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  #1  
Old 06-11-2008, 09:01 PM
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Join Date: Dec 2005
Location: Carson City, NV
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The Vast Zenith Rebuild Saga

After some other attempts to get my '71 250/8 running right, (see link)

Is a carb rebuild in my future?

and a nastygram from the Nevada DMV about its large clouds of smoke (when it even ran), I decided to rebuild the carbs. I got the rebuild kits yesterday and picked up a bucket of carb cleaner today. I still don't have a balancing tool, but I'll cross that bridge when I come to it.

Step 1 for today was removing the carbs. In accordance with what I read here and elsewhere, I removed the valve cover first and this did make it much easier to get the carbs off. In removing the carbs, I found that the wires to the idle solenoids don't look so good. This will be something else to evaluate when it comes time to put the carbs back on. I decided to call it quits a little early today, so tune in tomorrow for Step 2.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #2  
Old 06-12-2008, 11:04 PM
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Location: Carson City, NV
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Part 2

Today I took apart the rear carb and began soaking various parts in the can of carb cleaner I got at Kragen. I had had the cover and jet block off several times already, so removing the screws and the accelerator pump cover were nothing new. It was then that I realized the instructions in the manual were a little vague. My notes to self on dissasembly went like this:

Primary air correction jet 90
Secondary air correction nozzle 140
Primary mixing tube 4N
Secondary mixing tube 4S
Primary main jet X115
Secondary main jet X125
Accelerator pump inlet valve small
Pump pressure valve bigger

The cover, jet block, and removed jets and nozzles along with the accelerator pump cover got full immersion soaks in carb cleaner. With the float housing, I left the actuating lever and the bracket for the closure damper on and used those to let the housing soak partially immersed. I did this to keep the choke control out of the nasty stuff. I did remove the secondary throttle vacuum diaphram and cover beforehand. I did something similar with the throttle valve housing.

In other news, the float valve, which had been sticking, looks brand new. I'll be replacing it anyway.
__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #3  
Old 06-13-2008, 12:13 AM
Blue 72 250's Avatar
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Posts: 277
It sounds like you are on your way to having a clean set of parts to work with. Enjoy cleaning off the "nasty stuff" and don't forget eye protection. BTW when you are done with the carb cleaner you will need to find a household toxic waste collection site for disposal.

Now that you are clean, you will want to do some inspection of the mechanical elements of the carbs. You can see how flat the mating surfaces are with a simple test. I would recommend using some 220 grit water proof sanding paper and a piece of glass to wet grind a flat surface on the carb top plate. Just a little sanding will tell you how flat the piece is. Because of stuck heat risers the carbs could be a little warped.

Diagram http://i151.photobucket.com/albums/s131/Blue72W114/CarbINAT32.jpg

Also consider looking at the linkage stud and bushings (part # 157 - the second one from left) to determine the amount of wear that has occoured. Since they are brass and see a lot of use (with every action of the throttle) they often have significant amount of slop in them. Slop is bad because it causes an imbalance of the carbs over the throttle range. Such an imbalance can be annoying and cause excessive fuel consumption.

Anyway, if worn studs are the case, you essentially have 2 options due to the fact that the part is difficult (if not impossible) to locate. (1) locate a good hardware store to supply you with a similar brass bolt - finding a metric bolt the right length with a smooth shank will be hard, however. The other option that I have considered would be: (2) find a buddy with a hobby metal lathe and turn down the studs that you currently have. Or, in the alternative, try using a drill motor to mount and spin the stud. Sand with emory cloth. Once you have a smooth and straight stud again look for a bushing that will compensate for the smaller diamiter shaft.

I must disclose that neither of the two options has been attempted by me. I did spend a significant amount of time thinking of the solution and was about to impliment it before I found a "new old stock" replacement kit on ebay over 1 year ago. I chose to replace the front linkage as it sees the most wear.

Finally, if you are stuck I can send you two studs that I have that are in decent condition. I would put them at a "7 out of 10" for condition.

good luck and keep us posted.
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  #4  
Old 06-13-2008, 01:05 AM
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Join Date: Jan 2007
Location: Santa Barbara, CA
Posts: 179
Pin gauge that main fuel jet!

At a minimum, you should pin gauge measure that main fuel jet. The numerical sizes are all in hundreths of a mm, so the 115 main jet is 1.15/25.4=0.0453 inch. If you cant find the metric pin gauges, you can see about getting a metric drill from a tool supply. That main fuel jet is going to have the most wear.

I'm curious about the smoke. Is this black smoke, grey smoke or white smoke? Does it happen under load, idle or what?

If it's black smoke happening under hard acceleration, then there's another possibility on the carbs which would be that the float chamber vent valve may have fallen out. It's mounted upside down by press-fit and those things have a way of falling out sometimes in advanced age.

This is on the front carb only, and should be seen as a little spring loaded pin pointing down that the long arm on the bellcrank on the side that sits roughly horizontal at idle pushes up on at idle. If the little pin with the spring isn't there, then the vent valve isn't there.
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  #5  
Old 06-13-2008, 01:30 AM
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Location: Carson City, NV
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Blue 72-I noticed the linkage seemed to have an unusual amount of play in it.

Daidnik-I will see if I have anything appropriate to measure the jet size. How far out is too far? The smoke was gray to white, didn't always happen, but when it did it was a little after sitting at idle (actually idling when it would do that or otherwise stopped in gear with me giving it a little gas) followed by a great deal more upon resuming forward motion. After a couple seconds of hard throttle the smoke would stop. I was looking for the float chamber vent valve earlier today and couldn't find it, but your description of the location is better than the book. Second thought-you said it's on the front carb only. I'm still working on the rear one.

It's bed time. I'll see about dinking about with the rear carb a little more tomorrow before my Friday appointment at the local watering hole.
__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #6  
Old 06-13-2008, 08:51 AM
todds's Avatar
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Location: Boston, MA
Posts: 511
One thing I noticed while rebuilding these carbs is that it seems almost like there is a place for a secondary accelerator pump designed into the carbs. What a weird thing. Were there REALLY heh, "double pumper" INATs?
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  #7  
Old 06-13-2008, 09:49 AM
Brian Ostosh
 
Join Date: Mar 2007
Location: San Diego
Posts: 504
When designing and build a precision die-cast die, it is cheaper (smarter) to add the blank for future use once, rather than create a new die.
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  #8  
Old 06-13-2008, 08:38 PM
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Join Date: Dec 2005
Location: Carson City, NV
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I checked NAPA today for pin gauges and synchronizer tools. No luck on either. I did get a surprisingly good price on a valve cover gasket, but it won't be here until Wednesday. The guy at NAPA suggested I try the local motorcycle/quad shop for the pin gauges. I may do that tomorrow. My plans for this evening consist of a long meeting with Mr. Miller, and probably his associate from across the pond Mr. Jameson.
__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #9  
Old 06-14-2008, 09:49 PM
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Location: Carson City, NV
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Part III

I put the rear carb back together today. I must be doing something wrong with the float level measurement, since I got over 30mm with the thinnest spacer/washer on the float valve. I tried the cycle shop for pin gauges today, no luck. Where do you get those things? I also managed to lose a screw for the choke control housing.

I also took the front carb apart and have some parts soaking in the carb cleaner now. I looked for the float chamber vent valve and didn't find anything that looked like it. Does anyone have a pic? I think the adjustment on the fuel return valve was way off, and this may have contributed to the running problems. I'll put that right when I put the carbs back on. I'm planning on finishing soaking the parts, washing them (in the kitchen sink-it's great not being married) and letting them dry on paper towels overnight before reassembly. I did the same with the back carb.

Edit: I just saw the part about using a metric drill as a substitute for a pin gauge-slaps forehead.
__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #10  
Old 06-15-2008, 05:52 PM
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Location: Carson City, NV
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Part IV Houston We Have a Problem

I put the carbs back together and put them back on the car. I started with the idle mixture screws two turns out and the throttle closed but just about to open like I read on here. Unfortunately, it won't start. It doesn't even cough. I went ahead and hooked the throttle linkages back up so I could try giving it some gas while it was cranking, but that didn't work either. I took the cover off the front carb and verified that the float bowl was full. With ether, the car will run for a couple seconds, so I think it's getting spark. Also, in those few seconds I found out that it's not good to run that engine with the valve cover off

What to check?
__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #11  
Old 06-16-2008, 10:51 AM
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Location: Nova Scotia, Canada.
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The chokes on hard should be pulling enough gas out of the main venturi to run on. . Do you have the floats set right? Or you might have really bad vaccum leaks. Hard to check for that without engine running. Accelorator pumps spraying well? Pump the pedal ten times. It should start on that. At least for a short time.
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  #12  
Old 06-16-2008, 11:08 AM
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Posts: 758
If you had the cam cover off, you probably also had the vacuum line to the brake booster off. Massive leak potential, so check it. Also, when the cover is on and the brake vacuum line is on, you still need to connect the air cleaner vent hose to the PCV inlet down between the carbs, or you will have a massive leak there, too.

230/8
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  #13  
Old 06-23-2008, 10:48 PM
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Location: Carson City, NV
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The Rest of the Story

Vacuum line to the brake booster was connected. Oil vapor passage into intake manifold was plugged. At that point, my patience was exhausted and the deadline from the DMV was starting to get to me. I had it towed to a shop.

It turns out, the person who rebuilt the carbs before I did put them back together way wrong, and I took them apart and put them back together the way I found them. Then a tech who knows carburetors got ahold of it and now it runs almost right. While it was there, I had them change the spark plugs (I could have done it, but was too lazy), and do a compression test. The compression test (dry) came back 160-165 on all cylinders, and my Cheech and Chong smoke clouds are gone. It still has some issues at light part-throttle, but it's driveable.

I added 30 bucks worth of premium (still cheaper than diesel), and plan on taking it to work and then to Reno tomorrow before I call the PD to come look at it and verify its non-smokiness. After that, it's mostly cosmetic work and then the For Sale sign goes on.
__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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  #14  
Old 06-24-2008, 10:00 PM
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Join Date: Nov 2004
Location: Nova Scotia, Canada.
Posts: 6,510
It is things like that that really catch us. A friend of mine got a honda nine or ten horse four stroke outboard motor at a yard sale that would not run. Someone had put the carb on backwards. The linkages all hooked up well but operated strange. It seems to be the stupid stuff that complicates things occasionally.
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  #15  
Old 06-25-2008, 08:34 PM
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Join Date: Dec 2005
Location: Carson City, NV
Posts: 3,848
I drove the car to Reno and back yesterday. I had put a hair under 7 gallons in it the day before, drove it to work, and then to Reno, and then had to stop for gas on the way back. It's tough to get exact numbers without a working odometer, but I think I'm getting about 11 mpg. This is a big hit from the 21-25 on B20 that I'm used to, but I can get gas for free.

I got the good people of the Nevada Highway Patrol to look at it today and verify the lack of excessive smoke. Now that I have that out of the way, the transmission is starting to annoy me, but that's a topic for another thread.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
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