Carb Issue

[bart]

I had the same problem; fuel level turned out to be too high. But I only found this after making small sight glasses in the carbs, so that I could actually see what happens inside, during running of the engine.
Cause of the problem was probably wrong size (thickness) of brass washer under the needle valve. I found the fuel level to be quite critical for good performance.

Bart

[Geoff]

One more pitch for checking fuel pressure levels. Quite critical, varies easily with mech'l pumps (a gasket thickness can change the pressure easily by 50-100%) and can wreak havoc on a fuel system.

[ZanettiZA]

An Update:

It seemed that somehow No. 1 had sorted itself out but it looks like it hadn't...

When I push the throttle while looking down the barrel of No. 1 there is no squirt of fuel, 2,3,4 are 100%

What could be causing a block there? or more specifically, what could cause this?

[Ralph deMasi]

Well it's the same pump for both of the throats on one carburetor so I would provisionally rule out the pump. You might want to remove and dismantle the pump, dump the fuel and trace the accelerator pump circuit, which are small passages through the body. These might have some dirt lodge in them.

You could do the tracing with either compressed air or a less-flammable, like mineral spirits, to replace the fuel. The compressed air might be able to dislodge whatever is blocking the passage. Pushing drills or stiff wires into the orefices needs to be done with the utmost care.

The Autozone near me sells a gallon can of a cleaner that you can lower the entire carb into and leave for a more thorough cleaning.

More to Geoff's point; in the future you might want to look at a Filter King fuel filter. It provides good filtering and the ability to set the fuel pressure using a screw and lock nut on top. I purchased mine on Ebay.

[Huib]

There could be something wrong with the valve. This is a steel ball under a small weight under a plug at the rear of the carb when you lift the cover.

Most likely however is that the pump jet is clogged. Take out the screw on the side of the barrel that closes the hole for the jet. You may try blowing compressed air into that hole. For me it never worked. I always end up using the hair of a steel brush to remove the dirt.

[ZanettiZA]

Thanks Huib and Ralph,

Huib I have removed the screw and pushed a nylon fiber through the jet, also spray some carb cleaner through the jet and rest of the carb.
Also checked the weight and steel ball bearing they are both in place, is there only one steel ball ? Also sprayed that area out with carb cleaner.
Started her and she was running better, smoother, this seemed to sort the "no fuel" issue (there is now a squirt of fuel when the throttle is pushed) but now the carb backfire is back upon acceleration and is running rough at idle (seems to be misfiring).

My assumption was that the backfire was caused by a lean condition since there was no fuel squirting at the jet...

Again removing cylinder no. 1 HT lead seems to have little or no influence on the running of the engine, this seemed to have been fixed with a quick clean of the plug, I have checked that there is a spark at the plug etc...

Any other idea's about No. 1?

[Huib]

With backfire you mean there is actually a flame coming out of carb barrel #1?

If so, this can only happen if the intake valve does not close or if the ignition timing is way off. There used to be bad quality points on the market with intermittent contacts through the rivets connecting the spring and the moving arm of the points. An intermittent contact would randomly misfire all 4 cilinders. However, there might be good reason for it to happen only at cilinder 1.

It may be a good idea to:

1. measure compression
2. replace points and capacitor and carefully set the timing at a fixed advance of 8 degrees

I never spend much time on carbs suspected of being messed up. I send them to CDM in Nichelino near Turin. In 2 - 3 weeks they come back considerably better than new.

[ZanettiZA]

No, not a flame but rather a popping sound... Could the coil be a problem? I have a Bosch unit which measures 3.3ohm and 10 000ohm, I have checked the points and the "seem" ok, no noticable pitting etc... will get a new unit there just in case.

How would compression cause this sort of issue?

[bmarler]

i agree with huib,
replace the points and capacitor and set the timing. i recently went through a similar problem with my 1,3 zagato. i couldn't adjust the carbs properly because the plugs were fouling too quickly. i ended up changing the points and capacitor, installed a new high energy coil and now all is well. when i changed the capacitor i saw a marked improvement in spark at the points. sometimes the simple fixes are the most effective.

[Huib]

Replace the capacitor as well. They cost very little.

Measuring compression is a way to check if the valves close.