Near disaster from carb

[Mitch Covington]

brass tube about 2" on that carb top right in middle staked on underside of carb. For viewing only check ebay for picture no affiliation.

Check here for expediency only
http://www.ebay.com/itm/Pair-of-Solex-4 ... 01?vxp=mtr

Is the highlighted tube in the sketch what you refer to? I see that my right side carb doesn't have one either. Is it unusual to remove these? I'm sure the car came like this... how critical are they?

[David Jones]

They prevent fuel from spilling out of the float chamber on hard cornering or on rough roads where fuel is being stirred up. On the later carbs the vent line was shorter and of three times the diameter. You could easily make your own from 5/16" brake tubing.

[Bruce Smith]

David - I believe there's a bit more to it than that. I've played around with changing the air flow across the top of vent tubes (long and short), which can influence the float level in the carb through pressure variation. I think the length and diameter of the tube was chosen to provide a stable location for the vent opening. A taller tube is further from the throats while a wider tube may be less influenced by pressure differences. I haven't seen any documentation but have a hunch it was part of the design.

[David Jones]

Bruce you may be correct. I just thought I had remembered reading many years ago that the reason was as I stated but it could be the result of an over active imagination. Meanwhile here is a thread from a couple of years ago on carb tops. Note that there was a factory bulletin to replace the tall skinny breathers with the short fat one. I also edited my first post to reflect the correct diameter tubing that will fit the tall vent tubes.
viewtopic.php?f=1&t=40169

[Mitch Covington]

Thanks for that link Dave. I was interested to read what Jim Kaufmann said:
 "The tall breather was discontinued during late S-90 production. Also, some late S-90's and very early SC's with the small hole for the tube, but no tube. I've seen enough of these know it was delivered from the factory with no tube."

Well, I figured if they sometimes come with no tube, can't be that critical, so I won't worry about it. Then the light bulb went on... perhaps this was why my car stalls just a little whenever I corner it really hard while giving it the gas... is this the reason? Seems obvious now.

[David Jones]

Mitch I doubt that is why it would stall on hard cornering unless it was a very long corner as the pick up point for the gas is at the bottom of the float bowl, unless the float level was very low to start with. That is a future problem to fix once the carbs are overhauled and a tune up is completed. You may find the stalling problem will just have gone away. Take this time while the carbs are off the car to check the valves and overhaul the distributor. It is surprising what a tune up can do. Also if you have help check that you are getting full throttle when your throttle pedal is all the way down.

[David Green]

I've been cautioned not to soak float valves in carb cleaner as some (all?) have an internal rubber seal: experts please chime in on this. Also, don't forget to check the fuel pump output pressure. On my '53 1500 normal I forgot to add the 3rd (2 and 1) paper gasket to the pump spacer and the increased pressure kept one float from closing.
David

[Mitch Covington]

Update:

I rebuilt the left carb only, the one that was flooding. Had no problems at all with the procedure. I took pics of all adjusting screws, and reinstalled them to the same adjustment as before. Things that were easily removable I soaked in carb cleaner -- the kind with the basket in a gallon can. I did not soak the main body, but did blow out every orifice with compressed air. I replaced the needle valve with a new one. Of course, new gaskets everywhere.

While I had the left carb out, and the spark plugs were a little easier to get to, I checked the compression. All were 120 except for #3 which was roughly 122. I realize that the engine should be warm for a compression test, but of course that was impossible without the carb installed. I have to think that the consistency of these readings is very encouraging though, right?

I took it out for a quick test drive without tuning the carbs. She ran great, though as before, it idles too low. So the rebuild seemed to cure my problem of the car running badly when she got hot. I'm thrilled about that!

Now I'll tune the carbs using the Harry Bieker article and shop manuals. As before, any advance suggestions of what to be careful of would be appreciated. I have the P78 tool, the Unisyn, and will make the pump injection measuring vial tonight.

Thanks to all who shared experience and time.

[David Jones]

Mitch, One suggestion on tuning. When adjusting the mixture screws. Once you have found the sweet spot open the mixture screws out a half turn which will help when starting from cold and give a better idle as with modern fuel I found that slightly richer setting reduces the carb backfires.

[WilliamVaughan]

re David Jones suggestion of an additional half turn on the idle mixture adjustment screws, I agree because: engine runs more smoothly, exhaust smell reduced, exhaust quieter, more torque. Idle mixture richer than the peak rpm setting is also less likely to explode in the muffler during downhill in-gear engine braking. Carbs probably have a hard time maintaining mixture during engine braking with throttle plates closed at midrange RPM.

re Unisyn, they are okay, but in my opinion the synchrometer product is easier to use because: no messing with flow restricter plate is required, measurement is very repeatable and does not bounce a great deal at idle, and it does not choke the engine to the extent the unisyn does when adjusted to yield a mid scale (bouncing) reading at idle. Treat yourself. Try it.

re vial, I made a vial, then I bought a vial from a noted vendor. I use the one I bought. I use it with a long piece of telephone wire wrapped around the formed lip at the top. Try various settings, and take notes on drivability versus setting.

[Mitch Covington]

While waiting on a fuel pump, I went ahead and rebuilt the right carb after doing the left one a couple of weeks ago. This checking the fuel level with the P78 tool while the car is running is very unsettling to me, so I want to do this with the carbs on the bench.

From other posts, I understand that you need to supply the same amount of pressure to the carbs that would be given by the fuel pump, so I will need to rig up a fuel supply line that extends toward the ceiling up to a certain height above the carb to take advantage of gravity. Or use an electric fuel pump.

What are your thoughts on this... what set up have you used? Anybody willing to supply a picture? My biggest concern is getting a fitting for the line that replaces the banjo fitting on the carb, what have you used?

thanks!
mitch

[David Jones]

Mitch, I have used both methods. A funnel attached to the fuel line and a step ladder up to the 2 meter high funnel. I used mineral spirits as my liquid medium as it is less volatile than gasoline. I have also used a fuel pump. If the float valves are in good shape the carb should not flood but if you have suspect float valves you will find out quickly.
I like the overflow method of checking even though I have the tool as I can drain some of the liquid out then see if it fills again after making adjustments but you can still leave the plug out and make small adjustments upwards until you are happy with the level.

[John Brooks]

I do them off the car. I have a small tank 12v pump and manifold. It's easier off the car and more accurate and you can get to everything.

[David Jones]

This banjo fitting looks correct Mitch.
https://www.partsklassik.com/Porsche-35 ... oC0h3w_wcB

[John Brooks]

14mm banjo fitting a 14x1 bolt. Webber's are 14 X 1.5 I found a bolt will a 1/4" pipe hole for a pressure gage. I use jet reamers to verify the size, the stamps are not always correct.