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Group: Forum Members
Last Active: 5 days ago
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Group: Forum Members
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Freoway57 (5/30/2018)
I then started spraying around with some "Start Ya Bastard" (a highly volatile engine starter in a can). Nothing around the manifold to head connection. I then noticed a change in revs when I sprayed the mushroom-like fitting on the driver's side. I believe that's a cap to the hot air tube that runs across the manifold to the choke assembly. Is it possible that the pipe could corrode inside the manifold? But then why would it affect the intake and not the exhaust? It's hard to tell exactly where it runs through. I removed the mushroom cap, cleaned it solvent and sealed it with solder. When I refitted the mushroom cap, there did seem to be a noticeable improvement. That is, the revs dropped when I disconnected the lead to cylinder #8. Does it run through the inlet plenum as well? Maybe I'll cap the side to the auto choke and fit a manual choke, based on advice received. What you experienced with the rise in RPM when hitting the hot air choke fresh air intake was as a result of an enriched mixture to the carb. The tube rides entirely in the exhaust gas cross-over and should have no influence over the miss even if the tube is corroded and allows exhaust gas into the choke fresh air inlet. If the tube is compromised you should have a lean fuel condition and also hear exhaust noise @ the tube on either side. Have you put a vacuum gauge on the engine? When you blocked off the booster and vacuum pump from the fitting on #7 and #8 intake runner, the fitting or it's mounting may be defective also. When using propane, I use a special wand to control flow. The valve is turned withe the wand @ the carb air-horn until RPM is stabilized and then you go on search and destroy with that setting. Probe the fitting itself and both #7 and #8 runner sealing and the actual runners in case there is a stress crack or something similar.
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The carburetor pulls a vacuum through the choke, so maybe that would explain the RPM increase when the start fluid is sprayed on the intake for the choke vacuum. But I don't see how it would connect to the miss on #8. Maybe there is some defect in the intake manifold? I hope someone can fill in the blanks.
The choke might not release correctly since you stopped the intake air to it, unless it is rusted through on the inside of the manifold. If you remove the choke, be sure to plug the vacuum port on the carburetor that draws the hot air into the choke.
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My '57 T-Bird 312ci has a problem I can't identify. If I pull off leads one at a time at the dizzy cap, the rpms drop about 40-50rpm, except on cylinder #8. I've changed the lead, swapped leads with ones that I know are good, swapped plugs, bought new plugs, etc. I've also replaced the distributor cap and rotor, just fitted new points and condenser (it was running a Pertronix electronic ignition module - so I removed that just in case). I've run a compression test - getting around 130psi or so on #8. Pretty much the same on all cylinders. I've done a leak down test - nothing leaking past the valves, although there is leakage past the piston rings, same effect on other cylinders. I can't get a percentage leakage as my leakdown tester gauge is dodgy. I'm at a bit of a loose end as to what else to check. I haven't checked the valve clearance on my solid lifters, but I did take the rocker cover off and there was a similar amount of play when the valves were closed, like other cylinders. I'm missing something! Can anyone else suggest what I can look at or test. I'm assuming an inlet manifold leak wouldn't affect a single cylinder. Maybe a valve isn't opening?? This one has got me befuddled!
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