The Ford Barn

flatheadute1934 · 06-17-2013, 09:47 PM

My uncle touring has a miss over 40 mph. He said if was only over 40 mph. Thoughts and suggestions. Stock 1930

Doug in NJ · 06-17-2013, 09:59 PM

Getting too lean?
What happens if he opens the GAV?

Point bounce? (whatever that is...)

Doug

Gary WA · 06-17-2013, 10:11 PM

Check point and rotor to cap gaps.

van Dyck · 06-17-2013, 10:40 PM

Point bounce = weak point arm spring. Actually the weak spring will not allow the points to close when the engine reaches a particular RPM. Also check to see if the point gap has increased.

Dave in Boise · 06-17-2013, 10:52 PM

open the GAV a bit.. Easiest to try

Then I'd go with the ignition advice above (don't forget the condenser and coil as they will also exhibit some issues at higher rpms, especially as they get hot), a well as to check for good strong flow to the carburetor from the fuel tank..

Napa Skip · 06-17-2013, 11:12 PM

Sponsored Links (Register now to hide all advertisements)

In no particular order:

1. Air/fuel mixture too lean:

a. Restricted fuel supply
(1) Plugged fuel filter (if installed)
(2) Gas cap not venting
(3) Plugged fuel tank outlet
(4) Carb float set too low
(5) Carb passage(s) restricted or plugged

b. Vacuum leak:
(1) Between carb and inlet manifold
(2) Between inlet manifold and block

2. Ignition:

a. Coil:
(1) Weak
(2) Polarity reversed

b. Distributor body:
(1) Rotor-to-body gap unequal
(2) Body cracked

c. Points:
(1) Not gapped correctly
(2) Corroded
(3) Spring weak or broken

d. Failed or weak condenser

e. Spark plugs:
(1) Incorrectly gapped
(2) Cracked insulator
(3) Fouled
(4) Wrong type or heat range

johnbuckley · 06-18-2013, 03:26 AM

add to list : sloppy bushes in distributor.
Any more wanted?

Patrick L. · 06-18-2013, 05:34 AM

All good info. Could also be reversed coil polarity.

Purdy Swoft · 06-18-2013, 11:07 AM

Check the spark plug wire strips on the distributor. Some spark plugs are shorter than others and need longer plug wires. if the wires are too short and contact the distributor cap , the number three wire can burn through the cap and cross fire to the number four wire inside the cap. I had this problem. My car would run ok at low speed but miss at highere rpm. I happened to be looking under the hood one night with the engine running and saw the sparks flying between the edge of the cap body and the number 3 plug wire strip when I reved the engine. Check the distributor cap body for melted spots under where the wire is contacting the cap. this usually only happens if the plug wires are too short and touching the cap body. Just a thought.

06-17-2013, 09:47 PM	#1
flatheadute1934 BANNED Join Date: May 2010 Location: Brooklin Posts: 205	Miss over 40 mph My uncle touring has a miss over 40 mph. He said if was only over 40 mph. Thoughts and suggestions. Stock 1930

06-17-2013, 09:59 PM	#2
Doug in NJ Senior Member Join Date: May 2010 Location: Princeton, NJ Posts: 965	Re: Miss over 40 mph Getting too lean? What happens if he opens the GAV? Point bounce? (whatever that is...) Doug __________________ My '31 S/W sedan project:http://31ford.dougbraun.com My restoration diary: http://dougbraun.com/blog

06-17-2013, 10:11 PM	#3
Gary WA Senior Member Join Date: May 2010 Location: Clinton,WA/Whidbey Island Posts: 4,105	Re: Miss over 40 mph Check point and rotor to cap gaps. __________________ www.whidbeymodelaclub.com

06-17-2013, 10:40 PM	#4
van Dyck Senior Member Join Date: May 2010 Location: Saskatchewan, Canada Posts: 190	Re: Miss over 40 mph Point bounce = weak point arm spring. Actually the weak spring will not allow the points to close when the engine reaches a particular RPM. Also check to see if the point gap has increased.

06-17-2013, 10:52 PM	#5
Dave in Boise Senior Member Join Date: May 2010 Posts: 330	Re: Miss over 40 mph open the GAV a bit.. Easiest to try Then I'd go with the ignition advice above (don't forget the condenser and coil as they will also exhibit some issues at higher rpms, especially as they get hot), a well as to check for good strong flow to the carburetor from the fuel tank..

06-17-2013, 11:12 PM	#6
Napa Skip Senior Member Join Date: Mar 2012 Location: Napa CA Posts: 412	Re: Miss over 40 mph Sponsored Links (Register now to hide all advertisements) In no particular order: 1. Air/fuel mixture too lean: a. Restricted fuel supply (1) Plugged fuel filter (if installed) (2) Gas cap not venting (3) Plugged fuel tank outlet (4) Carb float set too low (5) Carb passage(s) restricted or plugged b. Vacuum leak: (1) Between carb and inlet manifold (2) Between inlet manifold and block 2. Ignition: a. Coil: (1) Weak (2) Polarity reversed b. Distributor body: (1) Rotor-to-body gap unequal (2) Body cracked c. Points: (1) Not gapped correctly (2) Corroded (3) Spring weak or broken d. Failed or weak condenser e. Spark plugs: (1) Incorrectly gapped (2) Cracked insulator (3) Fouled (4) Wrong type or heat range __________________ Skip Keyser Napa Valley A's Olympic Vintage Auto Club (1980-1982) MARC of San Diego (1977-1978) MAFCA (since 1978) MARC (since 1977) ---------- Model A owners belong in their Model A’s; Model A’s belong on the road. Last edited by Napa Skip; 06-18-2013 at 07:50 AM. Reason: typo

06-18-2013, 03:26 AM	#7
johnbuckley Senior Member Join Date: Jul 2010 Location: United Kingdom Posts: 1,444	Re: Miss over 40 mph add to list : sloppy bushes in distributor. Any more wanted?

06-18-2013, 05:34 AM	#8
Patrick L. Senior Member Join Date: May 2010 Location: Largo Florida Posts: 7,225	Re: Miss over 40 mph All good info. Could also be reversed coil polarity.

06-18-2013, 11:07 AM	#9
Purdy Swoft Senior Member Join Date: May 2010 Location: Alabama Posts: 8,099	Re: Miss over 40 mph Check the spark plug wire strips on the distributor. Some spark plugs are shorter than others and need longer plug wires. if the wires are too short and contact the distributor cap , the number three wire can burn through the cap and cross fire to the number four wire inside the cap. I had this problem. My car would run ok at low speed but miss at highere rpm. I happened to be looking under the hood one night with the engine running and saw the sparks flying between the edge of the cap body and the number 3 plug wire strip when I reved the engine. Check the distributor cap body for melted spots under where the wire is contacting the cap. this usually only happens if the plug wires are too short and touching the cap body. Just a thought.