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318 top end trouble

D

Dennis B.

Guest
"Hey gang, have a 1986 318cu.i

"Hey gang, have a 1986 318cu.in. with top end power loss. I have replaced cap,rotor,plugs,coil and fuel filter. Ignition is a newer Mallory electronic (ie:no points). Old plugs were good color (80hrs.)Also replaced carb,Qjet needed rebuild but good price on Holley.Runs great to 2800rpm and then seems to go flat, Floscan meter shows fuel use (20gph at W.O.T.)Did the same with other carb on it. Have already checked under boat for marine growth and removed what little was there. Normal rpm at W.O.T. is 4100, best I hit is 3100rpm."
 
"Did it lose performance after

"Did it lose performance after you replaced the cap, rotor and spark plugs?"
 
"No, performance low before al

"No, performance low before all items done. Getting ready to do compression check now."
 
"Just finished compression tes

"Just finished compression test, 120psi on cylinders. Within limits in the book."
 
"The fuel pump might be weak,

"The fuel pump might be weak, too low pressure or inadaquet volume. This is one item that is a marine specific part."
 
"My Flo-Scan meter shows good

"My Flo-Scan meter shows good fuel flow, if not slightly higher than before."
 
That does not tell you if the

That does not tell you if the pressure and/or volume is low. It will tell you if fuel is being wasted due to poor carbueration or a defect in the ignition system. What type of fuel pump is it (electric or mechanical)?
 
Does it look like it is rebuil

Does it look like it is rebuildable ( held together with screws )?
 
"If you're burning 20 GPH

"If you're burning 20 GPH at WOT, your motor is getting all the fuel it needs. Whether it's getting too much is still in question. I can tell you this: if ANYTHING is holding her back from planning off (you didn't say it gets on top), then it will stall down like this.

Here's what I'd check: Put a timing light on it and see if the spark is advancing at least 26 degrees. I know it's a new distributor, but the springs might be too stiff. The advance should be all in by 2500 rpms.

Jeff"
 
"Jeff, It will get on plane at

"Jeff, It will get on plane at 2800rpm. I did check the timing advance at the dock with no load and it does advance.Have had this distributor on for the past (3) years without problems. Will try running tonight to check advance under load. Also just replaced the ballast resister, ohm value different than the new one."
 
"The advance under load is NO

"The advance under load is NO different than at idle, so save yourself some trouble. Does the advance come all the way in by 2500 rpms, or does it creep in at 3,500 rpms plus (as car distributors are often set up). That might be your problem.

Jeff"
 
"No,it does come in very early

"No,it does come in very early in the rpm range"
 
"I had a similar issue with my

"I had a similar issue with my 318 last season. Is the choke plate completely vertical when the engine is warmed up? The linkage / choke thermostat coil in the manifold may need a little tweaking if not. Did you check the vacuum at the choke? After confirming no vacuum leaks, I eventually sent may carb out for a rebuild, which solved my problem. You can do it yourself, but that's a little beyond my ability. I wanted it done by someone with experience. After the rebuild, the secondaries kicked open and got her up to 4,000 rpm where I was running around 3100 before.
Good Luck,
Chuck"
 
"Chuck, No problems with the c

"Chuck, No problems with the carb(brand new) Thought I had problems with old carb, bought new and rebuilding old one. Could not test tonight, tide is very low."
 
"Even with the new carb, give

"Even with the new carb, give the choke linkage a close examination. On my Carter AFB, the choke linkage locks out the secondaries so they won't open unless choke is coming off all the way. Check for sticky shaft or linkage. Is the thermal pull down allowing the choke to open all the way when warmed up?
Good Luck,
Chuck"
 
"Chuck, Choke is opening witho

"Chuck, Choke is opening without problem.I am running a Holley carb with electric choke. After short warm up it choke is open."
 
"It wouldn't hurt to remov

"It wouldn't hurt to remove the distributor, check, clean, and lube the advance mechanism. Should be done periodically anyway. Replace any old rubber fuel lines with CG approved marine fuel line, especially from the fuel tank to the fuel pump. Possible it's sucking air through a crack in the line. I would not rule out the fuel pump yet."
 
"Okay finally got out this eve

"Okay finally got out this evening for test ride. Ran better than before 3800rpm. Only thing that I just replaced was the ballast resister and voltage regulator. Thought all along it was electrical, but confused on how these parts effect performance. Will take out a second person and try to dail in the timing at W.O.T."
 
".."Will take out a second

".."Will take out a second person and try to dail in the timing at W.O.T."

Why go through that hassle? Just let it high idle at 3,000 rpms set it that way.

Good just can't believe the advance works the same in neutral, can you!

Jeff"
 
"Jeff, you have to try differe

"Jeff, you have to try different answers until you come up with one that he wants to hear."
 
"Alot of marine engines out th

"Alot of marine engines out there have the wrong tab on them for timing the engine. The TDC hole is right, but the "before" and "after" words stamped on the tab are backwards. Make sure that when you see the engine advance, it is actually advancing not just moving toward "before" because "before" might really be "after".
I had a heck of a time tuning my starboard engine. It was set at 5Deg BTDC. When I reved the engine while watching the mark with a timing light it moved the "wrong" way!! So I took the boat out and ignored the tab and timed it by ear. problem fixed!! The whole time with a badly marked tab I was running at 5deg ATDC!
Then when I was talking to Harry at Harry's in Westbrook CT he told me the first thing he checks when buying a core to rebuild is the tab. Alot of them are wrong.

More advance is good for power and economy. more advance causes pinging. pinging is really bad. so take it out and run it. give it as much advance as you can to get it to run great. but do not give it so much advance that it pings. just dial it back a little.
Watch your fingers!!!"
 
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