Joined: Jul 18, 2008 Posts: 639 Location: Melrose, MA and Santa Fe, NM
Posted: Tue May 31, 2016 7:02 pm Post subject: Heat Shield for Carb
OK, I know this isn't correct for our jeeps but I've been running into an issue mostly during hot weather but also during extended use or parade driving.
The issue is that a lot of the heat from the engine, exhaust manifold, and the heat riser is going into the carburetor. I visited my local "old car" mechanic who's more familiar with older engines and he used a temperature reader to see that the engine block and the carb were close to the same temperature.
I'm looking for ways to reduce the heat into the carb causing my modern gas to have vapor lock issues. It's possible that I need to use more spacers but what other suggestions/methods have been successful? I've got the fuel line running the changed path but is there a heat shield or something that I can use to help isolate my carb more from the heat coming off the exhaust manifold and engine? My mechanic's explanation also was that modern gas has a lower boiling point to work with modern engines. All the ethanol added in these days impacts how the carb and fuel system work on our jeeps, particularly in hot weather and extended hot weather use.
My jeep is functional more than period correct. i want to use it and run it more than have it in shows. I want to take it on trail rides and not have to worry about some of these things.
Suggestions?
Thanks!
-JJB _________________ North Shore, MA
Santa Fe, NM
1942 GPW
1952 M38
1964 Apollo 5000 GT
If everything is functioning correctly you should not need a heat shield.
It helps if you ID the model jeep & engine you have. I am sure you are not talking about your 64 Apollo!
You can add the model jeep you have in your signature right next to your Apollo!
I am going to assume you have an M38 with a L134 since you did mention "heat riser". This time of the year the heat riser should stay closed. If not then you should fix it.
The carb was suppose to be mounted on a very thick spacer type gasket which was designed to help the carb escape from the extra heat of the exhaust manifold and heat riser.
Also the M38 had a service bulletin issued to re-route the gas line between the carb bowl and the fuel pump to expose the tube to less heat.
Higher engine coolant temps than normal will add to your heat problem. If you run a 190 or 200 thermostat for winter heat then you should swap it out in the spring for a 160 or 180 unit. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Jul 18, 2008 Posts: 639 Location: Melrose, MA and Santa Fe, NM
Posted: Wed Jun 01, 2016 3:36 am Post subject:
Thanks Wes! Yup, my 1952 M38 with the original-type engine...
The Apollo is another story - working on getting the right seats built for it.
My jeep does not have have the re-routed fuel line so I'll need to do that - thought it did but as looked at the picture again... And it has a thick (to me, though) spacer but I have another one as well, without the pointed triangle part.
The heat riser may be part off the issue. I suspect I have the original spring there but I'm not sure how strong or stiff they're supposed to be. Maybe it's too old? Also, how do you make sure it stays closed? Is it the position of the spring on the lever?
I asked John Bizal as well if he knew of anything or had a suggestion and his was an additional spacer but knew of nothing else. I admit that my jeep is most likely not perfectly set up. It runs but is very sluggish accelerating, especially off a start and when it's hot outside or the engine is hot from running for a good while. The jeep also is sluggish going up hills or slight inclines or from a stop light. And when starting after running for a while it sometimes takes a long time to get restarted.
I don't have the space or time to pull things apart these days so looking for ways to narrow down the potentials so I can have my mechanic friend do some work on it to get the jeep running more reliably. I've lived with it all since I got the jeep but would like to fix as many of these "quirks" as possible.
Thanks! _________________ North Shore, MA
Santa Fe, NM
1942 GPW
1952 M38
1964 Apollo 5000 GT
De Opresso Liber
Last edited by whydahdvr on Wed Jun 01, 2016 6:13 am; edited 1 time in total
Joined: Aug 31, 2015 Posts: 29 Location: Asheboro, NC
Posted: Wed Jun 01, 2016 4:27 am Post subject:
A quick question. Has the motor been overhauled and, as of the latest rebuild, to what size were the cylinders bored? The reason I ask is that the larger the bore, the warmer the engine will run. Couple that with timing which may be a degree or two too far advanced and too lean a mixture at the carb and yes, heat is inevitable.
The heat riser’s lollipop indicator should be down (open valve) when cold and up when closed at operating temperature. There does exist a metal heat shield which mounts between the carb and gasket. _________________ Old fashioned service never goes out of style.
Joined: Jul 18, 2008 Posts: 639 Location: Melrose, MA and Santa Fe, NM
Posted: Wed Jun 01, 2016 6:11 am Post subject:
I've never rebored the cylinders, don't think it needs it. No data on the engine though - bought it from the owner's estate and any identifying numbers were either not stamped or ground off from the usual spot.
It could well be that the heat riser isn't functioning properly. I'll have to double check that. And the timing is off so that's being addressed. But the first step is new points, etc.
However, I would like to track down the heat shield you mention in case I need to try that pdf my other efforts are unsuccessful.
What about a rubber fuel line instead of the metal one, as I've got re-route it anyway?
Thanks. _________________ North Shore, MA
Santa Fe, NM
1942 GPW
1952 M38
1964 Apollo 5000 GT
Joined: Jul 18, 2008 Posts: 639 Location: Melrose, MA and Santa Fe, NM
Posted: Wed Jun 01, 2016 8:18 am Post subject:
I'm not as worried about originality as functionality and reliability today with today's modern gasoline vs leaded gasoline. I don't have access to anything else.
Looking at the heat riser spring, aside from how the flange sits on the stop and the direction the spring winds in, is there a difference? Are they the same spring type and metal "lollipop"? Is there a way to determine what I have?
Thanks. _________________ North Shore, MA
Santa Fe, NM
1942 GPW
1952 M38
1964 Apollo 5000 GT
Joined: Aug 31, 2015 Posts: 29 Location: Asheboro, NC
Posted: Wed Jun 01, 2016 8:47 am Post subject:
I agree that rubber is not a good permanent solution.
The lollipop for either heat riser valve setup will be UP when the motor is at operating temperature. So it doesn’t matter which you have as long as COLD = DOWN and WARM = UP. If the valve is stuck open or for that matter the butterfly is completely gone you will continue to have the problem you are experiencing now. For a long time there was a school of thought that stated that the heat riser wasn’t necessary for the efficient operation of the motor. A lot of owners simply wired it either closed or open, or removed the butterfly altogether when it became a problem. When sold, they never told the buyer. There is only one way to be sure and that is to separate the manifolds and look down in the heat chamber. _________________ Old fashioned service never goes out of style.
Joined: May 30, 2014 Posts: 3447 Location: Texas Hill Country
Posted: Wed Jun 01, 2016 11:46 am Post subject:
J,
I don't think the operating temperature is affected by ethanol
versus non-ethanol gas. That is controlled by your thermostat.
These guys have operated for 65 plus years in the original
configuration and if any gasoline change would have an effect
it would be the lower vapor pressure during the summer
which would have a positive effect on vapor lock. It's June
1 and all terminals should be converted to 9.0 or 7.8 Rvp
gas. You may depending on how long it's been in the tank,
have some higher Rvp winter gas in your tank. If it's been hot,
you could be having vapor pressure issues or vapor lock.
There might be some tweaking of the advance, as well as
fuel/air ratio on the carb, but if everything is installed and
functioning as should be it should run properly when warmed
up.
The real detriment modern fuels have on period engines
is the minimum amount of lead. These engines were originally
designed metallurgically to be "lubricated" on the valve train
with the lead in the gasoline. If anything you should consider
the additives available for the older engines, and/or modify the
valves and seats.
If you are having issues with it running poorly when hot,
as noted check your actual engine operating temperature
and change the thermostat if needed. In addition, as noted,
make sure the heat riser valve is installed and working properly,
and lastly move that fuel line per the TM.
Joined: Jul 18, 2008 Posts: 639 Location: Melrose, MA and Santa Fe, NM
Posted: Wed Jun 01, 2016 12:07 pm Post subject:
Engine temp was running around 150-180 - same with radiator. The carb was clocked at around 150 as well with the same remote reading device. And the engine is circulating coolant so that's doing its job.
However, there does seem to be a vacuum issue/leak. And I filled the jeep up last Fall but it was filled up again on Sunday so that would be the Summer fuel.
I'll start with the timing and a tune up and see what I get. _________________ North Shore, MA
Santa Fe, NM
1942 GPW
1952 M38
1964 Apollo 5000 GT
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