HI Guys!!

I did the dashpot adjustment.....that's all a-ok. It is now working, but isn't the answer to my problems!!

The car is doing the same thing! I tried to take it for a ride. I checked out the balance....the unisyn is doing the same thing on both carbs! I checked the idle drop and each carb dropped from 1000 rpms to 700 rpms....I thought this meant they were balanced!

BUT........this car is STILL powerless!! When I step on the gas (in gear), it backfires through the carbs and stalls!!

I couldn't get it back up the driveway, until I put it in 2...then it slowly climbed up.

Call me crazy...but the car drives really good in 2 and R.....4 is a nightmare....(or is that just my imagination??)

What could it be??? Carb adjustments?? Timing??? I don't know what else to do???

Any suggestions welcome!!!!
HELP!!!!!

~Christy

At 1,000 RPM idle, when you put it in gear, you should be getting a "thump".

Also that's a significant RPM drop closing the bore. I recall a much smaller number, but I don't have a wide enough range of experiences to say authoritatively.

How about turning each mixture screw out a full turn and then lowering the idle closer to 800 RPM by adjusting the linkage.

I'm thinking the mixture is too lean at low RPMs still.

BTW, there is nothing wrong driving it at 2, just don't do over about 40-50. It should get you to Dave's (did he ever call back?).

-CTH

__________________
- cth350@gmail.com
http://www.111lakeside.com/

Hi!

Thanks for the speedy reply.

I think I just need to start over. As I recall, I have the vertical, springy, adjustment screws MAXED out, meaning that one more turn and they're falling apart!!! Yikes!

So......Do I want these guys to be short or long?? Or inbetween??

MY mixture screws look weird too. BEFORE, when mine were broken, they looked really screwed in far. NOW....I see ALOT of spring on them....is that normal??

Yeah...about that idle spped.....it seems that when I adjusted the dashPOT, the idle never really dropped back down.....(I cranked the little bolt, to push back the throttle to 1200 rpms....then backed off the BIG NUT to make the card fit in between the screw and the lever...right?)

~Christy

Since I just jumped in, I have to assume we are talking about twin Zeniths?

It sounds like one carb or the other has a restriction in the primary main metering system. Try running the engine at increasingly fast constant throttle and view the flow of fuel from the center venturi. Both carbs should look the same. Problems can occur do to lowered float level or restricted main jet which sits in the bottom of the float bowl. The compensation ports also could be plugged.

Most minor carburation problems can be overcome with timing. These motors liked all the timing you could give them up to the point of pinging.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

BTW, don't stick your face in there to watch untill you have achieved a steady speed. The backfire in the face will smart!!!!

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Christy:

I would have to go with Steve now and look at your timing. I had "assumed" that had been set but after reading the latest posts I now "assume" it has not been set (or verified). I run with my timing at 10 degrees BTDC (Before Top Dead Center) vs the "book" timing of 4 degrees ATDC (After Top Dead Center). Also, I do not have the vacuum retard side of the distributor connected. If you still have the retard side connected you might try plugging that until you get the rest of the problems sorted out. (retard side is the nipple on the distributor that points towards the front of the car). Just a suggestion here.

BTW: I run 93 octane at 10 degrees advance and have never noticed any tendency to ping - even under load when the outside temp is in the 100 to 107 range.

Dan

__________________
Dan Taylor/ Tulsa, OK MBCA
'84 300D/'90 Jaguar XJ6/XJ40

GUYS!!!!!!!!!!!!

So......you guys sound pretty sure that timing IS the answer!!!!!!!! Is it????? I'm getting soooo excitied!!!!!!!!!

Dan, my distributor has a "mushroom" vacuum on the side of it, with a hose coming off of it. Is THAT what I should plug??

One more thing that I didn't mention about my carbs is this...when I covered that tiny hole on the top, to see the idle drop, both carbs went to the same place..BUT if I would have held the hole shut for a few more seconds....the car would haved DIED....(or will die)....so I probably still have carburetion problems...huh.

I'm so pumped!!! This car is getting CLOSER all the time!!!!

~Christy

Yep, that "mushroom thing". However, if you don't have places for two vacuum lines, then don't plug anything. Only if you have two lines (one points to front of car other to rear) do you want to plug the front.

My experience with plugging the air-bleed hole would indicate that if the car died then the idle mixture screws are set too lean (in too far) AND/OR the carb is not adjusted correctly for the idle circuit. Again, Stevebfl would be more expert in that than I but it is how I "think" I remember it when I had the Zeinths.

Dan

__________________
Dan Taylor/ Tulsa, OK MBCA
'84 300D/'90 Jaguar XJ6/XJ40

Does anyone want to explain to me what the idle circuit is all about???

~Christy

Dan,

The way you have your timing is very close to factory specs. The factory spec of "4deg ATDC" is to be with the vacuum retard hooked up AND with vacuum in it AND with it moving the timing about 10-15 degrees retarded.

This is critical when timing these cars. One must understand what the spec means, related to vacuum system function. Any car with a vacuum retard will have its specs stated for the above conditions. In other words, If you apllied the vacuum to your retard and got 15 degrees of retard, you would be at 5degATDC; one degree retarded from factory specs.

Factory specs on the vac retard 130 motors went from 8deg ATDC to 4deg ATDC. I would always suggest pulling the vacuum off and verifying that the "no vacuum" timing is at least ten degrees above the vacuum setting.

I would consider your car to be timed 5-10 degrees advanced if your "no vacuum" timing was 11-16 degrees.


As to idle testing. The method of plugging the idle air bleed to establish relative balance is only semi usefull. The event should NOT kill the motor. The car should idle fine on one carb (though much lower). This tells me that the running condition is not basically strong. Seriously hints at a timing PROBLEM, but maybe only a lack of overall engine speed.

One of the reasons why I so like fuel injection over carbs is that there is really only one system and what you see at idle can be extrapolated to any rpm or load range. That is not the way of a carb. The carb has multiple systems that sometimes work alone and sometimes work together and most times are untestable.

The main metering system of each side of the carb does most of the business, depending on air velocity (engine spead/load combination). This system is basically a tube with a narrowing at a point a small distance higher than the float level in the bowl. As the air velocity speeds up to go through the narrowing a hole placed at that point has a partial vacuum created. This vacuum pulls the fuel from through the manin jet up through the emulsion tube where a proportioned volume of air is mixed before being emitted into the engine airstream.

At very low flow rates (idle and slightly above - throttle positions of zero to maybe five degrees of rotation) thsi system breaks down. With the throttle just slightly open, allowing enough air fro engine speeds around 800rpm there is no velocity at the venturi but there is lots of vacuum below the throttle plate. The idle circuit is a separate passage out of the main fuel jet circuit leading to a series of small holes above and below the almost closed throttle plate. The biggest one is below and has the tapered adjusting screw to vary the flow. The holes above add to idle and compensate the main system as the transition takes place from idle adding fuel with a dead main circuit to a main circuit handling metering while the idle circuit deminishes.

Go to go, so I'll stop and wait for questions.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician