I have a friend who brought me his 1998 Evo Softail claiming that it was dying on him running down the road, although whenever I would start it or ride it I couldn't get it to die on me. Also it was leaking oil from the rocker boxes. I did a whole topend gasket kit on it which solved the leaking problems. I let it set for a week or two over Xmas before I could get back to it. The whole time I had my trickle charger on the battery. When I came back to it, I tried to start it and when I finally did get it started, only the front cylinder was firing. I turned it off, double checked the placement of the spark plug wires on the plugs, double checked the gap (both at .040), both plugs are getting fire. Started it again and it's the same thing. Only firing on the front cylinder. I checked the plugs again and noticed that the front spark plug spark is larger than what the rear one is, and the rear spark plug does have fuel on it when I pull it out of the cylinder. The only thing I can think of right now is that the electronic ignition might be going out. Does anyone have any other ideas?

 

Not likely that a stock ignition "going out" would cause it to fire on one cylinder...it fires both plugs at the same time...so if it is not the plug wires or the plugs themselves...you need to check the compression.

 

Hi,

When you ran it before christmas and after you replaced the gaskets, did it run OK then-(on both cylinders)?

You have two different spark plugs...Get new ones and try again.

Ignition, is it dual fire or single fire? You can swap the leads around if it's dual fire and see if the working cylinder switches with them.

The original issue was the bike dies while running, if it's none of the above then it could be a bad coil. That is one of the symptoms, dieing for no obvious reason and it's not impossible to loose one cylinder with a bad one as well..

Few easy things to try befor we get carried away..

Ds

 

Waste Spark ignition fires both cylinders at the same time. You need compression, spark and fuel to run. You stated the spark is there and the non-firing cylinder plug is wet with fuel. Leaves compression, you replaced rocker box gaskets, did you have adjustable pushrods or no-adjustable? The pushrods non-adjustable are color coded, did you mix you intake and exhaust and now have a valve staying open which will give you no compression?

 

Found this on the net, not sure it is correct but several techs agreed

Purple, Blue, Yellow, Green from back cylinder to front......***** Bought Yields Gonnerea....as taught in HD school

 

Small engine manufacturers have been putting small bumps on exhaust cam profiles for years in their effort to reduce startup compression. The concept is at cranking speeds the cylinder bleeds a little compression making it easier to start and at normal operating speeds the small bump happens so fast that no cylinder leakdown is detected. It is possible to have a cylinder fire under compression at higher RPM's but not at slower RPM's as leakdown is a function of time and the extra lift.

***** Bought Yields Gonnerea
OEM Pushrod Color Codes
Front Exhaust is Green
Front Intake is Yellow
Rear Intake is Blue
Rear Exhaust is Purple

 

The engine has non adjustable pushrods and they are in the correct order PBYG front to back. When I did the gasket kit I made sure and double checked the order of the pushrods. I had duty today on base so wasnt able to mess with it, but I'm gonna mess with it again tomorrow. I'll do a compression check on it and see how that comes out.

I was talking it over with a local wrench and he was saying that if the battery gets below a certain voltage it runs the risk of burning out the electronic ignition which would only make it possibly fire on one cylinder. Not sure how true that is, just throwing it out there.

Ill get back in the garage tomorrow and take all these suggestions so far and see what I come up with. Thanks so much so far for everything!!

 

Very unlikely to run on one cyl due to ign burnt out....its both or nothing usually.

New plugs is the first place to start with an Evo.

 

No expert here, but I did have a similar problem on my 1988 FLHTC. When out riding with a buddy the bike began to run rough, backfire, and RPMs dropped to half what was normal for the speed I was going. I assumed that meant she was only running on one cylinder , but again, I'm not an expert. Oh, and the battery was DEAD! So, I got her home. Put the charger on her and charged the battery up and she started and ran fine.

That's when I checked the stator output and found my stator was bad, explaining the dead battery. So anyway, I replaced the stator (and compensating sprocket while I was in there) and she's been running like a scalded cat ever since. That was about 2000 miles ago.

So yes, in my experience, low battery voltage can cause the bike to either run on one cylinder or seem like it is. So a real cheap easy check would be to charge your battery fully and see if it makes a difference. If it does, then check your battery and charging system.

Just my 2 cents.

 

During the compression check, stick your finger in the hole and cycle through a round to confirm both intake suction and compression pressure to confirm the valves are opening and closing as expected. The compression check will confirm adequate cylinder pressure to burn. Assuming the pushrods are right, it it possible on an EVO to leave a rocker assembly bolt loose and loose the cam lift on a valve.

As for the ignition. Most are waste spark ignition meaning both cylinders fire at the same time, 1 on compression and 1 on exhaust. If the electronic ignition is firing 1 cylinder it is also firing the other unless...you have a fouled plug or bad wire. Simply swap the plugs front to back and try again. If the problem follows the plug change them. If not swap the wires front to back and see if the problem follows the wires. If no for both you should stop looking at the ignition.