Not Firing on 1 and 2 Usually

Like the title says, my 1980 xj650 maxim is not firing on cylinders 1 and 2 all the time. It goes in and out intermittently, but it just really isn't firing on those 2. I've checked all the wiring, it looks like everything is good. There is spark on every single cylinder and it looks like a pretty strong spark. The resistance of the plugs is just the one last thing I am going to try to do before testing compression and possibly having to rebuild the engine. I had 5k ohm plugs with 5k boots which is 5k out of spec. I am getting new valve shims this Friday, but I don't know if that will fix the issue (really hoping it does though). When I got the bike a few weeks ago I cleaned the carbs and made pretty darn sure they seemed like they would work before I had to wrestle them back in the bike. Cylinder 2 seems like it works a lot better and the exhaust pipe actually feels warm after some time, not hot like 3 and 4 but like it works reasonably. Although 1 barely feels lukewarm at all. I am hoping it is the plugs, but am thinking it may be a compression issue. Have you guys had any experience on this? (extra info: my bike has got 48k miles and the only service I know has been done was the carbs were re-jetted for Colorado and the starter is new, so I know some things have been done, but not much)

 

you should not have resistor plugs.

swap plugs from cyl 1 and 2 into cyl 3 and 4 see if the problem follows the plugs if not
next swap the plug caps see if problem folows caps

XJ650 models:

Pick-up coils:
1980-81 XJ650 Maxim and Midnight Maxim: 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
1982 XJ650RJ Seca (non-yics engines): 700 ohms +/- 20% = 560 ohms to 840 ohms acceptable range
1982-84 XJ650 Maxim: 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
1982 XJ650RJC Seca (yics engine): 650 ohms +/- 20% = 520 ohms to 780 ohms acceptable range
1982-83 XJ650 Turbo: 120 ohms +/- 20% = 96 ohms to 144 ohms acceptable range
Ignition Coils:
Primary side (input from main wiring harness):
2.5 ohms +/- 10% = 2.25 ohms - 2.75 ohms acceptable range

Secondary side (spark plug wires, without their end caps):
11K ohms +/- 20% = 8,800 ohms - 13,200 ohms acceptable range

Spark plug caps:
5K +/- 20% = 4,000 to 6,000 ohms per cap acceptable range

Spark plugs:
0 ohms per plug

 

I just got 4 new plugs in today and will test them out tomorrow. They all showed 0 ohms of resistance this time, and hopefully they are good to go after I gap them properly. The caps are all at 5k ohms +- about 50 which is perfectly specked. I will try swapping the caps but since they all are in good shape I think its a different issue, but I will test it tomorrow. I'll also take a look at the ignition coils and pickup coils as well, but since there is a pretty good spark, I am not sure its the issue. Thanks for the chart. I've seen it floating all around this forum everywhere, and its very helpful!

 

Update: cleaned the carbs, fixed most issues with the bike. It was running super rich in 3 and 4. I got 3 to be better, 1 and 2 are lean, and 3 is now oily. After riding my bike, and trying to figure out why cylinders 1 and 2 are running lean, what 3 is up to, and why 4 is rich, 3 randomly started getting oily during my vacuum sync test. I don’t have a color tune yet as my friend with a seca will be getting one. I pulled the carbs again to see if that’s my fuel issue or floats set wrong (I forgot to set floats before putting on carbs so had to do it anyways). Also it runs beautifully in the first 5-10 miles of riding and then kind of stutters and struggles to accelerate around 3.5k rpm and sometimes 5k rpm after the bike is hot. I’m doing an oil change soon to see if there is gas in the system, but I’m unsure what to do... compression test will be coming soon but I have no access to a tool for that. What would cause cylinder 3 to randomly get oily like this? It’s the plug tip. Not the threads so nothing is leaking through the top. The exhaust also smells a bit like unburied gas, and I’m getting ~30 mpg too :/ any advise from you guys? (Also it’s got an aftermarket exhaust, and also has jets adjusted for it. The owner said it got 40 mpg when he owned it)

 

Can you describe your process here? I'll repeat what I read on this forum "40 year old carbs don't need cleaning, they need rebuilding".

I suggest reading the "church of clean" thread on this forum.

I think you need to completely disassemble the carbs down to the bare bodies, follow the advice in "the church of clean" in XJ4ever section.

 

Sorry, That’s what I did. I completely tore them down, replaced throttle shaft seals, cleaned every nook and cranny. Then threw them in my ultrasonic cleaner to be 100% sure. I don’t think there is a surface left untouched on the carbs.

 

OK good. Did you make sure the tiny passages in the throat were clear by spraying carb cleaner through them?

How many turns out do you have the mixture screws? Were you successful getting it to idle at 1000rpm and all 4 synched?

I read that it was jetted for Colorado (suggesting leaner) and I read it is jetted for an aftermarket exhaust (suggesting richer).
What jets do you have in there?

 

Yes I sprayed carb cleaner through the tiny passages. Everything seemed clear. I will spray them again just to make sure.

I was unable to get them vacuum synched. The throttle would stick at 3k rpm and wouldn't go down while synching it. This would also sometimes happen during a ride. The throttle would stick to around 2k-3k rpm once the engine was hot. 1 and 2 are both out 3 full turns. 3 is out 2.5 turns, and 4 is out 1/2 a turn as it is still sooty.

When I originally bought the bike, the owner said that he got it jetted it for Colorado, but he also got a new exhaust. I assumed the shop he went to tuned the bike for both Colorado and the exhaust. The big jet looks like a 110, and the small one is a 40. The air intake jets (dont know how else to explain them) are all 36, and the jets on the diaphram side are 50 and 195.

 

Sorry, should have also asked if you have carb cleaner flowing through the thin tubes in the bowls?
They are very tiny and easily plugged which might be why 1-2 are reluctant to fire.

 

that misfiring issue was fixed with a second carb cleaning. I am now wondering why it stutters once the bike is hot, and why the plugs are lean/too rich and why 3 is kinda oily. 3 got oily randomly during the vacuum sync. I haven't had a problem with it before.

 

Can we go back a step and make sure that the plug wires are routed correctly?

As sitting on the bike:
Left coil fires 1 and 4 (orange primary wire)
Right coil fires 2 and 3 (grey primary wire)

 

Have valve clearances been checked?

 

Yes. I checked, and re-shimmed those a few weeks ago. Since then, I've probably only ridden <200 miles so they should still be good. The plug wires are routed correctly as far as I can tell.

 

You said you were unable to get them synched and your mixture screws are all over the place.
The bike is not synched so it's never going to run right.
It really shouldn't be leaving the garage in this condition. The fact you've ridden 200 miles like this suggest it is not getting fuel on 1-2 at idle, I'm assuming it kicks in on the mains later as you wouldn't get around the block on the 2 remaining cylinders.
You mentioned a compression check is on your to do list and I agree that might tell you something.
I still suspect you've got some passages plugged in 1-2 carbs. How are the carb diaphragms and are they correctly seated?

 

1 and 2 are running fine now and are getting fuel on idle as well as when I accelerate. The bike sounds great idling when it idles at 1k rpm. All 4 cylinders are doing great when I start the bike up. All the diaphragms are in good condition, and correctly seated with the little notch in the correct place. I will run some carb cleaner through the passages to make sure they are clean. By it not being synched do you mean take a vacuum gauge and adjust the butterfly valves to make the same vacuum? or sync them with a paperclip while the carb is still off the bike? I am also going to add some more grease to the shaft seals, as I could have a vacuum leak which could also cause this...

 

A running vacuum synch is necessary.

 

Ahh ok. I have one gauge, so I will use that to perform the vacuum synch. Ill update once I have finished checking the carbs, and have done a synch.

 

I wouldn't attempt that with a single vacuum gauge.
I know some have made their own with glass jars and such, sounds clumsy to me.
Buy the Motion Pro stick I've attached and your good for life.
Nice and compact, hangs on the wall out of way. Costs the same as 1 current shop labour hour.

https://www.baysideperformance.com/...MI7tqtiNGo7gIVRODACh2oWwXVEAQYASABEgK3avD_BwE

 

Okay. I was hoping I didn't have to spend money on one of those, but using your logic, it sounds like a good investment. I could even charge to tune my friends carbs haha. Are these better than 4 vacuum gauges?

 

I'm not sure if they're better, likely cheaper and takes up less space.
I bought a mercury stick 30 years ago, still using it but the tubing is getting stiff, might have to replace that.
I noticed they no longer use mercury in that add.

 

I would, and have. No big deal, just a bit of extra time.

 

Use the single gauge, or build a simple 2-bottle manometer.

How To: Make a 2 bottle synch tool

A stick-type manometer is wonderful to have, but not needed unless you're working on bikes all the time or want to invest in tools that you hardly ever use.

 

As a happy user of 4 vacuum gauges I can say with certainty that when they eventually need replaced, I'll be buying the Carbtune.
I've had these gauges for decades and they're much better than the outwardly identical cheapo gauges on ebay / amazon - these are the originals.
However, they won't last forever, and the reason I bought them at the time was the only other ones available were mercury based, which I didn't want.

 

Two bottle manometer works great. Easy to make and inexpensive. I used glass baby bottles. I agree with k-moe, the stick type works well, but until you get it running well I wouldn't spend the money. You will probably need the money for something else.