IML: Carb Problem analysis

[staffel@xxxxxxxxxxx]

Well, how timely- talking about Carb overhauls!  I recently included the following paragraphs in my post about our Mid-Atlantic Imperial Adventure: 
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The mighty 413 ran smooth  (no pinging with brisk  acceleration) but needs  a bottle & 1/2 of Octane Boost with full tank, but this allows the  timing to be set  close to factory specs (-2^ retard). There is a still a slight hesitation in the Carter AFB, (from stop) which may be just a slight  float adjustment (Mixture screws reset per specs and 
idle is smooth at 565 rpm. The book says 500, but 500 in N put the idle in D at 
475- just a bit too slow-with some vibration to the interior. 560 in N gives me 
525rpm in D- no vibrations.

My friend Bob also has a Jensen Interceptor with the 440 drivetrain. A few years ago, He bought an Edelbrock 600 cfm carb for it, but later, like I did, he put an Edelbrock 795 cfm on the 440. He gave me the 600 cfm carb to try on the Imperial. 
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I was checking the Specs in another Imperial Tuine Up spec sheet, and it said that idle should NOT be below 500 in D--interesting- just what I said to myself.
SO that confirmed my idle mixture adjustments and then 'idle stop screw settingts' were correct 'the moment'-- I am looking elsewhere for the source of the 'hesitation' (Other than the mixture adjustments).
THis carb was 'recently' rebuiolt by a specialist sub-contracted by the Previous owner. So it 'should' be clean inside. The fact that I put 1989 miles on it soince May- confirm it's 'functional'. But it's not 'PURRFECT'... 

I have rebuilt many many carbs over the years. I agree 1,00% with Kenyon about the rebuild kits-getting then most comprehensive kit IF the 'opening' and thorough  cleaning 'of the obvious' doesn't  solve the problem.  However, sometimes the problems are not worn parts but -as in the IML archives from 1948 on carbs: vacuum leaks,  weak(dry or brittle or not as flexible) accelerator pump leather,  dirt in orifices, or the winter/summer adjustments.

Since writing the above, the temps have dropped drastically here in MD. I had to return the Imperial to the garage before the 1st snow (we had 8" BTW), and so I ad to move about 5 others to sequence the Imperial up the driveway & under the lift, putting its 'later Cousin'-the Jensen Interceptor 440 on the lift 1st.

The CARB point here is that it was about 33^ the morning  I started the Imperial. It started quick and oil pressure came right up.  Throttle action response was instant. The hesitation was never at idle, only under load from a stop.  Now, I don't like to just 'start, move and shut down' big pushrod hydraulic tappet engines; so I took the Imperial for my standard 8 mile 'loop' run. This brings everything up to normal operating temp, a 5 mile stretch at 65, etc.  There was NO HESITATION That morning.

The only difference since the 670 mile trip- was the Outside air temp. The choke obviously was working- more so than two weeks ago.  I reinspoected my carb settings- the idle mixtures are -per the book- on the lean side of peak adjustment. Refreshing my familarities with the usual 'culprits': vacuum leak, base gasket leak, accelerator pump, float adj-- I am thinking maybe I'll wait a bit before swapping carbs--with salt on the roads right now- No Imperial of mine will be cruising for awhile anyway.

So clealy this cold AM morning verified that the 'problem' is mixture related. Now more dense air usually means a weaker mixture, not a richer mixture, but of course the choke adjusts' for the air temp- making a richer mixture.  ANother brain challenge- isn't that why we love these cars- keeps our intellectual faculties 'sharpened'???  

Sherman D. Taffel
Columbia MD  (28^, 19^ this AM)
63 Crown   (safe in the garage)


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