Exhaust Heat Riser Question

[chitown40]

Could a heat riser in a stock exhaust manifold that is stuck in the closed or cold position affect running performance. I think mine might might be toast and stuck closed and I can feel the 60 bog down down under load while accelerating. I can also hear a restriction in the exhaust near the manifold. Can this all be related? The carb is a fresh rebuild, all vac lines replaced, manifold/manifold gaskets were recently machined and replaced, recent valve/head job, and all vac components tested out ok per FSM. No obvious exhaust leaks, but I can hear some low end rumble coming from near the base of the carb. As far as I know the catalytic converter is functioning fine as well. 19mm/hg idling at 650rpm. Idle is smooth. No hesitation or stumble during grandpa acceleration, under increased throttle it feels restricted and top speed on the highway dropped off about 5-10mph and you really have to mash on the accelerator to keep 65-70mph.

All the info I found doing a search on heat risers explained that a stuck one can toast an intake, but nothing about performance.

All help and even wise-ass comments are appreciated.

 

[Tinker]

This problem is legendary: I heard about it years before I bought my first 60. Finding out for sure is a PITA, but then you have opportunities for improvements over stock: exhaust headers, fixing possible (eventual) intake manifold leak, etc.

My 83 had both the rusted/broken/restricting exhaust riser baffle problem and the intake leak. Used the opportunity to change to a MAF 6-2-1 ceramic coated (& thermal wrapped) header & coolant heat riser, and SOR thick Kevlar gasket to fix both problems. Made a big difference.

Then the head warped/cracked & I got real crazy. Now the parts are for sale.

 

[FJ40Jim]

When the heat riser sticks in the cold position, it increase the restriction in the exhaust a little bit, but it also cooks the hell out of the intake & carb.

You can check the heat riser by attempting to move the shaft by hand, or putting a paint mark on it cold, then watching for movement when hot.

Your symptoms could be restrited exhaust, which might also be a restricted catalyst.

 

[Landpimp]

I cured all my leaks.....I bought a new set of intake and exhaust manifolds for $500.....best money I have spent on the 40.

if you start pricing out all the little bits of the heatriser, gaskets, bushings ect......its not much more for the new complete manifolds.

turns out the heatriser gasket in mine as leaking also.....

 

[chitown40]

When the heat riser sticks in the cold position, it increase the restriction in the exhaust a little bit, but it also cooks the hell out of the intake & carb.

You can check the heat riser by attempting to move the shaft by hand, or putting a paint mark on it cold, then watching for movement when hot.

Your symptoms could be restrited exhaust, which might also be a restricted catalyst.

Tinker - Live in IL so no-smog is not an option, but thanks for the suggestion.

FJ40Jim - I was laying in bed this morning thinking how I would be able to check to see if the coil was moving, and I said to myself, just put some paint on it and watch for it to move. I have a spare set so I was checking how it operates and I've sure I could at least open it up if it's restricted and block it open. That gives me all summer to decide what to do. If any of you remember, I just had the manifolds and head off and rebuilt the carb and it actually runs great with no leaks and good vacuum. This heat riser debacle just sorta popped up a few days ago.

And Pimp, this thing's already a money pit, so I'm not going to buy a new set just yet. But, if it all ever comes off again for some other fix, I'll go new OEM.

I'm also going to check the cat, but the restriction sounds like it's coming from just below the carb.

Thanks all.

RB

 

[Civil1]

I cured all my leaks.....I bought a new set of intake and exhaust manifolds for $500.....best money I have spent on the 40.

if you start pricing out all the little bits of the heatriser, gaskets, bushings ect......its not much more for the new complete manifolds.

turns out the heatriser gasket in mine as leaking also.....

Pimp, where did you get them at?

I noticed that my heat riser has come apart best I can tell. I can pull the shaft out about 4 inches and have leak in my exhaust. I think the valve/flapper has come off and don't know if I should gather the parts to fix it or just by new.

Its been like this for at least a month and I don't know what position the valve/flapper is in, it could be restricting the exhaust and may or has caused my intake to crack.

Sorry about the hijack

 

[chitown40]

I rigged mine open all the time by turning th spring one full turn counterclockwise (looking from the front of the engine) and then reattached the coil spring. It takes a couple extra mins to warm up the carb but saved me from removing the manifolds again. Not a permananent fix, but good enough until I need to pull them off for something else. Hopefully not for another 100K though.

 

[Landpimp]

from my dealer but Dan can hook you up. for me it was some of the best money I have spent on the 40

QUOTE=Civil1]Pimp, where did you get them at?

I noticed that my heat riser has come apart best I can tell. I can pull the shaft out about 4 inches and have leak in my exhaust. I think the valve/flapper has come off and don't know if I should gather the parts to fix it or just by new.

Its been like this for at least a month and I don't know what position the valve/flapper is in, it could be restricting the exhaust and may or has caused my intake to crack.

Sorry about the hijack[/QUOTE]