Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 10-18-2020, 10:26 PM   #1
SteveR.
Member
 
Join Date: Nov 2017
Location: Aledo, TX
Posts: 58
Default New engine - intermittent backfiring - stuck valve?

I have a new engine with maybe 80 miles on it, built by a reputable manufacturer. It has started intermittent backfiring "fits" and corresponding power loss after it gets warm. I don't think it is the distributor or ignition, timing is correct, point gap is .020. Wondering if it is a stuck valve, is that common or likely for a new engine? What is the easiest way to check?

I checked between the upper and lower distributor plates, don't think there is a short there. Distributor worked fine with the prior engine. Low RPM & low load it runs fine, but when hot, it will intermittently run OK, then go into a fit of lost power & backfiring. Enrichening the GAV might help slightly, but the problem remains.
SteveR. is offline   Reply With Quote
Old 10-18-2020, 10:39 PM   #2
Brentwood Bob
Senior Member
 
Join Date: May 2010
Location: brentwood, ca
Posts: 3,253
Default Re: New engine - intermittent backfiring - stuck valve?

I would contact the builder.
Brentwood Bob is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 10-18-2020, 10:41 PM   #3
Mulletwagon
Senior Member
 
Mulletwagon's Avatar
 
Join Date: Jan 2019
Location: Florida Panhandle
Posts: 443
Default Re: New engine - intermittent backfiring - stuck valve?

Might try some Marvel Mystery Oil as a first step. Squirt some directly in the carb and then add 4 oz. to a full tank of gas. Sticking valves are not unusual and MMO is often the cure.
Mulletwagon is offline   Reply With Quote
Old 10-18-2020, 11:10 PM   #4
McMimmcs
Senior Member
 
McMimmcs's Avatar
 
Join Date: Sep 2019
Location: Michigan
Posts: 1,474
Default Re: New engine - intermittent backfiring - stuck valve?

What did the builder say.
McMimmcs is offline   Reply With Quote
Old 10-18-2020, 11:36 PM   #5
alexiskai
Senior Member
 
alexiskai's Avatar
 
Join Date: Apr 2018
Location: Mebane NC
Posts: 1,142
Default Re: New engine - intermittent backfiring - stuck valve?

Similar problem posted in 2013 turned out to be poor fuel flow.

https://www.fordbarn.com/forum/showt...0452&showall=1
alexiskai is offline   Reply With Quote
Old 10-19-2020, 07:58 AM   #6
30 Closed Cab PU
Senior Member
 
Join Date: Aug 2018
Posts: 2,332
Default Re: New engine - intermittent backfiring - stuck valve?

Sponsored Links (Register now to hide all advertisements)
Also consider it may be electrical, bad connection. Flakey ignition switch, terminals on the back side of the ignition switch intermittently shorting to the gas tank, ammeter nuts loose, points gap, etc.



If the motor was repainted sand distributor base and head off where the distributor sits on the head (major ignition grounding point for ignition). Another major ignition grounding point is through ignition cable - threads where the ignition cable screws into the distributor should be clean/paint free. And the stud/nut threads/ignition cable clamp for the ignition cable should be clean/paint free. Ive seen this on my A when its motor was rebuilt and a rebuilt distributor installed, both which were freshly repainted
30 Closed Cab PU is offline   Reply With Quote
Old 10-19-2020, 08:34 AM   #7
old31
Senior Member
 
Join Date: Jan 2016
Posts: 1,528
Default Re: New engine - intermittent backfiring - stuck valve?

Open up the GAV as you are driving and see if that stops the problem.

It could be starving for fuel, add MMO and do as the others have said.
old31 is offline   Reply With Quote
Old 10-19-2020, 08:49 AM   #8
Big hammer
Senior Member
 
Join Date: Jun 2014
Location: Land of Lincoln
Posts: 2,303
Default Re: New engine - intermittent backfiring - stuck valve?

After it gets warmed up and is acting up, pull the coil wire and hold it 1/4 in for a head nut, you should have a blue spark. If you have good spark ,look at fuel flow remove the carburetor drain plug to see good flow. On a fresh engine it is tight so MMO in the gas could help, 4oz per 10 gals or more.
__________________
Don't force it with a little hammer tap, tap, tap
get a bigger hammer tap done
Big hammer is offline   Reply With Quote
Old 10-19-2020, 09:05 AM   #9
Billy
Junior Member
 
Join Date: Jun 2010
Posts: 3
Default Re: New engine - intermittent backfiring - stuck valve?

It sounds like you have one valve guide that's little too tight..

Just my two cents,

Bill
Billy is offline   Reply With Quote
Old 10-19-2020, 09:31 AM   #10
1crosscut
Senior Member
 
1crosscut's Avatar
 
Join Date: Feb 2011
Location: Lincoln, Nebraska
Posts: 1,541
Default Re: New engine - intermittent backfiring - stuck valve?

Did you happen to get the radiator cap and gas cap switched? Run it without the gas cap on or when it starts to act up take the gas cap off and listen for it sucking in air when you do.
__________________
Dave / Lincoln Nebraska
1crosscut is offline   Reply With Quote
Old 10-19-2020, 10:40 AM   #11
jetmek
Senior Member
 
Join Date: May 2010
Location: albany
Posts: 431
Default Re: New engine - intermittent backfiring - stuck valve?

Contact the builder My wAG would a tappet came out of adjustment
__________________
engine and component overhauls my specialty!
Website- www.godevilgarage.com
jetmek is offline   Reply With Quote
Old 10-19-2020, 11:06 AM   #12
Will N
Senior Member
 
Will N's Avatar
 
Join Date: Jul 2010
Location: Pennsylvania
Posts: 845
Default Re: New engine - intermittent backfiring - stuck valve?

Quote:
Originally Posted by jetmek View Post
Contact the builder My wAG would a tappet came out of adjustment

Agreed- it's a new engine and the builder should guarantee his work. But since this is happening when the engine warms up, one possible reason is that, as jetmek said, valve clearance has come out of adjustment, getting too small. And as the valves heat and expand, they aren't seating fully. Running the engine like this can cause the valve(s) to burn.
Will N is offline   Reply With Quote
Old 10-19-2020, 02:41 PM   #13
Ak Sourdough
Senior Member
 
Ak Sourdough's Avatar
 
Join Date: Jul 2014
Location: Fairbanks, Alaska
Posts: 118
Default Re: New engine - intermittent backfiring - stuck valve?

It's lean. Find out why it's not getting enough fuel. Put a pan under the carb and pull the drain plug, then let it flow a couple minutes. I think you'll see it taper off to a trickle.


If an intake valve was not closing, it would puff flame into the intake manifold on every combustion stroke... EVERY combustion stroke. Not just a backfire once in a while. An exhaust valve that isn't closing would burn and you'd have a dead miss.


It's lean.
__________________
I still have an excellent rememberer, trouble is my forgetter is so much better that it often overrides the rememberer.
Ak Sourdough is offline   Reply With Quote
Old 10-26-2020, 09:24 PM   #14
SteveR.
Member
 
Join Date: Nov 2017
Location: Aledo, TX
Posts: 58
Default Re: New engine - intermittent backfiring - stuck valve?

A little more information on this...

I haven't contacted the builder until I know for sure it is a valve...don't want to waste his time if it isn't his issue, and now I don't think it is.

Appears to be a fuel issue as Ak Sourdough suggested. The car runs great, always, under 40-45 MPH. No missing, good power, very smooth. Always fine in 1st & 2nd gear. When I get to 3rd gear, it will run fine even at full throttle until 40+ mph when I get deeper in the throttle. If I let off the gas for a few seconds then get back in it, it will be fine for a second or two until it gets starved of gas again. I disconnected the fuel line from the carb and get a steady, strong stream of fuel. Must be something in the carb. It is a Tillotson, should I just take it apart and clean it, or is there a specific place to check for trash?
SteveR. is offline   Reply With Quote
Old 10-26-2020, 09:37 PM   #15
SteveR.
Member
 
Join Date: Nov 2017
Location: Aledo, TX
Posts: 58
Default Re: New engine - intermittent backfiring - stuck valve?

According to this chart, either my float is set too low or the main orifice has trash in it:
https://www.modela.org/troubleshooting.gif
SteveR. is offline   Reply With Quote
Old 10-26-2020, 11:59 PM   #16
Chuck Sea/Tac
Senior Member
 
Chuck Sea/Tac's Avatar
 
Join Date: May 2010
Location: Between Seattle & Tacoma
Posts: 2,082
Default Re: New engine - intermittent backfiring - stuck valve?

Sounds like a start. Do they show jet orfice flowtesting criteria? With a zenith, I have had to open the high speed jet.
Chuck Sea/Tac is online now   Reply With Quote
Old 10-27-2020, 03:18 AM   #17
Ak Sourdough
Senior Member
 
Ak Sourdough's Avatar
 
Join Date: Jul 2014
Location: Fairbanks, Alaska
Posts: 118
Default Re: New engine - intermittent backfiring - stuck valve?

Disconnecting the fuel line at the carburetor will not tell you if there is a wad of crud against the inlet side of the float needle seat or if the float stop is bent so the needle barely opens and doesn't allow enough fuel into the carb for sustained high speed travel.


Put the line back on and pull the plug out of the bottom of the carb, then try your flow test again. Or, just take the carb apart and find out what the problem is. You already know you have good flow to the carb so the problem is inside.


Pretty comprehensive description here.
https://www.youtube.com/watch?v=-wBALe0MUgs
__________________
I still have an excellent rememberer, trouble is my forgetter is so much better that it often overrides the rememberer.
Ak Sourdough is offline   Reply With Quote
Old 10-27-2020, 05:38 AM   #18
wwirz
Senior Member
 
Join Date: May 2020
Location: Corning NY
Posts: 114
Default Re: New engine - intermittent backfiring - stuck valve?

Change out the condenser to see if that would make a difference. Nice Article in the most recent issue of the "RESTORER" about condenser.
wwirz is offline   Reply With Quote
Old 10-27-2020, 06:08 AM   #19
Patrick L.
Senior Member
 
Patrick L.'s Avatar
 
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 6,182
Default Re: New engine - intermittent backfiring - stuck valve?

Haven't read all the comments, sooo,,,,

Try loosening the fuel cap if it hasn't been mentioned or you haven't done it.
Patrick L. is offline   Reply With Quote
Old 10-27-2020, 07:24 AM   #20
Pilotdave
Senior Member
 
Pilotdave's Avatar
 
Join Date: Oct 2010
Location: Grafton, MA
Posts: 1,220
Default Re: New engine - intermittent backfiring - stuck valve?

Fuel cap suggestions might be correct. A car on a recent tour had similar symptoms. Loosened the cap and the problem went away. Worth a check.
Pilotdave is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 09:54 PM.