Engine mods/chev 350 help

[RonR]

Anyone a Chevy 350 expert?
Twin 350 Crusaders. 450 hours each, replaced in 2006 with complete factory replacement, everything was new.
Port side (Angela) runs well, but diesels when you turn her off.
Starboard side (Brittany)has only ran well one time. Last trip out she would not run above 2500 rpm for about 5 min regardless of fuel.
Exhaust shows fuel coming out. As your facing the engine the left bank sounds like it has a miss or two. Plugs show it’s running really rich. I have adjusted the carb to match the good running engine, about 1.5 turns out on each side (Holley with vacuum secondary’s). I have checked timing and it’s at 10 per the manual, no vacuum advance on these distributors. New plugs/cap/rotor/oil/filters to include fuel.
I pulled each spark plug wire to try and find the cylinder/s that are not firing and I can not tell a difference, but strong spark coming off the cap. It did run well for about 5 min today and I was able to adjust the idle down to 600 per the manual and check timing, but right after that it started missing again and would not run below 950. I’m not sure if I’m fighting a carb issue or some kind of electrical issue. This engine also diesels when you turn it off.

 

[tiltrider1]

Are these old style points distributors or are they the newer AC Delco electronic distributors or did some one add some after market distributor.

If they are the AC Delco distributors you need to plug in the timing plug before you can time them.

The AC Delco distributors have a small pot metal cage With fingers for telling the coil when to fire. After about 20 years there is enough corrosion that this cage Sends faulty signals. The only solution is a new distributor.

You sound pretty confident that it’s not the carburetor but when was the last time the carburetor was hot tanked before being rebuilt?

 

[Art]

Sounds to me like carburetor interior problem. Of course could also be electrical...

I take it both engines were not remanufactured/rebuilt... but rather were factory new... is that correct?

Were both carbs also both brand new to match the new engines in 2006; or did you rebuild one or both of the old carbs?

How long since the engines were run for at least a short cruise?

If the carbs' innards got gummed up [due to not having gasoline run through them for too long] there are a couple ways to clean them without complete dismantling/rebuild; using concentrated amount [not just poured into fuel tank] of Berryman B-12 Chemtool https://www.tooltopia.com/berryman-...MIrYCXldyy6QIVBo_ICh0XQQRvEAQYCCABEgL5IvD_BwE

Good Luck!

 

[FF]

MY guess would be too high fuel pressure or bad float level in carb flooding engine.

Dieseling is caused by an ignition source in the combustion chamber. Running very rich can leave carbon deposits that will do it.

Simple procedure to clean out combustion chamber is to run at 1500 or so and slowly pour fresh water down primary side of carb . The amount trickeled in should cause the engine to stagger , but not shut down. Really simple with an old pump insect sprayer. 5 min will usually be enough.

With a car a piece of newspaper behind the exhaust will show the chunks removed, with a boat wet exhaust that doesn't work.

After you get the carbs right and the engine runs well if it still Diesels , the outboard folks sell cures that are stronger than just water.

 

[Bacchus]

First - admit up front I'm no expert.
You said no vac advance so I'm taking that to mean mechanical then. If so, have you pulled the distributor plate to check the mechanicals?
I had a similar issue many moons ago and issue was corroded springs and therefore advance not working - actually not returning properly.
I could get it run good at either lo or high speed by messing with timing w/o a light just tuning "by ear"

 

[High Wire]

Those plugs are covered with carbon. If they are the specified plug then mixture too rich. Is the choke full open?

 

[sunchaser]

Ethanol fuel can screw up an older design carb in no time. Can you get E free fuel and try a few tanks after an old smart grizzled guy has done a carb rebuild? We had twin 350s with TBI on 1995 Mercruisers rather than carbs. Nary an issue.

I'm surprised your engines have carbs as by the late 90s marinization history had pretty well abandoned carbs on the 260+ HP 350s. Are you sure the engines are year 2006?

 

[av8r]

Sounds a lot like float level problem or heavy float from ethanol damage. You could change carbs side to side to see if the problems follow.
If both engines are standard rotation you can check distributors the same way.

 

[bayview]

Obviously you are getting plenty of fuel so I would look carefully at the ignition.

Go back to the beginning and recheck everything, assume nothing. Check the base timing carefully, is the distributor in the correct gear? An easy mistake on those engines.
Reread the proper timing procedure in the manual. If you loosen the distributor rotate it a bit in either direction and see if the idle smooths out. Are you absolutely certain that the plug wires are in the correct order? Another easily made mistake. Assume nothing. If one engine is reverse then the firing order will be reversed. 18436572 becomes 12756348
Check the distributor cap for moisture and carbon tracks

 

[RonR]

The engines are 2006, you can still buy carb engines from Crusader now. I have all of the paperwork, everything was new, new drop in. Im thinking the bad engine is a carb issue, but the dieseling of each has me stumped. I have had this problem years ago with an old motorcycle. It ended up being some goofy feed back from the electronic tachometer.

And thank you everyone for the imput. I will check wires/rotation.

Back note, this boat was parked for 4 years before I got it.
Each 100 gallon tank had about 25 gallons of fuel in them. I pumped out what I could, on set #3 of Racor fuel filters.
Everett only sells non-ethanol, but who knows what was really in the tanks, it did not small all that bad, in fact I used up that 50 gallons of fuel in my old farm truck, but Ford 460 will run on most anything they can swallow!

 

[Art]

The engines are 2006, you can still buy carb engines from Crusader now. I have all of the paperwork, everything was new, new drop in. Im thinking the bad engine is a carb issue, but the dieseling of each has me stumped. I have had this problem years ago with an old motorcycle. It ended up being some goofy feed back from the electronic tachometer.

And thank you everyone for the imput. I will check wires/rotation.

Back note, this boat was parked for 4 years before I got it.
Each 100 gallon tank had about 25 gallons of fuel in them. I pumped out what I could, on set #3 of Racor fuel filters.
Everett only sells non-ethanol, but who knows what was really in the tanks, it did not small all that bad, in fact I used up that 50 gallons of fuel in my old farm truck, but Ford 460 will run on most anything they can swallow!

"Back note, this boat was parked for 4 years before I got it."

4 years - Without Starting? Carb interiors might be a gunned up mess. What I mentioned in post # 3 may do the trick in a relatively simple fashion. PM me with your email address and I'll reply with my methods that have worked well for me.

 

[Lepke]

If gas sits more than 6 months without a fuel stabilizer you can have problems. The gas will separate and a varnish like coating can form in the lines and bottom of tanks and carbs. It usually restricts the jets. Fresh gas added will clean the deposits if a large volume is run thru the system.
You had large deposits on the tank bottoms from sitting and it was probably partially absorbed by the new fuel and moved to the lines and carb. Once the deposits become liquefied, the average filter is not going to remove them.
It these were my engines I use a heavy dose of a fuel system cleaner and then use up all the fuel. And use a stabilizer every new fueling.

 

[Art]

If gas sits more than 6 months without a fuel stabilizer you can have problems. The gas will separate and a varnish like coating can form in the lines and bottom of tanks and carbs. It usually restricts the jets. Fresh gas added will clean the deposits if a large volume is run thru the system.
You had large deposits on the tank bottoms from sitting and it was probably partially absorbed by the new fuel and moved to the lines and carb. Once the deposits become liquefied, the average filter is not going to remove them.
It these were my engines I use a heavy dose of a fuel system cleaner and then use up all the fuel. And use a stabilizer every new fueling.

https://www.tooltopia.com/berryman-...MIrYCXldyy6QIVBo_ICh0XQQRvEAQYCCABEgL5IvD_BwE

NAPA carries Berryman B-12 Chemtool. IMO - bad assss stuff!

Watch this!

 

[KnotYet]

You will damage the engine by running it too rich by washing the oil from the bores.

Unless you have a lot of time to rebuild the 'bad' carburetor, buy a new replacement.
Open up the old one to verify the jet numbers and other settings. Swap if needed.

Get a fuel pressure gauge and install it after the fuel pump. You need to know this.
It is often a bit higher than the carb manufacturer specifies. Check both engines, too.
If needed, get fuel pressure regulators and verify the carb's recommended pressure.

I have just done this to a new-to-me 1963 Land Cruiser that was running way rich.

At the very least buy new floats for both carbs and install them to the correct height.

Distributors for these engines are very simple and yours are hopefully OK. Make sure
the wires and caps are in good condition. You can swap the bits to test each engine.

 

[RonR]

Well... I took the carb off, bought a kit and a gallon bucket of carb clean.
When I opened up the carb it was spotless. No gum/varnish or dirt at all. Went ahead and let everything soak over night. Blew it down well. Checked the floats to make sure they float. This is the cheap Holley marine 600 with vacuum secondary's and non adj floats. Put it back together and installed on the boat. If fired right off, no gas coming out the exhaust, runs like a champ. I have no idea what was dirty/plugged but it fixed all of the problems. So to be on the safe side I did the same service to the good engine.

Thank you everyone for your input.

 

[RonR]

https://www.tooltopia.com/berryman-...MIrYCXldyy6QIVBo_ICh0XQQRvEAQYCCABEgL5IvD_BwE

NAPA carries Berryman B-12 Chemtool. IMO - bad assss stuff!

Watch this!

I picked up 4 cans, two for each tank!

 

[rsn48]

Unfortunately the only long term solution to insure your boat engines remain healthy is go have fun on your boat every month. Heck in our neck of the woods, you can have a nice sunny windless day in all the crappy months, late Oct to March, take advantage of some of these days.

 

[bayview]

Before replacing stuff try running from fresh fuel in a container. No chemicals just clean fresh fuel.

 

[Art]

Well... I took the carb off, bought a kit and a gallon bucket of carb clean.
When I opened up the carb it was spotless. No gum/varnish or dirt at all. Went ahead and let everything soak over night. Blew it down well. Checked the floats to make sure they float. This is the cheap Holley marine 600 with vacuum secondary's and non adj floats. Put it back together and installed on the boat. If fired right off, no gas coming out the exhaust, runs like a champ. I have no idea what was dirty/plugged but it fixed all of the problems. So to be on the safe side I did the same service to the good engine.

Thank you everyone for your input.

Congrats!

 

[RonR]

Before replacing stuff try running from fresh fuel in a container. No chemicals just clean fresh fuel.

I have put about 150 gallons through each engine.

 

[PM]

Check the timing on both engines. Also trace the spark plug wires, there may be one or more out of sync.

pete

 

[RonR]

Check the timing on both engines. Also trace the spark plug wires, there may be one or more out of sync.

pete

Got it fixed with a carb rebuild.

 

[skipperguy]

Re-check

Had the same problem with the same engine years ago. Found the firing order wiring was incorrect-Sounds silly but just trying to help

 

[High Wire]

Got it fixed with a carb rebuild.

Thanks for closing the loop.

 

[Newtrawlerowner]

Engine Mods 350 Chey Help

Well... I took the carb off, bought a kit and a gallon bucket of carb clean.
When I opened up the carb it was spotless. No gum/varnish or dirt at all. Went ahead and let everything soak over night. Blew it down well. Checked the floats to make sure they float. This is the cheap Holley marine 600 with vacuum secondary's and non adj floats. Put it back together and installed on the boat. If fired right off, no gas coming out the exhaust, runs like a champ. I have no idea what was dirty/plugged but it fixed all of the problems. So to be on the safe side I did the same service to the good engine.

Thank you everyone for your input.

Some things to consider.

When you rebuilt the carb(s) did you replace the power valve(s). 1 per carb. These will typically leak when they are bad causing excessive fuel fouling. More than likely they came in the kit. If the engine ever back fires, these valves will go bad.

Also you mention the engine "dieseling" This is caused by low octane fuel and/or high compression. If you run low octane or old gas, this will happen. Always buy the highest octane available. I would suggest adding a fuel stabilizer every time you add gas. Also mentioned was a warning about using gas with ethanol. Most marinas don't sell this, but you should always ask. The last thing to consider is pre-ignition knock. This can be caused by too far advanced ignition. Be sure to check the ignition timing.