed. As a result, I'd much rather try and stay ahead of potential issues.

As for the distributor sensor, I took a look at it and there is some minor corrosion on it so I ordered a new one. I put things back together and no change in the issue. I then checked the adjustment on the lower shift cable and things are in spec. Is it possible it's something with the kill switch connected to the shift cables? Problem is similar if I put it in throttle only both forward and reverse.

 

[achris]

Re-read your post. That's a carburetor problem. Sounds like the idle circuit is gummed up, or the idle mixture is just out of adjustment, or has dirt in it. Pull the carb, strip it and give it a good clean out and blow through with DRY compressed air. Then set all the adjustments as you rebuild.

Chris......

 

[watered_down]

I'll get a carb kit and will post an update once I get it done. I really appreciate the help.

 

[isaacs]

In the future, use ethanol free fuel; it'll keep your carb healthy and happy!

 

[watered_down]

I rebuilt the carb, and she started right up and ran great. We ran it all day Saturday with no issues. Thanks again for the help.

 

[achris]

I rebuilt the carb, and she started right up and ran great. We ran it all day Saturday with no issues. Thanks again for the help.