I am a novice (but trying to learn) when it comes to carbed engines, and I could use some help in diagnosing some spark plug issues.
This is on a 1971 Chris Craft Lancer with a 200hp 307Q sterndrive. My symptoms are as follows:
1. Hard starting when cold - I need to crank it 3-4 times, 5 seconds each time (even previous owner had this issue). I've throttled with the engine off and looking into the carb and can't see any fuel jetting, only a small plume of fine smoke rising up when the valves open. I think the fuel could be boiling off? I'm planning to replace the impeller (regular maintenance) and rebuild the carb over the winter. The carb has never been rebuilt on this boat (Carter AVS), so I'm sure it's far overdue for maintenance.
2. Loss of power - I was running near WOT two months ago and it suddenly/immediately dropped down to 2,500 RPMs. I cannot get it above 2,500 since then. The engine otherwise runs great at idle or low speeds. . I was waiting on the carb rebuild to see if this fixed the issue - could be related to secondaries not opening up or clogged jets? The AVS uses vacuum-activated secondaries from what I can tell.
Since 1-2, I replaced spark plugs (1 cylinder was very carbon fouled, others were slightly fouled), distributor cap, fuel filter (it was filled with floating debris). Last year I replaced the ignition coil as well, it was also converted to electronic ignition a few years ago.
3. Only recently, I'm getting a little white smoke at start-up that goes away after a couple minutes. I originally thought it was vaporization (after some heavy rains), but it's happened the last 3-4 cold starts now.
I ran a compression test and all 8 cylinders are between 135-140 psi. However, when I took out the plugs to run the test (they've only been in two months - probably 6-8 trips), they looked like below. Two plugs look brand new and the other 6 with varying levels of fouling and oil on the threads and what looked like oil stains on the metal shell.
I'm now thinking I have more serious issues than a need for a carb rebuild. Longer term, I'm thinking of replacing the engine with a rebuilt 350, so now I'm wondering if this is the time to spring for that vs. putting more money into this engine since I'll gain the additional HP along with starting again at zero hours.
Any thoughts on the seriousness of the spark plug issue and what I'm dealing with?
It depends on the year of the engine, or if someone has changed the heads. I replaced the heads on the stbd. engine and they are of the tapered type. My port engine has original heads (had them redone) and it has plugs with washers. The uj-6 champion plug was replaced by champion 823. I am currently using an autolite but can't remember the number off hand. My engines are 1969 and I believe the port one had work done to it as it had hardened valve seats and the stbd. one did not. 12 out of 16 valves were sucked in thats why I replaced both heads on that engine. Dave