Loud gunshot-like backfire when trying to start

My '82 xj750 has essentially been in storage since November with a tender on it and a full gas tank with Stabil.

Here in Wisconsin, it's been unbelievabley warm (for us) with today getting into the mid-50's. I tried starting up the old beast, and it cranks but won't turn over and then will backfire in dramatic fashion sounding like a gunshot (neighborhood dogs start barking). There is also a smell like a fried wire or something.

Any ideas? I'm not taking her out of storage since we're supposed to get our first real snowfall of the year tonight and more seasonal temps, but has me a little concerned.

Thanks

 

Did the backfire happen after a long time of turning over the motor trying to get it to start? yes-then you developed fuel vapor in your exhaust and it ingnited-boom! Very common when you can't get it to fire, are using lots of enrichment (choke), and continually turn over the motor. No-then your mixture is likely off.

Your carbs might need to be cleaned. You could try shooting some starting fluid directly into your carbs to see if it will fire that way and it may just go from there. Or drain your float bowls and make sure the gas in your tank is fresh (no water).

Good rule when it's not starting is to not crank it too long. Something else is up when it won't fire pretty quick. So crank for about 10-15 rev max, stop and wait a minute, try adjusting your choke to a different level and repeat.

 

This ^ Thanks. I cranked it 4-6 secs, several times, choke on. I think I'll just deal with it in the Spring since it's in the far front of the garage. Very good info to know - thanks.

 

If you got the "pop" right when you RELEASED the button, it means you have a slightly low battery. Just low enough to not have enough "oomph" left to spin the motor AND fire the ignition, even though it spins the motor quite vigorously. So there was no "fire" until you released the button, and it lit off the puddled fuel.

Common situation actually. I would never have believed it until I had it happen to me, and more than once.

Your "fried wire" smell was probably you overheating the starter a tad.

 

Yea, that's when it happened. So it could be a bad battery, but the tender is on it?

 

The battery could be:

Too cold

Low on fluid

or have a bad cell

You didn't say how old it was. If it is only a few months old then check fluid level and top off with distilled water. Then throw it back on the tender.

If it's older than that, very good chance that it went bad. These batteries have a short warranty for a reason, they don't usually last more than two years. There are exceptions.

I had a customer buy a battery last August because the battery he bought from me 6 years ago! finally took a dump on him. And that is on a Suzuki DR650.

But I also have a customer that comes in and buys a new battery every March because his '82 Goldwing is a battery killer.

After topping it off and putting it on the charger for a day, take it to the auto parts and have it load tested.

(speaking of auto parts, I need to stop at the new O'Riley's that opened Monday!)

 

Thanks. Given that batteries aren't bank-breakers, good idea to get a new one in the spring - it's the same one on there when I bought the bike used last summer.

 

The guy I bought my '83 from claimed it had a new battery "within the last couple of years."

When it finally packed it in last summer, after I'd had the bike less than 3 years, I decoded the manufacturer's date code.

It was seven years old+. Silly PO (which I already knew.) DEKA in case you're interested; since I rarely get more than 4~5 years MAX out of a motorcycle battery.

tskaz's advice is spot on; pull it, ensure good fluid levels, charge it and have it load tested.

I gotta say, BOTH of my XJs are way harder on batteries than my British bikes ever were. You really have to stay on top of your fluid levels, especially in the hot summertime.

 

It's funny about the battery, Fitz.............I picked up a running parts 550 this summer w/o title. So it got parted. The fellow I bought it from was trying to restore it til he found out that he couldn't do anything w/o a title so sold it to me. He bought a new battery (from a dealer) two months prior. He always had to start the bike on a charger anyway. Hm.....I looked at the battery.... many years old, already sulfited in the chambers, low water in some. So, he got really snookered on the battery.

The same dealer also told him he had a seized engine and charged him $150 to diagnose that. I told him I thought had a bad battery, not an engine issue. That's when he told me about the battery.

I said I can determine whether it's stuck or not in a couple minutes. I loosened the plugs, pulled side cover, 19mm wrench and turned the engine right around. He was NOT happy. I told him that he should fight the bill with the dealer. He said not even gonna get near the guy. But, he also said again....."it can't be the battery, it's new". Yeah. So I brought the bike home, tested battery......9.3v. Amazing what some dealers/repair shops will do and say..........more amazing how some people will believe what those dealers/repair shops say.

Anyway.......Yup, gotta have a good battery,

AND to address the original question..... these bikes don't like to start easily when it's really cold. Even if the air temp is warm, if it's still pretty cold inside the block it won't want to wake up too easily. May be best to just let it sleep til spring, like you said.

I have a couple that start relatively easy when cold, but the rest......they wait til spring.

Dave

 

Alright....new battery and fully charged. Turns over. Won't start.

 

OK, my mechanic says to do what the wise Mercury Man above told me to do and that is drain the carbs/float bowls.

 

They completely drained. Still won't fire. Turns over. Won't fire.

 

He meant you need to drain the float bowls to remove any stale gas, water, etc.

Then close the drain screws and let them refill. It won't fire with empty float bowls.

If in fact, the carbs are now full of fuel and it still won't fire, then the next step would be to fit a brand new sett of plugs as well; it's possible the set that's in there got saturated with fuel and are now useless.

 

OK, thanks.

 

Is there anything I would have to do in terms of measuring or can the new plugs go in pretty easily?

 

Measuring?

I'm talking about SPARK plugs. Try a brand new set of spark plugs.

 

Just make sure the new spark plugs are gapped properly and screw them in. Just remember, they are spark plugs not motor mounts, they don't need to be torqued down much more than finger tight.

 

Well, a tad more than finger tight.

As buttery as the XJs aluminum is I use a torque wrench for everything. I believe (IIRC) the plugs go to 14 ft/lb., but 1/4 turn after they stop when tightened finger tight is fine too.

 

One thing I've done with my V-Twin to help with the cold starts is to stick a drop-light up next to the jugs to warm up the engine a little. You'd be surprised how much a 100W bulb for a couple hours will help with starting issues.

 

Well, doesn't there have to be a certain gap for it to work right, like on a car engine? Or maybe it doesn't matter much.

 

Any 'ol kind of spark plugs? I'm having to go get the socket I need, too. Like I said, I'm not very handy mechanically.

 

Stick with NGK, the Japanese have used them in bikes forever for a reason.

And yes, 14ft-lbs is proper torque for the plugs. But I don't remember the proper gap at the moment.

 

check the oil level and sniff the oil fill hole for gas, then get a rag and pull the fuel line off and see if gas flows when you crank it with the valve in the on position

 

Spark Plugs 101: http://xjbikes.com/Forums/viewtopic/t=34431.html I did the piece; then TIME chimed in with the big bike gaps, and I added the gaps for the 550s. Have we let you guys down yet?

 

Success!

The suggestion to change the spark plugs did it. The old plugs were, well, charred. Looked a little like some oil around the 2 left side whatever they are...cylinders? (where the plugs go into) I tried to wipe them out best I could. Popped instantly after getting the plug cables back on and running smooth.

I'd like to thank you guys. In the span of one thread, I learned some valuable things that I can now do myself in the future pretty confidently: change battery, drain float bowls, change plugs. I had to buy a 3/8 socket wrench, but money well spent.

So, given it's going to be record breaking highs here in the upper midwest, I very well may take it in to work tomorrow!

 

Been there. (Soaked plugs.)

How many miles are on this bike, how long have you had it, and what do think has been done to it?

You may be riding around on a disaster waiting to happen; when it comes to a 30-year old bike, ignorance IS NOT BLISS.

I don't want to be sorry we helped you get it running.

 

Meaning we helped you get her running, now we'd like to make sure she's safe for you to ride.

 

27k. I have all the paperwork from a complete top end rebuild including the ignition from a reputable shop last spring from the prior owner. I bought it late last summer from him. I promptly had a windshield put on, an oil change, the brakes adjusted, the tires checked and a general inspection. I'm hoping the char on the plugs were due to my trying to fire it up in the middle of this winter, but they could have been due as well. That's what started all this with the gunshot sounds trying to start it up this past winter. I must've ignited something.

 

Uh-oh.....a reputable shop. So..... congratulations on learning how to do somethings yourself! You're gonna have eight or 10 bikes under your name in no time, now!

Uh-oh.....a reputable shop, huh? Ok, let me ask you these:

1. When did YOU last see the crystal clean insides of your carbs?
2. When did YOU last check the valve clearance to make sure that they are still in spec?
3. When did YOU last pull the rear wheel off to closely inspect the shoe laminations?

These are things you should do................soon.

Windshield is nice .....stops the bugs-----brakes stop the bike.
Ignition starts the bike and makes it go...
Tires help the bike go smoother....
Oil makes the engine go smoother....

BRAKES STOP THE BIKE. Make sure it stops with YOU in control of the brakes, not because a delaminated liner jams up and stops you a whole sooner than you expected......or worse--doesn't stop you at all when you need it the most.

It's not spring yet, the roads are still slick with sand and salt, so you have some time to keep improving things!

Stay with us, you'll be a pro in no time, AND end up knowing mor about your bike than a reputable shop.........LOL

Dave Fox

 

Cool. Good advice.

 

Right. Which you're going to completely dismiss until the next thing "goes wrong" with the bike (which it will) and the next, and the next and the next.

Save yourself some grief; at the very least get an OWNER'S manual for the bike and read the maintenance schedule. Then get a service manual, and study the maintenence procedures.

You're going to need to do a seasonal (not mileage-based, because of where you're located) oil and filter change; and you're going to need to learn some very basic maintenances routines before you get hurt.

Check the air in your tires before any riding, the bike sat all winter.

 

^^^
this

Got the owners manual...in pieces.