Triumph Spitfire carbs specialist Midlands?
Discussion
Posting on behalf of my 21 yr old Son who's bought himself a pretty tidy Spitfire.
He's got issues with the Carbs where by it smells to me like its running way too rich & generally not pulling cleanly lacking power & any kind of smoothness.
Any suggestions in or around the South Midlands area for either a Spitfire specialist who could resolve this or a rolling road with suitable Carb set up expertise at all please?
He's got issues with the Carbs where by it smells to me like its running way too rich & generally not pulling cleanly lacking power & any kind of smoothness.
Any suggestions in or around the South Midlands area for either a Spitfire specialist who could resolve this or a rolling road with suitable Carb set up expertise at all please?
Jigsaw Racing in Corby. Spitfire specialists.
https://jigsawracingservices.com/
(But not website specialists!)
JOhn
https://jigsawracingservices.com/
(But not website specialists!)
JOhn
Or just get your spanners out - that's the joy of simple classics like the Spitfire.
1. Start with the linkage. Press on the arm the throttle cable pulls on and make sure the linkage is starting to open both throttles at the same time. Adjust if not, leaving a tiny bit of free play before the linkage activates the throttles.
2. Get yourself a carb balancer and, with the air filters off use it to adjust the fast idle screws till you have a 800RPM tick-over and the same reading from the carb balancer when you put it on each carb.
You can get slightly cheaper ones but I'd recommend one like this - https://www.ebay.co.uk/sch/i.html?_from=R40&_t...
3. Under each carb you should find a little pin with a spring around it off to one side (not the big pipe in the middle with a spring around it, that's the jet). Assuming it's not gunked-up the little pin should press up and lift the piston a little bit. Press each one in turn until it just lifts the piston. If the RPM rise and then drop back the mixture's correct. I think it's if the RPM rise and stay higher you're too rich/if the drop you're too lean. Assuming you're rich you want to wind the jet up (nut on the big pipe with spring around it going in to the bottom middle of the carb) to lean the mixture.
To get your head around how the carb works it's probably best to start by removing the to parts.
i) Remove the damper piston (black plastic wheel in the middle on top).
ii) Remove the 3 screws from the hash pot cover and remove.
iii) Lift the main piston and needle vertically up and out. The needle is a little delicate and the tube on the top not quite full of oil so needs to be put down carefully. Thankfully just to your left, above the brake and clutch master cylinders you'll see the body coloured metal grill over the air inlet for the heater...which is deep-enough and has holes big enough for the piston to sit on/the needle to sit through.
Look down in to the carb body and you'll see a big hole with a brass bit in it (the jet and housing) that in turn has a small hole that the carb needle sat in. The piston needle is tappered and when fully home (i.e. at idle) almost blocks the hole, so only a little bit of fuel gets in, matching the only a little bit of air getting in. Open the throttle when driving and you change the vacuum in the carb, which causes the piston to lift up, pulling the needle up in the jet, meaning it blocks it less and more fuel can come through to match the increased air comeing in.
That's running but you can also turn the nut on the jet under the carb to move the jet itself up and down, and in the same way the piston lifting/lowering the piston when the engine's running changes how much the needle blocks the jet/how much fuel gets past moving the jet with the nut controls the base point for how much the needle can block the jet. Wind the jet up and the idle/starting point for the needle is further down the jet, blocking the jet more, letting less fuel through. Wind the jet down and the idle/starting point for the needle is further up the jet, blocking the jet less, letting more fuel through.
4. All that said and done put the carb back together (reassembly is the reverse of removal as they say) and take the car for a spin around the block.
5. Press one of the lift pins until it just lifts the piston slightly and listen to the engine RPM, tweaking the jet till it rises, then drops back to normal.
6. Do the same for the other carb.
7. Go for another run around the block and recheck.
8. Of course this is a case of spinning plates and adjusting the mixture will have changed the idle and correcting the idle will probably put them slightly out of balance (no matter how evenly you try to adjust them, so just keep going around and around.
1. Start with the linkage. Press on the arm the throttle cable pulls on and make sure the linkage is starting to open both throttles at the same time. Adjust if not, leaving a tiny bit of free play before the linkage activates the throttles.
2. Get yourself a carb balancer and, with the air filters off use it to adjust the fast idle screws till you have a 800RPM tick-over and the same reading from the carb balancer when you put it on each carb.
You can get slightly cheaper ones but I'd recommend one like this - https://www.ebay.co.uk/sch/i.html?_from=R40&_t...
3. Under each carb you should find a little pin with a spring around it off to one side (not the big pipe in the middle with a spring around it, that's the jet). Assuming it's not gunked-up the little pin should press up and lift the piston a little bit. Press each one in turn until it just lifts the piston. If the RPM rise and then drop back the mixture's correct. I think it's if the RPM rise and stay higher you're too rich/if the drop you're too lean. Assuming you're rich you want to wind the jet up (nut on the big pipe with spring around it going in to the bottom middle of the carb) to lean the mixture.
To get your head around how the carb works it's probably best to start by removing the to parts.
i) Remove the damper piston (black plastic wheel in the middle on top).
ii) Remove the 3 screws from the hash pot cover and remove.
iii) Lift the main piston and needle vertically up and out. The needle is a little delicate and the tube on the top not quite full of oil so needs to be put down carefully. Thankfully just to your left, above the brake and clutch master cylinders you'll see the body coloured metal grill over the air inlet for the heater...which is deep-enough and has holes big enough for the piston to sit on/the needle to sit through.
Look down in to the carb body and you'll see a big hole with a brass bit in it (the jet and housing) that in turn has a small hole that the carb needle sat in. The piston needle is tappered and when fully home (i.e. at idle) almost blocks the hole, so only a little bit of fuel gets in, matching the only a little bit of air getting in. Open the throttle when driving and you change the vacuum in the carb, which causes the piston to lift up, pulling the needle up in the jet, meaning it blocks it less and more fuel can come through to match the increased air comeing in.
That's running but you can also turn the nut on the jet under the carb to move the jet itself up and down, and in the same way the piston lifting/lowering the piston when the engine's running changes how much the needle blocks the jet/how much fuel gets past moving the jet with the nut controls the base point for how much the needle can block the jet. Wind the jet up and the idle/starting point for the needle is further down the jet, blocking the jet more, letting less fuel through. Wind the jet down and the idle/starting point for the needle is further up the jet, blocking the jet less, letting more fuel through.
4. All that said and done put the carb back together (reassembly is the reverse of removal as they say) and take the car for a spin around the block.
5. Press one of the lift pins until it just lifts the piston slightly and listen to the engine RPM, tweaking the jet till it rises, then drops back to normal.
6. Do the same for the other carb.
7. Go for another run around the block and recheck.
8. Of course this is a case of spinning plates and adjusting the mixture will have changed the idle and correcting the idle will probably put them slightly out of balance (no matter how evenly you try to adjust them, so just keep going around and around.
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