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Black & sooty rear end


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Hi all,

 

After the IWE, driving home in my 6. All was well and very good for an hr or so. Then slowly the engine started to miss a little, and started to puff a bit of black smoke on re-accelerations out of RAB's etc. This steadily became worse and then I slowly lost all ability to idle with a lot more black puffs out of the exhaust. I stopped, checked everything visible. Injectors all throbbing like they should, choke cable return OK, no valve or horrible noises, vacuum pipe all OK. So limped home, put her away and left her. Although before closing the garage door, the back end looks like it's been up the chimney. Woh...

 

Anyone with a possible diagnosis ? I'm thinking metering unit and diaphragm, fuel return pipe ?? Or perhaps something more sinister ? Valve/s ?

 

Appreciate any thoughts before I dive in.

 

Thank you

best Bill

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I would start with the vacuum to the metering unit ensure no leaks then suck / tongue test of diaphragm.

 

Possibly just a quick look at the plugs for re-assurance that all cylinders are the same'ish.

 

If symptoms were not there on the way to the IWE then I would immediately suspect choke cable not fully home.

I assume by choke return you had checked the metering unit end & pushed the choke / metering unit lever forwards firmly, not just looked at knob? It only needs a very small opening of the choke to enrich the mixture substantially.

 

Alan

Edited by barkerwilliams
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Agree with Alan..

Once drove a little way along the autoroute with the choke partially out.. the guys behind got choked by the black smoke screen I produced.

A bust diaphragm would do the same.

Cheers

tim

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Make sure the excess fuel lever ( choke) on the metering unit is free . I had one stick open slightly and caused similar issues . Just ensure that it snaps closed when the choke is released , if sticky , plenty of manipulation with a finger and some wd40 to clear the crud may help .

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Check the diaphragm first...the tongue test. Then I would check the little short hose on the MU cavity spill line back to the tank is not blocked located under the left hand rear wheel arch.

 

Dave

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If it's a fuelling problem with those symptoms your fuel consumption would have been through the roof.

 

Make sure the enrichment lever returns right back towards the firewall.

 

Check your idle vacuum with a vacuum gauge. My engine operates with an idle vacuum of 10" Hg , but many engines are set up to operate with a lot more. As the inlet vacuum is the key parameter operating the PI system I keep a careful watch on mine, connecting a gauge to the brake booster line whenever I suspect a problem with the PI.

 

Whenever I've had a split or leaking MU fuel diaphragm fuel has visibly dripped from a bleed hole on the assembly .

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Hi all,

 

After the IWE, driving home in my 6. All was well and very good for an hr or so. Then slowly the engine started to miss a little, and started to puff a bit of black smoke on re-accelerations out of RAB's etc. This steadily became worse and then I slowly lost all ability to idle with a lot more black puffs out of the exhaust. I stopped, checked everything visible. Injectors all throbbing like they should, choke cable return OK, no valve or horrible noises, vacuum pipe all OK. So limped home, put her away and left her. Although before closing the garage door, the back end looks like it's been up the chimney. Woh...

 

Anyone with a possible diagnosis ? I'm thinking metering unit and diaphragm, fuel return pipe ?? Or perhaps something more sinister ? Valve/s ?

 

Appreciate any thoughts before I dive in.

 

Thank you

best Bill

Hi Bill,

A dying M/U can give these symptoms when the shuttle is worn badly but as said by others the choke operation and vacuum needs to be checked very carefully and remember current petrol is very aggressive on the rubber parts in a M/U. How old is yours? My M/U died in similar circumstances early this year. KMI told me that it was completely knackered. What a difference in fuel consumption with the replacement!

 

Bruce.

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The enrichment lever can be fully home but the mixture mechanism can still be on. Put your finger down between the block and MU and feel for the little screw that the lever acts on. Push it as hard as you can, if it isn't fully home it will snap back. As noted above, if it does this use lots of WD40 and move it back and forward until it moves freely.

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Hi all

 

Thank you for all your suggestions.

 

To my surprise I've found a refurbed metering unit in my garage. I'd forgotten I had it !! I've had a quick look at the one on the car. The bottom choke lever looks and feels a bit stiff, but seems to be operating OK. So I'll check the return pipework, and will take off the old for a closer look and re-fit with the new one anyway. Just got to get going and change it etc. Maybe tomorrow. I'll report back when done. Then I'll clean my rear end..

 

Best Bill

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Update and life get's confusing and just tad frustrating. I've taken the old MU out and fitted a refurbished one. However in the process of taking the old one out. I couldn't remove the assembly with the pedestal attached. The pedestal was stuck solid. Well after 20 years it's not surprising. So had to take the MU off separately. A pain to get at the bottom bolt. Anyway I managed to get the pedestal off but in doing so the drive dog came out with the pedestal. Dam it.... Anyway after 4 attempts of putting it back, re-assembling everything and firing the car up, I can't seem to get it right. The best I've achieved is to get the car running but It runs rough and the I get odd pops from the exhaust. I've checked the timing each time and it's out by about 20 +/- deg on the timing marks. My actions have been.

 

1) 1st set TDC - Both inlet/exh valves closed on No.1 with TDC aligned on the timing pointer.

2) This is the vague bit. I've re-Inserted the drive dog through the worm drive until it engages the bottom slot and then inserted the distributor with the rotor arm and get it to point to around 7'oclock (no.1 plug lobe) It's not an accurate way to determine the correct position. I think I have guessed wrongly by no more that 1 tooth each time.

3) Then of course you have to line up No. 6 port (as per brown book) and re-fit. The best I have achieved is Example A and middle position shown within the Brown book diagram. Which apparently is acceptable. Although I'm now having doubts..

 

All looks good each time I've done it, and Iv'e confidently re-assembled and started her up. Only to find the rough running and popping, However, at least the black smoke seems to have stopped.

 

Is there any easier way to ensure I get the drive dog in it's correct position ? Or is it just trial and error ?

 

Best Bill

Edited by Bill Bourne
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Quite possible that you must needs bleeding. The generally don't run smoothly immediately after fitting.

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But how do you know the MU is good?

If has been that long since it saw the light of day...…...

 

Alan

Hi Alan,

The old one has been taken off and the refurbished one, was done about 4 months ago, so should be fine.

Best Bill

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What

Quite possible that you must needs bleeding. The generally don't run smoothly immediately after fitting.

Hi Tim

I’ve checked the fuel lines and all good. The injectors are all spraying well.

I’m sure it’s a combination of the drive dog position and the subsequent Dist drive position and then the MU hole line up on no. 6.

It’s maddening. The key point of getting it right is the drive dog position and the dist position. I can get it to point to roughly no. 1 plug lobe, but I always, so far anyway, seem to be 1 tooth out each way. You don’t know that of course until you re-fit everything and start her up.

There must be a surer way , but I’m stumped as to what that is.

Best Bill

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If you have set the timing marks correctly and the rotor points to the plug lead which is number 1 and the other leads are correct in order the position of number 1 which is normally 7 o-clock should not matter. I have seen cars with number 1 in positions other than 7pm.

When I tried to set my pedestal drive up getting it out to try another position it would not budge so it stayed where it was. Good luck.

 

Rob

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Sounds like you have it one ‘tooth’ out. So:

Remove the mu again.

Turn the crankshaft until tdc.

Note the rotor arm will now point to cylinder 1

Pull out the drive again turn it a few degrees and slide it back in ...note it will rotate as you slide it in due to the skew of the gears.

It may take a few attempts. The slot needs to be vertical.

Turn the MU drive until the slot is horizontal. The cut out portion should be at the bottom. Blob of grease on the plastic dog to hold it in position and refit the MU

Stick one nut on it to secure.

Double check the outlets/ injectors are actually going to the correct cylinders

Fire it up and check for leaks

Then install the other two nuts. Torque is one and a bit white knuckles about 100 in lbs for a 1/4 nut!

 

If you do end up removing the pedestal get a few gaskets before hand as they will invariably get damaged. Mic up the thickness of what you have and fit gaskets to the same thickness to maintain the running clearances.

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Hi all

 

Done. Dave you are spot on. That’s what I did. The trouble I had was the dist drive would sit on half a tooth and not wanting to be fierce I always ended up 1 tooth out. However last night with some wiggling it finally all came together. The MU hole at no.6 also took a few attempts. I aimed at the hole being completely open, which is as per the Lucas book, not the brown book. It’s a frustrating job, given that you have to take everything apart, then re-assemble, start her up, then find it’s not right and have to start all over again. I’ve done that 5 times!. Yep, in anticipation I had a pack of gaskets and seals to hand and renewed each time. Oh the joys. But she’s now running well and no black soot coming out of the exhaust. Just got to clean her rear end, take the rear lights off etc, as it’s a mess. But I’m happy again. Thank you

Best Bill

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Well I was happy, but took her out for a test drive, all was brilliant unti about 2 miles down the road and she suddenly died on me. Had to get some help to tow me back home, thank you Paul. Anyway after checking if there was fuel at the injectors. There wasnt any, it looks like the MU has gone wrong,or seized and the plastic lug has probably broken. Dont know yet until I take it out again. What a b,,,,,,,,,!

Couldnt do it today, so will do it tomorrow.

Edited by Bill Bourne
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As thought, the lug has broken and the MU seized. Fuel in the MU, so wasn't fuel starved. Don't know why it's seized as can't see any damage or muck inside. I guess this will have go back to Neil to find out why and then start the whole process all over again..

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