1947 Lincoln v12 carburetor jets

[billboos]

I am confused by multiple opinions about carburetor setup. One opinion is to use jets based on original specs. Another says larger diameter jets are required because of today's gas. My 1947 Continental; bought last year had the carb rebuilt before I bought it -- the shop said they had to drill out the jets to a larger diameter to get more gas to the engine. The car was still missing when hot and a well recognized expert on Lincolns rebuilt the carb again and installed original spec jets saying it is best to keep everything original. The car is still missing when hot so there may be some other issue. I am replacing the fuel pump flex hose from the gas line to fuel pump next week just because it looks old and brittle. My question is "what jets are best -- original or larger and if so how much larger." Anyone have any experience with carb setup. I am ready to replace everything fuel and ignition related just to get a reliable driver . Thanks

[carbking]

IF YOU CAN PURCHASE NON-ETHANOL-CONTAMINATED FUEL: then the original specification should at least be tried; and it is never a bad idea to at least try the original specs, even with the contaminated fuel, and then tune from there.

 

Having said that, if you must burn the ethanol-contaminated fuel; there is a very good probability that larger jets will help due to the reduced energy content of the ethanol. If you are having problems, then we suggest an 0.002 inch increase on the idle jets, and an 0.001 increase on the main metering jets.

 

In your case, since the carb has been rebuilt twice, once to original and once oversize, and you had problems both times; I would suggest that the carb is probably not the issue.

 

Before doing any additional work to the carb, how about a compression test, and if that is good, then a complete ignition test?

 

Jon.

 

 

[billboos]

8 hours ago, carbking said:

IF YOU CAN PURCHASE NON-ETHANOL-CONTAMINATED FUEL: then the original specification should at least be tried; and it is never a bad idea to at least try the original specs, even with the contaminated fuel, and then tune from there.

 

Having said that, if you must burn the ethanol-contaminated fuel; there is a very good probability that larger jets will help due to the reduced energy content of the ethanol. If you are having problems, then we suggest an 0.002 inch increase on the idle jets, and an 0.001 increase on the main metering jets.

 

In your case, since the carb has been rebuilt twice, once to original and once oversize, and you had problems both times; I would suggest that the carb is probably not the issue.

 

Before doing any additional work to the carb, how about a compression test, and if that is good, then a complete ignition test?

 

Jon.

 

 

Jon, thanks for the reply. I don't know where I would get ethanol free gas in California. The first time the carb was rebuilt with oversized jets it had other issues -- like parts of it were from an early Ford truck so a vintage Lincoln expert I found rebuilt an OEM carb with spec jets. Do you think spec jets with ethanol would cause missing only after heating up and under load at 40 to 50 mph. Runs great cold and idles smoothly. Should I mess with the idle jets since it is idling perfectly.  

I will install a new flex hose from the gas line to the fuel pump when I get it this week but that may not be the problem. It is old and stiff and I have read that they can swell up or collapse when hot -- anyway a cheap part for a preventative measure.

It's hard to find anyone who knows old cars --- most of the owners work on their own cars. I did locate a shop that specializes in old cars. I will have them flush and inspect the gas tank as there is some sediment in the fuel pump glass bowl. I'll also have them check out the ignition system.

[carbking]

For the most part, carburetors do not have "personalities".

 

I read your other thread about the issue beginning after 15~20 minutes. Just a suggestion, keep everything in the same thread; you tend to get better answers. If it runs smoothly for 15~20 minutes, the issue is PROBABLY ignition, with an indefinate maybe of fuel; but probably NOT carburetor. And if the car idles well, then leave the idle jets alone. As stated in my first post; build it stock then tune from there.

 

I would still do the compression test. From the information in your other thread, the compression is PROBABLY good; but if it isn't, nothing you do to either the ignition or the fuel system will correct for poor compression. Troubleshooting is nothing more than eliminating variables, without guessing. I am betting on the coil being defective, but don't change it without doing some testing.

 

Jon.

[billboos]

carbking, thanks for the advice. Others on this site, Matt Harwood and 19tom40 also suspect the coil. If the new flex hose and Heet in the tank to absorb water do not make a difference, I 'll send the coil to Skip Haney for a rebuild just to rule that out.At least I'll have assurance of a good coil for only $150

Sorry for the new post in addition to a duplicate post on original thread. I was trying to attract someone with specific carb knowledge 

[38ShortopConv.]

Original L/Z carbs. ran around # 52 main jet size.  Most carb problems are quite often ignition.

[billboos]

On 7/10/2016 at 7:47 PM, billboos said:

carbking, thanks for the advice. Others on this site, Matt Harwood and 19tom40 also suspect the coil. If the new flex hose and Heet in the tank to absorb water do not make a difference, I 'll send the coil to Skip Haney for a rebuild just to rule that out.At least I'll have assurance of a good coil for only $150

Sorry for the new post in addition to a duplicate post on original thread. I was trying to attract someone with specific carb knowledge 

This is an update to my posts re '47 Lincoln Continental v12 missing when at normal operating temperature and at higher speeds (40 MPH):

I replaced the dried out rubber flex hose from the fuel pump to fuel line and have taken the car for 3 test rides. Starts immediately (about 2 seconds) , idles smoothly and runs strong and without missing. Took it up to about 55 MPH and it was perfect except for high engine rev -- switched to overdrive and it purred along at 65. Can't say for sure it was the flex hose --- could it be that the plugs were fouled and burned off after driving a while --- what that cause a miss only when hot or at higher speeds?

 

Keeping my fingers crossed that problem may be solved. Driving at 65 MPH did bring up another question some members may have an opinion on.On the highway with some grooved pavement, the bias tires seem to "hunt" moving the front end laterally a bit and requiring a firm hand on the wheel. Those who show their cars may have a "bias" against radials as they are not original or authentic but does anyone have experience or opinions on switching to radial tires -- I understand they make them with wide whitewalls. Thanks to all for advice so far -- it really helped me..