Misfire Petrol related?

[Kojag]

Hallo,
My OTS Serie III has problems to accelerate after a few weeks not beeing used. Jaguar Classic is telling me it is due to modern petrol....The engine starts properly , it runs up to 2000 RPM and stops there which is a speed of 50 km/h ...when the engine gets warmer and I accelerate it misfires considerably and after a big bang it runs almost smoothly also at higher RPM.Recommendation is to run longer distances and clean the system this way...
Anoying.I hardly use the choke. Any idea what it could be?
Thanks!
Dirk

[mgcjag]

Checkout the dual fuel pump....you could just be running on one....with the second only comming in when warm or intermittant.....Steve

[Kojag]

Steve, many thanks for this info. I will check. My feeling is that it cannot be the but the pump is a possibility.I have other classic cars and with Super 98 or 100 it was never a problem to get them properly running.
Best regards
Dirk

[Paul Buckley]

The problem is certainly not the use of modern fuels. My V12 runs perfectly well on super grade petrol, and the valve seats were hardened at the factory during manufacture so the lack of lead is no problem either.

[Paul Buckley]

The recommendation to try running for longer periods of time is called an 'Italian tune up'.
I once bought an MGB from a lady who lived in a town on a small caribbean island. The car was incapable of more than 30mph, but after several runs of eight miles at full throttle the car became alive and became one of the best performing cars I have ever had. It had become 'coked up' from lack of meaningful use.

[Kojag]

Thanks Paul! The MGB theory is surely often the solution but I have been driving during confinement regularily as it was legal and the only thing you could on weekends, well ,apart from working on the car. But I will give it a try.
Best regards
Dirk

[mgcjag]

Hi Dirk....just to add re my mention of the dual fuel pump...a friend had a similar problem....but it was intermittant...the only way we found the problem was out on a run and the car started to mis fire.at higher revs...we pulled over with engine still running.....i had a close listed to the fuel pump and only one half was running...gave it a bang and the second half started up.......Steve

[driver]

Hi ,
had a similar problem when i first had my s3 ,
on investigating i found it was only running on a single pump.
Fitted a new electronic pump from SNG and all was cured.
All the best Rob Gill

[Kojag]

Thanks Rob, looks like a solution! Will test it and buy on top a spare pump!!!! You never know....
Best regards
Dirk