Intermittent backfire during acceleration

[Port]

I am trying to diagnose a strange new backfire/stumble issue i have

Specs:
1981 XS650 SH with
Ganzo Box ignition
BP7ES plugs
0.035" gaping
High output coil from Mikes
Carbs are well synced
Stock air boxes
Stock jetting (i believe)

Was running with no issue on a PAMCO before the Ganzo install
Starts first kick
Runs well in low range 70% of the time
No issue above 3000 RPM
All of the issue is between 2000 and 3000 rpm when accelerating
I swapped the plug leads and the issue remained predominantly on the left side
Used carb cleaner to check for vacuum leaks and found none

Description of the issue:
Sometimes, after a sustained high rev run >4000 RPM when i come to a stop the bike idles fine, no issue, maybe a little low rpm... when i come to try and accelerate i get significant backfiring from the left side and a loss of power. After a bit of this the bike seems to clear out (sometimes) after some more popping and then will run fine again and accelerate from a stop no issue and easily climb above 4k. Then SOMETHING will happen and it starts backfiring again after coming to another stop. in the 2000 RPM range. When the issue is happening, you can feel it before it ever backfires. In neutral it will be sluggish to get up to 2500 RPM and hover there for a bit. If you give it a little more throttle then it will backfire a bit and if you get up past ~2500 RPM then it will start to clear up. The problem seems to get worse/more likely the hotter the bike.

I pulled the plugs a couple of days ago and they were very dark and dry (rich?). Cleaned them up and ran em again. Same running issue but when i pulled the today they looked as they had been running lean. So im not sure yet when to take from the plugs. will check them again after another ride. How long is long enough to get a good idea if the engine in running rich or lean from the plugs.

Wondering if this issue is familiar to anyone before i break back into the carbs as they had been running well.

Possible issues:
Pilot jet adjustment?
New plugs?
Weak spark?
bad gas? should run higher octane?
debris somewhere in the carbs?

 

[Boog]

First of all brother, well written and awesome detail. I do not know all the troubleshooting steps to jump into next since I have not begun in earnest to tear down my own '81. Some Seafoam won't hurt in the tank for a few tanks of fuel. at least it will help clean the inside if there there is something in the fuel lines to the carbs.

I don't think timing is your issue, though I am not smart enough to say that with authority.

I suspect it may be in the fuel system somewhere. Or maybe the spark plug wires are old?

 

[5twins]

Your coil may be going bad. Many times when they do, they only act up when hot, kinda like yours is doing. A good low cost replacement is a Honda MP08. Details are here .....

http://www.xs650.com/threads/honda-mp08-coil.55408/

Or it could be the plug caps or their connections to the wires, especially if they're originals. They can and do go bad sometimes. Remove them and measure the resistance through them. Originals have a rather oddball rating of something like 8K ohms. When they go bad, that resistance starts climbing, eventually getting so high it begins to choke off the spark. If they measure OK, clip about 1/4" off the plug wires to get to some fresh wire before you re-install them. Honestly though, if I see original caps on one of these, the first thing I do is replace them with some new 5K ohm NGK caps. They're cheap, like $3 each. Also, prep the ends of the plug wires before installing the caps. Strip about 1/8" more of the insulation off and fan the wire strands out in a radial pattern like so .....

This will insure good contact between the wire and plug cap when you screw it on. I also coat the end of the wire with some dielectric grease before putting the cap on. I actually put it in a few more spots too ....

 

[Jim]

Call me silly, but I have an inherent distrust of electrical parts with MikesXS name attached to it. Maybe you posted this in the GN250 thread also? If it was you I suggested swapping plug leads and plugs to see if problem swapped sides? If it does, like 5twins points out the Honda MP08 coil is what I'd go with. If the problem stays on the left, I'd suspect the carb.
Fwiw... I'm running the GN250 box and Honda MP08 coil on my SG and they seem to be playing very nice with each other.

 

[Port]

Your coil may be going bad. Many times when they do, they only act up when hot, kinda like yours is doing. A good low cost replacement is a Honda MP08. Details are here .....

replace them with some new 5K ohm NGK caps. They're cheap, like $3 each. Also, prep the ends of the plug wires before installing the caps. Strip about 1/8" more of the insulation off and fan the wire strands out in a radial pattern like so .....

Just ordered a set of MP08 coils to swap over to. During some trouble shooting a few weeks back i fried some stuff while bypassing my reg/reck and afterwords i could hear a hissing coming from my coil. After letting it sit for a few hours it tested good and has been "working" since. But, now i dont trust it and i hate the way the plug wires are routed so i went a head and ordered the MP08s and now ill have backups.

Im already running 5K ohm NGK caps on new cplug wires. I did just cut a bit off and reconnected them as you suggested which looks like it was needed.

Maybe you posted this in the GN250 thread also? If it was you I suggested swapping plug leads and plugs to see if problem swapped sides? If it does, like 5twins points out the Honda MP08 coil is what I'd go with. If the problem stays on the left, I'd suspect the carb.
Fwiw... I'm running the GN250 box and Honda MP08 coil on my SG and they seem to be playing very nice with each other.

Yeah, that was me. I thought i had fixed it but that's when i learned it was intermittent. I didn't think the issue was strictly relevant to the thread anymore so i started this one. I did swap the plugs and it seemed that not to stay mostly on the left but i did hear one or two light pops on the right which was new. gogint o go ahead and get coils im confident in before digging into the carbs again.
-----------

What values should i expect to read off of the MP08 to verify they are good before instillation?
1. Using the lowest scale on the meter, measure the resistance between the primary terminals with the wires removed. Should read between: xxxx - xxxx Ohms
2. Using the highest scale on the meter, measure between one of the primary terminals and the center core of the coil. Should read: Open circuit
3. Measure between one of the primary terminals and one of the plug wire terminals. Should read: Open circuit
4. Measure between one of the plug wire terminals and the core of the coil. Should read: Open circuit
5. Measure from one plug terminal to the other. Should read between: xxxx - xxxx Ohms

 

[Jim]

Just ordered a set of MP08 coils to swap over to. During some trouble shooting a few weeks back i fried some stuff while bypassing my reg/reck and afterwords i could hear a hissing coming from my coil. After letting it sit for a few hours it tested good and has been "working" since. But, now i dont trust it and i hate the way the plug wires are routed so i went a head and ordered the MP08s and now ill have backups.

Im already running 5K ohm NGK caps on new cplug wires. I did just cut a bit off and reconnected them as you suggested which looks like it was needed.



Yeah, that was me. I thought i had fixed it but that's when i learned it was intermittent. I didn't think the issue was strictly relevant to the thread anymore so i started this one. I did swap the plugs and it seemed that not to stay mostly on the left but i did hear one or two light pops on the right which was new. gogint o go ahead and get coils im confident in before digging into the carbs again.
-----------

What values should i expect to read off of the MP08 to verify they are good before instillation?
1. Using the lowest scale on the meter, measure the resistance between the primary terminals with the wires removed. Should read between: xxxx - xxxx Ohms
2. Using the highest scale on the meter, measure between one of the primary terminals and the center core of the coil. Should read: Open circuit
3. Measure between one of the primary terminals and one of the plug wire terminals. Should read: Open circuit
4. Measure between one of the plug wire terminals and the core of the coil. Should read: Open circuit
5. Measure from one plug terminal to the other. Should read between: xxxx - xxxx Ohms

The primary (both wire connections) should be about 3Ω.... and open to ground (the frame).
The secondary is about 14KΩ between the 2 HT leads. It's a floating secondary so it should be open between the HT leads, the wire connections and ground.

 

[Port]

The primary (both wire connections) should be about 3Ω.... and open to ground (the frame).
The secondary is about 14KΩ between the 2 HT leads. It's a floating secondary so it should be open between the HT leads, the wire connections and ground.

The 14KΩ does not include the 5KΩ resistance of the each of the caps, correct?

 

[Jim]

The 14KΩ does not include the 5KΩ resistance of the each of the caps, correct?

Correct. Does not include the caps.

 

[bikefreakjon]

Two things:

1, it ran well before he swapped ignition parts!

2, 3000 rpm is about when full timing advance is achieved.

Hmm...

 

[Port]

Correct. Does not include the caps.

Thanks Jim the coils showed up today so ill get them installed asap

Two things:

1, it ran well before he swapped ignition parts!

2, 3000 rpm is about when full timing advance is achieved.

Hmm...

How dare you suggest this unproven ignition system might have something to do with my ignition issue. that being said, i dont think it is the box as the issue is intermittent and unless the particular box were defective, which is possible, then it seems unlikely. That, on top of the fact that i heard the coil hissing after a self induced over voltage i decided to start there.

 

[GLJ]

How dare you suggest this unproven ignition system might have something to do with my ignition issue.

I like your sense of humor.

 

[Port]

So i got the MP08 installed and went for a ride. Definitely a major improvement with the backfiring 95% solved. Still a little bit of an issue starting from a stop causing low power and requiring higher revs.

When installing the new coil i noticed that the plug wires each had a bit of scorching right where the wires exited the coil. Couldn't get a clear understanding of what caused this. I installed the MP08 with the plug wires that came with it and swapped out my 5K ohm NGK caps.

I suspect the bit of stumble/low power coming out of idle/stop is from a slightly out of tune idle mix screw. If i babysit the throttle while idling, give the throttle a blip or three prier to pulling away, or if i come to a stop and immediately pull away then the issue does not present itself. It seems to help to rev up to about 3K while engaging the clutch otherwise the engine wants to stumble under the load. Im going to give the dead cylinder method a try tomorrow and see if i can get the idle tuned in.

 

[Port]

Update: Mixed news

Did Idle Mixture Screw adjustment with dead cylinder method. Its idling better which i assume is due to the two cylinders matching better but i am now getting backfiring and power loss form both cylinders pretty evenly. Definitely worse when the engine is hot after a sustained few minutes at 4K RPM. Seems like i made the issue a little bit worse but now i think im looking in the right place.

One thing that was pretty concerning when doing the adjustment; I adjusted both of the needles in over a turn and a half but lost count. I felt the screw start to bottom out before the RPM started to drop. I used a rebuild kit a while back and have read these parts can be wrong in most kits.

One qualifying factor; I noticed the headlight was very dim when i pulled back into the garage. I might have drained the batter while doing the Dead Cylinder as the bike was running around 800 RPM for a while. I am going to charge up the batter and see if the issue might be due to week spark from low voltage but i am not betting that this is the case.

 

[bikefreakjon]

Or just attach a jumper battery

 

[Port]

Or just attach a jumper battery

I should have when i was doing the adjustment. I will definitely will do so in the future.

 

[Port]

Ok I think that I have it figured out. I was searching around more and found a few threads talking about weak pickup magnets for TCI systems that pretty well describe my issue. Years ago when I first got the bike I think this might have been the issue that cause be to install the Pamco. I spent many hours troubleshooting and couldn't resolve a similar issue so I bailed on the TCI and installed the Pamco so recently when I fried my Pamco and installed the Ganzo box I reintroduced the issue.

I unplugged my Reg/Rec to de-energize the charging system and the bike ran great. I ordered a 5mm x 1mm magnet to glue on over the existing one. I've read that a magnet can fit under the pickup but didn't see specific dimensions but I can shim the pickup a bit if need be. The one question i have is what to use to glue on the new magnet...? JB Weld or just some high temp 2 part epoxy or is there a better option?

@Jim Does I know in the Ganzo thread y'all have been talking about adding magnets to non-TCI rotors but this would be worth adding to any Ganzo guide that gets generated. I'll post over in the Ganzo thread if the magnet solves the issue.

http://www.xs650.com/threads/bad-reg-rec.28639/#post-286333
http://www.xs650.com/threads/1981-xs650-misfiring-video.11827

 

[Paul Sutton]

While waiting for your magnet to arrive just clean the top of the original magnet with a fine piece of wet and dry. This has been known to solve the issue.

When I added a magnet on top of the stock one I used ordinary clear two part epoxy glue. I spread the glue about 5mm all around the magnet and it stayed in place for about 1 Year before converting to a Boyer Bransden ignition.

 

[Port]

While waiting for your magnet to arrive just clean the top of the original magnet with a fine piece of wet and dry. This has been known to solve the issue.

When I added a magnet on top of the stock one I used ordinary clear two part epoxy glue. I spread the glue about 5mm all around the magnet and it stayed in place for about 1 Year before converting to a Boyer Bransden ignition.

I had a few other bits off while waiting for the magnet so i didnt try it after cleaning up the surface of the magnet but after installing the one I ordered the bike is running beautifully! That was definitely the issue and now i have a coil that i trust and two back ups, so that's nice.