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Detroit Lubricator Carburetors


TexRiv_63

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I posted this on the AACA Technical forum but have not had much response. I was advised by a Packard owner to also post it here since Packard also used this type of carb. I have been chasing fuel system problems on my 32 Cadillac V-12 in order to get it running dependably. The fuel pump has been rebuilt and I have run it both with and without the electric fuel pump. It runs better with the electric pump but still not smoothly and continues to backfire when coasting. This weekend I removed the fuel pump to check the actuator pushrod which had been suggested as the problem by a number of people. There appears to be no problem there as the rod is the correct length and does not show excessive wear at either end. So, I am left with the dual Detroit Lubricator model 51 updraft carburetors, which I also removed. These carbs were rebuilt by the previous owner and both look excellent on the outside but I have no idea what was done to them inside. The previous owner said he just cleaned them out as they had sat unused for a long time when he bought the car, but he did not check or change any adjustments such as float height, etc. My problem is I know very little about these carbs and do not want to get into them without some education. Does anyone have any literature, repair instructions, exploded views, etc. that they could copy and send? Has anyone personally rebuilt these carbs and could give me some insight on how to proceed? At minimum I need to know how to check and set the float height and how to baseline set the mixture needles so both carbs are synchronized, plus whatever other adjustments might be needed to get these running right. Any help will be greatly appreciated.<!-- google_ad_section_end --><!-- google_ad_section_end -->

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Much depends on the location of the backfire. If through the exhaust, it could be caused by too much fuel pressure on the carburetors (the Detroits don't like much over a couple of pounds). It could also be caused by a myriad of other ailments. If through the carburetor(s) the cause is almost certainly something other than the carbs.

Good luck on finding out much about the Detroits. I have been looking for about 40 years!

Some information in Packard Service letters; some information in Packard, Cadillac, and Graham service manuals; some information in the Dykes encyclopedia; some information in National Service Manuals.

All of it combined insufficient to really understand whats going on.

Jon.

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Jon,

If you don't have information on these carbs after all that time then I'm probably out of luck. My backfire is definitely thru the mufflers and seems to be worse on the passenger side. I have an electric fuel pump on the car but do not know the output pressure. Strangely, when I left that pump on all the time the car ran much better. Still a little lumpy but both banks seemed to be pulling, much less backfire but still a little when coasting or downshifting. I drove it for a while that way but the drivers side carb started to drip out the overflow tube. As an experiment I bypassed the electric pump completely and it went back to running poorly and backfiring more but the driver's side carb still dripped. This is what led me to remove the mechanical pump and check the actuator pushrod but it looks fine. I have read a number of older posts knocking these carbs but since they appear to be in nice shape and are original I would really like to get them working if at all possible. Thanks for any advice you can offer.

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Not having any particular knowledge of the DL carb I would still suggest running a pressure regulator with a return line to the tank to scrub off excess pressure and a pressure gauge between the carb and regulator. The old carbs usually need only 2 to 4 PSI maximum and most electronic pumps put out between 10 and 15PSI which will force the float needle open and flood the bowls. Different carbs deal with this in different ways; some dump it on the ground via overflow tubes and others just vent out the top and make a mess and others dump it in the intake where it gets sucked in to your engine making it run extremely rich. Usually a rich running engine will backfire through the exhaust and a lean mixture can cause a backfire through the carb although this can also be bad timing. My guess is you're fuel pressure is too high for these carbs. I think I would try and fix the stock system first but if not possible then add a reg and gauge to your electronic set-up. At least then you will know what your fuel pressure is.

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Tfee, the last test I did before taking off the carbs was completely bypassing the electric pump to eliminate pressure issues, the car ran worse and backfired more.

Tom, thanks for the manual link, I printed out the pages on the carb.

JB, I also assumed this was an ignition problem, I have replaced the plugs, wires, condensers, and coils. The points were checked and are like new, and I set the timing per the shop manual. The only items not replaced are the cap and rotor but they appear to be in good shape.

I talked to Jon at the Carburetor shop and I will go thru my carbs to verify the castings are OK and check the float and mixture adjustments, Ill let you know how it comes out!

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