I'm talking about the pipe on the top of the valve cover on the duke.

I do know this thing is supposed to heat up the air intake when the vehicle is warm, but how exactly does it work? From what I remember when I had the cover off its just a pipe made of sheet steel whose end is close to the top of the head. I had the engine running and the air horn taken off and I passed my arm over the pipe end and I felt air coming out of it.

My assumption prior would be that in order to get puffs of air from it from it I would have to have blow-by.

I would rather make the assumption that I dont have blow-by and that the stove operates in a mysterious way. So how does it work?

thats the PCV valve, not a heat riser. A heat riser takes air from around the exhaust manifold on a carburated engine. do a search for PCV and all your questions will be answered.

Errm, not on that side. Looking at the engine towards the front of the car I'm talking about the pipe on the left side, as opposed to the right side where the PCV tube is.

The round thing on top of the valve cover is a breather, and has nothing to do with the heat riser. It's got a filter in there to allow fresh air into the crankcase (via the head) to replace gases extracted by the PCV valve that go into the intake tract to be re-burnt.

The heat riser (thermac system) consists of a heat stove on the exhaust pipe, a metal flex hose, and a flapper door on the air cleaner. There's some sorta switch in the air cleaner, that when it gets hot enough allows vacuum to travel to an actuator, which closes the flapper valve, allowing ambient air to travel unobstructed into the engine. When it's cold, the door opens up and the engine draws warm air from the heat stove around the exhaust until the switch warms up enough. Helps with fuel vaporization and driveability in cold weather, etc.

So its supposed to pull in air? Mine's pushing it out.... wtf?

quote Originally posted by AP2k: So its supposed to pull in air? Mine's pushing it out.... wtf?

Which one? Thermac/heat stove or PCV?

quote Originally posted by Blue Shift: Which one? Thermac/heat stove or PCV?

A picture so we all know what we are talking about regardless of what we call it:

That's the PCV system. If you're blowing air strongly out of the valve cover when running then you have blowby problems. The heat riser/thermac system starts with the flexible foil and wire tube that connects to the heat shield on the exhaust manifold and connects to the air cleaner housing snorkel.

JazzMan

The heat risers on the earlier 2.5s attached to the exhaust right after the manifold. Regardless, it appears to be absent from the 87/88 Duke pictured. I don't see the vacuum pot on the air cleaner housing. Perhaps the later 'Tech 4' Dukes from the 87/88s didn't have a heat riser system (probably not necessary with the newer computer they used)? Can anyone confirm this?

Chris

That is correct. The '87-88 Duke does not have the heat stove.

The picture above depicts the fresh air intake for the PCV system. That hose supplies fresh air from the air intake into the valve cover. If air is blowing out of the valve cover, then your engine may have some piston ring blow-by. Either that, or your PCV valve isn't working properly.

quote Originally posted by Blacktree: That is correct. The '87-88 Duke does not have the heat stove. The picture above depicts the fresh air intake for the PCV system. That hose supplies fresh air from the air intake into the valve cover. If air is blowing out of the valve cover, then your engine may have some piston ring blow-by. Either that, or your PCV valve isn't working properly.

How do I test the PCV valve? Blow through it?

The simplest test is to remove the PCV valve from the engine, hold it in your hand, and shake it. You should be able to hear the check ball rattling around inside. You shouldn't have to shake it very hard.

If it doesn't rattle, or you have to shake it really hard to make it rattle, it's probably gunked up. You could try cleaning it out with spray lube. But if the gunk build-up is really bad, you may be better off replacing it.

It seems that the PCV grommet is leaky where it goes into the valve cover. I pushed it down and now the fresh air intake sucks in air like it should. As an added bonus, it doesnt bog down off idle anymore.

Still need to do a compression test, though. Its supposed to be around 120 psi, right?