Throttle Lag and Backfireing

[Ehdrian]

Hello!

Its been a while since I posted, but I have been reading as many threads as possible on this subject.

From what I understand:

Lean: Backfireing
Rich: Lag in response

However, my bike will lag in the low rpm before 3000 and will backfire when letting go of the throttle from 5000 when it reaches 3000 again. No backfire from 5000 to 3000. It starts 3000 and lower.

Since this kind of breaks the basic logic, does anyone have an idea about this?

Thanks in advance!
Adrian

[Ehdrian]

Hmmm after reading the cold start thread. I realize I do need to give it a little throttle to start with full choke - which would lean it out a little. It sputters and chokes when I have the choke on and then smoothens out with the choke off. She will idle at about 500rpm for at least a min and will want to die. After warming up (2-3 blocks of riding) she idles fine at 1000rpm with a little wiggle in the tach.

[clyderider]

running lean here too

My bike "clyde" does darn near the exact symptom! My guesses are 1. carb synch/slightvacuum leak from boots 2.Pulsar assembly/vacuum/advance-timing.3.coils/wires. so heres what I am trynig...I bought the mikes xs green coils and yellow solid core wires,attempting to repair pulsar wires per tech repair(2nd time)also have headlight issue uggggggggggr otherwise this machine is a total thrill to ride!wonderful powerband.Praying for a quick return to the asphalt. 1979xs11sf braided steel brake lines,fork brace,4-1kerker exhaust,ellite2tires,81 wheels and brakes -front dual drilled disc blades ,fuse box change,rlu by-pass,somewhere near 17,000 miles....sorry no scanner yet ...soon!black and chrome colored bike buckhorn handle bars.passenger floor plate footrest.

[Ehdrian]

"also have headlight issue"

I had the issue as well. Diode seemed to be good, so I bypassed the transformer under the front of the gas tank. I will wait until winter to sort it out properly.

[Ehdrian]

One Idea

I Might be figuring this out as I go along....

If my battery voltage at idle is 10.5 volts, that may mean that the plugs aren't always firing at low rpm before the bike gets the alternator up to speed (2500 rpm). The charging system is fine.

This would cause gas to get into the pipes and backfire while decelerating from 3000 rpm. It may also cause the bike to stumble when accelerating from 1000 rpm. This may explain both symptoms.

right?

[clyderider]

lean slight backfire at de throttle

I agree sir,so new coils and wires and caps seems fair to treat it??..praying so anyways for 156.oo dollars-post free! now for solving the headlight and no power intrmittenly.....uggggggggggggggggggggg help bike gods!!!!!!

[cywelchjr]

I Might be figuring this out as I go along....

If my battery voltage at idle is 10.5 volts, that may mean that the plugs aren't always firing at low rpm before the bike gets the alternator up to speed (2500 rpm). The charging system is fine.

This would cause gas to get into the pipes and backfire while decelerating from 3000 rpm. It may also cause the bike to stumble when accelerating from 1000 rpm. This may explain both symptoms.

right?

Well, idling at 10.5 volts isn't normally considered a sign of a good charging system assuming that you have a good battery. What does the voltage go to at 2500/3000 rpm? It should be 14.5 volts, if its not, then you have a problem with the charging system. Mine runs about 12.2 or so at idle and then slowly climbs to 14.5 if held up at 3k.

[jjwaller]

10.5 volts is several hundred percent discharged!!!
12.0 volts on a lead acid battery is 100% discharged.
12.6 volts is normal static voltage.
I doubt it will do any good, but try trickle charging the
battery for a day, and then let it sit idle for several hours.
If it falls below 12.6, 12.5 at the least, the battery is toast.
Need good battery for good ignition.

[Ehdrian]

Ya, I think its the battery. At the posts it never goes above 11v. I got it brand new just as the store was closing, so I think the guy never charged it right (he was in a hurry), but it is under warrenty for another four months.

I'll try getting the battery charged properly first, then look at getting the carbs synced, then the coils me thinks.

[Ehdrian]

Update

Update:

Got a new battery which solved some of the problems but not all. Might be time for a sync and new coils.

Seems to only lagg out now at low rpm when cold especially when climbing hills or leaning sharply. After warming up there is no lagg. But she still backfires.

Adrian

[XJOK2PLAY]

Ehdrian,

When you say "backfiring"... to me that's the same as the sound of a shotgun blast out the exhaust...

Then there's "popping", which can occur on decel or at idle, back through the exhuast... (caused by carb problems usually.) (And thanks to the wasted spark ignition.)

Just wanted to clearify which condition you're having...

Idle speed should be set to 1100 rpm. This can make a difference as to how fast or slow it decels... too slow idle speed, it decels too quickly... too high, it decels too slowly and continues to high idle... but if your about 1000 that's probably ok.

If you don't have a fully charged battery, or if your charging system is not doing it's job, too low of voltage will cause the bike to run like crap. TCI needs the proper voltage to send to the coils for the coils to do their job properly.

If it's been a while since the carbs were synched, or if you've made some major mods to it... a synch might solve the problem. From what I know about synching... the #3 carb has no adjustment, so synch 1,2,&4 to it's reading. Clymer's suggests this, and the main thing you're looking for is for all 4 to read the same.
Hope I'm not telling you something you already knew...

Ohhh.... and my experience so far with these 'ole bikes is that most of them are kinda cold natured even if their in great tune...
from what you've said, sounds about right.
Good luck.
Bob

[Larrym]

Orville Redebacher??

Hello!

Its been a while since I posted, but I have been reading as many threads as possible on this subject.

From what I understand:

Lean: Backfireing
Rich: Lag in response

However, my bike will lag in the low rpm before 3000 and will backfire when letting go of the throttle from 5000 when it reaches 3000 again. No backfire from 5000 to 3000. It starts 3000 and lower.

Since this kind of breaks the basic logic, does anyone have an idea about this?

Thanks in advance!
Adrian

Basically that's right. However that premise is the standard for engines which have one spark plug which fires only one time during the Suck-squeeze-bang-blow cycle.

The XS's use a wasted spark system where each time the coil fires for the "power producing" cylinder, it also fires a spark into that cylinder's running mate. This happens on the exhaust stroke of the running mate. If the fuel/air mixture has not completely burned due to a "rich" mixture or because of a higher octane fuel then the spark will ignite the "leftover" mixture. This can lower the unburned hydrocarbon readings at the local emission testing station.

The actions of letting off the twist grip quickly and the shutting down of the carb butterfly stops the air from flowing but not everything happens immediately. There is still a dollop of rich fuel/air mixture waiting to enter the cylinder and the engine may make a couple rev's trying to gulp this mixture down.

Soooo...a pop or two on a sudden decelleration/throttle chop isn't a fatal flaw. The question is whether you backfiring/popping is continuous as the rpm's drop.

[Ehdrian]

Idle purrs at 1050 when warm (10-15mins of riding it easy) and drones at 650 when cold/warm (less than 10-15mins of riding it easy).

It does not shotgun out the back, it pop,pop,sput,tick,pops out the back continuously from 3000rpm down to idle.

Thanks!
Adrian

[XJOK2PLAY]

Yeah, I know what your saying... that's "popping", not backfiring. (2 different things.)

I've been told improper float levels or sometimes worn out jets/ needles can cause this if it's XSive... (lean).

My XJ has had the same problem, even at idle!

Just installed a Dynojet kit, but haven't had time yet to check it all out to report yet.

Already seeing some improvements concerning a few bugs my carbs had, but also need more tuning time to solve some new issues... mainly idle speed won't stay right... but the popping problem is much better... cause the carbs are now jetted much fatter, but w/ new and longer needles.
(Especially XJ carbs...unbelievably small...)

If you have several miles on your plugs, you might pull them and give 'em a read. If you find they're white, you're on the lean side. Black would be rich, of course... grayish is what you want to see.

Dynojet kits aren't cheap... but they are good stuff! I've had 2 other friends install these kits, and they both have seen a 10 mpg jump... low 30's to low 40's. Time will tell on mine... fingers, legs, toes all crossed!

Might be something you might consider as well.

[Larrym]

Around the Mullberry Bush...POP!

I'd say the "popping" could be tweaked out by adjusting the idle mixture screws and then doing a few test runs.

But then ideally this would be the last thing to do after one has verified the ignition timing, carb clean, float check/adjust, carb synch, and exhaust leaks. Otherwise this tweaking may be just a failed attempt to compensate for a true problem in another area.

You have the stock exhaust and it generally deadens just about any "anomalies" to the point where they are unnoticable. (Ask anyone with an aftermarket 4 into 1...). If it's a poppin' then it just ain't natural.

Chase it round the bush. You may find something worthwhile.