Harley Reversion Problem
Harley Reversion Problem
(OP)
Hey guys. I found this forum through Google and was blown away at the knowledge I saw here. I found another reversion thread on here and did find some information useful but his problem was a little different than mine.
I have a 79 Ironhead and I'm fairly certain I'm dealing with some sort of reversion problem. I've done every test I possibly can in regards to ignition, and fuel and I know that neither of these are the cause of my problem. There is good compression on both cylinders.
I can't get the bike at suggested idle rpm at all. The rear cylinder is firing but is very weak. When the bike is idling I can pull the rear plug wire and not a lot changes. When the front wire is removed the bike falls on its face and dies. The front cylinder is running super rich and the rear seams to show little to no color on the plug.
At idle the carb spits a little fuel here and there and when the bike is shut off it appears to have steam coming out of the carb. I pulled the intake manifold and carb off and both intake runners are soaked in fuel.
I know cam timing can very well be an issue but I pulled the cam cover off and the cam timing was spot on. The rear exhaust pipe sounds almost like a under water boat exhaust or something. Also, When I unplug the rear cylinder while idling and leave it unplugged for a few seconds, When I plug it back in I can get a few strong fires out of that cylinder until it goes back to the way it was.
So with all this being said I'm fairly certain I'm having a really bad reversion problem that's keeping the rear cylinder from running right. If its not cam timing what else can it be? I'm runnin out of ideas and I really want to start riding before the weather gets bad. Thanks in advance fellas.
-Chris
I have a 79 Ironhead and I'm fairly certain I'm dealing with some sort of reversion problem. I've done every test I possibly can in regards to ignition, and fuel and I know that neither of these are the cause of my problem. There is good compression on both cylinders.
I can't get the bike at suggested idle rpm at all. The rear cylinder is firing but is very weak. When the bike is idling I can pull the rear plug wire and not a lot changes. When the front wire is removed the bike falls on its face and dies. The front cylinder is running super rich and the rear seams to show little to no color on the plug.
At idle the carb spits a little fuel here and there and when the bike is shut off it appears to have steam coming out of the carb. I pulled the intake manifold and carb off and both intake runners are soaked in fuel.
I know cam timing can very well be an issue but I pulled the cam cover off and the cam timing was spot on. The rear exhaust pipe sounds almost like a under water boat exhaust or something. Also, When I unplug the rear cylinder while idling and leave it unplugged for a few seconds, When I plug it back in I can get a few strong fires out of that cylinder until it goes back to the way it was.
So with all this being said I'm fairly certain I'm having a really bad reversion problem that's keeping the rear cylinder from running right. If its not cam timing what else can it be? I'm runnin out of ideas and I really want to start riding before the weather gets bad. Thanks in advance fellas.
-Chris





RE: Harley Reversion Problem
The ignition timing is out of phase.
The carbies are out to lunch or have a sinking float.
The valves are sticking.
It has a broken valve spring.
It has a defective high tension lead.
It has a blocked exhaust pipe.
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RE: Harley Reversion Problem
The cams looked to be in good shape and weren't missing any lobes.
I'm pretty sure the ignition timing is fine cause the front cylinder is firing good and is really strong.
The engine only has one carb that feeds both cylinders. I've tried to different carbs and nothing has changed. Also if it was a carb problem I'm fairly certain it would effect both cylinders.
A valve sticking or a broken valve spring is very possible.
Every single ignition component is brand new. I have tried different wires to just in case and still no change.
The exhaust isn't blocked at all.
-Chris
RE: Harley Reversion Problem
s a Harley is a V twin, the firing sequence is not evenly paced. If you use #2 led on cylindr #1 then time it to fire correctly, the #1 lead on cylinder #2 will be way out of timing.
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RE: Harley Reversion Problem
Yours is not running right, and the symptoms you've reported point to an ignition problem or a valve problem. Expose the valve springs, crank it through a cycle with a wrench, and check the static timing of both cylinders and the valve operation.
Mike Halloran
Pembroke Pines, FL, USA
RE: Harley Reversion Problem
RE: Harley Reversion Problem
This problem has been like this ever since I got the bike. I changed all of the ignition components just to rule out a possible ignition problem.
That's really interesting about the misfires Harley has right out of the box.
Yes the ignition setup on these older Harleys are wasted spark systems.
I have done every check I possibly can. I have swapped the secondary ignition leads at the coil and nothing changes. I did a resistance check on the coil and everything looks good. I swapped ignition wires numerious times and nothing changed. The point gap is good on both the front and rear cylinder lobes.
I will check static timing on each cylinder when I can and see if that tells me anything.
Thanks again guys.
-Chris
RE: Harley Reversion Problem
Regards
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RE: Harley Reversion Problem
Welcome to the world of Harley ownership.
If your bike still has the stock waste fire "dual fire" ignition, that could likely be the problem. If the coil has 2 low voltage connections, it's dual fire, 3 terminals (or dual coils) for single fire. Just about any cam change requires a "single fire" ignition be installed, it will also improve low rpm running even on an unmodified engine so the investment won't be wasted. These systems aren't cheap, so people often remove them prior to selling the bike, to increase their bottom line a little.
Good Luck,
Bob D
RE: Harley Reversion Problem
1979 ironhead = sportster
sportster = 4 independent gear driven cams
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that makes it at least 16X more likely I'd mess up the timing on at least one of them.
Rather than pull the cover and check the various timing marks, I'd locate and record the actual valve opening and closing timing events.
RE: Harley Reversion Problem
I have not touched the plug gaps since I initially set em to factory specs.
The bike does still have the a dual fire ignition system. I had someone else recently tell to convert to a single fire setup as well. Problem is I don't have the cash at the moment to do so.
The sporty does have 4 cams but the marks are very easy to see and it would be very difficult to miss align even one of them. Also the teeth on the cams are pretty big so if one was off even a tooth it would be very apparent.
Thanks again guys.
-Chris
RE: Harley Reversion Problem
Regards
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RE: Harley Reversion Problem
"Have you tried closing the plug gap a bit."
The OP mentioned an idle misfire. That would indicated, if anything, the gap is too small, no?
(I'm going out on a limb here and aSSuming there is no misfire under load
RE: Harley Reversion Problem
Its hard to tell if its a misfire or not to be honest. I can feel (weak) pulses on my palm from the rear exhaust like its not missing a beat but every once and awhile I can feel and hear a good fire.
When I pull the rear spark plug wire off for a few seconds and put it back on I can get a few good fires until it goes right back to how it was.
I can't put a whole lot of load on it to be honest because my clutch is slipping really badly. Even in higher rpm's though the bike still just doesn't feel right.
This problem is very frustrating because I just cant figure it out. The front cylinder runs awesome but the back is just very weak.
Thank you again fellas.
-Chris
RE: Harley Reversion Problem
So it seems like it fires great for a short period of time in the morning with the choke on.
I can also get a few good fires after unplugging the rear cylinders spark plug wire for a few seconds and then plugging it back in.
Thanks guys.
-Chris
RE: Harley Reversion Problem
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RE: Harley Reversion Problem
RE: Harley Reversion Problem
Due to the uneven firing order of that engine, it will be impossible to get both cylinders running the same air/fuel ratio. Have you got any way of checking this - preferably in the exhaust of the cylinder that's running, without being mixed in the exhaust from the non-firing cylinder?
RE: Harley Reversion Problem
Brian
I forgot the problem was only at idle, so therefore if the rear mixture is lean, the idle system needs enrichment.
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RE: Harley Reversion Problem
I'm fairly sure that it is not a jetting or carb related problem because the front cylinder runs so nice.
I'm pretty sure its a mechanical related problem of some kind.
When I performed the cranking test I did it cold and warm and the rear cylinder still had compression warm.
I will loosen the rear push rods a little and see if that's helps at all.
The cams could very well be stamped wrong from the factory.
The only time I can get some color on the rear plug is when I ride the bike around a little. (putting what little bit of load I can on the engine because of my bad clutch)
Is there any way that maybe the rings might not be sealing while running?
Thanks again fellas.
-Chris
RE: Harley Reversion Problem
If the ring lands on the piston are worn you might get good static but poor running compression. Pistons damage lands if the motor is still used when it gets hot enough to substantially increase friction.
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RE: Harley Reversion Problem
Once I get the rear jug firing I would like to dual carb the engine as well as convert to a single fire ignition. This problem would be much easier to diagnose with the engine setup the way it should have been from the factory.
I was thinking about the cam thing tonight. The cams are numbered 1-4 from left to right. The #2 cam (rear cylinder intake) runs off of the crank and then drives all three of the other cams. If the #2 cam was off then both the intake and exhaust cams for the front cylinder would be off as well. Also, The points system runs off of the #2 cam.
So I guess we can all assume the #2 cam is fine because the front cylinder runs perfect. Both ignition timing as well as cam timing for that cylinder is ran off of the rear intake cam (#2).
With that being said it makes me wonder if something is up with the rear exhaust cam. I know its lined up cause I checked them awhile ago but it makes me wonder if maybe the lobe is worn or maybe it was stamped a tooth off from the factory. Also, I know the rear cylinders intake cam is timed right but the lobe on that cam could also be worn.
I'll loosen the push rods tomorrow and see if that helps. If it doesn't I may try to get a new cam set and see what happens. Any other ideas fellas?
-Chris
RE: Harley Reversion Problem
Roughly plot each valves movements. To do a perfect job, use a dial indicator, but for these purposes steel rule would do.
The idea is to determine actual valve position relative to crank and verify it is OK.
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RE: Harley Reversion Problem
Does your Harley have a double walled exhaust pipe? Inner wall can collapse causing excessive back pressure. Can't see the problem on the outside of the pipe; however, we would roll a large object through the pipe or test the back pressure if there was access. The problem can be a broken muffler baffle as well.
Does your Harley have hydraulic valve lifters? It is possible for a dirty/defective hydraulic lifter to pump up while operating (yes, even with proper spring tension) such that a valve does not completely close when running with oil pressure. Very annoying to find because everything is good when you run a compression check or turn the engine by hand. We used to back off the valve adjustment such that there would be clearance when the lifter's piston was fully extended. If this corrected the misfire, then disassembling and cleaning the hydraulic lifter would usually take care of the problem.
Does your Harley have a solid grind cam and hydraulic lifters? Similar test as described above. There can communication from the exhaust and intake runners. The misfiring cylinder will have a diluted charge that may be difficult to fire. Effectively it is excessive exhaust gas recirculation.
RE: Harley Reversion Problem
Cheers
I don't know anything but the people that do.
RE: Harley Reversion Problem
I loosened the rear push rods a little and its still running the same. I'm gonna try to get a hold of another set of cams, swap em in and see what happens.
I did get some info from the previous owner today. I guess it all started when he was riding the bike at a steady cruise. Out of no where power was lost and came back but to a limited degree. Every sense then the rear cylinder has been off.
Any other ideas until I try the cam swap?
Thanks again guys. I really do appreciate the help.
-Chris
RE: Harley Reversion Problem
That engine is roughly 29 years old, probably at least as tired as the clutch, and could have a lot of fairly unusual things gone wrong at its advanced age. Without numbers, we're shooting in the dark... and so are you.
Speaking of shots in the dark, at this point, considering the previous owner's report, rather than trying a cam swap, I'd pull the rear jug, and see, e.g. how many pieces of piston and ring fall out. Do stuff a rag in the crankcase before lifting the jug very far.
Mike Halloran
Pembroke Pines, FL, USA
RE: Harley Reversion Problem
The cranking numbers were 126 front and 125 rear. My manual says to expect over 120.
I have not measured valve lift but did make sure the cams were timed. The cams were timed and appeared to look fine.
The ignition timing looked fine but was kind of difficult to set for whatever reason.
I had it running yesterday for a bit and shut it off. I pulled the carb off and the intake manifold was soaked.
I'm fairly certain the rear cylinder is firing because it gets just as hot as the front cylinder. Also, the pulses out of the rear exhaust pipe are warm but the sound isn't the same as the front.
It just seems like fuel isn't being pulled to the rear cylinder. I'm also afraid that the rings might be cracked or something.
Like I stated earlier when I pull the rear plug wire while running and put it back on after a few seconds I can get a few good strong fires before it goes back to normal. I think its because fuel is collecting in that cylinder while the plug is not firing. When plugged back in it burns off that fuel. This is what leads me to believe the ignition timing is fine.
Thanks guys.
-Chris
RE: Harley Reversion Problem
But based on the news that something changed suddenly during a ride, I tend to agree that the rings cracked or otherwise went south.
RE: Harley Reversion Problem
That's probably the only thing I haven't checked and the rockers have crossed my mind one or twice. I haven't checked them because it just sounds so unlikely that something like that could be the cause but you never know.
I forgot to mention that the pulses coming from the rear exhaust feel very weak.
I will check a few things out tomorrow. Thanks again guys.
-Chris
RE: Harley Reversion Problem
I'd repeat with the rear plug lead.
I'd but 3 new plugs. I'd widen the gap on one to about 0.08 inch, and put it in the front lead and ground the shell, then crank/kick the engine. I'd expect a healthy blue spark. Then I'd put it in the front lead.
If the spark at both locations is fat and blue, I'd install the other 2 new spark plugs and see how it runs.
RE: Harley Reversion Problem
Had a similar situation on my Pan checked everything to no avail....... cause was an air leak into the rear cylinder from the inlet manifold.
Maybe worth a try.
RE: Harley Reversion Problem
I had a similar problem with my friends "79 Iron head. This bike had a history of being converted to Points ignition and them replaced every 6 months.It was also a pig to ride.I found the air supply to the emulsion tube was blocked. When you look into the air horn of the carb there is a brass tube about 4mm in diameter in the bottom section.I used cleaning products at first, but to no avail. I then had to use a peice of wire from a wire brush to clear the blockage.The problem this causes is the fuel isn't being Aerated. So it is delivered into the air stream in blobs.This causes the poor fuel mixture.It's an easy check and costs nothing to do.
Good luck
RE: Harley Reversion Problem
It's time to remove the rear cylinder's exhaust pipe and rod it out from front to back. See how big a marble you can get to roll through it.
Mike Halloran
Pembroke Pines, FL, USA
RE: Harley Reversion Problem
also agree with Patprimmer on the ring issue, if the cylinder had see high temps. or M/C was mistreated (as most older sportsters have) some ring land/piston damage could be possible. By what you mentioned earlier about "steam coming out" I'm assuming that you have the air filter off? I have seen where a filter element has gotten fuel/oil soaked, is the crankcase vented to the air filter housing?
RE: Harley Reversion Problem
I have the same problem with my 89 evo.Runs fine under load but misfires on rear cylinder at idle have checked all electrics, timing and carburation.
The stupid thing with mine though is that if i turn the idle up i can pull the front lead off and it will run but it is firing every 8 strokes not 4.
Strange??????
RE: Harley Reversion Problem
Is that a quetion or a simple statement. I it's a question how about starting your own threa instead of hiacking this one.
You cold also red flag your post here and save me the trouble. I looks so much better for you if you red flg it rather than if someone else does.
Regards
Pat
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RE: Harley Reversion Problem
Sorry for any inconveniance.
RE: Harley Reversion Problem
Its a common problem with old HDs to have a miss at idle ,through poor design and wear the points gap varies
Best option-: convert to electronic ignition
RE: Harley Reversion Problem
RE: Harley Reversion Problem
RE: Harley Reversion Problem
RE: Harley Reversion Problem
Regards
Pat
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