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Running rough. Herald 13/60


kashmir67
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Hello all can anyone provide an answer... 

Yesterday afternoon my herald was running just lovely untill a small stop for five minutes. 

After pulling away the engine became rough and lumpy, holding back almost like on choke or running on 3. I recently serviced the engine including ht leads, cap, sparks. I've rechecked the leads all are fine after checking them individually with a previous one i have. 

Fuel appears good. Flow from tank fine. 

Any thoughs...? 

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Hello thanks for the replys. I've had the top of the carb off. There's no tear in the diaphragm and I cleaned the interior while i examined it. 

Could be the plunger oil. Can you please tell me which oil to use an the filling level? 

 

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If you have had the damper out have you orientated it correctly when you replaced it in the carb body? I'm talking about the 'pips' on both rims of the diaphragm.

When I purchased my Estate it ran perfectly for many miles, I then cleaned the damper. I put the carb pips back in their recesses as per the book and it ran like a box of spanners, reason being, the previous owner had not assembled the diaphragm and damper correctly, easy mistake to make. 

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Hello. Yes. On mine the diaphragm has a profile ledge that fits into a corresponding recess on the lower carb body which makes it a fit correctly. 

The damper does slde in without resistance but is oiled on the bulb, maybe the tube needs topping up? 

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The fact it was running fine until you stopped, suggests to me something heat related. You lose the cooling airflow, everything in the engine bay soaks up heat from the engine & exhaust, something gets too hot and causes a problem.

Prime suspect from previous experience and your description is fuel vapour lock, or possibly fuel boiling in the carb.

Other possibilities would be coil and maybe condenser, as suggested by Wendy.

Don't ignore the clue that it happened abruptly after a short stop. It's not your dashpot oil, that doesn't suddenly disappear.

Pete

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17 hours ago, Wendy Dawes said:

Condenser ? Or sticking needle valve in carb 

Maybe dash pot oil is low 

It could be that you have pulled some sediment through and partly blocked  the float chamber valve, or, as Wendy suggests, a sticking dashpot needle.

To check the needle have you pushed the test pin up (arrowed in the photo)? If the needle is free there should be a distinct clunk when you push the pin up and the same when you let the needle go and the piston drops back down. This is done with the carb top on and dashpot piston in place.

carb pin marked.jpg

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Oil in pot topped up. Still the same.

Clunk heard on operating the test pin and on release. 

Can't see a condenser. Has an Accuspark system installed. 

Checked all sparks are firing. 

Any other suggestions? 

 

 

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Is it still running badly or not running at all? 

You said you recently renewed a lot of ignition parts so can you try swapping the old bits back over one by one to see if anything changes?

Any evidence of oil in your radiator coolant, or mayonnaise-type residue under the oil filler cap?

 

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On 27/07/2022 at 16:44, kashmir67 said:

 I recently serviced the engine including ht leads, cap, sparks. I've rechecked the leads all are fine after checking them individually with a previous one i have. 

Try putting your old distributor cap back on.

Before I bought my Dolomite the previous owner changed the cap, twice, for brand new OEM caps, both were crap and had micro-cracks in them.

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I think ive found the problem. 

I replaced all sparks, all are firing. 

Removed the top of the carb amr re inspected the diaphagm. I found a small split approximately 2mm long that opens when pressed. I suspect this is the cause? Un balanced air fuel mixture. Sound likley? 

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My understanding is that many (hopefully not all?) repro diaphragms are a lot thicker than original and this is the main issue?.

Maybe worth communicating with suppliers about this.

As Rob says Burlen is probably a good bet, there are a few other more specialist carb part suppliers I think, though can't remember them offhand,

Edited by Dave Clasper
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17 hours ago, kashmir67 said:

Removed the top of the carb amr re inspected the diaphagm. I found a small split approximately 2mm long that opens when pressed. I suspect this is the cause? Un balanced air fuel mixture. Sound likley? 

You have to be pretty brutal when inspecting diaphragms and give them a good stretch. Over the decades I've experienced problems you've had with just a small pin hole, having first ruled out low oil in the dashpot. 

I keep a spare diaphragm in the glove compartment for a quick 5 minute fix, and a spare in the garage, both stored with talcum powder (or chalk dust) in the bags to preserve the rubber.

 

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