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Only running on two cyl


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Hi all, my 4a was out last week running fine, then this evening went to get it out to go to monthly TR meeting and. ------ it started with some choke as usual sounded fine, left it on fast idle to close garage door and it dropped onto 2 cylinders. Checked plug leads ouch! Sparks on all 4 and up arm! But removing 1 or 2 made no diff to lumpy running. Removing 3 or 4 made it stall, Writh choke right out managed to keep it running and put back in garage to look further tomorrow.

Did check all valves an pushrods moving as normal and tried tapping carbs. (Strombergs ) in case needle valve stuck no joy. So before I look tomorrow any suggestions what's up. I have some ideas but don't let me influence your deductions. When it's fixed I will post with solution.

Best regards Chris

Edited by potts4a
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Had the very thing, and only found by accident.

 

Some 'Expert' had used airline for the feed between the carbs, this had closed internally

shutting off the fuel to front carb, but looked fine at a glance,

back to copper now!

John.

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Chris

 

My problem was some **** in the strombergs following new filter fitting ( must have dislodged something)

 

Responded to ' tough love' as directed by the forum - a good belt or 2 with wooden mallet

 

Graze

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Well, noting all comments I started with carbs as it sounded like lack of fuel, on Strmbergs it's easier to remove the dash pots than the float chambers so I removed both dash pots and found two splits in the diaphragm on the rear carb. Replaced diaphragm and engine runs fine.

Strange thing is it was the rear two cylinders which were running and yet the splt diaphragm was on the rear carb.

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Strange thing is it was the rear two cylinders which were running and yet the splt diaphragm was on the rear carb.

the beauty of British engineering...

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  • 2 weeks later...

UPDATE

Having driven 10 miles i thought i had fixed it but today it did the same again - dropping onto two cylinders. So after checking diaphragms, ok

Dist cap ok, spark ok I thought lets remove the fuel feed to the carbs and check the pump which is only 4 months old. You guessed no fuel flow at all. Replaced pump with 50 year old refurbished spare and runs fine.

Done over 80 miles today with no probs.

I will be onto a well known TR shop in west London tomorrow, but i dont want another the same so where to go pref for a good refirbished original?

Any info appreciated,

Chris

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Chris

 

My experience is that this is simply about the quality of those fuel pumps and the amount of fuel that the vacuum of the diaphragm allows to pump in the first place, then how much the valves allow through.

 

The valves themselves are usually ok, but they tend to rotate or fall out of position (so obviously can't work in the right direction) because the quality of the cast alloy body is poor, which means they don't stay put.

 

A reconditioned original pump is the way forward, or a hidden electrical pump. There was a recent post on a good source as I recall.

 

Regards

 

Tony

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As regards the two non-return valves inside the pump.

If they are simply a push fit then they may well fall out - given time and miles.

 

I drilled and tapped a 3mm hole between mine and then fitted a washer that covered the edge of the valves - not had a problem in over a year now

 

Roger

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