1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

[rlambert]

Ok. So I know I have a mechanical advance timing mechanism in the base of the distributor. That is why I replaced the distributor when I first noticed the problem with a Sierra Replacement Part which is really the Mallory distributor. Unfortunetly, that did not solve the problem. The engine now misses intermitently and still stalls at the same RPM as the previous original distributor. Plugs, wires are a year old. Coil is brand new. Carburetor was recently rebuilt.

Seems to be getting flooded between the missing even at low RPM after a while and certainly at the advance RPM. What the heck is going on??????

Should I check the spring tension on the mallory centrifugal advance weights?

Could the exhaust manifold have internal scaling causing backpressure?

Any advice on the mallory distributor quality in general? I did have a problem with the distributor cap I first received. Had to send it back on account of major cracking after just an hour of running. Oh, by the way, when I first replaced the distributor before the cap cracked the boat ran normal for that hour. No RPM stalling or anything.

 

[Don S]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

Why do you keep assuming it the advance mechanism causing your problem. Sounds to me like it's more of a carb problem at first thought.
Have you done a compression test? What were the results.
Did you set the point dwell with a meter?
Did you set the timing with a timing light, did the advance work properly when checked with the timing light?

 

[rlambert]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

I initially thought, like you, that it was a carburetor problem. That is why I rebuilt the carburetor about eight months ago. That did not solve the problem. I then found out about the centrifugal advance and it seemed to make perfect sense. Especially since when I spray silicone lube on the weights it always worked for a couple weeks to get on plane and run around. I got tired of taking the distributor apart every couple weeks and it stranded me in a storm with a top speed of 7 mph. Had to hide under a bridge.

That is why I replaced the distributor. Haven't tested compression but I think it is good. The boat always runs great when I can get it past that point.

Figured the new distributor would solve the problem. Really only complicated them. Now it misses intermittently when it feels like it and still can't get past the advance RPM without backfiring and stalling. I gapped the points using a tool (Mallory single point distr. 0.018"). Don't have dwell meter. Wondering if I made a mistake buying the Mallory Distributor. I can almost bet that if I put back in my old distributor and lube up the weights, it will run right. Sorry about the long post. It is just frustrating.

I mean what in the carburetor can still be causing a problem? I rebuilt it. Should be ok right? Ran fine with the lubed up weights.

 

[rlambert]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

I will check the timing advance to make sure it is advancing but my tach has never worked since purchasing the boat in 2006. Tough call when you don't know the RPM. Oh, by the way, only happens in gear. No problem idling at high RPM.

 

[Don S]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

I run into a lot more carbs that are not rebuildable, than I do distibutors. How many carbs have you rebuilt in the past? Did you soak it in carb cleaner and blow out all the passages? Was the bottom of the float bowl covered with corrosion and crud?
I can't see your old distributor, and a new Mallory distributor having the same exact problem.
You need to stop throwing parts at it and do some testing.
Compression test, vacuum test, fuel system tests, lots of things to check before

 

[Alpheus]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

Haven't tested compression but I think it is good

You gotta get to some testing. You are just throwing money at the problem and it could be something simple. You have to start at the beginning.

Fuel = Pressure,filters,floats,jets.

Compression = Valve seats,gaskets,rings,cracks.

Ignition = cap,rotor,points,plugs,wires,timing.

Guessing can only go so far and that comes from experience...

 

[havasuboatman]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

You replaced the dist. and have the same problem....
IT'S NOT THE DISTRIBUTOR
It revs under no load, but not under load
It's flooding
It's backfiring (thru the carb, right?)
Are ALL of the ign. components new?
You haven't checked compression (do so)
Have you bothered to check the plug wires are correctly installed? (firing order)
Just because they are new doesn't mean they were correctly installed.
Do you have the correct spark plugs installed?
ALWAYS start with the easy things and anticipate the questions we are going to ask before you post.
A run/performance issue is always a compression check indicator.
When you get the carb apart again pay close attention to the accellerator pump function.
Listen to Don and Alpheus. Carbs don't last forever, and unless you have proven a part of a system is functioning properly, it's suspect.
Hell, your water seperating fuel filter, if full of water, can cause some of the symptoms you describe.

 

[rlambert]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

You guys are right. I need to test for a dianosis.

I've done all the work myself. I completely rebuilt the ignition system over the past two years due to various issues and just regular tune-ups: key switch ignition, wiring, spark plugs, wires, ignition coil, breakers, distributor cap. All of this stuff works. I've timed the engine perfectly. I've run the boat for 6 months or so with this stuff in full working order. That's the only reason I've ruled it out. I know it works.

Now replacing the distributor itself. It's the only real money I've spent without remedy and my old one was pretty shot so I'm not upset about that. Plus I did think I confirmed the issue by lubricating the mechanical weights. Every time I did, the engine worked normally. That was my test. All of the ignition tests I've done through the Seloc manual check out ok. I'm certainly no expert but I've been around a wrench or two. Now the entire ignition system is effectively rebuilt.

I wish I had the tools required to do all of the testing you guys suggest such as compression and such. I guess it's time to give it to a mechanic to do those tests and pinpoint the problem. So I plan to do that.

One last thing I want to check on my own is regarding the carburetor. I did rebuild it once I started having this stalling/backfiring through the carb issue at a certain RPM under load and had ruled it out since it did not seem to solve any bit of the issue. This was exactly 11 months ago when I first had these issues. One thing but I did notice that the linkage that drives the accelerator was worn pretty good. This is the linkage on the outside of the Mercarb carburetor. I wonder if that could have an effect. For example, at this RPM the timing advances but the accelerator pump doesn't deliver the proper fuel burst and the engine starved of fuel stalls.
Any chance or should I just send it to the mechanic now?

 

[rlambert]

Re: 1986 Sea Ray Mercruiser 140 Backfires/Stalls at certain RPM

thanks