100DashSix
Jedi Trainee
Offline
Sorry in advance for the length!
Here's the procedure I've used to tune my MG.
- Replaced dampers and caps
- Got idle screws that will stay where I set them
- Cleaned the inside of each carb, pistons move freely.
- Warm up engine
- Remove air filters
- Remove the tube running from the vacuum advance to the intake manifold (I've tried the entire procedure with this on as well, as I wasn't certain if it should be removed)
- Set the jets to the same default height (full lean, 2 turns richer)
- Set the idle screws to the same default (loosen until at the point of first touching the carb body, 2 turns in)
- The choke and throttle linkages don't prevent me from adjusting each HIF-4 independently, so I've left them alone (with the exception of making the throttle cable pull on each carb the same amount, at the same time)
- Turn the car on.
Car is idling high, maybe at about 1,800 RPM. The exhaust is warm and slightly wet, and the note sounds very even.
Bring the idle speed down to ~1,000 RPM, each idle screw a quarter turn at a time. Very carefully. The exhaust note has changed to a terrible "putt putt PUTT putt PUTT putt putt" note. It's intermittent, not rhythmic. Verify the hiss is equal, adjust an idle screw or two if necessary. Lift the pistons in turn, adjust the mixture for both carbs if necessary (a little richer, usually), recheck hiss, adjust if needed. Go behind the car, put my hand up to the exhaust, and find that the uneven note is still there. /ubbthreads/images/graemlins/mad.gif
I don't think it's timing because the exhaust note sounds fine before I turn the idle down from 1,800 RPM. I don't think it's a leak because I've sprayed WD-40 where the carbs meet the intake manifold and the spots where the throttle shaft meets the carburetors, and there hasn't been any discernable effect.
Any ideas?
A 2 minute test drive has the car feeling good up until 3,500 RPM, where it stutters a bit and will--if I don't let up--backfire/sputter from the carburetors.
Despite having a feeler gauge, I haven't checked the gap between the points, as I need a wrench that will fit the nut on the alternator, to turn the engine.
Here's the procedure I've used to tune my MG.
- Replaced dampers and caps
- Got idle screws that will stay where I set them
- Cleaned the inside of each carb, pistons move freely.
- Warm up engine
- Remove air filters
- Remove the tube running from the vacuum advance to the intake manifold (I've tried the entire procedure with this on as well, as I wasn't certain if it should be removed)
- Set the jets to the same default height (full lean, 2 turns richer)
- Set the idle screws to the same default (loosen until at the point of first touching the carb body, 2 turns in)
- The choke and throttle linkages don't prevent me from adjusting each HIF-4 independently, so I've left them alone (with the exception of making the throttle cable pull on each carb the same amount, at the same time)
- Turn the car on.
Car is idling high, maybe at about 1,800 RPM. The exhaust is warm and slightly wet, and the note sounds very even.
Bring the idle speed down to ~1,000 RPM, each idle screw a quarter turn at a time. Very carefully. The exhaust note has changed to a terrible "putt putt PUTT putt PUTT putt putt" note. It's intermittent, not rhythmic. Verify the hiss is equal, adjust an idle screw or two if necessary. Lift the pistons in turn, adjust the mixture for both carbs if necessary (a little richer, usually), recheck hiss, adjust if needed. Go behind the car, put my hand up to the exhaust, and find that the uneven note is still there. /ubbthreads/images/graemlins/mad.gif
I don't think it's timing because the exhaust note sounds fine before I turn the idle down from 1,800 RPM. I don't think it's a leak because I've sprayed WD-40 where the carbs meet the intake manifold and the spots where the throttle shaft meets the carburetors, and there hasn't been any discernable effect.
Any ideas?
A 2 minute test drive has the car feeling good up until 3,500 RPM, where it stutters a bit and will--if I don't let up--backfire/sputter from the carburetors.
Despite having a feeler gauge, I haven't checked the gap between the points, as I need a wrench that will fit the nut on the alternator, to turn the engine.