Topic: loudest backfire I've ever heard! Ever! help with why?

[jason teamshralp]

Okay so I have had some issues with getting my bike running good. It's a 78 cb550k. the carbs are clean, but she still wants to die with a hard twist of the throttle. I was trying to avoid having to re jet the carbs so i bought an electronic ignition hoping it was a timing issue. I painted the tank and seat while waiting for the Elec. ignition. So I had everything back together and tried starting the bike... battery was dead. So i hooked it up to a charger and tried to start it to see if i could time it in the garage.

about 2 seconds after hitting the start button, Bang! I was honestly deaf for about 5 seconds and a little disoriented. neighbors were coming out of their houses going "What the F... was that?"

after walking it off. Went back and tried moving the ignition plate, and got another but little backfire. moved it again and nothing. so now I'm wondering...
why did it backfire?
If i broke something with that crazy backfire?
What my possible solutions are.

[CBJoe]

I can't chime in too much on this, but what model electronic ignition did you install ?

[754]

if you keep Hard Twisting the throttle when its not running, then trie to fire it up it will go boom!!

Not sure if yours has an accelerator pump, if it does that could have caused it..

[hapsh]

If you put a Dyna S in the bike, did you set the timing?  Could be severely retarded timing.  There is a procedure in the documentation to get the static timing close enough to get it started properly.  The thing about Dyna S ignitions is that they seem to be more sensitive to the amount of plate movement required to change the timing. A small amount changes the timing quite a bit.  I set mine statically and then set it at full advance with a timing light.  Even then the 2-3 timing was still fairly far off and needed to be adjusted as well.

[TwoTired]

It's a 78 cb550k. the carbs are clean, but she still wants to die with a hard twist of the throttle.

OK, your bike has no accelerator pump, and mechanically actuated slides.  So, you won't be able to make large changes in throttle position and expect it to pick up smoothly.  About 1/2 of total throttle travel is normal... for a stock bike.  Speaking of which...
Changes in air filtration and exhaust (away from stock) will effect throttle transition, too.  Enough, the many, if not all carb settings must be changed.
So, if you changed the air filtration and exhaust, you're not done adapting to those changes.

I was trying to avoid having to re jet the carbs so i bought an electronic ignition hoping it was a timing issue. 

Hope is not part of a mechanic's tool kit, and never came with the bike, even when new.  Hope (the emotion) doesn't ever fix anything mechanical.  While the bike will treat you nicely if you do nice things to it.  It will never love you.  You might as well resign yourself that emotions simply don't fix bike problems.  Some emotions, like anger, just make the bike worse.  So, I recommend a new approach to motorcycle repair.  If you HAVE changed the the exhaust and air filter design, electronic ignition is not going to substitute for proper carb jetting and settings.

I painted the tank and seat while waiting for the Elec. ignition. So I had everything back together and tried starting the bike... battery was dead.

See?  All that love and it's still a cold emotionless beast.

So i hooked it up to a charger and tried to start it to see if i could time it in the garage.
about 2 seconds after hitting the start button, Bang! ...... so now I'm wondering...why did it backfire?

Back fire in carbs or in the exhaust?

My guess right now is that you installed the ignition and/or wiring so that it now fires 180 degrees out of proper time.  So, the spark lit off the air/fuel mixture in the intake runners or in the exhaust system.  If exhaust, check for bulged/split pipes and damaged internal baffles.
If it is induction, check your filters and carb couplers for explosive damage.

Recheck your ignition installation.  New coils, too?  Hope they weren't 3 ohm types.

Cheers,

[mystic_1]

My guess right now is that you installed the ignition and/or wiring so that it now fires 180 degrees out of proper time.  So, the spark lit off the air/fuel mixture in the intake runners or in the exhaust system.

That's what I was thinking.

mystic_1

[jason teamshralp]

okay I'm in the garage now and have the timing light hooked up and I'm testing the timing static and when the light is hooked up to plug #4 it flashes at the marker 2/3 line. so I'm guessing my timing is retarded, as am i? how do i fix it?

it is a dyna electric ignition. should i just flip the whole plate around?
Or does it have to do with the magnet that is on the shaft?

[754]

Sounds like you are firing..180 degrees out...

[mystic_1]

Have you tried swapping the leads at the coils?


mystic_1

[jason teamshralp]

fixed the timing issue. i flipped the sleeve that has the magnet in it, that slides over the shaft. Static timed it, pushed the start button and go!

Went out rode for about a hour. she ran badly which i knew was going to happen, but was ridable.

after about 45 min. the engine wanted to sputter die when shifting into first gear. It was like the clutch wasn't pulled all the way. Is this a fuel issue? I think it needs carb jetting, but would that cause it to just start after a 45 min. ride?

Does the Transmission share the motor oil? if so could it be low and thinning out?

Any suggestions? Thanks for the input so far.

[seaweb11]

TwoTired
One of the best quotes I have seen in a long while

"Hope is not part of a mechanic's tool kit, and never came with the bike, even when new.  Hope (the emotion) doesn't ever fix anything mechanical.  While the bike will treat you nicely if you do nice things to it.  It will never love you.  You might as well resign yourself that emotions simply don't fix bike problems.  Some emotions, like anger, just make the bike worse.  So, I recommend a new approach to motorcycle repair.  If you HAVE changed the the exhaust and air filter design, electronic ignition is not going to substitute for proper carb jetting and settings."

[jason teamshralp]

TwoTired
One of the best quotes I have seen in a long while

"Hope is not part of a mechanic's tool kit, and never came with the bike, even when new.  Hope (the emotion) doesn't ever fix anything mechanical.  While the bike will treat you nicely if you do nice things to it.  It will never love you.  You might as well resign yourself that emotions simply don't fix bike problems.  Some emotions, like anger, just make the bike worse.  So, I recommend a new approach to motorcycle repair.  If you HAVE changed the the exhaust and air filter design, electronic ignition is not going to substitute for proper carb jetting and settings."

I know i laughed reading it. It actually made me delete the line that I typed in my last post saying how pissed I was getting at the bike. But I've decided to leave that out.

that also reminds me.

my bike does have a Mac 4-1 exhaust, and pods on it. The previous owner lived at a higher altitude so I think thats why the jets need some testing.

[hapsh]

fixed the timing issue. i flipped the sleeve that has the magnet in it, that slides over the shaft. Static timed it, pushed the start button and go!

Went out rode for about a hour. she ran badly which i knew was going to happen, but was ridable.

after about 45 min. the engine wanted to sputter die when shifting into first gear. It was like the clutch wasn't pulled all the way. Is this a fuel issue? I think it needs carb jetting, but would that cause it to just start after a 45 min. ride?

Glad you got the timing thing figured out.  Now on to the original problem.   My bike had Mac 4-1 and pods and the owner over compensated for them by lowering the needle clip all the way to the bottom and went to 120 mains.  It ran way rich.  I ended up going back to the original stock needle position (middle) and to a 105 main.  I was surprised at how little needed to be changed to make the bike run well with the pods and Mac.  What settings do you have on your carbs now; needle clip position, airscrew turns, main jet?  Check your plugs and see what they look like (black and sooty, or clean and white, or tan).  On a badly running bike I usually try to dial in the mixtures from lower throttle position up (idle - needle - main), because it does not matter what main jet you have if it runs like crap at idle and mid throttle, unless of course it is completely clogged.  You mentioned it wanted to die when you put it into first gear, it very well could be the clutch out of adjustment and causing a bit of drag.  I had my lock nut come loose on my clutch adjuster after a short ride and when I went back the next day to ride it some more it would kill the engine when I put it into first from obvious drag from the adjuster backing out.

[754]

Seeing as it ran fairly good for 20 minutes or so, I am thinking you may be getting some crud from the tank inti the carbs, or your plugs are fouling..

[jason teamshralp]

I'll Check the plugs tmw morning.

How do you adjust the needle height? do you just bend the tab the needle hangs on? I know that they are set level with the rest of the float arm. (if that makes sense) I don't see where there would be a low, med, high setting.

i think i have 98 main jets in my carbs.

and the ideal screws are out 2 turns i think?

[mystic_1]

You're talking about the float needles, hapsh is referring to the needle jet, which is the long tapered needle attached to the throttle slides.  It moves up and down inside the main jet, and varies the size of the opening as it does so due to the taper.  It regulates mixture at medium throttle settings.

At the top of the needle are several grooves.  There is a C-clip, or rather an E-clip, that you can move up or down in order to vary the mixture.

hth

mystic_1

[jonbuoy]

TwoTired
One of the best quotes I have seen in a long while

"Hope is not part of a mechanic's tool kit, and never came with the bike, even when new.  Hope (the emotion) doesn't ever fix anything mechanical.  While the bike will treat you nicely if you do nice things to it.  It will never love you.  You might as well resign yourself that emotions simply don't fix bike problems.  Some emotions, like anger, just make the bike worse.  So, I recommend a new approach to motorcycle repair.  If you HAVE changed the the exhaust and air filter design, electronic ignition is not going to substitute for proper carb jetting and settings."

about 2 seconds after hitting the start button, Bang! I was honestly deaf for about 5 seconds and a little disoriented. neighbors were coming out of their houses going "What the F... was that?"

  damn you guys are hilarious without even trying, I spat my drink out over myself at these two.

[Hope]

TwoTired
One of the best quotes I have seen in a long while

"Hope is not part of a mechanic's tool kit, and never came with the bike, even when new.  "

Say what?  I am the most important part of my tool kit!  Without me, the tool kit would be fixing the bike all by itself...

[Cvillechopper]

Jason, have you bought or downloaded the manual yet?  If not, go do it now.  You and your bike will benefit from it.  It's very easy to get overly ambitious with older machines (partly BECAUSE they are older) and really screw something up.  I've done it and I'd bet a shiny nickel that I'm not the only one. 
Reading through the carb section in the repair manual will help.  Searching on these forums for carb issues will help more.  Reading the Carb FAQs will help the most. http://forums.sohc4.net/index.php?topic=5410.0

Good luck.

[mystic_1]

Without me, the tool kit would be fixing the bike all by itself...

Wow, where can I get one of those toolkits?



mystic_1

[TwoTired]

TwoTired
One of the best quotes I have seen in a long while

"Hope is not part of a mechanic's tool kit, and never came with the bike, even when new.  "

Say what?  I am the most important part of my tool kit!  Without me, the tool kit would be fixing the bike all by itself...

Classic example of having a quote taken out of context.    
But, I AM rather surprised you're offering your self as a "tool".   
Are we all going to need sidecars to carry the "complete toolkit", now?   (since you won't ride '#$%*').   

Just funnin' with ya....

Just how far will this thread degenerate, I wonder?  Not, too contentious, I HOPE!

We all enjoy hope
We all dream of hope.
We all think of hope daily.
We all need hope.
We don't want to lose hope.
Hope that's clear.

Cheers,

[Hope]

Without me, the tool kit would be fixing the bike all by itself...

Wow, where can I get one of those toolkits?



mystic_1

My sentiments exactly.  I was trying to say that the tools don't do the work themselves....  My tools need a little Hope to make them work!

[mystic_1]

I was trying to say that the tools don't do the work themselves....

Oh drat!   


mystic_1

[TwoTired]

You don't need hope to make those toolkits work.  (note no capital H)  What you need is will.

Anyone here named William?  You're going to be very busy and popular, soon!

Cheers,