miss

npca-vike · Post by **npca-vike** » Thu Mar 02, 2006 1:49 am

my 67 has a miss that is driving me around the bend trying to eradicate - and hence my plea for the wisdom of those of greater experience, skill, training, gut instinct. The carburator is new but I did goof up by messing with the float adjustment. (before I installed an electric fuel pump which fixed the fuel delivery issue) The engine is a complete rebuild with new bearings, pistons, valves - the works... It has less than 10 hours on it. The points are new and clean - adjusted at 20 thousand. The wires check out perfectly re continuity. The spark plugs are new and gaped at 30 thousand - but there is this anoying miss at idle. vacuum guage sits pretty steady at 18 to 20 with a little jerk to the lean when the miss occurs. Ideas? valve adjustments were done cold as the engine was in the midst of the rebuild when they were installed. Is it possible that one or more are off a tad and causing this? The engine seems to have power galore otherwise but maybe the miss is still there but just not so noticeable when the engine is at a higher rev.

npca-riverpatrol · Post by **npca-riverpatrol** » Thu Mar 02, 2006 8:40 am

I'm sure you've set the timing correctly, right? The points are supposed to gapped at .018, not that that should make much difference. You must adjust the valves when the engine is hot. You only adjust them cold when you put the engine together, but as soon as you start the engine the first time, you let warm up to operating temperature and adjust them a final time. The gap for all the valves is .016. A bad valve adjustment could definitely cause a miss.

npca-vike · Post by **npca-vike** » Thu Mar 02, 2006 10:15 am

Thanks. Timing is set 10 degrees before d/c as per manual - but I have not re-adjusted the valves since cold set - so I know what this weekend brings...stay tuned (well sort of)

npca-superk · Post by **npca-superk** » Thu Mar 02, 2006 9:28 pm

I agree you need to adjust the valves when it's warmed up. If you still have the miss after that, you can start narrowing down the possibilities. First, while the engine is running, pull the plug wires one at a time and watch/listen for rpm drops and/or a second cylinder miss. When you pull the wire from the one that's missing there won't be an rpm drop. While the plug wire is off, you can check that wire to see if it's got spark. The spark should be a healthy blue and about 1/4 to 1/2 inch long. If not, could be a bum wire or cap. Check the wire ends and the contacts inside the cap (make sure the inside of the cap is clean and crack free). If it does have a spark, it's one down and a few to go. Try swapping plugs with another cylinder to see if it's the plug. If after swapping the other cylinder misses, it's the plug. If not, well there's some other stuff you could check but rather than write all that stuff down I'll wait to see if the re-adjustment fixes it. I'm betting it does. One more thing, the Model P manual says the point gap should be .018-.021 and the dwell angle 35-40 degrees. Adjusting one affects the other but if you've got a good solid spark don't mess with it. Ok, I'm starting to ramble so I'm quitting. For now. SuperK

npca-eccook · Post by **npca-eccook** » Fri Mar 03, 2006 4:30 pm

Helo Vike Check this website for previous missives about distributor inards . Specificly point plate slop. goodlucked

npca-abuelo442 · Post by **npca-abuelo442** » Fri Mar 03, 2006 7:01 pm

Make shure that you don't have any exhaust leakage. Check the manifold to pipe connection, and also the pivot for the internal butterfly, the one that has a bimetalic spring on the outside of the manifold (this is used in cold weather to divert part of the exhaust gas to heat the base of the carburator). Any leakage will cause this miss, but at higher rpm it will disappear. Good luck, Esteban

npca-vike · Post by **npca-vike** » Wed Mar 08, 2006 9:59 am

set the points at .17 and what a great improvement over my earlier .2! starts immediately - and has less of a miss. will get to the valves this coming weekend. Intake manifold leaks can sure cause a miss but my vacuum guage says that is not happening. I am curious about the mentioned connection between an exhaust leak and a miss. Beyond reducing back pressure and hence increasing the force of the valves against their seats, I don't see how a leak on the exhaust side could cause a miss. I am curious. How?

npca-leop454 · Post by **npca-leop454** » Mon Mar 20, 2006 2:47 pm

I worked on a rig for days and then I changed the gas in the tank?? It had been stored long enough it was flat ....put some premium in? With the electric fuel pump did you add a pressure regulator? Is there some distance between the gas line and the front of the engine (mild vapor lock)? The best one is the squeek in rear of the vehicle I couldnt find. Didnt match the speed of the vehicle, engine speed, bumps or any other condition. It just went on and off at crazy intervals. Had a nest of mice who had moved in during the winter. good luck Leo

npca-vike · Post by **npca-vike** » Thu Mar 23, 2006 8:59 pm

Put in a low pressure Carter in-line electric pump - 4 psi so no problems re pressure regulation. gas lines are new steel ones routed to insure no heat issues re potential vapour lock problems. lots of experience with that in my collection of old Willys and Ford army jeeps. I hope to get at the valve adjustments this weekend - but life keeps getting in the way....

npca-abuelo442 · Post by **npca-abuelo442** » Fri Mar 24, 2006 1:14 pm

Regarding Valve Adjustment: If you place CYL 1 at TDC, the following valves (from front to back) can be adjusted without turning the engine: 1, 2, 3, 6, 8, 9 With CYL 6 at TDC: 4, 5, 7, 10, 11, 12 I learned this by looking at the P40 engine manual. Esteban