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Discussion Starter #1
Hey guys, I have been having some issues trying to tune my dual webers.
I recently replaced my head gasket, now I am tuning the fuel system. Before I had to replace the head gasket, the carbs were leaking a bit of fuel out. Now, they are much worse.
Ive taken them off and synced the throttle bodies. Ive cleaned the jets in parts cleaner. I attempted to set the floats, but here lies my issue.
If I turn the key and prime the fuel pump and wait a minute, fuel dumps out of the carbs on the intake side-a lot. It will do this on both sets of carbs, but the left/rear most is the worst.
These are weber 40DCOE151 carbs. They do not appear in bad shape, I was going to adjust them with the uni-sun yesterday but it seemed like the fuel leak was only getting worse and worse.

What could be causing this leak?
When I attempt to test float bowl level, I start the car, idle for a few seconds, shut off, take out both main jets, then stick in my caliper for measurement. Correct bowl from the rim of the jet is 29mm +/- .5 correct?
To adjust the floats, I measured 12.5mm from the float to the gasket on the rim from the furthest point on the plastic float (end that travels the most). Then 25mm from the center of the float to the gasket for the most open point.

What did I miss? I am completely new to carbs, I understand the general aspect of how they work but this is my first go at setting them.

I did use a drill bit to measure the close position on the float.

I cleaned the little mesh filter in the caps.
If I test the floats off the car, I can close the float and blow through the tubes, and it will stop-no leaks from what i can find.
 

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Richard Jemison
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7,593 Posts
Webers leaking

Well, hopefully it`s as simple as too high a fuel level in the carbs. This can be caused by too high fuel pressure. Fuel pressure over 3 lbs will cause it.

Don`t rely on a pressure regulator as when fuel is "deadheaded (no outlet for fuel with the pump running and needle valves closed in the carbs) pressure WILL rise. Get a proper low pressure pump. I use Airex pumps, designed for Onan generators. (Ebay or Amazon) under $30.00
 

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Discussion Starter #3
I checked under my car to see what fuel pump is mounted, I found this generic from eBay-
https://www.ebay.com/itm/Universal-Standard-12V-Electric-Fuel-Pump-Self-priming-Petrol-Diesel-2-5-4-PSI-/202245166427?_trksid=p2385738.m4383.l4275.c10

It says its rated 2.5-4 PSI, from what I can see its non adjustable, so who knows what pressure it is actually pushing out.
Looks like the fuel pump is a good place to start.
The pump looks brand new out of the box, so my bet is that the previous owner put it on not too long before I bought the car.
 

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Discussion Starter #4
To correctly run webers, do I need to change the fuel pump to a pump that is 3.5 PSI at max?
Or do I need a fuel pressure regulator to bring down the pressure? Or both?

Currently the system is completely deadheaded, no tank return.

The issues that have made me jump into this are the leaking and when I was trying to adjust the mixture screws the other night, some screws changed the engine significantly and others did not seem to affect the idle at all. Thats what drove me to dive into checking float setup.
Then after adjusting the floats, my fuel dumps everywhere (worse)
 

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Richard Jemison
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Fuel level

Then after adjusting the floats, my fuel dumps everywhere (worse)
Drop the fuel level 1/8 inch from where you have it now. That is 1/8" more space between the top of the floats and the top gasket.

Easy way to avoid the "deadhead" issue is to put a "T" in both the feed line and the output line close to the pump. Run a hose between the two, but put a restrictor in the line with only a .040 (1mm) hole in it to maintain pressure to the carbs. The tiny orifice will reduce the pressure spikes from the pumps delivery.

Excess fuel is not just running out of the carbs it`s running into the cylinders!
 

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Filter King regulators will hold the set pressure even when they are dead headed.
 

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Discussion Starter #7
Filter King regulators will hold the set pressure even when they are dead headed.
So I can plump in the filter king filter without a fuel tank return? Its a strong enough regulator to put back pressure on the pump instead of re-routing excess fuel?
 

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Discussion Starter #8
Drop the fuel level 1/8 inch from where you have it now. That is 1/8" more space between the top of the floats and the top gasket.

Easy way to avoid the "deadhead" issue is to put a "T" in both the feed line and the output line close to the pump. Run a hose between the two, but put a restrictor in the line with only a .040 (1mm) hole in it to maintain pressure to the carbs. The tiny orifice will reduce the pressure spikes from the pumps delivery.

Excess fuel is not just running out of the carbs it`s running into the cylinders!
What could I use as a restrictor though??
 

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But Mad North-Northwest
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10,740 Posts
You don’t need a return line. Just a proper pressure pump, or a pump and inline regulator. Dead-heading carbs isn’t a problem provided your pump setup is correct.

Before messing with your pump, make sure your float levels are actually correct and your needle valves aren’t leaking.

If you’re worried about pressure suggest also measuring what you’ve got with a gauge before swapping parts. Most car parts stores will rent you a gauge.
 

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Discussion Starter #10
It doesn't look like there are too many Filter King regulators available in USA, they are all UK?
Could I use a Holley adjustable Fuel regulator that does not have a fuel return?
 

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Discussion Starter #11
You don’t need a return line. Just a proper pressure pump, or a pump and inline regulator. Dead-heading carbs isn’t a problem provided your pump setup is correct.

Before messing with your pump, make sure your float levels are actually correct and your needle valves aren’t leaking.

If you’re worried about pressure suggest also measuring what you’ve got with a gauge before swapping parts. Most car parts stores will rent you a gauge.
Thanks, ive done regulators and adjusted these sorts of things on cars before, just never a car that was A. Deadheaded and B. converted to carbs.

Thats what I was thinking, I can rent a gauge and check it.
I washed out the tops of the carbs where the float receives fuel, there was crud in there so I thought maybe that was pushing the float open. But when I tested the float off the car, it wouldn't leak past the needle valves and they looked to be in great shop-basically new(though it could be the issue).
These are spanish webers, so I doubt the parts are all that worn. They look close to new. (again, could still have broken parts, just wouldn't be my first guess).
 

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Buy this Filter King on e-bay. Mount it up front by the Webers, adjust for 3#. Problem solved.
 

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Discussion Starter #13
Filter is on the way!
 

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Discussion Starter #14
Ok an update. Its taken me some time to come back around to this part of the project, but heres where I am currently hung up.

The new regulator is on and set to 3.0 PSI, I have an inline fuel gauge after the regulator, before the carbs.
The carb float level is measuring 29.0 on the dot, with the main jet removed and measuring down the hole.
Main jet- emulsion tube is an F11, jet is a 135.
Idle Jet-50F17
I verified that all the jets in both carbs match, same with the venturis.
So no mismatched parts here, at least that I can find.

The issues-The engine still runs rough and bounces back and forth. I have to set the throttle screw so that the car idles at 1500RPM so that the car doesn't stall out, even then it will sometimes.
Ive taken the carbs off (multiple times)and manually synced the the carbs opening and closing.
If I turn the adjustment screws, no change happens. Ive tried on all 4 throats, no change. I can turn all 4 closed and still no change. The car is also hard starting from cold, big time.

After running the engine for a few minutes I can take the air cleaner off, and there will be dribbles of gas sitting in the opening of the throats and in the bottom of the air cleaner. Not nearly as bad as before, not even close. If I turn the key and let the fuel pump run, the gas doesn't pour out of the carbs like it would before the fuel regulator was added. I ordered the exact FPR that Gordon told me too. Ive tweaked around on the FPR, ive turned it down to 2.5PSI and not noticed any change.

I also tried unplugging the brake servo and blocking the pipe, in case my servo is leaking. No change there.

The ignition coil, spark plugs, rotor and cap, points/condensor, FPR, battery, are all new. The head is newly rebuilt, 100%, ground up rebuilt (had this issue before the rebuild also). All of the gaskets are new, the airbox/carb gasket, the carb/manifold, and the manifold to head gasket are all brand new. All the nuts and bolts have been tightened twice (no play there).
Ive probably replaced more parts than mentioned.
The floats dont leak, I tested those. Ive had floats go bad on fish tanks before, usually ending in a catastrophic or minor flood. In all my instances it was obvious the float had become a sink. So I would like to think I am confident that the float isn't the issue...

The cams are all timed correctly, Ive more than triple checked that one.

Its stumping me why the adjusted screws on the carbs arent doing anything. Im sure that this is a big hint and will be obvious to a well seasoned person, but this carburetor thing is new to me...

Ive been searching the BB, and will keep searching. But in the meantime, does anyone have any ideas as to what I can check??

Thanks in advance, Aaron.
 

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The more the throttle plates are opened the less effect the idle mixture screws have. It could be that you are idling on the first progression holes.
 

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Discussion Starter #17 (Edited)
Since its been about 6 weeks since I actually worked on the carbs last, I decided to take them apart again to verify the jets inside. (again, made sure all parts were identical between every throat)

F11 Emulsion, Main jet 135, 210 Air corrector.
Idle Jet 50F17
Pump Jet 35
Aux. venturi 45 (and it had an S on it), or is that 4.5?
Main venturi 32
Starter jet? 85-F9, 150 air corrector screw on top.
Needle Valve 150
Since I am new to carbs, I followed this link to ID each individual part. The only part I couldn't locate would be the pump exhaust jet.
Weber 40 DCOE 151 Diagram

Also, choke size? How do I find mine? Does it matter all that much?

My jet sizes dont match the sizes in that diagram for a standard weber 40 DCOE 151. Could I need to re jet my carbs?
It runs rich, you can smell unburnt fuel in the exhaust.

@alfaparticle That probably is the case, it just won't idle on the low side. I started at a base of 4 full 360 degree turns on each corrector screw before working on the adjustments.
 

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50F17 is the wrong idle jet for 40DCOE151. They are intended for emissions Webers and are very lean on yours. You should try 50F8, Also F11 is an unusual choice of emulsion tube. F9 and F16 usually work best on Nord motors but it is not influencing the idle.
 

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ArronsSpider said:
F11 Emulsion, Main jet 135, 210 Air corrector.
Idle Jet 50F17
Pump Jet 35
Aux. venturi 45 (and it had an S on it), or is that 4.5?
Main venturi 32
Starter jet? 85-F9, 150 air corrector screw on top.
Needle Valve 150
Though I've had zero experience tweaking the "Spanish" emissions Webers, I've plenty with the vintage variety. Retro-fitted all my personal cars and many customers' as well.

Others with more 'modern' experience may correct my assumptions, but if I were trying to get this car running, instead of the 50 F 17 idle jets, I'd fit 50 F 8's to start.
And get a good magnifying glass and light to inspect the seats of those idle mix screws for cracks. No discernible change in running is usually either (as alfaparticle suggests) the throttle plates are past the progression holes or there are cracks in those idle screws' seats. I've even seen one set with a shaft so twisted from overtightening the shaft nuts it twisted the shaft to the point where air could pass thru at the point where the shaft met the plate in the barrel.
 
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One and a half to two turns out on the idle screws to start... with the 50 f 8 jets.
 
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