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]

It lost a lobe.

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.

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.

 

[captain16vgti]

Thanks for the quick reply.

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

 

[patprimmer]

Re ignition, new is not always OK. Did the problem start when you replced some igniton parts.

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.

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.

 

[MikeHalloran]

There's only one carb. When H-D first went to fuel injection, the engines didn't sound 'right'. A fair amount of research (I think documented in an SAE paper) revealed that, because of the dynamics of gas flow in the shared intake manifold, five of every twelve cycles produce a misfire in a carbureted Harley that's running perfectly. So the fuelie computer had to be reprogrammed to simulate misfires in order to get the sound right.

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

 

[thruthefence]

Please correct me, but doesn't the Harley v twin fire off of one coil, with two secondary leads? One jug being on the power stroke, & the other is on exhaust? A sort of "wasted spark" arrangement? That is, both plugs fire at the same time, but only one does any 'work'. This would suggest swapping the spark plug leads front to back,seeing if the symptoms follow the lead, or checking the coil resistance for that problematic rear cylinder.

 

[captain16vgti]

Thanks for the replies fellas.

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

 

[patprimmer]

Have you tried closing the plug gap a bit.

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.

 

[socrace]

Hi Chris,
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

 

[Tmoose]

The next part I'd buy would not be a part, but a tool, a degree wheel. They can also be downloaded and printed.

1979 ironhead = sportster

sportster = 4 independent gear driven cams

http://lh6.ggpht.com/_gAeOQKjnQms/RzgWB1UCf5I/AAAAAAAAAJk/WgS6QgH8HJw/100_1389.JPG

http://home.sandiego.edu/~ekim/harley/tstorm/bike1002o.jpg

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.

 

[captain16vgti]

Thanks again for the help guys.

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

 

[patprimmer]

One tooth out normally means it won't run or it bends valves or both

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.

 

[Lou Scannon]

Pat,
"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 )

 

[captain16vgti]

I swapped the rear head today just to see what happens and its still running the same.

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

 

[captain16vgti]

Another thing I noticed is that the rear cylinder sounds like its firing great when first started (cold) with the choke on. It sound great for maybe 20 or 30 seconds and then it sounds like the rear cylinder falls off without me even touching anything.

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

 

[patprimmer]

Have you tried a richer main jet

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.

 

[swall]

I am thinking that your valve clearances for the rear cylinder are set too tight. As the engine warms up, you loose clearance and the valves aren't closing all the way. You would have missed this with your compression check if it was done on a cold engine. A remote possibility is that one of the rear cylinder cams is made wrong--timing mark in the wrong place relative to lobe position.

 

[BrianPetersen]

If this is an air/fuel ratio problem, it will be in the pilot or idle circuit of the carb, not the main jet.

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?

 

[patprimmer]

I agree with Swall. The rear cylinder will run hotter and my close the tappets to the point of a compression leak when it heats up.

Brian
I forgot the problem was only at idle, so therefore if the rear mixture is lean, the idle system needs enrichment.

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.

 

[captain16vgti]

Thanks for the help guys.

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