Vapor Lock
Posted: Sat Aug 26, 2023 5:09 pm
I had an interesting case of Vapor Lock on my Carb'd 712 that initially surprised me.
Turned out to be a classic case of heat soak. Some context, I have a Hardi 24V
electric fuel pump, located external to the engine about center line of the tank,
well within the siphoning limit of this diaphragm pump.
So....motoring up in the Sierra's at about 7,000' and a warm day. Stopped on a steep
grade to spot a couple of trucks through an obstacle. Thereafter went back to my
712 and she just would not start, absolutely no hit of any ignition. Removed the
dog house cover to do a visual, nothing obvious. Checked the fuel pump and it was
no warmer than the gas in the tank. After scratching my head for 15 minuets or so,
went back to the truck and turned the IGN switch on, heard the Hardi pump make
it's chug chug noise -- Oh! OK, the pump works...So I hit the starter and she started
like there was never anything wrong -- WTF?? Well, that was just enough time to
drop the temp in the intake manifolds and stop gas from over vaporizing. I must
have had an extremely lean condition.
Made me think about the two major types of intake manifolds (Pants). One set
are bare aluminum, as was in my case, the other is insulated. Talked to Jim L. the
insulated version was done for the Hot Climate version of the Pinz, That's interesting.
It all makes sense to me now, I believe this was a mode to prevent heat soak. Since
the intakes are directly in the cooling air stream, as long as the engine is running I
don't think insulated or not matters -but- when you turn the motor off, then insulated
would make a huge difference as the intakes will get very hot sitting directly over the
heads and cylinders.
Ordered the pre-cut insulation from SAV, they can be installed by removing the top
tins, Carbs, and the side tin. Pix below of before and after, I used Stainless Steel ties
but ran short. I'll gussy up that one Pant leg next time I'm in there. I won't know how
much this staves off the issue until next time I'm up in elevation and it's hot.
Turned out to be a classic case of heat soak. Some context, I have a Hardi 24V
electric fuel pump, located external to the engine about center line of the tank,
well within the siphoning limit of this diaphragm pump.
So....motoring up in the Sierra's at about 7,000' and a warm day. Stopped on a steep
grade to spot a couple of trucks through an obstacle. Thereafter went back to my
712 and she just would not start, absolutely no hit of any ignition. Removed the
dog house cover to do a visual, nothing obvious. Checked the fuel pump and it was
no warmer than the gas in the tank. After scratching my head for 15 minuets or so,
went back to the truck and turned the IGN switch on, heard the Hardi pump make
it's chug chug noise -- Oh! OK, the pump works...So I hit the starter and she started
like there was never anything wrong -- WTF?? Well, that was just enough time to
drop the temp in the intake manifolds and stop gas from over vaporizing. I must
have had an extremely lean condition.
Made me think about the two major types of intake manifolds (Pants). One set
are bare aluminum, as was in my case, the other is insulated. Talked to Jim L. the
insulated version was done for the Hot Climate version of the Pinz, That's interesting.
It all makes sense to me now, I believe this was a mode to prevent heat soak. Since
the intakes are directly in the cooling air stream, as long as the engine is running I
don't think insulated or not matters -but- when you turn the motor off, then insulated
would make a huge difference as the intakes will get very hot sitting directly over the
heads and cylinders.
Ordered the pre-cut insulation from SAV, they can be installed by removing the top
tins, Carbs, and the side tin. Pix below of before and after, I used Stainless Steel ties
but ran short. I'll gussy up that one Pant leg next time I'm in there. I won't know how
much this staves off the issue until next time I'm up in elevation and it's hot.