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More trouble getting the B to run well

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100DashSix

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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.
 
Sounds like you've done everything right. Lean at the top. Or timing advance going berserk. Where is it set now, and how? IIRC, with a proper points gap of .014"~.016" you should static set it at 8° to 10° BTDC. If all that is done, maybe start looking at rotor fit on the shaft, sloppy shaft in the dizzy, other iggy problems. The carb proceedures you've related would rule out induction as a cause, IMO.

BTW: A regular ~matchbook cover~ is a fair replacement for a feeler gauge to gap the points, FWIW. Make sure they aren't pitted or glazed. An emery board will work to "dress" them.
 
(Ah, the needles are ABD also)

The points certainly didn't look shiny and new, but I don't think they were excessively worn (replacing them to be safe is a next step). I haven't checked the static timing yet, I'll have to work out how to do that exactly (looking down to the crankshaft and those little metal marks is a bit awkward...silly tiny British car!). You can use a 12V light connected to the positive terminal on the distributer and a ground to determine the degrees BTDC, correct? (Turn engine by hand so rotor is on plug #1, wiggle distributer shaft, check mark on the pully connecting to the crankshaft when light flickers?)

Say I am wrong about the points being not pitted and peaked, this could be the cause of the erratic notes at low RPMs, but not higher RPMs?
 
Might wanna take a look at the coil....I had similar problems with the LE that were solved by replacing the coil.
 
If I was just going to guess, I would say coil as well.
 
Similar problems from the coil, you say? I'll keep that in mind, thanks. At $22 from Moss, that's a relatively painless part to replace.

Is there a special significance associated with a Lucas condenser and points set, or can one from an automotive store do?
 
NAPA, CS 207A Echlin or Standard Parts LU-??? I FORGET!!!
...but yes they all have replacements that work.
 
Is the valve lash set?

If you do Doug Lawson's bit and it's still acting up, check the valve lash. Sounds a bit familiar. Also, my dad used to check for burnt valves on cars he bought by holding a dollar over the exhaust at idle. should thump thump thump really hard, but if on one of those thumps regularly wan't to suck the dollar into the pipe - burnt valve (or maybe one not adjusted properly). I don't know how much fact lies in this test, but seems like your problem would be rythmic if it was something like that. Just adding another possible.
 
It seems very possible that the exhaust would want to eat a dollar, the car not being satisfied with eating all those other dollars I used to have!
 
[ QUOTE ]
It seems very possible that the exhaust would want to eat a dollar, the car not being satisfied with eating all those other dollars I used to have!

[/ QUOTE ]

/ubbthreads/images/graemlins/lol.gif /ubbthreads/images/graemlins/lol.gif /ubbthreads/images/graemlins/lol.gif
 
Points look good from Florida.
 
I do notice a lot of dust from them on the plastic of the actuator. Clean 'em with an emery board and check/set gap, and static time the beast. Then see if the run characteristics change.
 
Will do tomorrow, DrEntropy, thanks. And to turn the engine over by hand so the point gap can be checked, is the best way to slap a big wrench on the alternator nut and turn clockwise?
 
My suggestion is to grab a handful of fan/hub with the plugs OUT, put tension on the belt and turn it that way 'til the timing mark is aligned with 8°~10° BTDC, loosen the dizzy clamp (Make sure the rotor is pointing to #1 'trode first) and rotate the dizzy body to open points and gap 'em... ya gotta loosen it anyway to reset timing so make life easier and whack two birds with one rock. Once you have gapped and timed, clamp (GENTLY! It doesn't need TORQUE) the dizzy and refit all the bits. It ~should~ light off so quick you can't let go of the key fast enuff /ubbthreads/images/graemlins/wink.gif

Above all: Have FUN and learn!!!
 
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