Quote:
Originally Posted by Sharps40
Question time...looking for direct experience.
Problem: Modern high alcohol/low boiling point fuel and carb boil over about 20 minutes after shut down.
Yep, phenolic spacer and heatshield is the best solution for this modern fuel that works well under 35 PSI in EFI but not so much in carbs...but
Marvel Mystery Oil and/or ATF at 8 oz oil per 10 gallons of gasoline is touted as a cure for shut down boil over.
Internet myth or are ya doin it successfully?
If successful, MMO or ATF as your choice of Boiling Point Modifyer?
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Hi Sharps, I had a thread on here a short while ago re: boiling over on a stock 327 with 300 hp--while driving, on hot days--using the AFB 4bbl(perhaps identical to today's Edelbrock) from back in the '60's. Happened intermittently, and we tried all the known logicals first--finally cured it by placing a heat dissipator between carb and original 327/300 hp cast iron manifold.
One of our 1st attempts was to lower the floats as low as possible(to allow more unused bowl to contain the fuel-expansion) and still avoid stumble on acceleration: no avail. Another tho't was to raise floats as high as possible to supply greater volume of fuel which hopefully would be too much for the heat to boil so easily: to no avail. Tried adjusting timing as well as cooler thermostats to lower engine temperatures: still no avail.
When it happened, I'd raise hood, raise the removable rods(each held by 1 screw and a tab), replace them with NO other change, and go back running correctly. Finally determined the time taken doing this had more to do with cooling--than rods raising-and-falling improperly--so after this cooling-off period, it went back operating as sweet as could be asked.
So, it boiled down(not intended as a pun!)to dissipating the heat with a proper spacer. Hope your cure is as simple as this was--even tho' ours came after wasted expense of hours of experimenting and a few inexpensive parts. We finally used a dissipator, which we had to modify slightly with a dremel grinder, that my partner had lying on a shelf, w/out our knowing its composition(phenolic?) or source...but it worked!
Assuming you must be using some type of adapter(s) to mount your carb, you may even benefit from using, like 2 dissipators: one between manifold-and-adapter, and 2nd one between adapter-and-carb. Shouldn't cost but a few dollars to buy/build one or two heat dissipators to try. Hope it works as well for you.
Sam