Leaky Carb

[hashman]

Car was running a bit rough lately even after replacing the coil. Lots of popping and banging on the over run coming down the revs. A look in the engine bay and there were signs of fuel leakage on the left carb. So a quick tighten up of the screws of the top half of the carb, seems to have done the trick.

20180707_150944 by karlhash, on Flickr

20180707_150926 by karlhash, on Flickr

then a quick stop on the test run......by the way, I recommend test drives while the world cup England game is on....nice empty roads....then back in time to see wins all round! Yay!

20180707_205614 by karlhash, on Flickr

God must have been watching.....

20180707_205835 by karlhash, on Flickr

Must rebuild my carbs one day.
Karl.

[Kneeslider]

Probably worth taking a look at the carbs with the engine running and the air cleaners off. I found that I had a float that no longer floated in my left side Solex 40 Pii.

Maybe if your float is in tact, then the level is too high. Its a fairly simple procedure to set the levels by taking out the blanking plug on the side of the float chamber facing the engine, and winding the float up and down till fuel just starts to drip from the level plug.

After that, sync the butterflies with a Unisyn, and set the idle speed.

Sorry if I am telling you to suck on an oeuf, but its fairly straightforward to set up carbs 90% of the way, the last 10% is the tricky bit.

Have you used a can of carb cleaner sprayed around the manifold and joints to check for air leaks? There will be some leakage around the throttle spindles...

[hashman]

Thanks I will check the float level as I havent ever. I did get a flow meter job thingy on them, but they just need some love and attention after many years of neglect.
Ill try the carb cleaner trick too.
New gaskets and Im thinking of getting an ultrasonic bath to clean the carbs in also.
If anyone has any tips for the best cleaning solution for the ultrasonic bath i would be grateful.
Thanks for your reply kneeslider.

Karl.

356 by karlhash, on Flickr

[mycar]

Hello Karl, not sure which carbs you have, are they Solex's. They don't look like Zeniths so I can't really help.

What I can say is becoming familiar with your carbs is an excellent adventure and can pay huge dividends when it comes to performance (or fuel economy. }

Checking things like the float level, balancing the carbs left and right and tuning them just right is a lovely thing to do. Lots of info over on the Registry.

This sort of thing....https://porsche356registry.org/article/47?

[Kneeslider]

Hi Karl,

After having a think about it, you shouldn't be getting any leakage out of the tops of your carbs (well, the flange bit where the top screws on) because the float level should be below this level. It would only get wet when the fuel sloshed around during cornering or braking or gaining speed. My bet is that the float level is too high, but its dead easy to sort.

Are those solid throttle shafts or split ones? Mine are split shaft 912 carbs, and have a large diameter (approx 3/4 in) tube in the centre of the carb top, and yours look different.

The old rule applies when tuning a 356, that you should make sure the valve clearances are spot on, (6thou exhaust, and 4thou inlet) then make sure that the timing is correct, 5° advance from TDC at idle, and then 35° all in at 3,000rpm. Only when this is right, should you look at the carbs. Check first for air leaks with the carb cleaner, then I balance all the butterflys at idle with the Unisyn by adjusting the idle stop screws with the cross bar linkage undone to get Cyl #2 and #4. Once this is right, compare the #1 and #3 with the others. On a split shaft solex I can adjust each throttle plate individually to get them just right. Only then look at the mixture screws... Want to know more or is this old news?

[Kneeslider]

Ultrasonic baths are great, but make sure that you get a big enough to put a carb in. Mine is OK for bike carbs, but I have to turn a Solex over a few times to get coverage. I bought mine from Maplin about a decade ago, and have just used the solution that comes with it. The best stuff for organic petrol like deposits would be caustic soda pellets, but these would probably be very bad news for the aluminium or whatever alloy the carbs are made of. Personally I think that there is very little wrong with giving all the orifices a good blow through with carb cleaner, and the same with the jets, and that the effectiveness of ultrasonics is rather over played.

Usually a rich condition will make itself known with black smoke and rubbish fuel economy, however you can dump quite a lot of fuel into a cylinder and it will not kill the power, just soot up plugs. A lean one normally shows itself with flat spots and the engine only being happy at certain rpms. Mixture screws and idle jets control the power up to about 3000rpm, and main jets after that. Blocked jets will naturally make things lean. Carbs usually take a long time to wear or go out of tune, so what has changed?

[hashman]

There is no problem with the carbs now. and the car runs fine, just thought it best to rebuild them before anything does deteriorate beyond repair.
I would like them to look clean also.
Plugs are all a goodish colour all round.
Plus I get to spend time in the garage.
Thanks all the same though.
It is all useful information.
Much appreciated.
Karl.