Rough running

[TimG]

My 3A was running rich with black plugs & exhaust and would not idle hot or cold. I had a go at setting the carbs up better using rubber hose to check balance & a Gunsons colour tune to check mixture. I found that the rear carb jet mounting nut was loose. I did my best but really need to get it to someone with experience.

It starts better from cold but will only run at low revs seemingly on only two cylinders & will eventually pick up to fire properly. The choke does not open the enrichment equally with the front moving down more but I dont see any way to adjust to get even movement. With the choke out the front carb drips fuel but stop with choke in. I took the top of the float chamber & float seems fine & I blew across the needle valve but no change.

I did a 12 mile run & initially it was hesitating unless revs were over 2500. With engine fully warm Its better but still hesitating at low revs. Hot idle maybe a bit better. Plugs still black, gaps are correct (25thou). I used a Gunsons Spark check & it says the ignition is good. I noticed that with a plug lead off to use the Spark check that there was some spark jump from coil centre HT to black -ve terminal. Its OK with all leads on.

Is there anything I should check or is professional attention the way out

 

 

[Richardtr3a]

My 3A would not start when warmed up. It would start on a push start but I could not therefore go out alone. I changed the points ,plugs, leads etc until I was advised to change the condenser. This made a difference and I then bought a racing condenser for a mini minor/Ford 105e etc. It cost over £30.00 and was too big to fit inside the distributor.  I mounted it on the engine using one of the mounting bolts for the coil. It has worked very well for years.  The condensers  sold by some major retailers have the internal material too short.

The Distributor Doctor knows all about this problem and has researched the answer. He sells a proper condenser and overhauled my distributor with all the correct parts

It is worth trying. Good luck

Richard & B

[RobH]

A duff condenser will affect ignition but it doesn't make a car run rich. It could be the  carb float valves not sealing properly.

You shouldn't get tracking across the coil insulator.  It probably needs cleaning.

If the carb jet mounting nut was loose is the jet still centred? If you lift the carb piston with a finger it should drop back with an audible 'click' as it hits the bridge. If it doesn't the needle is binding on the jet. 

You could take the tops off the carburettors and lifted out the pistons with the needles (careful not to bend them and don't mix them up - they need to go back in the same carb. )  Prime the carbs with the hand lever, and look down the jet tube. The petrol level should be 1/8" to 1/4" below the top (4 to 8mm).  If it is higher either the needle valves are not sealing or the float level is not adjusted correctly. A bit lower is OK as long as you can see petrol. 

 

 

 

Edited September 30, 2023 by RobH
typo

[Ralph Whitaker]

Check that the jet tubes are not binding and  going fully up when the choke is off, that was the problem with my car when it was running rich. Are both return springs there on the choke linkage (one on each carb). Choke linkage rod is adjustable for length to get both chokes working together. As Rob says, check that the needle is not binding on the rear carb and if neccessary re centre the jet.

Ralph

[TimG]

Richard It broke down not long after I bought it, sellers had fitted new points & condenser. New condenser had failed & refitting old one it was away after trying a new coil.

Rob the jet is centred & piston falls with a click. I have an electric pump, I will check petrol level in jet tube. & look at float on rear carb.

Ralph both return springs are there & jet tubes appear go fully up with choke off. I'll look again at linkage to get chokes working equally. Thanks all for your help

[RobH]

11 minutes ago, TimG said:

I have an electric pump,

What type is it?   Could it be providing too high a pressure so it overcomes the float valves?  SUs only need 1.5 to 3.5 psi. 

What are the valves?  Grose ball-type can be iffy for sealing as can worn viton ones. 

[TimG]

Rob I need to check what the pump is. I think I have the mechanical pump in a box of bits that came with the car. I have a fuel pressure check gauge so thats something I need to do. I cannot nip out to check as it lives elsewhere.

[TimG]

Rob I have had a look at the pump its no name & I cannot see any way to adjust delivery pressure. A check of the delivery pressure gives 8psi but that not be very accurate as the gauge reads up to 100psi. I have the old AC mechanical pump, but presumably that does nor work or why change it?

Lifting out the pistons I cannot see petrol in the jet tube where the needle goes. The pistons fall back with a click so not binding. I checked the rear float & it seems fine. I'm still not clear how to get both chokes working equally.

 

[RobH]

8psi is way too high Tim.  You probably need a pressure regulator:

https://www.merlinmotorsport.co.uk/p/malpassi-petrol-king-fuel-pressure-regulator-king-pet

https://www.demon-tweeks.com/uk/malpassi-filter-king-fuel-pressure-regulator-and-filter-243259/

[TimG]

6 hours ago, RobH said:

8psi is way too high Tim.  You probably need a pressure regulator:

https://www.merlinmotorsport.co.uk/p/malpassi-petrol-king-fuel-pressure-regulator-king-pet

https://www.demon-tweeks.com/uk/malpassi-filter-king-fuel-pressure-regulator-and-filter-243259/

I've ordered the Bemon Tweaks 67mm glass bowl regulator. I already have an inline filter in front of the pump so perhaps best to take that out.

[2long]

One comment you made about starting from cold was that it sounded like it was running on two cylinders, and then it picked up after a bit to fire properly.  My 2 (H4 SUs) was doing the same thing, and I am sure it was the carb float valve sticking in the closed position.  When I rapped lightly on the carb body where the valve is (with a tire gauge) the valve dropped and the car starting running correctly.  That might be one of the issues for yours, but I am no expert so just a thought for consideration.

Cheers

Dan 

[TimG]

I have fitted the pressure regulator that has not solved my problems. Dan I dont think its a sticking carb float. In trying to get it running properly there has been a lot of starter motor churning with it eventually starting but running badly not on all cylinders initially & miss firing out on the road. I think there has been a lot of unburned fuel that has ended up in the sump raising the oil level & blowing out of the crank case breather, oil on the floor alerted me.  Its not coolant as the level is steady.

I have been using NGK BP6HS plugs gapped at 0.025". I tried cleaning with brass brush to no effect, they are very sooty. Green Spark Plug recommend Champion L82C gapped  0.025. I am going to try new plugs before any further actions as its barely drivable currently.

[John McCormack]

Why do people use 25 thou plug gap? The manual says 32 thou, which I've used for 48 years.

[TimG]

12 minutes ago, John McCormack said:

Why do people use 25 thou plug gap? The manual says 32 thou, which I've used for 48 years.

The Instruction Book 6th edition says normal use plugs Lodge CNY gapped 0.025". Not got Haynes manual to hand but I think that says 0.025"

[BlueTR3A-5EKT]

47 minutes ago, John McCormack said:

Why do people use 25 thou plug gap? The manual says 32 thou, which I've used for 48 years.

Which coil do you have?

I had always thought the gap was enlarged to 0.032” from 0.025” when a sports coil was installed in place of a regular one.

[mike ellis]

Spark plug gaps is a very confusing subject, there is previous discussion here 

My Haynes manual says 32 thou for TR2-3A and 25 thou for TR4/4A.  The handbooks (4th edition onwards anyway) state 25 thou although the 6th edition mentioned above is effectively a TR3B one.  My take is to run with whatever setting works best.

Could it be that at S-T (as in many other large organisations) different departments were not talking to each other.

Mike

[TimG]

Peter I think its a standard coil, it was replaced, old one was Lucas DLB 105 , box says GCL110HP 12V high perf Lucas & in big numbers 134. Thanks Mike I had seen that thread.