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56 pan misses on acceleration

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sprucecreek
Posts: 69
Joined: Tue Jan 08, 2008 10:04 am

56 pan misses on acceleration

#1

Post by sprucecreek » Sat Mar 15, 2008 10:20 pm

Hello, folks. I'm sure this question has been asked lots of times, so I apologize in advance. I recently acquired a 56 FLH (the bike of my dreams) and finally have gotten some weather to take it out. I notice that it misses on acceleration and backfires, which I figure is the unburned gas in the pipes. This is my first FL (had a sportster 15 years ago), but I am well versed at troubleshooting ignition problems (I've had a 72 MGB for 30 yrs). I made sure the points were adjusted (.022 as the book says), and checked the circuit breaker timing (everything lines up fine). Cleaned the plugs (black, but not fouled), checked the gap (between .025 and .030) and made sure I had a good spark (it jumped about half an inch to the head).

So, I am thinking that this is probably not an ignition problem (although failure under load could be a cracked plug...I'll try new ones next...or maybe the coil, since when they go bad they often do strange and intermittent things).

The bike idles like a charm, but even at standstill will miss when the throttle is opened up.

I hate to mess with the carburetor except as a last resort, but the pipes are pretty black...could this be a mixture problem?

By the way, this forum is the best thing since canned beer for a harley guy. I have learned a ton already reading about other folks' problems!

:-)



john HD
Moderator
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Joined: Sat Aug 20, 2005 7:24 pm
Bikes: '42 WLA X 2, '55FL, '93 Ultra Classic, '91 Fatboy, '97 883, '71 Suzuki Duster 125, '83 GPz 750.

#2

Post by john HD » Sat Mar 15, 2008 10:34 pm

sprucecreek,

first, welcome to the forum! yes this is the high life of forums, lotsa good info here.

when my '55 does the same thing you describe, the first thing i check is the condenser.

be aware they can be "bad" right out of the box nowadays as they seem to sit around for quite some time before being sold.

you may want to try a couple if you get no change with the first one you try.

my personal favorite and the ones that seem to last the longest are the "blue streak" brand.

good luck and report back!

john

mogman
Posts: 103
Joined: Sun Oct 01, 2006 4:29 pm

#3

Post by mogman » Sat Mar 15, 2008 11:04 pm

I do not mean to offend, but are you advancing the timing (left hand grip)after starting the engine?
Craig

sprucecreek
Posts: 69
Joined: Tue Jan 08, 2008 10:04 am

#4

Post by sprucecreek » Sun Mar 16, 2008 12:30 am

john HD wrote:sprucecreek,

first, welcome to the forum! yes this is the high life of forums, lotsa good info here.

when my '55 does the same thing you describe, the first thing i check is the condenser.

be aware they can be "bad" right out of the box nowadays as they seem to sit around for quite some time before being sold.

you may want to try a couple if you get no change with the first one you try.

my personal favorite and the ones that seem to last the longest are the "blue streak" brand.

good luck and report back!

john
Thanks, John. I ordered a tune-up kit, and figured I would give that a try. I'll let you know how things go.

sprucecreek
Posts: 69
Joined: Tue Jan 08, 2008 10:04 am

#5

Post by sprucecreek » Sun Mar 16, 2008 12:35 am

mogman wrote:I do not mean to offend, but are you advancing the timing (left hand grip)after starting the engine?
Craig
Not offended at all, Craig. Yes, I retard to start (to keep it from kicking my butt into orbit), then advance as soon as it fires. But, the problem has all the hallmarks of the timing not being sufficiently advanced....the symptoms remind me of when the springs for the advance weights went bad on the sportster, and when the vacuum advance on my MG went south.

I am going to put in some new plugs and, as John suggests, a new condenser as well. I ordered the accel tune up kit from J&P. I'll be in touch as things progress.

john HD
Moderator
Posts: 3674
Joined: Sat Aug 20, 2005 7:24 pm
Bikes: '42 WLA X 2, '55FL, '93 Ultra Classic, '91 Fatboy, '97 883, '71 Suzuki Duster 125, '83 GPz 750.

#6

Post by john HD » Sun Mar 16, 2008 1:21 am

sprucecreek,

this may be obvious, but the timer needs to have the cap and bail properly installed to work correctly.

look under the timer with a flashlight and see that the ends of the bail are properly engaging the c shaped clip. there are dimples the ends register to.

the whole assembly needs the spring tension provided by the bail to not rock around and cause erratic operation.

a little squirt of wd 40 makes it rotate easily.

john

Cotten
Posts: 6911
Joined: Mon Aug 26, 2002 9:09 am
Location: Central Illinois

#7

Post by Cotten » Sun Mar 16, 2008 1:57 am

I must once again bring up the probability of a vacuum leak.

....Cotten

51Hog
Posts: 664
Joined: Fri May 20, 2005 7:29 pm
Bikes: 1951 Fl
Location: Wasilla, Alaska

#8

Post by 51Hog » Sun Mar 16, 2008 6:32 am

Mine misses and pops when I don't get the choke off all the way. Just takes one nothh of choke.

Pooka
Posts: 56
Joined: Sat Nov 24, 2007 2:22 pm
Location: Lebanon, Missouri

#9

Post by Pooka » Sun Mar 16, 2008 8:29 am

" Cleaned the plugs (black, but not fouled). "
Sounds a tad rich, but Cotton thinks you might have a vacuum leak.
What I'm wondering is ? How long has this bike sat ?
Could have a combination of evils going on at one time.
Start it at night, with the cap off the distributor, in your garage.
Turn out the lights, close the door.
Watch for arching in the distributor and wiring.
And if the exhaust fumes run you out, before it gets to hot, it's to rich.
Cotton has a way to test for vacuum leaks.
I haven't had to use it, but it sounds like the right way.
And it could be something as simple as a weak battery.

Cotten
Posts: 6911
Joined: Mon Aug 26, 2002 9:09 am
Location: Central Illinois

#10

Post by Cotten » Sun Mar 16, 2008 1:30 pm

It is common to have to over-enrichen for a vacuum leak.

The test is simple, and a big cork with a hole in it will do, as described at:
http://virtualindian.org/11techleaktest.html

You may end up chasing your tail if you do not eliminate one variable at a time.
And please test the pan cover screw over each intake port as well!

....Cotten
Last edited by Cotten on Sun Mar 16, 2008 3:03 pm, edited 1 time in total.

sprucecreek
Posts: 69
Joined: Tue Jan 08, 2008 10:04 am

Thanks for the suggestions

#11

Post by sprucecreek » Sun Mar 16, 2008 1:39 pm

Thanks, Guys, for the thoughts.

The bike sat for awhile before I bought it, but it appears to be in great shape and it ran fine a month ago. So, this seems to be a recent development. I'm going to start with the easy stuff (new plugs, wires, condenser), and see what that does. Probably should check the coil, too, just to be sure. It does seem to be running a bit rich, but that could be the choke to start and the unburned gas from the missing. It would seem that if the Linkert was too rich, it would have given me problems last month. The sudden onset of the problem would seem to suggest ignition issues, but you never know. I'll try the dark garage suggestion, too...I used to do this on my son's Z28 looking for burnt plug wires (headers are hell) .

Cotten, I recall from an earlier posting that you have a gizmo that you use to check manifolds for vacuum leaks...do you know where I might be able to get one? Thanks in advance. But, the cork sounds like a nice short term solution. Can this be done with the carb installed, or does it have to be removed and just the manifold checked?

By the way, what octane gas do you guys use? Unleaded work ok? (I ask because I need a lead additive for my old MG).

john HD
Moderator
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Joined: Sat Aug 20, 2005 7:24 pm
Bikes: '42 WLA X 2, '55FL, '93 Ultra Classic, '91 Fatboy, '97 883, '71 Suzuki Duster 125, '83 GPz 750.

#12

Post by john HD » Sun Mar 16, 2008 1:44 pm

spruce

i run 87 octane with a couple of ounces of marvel oil per fill up.

stay away from resistor spark plugs, my buddies 62 will run about 5 miles with them and then start missing.

john

sprucecreek
Posts: 69
Joined: Tue Jan 08, 2008 10:04 am

things get stranger

#13

Post by sprucecreek » Sun Mar 16, 2008 5:42 pm

well, it's a sunday afternoon, no football, and the harley dealer is closed so i can't get any new ignition parts on short notice...so, i figured that i would fiddle with the bike. I had checked the ignition timing using the procedure in the rider's guide, but i see the panhead manual has some additional steps using a test lamp (p. 207). I used a volt meter instead.

anyway, with the meter hooked up to the low voltage terminal on the coil and the positive terminal on the battery, and the ignition off, i have 6 volts indicated. turn on the ignition, nothing. no voltage, whether the points are closed or open. even if i try to short across the points (just in case the points themselves are bad, although i have filed them), no voltage.

it looks like the voltmeter does a slight quiver (less than one volt) and i hear the spark from the plug wire snapping as it grounds on the head. so, i am getting some spark.

points closed should mean voltage, right? what do you think...maybe a shorted condenser?

i'm glad that i enjoy working on these kind of things....

:-)

VT

#14

Post by VT » Sun Mar 16, 2008 6:24 pm

Our book Vol. 1 explains a method for using a single bulb to check for timing. A hiddnen factor with timers (later called circuit breakers) are worn (2) timer shaft bushings. Everything is ok at idle until you give it some throttle, then you might get pops and wheezes from the motor.
The key to detection of this probelm, is during the "retard" portion of the test, with the ignition switch "ON" the test bulb is suppose to light up immediately as the timer is twisted to retard. If the lamp doesn't light till further in the twist, then it's because, with worn bushings, the pressure of the points rubbing block is allowed to push the shaft away from true retard rotation axis.
The timer shaft bushings are rarely replaced. "Too much trouble and I want to ride it now, not later" is the usual culprit.
You can get an excellent vacuum tester from mbskeam who frequents this site.
Last edited by VT on Sun Mar 16, 2008 6:32 pm, edited 1 time in total.

john HD
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Posts: 3674
Joined: Sat Aug 20, 2005 7:24 pm
Bikes: '42 WLA X 2, '55FL, '93 Ultra Classic, '91 Fatboy, '97 883, '71 Suzuki Duster 125, '83 GPz 750.

#15

Post by john HD » Sun Mar 16, 2008 6:32 pm

spruce

try disconnecting the coil from the timer. then you are checking just one component at a time.

try, voltmeter to battery and voltmeter to timer lead and then rotate the motor.

you should see the needle/display change as the points open and close. now you can check your timing. make sure it is at full advance.

if you get a constant voltage reading then i would agree your condenser is shorted. lift the condenser lead to confirm.

john

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