Carb Issue

[ZanettiZA]

Hi All,

After replacing my spark plugs and HT leads, I noticed that with cylinder 1 HT lead removed it made no difference to the engine (still not running smoothly) all other cylinders with leads removed the revs dropped...

Checked lead and spark plug but spark is 100%

Pushed the throttle and checked for fuel squirting in to the barrel of the carbs, all was fine in 1 2 3 4... with the engine off.

Started the engine checked for fuel by looking down each barrel and I found the when pushing the throttle just a drop comes out of No. 1 but 2 3 4 are fine... they squirt fuel...

All the gaskets on both carbs have been replaced and everything was 100% previously.

Any ideas what the problem is???? Also No. 1 Backfires through the carb now but I guess that is because of a lean mixture.

Thanks

[Ralph deMasi]

You removed the HT lead while it was idling and found that No.1 was not firing. How about when you rev the engine to a point past the idling circuit, maybe 2500 rpm. Does cylinder No.1 come back into action? Is the spark plug loaded up (black)?

If you don't connect the HT lead back to the spark plug but sort of hold it about 3/16" to 1/4" away from the plug does the cylinder seem like its starting to fire? Did you swap the leads and plugs between cylinders one and two to verify that the items are in fact good?

Ralph

[ZanettiZA]

Thanks for the response Ralph.

Yes the spark was "loaded up" but despite that there was still a spark but is guess it just wasn't strong enough. I cleaned it and all is back to normal for now BUT...

That means that the mixture is too rich... In fact I know it is...

I replaced the floats as the carbs were leaking out of the top, I used floats from a pair of Solex C35PHH-23 that I had, this solved the leaking problem but I have noticed that it has recurred, is the only way to cure this and the rich mixture issue by adjusting the floats?

Thanks

[Ralph deMasi]

I believe that the level of the fuel in the bowl, which is set by how high or low the float is, will effect how quickly fuel is pulled into the motor. By "how quickly" I mean at what rpm range of the motor. If set incorrectly the motor could be pulling in fuel from not only the idle fuel circuit, which is adjusted by the idle screws, but from the main fuel circuit as well. But a float height issue should have affected both cyclinders, not one. Again the float could be okay but the needle valve, which the float opens and closes, could also be a problem if it's not closing properly, thereby flooding the bowl with more fuel. But again that should affect both cylinders.

Does the idle screw have an affect on the idle? The optimum setting should give you the highest idle with movement to the rich or lean setting resulting in a lower idle. Also there are two very small screws, I think to the outside of the idle screws, which I do not completely understand, but from what I can see provide another way of adjusting fuel into the cylinder, bypassing the idle screw. I have seen these uncovered and also covered by putty or epoxy as I believe these are set at the factory and are not meant to be touched. If they look like they haven't been touched I would leave them that way.

Obviously, as everything I ever read about troubleshooting the fuel system says, make sure the ignition system is working before blaming the carbs.

Ralph

[Huib]

The two small usually covered screws are the by pass screws. They are used to correct any differences in opening of the butterfly valves at idle. They are set in the factory / workshop using the proper measuring equipement. They are not intended to compensate for any differences in the engine such as compression. In practice it means you and I don't touch them.

[Huib]

Your fuel pressure may be way too high. Do you still have the original fuel pump?

Where is the leakage exactly coming from?

Does it leak when running the engine without touching the throttle or only when you flip the throttle? If the latter the acceleration jets may be blocked. The pressure from the acceleration pump then builds up causing the fuel to finally go where it should not go.

[ZanettiZA]

Hi Huib,

Yes it's the original pump. The leak is coming from the top of the carbs, from the two holes on the small air correction jet cover, this is on both carbs but on the 19 which feeds No. 1 & 2 cylinder it also appears to be leaking a bit from the float bowl cover around the gasket in the front of the carb but not on the 16 which feeds No 2 & 3 cylinder.

I have checked all sparks and the are quite sooted, dry black colour. I was under the impression that this is from an overly rich mixture? She also drinks petrol, there's no sipping here! Again making me think that the mixture is too rich.

I had installed aftermarket needle valves, I still had the originals to I put those back and the backfire that I had on No. 1 seems for now to have disappeared and so far there has been no leaking but I still convinced that the mixture is too rich, what is the best way to sort that? I also seem to have some hesitating when I accelerate.

Thanks

[Ralph deMasi]

The problem might have been the aftermarket needle valve from the start. You might want to return the original float and hopefully you didn't change the setting of the tab on the float that activates the needle valve.

If you're really ambitious you could let the car run for a bit then remove the tops of both carbs and compare the level of the fuel, taking all obvious precautions because of the open fuel source. A large difference might point you to the problem: an incorrectly set float level. I believe there is a special gauge which is used to set this but Huib might have a shortcut or suggestion in leiu of the tool.

Do the idle screws affect the engines performance or not?

Ralph

[lancialulu]

Re the auxilliary by pass screws, I had difficulty getting No 1 cylinder on a 1.3S to respond to the idle adjustment so I asked Martin Cliffe of Omicron to have a look and he finally dug out the putty of one of the screws and gave it a slight turn and after that the idle screw had some effect. So I suspect if one goes carefully and makes small adjustments this is the area to look to get a non responsive cylinder to work at tickover. Needless to say this was at a very low tickover of 700rpm so maybe the butterfly was shut on this cylinder. Above that all cylinders ran smoothly. My 1600 HF also exhibits a rich No1 so much so that if not used will always foul on starting so need to change the plug.

Tim

PS if you want the drawings for the float tool send me a PM with your email address!

[ZanettiZA]

Possibly was the needle valve but the floats are original, well actually they are from another set of carbs (from the same model 1.3) that I have as the ones that were in there, on the No. 1 & 2 side were stick on the barrel inside the float bowl.

In terms of the float tool I do have the diagram to build it, which I am in the process of doing...