Carb tune-up?

[JimG]

I just acquired an A4 (actually, it came in a 33' fiberglass envelope). The previous owner had it "inspected" by a professional mechanic recently, and his only suggestions were "could use a new carb gasket someday". It apparently ran pretty well for him.

The engine was rebuilt in 1997 and supposedly has only 250 hours on it, although there have been a series of owners, so I'm not sure how that number was generated. I do believe the boat sat at the dock for most of that time.

The day before I took possession, the seller's "friend and A4 expert" stopped by and "tweaked the carb adjustment".

Now it runs horribly. It starts easily, but won't keep running without the choke on full until the engine is hot (takes 15-20 minutes). When cold or warm, with or without the choke on, it stalls immediately when the transmission is engaged.

Not very good for emergency use or quick trips around the docks.

If you turn off the choke at min throttle, it stalls. Once hot, it idles nicely.
There's no tach, so I can't tell much more (yet). I live 80 miles from the boat, so tinkering is a bit painful.

When hot, it runs ok, but even the seller thought it was anemic when we were motoring from the dock to the yard. It's got a Martec prop, so I didn't expect high speeds, but I thought the engine would be able to run faster than it does - maybe even cavitate the prop...

The locals don't recommend any local mechanics, as they are all commercial fishing types. Any ideas of things to try? I do plan to buy your book and educate myself, but I want to be able to get to the fuel dock without a boat hook:)

[JimG]

I forgot to mention it's a 1975 model. It does have a flame arrestor, which seems to make it a "late model"?

[Banyan Day]

Jim,
Assuming the engine ran fine before "the adjustment", try readjusting the idle screw - turn clockwise all the way in until it just stops, then counterclockwise out one-and-a-half turns only. I would also check under the flame arrestor and make sure there isn't any liquid sitting in there. If this doesn't solve the problem then at least it's a good place to start the diagnosis! The fact that it starts easily is a good sign - so smile! I'm sure Don will chime-in with some excellent advice soon, so stay tuned!

[Davis Modlin]

Hello Jim

First: Where do you live? on the left, the right, or in the groove. Also, Did the machanic adjust the carb only or did he adjust the timming aswell? If he adjusted the timming, Just set it back ti top dead centure. If he adjusted the carb, It sounds like he more than likely leaned it out (since you have to leave the choke on for so long). I would turn the mix screw out a little bit (1/4 to 1/2 turn counter clockwise).

Davis

[JimG]

The villain (the seller's expert friend) is incommunicado in Costa Rica for a few months. The seller says "he simply adjusted the intake valve that controls the idle". I assume he means the idle misture.

The boat is in Brookings OR.

I'll try the procedure to reset the mixture and idle speed found all over the web.
(e.g. one turn open, set idle in gear to 700, adjust mixture for max rpm, set idle, repeat)

Can someone explain how the flame arrestor works?

[Davis Modlin]

The Flame restrictor works by simply restricting or "choking off" the path by which the flame would travel. In other words the air going into the carb is moving at a slow and even pace, But when the engine backfires thru the carb, The air and the flame are moving much faster. (also see: rocket engines). The arrestor (ie:suppressor) restricts the path of the flame and keeps it from hopefully reaching anything flamable in your engine compartment.

P.S....... The fins in the arrestor restrict the air flow, But also create an area that has limited air to fuel the fire.

Davis

[Don Moyer]

Jim,

My advice to this point is exactly the same as Banyan's. On the basis that the engine ran fine before the prior owner's friend worked on it, you should contact that person and get a list of exactly what he did to the carburetor, and/or anything else.

Late model carburetors only have one adjustment for fuel mixture, and that is the idle adjustment. Pending his response (or in case he's unavailable for comment), we are left to assume that the friend of the prior owner (at least) moved this adjustment.

Remember that the idle adjustment (on top of the carburetor with a screw driver slot) adjusts the air portion of the mixture, so turning the adjustment in makes the mixture richer, and backing it out makes it leaner.

You might also check for a small "T" handled adjustment extending out the bottom of the carburetor. This would be an adjustment for the high speed mixture. While this adjustment was not standard on late model carburetors, some folks have installed one. Adjustable main jets control the amount of fuel in the mixture, so turning the "T" handle in will lean the mixture. If you have an adjustable main jet, I'd start by backing it out a half turn or so (counter-clockwise).

Best regards,

Don Moyer