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b73 Nautique w 318

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ccskinautique

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"I've been workin on a goo

"I've been workin on a good friends Ski Nautique boat for about 5 months now. Here's the story-
Its a 1973 Nautique w/ a chrysler 318 v8. I'm pretty familiar with the 318's but this one has me stumped. The boat manual calls for leaded fuel but obviously it hasn't been getting that in the last 30 somethin years. My friend has always just pumped the gas into it and ran it w/ no lead additive. Is that a guarenteed valve sinker? What started the suspicion was back in March it started running terribly so I asked the last time it had a carb kit and he didn't know so I put a kit in it thinking that would be the fixer. Not so. It got a little bit better but nothing to write home about. That was with the original carter carb. Then he talked to a guy who works on old nautiques and he said you can't rebuild the carters (whatever that means) so my friend bought a marine edel 600 w/ mech secondaries just like the carter. Now it runs alot smoother but something that carried over from when it had the carter on it is when you're on takeoff or goosing it, it pops/backfires back through the carb. It did it so much with the carter that the entire inside of the throat of the carb was jet black when i pulled it off. Now it pops the same way with the edel but not as bad. I think i had a richer condition with the carter that made it pop more frequently but now since it has been leaned out a bit with the proper carburation it doesn't do it as often. So does this sound like a burnt/sunk valve allowing fire back through the motor? Thanks guys."
 
"30 years, nothings forever.

"30 years, nothings forever.
Sounds like you need to verify the engine ignition is up to par and timing is correct and consistent.
Check the compression or better yet, do a leak down test. See if you can isolate a burnt valve or cracked seat.
A sticking valve may be a bit harder to locate.
Also, very remote though, check for exhaust restriction."
 
"Ya I'm gonna go get plugs

"Ya I'm gonna go get plugs, wires, cap/rotor tomorra and install later this week to see what happens. The boat is going back out this coming sunday so then I can see some results again since I can't see a whole lot in the driveway. I'm also gonna check timing chain slop after installing the above."
 
Ok well i at least got my igin

Ok well i at least got my igintion wires installed and that helped a ton. The old ones were cracked and grounding out on the upper riser manifold which was totally killing the spark under a load. It still has a roughness to it though and just donesn't have the get up and go it should. I checked the timing and set it at 5 only b/c i seen someone else on here say that for their 318. I think I may advance it a bit though after I order/install my cap/rotor. My temp only got up to about 110-115 the whole time I was running too so I'm gonna go ahead and put a thermostat in it too since I'm sure that hasn't been replaced in a while. Anything else I should be thinkin about?
 
Try improving the accel pump s

Try improving the accel pump shot by adjusting the linkage for the maximum shot.

I agree that those old Carter AFBs can't always be rebuilt. I have one now that slow floods regardles of what I've done to it--the body must be micro-pourous (thanks to that ethanol crap!)

Get that temp up to at least 150 'F.

Jeff
 
"I also forgot to mention that

"I also forgot to mention that at part throttle, prolly about 5mph, it misses really bad. Bad enough to shake the boat and feel like a bent prop shaft but its the engine running rough. Not sure what thats all about but I'm thinkin that and the lack of power on acceleration are in common."
 
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