Can a Faulty Flame Arrestor Screen Lead to Throttle Issue?

[chanlmee]

Hello Afourians,

I have a 1974 C&C 27’ CCY273581073, with an Atomic 4 engine #YW# 13064-1332468. I’m not sure if this makes it a late model or not. I have an electric fuel pump and polishing filter installed. This engine is generally very clean and awesome!

This past season 2015, I’m pretty sure the engine ran for 5-30 hours without the benefit of the flame arrestor screen in position. One of the 2 screws securing the flame arrestor screen in place became dislodged and hence it swung to the side leaving the mouth of the flame arrestor housing wide open.

What works:

1. I can start my engine without too much problem with the choke on.
2. When the engine is warm, I can close the choke and the engine will run smoothly for hours as idle speed.
3. I can increase or give more throttle to a certain extent…. maybe 10-35% more but I need to open (or find the right level of) choke to match the additional throttle level.

What does not work:
Once warm (or not), if I try to increase throttle past 25-35% without opening the choke, the engine will come to chugging stop within seconds. Even with the choke fully open, if the throttle is opened to more than 35% or so the engine will come to a slow stop.

I cannot be sure but its almost like the air to fuel mixture is not right. Too much fuel? Dirty carburetor not allowing more air when needed? Not sure.

If I open the throttle and it starts to come to a chugging halt, I can throttle back down and the engine will mostly return back to it’s smooth rhythm, if I catch it in time.

Needless to say I’ve become very attuned to listening and adjusting my levers to keep my Atomic 4 engine working. BUT this is not sustainable.

Spring if fast approaching and I am shopping around on the Moyer Marine site to sort out if/ what I will need. I’m not even sure if I need to get the early or late model carburetor servicing kit. Any advice is appreciated. What I’m trying to avoid is spending a good deal of my short Canadian sailing season not going out because of engine issues.

Thank you
C&C '27 - Pegasus, BYC, Ottawa

[ndutton]

I'll take a guess.

Sounds like insufficient fuel for the amount of air. When you open the throttle all you're doing is allowing the engine to suck in more air. The carburetor supplies an appropriate amount of fuel to suit the air volume. Adding choke to keep it running pretty much confirms it.

So what can cause insufficient fuel to air ratio at higher RPM?

1. Dirt in the metering jet and if so, from where?
2. Vacuum leak - many possible places
3. Poor supply from the pump/tank/filters
4. and as always, maybe a combination

[JOHN COOKSON]

You're running lean.
How long has it been since you replaced the polishing filter? You could remove it temporally and see if things improve.
You are going to have to start somewhere, working through the possible causes of lean running until you find where the problem is. Why not start with the easy stuff first?

TRUE GRIT

[roadnsky]

I strongly recommend you download the CARB video that Don made.

http://www.moyermarine.com/cgi-bin/s...rebuilder.html

Only 12 bucks and the private lesson with Don is priceless.

[edwardc]

Originally Posted by chanlmee

... One of the 2 screws securing the flame arrestor screen in place became dislodged and hence it swung to the side leaving the mouth of the flame arrestor housing wide open. ...

When its properly in place, I've got to believe that the flame arrestor provides some amount of restriction, especially if it hasn't been cleaned for some time. With the arrestor open, this would allow more air in, producing the lean conditions you described. Have you reattached the flame arrestor? Did you clean it before you put it back?

[chanlmee]

Thanks everyone for your thoughts and insights.

Neil -

1. It could be dirt. The local marina engine person thinks anything could have gotten into the carb with the flame arrestor open...
2. Vacuum leak - maybe - I have no idea - but in general this engine is very tight and clean
3. Supply - unlikely from the tank to the polishing filter, i cleaned my tank 2 years ago until she was spotless. When I change the polishing filter the remaining fuel in the line normally has no problems splashing everywhere!

John -
I had to look up what running lean was but when I learned what you meant I realized you are thinking the same lines as Neil (too much air not enough fuel). I also like the idea of checking the easy things first. I will change the polishing filter first and see if it makes a difference.

I will look into the video if I plan on taking apart the carb - I will need it as I'm not much of a mechanic!

Edward -
I did put the arrestor back in place but I don't think it made a difference. As for cleaning it, I may have soaked it in gasoline. I'm happy to retry to clean it. How does one clean a flame arrestor?

Thanks all

[ndutton]

Dirt in the jet comes from the fuel system, not the air via the intake. When was the last time the carburetor was removed and cleaned?

Also, please take caution to avoid assuming something is good because it was previously. Solid troubleshooting is starting with what the symptom suggests and following it thoroughly and methodically from source to end.

Getting back to possible debris sources, non-alcohol rated fuel hoses are a common issue, marina gas dock systems dispensing krap, deteriorated O-rings at the fuel fill deck plate too. Simply removing and reattaching fuel hoses from barb fittings can slice the hose interior at the fitting and send debris downstream. Consider that debris found inside the carburetor does not grow spontaneously, it came from somewhere. Once found and cleaned, it's source must be found or you'll be in for a repeat performance sooner or later. Something simple and difficult to find is a clogged screen at the bottom of the pickup tube inside the tank, we've seen that before too.

Anytime I'm involved in such troubleshooting I prefer to replace as I go, particularly fuel hoses. In the big picture of life they don't cost that much and when you're done the system is as good or better than factory new.

[edwardc]

Originally Posted by chanlmee

...I did put the arrestor back in place but I don't think it made a difference. As for cleaning it, I may have soaked it in gasoline. I'm happy to retry to clean it. How does one clean a flame arrestor?...

Gasoline is probably fine. My thought process was that maybe the arrestor was a bit clogged (which would make things run rich, like a partial choke), and the engine was tuned to compensate. Cleaning it would make things then run lean.

[romantic comedy]

I am big on learning the engine like the back of your hand. Now is the time to get to know your carb. Get Don's video and take the carb off and rebuild it. you will then become at one with your carb and feel totally comfortable with it.

The same goes for the ignition system, by the way.

Good luck, it is not hard and there is plenty of help here.

[JOHN COOKSON]

I don't know what is in the Moyer carb video. Note the parts in the exploded parts diagram on page 76 as you take the carb apart. It will help you get the carb back together right.

TRUE GRIT

[chanlmee]

Neil, the carburetor has not been cleaned since I took ownership of the boat. That would be 2011. That would be 4 years. In these circles of the Afourians I expect to be shamed! Go ahead .... let me have it! <walk of shame>

Thanks for the pdf John. I do have all the atomic 4 manuals but I am not exactly mechanically inclined. Since I started sailing this has been a lesson in not just sailing and boating but also engine maintenance. This forum has been amazing. Thank you

I'm going to take the plunge and get this carb properly serviced but I will try replacing the polishing filter first. I've figured out that I have a later model engine so I will try to order the following parts off the Moyer Marine online catalogue:

• 2x Fuel filter, inline secondary (polishing filter), FPMP_07.1_473
• 1x Carburetor late model service kit (jets, nozzles and gaskets), FCAR_02_54
• 1x Electric fuel pump (2-3 PSI), FPMP_01_44

I don't think the fuel pump is the issue but it may be? Normally I'm of the mind that if it aint broke don't fix it but if I try to change the polishing filter and I still have this issue AND I end up servicing the carb then I may as well replace the pump too.

Makes sense? Have I missed anything? Thanks again and I'll come back on the forums in late spring once I've splashed and sorted things out. Right now she is on the hard and all wrapped up.

Cheers,
C&C '27 - Pegasus, BYC, Ottawa

[ndutton]

No shame from here. We had a poll a while back asking the members how often they rebuild their carburetor. The overwhelming majority wait until problems emerge. I'm not a big fan of such a strategy but nevertheless that's how it is. If it ain't broke don't fix it is the popular approach. Said another way, you fit right in.

Your non-mechanical admission suggests Moyer's video is perfect for you.

[roadnsky]

Originally Posted by chanlmee

I don't think the fuel pump is the issue but it may be? Normally I'm of the mind that if it aint broke don't fix it but if I try to change the polishing filter and I still have this issue AND I end up servicing the carb then I may as well replace the pump too.

What Neil said...
No shame here. Everyone starts and learns at some point.
(Some never learn tho )

Before you order a new pump, you can verify that it's working by disconnecting the hose at it's output and turning it on to see if it pumps fuel.
(Have a container ready to catch the fuel please)
If you get fuel output, no need to order a new pump unless you're looking to have a spare.

[chanlmee]

I'm pretty sure the fuel pump is working. As I mentioned I can run the engine indefinitely. It's only when I throttle up significantly (adding more air) that the engine misbehaves (dies out). When I open the choke I can get more revs/ rpms to a certain extent.

From what I've learned here, since its the carburetor that is supposed to manage the ratio of air/fuel I would think its with the carb.

For now I'll pass on the new fuel pump and save $100. I'm still a few weeks from being to access the boat but thanks for all the help so far!

[JOHN COOKSON]

Originally Posted by chanlmee

(3) I'm pretty sure the fuel pump is working. As I mentioned I can run the engine indefinitely. It's only when I throttle up significantly (adding more air) that the engine misbehaves (dies out). When I open the choke I can get more revs/ rpms to a certain extent.

(2) From what I've learned here, since its the carburetor that is supposed to manage the ratio of air/fuel I would think its with the carb.

(1) For now I'll pass on the new fuel pump and save $100. I'm still a few weeks from being to access the boat but thanks for all the help so far!

(1) This is sound troubleshooting. Change only parameter at a time whenever possible. Another example would be don't go to an EI if the engine is not running normal with points.
(2) This is true if the carburetor is working as it should. It ties in with (1). Once the engine is warmed up the carburetor should do the job at all RPMs with the choke fully open. You should have to "help" the carburetor do it's job with the choke. Also see post #1 "what works" item #3.

TRUE GRIT