Carburetor education please
 

I dont really understand the way the carb works, so please help me. I recently found a small clip on the starboard side that holds the "flapper" for the front two bowls was gone and therefore was keeping the "flapper" 3/4 closed apparently all the time. I replaced this clip(with a small copper wire) and it seems to hold it where its intended to be. You can easily move this flapper to the full open position manually and when released it goes back to about 3/4 closed.

So, I started the boat and the warmer the motor got, the more open this went until it was in the vertical position. When I would restart the engine, it would fire and run much better now, in fact its amazing how fast it starts now and how it seems to run much better, in the driveway anyway. Was this just making the engine run too rich?

What is the "flapper" connected to on the port side and what else does it do? I see another couple rods and things attached to it but it dose not look like they really do much? Im sure they all have a purpose, and I was just hoping you could help me understand it a bit better.

Another question I have since on the topic is where is the choke? and how do you activate it? Or does it just know when the engine is cold and self activate? I tried just cranking and starting, but, that didn't work, so my typical method that works well is a couple shots from the throttle and she fires up pretty easily when cold.

Here are some pics of the carb, so you can walk me through this, and as always, thanks for the education.

Re: Carburetor education please
 

Ok,,,, had a day on the water and want to get some help please.:confused:

The boat starts and runs perfectly. It sort of chokes a bit when you nail it to get on plane, and takes a while to get there. Top speed is about 35 trimmed out:shakehead:

I have replaced fuel, fuel filter, newly tuned prop, and it is not aggressive it is only a 19 3 blade( I have a 21p SS as well) both with same results.

PROBLEM: I can only get 3500-3700 rpm WOT!!! :mad:

Many of you have made reference to the fuel pump and a couple other things here, but can you please give me some advice to diagnose what is wrong and what I need to replace? Its driving me a bit crazy.

Thanks for the advice and education.

Re: Carburetor education please
 

If, by "flapper," you mean the rectangular thing over the carburetor primary throats (the two smaller one in the "front" of the carb), that I've circled here:

http://www.linxnet.com/misc/pwrboat/...etor_choke.jpg

it should probably be connected to an electrical choke control, because, you see...

...that's the choke :).

As far as to what it's (supposed to be) connected, and how: There I cannot help you, as I've never closely-examined the choke linkage or electrical choke system on these engines.

Back in the day, when I used to wrench on cars, the chokes were all heat-controlled. (Talk about taking something simple and making it more complicated than it has to be :rolleyes:)

Sounds like a bad accelerator pump.

All things considered: I suspect you need a carburetor rebuild.

If you don't know enough about carburetors to know what a choke is (sorry, just callin' 'em like I see 'em), I would suggest this is probably not something you should try yourself, especially with a 4bbl, spread-bore carburetor--unless you like throwing away money.

Jim

Re: Carburetor education please
 

I figured this was the choke mechanism, what i meant was what controls it and how is it activated? It just is connected to a control arm that disappears under the carb. So it likely is just heat controlled and therefor automatic. That seem to work fine.

So, the accelerator pump, where is it and what does it look like? I have read many of your references to it and the need for it to keep up with fuel at the rate of air and all, but I do not see anything controlling fuel expect my fuel pump. Is it part of the fuel pump?

I can do a lot of stuff, but unless it was winter and I had a couple months to learn, no, I will not be rebuilding the carb myself.

Would the carb run perfectly except just not allow high RPM's if it needs rebuilt? That just doesn't quite make sense to me.

Re: Carburetor education please
 

As I wrote: On newer carbureted engines, they're mostly electrically controlled, as I understand it.

It's inside the carburetor and it looks like this:

http://www.linxnet.com/misc/pwrboat/...rator_pump.jpg

It's not "running perfectly." It's got a replacement part hand-fabricated from a piece of wire by somebody who doesn't know the first thing about carburetors, you've got pretty serious hesitation on acceleration, and you're not reaching rated RPMs at WOT.

Carburetors are twitchy things. If you get it wrong the engine will run poorly, or not at all, and use more fuel than it should. Worst case... well, my brother, messing with his carburetor, lo these many years ago, after ignoring my admonishment "If you keep if up, you're going to set your car on fire," set his car on fire :rolleyes:

I'm not trying to belittle you. I'm trying to save you a lot of grief. And I'm usually the last person to suggest that somebody not do as much work on their own boat as they can. But carburetors, especially spread-bore carburetors, like you have, are easy to mess up. They're best left to people who know what they're about.

Remember: You're dealing with gasoline, which is highly volatile, in a boat. Boat + gasoline + getting it wrong =

http://www.linxnet.com/misc/boats/misc/LE_boat_fire.JPG


Jim

Re: Carburetor education please
 

Geez Jim, sorry I asked.

Thanks for the advice on blowing up my boat.

As for the fabricated clip to hold a control arm, what does it matter if I made it out of a piece of copper or a chinaman made it out of a piece of brass? It does the job well either way.

I do appreciate the picture of the accelerator pump and the location.

When I say run perfectly, obviously it was with the caveat of the imperfect features I was explaining. If it was actual perfection, I would not be posting this thread.

Yes, thanks for the gasoline explodes explanation. I had no idea.

Re: Carburetor education please
 

Took her to a merc tech and " nothing wrong"= $320.00..... Well,, replaced her custom fuel line with the ORIGINAL fuel line and shazam,,,,,, she runs like a skorched feline!

For some reason, the custom made fuel line they created at the custom line shop does not let enough fuel through. Now that i am back to the stock line, all is good. WOT 47-4800 and good speeds to be documented

Too bad I couldn't get a basic carb explanation here on the thread though. I love the site but this let me down a bit.

Re: Carburetor education please
 

Sorry to have let you down on the eduction bit. A quick Google search will provide a link to a site that does do a decent explanation on how a 4bbl carb works. I dont know that there are any carburetor specialists on our site who have a detailed knowledge on how every part of a carb functions particularly with the number of different carbs used on the various engines. There are a few of us who have a bit of an understanding of how a carb works but to give a detailed explanation is best left to the specialists. I agree with Jim here. I wont touch my 4bbl carb except to give it a cleaning. Unless you know what you are doing or are very mechanically inclined, carb repair is best left to the pros for exactly the reasons he stated.

Re: Carburetor education please
 

Mikey, your right, I agree.

Re: Carburetor education please
 

Yeah sorry bud I would have piped up myself but I leave the carb to a buddy of mine who is presently out of the country. He is like a magician with carbs especially rochesters, aka spread bore types.