which carb to upgrade/replace too

[Lou C]

Also there are other things that can cause fuel delivery problems, such as a fuel pick up tube with a clogged filter, or a blocked/corroded anti siphon valve.
I rigged this up to test mine for leaks, both were fine, my performance problems were simply from bad gas this past season. I tested it to -10" of mercury which is what a mechanical fuel pump pulls usually. I found that a good anti siphon valve opens between -1-->2" of mercury
The way to rule these causes out is simply hook up an outboard fuel tank to the fuel pump and run the boat on that. If you still have problems, it's definitely the carb, but if it runs perfect it's the boat fuel system. So, you'll be pulling the fuel pick up tube and looking at the anti siphon valve.
When I did that, the boat leaped up on plane and ran perfect. Shoulda done that before going through the points and cleaning/rebuilding the Quadrajet!
PS if you do this it's a good idea to put a shut off valve on it, in case the fuel line to the pump leaks! Use good clamps too!

 

[bigtoe]

to the OP: As a second opinion,
Danforth is right.

Many thanks

 

[bigtoe]

Also there are other things that can cause fuel delivery problems, such as a fuel pick up tube with a clogged filter, or a blocked/corroded anti siphon valve.
I rigged this up to test mine for leaks, both were fine, my performance problems were simply from bad gas this past season. I tested it to -10" of mercury which is what a mechanical fuel pump pulls usually. I found that a good anti siphon valve opens between -1-->2" of mercury
The way to rule these causes out is simply hook up an outboard fuel tank to the fuel pump and run the boat on that. If you still have problems, it's definitely the carb, but if it runs perfect it's the boat fuel system. So, you'll be pulling the fuel pick up tube and looking at the anti siphon valve.
When I did that, the boat leaped up on plane and ran perfect. Shoulda done that before going through the points and cleaning/rebuilding the Quadrajet!
PS if you do this it's a good idea to put a shut off valve on it, in case the fuel line to the pump leaks! Use good clamps too!

View attachment 414535
View attachment 414534

Thanks for the info, now the old fuel last year they said was bad, so they did as you did and fitted the outboard tank to run it up in there work shop. Told me to empty and clean the tank , which I did . I didn’t think the fuel looked to bad , and not really any dirt in there as I cleaned it out two years ago.
So my question is , where would the anti siphon valve be? I’ve not heard of that before , this could also be part of the problem!
Thanks

 

[Scott Danforth]

its the barbed fitting on the tank

 

[Lou C]

Yep in my pic above you see the alu pick up tube, the anti siphon is screwed into that on the left side of the pic, with the rubber fuel hose attached to it. They can be tough to remove, if not removed for a long time. On mine I got lucky, both the anti siphon and the pick up tube came out easily. The fuel tank and pick up tube are 38 years old! The anti siphon valve was replaced back in 2004. Still good though. This tube didn't have a screen on it but some do and cause fuel starvation, you won't know unless you pull out that tube.
When I first bought this boat in 2002 the engine would start and run at idle fine and would move the boat at idle and just above but would not plane off the boat. So the mechanic I used at the time found the anti siphon valve was stuck and the carb needed to be rebuilt and it was fine after that.

 

[Lpgc]

Had a problem with a stuck anti-syphon valve on my boat's tank too, was advised to remove and clean it by some of the same people who have posted on this thread, fixed it. Before fixing it would run OK up to about half throttle but lean off or cut out if I gave it more throttle. IIrc there was a ball bearing in it which had become stuck in the near closed position, cleaning it all up inside and getting that ball freed off was a complete fix.

 

[bigtoe]

Well I will say mine has had similar issues , at times, possibly it jams then frees itself .
I normally find I have two issues going on, I do know that fitting , I tried to remove it last year to aid cleaning the tank. Tight as a tiger it is. I’ll have to try harder . Thanks

 

[Lou C]

I made the sign of the cross and said a couple Hail Marys before trying to get mine loose! And sprinkle Kroil and Freeze off etc like holy water! Time, patience will get it done.

 

[Scott Danforth]

some of those Anti Siphon valves are aluminum, some are brass. use a deep well socket or a box end wrench before using a flare wrench. do not use an open wrench.

 

[Lou C]

Yep be careful, give the penetrating oil time to work....
the ones that are Alu are usually for under 200 hp engines, brass for those above IIRC. There are actually different flow rates, I saw something about that in my OMC factory shop manual.

 

[jlh3rd]

off topic.....but,
gotta thank this site as I never knew there is an anti-syphon valve in my fuel line.
Because of an issue that developed out on the bay last year, I'm pulling my fuel pickup and examining my 20 year old tank, for the first time (my bad) and supply system. In stalling a fuel/water separator, engine fuel filter....and just ordered the valve.
The engine is a '21 so it's the least suspect. Fuel line is all new.
.....and no Chinese parts.

 

[bigtoe]

Thanks , from memory ( of only late last year ) my pick up tube is plastic going down to a filter at the bottom in the tank.
If it ever stops raining here , I’ll get out and take the cover of and have a look!

 

[bigtoe]

FYI, you should not need to pull the carb or strip it, only remove the bowl and metering plate to clear the accelerator pump circuit.

this will help you. https://www.carburetor-parts.com/assets/manuals/holley-2300-4160-manual.pdf

View attachment 414530


clean out this passage. you will need to carefully remove the accelerator pump cover and diaphragm. you will have either the rubber mushroom check or a real check ball check for the primary check

View attachment 414531


the secondary check is in the discharge nozzle, make sure that is removed and cleaned too. with the throttle blades closed, choke blades held open, use a #3 Phillips screw driver, and remove the screw holding the discharge nozzle, there is a round crush washer under the nozzle, and in the nozzle is a weighted ball check or a fuel needle used as a check. simply make sure the check moves freely.

At last I have managed to get to the boat !
Ive got the bowl and metering plate of . The hole you said to use fishing line on , I do think may of been blocked, it felt like I had to push through something ( like a light film ) when I started probing. I can blow freely through the hole now. Do you tink I need need to remove the accelerator pump still or as I can blow through accept its clean?

Is this strange, I had zero fuel in the carb , I also removed the anti syphon fitting on the fuel tank, again zero fuel there either. Pipe completely dry. Could it be the anti syphon ( is it a non return valve? ) valve is not seating properly so there for fuel running back to the tank?

The anti syphon valve didn't seem bad, If I blow through it I can feel the spring operand ball bearing move. I do have to give it quite a puff though , is that right?

Last question, the fuel inlet pipe is not good, im going to need to replace it with an adapter to rubber 8mm fuel hose. can I get the fitting ( needs to be an elbow) easily enough ?
Many thanks for all the advice

 

[Scott Danforth]

I can blow freely through the hole now. Do you tink I need need to remove the accelerator pump still or as I can blow through accept its clean?

you can test it, just put a bit of fuel in the bowl (at an angle), covering the check valves of the pump itself and actuate.

Is this strange, I had zero fuel in the carb ,

if you havent run the boat in a few weeks, the fuel will evaporate out of the vent tubes. very common. also common for dirt daubers to build nests in the vent tubes if you let it sit without the spark arrestor.

Last question, the fuel inlet pipe is not good, im going to need to replace it with an adapter to rubber 8mm fuel hose. can I get the fitting ( needs to be an elbow) easily enough ?
Many thanks for all the advice

post a pic of what you are talking about.

 

[Lou C]

The anti siphon valve is not for preventing fuel from running back to the tank it is there as a safety device, in case the fuel line from the tank to the fuel pump leaks, fuel cannot siphon out of the tank into the bilge. This can be the case if the fuel line drops lower than the top of the tank in the bilge. The spring will shut the valve, then when you start the engine, the vacuum developed by the fuel pump sucks it open. A good anti siphon valve (I tested a brand new one) will open at approx 1-2" of mercury vacuum. A good mechanical fuel pump pulls about 10" of mercury vacuum (according to my OMC shop manual).
It sounds like your original problem could have been simply clogged passages or air bleeds in your Holley carb. I knew your shop didn't know what they were talking about when they said the jets were "worn" they don't wear they get clogged by crud. Now if they meant that the slot was buggered up by a fool using the wrong tool to remove them to clean the passages and now they can't get the jets out and can't clean your carb correctly, well that's a whole different thing! That could be right, if that's what they actually meant.
Carb cleaning and rebuilds take time and the cleaning is the most important part. I have had my old Quadrajet apart 3 times over the years. A bit more complex than the Holley, but some like them better.

apart

all done
I also have spares: