MG Midget Forum

So… a few years back I installed a Pertronix, and a sales rep said I didn’t need the distributor vac line (which I believe in my case is a “retard” not an “advance”). I now think the sales rep thought I had one of their distributors which does not have a vacuum line connection. Long story short, I’m trying to better tune my Midget and make use of the existing distributor vacuum retard.

I have the 45d distributor shown below. When, looking at my workshop manual, it shows the vac line running to a vacuum port on the carburetor. The problem is my CD 150 does not have any such vacuum port.

Any ideas on where this should be connected?

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Thomas (Count) Basey
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“With each replacement of parts, my British car slowly becomes Chinese.”



Edited 1 time(s). Last edit at 2024-04-11 07:08 PM by CountBasey.

Why do you want to use vacuum retard? It's only reason for existing is for emission control. It does not improve any part of your driving experience.

I guess I was asking for confirmation that it is, in fact, a retard and not an advance.

If it is a retard, I guess I’m fine as is. If it was an advance, I have heard it should be connected for better low end tuning.

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Thomas (Count) Basey
_______________________________________________________
“With each replacement of parts, my British car slowly becomes Chinese.”

The distributor in my '79 had a vacuum retard unit that was disconnected when I bought the car. It was still disconnected when I sold the car.

WHOA. WHOA, I am NoT seeing a RETQARD UNfTm but an ADVANCE unit. If the -hose Nipple in on the FRONT of the can, it is ADBVANCE,it it comes in from the back side, a RETARD unit First check to see if it is good, if it pulls the advance plate "Clockwise", it is an advance unit. .

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021

Joseph,

Thanks for looking - that's what I thought as well... but other links said the other way around. I'll hook up a hose and test it out.

Now, assuming it is an advance unit and it works, I'm back to my original question. My 1500 Workshop Manual does NOT show where this should be connected. Some other on-line references show a vacuum port on the CD150 carb that I do not have.

Does anyone have a manual choke (non-water choke) CD150 carb with the vacuum advance line attached? I'd be curious to know where?

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Thomas (Count) Basey
_______________________________________________________
“With each replacement of parts, my British car slowly becomes Chinese.”

I am having a hard time determining what distributor that is. Is it points or electronic. Is it advance r retard.Furst determine what yu have, and go from there. Agood closeup picture of the crv, near the mounting flange would help. IF there was a option for on carb advance, it would be on the top edge f the flange, like an 175CD MGB carb/

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021

So... I think I found a very definitive answer about vacuum advance and retard units.

These units are very simple - basically a diaphragm and a lever arm that connects inside the distributor. If you think about vacuum being applied at the nipple - which way will the lever inside move? In my case the lever pulls towards the front of the unit, and since my unit is on the right side of the distributor, that means the lever is pulling OPPOSITE to the direction of the distributor rotation (which is counter-clockwise on a 1500). That means my unit is ADVANCING the spark (if I'm understanding correctly).

So I think I've solved that riddle. I'm back to finding a vacuum source. My distributor is a 45d mechanical distributor - but I have a pertronix unit in there (basically making it electronic). My CD150 only has one (1) vacuum port that I can find - and that's for the manifold PCV line. I'm trying to find some documentation on my particular CD150 - but it does appear different from the ones I'm seeing on-line. Most of them have 1 or even 2 other smaller vacuum ports. Maybe this one isn't original.

The car is running fine - I'm just tinkering trying to get the most out of it. Sometimes it might just be better to leave working things alone!

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Thomas (Count) Basey
_______________________________________________________
“With each replacement of parts, my British car slowly becomes Chinese.”

For those of you, who, like a mystery, here are some photos of my carb.

Photo 1: the front of the carburetor facing the radiator. only one vacuum line, which is connected to the PCV port on my valve cover. some photos I found online show one or two other vacuum lines on this side – but not on mine.

Photo 2: the top of the carburetor. As you can see, there is no vacuum port where it connects to the intake manifold. Some photos online often show a small nipple on the top – again, not on mine.

Photo 3: the rear of the carburetor facing the firewall. Only two lines here on the right hand side, the top is the vent, and the bottom is the fuel line.

Anyone else have this same CD150?

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Thomas (Count) Basey
_______________________________________________________
“With each replacement of parts, my British car slowly becomes Chinese.”



Edited 1 time(s). Last edit at 2024-04-12 10:52 AM by CountBasey.

XXXXX Stand by. SIRI HERE. You are 100% correct in the way your vacuum unit works whether retired or advanced you have an advanced unit and I suspected it is a 45D distributor since it’s basically the same unit I run on my race car and I might MGBGT without a repeat without vacuum. For vacuum advance to work properly there are only two options ported vacuum which gives the distributor a vacuum post only when the swaddle plates are opened, or secondly manifold vacuum and that requires a special calibrated vacuum unit for the distributor. I do not know if there is such a can available for that particular distributor. The two areas that you are showing pictures of your carburetor none of those ports are suitable for vacuum advance you’re showing the DSL valve area which operates only when you get off to swallow not on the throttle so if we get those areas completely they will not work your carburetor body if you want vacuum advance is the wrong carburetor maybe one of the distributor rebuilders would have a vacuum unit suitable for your purpose. I it is possible to drill and tap the back edge of the carburetor for vacuum advance and I personally have done this on TR six 175 CD carbs that do not have the vacuum takeoff. Triumph TR six use a similar distributor in 72 I believe to 74 it looks similar to a 25D distributor but had to vacuum units attached to it one advance one retard and the person was modifying a TR six you had to change distributor since there was no way to add vacuum advance then the carburetor itself had to be drilled and tapped for a vacuum port it can be done. Possibly somebody in your area would be willing to undertake this operation it has to be pretty spot on good luck

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021



Edited 1 time(s). Last edit at 2024-04-12 10:57 AM by oleanderjoe.

THOMAS: FINAL OFFER. "Send me your carb body and I will drill and install a vacuum port on the top of the rear flange like a 175 Zenith" NO CHARGEWorst case scenario, we will have to JB weld up the hole. You pay the postage BOTH DIRECTIONS.
If this is something yu want to do/ Prepare the carb like this. 1. Remove fuel bowl and Float.
2. Remove upper chamber, piston and diaphragm. Place in a ZIP LOCK freezer bag. with some "Clothes Dryer Sheets" to kill the gas smell. and send me a PM message for my address. Worth a shot. In the mean time, I have another 150 carb bdy out in the shop and I will check to see if it is feasible today. I will let you know.

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021

stand by: XXXXXXX. HERE. I have two digit 1500 carburetors 150 CD with vacuum port on back up edge of carburetor they are available or have been available for certain models. Yours did not come from the factory with one because it had a vacuum retard some California models 1500 with the opus distributor did not even have a vacuum advance unit on the car. The opus ignition box Port where the advent attached to was plugged no vacuum advance distributor plate was bent hope this helps you with the whole carburetor I can see the whole carburetor want to take a shot at me drilling a hole in your offer still stands for the weekend Monday I may not be interested. Have a great weekend bye for now

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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021



Edited 1 time(s). Last edit at 2024-04-12 05:07 PM by oleanderjoe.

Thanks for the offer Joe, but I’ll pass. Plenty of other CD150s out there for cheap if I ever want to try one with the vac port. The odd thing is my 76 is an east coast high compression model (flat pistons, no cat) - so not a California emissions version when new. I think my carb may have been replaced at some point.

I consider the issue closed. Thanks everyone who confirm my hunches.

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Thomas (Count) Basey
_______________________________________________________
“With each replacement of parts, my British car slowly becomes Chinese.”

10-4 Leave well enough alone. Cheers.
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IN ALL SUBJECTS.: For those who believe, no proof is needed. For those who don’t believe, no proof is possible.

"Strive for perfection in everything. Take the best that exists and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough"
Sir Henry Royce
co-founder of Rolls-Royce .

"I take no credit for my own, of another man's fame".
Joe Baba 2021