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EFV-8 Club Forum / General Ford Discussion / Stumble/Hesitation When Hot at Steady 60mph

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Posted By Discussion Topic: Stumble/Hesitation When Hot at Steady 60mph     thewmon 05-17-2018 @ 12:41 PM reply profile send p.m. Member Posts: 5 Joined: Jun 2017 Hello! Looking for some suggestions to diagnose a stumble/hesitation when engine is hot going 60mph on freeway. It is not so bad that I cannot get to where I am going, more annoying than anything. I have done the following over many months (not in order): 1) New "lifetime" condensor from Bubba's ignition 2) Rebuilt distributor, timed on machine 3) Rebuilt coil from Skip Haney (which solved my hard to start when hot issue BTW) 4) New plugs, good spark at each 5) Fuel pressure as measured in-line between mechanical pump and carb = just under 3psi, goes to 2.5-2.75psi higher RPMs 6) Vacuum 20inHg steady at idle, have not tested on the road yet 7) Checked all grounding, newer Optima 6V battery 8) Made sure fuel lines are tight 9) New Holly94 carb, runs slightly rich 10) New in-line fuel filter 11) Have adjusted the timing +/- a few degrees, test drove with no change 12) Have adjusted the distributor vacuum brake in and out, test drove with no change Many thanks! Matthew carcrazy 05-17-2018 @ 3:05 PM reply profile send p.m. Senior Posts: 1582 Joined: Oct 2009 How hot is the engine coolant temperature when this missing or surging occurs? You could be experiencing a form of "vapor lock" if the fuel is getting too warm. Your problem could be a lean surge as the fuel/air mixture is too lean at the 60 MPH speed. Your fuel pump could be going bad - is the problem worse as the car climbs hills? If you are using radio resistance ignition wires, the resistance of the wires may be too great to provide a reliable spark for the compression pressure at 60 MPH. Your spark plug gaps or heat range may not be correct for the engine conditions at the speed where you are having problems. You could have some electrical connections within the ignition system circuit that are marginal - check all connections and make sure they are clean and tight. 40 Coupe 05-19-2018 @ 8:34 AM reply profile send p.m. Senior Posts: 1643 Joined: Oct 2009 what makes you believe the car is running rich? with 20" of vacuum at idle your good. Are the plugs turning black or have soot deposits? Plugs are gaped at 0.018" the plug wires are copper wire core and not resistor plugs or wires. ken ct. 05-19-2018 @ 9:27 AM reply profile send p.m. Senior Posts: 1513 Joined: Jan 2010 Plug gap is NOT .018 should be .025-.030. What yr is the engine ? I would check carb main jets will run better at #049 or 050 . See what is in there. Idle mix screws should be 7/8 to 1 turn out. Don't know where fella got .018 plug gap???? ken ct. I would also check point gap deluxe40 05-19-2018 @ 11:17 AM reply profile send p.m. Member Posts: 413 Joined: Oct 2009 What kind of plugs are you using? I had a similar problem with Champion H10C plugs. They are not the same as the old Champion H10 plugs and are designed for lawn mowers. I also had a similar problem caused by a leaking intake manifold. The gasket surface on the block had a slight residue left from a previous gasket causing a leak after about 10 miles at speed. A meticulous cleaning and a new gasket fixed the problem. thewmon 05-19-2018 @ 4:49 PM reply profile send p.m. Member Posts: 5 Joined: Jun 2017 Thanks... coolant temp after a 20 mile freeway run is 155F. Problem is worse uphill going over the Sierra's on 80 from Reno last August. Actually the more I hone in seems hesitation is upon acceleration as well.. so maybe leaning towards checking power valve? Easy method to check that? even though its a newer carb, well I guess the carb probably has 2000 miles on it. Thought it was a little rich as the shop around the corner hooked it up to their machine. Using Autolite 216 plugs, need to check the gap TomO 05-20-2018 @ 8:01 AM reply profile send p.m. Senior Posts: 7243 Joined: Oct 2009 Do a fuel delivery test to see if your engine is starving for gas at the highway speeds. Vibrate your ignition switch by tapping on it with the handle of a screwdriver while sitting in the driveway to see if the engine misses. Do a cylinder balance test with the engine running around 1,000 RPM to see if the problem is cylinder related. Connect a vacuum gauge and take it for a ride to see if it is a plugged exhaust or sticking valve. Power valve should stay closed at vacuum above 8 inches. The timing adjustment on the early distributors should not cause your problem and neither should the vacuum brake. Tom thewmon 05-23-2018 @ 11:29 AM reply profile send p.m. Member Posts: 5 Joined: Jun 2017 Thanks... I pulled the Autolite 216 plugs I had installed for 2 years, ~2000 miles and they had black soot and measure ~0.032-35. I put in new plugs gapped at 0.025 and will test drive soon. I do have constant 20inHg vacuum at idle and constant speeds. How do you perform a fuel delivery test? TomO 05-24-2018 @ 7:41 AM reply profile send p.m. Senior Posts: 7243 Joined: Oct 2009 Here is a link to the procedure: https://www.earlyfordv8.org/forum/viewmessages.cfm?Forum=16&Topic=7440&keywords=fuel%20delivery Tom

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