Poor idle when hot (1 Viewer)

[primer7]

So at the meeting I told Mike that the truck idles poorly when it gets hot and that the carb has been rebuild recently and he mentioned the heat control valve on the exhaust manifold and perhaps it's stuck. So I thought I'd take a look see and yeah it's stuck, rusted, frozen, was a valve maybe oh 20 years ago, so good call Mike. However, the only way to effect repairs is to remove the Intake/Exhaust assembly and well those bolts are rusted/fused as well. I could cut the exhaust pipe and remove the whole thing?

 

[primer7]

Another pic, are their shops in town that get rework this stuff if I can get it off the engine?

 

[rusty_tlc]

If you remove the heat riser your truck will run like crap in cold weather. IMHO the best thing would be to get the OEM stuff working again.

 

[primer7]

Thinking maybe just get the Sawsall out and cut the exhaust pipe? No way to get at the Valve other wise.

 

[chicago]

Can you get the manifold off?
If Im getting this right, its just the manifold to the exhaust flange bolts that you are having issues with? Or is it ALL the bolts including the manifold bolts?
Least invasive measures would be my option since you have TIME. Can you get a wire wheel, or wire brush in there at all?
Keep soaking those nuts, try wire brushing some of the rust off from both the top and bottom and see if you cant get those studs out or the nuts off.
If it IS just the manifold to the exhaust, if you cut the bolts, youll still need to get the manifold off to replace the studs? Right?

Hope Im getting this right....

 

[chicago]

BTW...I have used a dremel with a cut off wheel (several actually) to cut into the nut enough that I could split it off carefully. It takes a while, but...can be done. In your case since you have that access, you could use the dremel/ cut off wheel method and make a diagonal cut on the nut being careful not to cut into the manifold (hence why I say to make the cut diagonally), once you are about/ through the nut you can tap the nut free with a chisel and hammer...

 

[primer7]

Yeah, the exhaust flange nuts are rusted and won't budge, I'll keep soaking them and see. I do have a dremel...good suggestion.

Thanks Keith

 

[WILLD420]

Do you have a good impact wrench?

A lot of time an impact wrench set on low, will hammer a rusted bolt out, where a wrench with a constant pull will just break the bolt/stud.

Soak them with PB-Blaster or some other "Penetrating" oil. WD-40 doesn't cut it when it comes to frozen stuff. I've also seen the "Freeze" spray, but never used it. Don't know if it will work or not.

An old trick that will sometimes work is getting the engine up to operating temp, then spraying cool liquid on the stud and removing the nut real fast. You have to be quick to take advantage of the hot nut and cold stud being different sizes for just a split second.

You can heat the nut with an acetylene torch as well, and spray something cold on the stud and get the same or better results.

 

[primer7]

VICTORY IS MINE! Behold the end of the beginning. Used the Dremel on one nut and...well...the PB worked on the other as the stud came out with the nut. So the whole system is still intact. The Heat Valve is stuck in the middle which would contribute to the poor idle at hot.

 

[primer7]

More Pic's

 

[chicago]

RIGHT ON!!!!!
That is SUCH a good feeling when you get that stuff out!
Crazy that no one besides Mike picked up on that valve problem....
Especially Mark who rebuilt it. Its usually the littlest things that get over looked.

how much is the part?

 

[primer7]

So I got the Manifold and air intake back from the sandblaster and started priming and painting. The heat riser will have to be manually operated from now on as the spring and counter weight did not survive, but you can see the flapper is still intact and functioning.

 

[primer7]

Some more pic's

 

[primer7]

and some more

 

[rusty_tlc]

Nice work, maybe we can find you some parts to finish the fix.

 

[WILLD420]

Seems a waste not to put a header on there while you've got it apart.

 

[primer7]

Header won't fit with a PTO winch...unfortunately

 

[chicago]

Where did you take it to get sandblasted?
how much did that run?

 

[locrwln1]

Congrats on getting it apart and getting it cleaned up. Just making sure the valve was stuck in the open position? Or was it stuck in some not quite open, not quite closed position? If it was stuck in the open position, I'm not sure why that would effect the running condition when hot.

I know from older carb'd chevy's when that valve and the whole cold start system wasn't functioning, they made for a very cold blooded/hard to start when cold running vehicle, but as long as it stuck open, it didn't affect the motor when hot.

Hope you get it figured out.

Jack

 

[rusty_tlc]

Seems a waste not to put a header on there while you've got it apart.

I don't recall the header making a drastic difference in performance. The only reason I installed it was the stock exhaust manifold was cracked and it was cheaper to replace it with the aftermarket header than factory. Given the issues removing the heat riser caused I kind of regret that move.

He might shave a couple of tenths off his 1/4 mile time though.