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One barrel spitting
contaminated - 14/3/12 at 01:54 PM

Chaps

For a while I've had an issue where one barrel of the twin webers is prone to spitting. It's a zetec on weber 45s and megajolt. The barrel nearest the front of the car is the one. The other barrel on the same carb doesn't seem to do it. Other than a carb issue (perhaps it's a bit lean or a slight air leak) the only thing I can think of is a bit of carbon build up on the valves and a bit of pre-detonation. Not that likely though surely?

Anyway, long story short it's not a big issues and I've left it. At the weekend the car started to splutter and die so I pulled over and took the bonnet off. There was petrol pi$$ing into the same barrel on one carb. I thought maybe the float was stuck, but in that case why only one barrel? Eventually it stopped and I started the car, it ran lumpy for a couple of mins and then ran fine.

Do you think the above issues are connected and any idea what's going on? I currently have that carb stripped down, nothing obvious is wrong.

Thanks all

Dan

HOL - 14/3/12 at 02:43 PM

Dan,

Spitting through webers is normally a valve seating issue where the inlet's leak during compression and spit out anything in the inlet tract waiting to go in.

BD Engineering in Newington have a pressure tester that screws into the spark plug. If that is the problem, you will hear air escaping from the carbs when they pressurise that cylinder slightly.

contaminated - 14/3/12 at 02:50 PM

Interesting. That could be it then.

MikeRJ - 14/3/12 at 04:23 PM

quote:
Originally posted by HOL
Dan,

Spitting through webers is normally a valve seating issue


That may be a possibility but IME by far the most common cause of DCOE's spitting back is a weak mixture. The fact that only one barrel of a DCOE is doing it suggests either a blocked jet or drilling within the carb or an air leak between that barrel and the manifold or between manifold and head.

HOL - 14/3/12 at 04:56 PM

Fair do's, it could be any number of possible things tbh.

I only mentioned it, as id seen it diagnosed down there before. Also its barrel specific as inlets are chamber specific.

But, BD engineering is one of the few Rolling Roads that specialise in Weber Carbs. And its local to Dan, so should be able to diagnose and possibly fix the problem before he can eat a full fried breakfast on the sly in the cafe down the road.

Where IS the downside??

[Edited on 14/3/12 by HOL]

britishtrident - 14/3/12 at 05:23 PM

Although a cylinder leak down test is a valid test with one throttle per cylinder as on DCOEs you can check the inlet valves are seating by using a tube as a stethoscope and holding business end to each trumpet in turn (in the same relative position), if the inlet valve isn't seating you will hear a distinctive plop-plop sound at idle.

However it might also be a good idea to check the jets are clear


see this http://www.locostbuilders.co.uk/viewthread.php?tid=34279

Bad link fixed

[Edited on 14/3/12 by britishtrident]

contaminated - 14/3/12 at 06:06 PM

Top blokes, as always.