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Author Topic: kickback / coughing carb  (Read 4570 times)

JordanMix

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kickback / coughing carb
« on: April 04, 2008, 01:13:58 PM »
I reassembled my engine/transmission/carb/adjusted the timing last night and ran into some trouble trying to start it. First I should let it be known that I always had a problem with the carburetor occasionally couching out the air filter (K&N cone previous to winter engine work) when starting the bike up.  I am having two problems now… first is a very violent kickback of the kick start leaver. It kicked back on me 3-4 times out of the 10-12 or so attempts to kick it over. They were very hard kickbacks, one hard enough make me sit down while my ankle recovered. I did get the bike started twice and it seemed to be pretty good, just idling a bit fast.

The other problem I am having is sever coughing/spit back from my carburetor. This happens on the occasions when the bike does not kick back, maybe 3 times out of the 10-12 attempts to kick it over. This is not a little spit either. I now have the velocity stack fitted and it spits back so hard that it turned the wire/mesh screen of the velostack inside out.

My question is, is it likely that both of these problems can be attributed to timing that is too advanced? I used the TDC tool out host provides and a test light to set the timing right before TDC on the compression stroke. By all means I am not a seasoned mechanic. I have some experience with autos, but the RE is my first bike… I am learning as I go.

I have a 1999 bullet 500. Running a free flowing exhaust with no baffle, pilot jet is 30, main jet is 125, velocity stack as an airfilter. Valve timing is good, no up and down movement but I am able to spin the pushrods.

baird4444

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Re: kickback / coughing carb
« Reply #1 on: April 04, 2008, 01:39:12 PM »
I would say that your pilot jet is to rich...   mine was doing the same cough on start. I went down to a 27.5 and all was well. Also check your points... are they to wide??  if you close them up just a little you are retarding the timing.
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deejay

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Re: kickback / coughing carb
« Reply #2 on: April 04, 2008, 01:41:26 PM »
Your timing is off, sounds advanced. I've found that the best way to set my timing is to ride it pinging, then retard it until it goes away. Finding TDC and setting it without the bike running never worked for me.

JordanMix

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Re: kickback / coughing carb
« Reply #3 on: April 04, 2008, 06:23:00 PM »
Thanks for the help. Am i correct at saying you will retard the timing if you turn the points plate clockwise and advance it if you turn it counter clockwise?

From everything i have read today and from your replies i believe once i get the ignition set properly and possibly purchase a richer carb slide most of my problems should disappear and then i can start fine tuning.

cyrusb

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Re: kickback / coughing carb
« Reply #4 on: April 04, 2008, 11:13:26 PM »
You are right on the plate direction for advance and retard.  As baird4444 said earlier ,set the points correct first, then time it. You sound way advanced. Once this is done then get into  the carb.
« Last Edit: April 04, 2008, 11:15:07 PM by cyrusb »

Peter

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Re: kickback / coughing carb
« Reply #5 on: April 05, 2008, 01:38:21 AM »
You got kickback and backfire. Kickback is backfire transmitted to the kicker because it is still engaged. Backfire is when your filter gets blown off and the causes are the same as for kickback. Now, if you follow kickstart procedure meticulously, the Bullet should not be able to kick back at all. But it still can backfire and take out a sprag clutch (not an issue with a KS) and damage the worm drive.
I do not believe that kickback cannot happen with proper procedure; I know this kickback cannot happen but I'm not a believer. I still have on and off problems with my right ankle because I was careless in 1979. Shattered the whole thing and I was limping for a year. These days I'm happy to kick anything you show me but I will kick with the ball of my foot very slightly behind the kicker pedal and being sure that the kicker lever will clear my shin if it slips out because of kickback. Takes some practice and patience to make it a habit. With the Bullet it's standing on the right and kicking with your right foot. So don't break your friggin' ankle and be reminded that what you experienced does not qualify as a "violent" kickback. It was just a taste of one.

Make sure that the points have the proper opening clearance and retard a little bit if they are ok. By the way, it's generally a lean condition contributing to backfire, not a rich condition. Getting the carb and timing sorted out at the same time is back and forth a little bit at a time and keeping accurate track of your changes. Patience is all that's required except for being really careful not to crash while you are sorting it out - I'm serious, this stuff is very distracting while testing on the open road.
As far as I'm concerned, static timing is just for getting the engine running and it's ping timing from there on.

Be safe, and good luck
Peter
« Last Edit: April 05, 2008, 01:57:41 AM by Peter »

geoffbaker

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Re: kickback / coughing carb
« Reply #6 on: April 05, 2008, 02:44:38 AM »
When my RE got back to Tucson she was DOA.

I rebuilt the head, new rings, and rebuilt the carb. It was set for the richest mix and the float was WAYYY off.

Once I got the carb rebuilt and running right, it was just a matter of retarding the timing till the kickback went away.

JordanMix

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Re: kickback / coughing carb
« Reply #7 on: April 07, 2008, 11:45:58 AM »
i got the kickback/backfiring issues sorted out for the most part this weekend. I haven’t had a kickback at all, and the backfiring out of the carb is not nearly as bad. I am still having carburetion/mixture issues i need to sort out (ran out of time over the weekend).

My engine is running what seems to me as dangerously hot (lean mixture right?). I installed a 125 main jet, 30 pilot and moved the clip to the second from the bottom on the needle and it still is running just as hot. It should be noted that i have had engine work done, new rings, piston (oversized +20 and a rebred as well as new guides and valve work.

I took off the velocity stack and put back on the K&N air filter and also put the small removable baffle back in the exhaust thinking this might help with my car being to lean but it didn’t seemed to help. At the current time i have a K&N filter, shorty style exhaust with the silencer fitted, 125 main jet and 30 pilot jet, second grove from the bottom on the needle, stock throttle slide and stock but new needle jet.

Leonard

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Re: kickback / coughing carb
« Reply #8 on: April 07, 2008, 04:02:41 PM »
  Sorry if you have already checked but make sure that the rubber hose connecting the carb to the head isn't leaking.
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JordanMix

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Re: kickback / coughing carb
« Reply #9 on: April 07, 2008, 05:00:48 PM »
Leonard.

in my attempt to rule out all possibilities i replaced the hose with a brand new unit at the onset of my problems. It did not make a difference.

I have actually just become so frustrated me with inability to get the job done that i scheduled a service appointment with my local RE dealer. It does concern me a bit that they have only worked on a few RE's over their years. They are a Honda dealer and are accustom to working on newer technology bikes. I know both of the service techs are fairly young guys, i am hoping they have some knowledge/training in old technology bikes to get the job done. A further complication to this problem is that i have a new piston/rings/rebore/valve guides so you really cant go out and rip around on the bike to see if you have it tuned properly.

deejay

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Re: kickback / coughing carb
« Reply #10 on: April 07, 2008, 05:39:04 PM »
I'm running a 127.5 and a 30 pilot, needle is on the bottom notch, air mixture and idle adjusted to suit...

I'd try slowing the idle, a bigger main jet, and raising the needle before bringing it to some kid at a shop.

Peter

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Re: kickback / coughing carb
« Reply #11 on: April 07, 2008, 11:04:07 PM »
Looks like your jetting is close to what works for others and you have ruled out intake leaks.
I would work with the mixture adjustment screw at this point (richer). Timing could still be too advanced as well.
I have an Amal so I can't give you specific advice for your carb.
You don't have to worry about the main jet much while opening the throttle only partially during initial break-in.
Also, remember that the engine will run much hotter for the first few miles with a new piston and rebore. I don't mean that you should ignore it, but what I do is to warm it up with little load and let it completely cool down right several times after a rebuild, especially with a cast piston. In fact you are concerned about exactly the right thing at this critical time.
How many miles do you have on it since rebuild?
Is your header pipe turning blue? How far down? Got ping?

Deejay is right, bad time to let someone else touch the motorcycle and possibly even test ride it.

Peter
« Last Edit: April 07, 2008, 11:08:46 PM by Peter »

cyrusb

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Re: kickback / coughing carb
« Reply #12 on: April 08, 2008, 12:43:09 AM »
With those jets installed  you should have a black exhaust pipe. If not, you must have a float level or fuel starvation condition . A 30 pilot is a fat jet, What else could it be?

JordanMix

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Re: kickback / coughing carb
« Reply #13 on: April 08, 2008, 12:25:26 PM »
i am going to try the 127.5 / 30 jetting, clip in lowest position and see what that does for me.  I think i may have a problem with the float level/fuel starvation problem. I was messing around with it a bit last night and noticed fuel coming out of the overflow hose. I disassembled the carb to see if i had a bur or anything and the float did not seem to be sticking. I took measurements as follows: carb inverted with bowl and gasket removed, i measured 26MM from the surface where the gasket sits to the top center of both sides of the float mechanism. From there i hooked up a crude device to test fuel flow. I got my Nalgeen hydration pack bladder and filled it up with water, hooked up the tube from the pack to the fuel in line of the carb then placed my carb into a small rocks glass with the car resting on the rim of the glass to test the fuel flow. The gas seemed to flow well and stopped about 10MM from the surface of where the gasket would sit.

If i am missing something here please let me know. I also sprayed out all the holes, ports and nooks and crannies of the carb with cleaner.

To answer some questions:

I am pretty sure i am hearing some pinging but my timing is set about 1MM after top dead center just to make sure i am not advanced.

I have only put about 1.5 miles on the bike because it was running so hot i was worried to ride it any longer. i went straight back to my garage. My header pipe was always blue/golden at the top, maybe the first 15-20 centimeters.

when you say "with those jets installed you should have a black exhaust pipe". do you mean i should have black smoke coming out of my pipe? I didn’t notice any, which could mean that you are correct in your assumption that i am having a fuel starvation problem. I am hoping to get some time to look at it this week or weekend. My appointment is not scheduled until the 18th, so maybe i can get it sorted out before then.

Leonard

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Re: kickback / coughing carb
« Reply #14 on: April 08, 2008, 12:53:46 PM »
 With the timing retared that much you shouldn't get any ping.  According to Snidel:
Spark is too late: The flame front has to "chase" the descending piston down the cylinder, catching up with it at some time, resulting in some burning of the fuel. The exhaust valve opening will be greeted by a burn that is still well in progress, with lots of burning left to do in the exhaust pipe,resulting in overheating of the entire engine, and signalled by a flatter exhaust note, burning of the chrome on the pipe, and generally poor efficiency. Retarded timing will also burn your exhaust valve, necessitating a valve job at minimum.

I am pretty sure i am hearing some pinging but my timing is set about 1MM after top dead center just to make sure i am not advanced.
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