Diagnostic Help Backfire through carb

[Acollin]

I agree with rootesrooter-- it sounds like a carb problem.

The floats rise to a prescribed level in the float bowl and shut off the flow of fuel by closing a valve when the demand ends. As the car uses fuel---recreating a demand---the floats ( which actually do float in a pool of gas), will allow the valve to open meeting the demand for more fuel. When these valves malfunction or are not set correctly the carb can flood with fuel and will spill out at the first available opportunity. It will sense a demand when there is none and continue to allow fuel to pass into the carb unimpeded.

If fuel is running out of both carbs at about the same rate, it would be a real good guess that the float level in both carbs is not set correctly.

Do you have the procedure for evaluating whether or not the float level is set correctly?

 

[RootesRooter]

Here's a link to a supplier of various Stromberg 150CDSE/175CDSE parts. (Wish they had spindle seals for 150's!) The description for the Grose Jet gives a nice concise description of the function of the inlet valve (AKA needle & seat) and floats.

Are you certain your inlet valves were replaced during the rebuild(s)?

http://www.obsoleteauto.com/flyers/april_2010_20120910/files/assets/downloads/page0018.pdf

One last thought. It might be my imagination, but I thought your plugs looked a bit dirty for having only 2,000 miles on them. Could be from running hot, but maybe your neighborhood gasoline of choice isn't so good. The linked page mentions that it only takes something the size of a grain of sand in the gas to keep the inlet valve from fully seating.

 

[Green67Alpine]

Actually my carbs have Grose jets, I'm going to by pass the regulator to see if the bowls over flow,I will however do it outside.

 

[beamdream]

Actually my carbs have Grose jets, I'm going to by pass the regulator to see if the bowls over flow,I will however do it outside.

Could I suggest you have a quick look at the spacer thickness under the fuel pump before doing anything else, most I have seen are about 1/4" thick.

If its wrong (too thin) you are certainly at risk of the carbs overflowing when you remove the regulator, best to avoid this if you can.

 

[Green67Alpine]

Could I suggest you have a quick look at the spacer thickness under the fuel pump before doing anything else, most I have seen are about 1/4" thick.

If its wrong (too thin) you are certainly at risk of the carbs overflowing when you remove the regulator, best to avoid this if you can.

After checking, the spacer is at least 1/4 plus some gaskets.

Tom j

 

[RootesRooter]

Actually my carbs have Grose jets, I'm going to by pass the regulator to see if the bowls over flow,I will however do it outside.

When you fire it up, have the air cleaners off so you can look down the throats. If fuel is really overfilling the bowl(s), you should be able to see a stream of fuel flowing from around the jet(s).

Googling the Stromberg problem turns up a number of MG/Triumph sites with lots of information. One quote that jumped out at me was "Be sure to order the Grose Jets for Strombergs, not SU's." Any chance you've got the wrong parts installed?

 

[Green67Alpine]

Not to let this post just fade away,
we managed to get LC running enough to make it to the Norcross show although it stayed running it had about what seemed to be 2 cylinders worth of power, later that day after some BBQ ribs and refreshments the "pros from dover" took on the challenge, turned out there was nothing really wrong with the engine that flow meters, colortunes, a bit of syncing, a few burnt fingers, and some hands on the hips and a bit of head scratching couldn't reset, seems some of my earlier efforts just got her so out of wack it took the best part of the evening to get it right.
steve or greggers may chime in about what really happened as I was just a helper.
The only parts that we changed were the plug wires just because I had a new set and thought it would eliminate a possible fault, btw didn't seem to make any difference.
As far as the intermittent back fire through the carb talked about earlier, don't know,will have to wait for a longer drive to find out if it's gone.

Another head scratcher, as suggested I removed the pressure regulator from the gas line and had no overflowing problems on the carbs, I am however going to watch very closely.

Tom j