1275 Marina engine runs better with air filter sealed?

[jammmorris]

Hi, a strange question potentially. (Thanks for everyone's advice about some issues I've had with the thermostat by the way, this one is unrelated). I have a '66 Minor with a 1275 Marina engine. When I bought the car earlier this year I noticed that the pancake air filter had electrical tape round the vent/mesh which I thought was strange. I asked the owner who said it runs better with it sealed up- apparently this is common practice on some classic cars to restrict the cold air, and it will still get air so don't worry. I wasn't sure so I replaced the air filter, spark plugs and HT leads. It starts OK but even after warming up when I press the accelerator the engine dipped whatever gear in was in to the point of almost stalling. The new HT leads were longer than the ones I replaced so initially I wondered if that was the cause so I swapped them back to the ones it came with. There was a marginal improvement but it still dipped. I then decided the only thing that was different was the air filter. I taped up the new one around the vent mesh and instantly it was better. It had torque in every gear and didn't dip when accelerating. I really don't understand the science of this! I'm thinking that if it runs don't mess around. Is there a reason that taping up the air filter improves the running? (When I replaced the spark plugs 3 out of the 4 were a bit blackened with carbon but it's hard to say how long it has been since they have been replaced). Thanks for any enlightenment!

[geoberni]

If I read your information correctly, and I must say it would be a whole lot easier to read if you broke it down into paragraphs....
I would say the problem is the mixture adjustment on the Carburettor, or even something as simple as the oil level in the Carb Damper, assuming it's still got an SU Carb fitted.
If it's not an SU, then however that Carb has an Accelerator Pump function, to enrich the fuel on pressing the pedal.

apparently this is common practice on some classic cars to restrict the cold air

No, it's not common practice, at least so far as I've ever heard of; it's not just restricting the 'Cold Air', it's restricting all the air no matter what the air temperature is...It's a Bodge fix!

By restricting the air filter with tape, you are by default making it harder for the engine to suck any air in, thus affecting the fuel/air mixture.

[philthehill]

I am in agreement with the above.
The air/fuel mixture is not right.
Having the tape makes the air/fuel mixture nearly right.
What carb is currently fitted? (looking at the engine bay photo in your other thread it looks to be a HIF38 or similar) There should be a tag attached to the carb stamped with the carb number.
The Marina is normally fitted with a HS4 carb.
What carb needle is currently fitted?
You have a pancake air filter fitted. Having that style of filter usually means a weak mixture.

Once we know the answers to the above we can advise accordingly.

I would suggest that you fit a Morris Marina air filter assy and go from there. That could be all you want to get the engine running right.

[jammmorris]

Hello, thanks for your replies. I have looked everywhere for a tag but can't see one anywhere. The only letters stamped on it are on the photos attached. Not sure what needle is fitted. Do any of the photos help?
I've trawled for an air filter for the Marina and only the pancake one that I bought gets thrown up. If you could recommend where I could find the correct type I'd be very grateful.
Thanks.

20230403_150633.jpg (1.3 MiB) Viewed 1112 times

20230403_150658.jpg (1.19 MiB) Viewed 1112 times

20230403_150716.jpg (1.26 MiB) Viewed 1112 times

20230403_150725.jpg (646.11 KiB) Viewed 1112 times

20230403_150753.jpg (960.14 KiB) Viewed 1112 times

[svenedin]

Hello, thanks for your replies. I have looked everywhere for a tag but can't see one anywhere. The only letters stamped on it are on the photos attached. Not sure what needle is fitted. Do any of the photos help?
I've trawled for an air filter for the Marina and only the pancake one that I bought gets thrown up. If you could recommend where I could find the correct type I'd be very grateful.
Thanks. 20230403_150633.jpg20230403_150658.jpg20230403_150716.jpg20230403_150725.jpg20230403_150753.jpg

If you search for “Morris Marina air filter assembly” I think there’s some listed on eBay

[philthehill]

Here is a Morris Marina air filter assy.
https://www.ebay.co.uk/itm/285206108747 ... R8SOn7DpYQ
You will still need to obtain the elbow and inlet to the air cleaner.
See also this thread regarding air filters.
viewtopic.php?p=683043&hilit=MG+air+filter#p683043

[mowogg]

Someone told me the standard marina filter set up did work as it hit the r bonnet cross member. I have not tried it so I don't know for certain and itight be incorrect

The flat mini type fits as is routinely fitted

[svenedin]

Can’t the mixture just be adjusted properly? Take the tape off the air filter and adjust the carburettor mixture.

[philthehill]

I suspect the tape is to get around the fact that the needle is not correct for the application.
In my post above I did ask what needle is currently fitted.
I also suspect that the carb has been previously adjusted with no success.
Get everything back to as near standard as possible and then go from there.

[svenedin]

I suspect the tape is to get around the fact that the needle is not correct for the application.
In my post above I did ask what needle is currently fitted.
I also suspect that the carb has been previously adjusted with no success.
Get everything back to as near standard as possible and then go from there.

Ah I see. Looking again the OP is quite correct that the original Marina filter assemblies are very hard to find

[jammmorris]

Thanks as always everyone, much appreciated advice. I took her to my garage today who are going to take a closer look at her in a couple of weeks as well as doing a few other jobs.
The idle is too high and it needs tuning so hopefully they'll start the process of getting to the bottom of it but I fed back everyone's advice from this post. It's not something I want to start fiddling with and messing up as I don't have enough experience.
The air filter is still a conundrum, looking at the space I have available there isn't much for something the size of the original Marina but the Mini one from the post Phil sent looks interesting.
Thanks again.
Andy

[Harryhotrod]

Try change the needle in carb to AAA

[jammmorris]

For information- it turned out to be the dashpot. I watched a useful video on youtube about servicing Minors https://www.youtube.com/watch?v=O91aTqcvBJI
I topped my dashpot up with 20/50w and it transformed it. Much more responsive acceleration. My garage also replaced the distributor parts and adjusted the idle. Much better now.
Thanks.