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| Runs worse when hot--manifold gasket? https://slantsix.org/forum/viewtopic.php?t=37305 |
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| Author: | Daddiojoe [ Tue Sep 29, 2009 3:57 pm ] |
| Post subject: | Runs worse when hot--manifold gasket? |
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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| Author: | 65Dodge100 [ Wed Sep 30, 2009 2:50 am ] |
| Post subject: | |
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 |
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| Author: | emsvitil [ Wed Sep 30, 2009 3:21 am ] |
| Post subject: | |
Have you tried readjusting the mixture once it warms up? |
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| Author: | SlantSixDan [ Wed Sep 30, 2009 5:17 am ] |
| Post subject: | |
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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| Author: | FrankRaso [ Wed Sep 30, 2009 6:08 am ] |
| Post subject: | |
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. |
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| Author: | Daddiojoe [ Wed Sep 30, 2009 1:03 pm ] |
| Post subject: | |
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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| Author: | Doc [ Wed Sep 30, 2009 1:47 pm ] |
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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 |
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| Author: | Daddiojoe [ Thu Oct 01, 2009 2:58 pm ] |
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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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| Author: | ceej [ Thu Oct 01, 2009 5:34 pm ] |
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Ran into too tight of specs on my Erson cam. Which cam did you get? CJ |
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| Author: | Doc [ Thu Oct 01, 2009 5:39 pm ] |
| Post subject: | |
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 |
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| Author: | Daddiojoe [ Thu Oct 01, 2009 7:05 pm ] |
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AHA!!! Thanks very much, Doc. It's good to have an expert to go to, Joe |
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| Author: | slantfin [ Sat Oct 03, 2009 3:16 am ] |
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I don't know about propane, but if you have an exhaust leak, you might have a vacuum leak, too. |
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| Author: | Daddiojoe [ Mon Oct 12, 2009 8:23 pm ] |
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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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| Author: | slantfin [ Tue Oct 13, 2009 5:57 am ] |
| Post subject: | |
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. |
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