Air filters,plug caps.

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noc668r
Posts: 22
Joined: 18 Jan 2026 11:48
Location: Northampton UK

Air filters,plug caps.

Post by noc668r »

Hi, checking over my recently acquired 77 Strada.
Is there an easy way to remove the air filters, they're off now, but I really struggled and I'm not new to bikes?
Or should I have called a midwife?
Also I decided to fit non suppressed HT caps , but I bought some from a company called Auto Electrical Services , and they're absolutely hopeless.A poor fit on the plugs and wobble about alarmingly.
Can anyone recommend a decent supplier please?
TIA
John
3potjohn
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Joined: 02 Jun 2007 13:58
Location: Devon

Re: Air filters,plug caps.

Post by 3potjohn »

On my late Sport (K1) I had red NGK 5 Kilo ohm plug caps. After some years I got hold of some black NKG SB01F which were 1 kilo ohm.
I can’t say I noticed a difference.
The stock airbox does require a bit of dismantling to change the filters. I would advise to keep this standard.
Last edited by 3potjohn on 14 Feb 2026 22:13, edited 1 time in total.
morini_tom
Posts: 1109
Joined: 05 May 2006 13:47
Location: Northampton
Location: Northampton

Re: Air filters,plug caps.

Post by morini_tom »

When I can get them I use NGK SB01F but it’s getting hard to get low resistance plugs let alone no resistance ones.

Otherwise I use NGK SB05F (the 5k ohm version) and these seem to be fine on a Morini.

There is a post somewhere on the forum about removing the resistor from the NGK plugs which can be done with care although I never have.

Use copper core HT lead not carbon core.

There are plenty of fake parts online so buy only from a trusted supplier.

As John says, the airbox is a pain to get to and to change filters but definitely wants to be kept.
noc668r
Posts: 22
Joined: 18 Jan 2026 11:48
Location: Northampton UK

Re: Air filters,plug caps.

Post by noc668r »

Thanks, guys,the existing caps are 1K ohm so not standard?
Didn’t know that.
A previous owner has fitted some very nice quality copper core HT , which saved me a job.
I was surprised how long the HT leads are, if I designed the bike I would have positioned the coils closer to the plugs.
J
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Daddy Dom
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Joined: 16 Nov 2006 19:48
Location: Auckland, New Zealand

Re: Air filters,plug caps.

Post by Daddy Dom »

I have always successfully used plain rubber plug-caps with no resistance at all, for what it's worth.
DD
MRC 3082½
BumbleBee
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Location: Reading

Re: Air filters,plug caps.

Post by BumbleBee »

TBH most everyone finds the standard setup with a resistor cap more than fine because the BP7ES plug has no resistor. Is there a specific reason you were wanting to go off piste? Your choice of course. I know some people say because they race and some say their old 6V brit bikes benefit as they were not designed for resistors. The 3½ with its eletronic ignition has more than enough spark for it, and the resistor can actually cause a higher voltage spark, because transient high voltages don't care about the V=IxR rule that the regular 12V on the rest of the bike follows.
BumbleBee
Posts: 248
Joined: 13 Jun 2017 21:10
Location: Reading

Re: Air filters,plug caps.

Post by BumbleBee »

TBH most everyone finds the standard setup with a resistor cap more than fine because the BP7ES plug has no resistor. Is there a specific reason you were wanting to go off piste? Your choice of course. I know some people say because they race and some say their old 6V brit bikes benefit as they were not designed for resistors. The 3½ with its eletronic ignition has more than enough spark for it, and the resistor can actually cause a higher voltage spark, because transient high voltages don't care about the V=IxR rule that the regular 12V on the rest of the bike follows.
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72degrees
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Location: West Midlands

Re: Air filters,plug caps.

Post by 72degrees »

I think if you are running NLM ignition module and 'scooter coils' resistor plugs (like NGK Iridium) and good (NGK) resistor caps are OK. Been a long time since I was reliant on the OEM system. I always used EV plugs back then with good results but alas no longer available.
Morini: 1980 2c/375 The Old Gal plus all that remains of the Forgotten Error (the engine)
Gilera: 1957 175 Sport
Honda: 1984 CB250RS
Husqvarna: 2019 401 Svartpilen
Wishlist: 2026 Morini 350
noc668r
Posts: 22
Joined: 18 Jan 2026 11:48
Location: Northampton UK

Re: Air filters,plug caps.

Post by noc668r »

Just wanted to get the best spark possible,as I need a bike that starts fairly easily, due to my ancient body.
I sent away for 2 sets of non resistor caps, the first were long ones, similar to standard, but unfortunately if you went above 5mph the breeze would have knocked them off.
The second set were stubby early HTC/Champion types that used the little plug screw on gizmos.
Very crappy fit, OK till you hit a speed bump.
Caveat Emptor, there’s so much rubbish out there on the web!
SO, I’m leaving the 1K NGK ones on.
They’re quality, real positive fit and good rubber covers.
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