Back firing. Not starting

Anthony1993 · Jul 13, 2020

hey guys , so I recently replaced my air filters and switched to 4-1/2 inch uni foam filters.
Also cleaned out my gas tank and replaced the fuel with premium and added a bit of sea foam to it.
Took the bike out and it ran the best its ever ran before for about 2 miles.
Then as I excellerated in first gear and was just about to switch to second, the bike began to bog down and back fire a bunch accompanied with popping from the left exhausted pipe (shifter side ) .
Shortly after this, it died and left me on the side of the road.
I was able to get it started a hand full of times after but every time I would put it in gear and begin To let off the clutch, no matter how much gas i would give it, it would just die again.
I got irritated after pushing it home quite a ways and I left it in the garsge for a month or so, I recently went out and tried to start with no luck. I hit the air filters with a tad bit of starting fluid, gave it a shot and it tried but back fired a bunch and never started.
Replaced gas and still had no luck.
Maybe new filters are giving it to much air?

member28833 · Jul 13, 2020

Anthony1993 said:
Took the bike out and it ran the best its ever ran before for about 2 miles.

Sounds like it ran out of gas. Perhaps a fuel blockage in the petcock? Line, or needle/seat .
What year / model are you working on? Carbs? etc..

WideAWAKE · Jul 13, 2020

Out of high school I worked at a shop doing service and restorations to vespas and lambrettas... I can’t tell you how many times we had people bring bikes in for service, stating they had tried EVERYTHING. Rebuilt the carbs, changed the plugs, checked wiring and well as Karl so brilliantly said...

mike in idaho · Jul 13, 2020

Take the spark plugs out so you can check for spark and the presence of fuel. That's the quickest, easiest way to get a clue about what's going on.

Brassneck · Jul 13, 2020

Doubt it's the air filters...that may cause a leaner condition, but should still run if all else is the same. The seafoam may have something to do with it (depending on how much you used). I have added some to one of my bikes in the hopes of cleaning up rough running condition (I suspected gummy jets), and I could definitely tell when it was making it's way through the carbs...I had to keep the idle really high in order to keep the bike running, it was stumbling really bad...and tons of white smoke blowing out the tailpipes was a give-away. Personally, I don't think it helped the carbs in any significant way...perhaps it cleaned the cylinders? Dunno.

Anyways, I would start with the simple stuff... pull the plugs, see if you're getting fuel (the plugs should be soaked in gas if it's not starting and your cranking on the starter). I would also drain the carb bowls into a clean/white cup and see how it looks... if you have water in your fuel system, it will be obvious. If one bowl isn't as full as the other, that may be an issue. If your plugs are wet, then move on to check for spark--and also check the timing as well to make sure that is correct. Essentially, it is likely to be one of those two things.

Good luck!

Brassneck · Jul 13, 2020

mike in idaho said:
Take the spark plugs out so you can check for spark and the presence of fuel. That's the quickest, easiest way to get a clue about what's going on.

Beat me too it...I was literally typing my reponse, and had to take a call...45min. later... posted, and you had me beat. Ha ha.

Anthony1993 · Jul 13, 2020

Machine said:
Sounds like it ran out of gas. Perhaps a fuel blockage in the petcock? Line, or needle/seat .
What year / model are you working on? Carbs? etc..

1968 xs650.
I'll post pics of carbs.
I just put fresh gas in and no difference. I dont think theres is blockage in both petcocks simultaneously.
My gas tank has 2 prtcocks that connect to one.
But even when I give it a birt of starting fluid it does the same thing, it should run for 30 seconds or so on just starting fluid alone.

Anthony1993 · Jul 13, 2020

Brassneck said:
Doubt it's the air filters...that may cause a leaner condition, but should still run if all else is the same. The seafoam may have something to do with it (depending on how much you used). I have added some to one of my bikes in the hopes of cleaning up rough running condition (I suspected gummy jets), and I could definitely tell when it was making it's way through the carbs...I had to keep the idle really high in order to keep the bike running, it was stumbling really bad...and tons of white smoke blowing out the tailpipes was a give-away. Personally, I don't think it helped the carbs in any significant way...perhaps it cleaned the cylinders? Dunno.

Anyways, I would start with the simple stuff... pull the plugs, see if you're getting fuel (the plugs should be soaked in gas if it's not starting and your cranking on the starter). I would also drain the carb bowls into a clean/white cup and see how it looks... if you have water in your fuel system, it will be obvious. If one bowl isn't as full as the other, that may be an issue. If your plugs are wet, then move on to check for spark--and also check the timing as well to make sure that is correct. Essentially, it is likely to be one of those two things.

Good luck!

Ok ill check that out today. I would assume its getting spark, since its trying to start.
In the past when I've had no spark I would kick it over and over again and I would get nothing.
As well as fuel. If its not getting fuel then it should have at least started when I hit it with starting fluid.

Brassneck · Jul 13, 2020

Well, it sounds like it WAS getting spark, but now it's not starting...so it's either not getting spark, fuel, or a combination of other things...so I wouldn't assume too much just yet. Check and be certain...start with the plugs. If wet= Gas present...dry off, and check for spark. If spark...check carb bowls for water/particles...if no spark, check battery, etc... and down the road to discovery.

A possibility that I've experienced is Vapor lock. The bike rides for a few miles and all is well, then it stumbles and dies...essentially, the gas tank can't breath and slowly starves the carbs and stalls the bike. Crank and crank, and you almost get it to start, but can't and soon you have a low battery. So you wait trying to figure out what to do...who to call, etc. After a little while the vapor lock diminishes so the fuel returns to the carbs but now your battery is too weak to really get it to turn over...however, it was enough juice to crank a few times and foul the plugs--so they're coated in fuel--and the bike won't start. Alternatively, a weak charging system and your battery dies over time...bike stumbles/stalls, and can't be started...you kick it a few times, and now have fouled plugs and same outcome.

Just tossing ideas out... good luck.

Anthony1993 · Jul 13, 2020

Brassneck said:
Well, it sounds like it WAS getting spark, but now it's not starting...so it's either not getting spark, fuel, or a combination of other things...so I wouldn't assume too much just yet. Check and be certain...start with the plugs. If wet= Gas present...dry off, and check for spark. If spark...check carb bowls for water/particles...if no spark, check battery, etc... and down the road to discovery.

A possibility that I've experienced is Vapor lock. The bike rides for a few miles and all is well, then it stumbles and dies...essentially, the gas tank can't breath and slowly starves the carbs and stalls the bike. Crank and crank, and you almost get it to start, but can't and soon you have a low battery. So you wait trying to figure out what to do...who to call, etc. After a little while the vapor lock diminishes so the fuel returns to the carbs but now your battery is too weak to really get it to turn over...however, it was enough juice to crank a few times and foul the plugs--so they're coated in fuel--and the bike won't start. Alternatively, a weak charging system and your battery dies over time...bike stumbles/stalls, and can't be started...you kick it a few times, and now have fouled plugs and same outcome.

Just tossing ideas out... good luck.

Hmm interesting. I'll keep that in mind. . Hopefully its what you all think. Those would be relatively easy fixes

Anthony1993 · Jul 13, 2020

WideAWAKE · Jul 13, 2020

Certainly suckin air through that barb.

surprised it ran halfway decent before.

joebgd · Jul 13, 2020

WideAWAKE said:
Certainly suckin air through that barb.

surprised it ran halfway decent before.

Oh man there you go. Unless you took that barb off or vacuum petcock line off that would cause you problems. Do you have vacuum petcocks? Check other side as well for barb or line.

Brassneck · Jul 13, 2020

WideAWAKE said:
Certainly suckin air through that barb.

surprised it ran halfway decent before.

Good eye!

Back firing. Not starting

Anthony1993

XS650 Enthusiast

member28833

Race the wind

WideAWAKE

Single Fins and Twin Cylinders

mike in idaho

XS650 Addict

Brassneck

XS650 Guru

Brassneck

XS650 Guru

Anthony1993

XS650 Enthusiast

Anthony1993

XS650 Enthusiast

Brassneck

XS650 Guru

Anthony1993

XS650 Enthusiast

Anthony1993

XS650 Enthusiast

WideAWAKE

Single Fins and Twin Cylinders

joebgd

XS650 Junkie

Brassneck

XS650 Guru

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