Fintail Ignition Tuning - Page 2 - Mercedes-Benz Forum

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post #11 of 13 (permalink) Old 11-27-2010, 07:16 PM
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Vehicle: 1993 MB 500E, 1965 MB 220b
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bi-metal spring diverting plates below the carbs

Originally Posted by carpenterman View Post
How much effect do the bi-metal spring diverting plates below the carbs have on cold starts? My springs are shot.
This mechanism could be affecting your starts to a certain degree...

Check to see if the plates on your car are frozen in position (grab the counter weight that the diverter plate shaft is attached to & try to roatate it). This mechanism is often neglected or not even known to exist by many owners. When cold, the plates are in the closed position. The purpose is to allow warmer air/gas to circulate about the base of the carb/intake area...assisting in cold starts & initial warming up conditions. As exhaust manifold/engine compartment temperatures increase, the bi-metal spring elements expand; rotating the plates to the open position allowing exhaust gases to escape directly thru the exhaust pipe.

The shafts of these diverting plate mechanisms will lockup if not maintained (they are subject to the incessant abuses of heat, weather, time & oxidation). If frozen open, the car could possibly be harder to start in colder conditions. If frozen shut, the base of your carbs & intake air will be subject to higher operating temps & exhaust will be restricted to some degree; resulting in rough idle & operation.

What I have done in the past is first liberally blast the rotating shaft surfaces with a penetrant like PB Blaster. You may have to use channel lock pliers to grasp & rotate the counter weight. Work it easily, don't force it. Once free, give it time to dry out before liberally applying a graphite-based lubricant to the rotating surfaces. Check & lube once a year & you won't have any future problem with it.

Since I'm a 3 season driver rarely running in truly Cold temps, i removed & stored the bi-metal springs & wired my diverter plates open using stainless steel wire to hold the counterweights in place for restriction-free flow.
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post #12 of 13 (permalink) Old 11-29-2010, 06:27 AM Thread Starter
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Vehicle: 1981 300TD 310k--1966 230 165k--1970 280se 172k
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Thanks for the info, Der Furor. My plates rotate fine--the springs are broken. How do you determine the position of the plates if I want to wire them shut? Is the plane of the plate the same as the slot in the shaft? That would make horizontal the closed position, right?

The car still starts hard after adjusting/balancing the carbs and corrected timing/dwell. I've been driving it as much as I can to see how it performs, and the other day after parking for a few minutes, it took 20 minutes to get it going again. Usually it is fine when it is warm, so that is something new. Sometimes it seems like a fuel problem and sometimes it seems like ignition. Once the car gets running and warm it is perfectly fine.

So I'm going back to square one. Check tank strainer, replace soft lines, inspect/rebuild/replace fuel pump. I may just bite the bullet and put in a Petronix system with their upgraded coil.

I have a question about the fuel pump. It appears there is some confusion about the type I see available online. A couple of posts referred to a lever-type and a push-type. The ones online appear to be the push type and I'm betting that my original is the lever type. Someone suggested a tapered gasket or somesuch to make the push type work. Was that a legitimate workaround? Or can I just find a new or rebuilt fuel pump (or a kit) that is a bolt on?

1981 300TD--310k miles
1970 280sel--172k miles
1966 230--162k miles
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post #13 of 13 (permalink) Old 11-29-2010, 04:51 PM
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Plate Position

Originally Posted by carpenterman View Post
How do you determine the position of the plates if I want to wire them shut?
With the shafts freely moving & the bi-metal springs removed, gravity will turn the counterweights to the normally closed position. You do not want to wire them shut (your car will run like crap once it warms up). The wiring would be done only to keep the plates open (i.e. holding the counterweights against gravity).

Your fuel pump may also play a part in the hard cold starts. The original-style mechanical fuel pump has a hand-primer lever which would allow you to prime the fuel system if the car had been setting long. Some aftermarket replacement pumps do not include this feature (I've had one of these before). As a result, if the car has sat for an extended period of time, for several possible reasons there may not be sufficient fuel within the carbs & supply line to start & keep the car running until the mechanical pump can deliver the required uninterrupted amount (this is a reason why you must keep cranking the car to finally get it started).

If your current pump does have the priming mechanism, pump it 10-12 times prior to starting the car. If you have the original pump, but it isn't working, it is worth getting a rebuild kit for it (the original lever-type is the better design).

If your pump has a screw-on lid, undo it & drain any water which may be present.

Coupes & later model sedans were outfitted with electric fuel pumps (which are fine as long as they keep getting electricity).

If you don't have a hand-priming pump, try this test next time you go for a drive & have a hard start (or hard restart). Take a squeeze bottle with a little bit of gasoline in it. Have your air cover off so you have access to the top of your carb(s). Squirt some gas down into your carb (this somewhat imitates the priming function). Turn the key. Does the car start right up? Does it keep running or die out? If it dies out, how many times do you have to squirt gas in the carbs before the car starts & runs normally? (This will be the approximate volume of fuel which is not but should be within the fuel line between the fuel pump & carbs for startup).
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