Carburetor Boils Fuel and Hard Restart

[calvinhunt]

When I park my jeep when hot and try to restart ten minutes later, it is hard to start. �

I've been watching this thread with great interest.  Was there not a thread on the old forum discussing this exact same problem?  I ask that question because I'm not really sure.  Some of you will remember that on the old forum I discussed the problems I was having with my carb overhaul.  It wasn't till after my overhaul that I started experiencing the problem exactly as Doug has it described above.  That's when it came to mind that someone else had sought help with a similar problem earlier.  Seems like a possible solution was that the metering rod was not dropping completely into the main jet far enough to stop the fuel from draining from the bowl into the hot intake manifold and boiling away.  But then, it takes a really good seal to stop fuel from flowing so I don't know how the metering rod could ever do that?  Nevertheless, after I went back into my carb, reinstalled the old metering rod and a few other parts, that problem as well as others went away.  Did I just get it right this time, did it really take the old metering rod, etc., to fix my poor running carb, or was I just luckier to get the settings right this time? I really don't know.  

I've been watching to see if some of the same answers emerged that I thought I saw on the other forum.  If someone knows of the location of that thread on the other forum please reveal it.  Thanks.

[Carls_jeep]

I guess it's possible for the metering rod to do that. One thing I noticed when reading the text about adjusting the metering rod I noticed some contradiction in the adjustment of it. They tell you to back out the idle screw on the throttle plate stop and adjust the metering rod linkage with the tool. Then they tell you to set the idle. Then they say that when the throttle is closed with the idle screw holding the plate open so it will idle the metering rod should be seated in the jet in the bottom of the carb.

Well, I'm here to tell you that is a contradictory statement. If you set the metering rod seated in the jet with the throttle plate completely closed and then open the throttle plate so the engine will idle the metering rod will NOT be seated.

One text goes into detail about how to test the metering rod seating after using the tool and describes how to set it without the tool. I don't have the tool and I have plenty of time to do the bench testing and I understand how it should work.

With that in mind I am going to devise my own way to set the metering rod and when I get everything worked out I will describe what I found and did.

I am also in the process of making my oversize throttle plate shaft. I have the body reamed out now and have the shaft fitted and a few cuts made. I am taking photo's and will do a thread on the subject.

[rocketeer]

This one:

http://cj3apage.proboards.com/index.cgi?action=display&board=Tech&thread=1583&page=1

or this one:

http://cj3apage.proboards.com/index.cgi?action=display&board=Tech&thread=1592&page=1

and this one:

http://cj3apage.proboards.com/index.cgi?action=display&board=Tech&thread=1500&page=1

Larry

[Carls_jeep]

Thanks for the links, I read them.

[calvinhunt]

Thanks Larry, for digging the links out.
  
Like Carl, I read each one of them again.  It was fun to relive much of my troubled past with my carb.  I thought there was a thread some time before I had any carb grief.  And because I was having no grief it didn't mean much to me so I paid it little attention.  It was probably something else.  

So now it comes down to this:
Doug, have you received anything here that has helped you with the original question you asked about?  I think there is an answer out there for your problem.  I believe it is more common than realized.   Since most carbs don't have that problem and others do, what is the difference?  Wish we knew.

[Doug]

I have not torn into the carb to figure it out. Been busy with holiday stuff.  However, it runs good except for this minor issue so I am hesitant to go finding a problem.     I believe it is one of three things, either the fat fuel line and large metal fuel filter hold more fuel which expands more than stock when heated and that overwhelms the float, bad float adjustment, or bad metering rod adjustment.   I started to read all that metering rod stuff when I was in a hurry and my eyes just glazed over.   I am going to have to read it sometime when I have the time to really study it.   Really have no idea what you are trying to measure when you set the metering rod length.

[rocketeer]

There is one more, somewhat obscure thing to consider and that is that some brands of ethanol boil easier than other brands. I have had good luck with Shell and Exxon/Mobil but have had problems, some serious, �with Sunoco. Ethanol is a PITA and can, and does, cause goofy problems. You might want to consider a change in gas before tearing into the carb. It's an easy test. Just a thought.

Larry

[calvinhunt]

To support what Larry wrote about different qualities of gasoline:

The very best quality gasoline for internal combustion piston engines is 100 octane aviation fuel.  It is manufactured to strict FAA standards regarding vapor pressure, additives, burn rate, etc.  I wold suggest that anyone experiencing any such problems as discussed above run a few gallons of aviation fuel (av gas) through the engine (empty out the last of the car gas first).  You'll be amazed at how well the engine will perform and it may prove that your carburetor problem is really a problem with poor quality gasoline.  Many race car drivers use av gas for better performance.  Av gas is a bit more expensive at about $4.50 per gallon at most airports.  

Just today I put my seasonal Jeep away for the winter.  Before doing that, since it is going to sit for up to five months, I always drain the last of the automobile gas from the tank and then put in two or three gallons of 100 octane aviation fuel.  It remains fresh for well over a year.  It never gums up or leaves varnish residue in the fuel system.  It is readily available at any airport that serves general aviation (small planes).  You can either drive your Jeep to the pumps / fuel truck or you could pick it up in a regular gas can.  

[jamesr]

Calvin, Would running av fuel full time burn valves, or do any other damage?  Jim

[calvinhunt]

Jim,

You've asked an interesting question. �When I was 25 years old (1969) I used to run a small aviation business. �I could buy 80 octane aviation fuel for about the same price as I could buy premium gasoline at the station. �I owned a large block Chevy at the time. The av gas actually performed better in that car than premium (in those days it was called Ethyl). �I ran it for years. �It was pure octane (hydrocarbon C8-H18) and had no lead in it. �Aviation fuel was also available with a 100 octane rating. �It had lead added to increase the octane rating, much like former auto fuel (lead was added to hexane [C6-H14] or heptane [C7-H16] in order to get it to perform like octane). Of course, now other additives have replaced the lead in auto fuel since it has become unleaded.  They also stopped making 80 octane aviation fuel and at the same time reduced the lead in the 100 octane fuel and called it 100LL. �The LL meant low lead so it could be used without harm in the earlier lower horsepower engines that had been built for the fuel without lead but also provided the higher octane rating required by the newer, larger engines. �The only aviation gasoline available now is the 100LL. � That's what I put in my Jeep yesterday to "winterize" it because it now has to sit for so long. �I drove it around some with that fuel in it yesterday before parking it and it actually seemed to perform better (but told myself that it was probably just my mind playing tricks on me). �All that said, I do not believe that the 100LL av gas would harm our little four cylinder engines at all. �The foregoing is the extent of my reasoning. �I welcome comments from others because I certainly am not familiar with all the aspects of the L head 134 engines.
NOTE: If you were to run av gas in a modern car it would quickly burn out the catalytic converter because of the lead in it.

[macrisel]

To followup on on that, when I was taking flight training in college, one of the A&P instructors had a replica Shelby Cobra with a 427 cid in it.  Talking with him one day, he admitted he would run 100LL (av gas) through it occasionally to help burn deposits off of the valves left by today's "clean" gasolines.  He did let me know rather quickly not to run this in newer engines because it would toast converters rather quickly.  At the time, I had an '84 Chevy truck with a slightly modified 350 cid and a roommate that worked at the airport.  Being young and adventurous, we put a few gallons of the 100LL in my truck and ran it through.  While it didn't turn it into a drag car, it did provide a slight increase in performance.