Vacuum diagram will tell you. If you can't find a diagram look for a thermal vacuum switch (the little trees with vacuum ports sticking out of them) and see if any vacuum lines head away from the intake towards the side/back of the engine.
I would hit it with a SeaFoam treatment to remove carbon from pistons and intake valves. Should run alot better after. May have to put new plugs in afterwards. Might want to drop down one heat range to reduce pinging as well (AC 45 to 44 for example)........
They typically operated with a thermostatic spring, like a choke thermostat. They looked like this, https://www.summitracing.com/parts/oer-3887023 I don't see one in the 1969 Chassis manual, at least not on the Skylark/GS.
I'll have to concur, I didn't see one on the driver's side, but it was looking from the top down. I'll confirm by looking under the car. Also, was that carb # from the airhorn helpful? Edit: looking through the FSM, there is a mention of the manifold control valve on page 60-43 in Engine Mechanical. According to the book it would be located on the (right) passenger exhaust manifold. It is the bimetallic type, I'll have a closer look under the car when I have a chance to.
I remember when I worked in my godfather’s service station tying them open with wire (not electrical) when they would get stuck.
Wire open for sure....if working properly it will be open once motor warms but but they were notorious for sticking closed or partially closed. There was even a special GM lube with graphite to keep them working but most people probably never did anything.
I would imagine leaving the valve open there's not a detrimental effect on performance, maybe idling a bit rough when cold?
I believe I have found the manifold heat control valve on the passenger exhaust manifold. I wasn't able to rotate it all, likely due to rust. Could the valve plate be rattling on the shaft or are they fixed on the shaft? I'll have to get the car on stands to take a better look
If it’s stuck in the closed position that could be your problem, too much heat in the intake manifold from the exhaust crossover.
Unfortunately the weather hasn't been cooperating so I haven't been able to get under the car to get a closer look, hopefully this week it clears up
Weather might be clear up here in Washington but snow is forecasted in the next couple days, might just bundle up and tough it out... or not. Hopefully it's not too cold but we'll see.
Hey, I have been under my car here in Seattle! Cold but no rain (or not much, lol). I actually removed that bit (the flap on the drivers side exhaust manifold), as it did make noise. It definitely could cause overheat too. Hopefully that's your answer...
It was a clear day today so I got the car on stands to take a better look at the heat valve. I tried freeing it up with some friendly taps from a hammer but no luck. I sprayed some penetrant on it to soak overnight so tomorrow I'll try my luck taking it off, fingers crossed for no broken fasteners. Once I get the size I'll have to see if Hector has any heat riser deletes available. Oh well, never bored with an old car
Well after our brief snow storm I was able to get the heat riser off the car. However it ended up seizing in the open position so I think I can safely rule that out as a factor, but with it back on I'll verify if there's a difference. I think next I'll retard the timing to 0* to see if the noise persists. If it rattles at 0* then I think something must be loose and rattling. More work to do
I think 5 degrees before top dead center was the factory recommendation? I would do that and not go to zero...
For a 1969 350 4 barrel auto the factory initial timing setting is 0*/TDC, according to the FSM. When I first bought the car and was unaware of the non-factory distributor I had it set to 0* initial and didn't notice any problems. It is wise to err on the side of caution though.
If Im reading this thread right.. somewhere you said Pacific raceways..... Your in SKC Correct? Where are you getting 93 ? All I know of in this state 87 89 92. you can get 100 at a place in Auburn or the track itself that above 100 ..... If someone is selling you 93 somethings wrong... Hopeful just a typo..... Now that lead substitute additive... You dont need that stuff. In Fact it does more harm than good.... And it will mess with your tuning big time.... Meantime there is corn free gas in SKC https://www.pure-gas.org/index.jsp?stateprov=WA
Also The gas sold here in Washington state is piss water... Try this fill your tank head east.. Fill up again do the math for your MPG. and again and again.. you'll notice your MPGs go up.. as you keep going east...If or when it goes down in MPGs IDK never I never crossed the Mississippi in that car.... Also if you do do this use a Cant really be noticed in a old carbed buick or ford 390.... But you will notice it in a EFI car
