Spluttering Spitfire

[Mad4classics]

8 hours ago, Pete Lewis said:

if it runs it wont be very happy

condensers also buffer the coil to aid it discharge cleanly,  a failing condenser can cause backfires if it discharges when you dont want  it

i found a local last week where the heel had worn down so far there was no adjustment left and the points were all but closed 

without a spare,  remedy was to grind the end which now fouled the condenser mount and slot the adj screw hole  the points faces  were as flat as new so  it had a brilliant condenser fitted ,    we need more like that .

if you get a duff one cut it open should have around 9ft of  waxed insulated foil wound up inside .

Pete

The condenser and coil primary form an LC resonant circuit which produce the high energy output from the coil; you need both to work properly.

Still looking at the condensers from the Dizzy Doctor, he has them made to his own specification, with the full length of foil in them.

David

Edited June 30, 2018 by Mad4classics
Typo

[SpitFire6]

Hi,

I learn something every day on this forum;

"If you remove the condenser, as suspect, then car will run ok"

"condensers also buffer the coil to aid it discharge cleanly,  a failing condenser can cause backfires if it discharges when you don't want  it"

& saving best for last:

"if you get a duff one cut it open should have around 9ft of  waxed insulated foil wound up inside."

Hats of to the Dizzy Doctor: "Still looking at the condensers from the Dizzy Doctor, he has them made to his own specification David, with the full length of foil in them." Somebody that's helping car owners.

Great information for everybody. Should make this sticky so everybody can benefit from this information and save trouble in the future.

Thank you,

Iain.

 

 

 

Edited June 29, 2018 by Spitfire6
Added info about Dr. Great.

[oliproctor]

Sealant and new gaskets bought and arriving Monday, hopefully they will solve this annoying problem! I'll keep you all posted. 

New gaskets look a little thinner compared to the old ones i took off this morning, hopefully that wont cause too much of a problem? I've bought 4 so two spares, could i stack them to create the same width as the old?

Thanks

[oliproctor]

On 6/27/2018 at 7:07 PM, Pete Lewis said:

once all is airtight you can readjust the needles to get the mixture and idle speeds under control and see how she runs 

pete

Good morning again all,

All new gaskets and sealant are changed and airtight (checked using the EasyStart spray test and no difference in revs occurred). I was surprised to find out the spluttering problem now began as soon as the car started compared to the 15 min delay before I had changed the gasket, I guess this means now there are no air leaks and all that needs to be done is to readjust the needles to get the mixture correct as above?

I have never done this before and wondered how to do so please? A step by step guide would be much appreciated please!

Thanks Oli

[yorkshire_spam]

Oli,

Twin SUs (assuming that's what you have) are not that bad, there are plenty of online guides. For example: http://sucarb.co.uk/technical-h-type-carburetter-tuning-multi

Ideally you need some way of measuring airflow. You can get fancy meters for this OR just use a listening tube as per the linked guide.

Essentially once idle airflow is set, lowering the jet makes it richer, raising the jet makes it weaker on each carb.

Cheers, Sam

[NonMember]

It's important to get the mixture right on both carbs but many of the methods for judging it (including those fancy electronic gizmos in garages) only look at the average. If you're not sure, it's best to start from the baseline - both jets flush with the bridge then turn both adjusters the same number of flats - and keep always turning both the same amount.

[oliproctor]

Thank you! I'll have a go today!

[Pete Lewis]

you may need to centre the jet body,  remove dashpot  damper, stick screwdriver down and hold piston down.

undo the big nut under the jet holder 1/2 turn and rasie the jet adjust nut to make the jet contact the base of the held down air piston

give the jet holder a light tap , make sure the air piston falls witha clunk , no sticking , nip up the big nut

wind the adjusting nut down 2 full turns   as a start point 

back off the idle screws and turn in to just touch the case abutment, turn in 1.5 turns to set the initial idle setting 

this should run,  every book you read gives slightly differeing jet down turns some say 1.5  some say 3 turns

as rob says if both are kept the same then things are in balance, thats how they arrived on the productio engine line   all to a preset mechanical setting

you will find a lifting pin under the air piston chamber  this gives some clues about your settings

there is no dark art but just gentle .feely with a finger   with engine up to temp and idling   raise the pin to just feel it contact the piston, then lift 1/32"   or 1mm , dont yank it up

you are looking/listening for a small change in revs , just hint of change , nothing dramatic  if it ups 50rpm its a bit rich  if it drops around 50rpm its lean 

if nothing its spot on

hope thats a step by step guide  all you need is a spanner and fingers 

one simple diy check on balance  is , remove damper , cut a card to fit in the damper tube and protrude above the carb top,  with it idling mark the heght it rises to witha fine pencil line on the card where the top is , repeat of 2nd carb and it should rise the same .  if not then small idle adjustment will equal it up , but with both set 1.5 turns in i expect this idea with a cornflake packet  will show you have it correct without any need for fancy tooling 

Pete

 

[oliproctor]

I take it the bend in this key isn't a very good sign... 

[Pete Lewis]

Its quite a rattling good fit int the piston slot,  if the piston will rise and fall with a clunk onto the bridge its not a problem

If this is enough to jam the rise and fall of the air piston then yes its not desirable  

Pete