View original topic: Intake Freezing???
70bugdriver Fri Feb 01, 2008 1:36 pm

Hey Guys,

Havin trouble with my74 Super Beetle 1600.
It idles ok, but when u give it gas or drive it it hesitates n sputters,and wants to stall. Also when your in neutral(sitting in ur driveway) and u go to floor real fast it will and does die out and stall. Today I noticed while it was running for a bit (before stalling out) the top part of the intake where it mounts to the carb was all frozen/freezer burnt... WHAT IS THAT?!I checked everything as far as plugs, points gap etc, vacuum lines...
I dont know what else to look for.
Any help would be great.

germanysfinest Fri Feb 01, 2008 2:58 pm

Sounds like a clogged heat riser.
The heat riser is supposed to preheat your intake manifold using the heat of exhaust gases. Without them, carb icing can occur wich would lead to your aforementioned symptoms.
The heat riser is the narrow pipe next to the larger induction pipes of your intake manifold.
Drive your car for a while and check if they are getting hot (careful, dont burn yourself). If not, there are several articles on how to clean them.

check out this procedure:

Navy8R Fri Feb 01, 2008 3:23 pm

I agree with gemanysfinest. The answer to "What is That" is that when a liquid evaporates it's temperature drops (it's physics). That is how a refrigerator or air conditioner works.

Since the purpose of the carburator is to mix the liquid gasoline with air and produce a combustable vapor and most of the gasoline is evaporating right at the bottom of the carburator, that spot will be very very cold - even when the temperature is mild. Once the engine runs for a while everthing heats up and you cannot tell. On stock VW air cooled engines the carburator sits a long way from the intake ports of the heads and it takes a long time for the heat from the heads to travel all the way to the carburator so VW added the heat riser. Without it some of the gas vapor will recondense in the intake manifold into liquid. When that happens the air fuel mixture as seen by the combustion chamber is not correct so the engine runs rough.

BTW with a dual carb setup you don't need a heat riser because the bottom of the carbs are only a few inches from the heads and the manifolds heat up real fast.

BugMan114 Fri Feb 01, 2008 6:07 pm

AHHH. I just went through this problem. DO NOT DRIVE THE CAR LIKE THIS!!!!!!!!!!!!!!!!!!!!!!!!!

The reason is that for some reason, the crank case will fill up with gas and you will sieze your motor!!! I'm not sure of the exact technical reason, but it will, IT HAPPENED TO ME!!! I had about 2 quarts of gas in my oil. I had the same symptoms, a sputtering noise on acceleration, when you floor it it dies, it has no power at all. Are you using a stock air filter, or an aftermarket one? Do you have a stock exhaust?? Are there any modifications (not stock parts) to the engine at all???

ALSO.. check your oil, and smell it for gas. To me it didn't really smell like gas, it just smelled bad, but it gave me a headache just smelling it. ANd the oil level had risen to almost the top of the dipstick.

bugninva Fri Feb 01, 2008 7:15 pm

aftermarket aircleaner?

fusername Fri Feb 01, 2008 7:45 pm

the reason your engine gets 'gas washed' and causes that damage is fairly simple. leeme see if i have it right.

the intake gets real reall cold from all that air rushing by, and from the gas trying to vaporize. so now when you squirt gas into this VERY cold pipe, it condenses back into liquid, and runs down the intake into the heads. this liquid gas will not burn in the cylinder, and instead seeps past the piston rings and into the crankcase, filling it with gas, and causeing tons and tons of extra wear as gas is a terrible lubricant. This also destroys the piston rings and cylinders as there is effectivly no lube there.
this can also happen to show cars that never reach operating temps, and are only run a couple minutes at time, or to cars run in very cold temps w/o a thermostat to allow them to warm up.

change your oil and you can keep running the motor while you diagnose the problem.

BugMan114 Fri Feb 01, 2008 8:13 pm

I ask about the aftermarket aircleaner because they don't have the opening in them for the heat riser pipe, like stock ones do. If he is running an aftermerket aircleaner, then he most likely doesn't have the heat riser. Just like me. When i put the air cleaner back on and the heat riser, it ran much better. Then i put a large piece of foam in the air intake part of the air cleaner, to clogg it up, so the motor will get all of the air from the heat riser.

Another poroblem is with the aftermerket headers. They have a heat riser flange on each of the two exhaust ports. This causes a back and fourth flow of exhaust gas to flow thru the heat riser on the intake manifold, which is in-effective, and doesn't help to heat the intake manifold. There supposed to be one flange on oe exhaust port, and another flange leading to where the pipes merge to one (i am talking about the headers used with stinger pipes). When one is routed there it allows the exhaust gas to flow in one direction, thus allowing the intake to heat up, thus the carb won't ice up. I am currently using a merged header normally used with a stinger (though i am not using the stinger, i just have the header, cause i like having the motor loud :lol: ). Anyway, on my motor, i can run the engine for hours, and then grab the heat riser on the intake, and it is just bearly warm. I had just rebuilt the motor and i completely cleaned them out, so they are no clogged. It is just the pulsating back and fourth flow of the exhaust, which is causing the heat risers to stay cold. A stock muffler does NOT have this problem. If fact if you take a look at a stock muffler, you can see how one of the heatrisers flanges are directly on the exhaust port, and the other heat riser flange is connected to a pipe and leads to the fat tin part of the muffler. Therfore, the exhaust gas will flow in only one direction.

Even though the heat risers are pretty much useless for me, the heat pipe on my intake seems to be working fine for now. I know its painful to take off that chrome pretty air cleaner and put back the ugly dull plastic one, but no one will see it anyway :wink: , unless you have a baja or something (or keep the decklid off, like me :lol: 8) )

bugninva Fri Feb 01, 2008 8:21 pm

BugMan114 wrote: I ask about the aftermarket aircleaner because they don't have the opening in them for the heat riser pipe, like stock ones do. )

that is why i asked that of the OP...wasn't questioning what you wrote..(if you recall i was in on your thread also...most icing problems are caused by lack of preheated air, but most folks immediately blame the heat risers)

BugMan114 Fri Feb 01, 2008 8:40 pm

oh, lol. Now i recall. I just love those technical answers. Makes life so much easier. 8)

I was just browsing around, as i was waiting for responses to my other topics, and this post just caught my attention. I don't want this guy to end up like me, or worse :cry: .

Quote: ...most icing problems are caused by lack of preheated air, but most folks immediately blame the heat risers)

I can see why. I can grab them after driving for a few hours and they are just kinda warm. I can see why people may think thats the problem. I haven't fixed that heat riser problem, but the heat pipe keeps the carb slightly warm even in 10 degree weather. I actually plugged up the cold air intake part, so the intake gets all of its air from the heat pipe. I had to do that besause i have a header, and the tin piece that the heat pipe attaches to (the metal tin that goes under the passenger side head) wouldn't fit as it was hitting the header, so i had to beat it in to shape, so it was flattened to about half its size, so i was afraid it was going to restrict the air flow, so i plugged it up. And it runs great now.

bugninva Fri Feb 01, 2008 8:54 pm

just remember in the spring to unplug that hole...if the intake air is too warm it's not good either...(used to have a "hotbox" i had to fab for a centermounted Dell...had to remember to remove it when weather warmed up...if i didn't detonation would remind me)

70bugdriver Fri Feb 01, 2008 11:08 pm

wow thanks guys!
yea i have an aftermarket air cleaner/filter.
my exhaust is an Original Kadron Glasspack exhaust system:header/glasspack.
This may be a problem too: The motor is out of an automatic. So it has the big tube coming out the side which has always been capped. COuld that be part of the problem?
I have a few intakes here so I may just put a new one on.

ClintCart Sat Feb 02, 2008 5:55 am

I had the same problem, I'm installing these when I take the Bug out of storage in the spring. :)

runamoc Sat Feb 02, 2008 7:17 am

I've had a hard time fitting those on engines with cool tin. Lot of snip and hammer time.

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