I haven't been able to check for leaks just yet, but do have access to the computer today, so some questions.

My truck runs on propane, but I think the problem isn't propane-specific.

It will idle nicely when cold, but when warm it starts to sputter at idle, and when up above 180 degrees has a very rough idle. Will sometimes stall and backfire.

I haven't been able to find any mixer (what I have instead of a carburetor) or line leaks.

Fuel flow is adjusted to run slightly rich.

Timing is fine, and a little conservative at about 6 degrees BTDC.

I'm thinking this is an intake/exhaust gasket problem. I do have an exhaust leak at the head that I know needs to be fixed. Would this cause
idle problems, too?

I currently have one of those nice graphite Australian gaskets on the engine. Could I double those up for a better seal? Put a steel gasket on top of the Aussie gasket?


Thanks for your suggestions and expertise,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

If the thick aussie gasket is leaking I’d guess you need to face your manifolds or head surface flat. It’s not a good idea to stack gaskets but I’ve seen some on here do it.


Have you seen this article?

Danny

Have you tried readjusting the mixture once it warms up?

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Frank Raso is our resident propane expert on here. His user name, if I'm not mistaken, is FrankRaso. Check with him.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

IIRC, you have a feedback system (Dual Curve PN 5952) on your truck which means that carburetor adjustments just affect the cycle time of the controller. The fuel mixture is supposed to be slightly rich because the feedback system is designed to lean it to stoichiometric. I think you had Franz Hofmann set up your truck so it was running as good as it possibly could. Since there is very little to go wrong with the fuel system, I would look elsewhere before I started making fuel mixture adjustments.

Have you sprayed any carb cleaner on your manifold gasket to pinpoint any vacuum leaks?

If you haven't already done so, you might also want to hook up the feedback controller's violet wire to an LED to give you another diagnostic tool.

Thanks for the tips. Frank, yes I've worked w/ Franz. Good guy. I need to spray WD40 to check for leaks. Just haven't had the opportunity lately.

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

You may want to double-check the valve lash adjustment if it's a solid lifter engine. Tight lash can cause poor idle quality.
DD

Doc--

The Erson cam instructions specified .015 inch clearance for both intake and exhaust.

Does this seem too tight?

Thanks,
Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

Ran into too tight of specs on my Erson cam. Which cam did you get?

CJ

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Part of Tyrde-Browne Racing

I am running my current Erson cams at .018 Int. & .022 Ex
If I go any looser, it starts to "tic".
The idle quality and vacuum is much better at a looser lash setting.
DD

AHA!!!

Thanks very much, Doc. It's good to have an expert to go to,

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

I don't know about propane, but if you have an exhaust leak, you might have a vacuum leak, too.

Doc--

Runs better with looser valves, but there's still a problem. I've taken the manifolds off and in removal, several of the intake/exhaust studs in the head fell out. Also, there was a nick in the gasket (I'm using the big one from Australia).

Manifolds themselves are straight. I'll let you all know if it makes any difference when I get it back together.

Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"

What if the manifold studs were so loose, there was a vacuum leak there? Maybe use a thread sealer when you reinstall them. Just lock two nuts together (sounds painful) and replace them. I think you could repair the gasket with some permatex, if you are cheap, like me.