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Twin 270 Crusaders running rich on fuel and 2500 rpm max throttle

C

chiswell_flyer

New member
"Both my 1986 270's are ru

"Both my 1986 270's are running with identical problem: Maximum rpm is 2500 and both engines are showing cold fouled plugs. The condition existed with old (rebuilt) Q-Jet carbs and older Mallory breakerless distributors. I've upgraded the carbs to Holley's and replaced one distributor (found advanced weight/springs rusted up) with a new Mallory distributor. I retained the points/condensor system. Same problem: not running smooth, and exhausting unburnt fuel/carbon. The engines ran extremely well before a long storage period. I ought to be at 4400 WOT with the props/boat/engines that I have. Any troubleshooting thoughts as to what system to check first?"
 
"How long has the boat been si

"How long has the boat been sitting in the water?

How old is the fuel in the tank(s)?

Did you check both engine for full spark advance?

How do the engines run at 2500; smooth rough, irregular, etc?"
 
That's kind of weird with

That's kind of weird with ethanol gas. My plugs run scary white with that stuff. I suspect you might have ignition wires breaking down on you.

What temperatures are your motors running?

Jeff
 
"1. Put the boat in Fall of 2

"1. Put the boat in Fall of 2007 after a few seasons out working on bottom and other house systems.
2. Fuel is brand new 87 octane, same octane that it has run successfully on.
3. Engines run smooth through the full range up to 2500 rpm. I'm also seeing normal speeds of about 18knots at that rpm. But run up the throttle at the setting achieves no additional speed/rpm.
4. Prior to changing the distributor I could manual advance the spark and increase the rpm. That's what lead me to dig into the distributor under the advance curve plate. Found the weights/springs badly corroded. Replaced the distributor.

Still seeing the same condition and now the engine is a hard start. I'm planning on starting over with timing, putting the #1 cylinder in TDC and checking the position of the rotor to #1 plug."
 
"Jeff,
Interesting thought on

"Jeff,
Interesting thought on the ignition wires. Its the only part that I have not replaced! Thought about it though along with the coil."
 
"Good. One more thing you need

"Good. One more thing you need to do: Get a timing light and verify the advance is working, and that it's coming ALL thew way back at idle.

Jeff"
 
"It depends on the quality of

"It depends on the quality of the applied bottom paint and how "hot" the harbor is and the effect on zinc's. The harbor my boat is in is close to if not the farthest north ice free port in Alaska. Hence the colder water temperature cuts down on growth, and other aquatic impacts. You can extend the haul out by using a diver to change zinc's and do a bottom check."
 
So the bottom should still be

So the bottom should still be relatively clean.

Full spark advance and high tension wires are at the top of the list.
 
"David, I may have similar tro

"David, I may have similar trouble. I have twin 1986 270 crusaders on my boat I brought up from Juneau. Got to Seward and had trouble with distibutors- very sloppy rotors. Changed both to Mallory Breakerless and engines are running well, but only advanced distributors manually. I need to time them with an advancing light. I haven't pushed them (past about 2600 rpms). I want to get them timed correctly before I push them. Have the boat in Homer now, and am replacing one thing at a time; plugs, belts, and want to pull alternators and clean them up. I am also wondering about oil, I've read Amsoil synthetic is really good with cold starts and at keeping the engines running cooler. Anyway the other weekend my port engine cut off (the breaker tripped on top of the engine)at about 2900 rpms. Got it started back up and it ran fine but I kept it at 2600. I wonder if ignition wiring is my problem. Thanks for the info and I would like to keep in touch if your boat is in Homer. Matt"
 
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