rear cylinder not firing properly

[bigmic]

i have a 79 flh and having trouble with rear cylinder not firing continuously. Front cylinder fires  continuously from exhaust pipe but when you check rear cylinder it doesn't fire repeatedly like the front one when you put your hand over front exhaust pipe u get a continuous thump but the rear cylinder only thumps every now and then. also it sounds painful when you stand behind the bike and your listening to both cylinders fire. Ive tried these things to over come the problem: new exhaust sytem-true dual exhaust with fishtails no baffles
            new ignition system-crane hi-4 single fire
            new charging system-32 amp regulator and stator
            New battery
            checked all pushrod adjustment
            now running CV carby 50 190 jets and mixture screw 2 turns out
            4 1/2 " flywheels with high compression s&s pistons
All i really wont is to have both pipes sounding the same which also means both cylinders running right!
           

[Tobias]

first thing I would look at is a leak at the intake manifold

[70weight]

What tobias said plus plugs, plug wires or coil breaking down?

[Dennman]

Alotta fellas wonder about that misfirin but it's the way Shovels work and where they get their distinctive sound.Some cams can have those symptoms at an idle.

[Hillside Motorcycle]

A compression check and/or leakdown test could help pinpoint that.
Scott

[bigmic]

What tobias said plus plugs, plug wires or coil breaking down?

new crane wires new singlefire coil new plugs

[bigmic]

first thing I would look at is a leak at the intake manifold

no air leaks they were chased for years and finally fixed

[bigmic]

Alotta fellas wonder about that misfirin but it's the way Shovels work and where they get their distinctive sound.Some cams can have those symptoms at an idle.

im running a b grind cam but i just thought both cylinders should have the same beat coming out each pipe

[dablaze]

I would watch the plugs...is one getting more fouled than the other? And what do they look like when you take them out?

Also, did you have the same issues before these changes. Is the rear cylinder timing set up in the middle of the pt on the Hi4?

Craig

[Dennman]

I run a b grind cam w/ points and the rear is offbeat at idle but smooths out w/ rpm.

[bigmic]

I run a b grind cam w/ points and the rear is offbeat at idle but smooths out w/ rpm.

how crazy is that its like one cylinder is doin more work than the other,thats like i was saying the front pipe went a bluey purple colour and the rear still looked brand new with no color change at all

[bigmic]

I would watch the plugs...is one getting more fouled than the other? And what do they look like when you take them out?

Also, did you have the same issues before these changes. Is the rear cylinder timing set up in the middle of the pt on the Hi4?

Craig

the plugs are runnin pretty good they both do have a little bit of shiny black on the intake side of plugs otherwise good and the timing i have the tdc mark just coming into the timing hole as soon as it comes into view on the right hand side of hole i turn the crane ignition clockwise till the light goes out then it is set

[Lew]

Have you done a compression check??

Lew

[shov60]

 

   How about using a meter to check for fire while the engine is running and see if the wire are not grounding out against the engine?

[Lilbigstew]

I have the same issue with my 79' when I first start it up, I have too much oil pressure (I know very unusual for a shovel) and it floats the rear valve, Have to let it warm up for a minute and then you can hear the rear cylinder drop in. The dealership lock-tighted the lifters (make then solid lifters) and wanted to drill out the oil pump back in 79' to solve the issue. We changed everything back and just let it warm up before taking off.

[dablaze]

I have the same issue with my 79' when I first start it up, I have too much oil pressure (I know very unusual for a shovel) and it floats the rear valve

I was overoiling my heads and did this kit, love it.

http://floheadworks.com/Products/Top%20End%20Oiler%20Kit.htm

Craig

[Lilbigstew]

That is Sweet! Graig

[nw69fl]

I was working on a ironhead sporty the other day and had the same problem. After checking for air leaks, fouled plugs, coil, and valve adjustment, I discovered that the ground strap on the battery was faulty. I replaced it and now both cylinders fire even at low idle. Hope this helps.

[dirtywhitewalls]

hey fellas, I'm bumping this thread to see if any thing was figured out or any new ideas.

i have the same deal with my '76 and can't figure it out. i was hoping to hear that bigmic got it worked out and what fixed it.



since the problem showed up I've these things

-check intake leak
-switched coil, plugs, and wires
-changed lifters to solids
-set timing with new points and condenser
-top end(rings, new valves and guides, even put seals on them)

i have not had time to check the ground strap yet, maybe this weekend.

[speedy103]

Here's my stab (short version) at why Harley's drop the rear cylinder at idle and won't fire it smoothly until the rpm is up.  The 45* V twin that shares a crank pin for both cylinders will have an intake flow that is not even.  Add to that the common ignition system that fires both cylinders at the same time.  A single fire system will help this but not eliminate the firing issues at idle.
Not having any baffles in the pipes will add to the troubles even more because the flow can run through the cylinder during the overlap phase.

The only way to have both cylinders fire evenly is to isolate the intake manifolds and ignition system.

Because of the shared intake manifold the mixture for the rear cylinder will float more to the lean and rich sides than the front because of this revisionary issue with the intake manifold.  Not all of the flow is into the engine.  Some will actually pass across the idles port more than once.
The front cylinder gets the cleanest flow and most correct mixture between the two.  If the mixture is too rich the rear won't fire.  If the mixture is too lean the rear won't fire.  Some times the mixture is good but since the front cylinder fires at near TDC at idle, if the spark is shared, the rear will fire about 35* into the intake stroke when the valve is open and the flow is just starting to move.  This can light off all or part of the intake charge for the rear cylinder.  Hence it won't fire. 
A separate ignition system (single fire) helps this. 
You've all had the "cough and die" at a light when you just crack the throttle?  That's because when you flipped the throttle open the mixture in the manifold went lean for just an instant before the accelerator pump could richen it up.  At that moment, if the spark in the rear cylinder occurs at just the right time in it's intake stroke, the flame front in that cylinder can escape into the intake manifold and light the entire mess off.  The "cough" is when the mixture lights off.  It dies because the oxygen is burned away and the mixture is too rich for a second or two as the engine stops.

Once the rpm is up over 1500 or so, the intake flow evens out and it won't matter much when the spark occurs since the flame front cannot escape the combustion chamber.

This entire issue is aggravated by longer overlap cams and lower idle speeds.  Idle speed should be 1000 rpm.  Lower may sound better but it will pound the rod bearings to death.  Raising the compression ratio adds to this issue too.  That's a longer conversation as to why higher compression effects mixture and intake function.

Or I could be completely wrong...
Hope this helps.
Speedy

[tbkickstart2]

On a V-Twin that only has one crank pin for both cylinder's, the firing of the cylinders will never be the same. That is why a 45 degree V-twin H-D has that off beat idle. If you give it alittle gas they will sound more even, but they will never sound the same...TB

[dirtywhitewalls]

speedy103, i believe every word, makes sense. i can live with coughing plumes of white, stinky smoke and sometimes dying at the light. I've been riding this kind a crap since the beginning, always with a super B. i know i could eliminate many problems and in convinces with different carb and ignition. i might have out of date junk but i like it that way. i useally can work out my own problems but I'm having a hard time with this one

the thing is, bike use to run good, i did nothing to cause the problem. all things i listed was trying to get back to the way it ran before.
it would make potato...potato...potato...sound.  now it makes pop...pop...pop...every now and then, the rear cylinder chimes in with a bloom ...bloom... at idle and oil smokes out rear pipe. on the gas, going down the road, still sounds pretty good and runs pretty strong.
even at idle if i crack the throttle back cylinder comes in to it. i also forgot to mention earlyer, i also replaced advance. perhaps i have missed something, i rode to work last night and man is it getting on my nerves. i just want it to sound like it use to. tomorrow I'm going to mess with the ground like dude said.

[flhswingarm]

Speedy.........pure genious  i.m.h.o.

[speedy103]

Bigmic.  You mentioned having a Hi4 single fire ignition.  I assume you used the later style rotor cup.  The main difference between that one and the earlier is the length of shutter window opening.  I'm not sure why they do that but it is wider on the new one.  In other words the pickup can see itself for a longer duration.
What I've found is the cuts on the rotors are not that accurate.  The Hi4 has an adjustment to offset the rear cylinder firing.  On every one I've installed (single fire) I've had to adjust the rear cylinder.  Some have been nearly 6 degrees off!  That adjustment is to compensate for the manufacturing tolerances and variation in that rotor cup. 
Most flywheels don't have a rear advance mark so in those cases I use a dial back timing light and just go from the TDC marks for the two cylinders.  I time the front first by moving the plate, then the rear.
When I have an engine apart I usually put a mark for the rear advance on the wheels.

If the timing isn't it then possibly the coil is the problem.  I figure it's new, but electrical stuff can go at any time. 
I've had coils last decades and some just give up or not function from the beginning. 
Electricity can't be seen except when it leaks out.  It usually comes out in billowing white clouds. 
Good luck.

[springer-]

The early ignitions cup were made out of aluminum and can not be used with aftermarket ignitions like the crane.  Not sure about the over all size.  I believe the early ignitions us an optical sensor and is the reason they are made from aluminum.  The later (after about 82-83) have steel cups.  They were made from steel because the sensors are hall effect (uses magnets).  The steel breaks the magnetic field, the aluminum won't.