More Stromberg problems

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More Stromberg problems

Postby Mike Robinson » Sun Jul 15, 2018 3:23 pm

I'm having problems with a newly installed Stromberg 150CD-SEV on my 1256 Viva. This is the model with an variable height jet using a castellated adjuster - the one you can adjust while its running, but burn your knuckles on the exhaust while you do it! It was supposedly NOS and seems unused, although fitted with an odd, incorrect needle. Using needles recommended by Burlen, firstly B1EU then B1DV, which is listed by Haynes for the 74-5 model, the engine starts and ticks over OK but stalls on any significant load. With the CO set around 3.5% the engine stalls when piston lifted. Even progressivly richening the idle mixture to about 8% CO, engine speed still drops when piston lifted and the engine still stalls under any load. (The plugs start fouling up with a tickover mixture this rich which doesn't help). I'm using an old analogue Gastester and can see the CO drop instantly with increasing rpm.

As the basic fault seems to be fuel shortage under any sort of load, after changing the (rust filled) filter and blowing through the pipes back to the tank without improvement, I bypassed the fixed fuel pipe with clear plastic hose and coupled up my (fake Facet) electric pump and the old mechanical one in series giving 5psi at the carb, so I'm satisfied there's enough petrol available!

I've checked for inlet air leaks but nothing apparent.

There is one odd point. All the literature I have seen says the base of the needle must be flush with the bottom of the piston but mine seems a bit proud - its not adjustable in any way though.

Any ideas would be welcome.

Mike
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Re: More Stromberg problems

Postby fistfullofV5's » Sun Jul 15, 2018 5:49 pm

Hi Mike , my first thought is that the float height might be incorrect or that the float valve itself might be faulty. The carb might not have seen any use but it's internal components may have some considerable age and have deteriorated. The engine might be emptying the float bowl before it gets chance to refill.
Regards, Dave.
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Re: More Stromberg problems

Postby redfirenza » Sun Jul 15, 2018 7:28 pm

I think 5psi for a carb is way too much, should be nearer 2-3? its common for the float needle valve to stick
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Re: More Stromberg problems

Postby lord13 » Mon Jul 16, 2018 7:49 am

The float needle valve could be sticking...but if it was the float chamber wouldn't fill up at all, or very very slowly...
so, when you lift the piston and it stalls, can you restart it straight away after dropping the piston, or does it crank for a while before firing? If it has to crank for some time before firing then i'd suggest a carb strip down and clean the needle valve. If, however, it starts straight away then I would guess the needle valve is working ok and the float chamber is being kept fed with fuel and your problem is something different.

When you set the carb up initially did you do the 'wind the jet all the way in than back off 3 turns' thing that the manual tells you to do? (sometimes it says 2 and a 1/2, sometimes it says 3 and a 1/2...so i go with 3 :) ) I'm assuming you did, it shouldn't take more than half a turn either way to get the mixture right, which it seems that you have judging by the readout data you have posted.

The needle being proud should not affect the settings much, it will, if anything, make for a leaner tickover, as it could raise the piston slightly off it's base...but it wont as the jet will be below the bottom of the inlet choke.

One question... if you drop the piston immediately after raising it ( hopefully before it stalls) will it continue to tickover? Try raising the piston ever so slightly in increments, use a long flat bladed screwdriver for more control... can you keep it running in this fashion whilst the revs increase? how far can you get? If you can get it up to a decent amount of revs whilst slowly lifting the piston or at least keep it running then I would say that your issue lies with the dashpot, or the diaphragm. If the piston raises too quickly it will stall, too little oil will cause the piston to rise too quickly, a weak or nonexistant dashpot spring will cause the piston to rise too quickly, a split or damaged diaphragm will cause the piston to rise too quickly, or will let too much air through, or something along those lines...

Check the piston and dashpot, I could be completely wrong but I have had the same issues before and a correctly sorted dashpot/piston assembly sorted this out.

hope this helps :)
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Re: More Stromberg problems

Postby Mike Robinson » Mon Jul 16, 2018 5:26 pm

Thanks for all the replies.

Dave, the needle valve did stick a bit even after I cleaned it up so I replaced it with new one from the correct service kit which has a larger bore size - but no effect. I've checked and rechecked the float level which is set per the Haynes manual at 16-17mm and there seems an open passage between the needle valve area and the petrol inlet. I agree it seems as if the float chamber is nor refilling quickly enough which is why I did the high pressure supply test.

Redfirenza, I agree 5psi is too much - it was just for a test to eliminate fuel supply as the problem. The standard mechanical pump gives 2.5psi (and is surprisingly rpm independant) but mine allows petrol to backsyphon to the tank. I use a regulator with the electric one set at 2.5psi but bypassed it for the 5psi test. Fuel flows seem quite low about 1 pint/min for either pump on tickover. As a useless fact and surprising to me, the engine ran for over 1 minute on the residual fuel in the float chamber.

Lord 13, the engine does restart straightaway if stalled by lifting the piston. If I drop the piston immediately after raising it continues to tickover. I have adjusted the jet starting from both 2 and 3 turns down setting but get lost when adjusting on the car. It will tickover evenly at very wide range of CO, from 1% upwards. I guess I am about 4.5 turns down currently which seems all wrong and of course its filthy rich! A quarter of a turn doesn't make a detectable change. I can't get the engine revs to increase by lifting the piston - I am twisting a screwdriver blade to control the lift but its difficult to judge a millimeter lift. The diaphragm looks perfect and the spring is there and I've tried different oils for the damper, currently its 20/50 engine oil. I'll change the diaphragm as a test anyway and think more about the potential for too much air rather than too little fuel

Mike
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Re: More Stromberg problems

Postby 1972nail » Mon Jul 16, 2018 6:34 pm

Looks like you've tried all bases. A few suggestions from me, 20/50 is far too thick. I use a very light oil, about 20 grade or a bit less. 3 in 1 has an organic content in the mix which when it heats up does cause a bit of glazing on the alloy dash pot.

Suggestion 2, Stromberg manifolds are prone to burning through or going porous at the hotspot where exhaust gasses come up through from the cylinder head. This can cause some strange symptoms.

3, the diaphram can be fitted the wrong way around. There is a location 'key' moulded into the edge which drops into a slot on the carb.
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Re: More Stromberg problems

Postby Mike Robinson » Mon Jul 16, 2018 10:52 pm

Hi David,

I'll try some 3 in 1 in - easier than pouring from a 5 litre can!

I think I checked the manifold . I did check the temperatures for anything odd. Cant find my note but I think the head about 105, manifold 70 something and carb around 45. And yes I did note the diaphragm lugs

Thanks
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Re: More Stromberg problems

Postby fistfullofV5's » Mon Jul 16, 2018 11:29 pm

This is becoming a mystery worthy of Sherlock Holmes, but with what's been suggested and the results given, I think I would turn the spotlight on the ignition system in case the spark is breaking down under load and effectively switching the engine off. I'm going to follow this one with interest until an answer is found though.
Regards, Dave. :goodluck:
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Re: More Stromberg problems

Postby lord13 » Tue Jul 17, 2018 7:27 am

^that is a good point...especially with the all the results from the previous tests, but I'd've thought any electrical fault would have been intermittent, I can't actually think of any scenario that would cut ignition in this way, and then re-instate it immediately after the piston in the carb is dropped.... but we learn new things all the time so i wouldn't be surprised if something did show up :D

I'm convinced its a fuel/air thing... I had one do the same, I eventually swapped out the carb, which stopped that issue...and raised another typically :(
If you have another carb spare, fit that and see if the same issue shows up, at least you can discount the carb being at fault if it does...
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Re: More Stromberg problems

Postby Mike Attew » Tue Jul 17, 2018 9:49 am

I fitted a B1EU needle to mine, I had to use a small flat blade screwdriver in the needle slot to wind it into the piston, on mine with the slot opposite the grub locking screw the shoulder of the needle is flush with the piston.
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