Harley Reversion Problem 1

[captain16vgti]

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

 

[patprimmer]

If it has poor fuel distribution due to manifold design, it may be perfect on one cylinder and lean on the other. The suitable compromise may be a bit rich on one and a bit lean on the other so neither run perfect but so both run OK.

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.



Regards

eng-tips, by professional engineers for professional engineers
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[captain16vgti]

Its hard for me to believe that its the dual fire ignition system or the intake manifold because these are stock parts. Of course stock doesn't mean its the best but they should at least work as intended.

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

 

[patprimmer]

find a way to accurately mark TDC and a workable number of degree increments. If I can't get hold of a degree wheel, on a car I count ring gear teeth and divide 360 by the number of teeth to get degrees per tooth, then count teeth.
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.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Zapster]

I am not a Harley guy; however, I owned/operated an automotive repair shop 30+ years ago. When I ran the shop, about every 3 months we would get an engine that would misfire on one or more cylinders similar to what captain16vgti describes. Everything mechanically/electrically would check out, valve spring tension, timing, spark, fuel system, etc. Three abnormalities that are difficult to see come to mind that would cause problems and were often overlooked by the line mechanics:

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.

 

[thundair]

I had a similar problem on an old Norton and after changing all the electrical, the barrel, the head and exhaust, (I had a bunch of them) the bike would load up and quit running in about 70 miles. In the end when I was ready to give up we degreed the cam and it was off from the manufacture.. My diagnostic ability was pretty raw back then.


Cheers

I don't know anything but the people that do.

 

[captain16vgti]

Thanks Zap for chiming in with all of those out of the box ideas. Right now that's exactly what I need but unfortunately none of those circumstances apply to me. My exhaust is single walled and my valve train is solid.

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

 

[MikeHalloran]

So far, you haven't reported an actual number, so it's not clear to me if you actually _measured_ the compression, the valve lift, and the cam and ignition timing, or have been using side of the road techiques, e.g. holding your thumb over a sparkplug hole while kicking it.

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

 

[captain16vgti]

Thanks Mike.

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

 

[RossABQ]

Another thing to check is the rockers. Unlike most engines, Sportster valve lash is set at the lifters with an adjustable pushrod. Your rocker bushings could be totally shot and only opening the valve enough to let in sufficient air at low RPMs to give a good compression reading.

But based on the news that something changed suddenly during a ride, I tend to agree that the rings cracked or otherwise went south.

 

[captain16vgti]

Thanks Ross.

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

 

[Tmoose]

I'd hook up an inductive timing light to the front plug lead and watch some reference mark on a component running at crank speed. It should be steady within a few degrees at constant rpm, never skip and increase smoothly when revved up.
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.

 

[finman]

Have you checked the seal between the inlet manifold and the rear cylinder?

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.

 

[brt650]

Hello,
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

 

[MikeHalloran]

The weak exhaust pulses, not much noise, runs ok for a while then runs out of power, etc., are the sort of symptoms you would get from a clogged catalytic converter if you had one.

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

 

[Lucky13]

Hello Gentleman, enjoy the site when I get chance to visit, the knowledge available is impressive. Have a question, does the bike have drag pipes? If so, the straight pipe can cause all types of reversion issues. Usually the rear cylinder runs slightly richer than the front because of the common manifold/single carb and inherent engine design. Wasn't doesn't get drawn into the front cylinder(air /fuel mixture) is in the manifold available to the rear cylinder.
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?

 

[mankind810]

Hello all.
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??????

 

[patprimmer]

Mankind

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
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[mankind810]

Its just a statement for captain16 to consider. He states in most of his posts that his bikes rear cylinder is faint and weak but does not mention if it can in any way run on the rear by itself.Thus if he tries what i have done and it works his problem may not be as bad or expensive to fix.
Sorry for any inconveniance.

 

[RGT58]

If you are still using the oem points setup check the points gap on BOTH lobes! they will be different .
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

 

[lwbrown]

if you are running a long drag pipe without baffles it could be reversion. at our shop we have fixed this problem on several bikes by putting a bolt across the the pipe near the end. it seems to break up reversion waves and cures the fuel standoff from the carb.