Leaky Quadrajet and or anti siphon valve

[wellcraft-classic210]

The problem statement:

On our Merc 260 ( 350 v8 with Quadrajet ) ) alpha 1 in a 1983 Searay SR260 I have had a lack of fuel issue at startup until the system builds pressure. This gets worse if the boat sits over 1 week and has been that way for some time now // However-- this season its getting worse.

Details

Starts right up if used in the last day -- Divorced Choke works OK if over a few hours // Runs great once started
Need to crank for about 10 seconds if the boat sits for over a week. ( Last 2 years I had this issue but not as bad -- maybe 5 seconds max )

I suspect that the Carb leaks via the passage plugs and also that the anti siphon is leaking as the cranking needed for over 1 week without use has increased.


My plan

1) I just ordered a new anti siphon valve as they are fairly low cost and an easy change-out. ( it was clean on prior checks and i suspect it may be scored or worn, )

2) I need to do something about that Carb -- ( Winter project ??? )

3) I should check the fuel pump pressure -- but that seems to be enough to supply the engine at full throttle so I don't think that's the culprit



My question is

-- Has anyone had good success sealing a leaky Quadrajet by using set screws and epoxy to seal the passage plugs or by any other method ?


I would like to try and fix this before switching to an Eldebrock carb -- But open to advice here. Their seem to me some mixed reviews on a successful fix to the passages.


Any other input is welcome -- Thanks in advance !

 

[alldodge]

My 1994 Rinker has been the same way for many years, think since new. To me its no issue, just crank for 5 seconds before pumping throttle. The gas is just evaporating

 

[jimmbo]

What is your starting procedure? Are you locking out the shifting mechanism, setting the choke and squirting some gas in the manifold via the accelerator pump? Sort of like what us old fogies had to do when cars/trucks had carbs.

 

[wellcraft-classic210]

Yes -- I use the acc pump & understand its operation

its just taking a while to get fuel and its been longer lately increased from 5 to over 10 seconds // Its seem to long for just low fuel in the float bowl.

 

[alldodge]

Might need a new pump, could check pressure

 

[kenny nunez]

When you remove the throttle plate you will see the 2 plugs under the float chamber. JB weld will seal them.

 

[wellcraft-classic210]

Kenny
Have you personally done the JB weld option with good success? ( I ask as their seem to be mixed reviews on that fix & similar ones )

Just to be clear -- I suspect I am refilling the fuel filter at startup if the anti siphon is not sealing properly which is accounting for added time -- or possibly low fuel pump pressure -- along with lack of fuel in the float bowl. Will dig into it this weekend hopefully -- gathering ideas now

 

[HT32BSX115]

Kenny
Have you personally done the JB weld option with good success? ( I ask as their seem to be mixed reviews on that fix & similar ones )

Just to be clear -- I suspect I am refilling the fuel filter at startup if the anti siphon is not sealing properly which is accounting for added time -- or possibly low fuel pump pressure -- along with lack of fuel in the float bowl. Will dig into it this weekend hopefully -- gathering ideas now

Howdy,


#1. I wouldn't use JB Weld in the carburetor (even though their own FAQ indicated it's completely impervious to gasoline)

#2. The anti-siphon check valve does not prevent the carburetor or fuel filter from staying full. It's there to prevent fuel from "siphoning" out of the tank when there are fuel lines below the level of the tank and they develop leaks.

#3. The automatic choke has nothing to do with your accelerator pump.....with that in mind, if you have to crank for 10 seconds you're either not pumping enough fuel PRIOR to cranking, or the fuel bowl is not full. I would look to the accelerator pump and fuel pump to solve this.

10 years ago when I installed the 7.4L Mercruiser in my current boat, the first thing I did was disconnect the automatic choke and adjust it completely out of the picture.

This does require a small amount of fuel to be poured into the carb at the beginning of the "season" to run and prime everything. Once I get it running, all it takes for subsequent starts is a couple of "pumps" of the throttle. It usually starts, primes and runs immediately............

There is a bit of a "warm-up" time required, but who starts a cold engine and goes directly to full throttle anyway?

I don't boat in cold weather so a choke is not needed.

If you're not flowing enough fuel, look at the fuel pickup (in the tank), anti-siphon check valve, filter and pump.

Also, if your fuel vent is clogged or partially clogged, it will put a slight vacuum on the tank that (with a leaking anti-siphon check valve) could suction fuel out of the fuel lines filter and carburetor bowl once you shut it down.

 

[jimmbo]

Have you checked to see if the choke is closing completely? Prolonged cranking on a cold start will be needed if the choke isn't closing fully. Pouring gasoline into a carb on a boat isn't the wisest thing to do. Aside from the fact that liquid gas will wash any residual oil off the cylinder walls, any spillage puts gasoline, which will evaporate into vapour in the bilge.
Has the carb been taken apart? If so perhaps the float was set too low. Or if replaced, the wrong float was used. The leaky fuel bowl plugs are not very common. but because they were mentioned in every Q-jet writeup in the late 60s it has been taken as gospel that they are leaking.
Are there any vacuum leaks. ie gaskets, disconnected vacuum lines, cracked or split vacuum lines?

If the fuel in the carb is draining, hopefully into the intake, the initial start up might be too rich if the choke is operating correctly. Next cold start, hold the choke open and see if it catches.

 

[HT32BSX115]

Pouring gasoline into a carb on a boat isn't the wisest thing to do. Aside from the fact that liquid gas will wash any residual oil off the cylinder walls

I agree that one should be extra careful not to spill any, I always ensure that the blowers are on and the carburetor flame arrestor is re-installed before cranking

I would disagree that there's any oil "washed" from the cylinders......., If that were true, you should never use the accelerator pump at all. The amount to "pour" in should never be more than the equivalent of 2-3 pumps of the accel pump in any case.

You would have to literally pour a half a cup of gasoline into the carb to get any liquid to the cyls. That would be of course WAY too much

And even using the accelerator pump 2 or 3 strokes, you only coat the intake manifold with liquid gasoline that begins to evaporate immediately...... little or NO liquid actually makes it to the cylinders. Only the vapor gets in anyway....(which is what ignites anyway)

Back to the OP's original problem

The problem statement:

On our Merc 260 ( 350 v8 with Quadrajet ) ) alpha 1 in a 1983 Searay SR260 I have had a lack of fuel issue at startup until the system builds pressure.

If true, and his accelerator pump is not pumping fuel to begin with, the problem IS the accelerator pump (or fuel delivery to it) not the choke.

 

[CamaroMan]

i would rather tap/seal those leaky plugs than jb weld them. its a much better fix. This is prob whats happening - however I had similar issues on my qjet for a while.. A warped body might also not seal the gaskets properly (from over tightening) - a common issue. Look up the lars quadrajet tuning document, get some coffee/beer (or not and!) and read it thru a couple of times - its long but VERY informative.

 

[kenny nunez]

The safest way to prime a carburetor is to use a trigger oil can and squirt the gas into the vent tube.
Leaking bowl plugs have been a problem since the Q jet came out in 1965. I never had a "come back" after using JB weld on my customers boats.
Some times the pipe thread compresses the area where the ball is located and cause a restriction inside the anti siphon valve.

 

[biggjimm]

Any luck figuring it out yet?

There is the very rare occurrence of having a "porous casting" where the fuel literally leeches through the float bowl. I've seen one & heard of another in 30 yrs. It is rare but it does happen.

If the fuel is actually disappearing from the float bowl, it has to be from evaporation or a leak in the bowl of some sorts. It's not going to drain back out the inlet & the fuel line. And likewise, unless your water separator filter is mounted upside down or sideways, it's not going to drain out of the filter neither. If it is mounted in a fashion that permits it draining back to the tank, it's not going to properly separate & isolate any moisture in the system.

Sounds like it could be seeping past a well plug or possible have a crack in the casting??

Good luck & keep us posted.
Jim.

 

[wellcraft-classic210]

Going to take a closer look today --- Thanks everyone for the thoughts and input

Will report any findings --

 

[Lou C]

One thing you can check, after running the boat, shut it off and then leave the throttle wide open, this way when you check it there will not be fuel from the accel pump being discharged. Let it sit for a day or two and then take off the flame arrestor and get a bright LED flashlight. Prop open the choke and look past the throttle plates into the bottom of the intake manifold, if you see wet fuel there, its a good chance those well plugs are leaking.

 

[wellcraft-classic210]

[SUP]OK Here is what I found after the boat sat for 6 days

--Float bowl empty as indicated by acc pump only o]puuting out a few squirts from its resevoir but not refilling from float bowl ( Fuesurpirse )
--Fuel lines at antisphon valve & carb entrance empty -- But the filter is full
--Fuel pump achieved 7psi fuel pressure ( or shuld I say air & fuel pressure ) quicky & held well with key oblff --
--Anti siphon valve was clean the ball is in position -- But the spring seems pretty wimpy and I can make bubbles with a little soap & blowing in the direction that the spring pushes -- so its not sealing 100%

-- 1 Key points

The fuel tank level is about 6 inches over the top of the carb when full & at the center of the crankshaft when empty -- Its currently at 3/8 of a tank which is about = to the top of the water pump( estimating ) . It seems this could allow the fuel to seek its own level to drain back into the tank if nothing else stops it such as a check valve. With the float bowl down air can enter the lines and it seems the check valve on the tank will not stop it from slowly doing just that. If I had fuel in the float bowl I doubt this would be noticeable and its also not likely to be happening with a full tank.[/SUP]

--Conclusion

[SUP]-- I need to fix that carb. // Keeping the tank low and adding a little on each outing as the end of the season approaches has made the problem seem worse.

I will order a rebuild kit and look for cracks, try to pressure test the passages with soap to locate the leak(s) / It seems if i can locate the leak(s) I can then test after and " patch work & tell if they are sealed.

It seems trying the epoxy will not be expensive or very time consuming and I can keep the boat original-- I surely know the symptoms if that fails

When the new check valve arrives I will compare the to the old on which has seen 1600 hours -- and probably well over 10,000 gallons of fuel in [/SUP]


-Thanks again for the input and thoughts - Any added advice on epoxy repair procedures or replacement base plate sourcing is welcome.

 

[kenny nunez]

When you take the carburetor apart and with the throttle plate removed try pouring some gas into the bowl and that should show where the leak is. It is probably the plugs but worth the test in case there is a porosity, you just never know. I cannot imagine how gas can siphon from a Quadrajet since the fuel level is below the needle and seat. I understand how it can happen with the fuel line draining back but if the carburetor was full there would be enough to to keep the engine running to refill the line. If you know someone with a glass bead blast cabinet use that to clean the area under the float bowl if you go the JB weld route.

 

[wellcraft-classic210]

Kenny thanks for the advice on the epoxy fix & bead blast is a good idea

I agree that gas is not siphoning back from the bowl-- I thinks its leaking into the intake manifold -- But I think air may be entering the fuel line once the float drops and may also be allowing the lines to siphon back-- Ill get the carb working & see how things go.

 

[wellcraft-classic210]

I found this link to video's interesting // [h=1]How to rebuild a Rochestor Quadrajet parts 1 through 12[/h] -- Video 6 shows a JB weld fix

https://www.youtube.com/watch?v=p-q_bk22TQQ

Its a good refresher -- -- I worked on a lot of these 2 barrels and 1 Q-jet back in the 80's --

 

[biggjimm]

As stated before Lars Grimsrud has some really good info in his Q-jet tuning papers. If interested pm me & I can give you his email. That is how he prefers people to get his papers as some of the copies floating around the web have been altered & added to with false information.

What type of fuel filter do you have? A water separator type (like an oil filter) or inline? It's puzzling that the lines are empty but you said the filter had fuel in it.

Also I guess I'm used to boats that have the fuel tank mounted way lower than the carb.

Jim.