Backfiring worse when hot

82 XJ650 Maxim, backfiring. In an earlier post I thought it was electrical. Certainly didn't help the situation, but didn't fix it when I sorted it out either. Took it out tonight for just a few kilometres and it started backfiring on me again. Thing is it's not so bad when the bike is first started. After it heats up is when it gets really bad. 5-10 minutes into the ride it starts popping... loss of power... worse and worse, as time goes on. Pulled it over for a bit to let it cool, managed to make it home. Even after 10-15 minutes still have ride with the choke in. Should be fairly warm by then. Could it just be so super lean that it requires choke to stay alive?

So, I've looked over the electrical pretty well... everything seems fairly strong now. Just ran a bit of Seafoam through the crankcase, drained from forward plug, middle gear plug, changed filter, refilled with about 2.65L of 20W/50. I don't think that's too much oil.. is it? Now it's not even starting really. Get about 5 seconds out of it, then it dies.

Now, my tools are still enroute to my new location. By next week I should be able to pull the plugs to see how each cylinder is running. I will then adjust the idle mixture screws all the way in, then back out 2-1/2 to 3 turns as appears to be the recommendation here. Until then, I'd love to hear some more guesses as to what the issue is.

Why do you think it gets so much worse when the bike gets hot? Seems to me if the mixture was off it would be bad to start. I guess the popping could take a while to start, since the exhaust has to heat up to ignite the fuel after the combustion chamber... but why is power loss and hesitation so much worse when hot as well?

I will try starting the bike again tomorrow. The battery was pretty low when I tried starting it tonight, so I figured out how to push start it myself. A useful skill to have in any case.

 

Lean = HOT

Backfire happening ...
LEAN, again ... malfunction related to the air to fuel ratio.
Usually, backfiring occurs in carbureted engines that are running lean where the air fuel mixture has insufficient fuel.
("Running lean" is typically a sign of mal-adjusted carburetors where there is not enough fuel for the amount of air).

Don't let an Air Cooled engine overheat.
Bad things happen in rapid succession.

Let's find-out why you are running Lean and fix that ... before we get to the point where something happens ... we can't fix!

 

General backfire guide:

When does the Popping happen?

If you are slowing down and therefore backing off on the throttle does it pop then?

The popping could be a lean backfire.

Lean is BAD!

If you get popping on acceleration check the exaust gaskets for leaks.

Popping on idle (and hesitation or surging at even throttle) check plugs and coils. Coils (or leads) breaking down under load.

 

Had the same thing happen with a car I brought. Started fine, longer I drove worse it got, hesitating and loosing power, by the time I got home could hardly do 5 MPH in first.. Answer: PLUG leads breaking down as they got hotter. New set of leads, still going strong 3 years and 80,000 km later.

New leads on XJ Coils

Oil: sight galss on right side of engine case, bike on level ground with centre stand used, oil at top (just) of sight galss.

 

Is it backfiring out the muffler or back through the carbs? Did you do anything to the bike just before this started?

 

Because your mixture is so far off (has to run on choke) I'd be looking there for your problem first, but, what you are describing sounds more like valve adjustment to me.

 

Haven't really done anything to it since I got it. Took it in to get certified roadworthy, and the mechanic put new plugs in. That's it really. First day I had it out for a couple of hours, and it ran pretty well. Making a little noise just before I took it in. Took it out later that evening and it started to sound more and more rough. In an earlier post I talked about the electrical problems I was having, and the beginning of power loss. Left it out overnight, then returned the next day to get it. By the time I got it home it was backfiring really badly. Now it gets bad faster and faster, as the bike warms up.

Maybe it's a problem with the mixture, which fouls the spark plug as time goes on making the backfiring worse and worse. However, I think it's a lean backfire. Left tail pipe is blueing just before the header. So, it's hot.. and if it's lean... that probably wouldn't foul a plug, would it? It would just be "super clean", right?

I believe it is backfiring out of the tailpipe. I think I can test the coils and wires and adjust the idle mixture screws with the tools I have on hand, so I'll try to do that when I get home tonight.

 

Actually ... you might have a "Combination of ingredients" causing your problems.

If your bike isn't making enough Electrical Power ... you start to have problems as the Battery ... not being charged-up by the Alternator ... falls below the power it needs to keep everything running right.

I'd check the Alternator Brushes and do a test to see how the Charging System is putting-out.

You should get a hair above 14-Volts happening when the bike is revving-up just over 17-hundred rpm's.

If not ... you become dependent on the Battery ... which cannot sustain the demand to keep things running very long without the bike beginning to:

Lose power.
Stall-out
Backfire
Ignition failure
Turn signals not working
Horn not playing
Headlight going off
Instruments going dim
Slowing down .... and, eventually
Rolling to a stop ... Dead in the water!

A Brand New - Fully Charged Battery - won't help the situation ... unless there's a couple of extra Volts being made, by the charging system, to let the Battery be getting a little charged-up while your cruising.

Getting a reading on the Charging System is going to tell us a lot!

This potential issue ... combined with Carbs set-up Lean isn't a good situation for the bike.

When you're running ... your running HOT.
When the Alternator and Regulator try to keep you running ... they both get over-worked.

The Brushes will try try to keep you in the game. If their too short ... they try to make-up the distance by arcing across to the Alternator Rotor.
Eventually, the arc is going to be just strong enough to burn the face of the rotor ... or, weld itself to a slow spinning rotor and break-off.

You have a number of systems and components at risk.
You need to Black Flag yourself and take a long Pit Stop to shake it all down.

Fill-out the "Signature" portion of your account with Bike stat thumbs.
_____________________________________________________
Year - Model - MILES - Stock or Mods - YICS Y/N?

We'll help you get it back right.

First thing ...
Undo the 3 Allen's holding-on the Alternator Cover and measure how much Brush Length you got left.
If they are below 11mm long ... a big chunk of your mystery is solved.

 

Stop in at the shop on your way and buy a spark plug spanner and some new spark plugs. Checking the condition of the spark plugs will tell you alot about what/where things might be going wrong.

Check out which number your spark plugs look like here:

Spark plug reading guide

If a spark plug is fowled changes you make to other areas are not going to help.

 

Deleted by author

 

Before we start Seafoaming and resistance checking; can we get an eyeball on the Alternator Brushes ... please?

Before we all set-off in the rowboat to go fishing ... can we check and see if the oars are long enough to reach the water!

 

Okay,

Primary coils both about 1.8 Ohms. One secondary looks to be right around 11K Ohms, the second... I can't get a reading on. Somebody has already replaced the plug caps with NGKs, and one of them was loose. Twisted it back and still nothing. No reading... what to do?

Pulled the plugs and they are black, black, black. Number 3 on that scale, Kiwi. So I guess that means I'm running rich, or an ignition problem. Since one of the coils seems okay, but all four plugs are black... so problem is further back? Alternator?

RickCoMatic, I'll see if I can find the set of Allen keys I know I saw around this house... I'll check out the alternator brushes.

 

Oops.. I'll tell you what I'm actually reading on the meter. Set it to 200K Ohm range, shows up as 22.2 on the meter for the secondary. Set it to 200 Ohm range, shows 3.8-3.9 on the meter for both primaries. I think I magically did some dividing there...

 

OK 21 K ohms +- 20% at 20 degrees C with the sparkplug caps on is right. The Caps have a 5 K ohm resistance in them, with caps off leads are 11 K ohm.

Other coil with no reading:
Test each cap should be at 5 K each and aftermarket NGK ones have this written on them. The caps un screw. Test the leads without the caps on also.

Caps could be faulty. Leads could be faulty. Coils could be faulty.
If you get no reading with caps off on the leads try the replacing leads link, test with leads removed from coil to see if coils them selves are still ok.

Put your meter on the R x 1 scale to test the little wires that you got no reading on they should be at 2.5 ohms +- 10% at 20 degrees C. 3.8 ohms seems high.

See attached picture.

Black sooty plugs will not be helping things but are a symptom rather than the cause in this case (I guess :wink: ) check the alternator brushes etc before going further. Then: Rectify the bad coil problem, replace the sparkplugs

 

Okey, checked the alternator brushes. Best ruler I could find is a scale draftsman's ruler (I think). I get 8.5 20ths of inch for one (10.6mm) and 9.5 20ths of an inch for another (11.9mm).

I took the caps off and put the leads right on the wire before -- nothing. I'm not sure why I'm getting absolutely no reading... you'd think if it was dead that I would have had a bigger problem than just some popping. Couldn't really see a bit of wire in the ends. Maybe it's deep in the insulated portion.

The smaller wires on my bike connect to a plastic connector, and I measured from that. Could there be a bit more resistance there, due to corrosion?

I'm open to more suggestions. I'll double check that coil tomorrow... so, what do you think? Could it be that my previous severe electrical problem put too much resistance in the system, brutally fouling the plugs with bad spark? Strange that it get worse when it's warm though... ugh. Help! Can I clean up the plugs a bit, carefully with a steel brush or some sandpaper?

At any rate, I took the tank off, which I hadn't even done before. Pretty easy to get around this thing.

 

New Brushes are 17mm
You're borderline bad. I'd replace them!

I'd clean-cut an eight of an inch off the Spark Plug Wires and strip some Ignition wire and stuff the ends of the Spark Plugs Wires with some strands of new wire to give the screw-ons some "Bite"

Clean the Ignition Pick-up's with some Isopropal Alcohol and a nylon toothbrush.

Pull the Connectors out of the Ignitor and Clean-off any corrosion.

 

Sounds like a plan Rick. I'll order the brushes tomorrow and try to clean up the wires on Saturday.

I'll search the forum for the best places for brushes. Maybe I'll spring for the carb kits while I'm at it.

 

I hope we're not overlooking something stupid.

Did you ever get a reading at the battery when the bike was running?

 

I didn't get a chance to do that. I guess I should replace the brushes no matter what.. only $12/pair from Z1, which is pretty good I think.

Just making sure though -- that's min 10-11mm exposed, right? Not total length?

Kiwi, how do I remove the leads from the coil? Seems like they're pretty much built in.

 

You're doing the right thing replacing them brushes right now. Better off doing them when YOU caught them short ... before THEY caught you and left you stranded someplace where you'd have to leave the bike and hope to find it when you got back.

12-Bucks. Cheap insurance.
Check 'em off the list; and we're a step closer to getting you on-the-road.

 

No it is a min. of 10 mm total length. There should be a Wear Limit line on the brush itself. Measure the total lenght of the brushes.

Removing the leads is part of the new lead procedure. Got a Dremil Tool?

Follow this guide: New XJ Coil Leads

 

Brushes, inline fuel filter and carb rebuild kits on the way. I'll track down wires on Saturday...

 

Okay, double checked the coils today. After scratching away some clean contact space on the solder joints I'm still getting 3.5Ohms at best for each primary. Secondary on one of them is 21.4KOhms with the caps on. The other secondary... no reading. Cut 1/8" off the ends of the wires and stuffed the leads in there -- nothing.

I guess the next step is getting the wires out of that coil to see if it's okay. But, given that both primaries are out of whack, is it time for new coils? I guess all 4 plugs being fouled at the same time could be bad coils or the alternator brushes, correct?

 

I wanted to make my bike pretty with some yellow wires from the Coils to some new, sexy Plug Caps.

I got into some scrubs and started the Coil Surgery.

Even with the optional snake and 20,000 Dremel Bits I got frustrated with it and quit.
Perfectly good Coil.
Still is.
Just no wires coming out of it at the present time.

There's some "Requires patients" jobs that I'm leaving on the far end of the bench ...
Until I find the patients ... or,
they get pushed-off the end of the bench and fall into the "Old Spare Parts Grab-bag."

 

Hmm... I'll see if I can find the Dremel around here, and see if I have the patience as well.

Question still stands though -- is it even worth it trying to fix the wires on a coil with primary resistance at 3.5 ohms?

I've been looking at the green Dyna coils, since the consensus is that's what an XJ needs. From what I understand mounting is a huge pain. Too bad those minis won't work. They look perfect.

If I go with the new Dynas, since the secondary resistance is 14.4K ohms, what should I be doing for the plug caps? Also found one of my plug caps is totally dead...

In my search of the forum somebody recommended some OEM type replacement coils for an XS 650. Take a look at the link below... says it's for the newer models 81-84 with TCI. I can't find what the actual specs are for these coils though. Hopefully the primary would be within spec for an XJ. Looks like mounting would be easier (provided they're not too fat), and at $32 a pop it's a lot cheaper than the Dynas. Has anybody tried this before?

http://www.mikesxs.net/mikesxs-electric ... ory_id=2.1

 

I don't think that mounting the DYNA's is all that Complicated, really.
I think its just a matter of having to make-up a small bracket because the DYNA's are smaller than OEM's.

Perhaps, to un-complicate matters ... you might find a good used set (or, only one ... if you just have one bad) ... and, get the bike going.

Having never had to mount a Set of DYNA'a for anyone; I can't speak to how difficult it is.
Although, with the frame already fashioned to accept new coils or for the OEM's; I can't imagine it being all that difficult to fabricate whatever is necessary for adapting the DYNA's to your bike.

For the increased performance and reliability you'll get by transitioning to DYNA Performance Coils ... I recommend you making the investment and out-sourcing the mounting to a sheet metal fabricator if you don't want to hassle with making-up a bracket.

You might even try having a metal-working class at a Vocational Technical School assist you.
I brought a 900 Head that had four broken Intake Manifold Studs over to a Vo-Tech School and they enjoyed having a project out-of-the-ordinary ... and they did a great job.

For a very modest donation to their Expendable Shop Supplies Fund.

 

Well, I emailed the mikesxs people to ask what the specs of the coil are.

I wouldn't mind taking fabricating up the brackets if I could get around a bit easier. I've got a horrible commute to work... suffice it to say if I try to do anything early in the morning it'll put me into work 2 hours late. I leave too late to get to most stores too. Might be able to find a some 90 degree bracket at Can Tire... anybody have any pics of their conversion so I can see how it's mounted?

I've searched and searched, and came across and XS11 site that had the same idea for replacing the coils with these high output jobs from Mikesxs. "And, if the bike has a ballast resistor....then yes it would need to be bypassed, these coils are rated at 2.5 ohms and are designed for 12 volt system."

http://www.xs11.com/forum/showthread.ph ... eadid=7092

Now, what are the chances that the mounting holes are the same distance apart?

I've got a bit of time to make a decision since I doubt anybody is going to ship me anything on a Sunday anyway. But if I can get away with $64 for two brand spankin' new coils...

And actually that mikesxs site has a lot of components that look common to both bikes. Kill switch/starter button assembly, mirrors, peg rubber...