point gap, Carb sync and heater valve..misc problems
 

My dwell is showing about 20 .. I have tried to adjust it both ways but in either case I can seem to only get a lesser value rather than a higher one. Any suggestions? The cam on the dist looks fairly worn.. is it time to find a replacement or can a new replacement part be bought?

I'm not entirely sure I have the dwell meter correctly attached. In the Haynes manula it say to connect it to the ground and the negative side of the coil but with the one I have it only registers when I connect to the ground and the positive side of the coil. It's multi function meter so this is the correct connection for tach/rpm as well.


Before I rebuild the top end on this engine and the temperature gauge worked I was getting synched airflow on my carbs but now I'm not. Is it because the temp probe is broken? The haynes manual says something about the carbs actually reacting to it but I'm not sure? Also I'm getting confused about what they mean by front and rear carb.. the rear is the one that is closet to the fire wall right?

I noticed that the rear carb is dripping fuel off the atomizer.. this is expected will idling right? but the front one with no airflow is not?


I've been noticing that the heater valve is dripping water.. I have a used replacement one but how do I replace it without damaging the wires that wrap around it's two valves?

Did you do anything to the carbs when you had them off? If not, nothing should have changed.

What you need to do to synch, I think, is to set the mixture and idle speed screws to the same setting on both carbs. Then attach the linkage. Do not use the linkage to synch them, you wil chase your tail forever.

If you have NO flow through one, you have a huge vac leak or the throttle plate is completely closed.

Drips from atomizer (?) are bad -- if you are talking about the main fuel delivery bore, only atomized fuel, no drips. If the accelerator pump outlet is dripping, the check valve is bad and fuel is siphoning through.

The Haynes manuals are hopeless on carbs, don't even usually have the correct illustrations, let alone the correct instructions!

Basic carb synch instructions are:
1) get engine mechanicals correct -- all valves to correct lash, manifolds sealed, etc.

2) get ignition correct -- all plugs must fire properly and timing needs to be close.

3) set throttle plate stop and mixture screws to the identical number of turns from closed, linkage between carbs off. This is very important -- both carbs must have the same amount of travel.

4). Synchronize air flow with the identical mixture adjustment using the throttle stops on the carbs. When this is done, adjust mixture, if necessary, by moving the screws the same amount on both carbs, then re-check and adjust air flow to match.

5). Adjust carb linkage to fix and re-attach. Recheck air flow and adjust linkage, if necessary, so that the air flow does not change when the linkage is attached.

This should get you going pretty well.

Leaking heater valves can be removed and new o-rings installed. Take out the screw and remove the operating lever, then remove the internal snap ring. Valve pulls out of housing. You will need to re-install the screw or one similar, and may want to make a puller from some small pipe and some washers to drag them out. Clean, install new o-rings (hardware store) and re-install.

Peter

>>>>Did you do anything to the carbs when you had them off? If not, nothing should have changed.

Nope, I only put them in a box

>>>What you need to do to synch, I think, is to set the mixture and idle speed screws to the same setting on both carbs. Then attach the linkage. Do not use the linkage to synch them, you wil chase your tail forever.

Oops I did forget to dettach the linkage

>>>If you have NO flow through one, you have a huge vac leak or the throttle plate is completely closed.

It looks like the throttle plate is open.. hard to see it though the choke even with a light ... When you say there might be a vacuum leak .. where are some likely places to check.. could it be bad tubing?

>>>Drips from atomizer (?) are bad -- if you are talking about the main fuel delivery bore, only atomized fuel, no drips. If the accelerator pump outlet is dripping, the check valve is bad and fuel is siphoning through.

Hmm it was dripping a little and then later when I looked it wasn't but I could see mist(atomized fuel) coming from it. Could it have ben dripping because the blance and idle are too high on that carb?

>>1) get engine mechanicals correct -- all valves to correct lash, manifolds sealed, etc.

All that should be good... the engine sounds great but not when it's at the correct idle speed

>>2) get ignition correct -- all plugs must fire properly and timing needs to be close.

Timing is dead on.. I guess I could still check the spark at each plug although I have no reason to suspect that they aren't all firing.

>>>3) set throttle plate stop and mixture screws to the identical number of turns from closed, linkage between carbs off. This is very important -- both carbs must have the same amount of travel.

OK I need to do this...

>>>4). Synchronize air flow with the identical mixture adjustment using the throttle stops on the carbs. When this is done, adjust mixture, if necessary, by moving the screws the same amount on both carbs, then re-check and adjust air flow to match.

>>>5). Adjust carb linkage to fix and re-attach. Recheck air flow and adjust linkage, if necessary, so that the air flow does not change when the linkage is attached.



Any suggestions for the point gaps? I'm supposed to set the gap with the breaker at the crest of the distibutor cam right?

TIA

Adrian

Adrian:

Point gap at max opening -- right on the point of the cam. Difficult to get exactly right (sigh).

Dwell should be 30. Make sure you have the meter set properly, no way it can only get 20 max unless the cam lobes are really worn down or the distributor shaft wobbles -- try moving it back and forth sideways -- too much play, and the point spring will push it away all the time.

I'm sure parts are available, but who knows what they will cost! Probably have to get them from MB.

A conversion to breakerless ignition might be in order, eliminate most of the mess with points and dwell.

On the carbs:

Vac leak could be bad or loose gasket or vac line, leaking manifold., etc. However, if it runs well except at idle, I think you have just fixed the airflow imbalance from a sick engine and just have to re-adjust the carbs.

Make sure you have the basic flow set with the linkage off, and that full throttle is the same with linkage on. Check the idle opening stop on both carbs, make sure the throttle plates are the same number of turns on the screw from completely closed. Set actual idle speed with the idle speed screw that works the linkage.

Ditto for mixture screws -- need to be the same number of turns from closed.

If it runs well off idle, you just need to re-synch!

Peter

Found my manual, here's the official MB system:

synchronize throttle plates with synchronizer (idle speed screw is up front, below and outside of the choke heater, vertical, not horizontal.)

Adjust idle mixture screws to the same position by blocking off the idle air bore in the top plate one at a time and matching the idle speed drop. Bore is beside the front venturi, opposite mixture screw somewhere -- just a hole in the top of the carb. Should be obvious when you cover it, as the rpm will drop.

You will have to fiddle the mixture and idle speed screws, using the synchronizer, until you have the correct speed, mix, and balanced air flow.

This should keep you busy for a while.....!

I wish I had a scanner, would scan the pics and send them to you!

Peter

>>I wish I had a scanner, would scan the pics and send them to you!
Which manual is it? I may have it as a pdf allready or xerox I think.. I have too many.. I keep misplacing them..

Adrian:

1972 factory training manual for technicians.

Peter

If you are dripping fuel from the atomizer, check to make sure that your idle circuit is not plugged. There is a tiny hole in the top front of the carb. Plug it with a pencil eraser and see if the idle drops. If it does not drop, then it is plugged and you are pullling fuel through the main circuit that should be fed by the idle circuit.

You can also get a plugged idle circuit if your idle solenoids are not working. If you have idle solenoid valves, check that they are working by plugging/unplugging them with the ignition on and the engine not running. You should hear a distinct "click."

An easy way to sync the carbs is with a piece of heater hose against your ear and hold it next to the venturi of each carb. This is with the linkage removed. Then adjust the idle on each carb to equalize the sound. Then re-install the linkage so that it does not disturb the relative position of the idle stops in the slightest.

If you are getting good spark and your timing is on, I would not worry too much about the dwell at this point.

Nope don't have that one..

I'll try that.. the solenoids do work..

I forgot the next step.

If the idle circuit is OK then the only other cause for the drips that I know is that the carbs are way out of sync. And the dripper is pulling way more vacuum, exceeding the fuel feed capacity of the idle circuit. The answer is to adjust that carbs idle so less air is going through and balance it by giving the other carb a little more.

But this should be apparent when you do the ear test.

This is all plausible, because you have radically changed the compression and hence the vacuum in the engine.

Yeah.. when I hand crank the engine now it is really tough to turn with the spark plugs in whereas it was too easy to turn before.

OK well I'm going to attack this again today!

Oh I had forgotten that I did get one of these it's a 4 page pamphlet..

Anyway .. I got the airflow synched. I adjusted the idle mixture screws and the idle air holes seem clear. I sprayed some carb cleaner down them and the idle accelerated telling me that the carb cleaner was going all the way through and giving the engine a little boost.

However the idle is still rough. Tomorrow I'm going see if the exhaust manifold needs to be tightened? I guess there is no sure fire way to know if there is any air getting through it? Is there any way to test it??

My rebuild of the heater valve was 50% succesfull.. one side is still leaking. The gaskets in it had turned to paste.

Other things to get around to.. find the small leak in the transmission, put on the new muffler and replace light in dash.

Adrian:

Are you sure you aren't working on my car?

The training manual is about a inch thick in a three ring binder, covers fuel systems, ignitions systems, and various other stuff, all loose leaf. Pretty handy.

Rough idle could be a number of things -- have you adjusted the mixture yet? Running a bit lean will make it shake, so will an iffy ignition.

Dwell should be 34-40 degrees on a six, by the way.

Peter

Assume that you used the little ring-like gaskets when you hooked up the exhaust. Best way to check for leaks is to hold your hand by the manifold-downpipe joint when the car is first started and the pipes aren't hot.

Now is the time to get the dwell right. If you set the point gap at .012" it will be close. Then time it to around 8 deg btdc w/o the vacuum.

Also make sure you have no vacuum leaks - all fittings on the intake manifold and carb either used or plugged.