Spitfire 1500 running on.
Discussion
Hi. My friends spitfire is running on & popping & farting under load after he fitted a new (well, eBay) engine.
All parts (dizzy etc) have not been touched apart from unbolting from old & re-bolting to new. He insists the timing is spot on & has tried other settings, but to no avail.
What else could cause this besides timing?
Cheers,
Gwaredd.
All parts (dizzy etc) have not been touched apart from unbolting from old & re-bolting to new. He insists the timing is spot on & has tried other settings, but to no avail.
What else could cause this besides timing?
Cheers,
Gwaredd.
Wrong side of the engine!
This will almost certainly be the mixture, not the timing.
Popping under load would suggest too rich (more fuel getting in than can be burnt in the cylinder so some is behing exhausted and burning in the exhaust pipe).
If you are running too rich (or too lean for that matter) the engine block will generally be getting hotter than with the correct mixture. From here it's a simple step to run on, due to detonation - cylinder is hot enough to ignite the fuel/air mixture even without a spark.
Get it warm as-is then try...
1) Set ignition to 10 degrees BTDC either statically or dynamically.
2) Take off the air filters and wind the mixture adjusting nut (underneath each carb will be a nut with a spring above it) on each carb up until the jet is flush with the floor of the carb (look through the hole where the air filter goes and where the needle goes in to the floor). Now wind each one back 2 turns (12 flats).
3) Loosen the links between the two carbs and balance them, but adjusting the fast idle screw on each carb. till they each pull the same level of vacume (These babies are great - www.demon-tweeks.co.uk/products/ProductDetail.asp?cls=MSPORT&pcode=A/A98001.000 but expensive. The budget option are these - www.gunson.co.uk/item.aspx?item=1813&cat=439 (available from Halfords).
If you have either an exhaust gas analyser (guessing not) or a ColorTune (also by Gunson and available in Halfords) you can start to adjust the mixture by 'fact'.
If you don't it's a matter of trial and error. Go for a test drive. If it's not happy try turning the two mixture screws say 3 flats up/down, re-balance, set tick-over and re-test.
If it's better, try some more. If it's worse, turn it 6 flats the other way (so if you went 3 flats up from the start you are now 3 flats down from start).
When you start getting close, try turning in single, or even half flats.
When your happy, give it a good drive, then check the plugs.
This will almost certainly be the mixture, not the timing.
Popping under load would suggest too rich (more fuel getting in than can be burnt in the cylinder so some is behing exhausted and burning in the exhaust pipe).
If you are running too rich (or too lean for that matter) the engine block will generally be getting hotter than with the correct mixture. From here it's a simple step to run on, due to detonation - cylinder is hot enough to ignite the fuel/air mixture even without a spark.
Get it warm as-is then try...
1) Set ignition to 10 degrees BTDC either statically or dynamically.
2) Take off the air filters and wind the mixture adjusting nut (underneath each carb will be a nut with a spring above it) on each carb up until the jet is flush with the floor of the carb (look through the hole where the air filter goes and where the needle goes in to the floor). Now wind each one back 2 turns (12 flats).
3) Loosen the links between the two carbs and balance them, but adjusting the fast idle screw on each carb. till they each pull the same level of vacume (These babies are great - www.demon-tweeks.co.uk/products/ProductDetail.asp?cls=MSPORT&pcode=A/A98001.000 but expensive. The budget option are these - www.gunson.co.uk/item.aspx?item=1813&cat=439 (available from Halfords).
If you have either an exhaust gas analyser (guessing not) or a ColorTune (also by Gunson and available in Halfords) you can start to adjust the mixture by 'fact'.
If you don't it's a matter of trial and error. Go for a test drive. If it's not happy try turning the two mixture screws say 3 flats up/down, re-balance, set tick-over and re-test.
If it's better, try some more. If it's worse, turn it 6 flats the other way (so if you went 3 flats up from the start you are now 3 flats down from start).
When you start getting close, try turning in single, or even half flats.
When your happy, give it a good drive, then check the plugs.
This guide might be easier to follow (pictures) - www.mintylamb.co.uk/?page=sutune.htm
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