Serious backfire

Seemingly out of nowhere I'm getting a backfire .... prior to it even starting. where do I look first? Less than 2000 miles on rebuilt carb and valve adjustment . Thoughts?

 

Is it a one time thing when you start it? Does it happen each time you try to start her? Will the bike run and drive normally or are you having other issues with it?

Main reason I ask is that I have had bikes that the jets in the fuel bowl have backed out and they would backfire and run bad or not at all. I hope this is not the case.

 

"Why does my engine sometimes backfire when I first turn on the key (without attempting to start the engine)?:

- When you kill the engine, the intakes will still have some remaining (un-burned) air-fuel mixture remaining in them. Upon powering up the bike (turning the key on), the ignition system will apply 12 volts to the coils, thus charging them. Of course, that constant current is not good for the coils, so few seconds later (if the engine is not started) the TCI shuts down the coils by grounding them (to protect the coils from overheating) which cuts the current to the coils and thus triggers a spark to the plugs. If there is enough un-burned fuel in the intake manifolds or the combustion chambers, and if the valves are held open by the camshafts, a backfire thru the exhaust header and/or thru the intake manifolds/carbs/airbox can result."

From:The Information Overload Hour

 

This is the first time it has backfired upon cold start. Month or so ago it died on me (total electrical failure, during ride), upon restart it backfired. Once up and running warm it seems fine.

Thanks for info

 

Can confirm it's probably normal. I had some sidestand switch issues with my 650 Maxim (it was dirty and sometimes killed the ignition while driving!) The switch cut the ignition once while it was running and really quickly cut back in, BANG, huge backfire out the exhaust, I thought my back tire exploded or a gun went off behind me! Fixed the switch (thus the engine never cut out like that again) and it hasn't happened since

 

When you say Cold start, could you explain that? Had it been running that day? Was it really cold from sitting overnight or longer? I can understand that if the engine is warm and running and then you turn it off and then the ignition back on but not start it, the TCI would then discharge and Bang, I get that. But if it is a cold engine and had not been running for a day or so and you did the same, just turned the ignitions and Bang still? I will trust those that have this bike, if that is the case that is a good head scratchier to me.

 

By 'cold start' I mean sitting in garage for a week. And, no, not just turning on key. I mean choke engaged and turning over numerous times without actually starting.
Then letting it rest a minute or so, upon cranking it over again I get backfire. Thanks for asking.

 

You enrichment circuits, or pilot circuits are likely clogged. One or more may be allowing enough fuel to pass so that it loads up they system enough to backfire (or afterfire) when you proceed to the second round of trying to start it.

The first start after a long sit can be difficult, but that usually takes months of sitting.

 

Thanks K-moe. Are you saying pull carbs and clean .... not my favorite project. Other thoughts on solution?

 

Yes he is saying that, need to take them all the way into the church of clean, not just the steps. We all had to do it, some of us (like me about six times) before I got mine to run correctly.

 

Buy a fuel-injected motorcycle instead?
You bought an old machine, and she has needs. Give her what she wants, and you will be rewarded.

 

Fuel injected .... can't even work on those! Yea, I talk sweet to her and rub her tank as often as possible. Guess I gotta step up my game. Thanks K-moe

Did 'church of clean ' , two years back. Hoping not to repeat so soon.

 

Oh sure you can (well I can anyway).

The whole sermon (including wet-setting the floats)?
If so, then there might be something else going on.

 

Yep, the whole sermon including wet set of floats. Running perfect for two years, then just recently .........
And yes, I meant I cannot work on fuel injection. I'm sure there are masters out there.

 

Now she does not want to start at all. I ear a clicking sound from below the fuel tank. Sounds similar to a spark, but not really. How to trouble shoot?

 

click below the tank might be the starter cutoff relay you should have 2 relays that click sidestand relay and starter cut off relay.

Starter/Ignition cut-off relay (no color): behind self-canceller, under rear of tank.
Sidestand (kickstand) relay (blue): behind the left frame side cover, on the plastic regulator-rectifier mounting plate.

if you think your spark plug wires are arcing out try starting in the dark look under tank for arcing or cover your wires with tape to see if bike starts.

does bike turn over ? "Now she does not want to start at all" is a broad term .
turns over but does not start or press starter button and nothing happens are better terms.

also have you charged your battery recently? do a voltage drop test.

if starter is not spinning remove sidestand safety switch

 

Yep, she turns over just fine. Just grinds on battery. Just won't lite. New battery in spring and kept on battery tender. Voltage test completed on charger and electrical system during summer for unrelated issue.

Sidestand relay seems fine ..... shut me down (killed engine two months back). Is clicking sound normal? do not recall hearing it previously.

 

when key is turned on you should hear startersafety relay and sidestand relay click with bike in neutral 1 click.

do another voltage drop test on battery just to rule it out as a problem does not matter how new a battery is they can fail

turn petcock to prime for a few seconds to ensure carbs are full the gas can evaporate from the carbs.

as for trouble shooting ignition check for voltages on red/white wire at tci this wire splits to coils test for same voltage at coil connectors unpluged

the sidestand relay grounds out the tci remove it
if your starter turns then the starter safety relay is working it supplies voltage to solenoid.

have you ohmed out the ignition system lately to eliminate ignition coils plug caps wires and pickup coils as the problem?
pulled plugs and clean regap (or replace) check to see if wet after trying to start.

what do you have for a fuse block

 

fuse block upgraded - no rust, fuses good. Battery strong, volt drop okay. Will look at sidestand again.

 

Post values please. That will help with diagnosis.