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Fuel Percolation
Just can't stay away
Joined:
2012/5/20 22:28
From Parker, CO
Posts: 52
I know this is a common topic but one that continues to frustrate me. I continue to have problems starting my 46 deluxe clipper after it is hot due to what I believe is fuel percolation due to the new gasoline. I already have a rear mounted electric fuel pump, I have read all the forums on how to start a warm car by not pressing down the gas pedal for 3 or 4 seconds and then slowly depressing a third of the way. I have tried adding lead additive to my tank and a cup of diesel to lower the boiling point, but the problem still persists and I frequently still need to let the car sit for 15-30 minutes before she will start. Although I understand these idiosyncrasies in my classic Packard, my wife and other passengers don't seem to appreciate it as much. Is there any permanent fix to this problem, new carburetor rebuild kit that works with the new gasoline, etc. that anyone has seen.

Posted on: 2017/8/2 10:31
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Re: Fuel Percolation
Forum Ambassador
Joined:
2007/3/14 16:01
From New Jersey
Posts: 16207
You didn't mention anything about your history with the automatic choke and anti-percolator valve adjustments.

Attach file:



jpg  WDO anti percolator valve adjust.jpg (87.84 KB)
177_598211b12217d.jpg 1500X764 px

Posted on: 2017/8/2 10:54
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Re: Fuel Percolation
Forum Ambassador
Joined:
2007/4/20 17:54
From Fresno CA
Posts: 15975
Definitely check the anti perc valves but if they are OK and you still have only the accelerator start I wonder if an aux push button would help.

Each time the accelerator is pressed gas squirts into the engine. If the modern gas is actually percolating and being forced into the manifold via the carb jets due to a hot engine, the engine already has plenty so extra from the starting push on the accelerator just makes it worse.

To help in such cases, several have installed an extra starter pushbutton hidden under the dash edge. I know my Dad had them installed in all his Packards back in the day so in case the engine flooded (which for some reason he always had problems with) he could work the starter without touching the gas pedal.

It is simple to do. Just get a starter pushbutton and run two wires out to the carb switch to place the PB in parallel with the existing switch. That way they are both still in the circuit and either can be used. The hole in the firewall where the temp gauge, speedo and OD cables exit is a convenient pass thru spot. If you get some of the old style fabric asphalt wire loom to cover the wires and run that thru the hole, dropping down behind the horns to follow the existing loom to the carb switch, it is an almost undetectable mod. Switches, loom and proper looking fabric covered wire can all be found on ebay.

Posted on: 2017/8/2 11:31
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Howard
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Re: Fuel Percolation
Just can't stay away
Joined:
2012/5/20 22:28
From Parker, CO
Posts: 52
Forum ambassador, I think you are setting me on the right track. I don't have 100% confidence in the guy that last rebuilt my carburetor and I have been so focused on all the discussion around the issues with new gas that I wasn't seeing the forest through the trees. I expect there are plenty of these Carter 2BBL carburetors out there dealing with new fuel if they are tuned and rebuilt correctly. I am going to do some visual inspection and maybe get some professional help as my next step.

Posted on: 2017/8/3 6:23
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Re: Fuel Percolation
Forum Ambassador
Joined:
2007/3/14 16:01
From New Jersey
Posts: 16207
I expect there are plenty of these Carter 2BBL carburetors out there dealing with new fuel if they are tuned and rebuilt correctly.

Correct, percolation is not to be expected with a properly functioning carburetor.

Tell us more about the electric fuel pump; are you using it as the primary fuel pump, or just to occasionally "prime" the system. If the former, what pressure is it delivering? Are you aware that many electric pumps produce more pressure than the max for the OEM mechanical pump and can overwhelm the carburetor needle & seat?

Posted on: 2017/8/3 7:11
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Re: Fuel Percolation
Just can't stay away
Joined:
2012/5/20 22:28
From Parker, CO
Posts: 52
I am only using the electric fuel pump to prime the engine. I recently replaced the mechanical fuel pump with a rebuilt one and I actually rarely need to use the electric fuel pump at this point.

Posted on: 2017/8/3 8:02
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Re: Fuel Percolation
Home away from home
Joined:
2013/7/17 6:26
From Clover, SC
Posts: 657
An aside: Just so happens, there's an article on this in the Packard newsletter that came today. It looks scholarly but I haven't reviewed it technically. I didn't like one of the explanation graphs, so I need to delve for my own.
If it's a push gas pedal to start carb, I'd bypass that silly contraption, either the HH button method or a simply jumper wire. If they worked so well, that'd still be around.
But were relegated to the trash heap of history.

Posted on: 2017/8/4 17:54
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Re: Fuel Percolation
Home away from home
Joined:
2013/7/17 6:26
From Clover, SC
Posts: 657
I keep forgetting, if you bypass the pedal switch, you need a momentary or standard ignition key switch with the start position.

I'm reviewing the ethanol study/situation (again), and there's widely reported a non-ideal distillation curve with addition of ethanol. This does NOT occur with MTBE, which was the oxygenate of choice pre-Clinton era ethanol. But the D86 test cited is done at atmospheric pressure and the fuel system is under some pressure, ~6 psig during pumping, raising BP. I don't have access to my Eng. computational tools anymore to predict. We're talking 120-150F range which is reasonable on an engine under convective heat transfer, ie sitting idling. I suspect a wide variation in fuels as each market is serviced differently via RFG regs and climate needs.
More interesting; the old, circa 1919-1935, gasoline curves show a much higher percentage of "high boilers"(HB) ie % >200C in the old gasoline than today's. No surprise knowing refinery practice history, but that also stands as evidence for the higher carbon deposits in the old days plus effects from low compression. (valve job anyone?) The percent particulate is known to increase with HBs(according to the EPA et al). Once I get in a position, I'll try to publish those curves for comparison.

Posted on: 2017/8/5 18:14
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