Engine fails out if very hot

Werner

Werner

Well-known member
I need some help, please.

I am a skilled mechanic with a thorough understanding of combustion engine, but I’ve reached the limit of my knowledge here.

My engine won't run properly when it gets very hot, it shut off. The mixture seems to be running lean; I have to open the GAV an extra 3 or 4 turns just to keep driving, and even then, it runs very roughly. Once the engine cools down a bit, it runs exactly as it should.

I’ve overhauled the ignition system, replacing the ignition coil, condenser, points, distributor cap, and ignition leads.
I’ve installed a new float needle valve, checked all the jets of dirty, verified the float level using a clear tube, and replaced all gaskets including the manifold gaskets.
The car runs well on flat terrain, but if I drive very fast or tackle a steep hill, it starts popping and loses all power.

Does anyone have any ideas?

Ich bedanke mich im Voraus!

 
If the temp at the carburetor gets hot enough to boil the fuel it will be partially bubbles that will not flow well through the jets and will also not contain enough liquid fuel to keep the air/fuel ratio correct. It will act and be lean.
 
Since you didn't post about this problem while driving in cool weather, the guys are on to a heat-related issue. Your gas cap may not be venting properly, which will interfere with the gravity-only fuel delivery from the gas tank to the carburetor. Try loosening or removing the gas cap before your next hot day drive. of course, if the tank is near full, you'd be better off just loosening the gas tank cap.
Marshall
 
Take the drain plug out of bottom of zenith carb and let it flow for a while to see if it slows down— if it slows take off gas cap to check for vent problem.

Check spark to see how far it will jump cold.
Go driving until problem happens.
Check how far spark jumps and its color.
I just hold the cap by the edge with the carbon button near a head nut.
Are you using one of the A&L burnout proof condensers?
when it slows down check fuel flow out carburetors drain and compare to your beginning baseline test.
 
Vapor Lock from high temps in Europe.


I had this happen to me when I lived in Colorado during the summer (100 degrees F).

Adding Marvel Mystery Oil, per directions on bottle, cured vapor lock for me.

Marc
 
There is an old school “solution” to vapor lock that is to wrap the fuel line and float bowl with aluminum foil. Supposedly it either helps insulate the fuel line, or it increases the heat dissipative surface area. I ran into vapor lock issues on a tour a few years ago and decided to give it a try. I cannot say that it helps, but I haven’t vapor locked since then. Pretty ugly, though.

Another “solution” I’ve heard is to clip a bunch of wooden clothespins to the fuel line. I have no idea how that’s supposed to work.
 
Preventing the intake manifold heat from the carburetor , can be helped with a micarta ( fenolic resin)spacer with a copper gasket on both sides . I made the micarta spacer from 3/16” sheet. I have laser checked both the intake manifold and carburetor after a run ,the intake manifold averaged 250 degrees, while the carburetor was 165 degrees. Your results may vary depending on altitude etc., could be worth trying . If you have difficulty finding micarta , send me a pm .
Don S
 
I put a clothespin on my fuel line, as is tradition. Does it actually help? Probably not, but I leave it there as a conversation piece. Any time an old timer sees it, they always comment about how it stops vapor lock.
 
My first question is WHY is your engine running so hot? Mine does not even on 100F days driving at a snail's ace behind a bike race.


IMHO I suggest finding out why it runs so hot before finding out how to make it run well while too hot.
 
I am still working on my Roadster to get it on the road.
It is hot here in Europe, but my test drive so far were good....
140 Fahrenheit on regular roads, 160 on hills...
Just had a discussion on heat related problems and my friend mentioned, that a guy here uses avgas (Aircraft fuel) due it is not boiling at all. Maybe you can get some at a small, local airport and do a test drive with it.
 
Hello und guten Tag at all.

Many thanks for all your advices. Let me quickly write through the details:
Fuel cap venting is fine; fuel enters the carburetor without bubbles (checked via a short transparent hose); flow rate is a stream roughly 1/4-inch with a full tank; the fuel line has been blown out with compressed air; I run a 1:1000 MMO mix; the condenser is the expensive one from Don Snyder (no spark failure, and the entire electrical system has been checked); coolant temperature reaches a maximum of 95°C/200°F.


The engine was rebuilt in May and has run without issues for 1,000 miles since then. The last job I performed was rebushing the carburetor shaft and a new 18° butterfly; I believe the problems started gradually after that. Perhaps.


The two manifolds are not rigidly connected to each other and the areas are flat; gaskets are new; torqued to 40 Nm/28 lb-ft.
A Gunson’s glass spark plug shows a light blue flame, but when the stuttering occurs, the flame colores gets white—indicating a lean mixture.
The bowl level checked with the clear U-tube shows the correct fuel level (5/8" / 16 mm) when the engine is off and at idle. However, the level drops down at medium RPM, every time, even when the engine is cold.


Since I’m at a loss, I’m considering ordering a rebuilt carburetor from US eBay. I’m skeptical, but perhaps there’s a hairline crack.


Regardless, indipendently of that, I’m going to follow Don S.’s advice and install a thick 1/4" gasket between the carburetor and the flange. That's allways a good hint; I do not dreive this car at winter time.
 
Is it electrical…………Or is it fuel……… Follow what Kurt from NJ in post #5 says ! ………..Simple and to the point …… then come back here for fixes !
 
Retorque the manifold to 63Nm, check the carburetor throttle shaft clearance, and replace the spark plugs. Opening the GAV 3 turns indicates poor input fuel flow. Do you have a standard distributor with manual advance/retard or a mechanical type like the B?
 
I have a couple clothes pins on my inside fuel line, not as a deterrent to vapor lock, it's just a convent place to keep them for emergencies, ie, we were on our way to a funeral and my friend's pickup kept bogging down. Opened the hood and looked around & saw the nut on the choke arm had fallen off allowing the choke to be drawn closed when the throttle was opened. With no time to look for a replacement I took one of my clothespins and stuck it on the butterfly shaft where the choke arm had fallen off. The counter weight of the clothse pin kept the choke open till he got home.
 
Werner said:
Regardless, indipendently of that, I’m going to follow Don S.’s advice and install a thick 1/4" gasket between the carburetor and the flange. That's allways a good hint; I do not dreive this car at winter time.
Click to expand...

I run a ¼" phenolic spacer between the carb and manifold. Also my "racing Scoop" to (hopefully) draw in cooler air away from the exhaust manifold.

588992
 

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Also I like to remind people that our gasoline today is formulated differently than it was in the not so distance past. Moderns have a pressurized gas tank so the gas is formulated with a higher vapor pressure. In our vented gas tanks and fuel system, this "new" gas evaporates (Boils) at a lower temperature.
 
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Have you checked the polarity of your coil?

I had a similar problem where it ran fine on flat roads, but up a hill or at full speed, it seemed to choke out. It turned out that I had installed the wires on the coil backwards. Once I switched them around, the problem was gone.

Viel Spaß,
Brad in Maryland
 
Lowering the coolant temperature might help , 200 degrees F is a little high for my liking. 50/50 mix of antifreeze will ran hotter than water + water wetter by 30-40 degrees F . 20/80 mix of antifreeze will run cooler than 50/50 , some makers of water wetter say add to antifreeze will also run cooler ( I’ve not experimented with that) 1000 miles on a rebuilt engine it may need more break in time ?!
 
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