+2S spluttering engine issues

[leedsj]

My twincam is _usually_ running lovely, but I understand several people have had issues with the new petrol?

It is losing power intermittently (every few minutes, especially when standing at the lights) then it comes back on song with full power before spluttering back.

I've changed all of the plugs, which helped a bit, but that is the limit of my skills, and it won't make it as far as my usual specialist (Gerald Turner).

Anyone have any suggestions / tuning tips to try?

[berni29]

Hi

If you think it is fuel related then Tesco Momentum is a 99 octane, and you should run the car on that. How about the coil? Do you have another could you can try? Also check the points if the car does not have electronic ignition.

All the best

Berni

[mbell]

What heat range are the spark plugs? (Have you the plug model number?)

What carbs do you have? Have you checked fuel pressure/flow?

[leedsj]

Hi

If you think it is fuel related then Tesco Momentum is a 99 octane, and you should run the car on that. How about the coil? Do you have another could you can try? Also check the points if the car does not have electronic ignition.

All the best

Berni

Am running on 99 already

What am I looking for with the coil?

[leedsj]

What heat range are the spark plugs? (Have you the plug model number?)

What carbs do you have? Have you checked fuel pressure/flow?

Spark plugs are NGK BPR6ES (same I always use). Where / how can I check the fuel pressure?

[69S4]

The ‘r’ bit suggests you’re using resister plugs. You don’t have resister plug caps as well do you, as both together is too much resistance in the ht circuit and can cause misfires

[leedsj]

The ‘r’ bit suggests you’re using resister plugs. You don’t have resister plug caps as well do you, as both together is too much resistance in the ht circuit and can cause misfires

Any alternative suggestions?

[EPA]

If you have Weber carbs try pushing the choke levers on the carbs to ensure they are both completely off. They can sometimes stick and cause the engine to run rough.
Ed

[69S4]

The ‘r’ bit suggests you’re using resister plugs. You don’t have resister plug caps as well do you, as both together is too much resistance in the ht circuit and can cause misfires

Any alternative suggestions?

Normal BP6ES plugs with resistor caps / leads or BPR6ES resistor plugs with no resistance in the HT line. I'm not sure what leads or caps you're using but the resistance is easy to check with a multimeter

[mbell]

Where / how can I check the fuel pressure?

You need a fuel pressure gauge and to connect it to the fuel line when running.

IMO most likely cause for this is spark plugs fouling or lack of fuel. Your plugs are correct heat range which suggest that the plug selection isn't the problem. So possible remaining causes:
- Fouled plugs due to too rich mixture
- Fouled plugs due to excessive oil burning
- lack of fuel due to carb or fuel pump(pressure) issue

Which carbs you have is important to diagnose this if a fuel issue. Webers/DHLA will pump fuel in to the engine when you press the pedal. Which can over come a lack of fuel for a short period.

Apart from checking the fuel pump you could remove a spark plug and asses it condition to see if it looks like rich/lean or oil burning.

[alaric]

Hi.

Re the coil they can develop a short which can cause poor spark as the coil heats up. I had this with a mini 30 years ago. It was fine for a couple of minutes after start up then would start running really badly unless I revved it really hard.

Anyway it was the coil. I replaced it on advice of a local mechanic and all was good.

Sean.

[leedsj]

Where / how can I check the fuel pressure?

Which carbs you have is important to diagnose this if a fuel issue. Webers/DHLA will pump fuel in to the engine when you press the pedal. Which can over come a lack of fuel for a short period.

Can confirm, they are Dellortos

[leedsj]

Hi.

Re the coil they can develop a short which can cause poor spark as the coil heats up. I had this with a mini 30 years ago. It was fine for a couple of minutes after start up then would start running really badly unless I revved it really hard.

Anyway it was the coil. I replaced it on advice of a local mechanic and all was good.

Sean.

Thanks Sean, this sounds very much like what is going on symptom wise. Apologies for the naive question, but this is the coil right? Does anyone know if the carbs have to be removed to get it out?

[alaric]

Yes that looks like the coil. It's a bit hard to tell but I can't think what else would be there. I had to remove my carbs to get to the coil and distributor. I have now mounted the coil on the wing in front of the air box. This gives me better access.

To get the carbs out I had to remove the air box, which was really easy. You may find you can get the coil out with the air box out of way without removing the carbs themselves.

I hope it's the coil now... you may get a clue from the resistance of the primary and secondary. I just replaced mine though. Not expensive.

Sean.

[leedsj]

Any suggestions for decent replacement coil, or is it a case of get it out and see what it is?