does backfire = lean?

[marvintheminnow]

ive got a backfire on the deceleration. does this indicate a lean mixture?

74 TX
130 main (one over)
47.5 pilot (one over)
needle clip leaned out one slot
mixture screw 3/4 (stock)
chopped exhaust
pod filters

if i lower the clip back down to stock it decreases the performance in the midrange.

maybe stock on the pilot and stock on the clip?

 

[Pandorasglocks]

so your pilot is one bigger than stock? You definitely don't want to go back to stock if it is popping on decel, if anything go another up. I would suggest cleaning the pilot circuit thoroughly, hell clean everything while your at it. I'm not familiar with the 74 carbs, i have 79 38s and a pair of 34s. You should use some wire to make sure the circuits are cleaned out completely, soaking/spraying carb cleaner may not be enough.
And when you say it pops on decel, is it only when you totally let off the throttle? Or if you go from holding WOT to mid throttle does it pop?

 

[jay760]

if you mean from the exhaust, you have probably got an air leak on the exhaust, they pop on decelleration

 

[inxs]

- backfire or pop ?

 

[marvintheminnow]

well when i let off the throttle i get as pop and flames shooting out the exhaust.

Pandor - if i went back to stock on the pilot i would move the clip back down to the center position to rich it back out a little.

 

[marvintheminnow]

it didnt start popping/backfiring until i moved the clip up one. but it also runs alot better with the clip there.

 

[bloodthirstysystem]

first, set the mixture screw using dead cylinder method. if you change pilots do it again. popping on decel could be a lean pilot jet or a leak in the exhaust.

if flames shoot out it is too rich, that's unburned fuel leaving the cylinder in the exhaust stroke and exploding in the pipes. you need to set the mixture screw, put the needle back to the middle, clean all holes everywhere, until carb cleaner flows easily..

ride it and check the plugs, they'll tell you whats up

 

[OakBehringer]

For the sake of conversation, what would it have implied if he was going from WOT to mid throttle?

 

[marvintheminnow]

first, set the mixture screw using dead cylinder method. if you change pilots do it again. popping on decel could be a lean pilot jet or a leak in the exhaust.

if flames shoot out it is too rich, that's unburned fuel leaving the cylinder in the exhaust stroke and exploding in the pipes. you need to set the mixture screw, put the needle back to the middle, clean all holes everywhere, until carb cleaner flows easily..

ride it and check the plugs, they'll tell you whats up

plugs show no sign of a rich mixture & the bike runs better with the current clip position. I thoroughly cleaned the carbs yesterdsy making sure carb cleaner flowed through every passage.

im confused as to the theory of flames meaning a rich mixture as my plugs show no sign of a rich mixture.

maybe try bumping up on the pilot one size?

 

[OakBehringer]

Fire coming out of your exhaust... that can only mean unburnt fuel is entering your exhaust and....................... burning. This could be from running rich or an ignition issue.

 

[marvintheminnow]

im trying to find instructions on the dead cylinder method. Im sure there has already been a postin g this somewhere but i cant find specific instructions.

 

[heckienawjoe]

there are a lot of writeups on 650rider but heres a link to one they gave me. near the bottom.

http://www.650rider.com/index.php?name=Forums&file=viewtopic&t=8298

 

[bloodthirstysystem]

yeah it could be some seriously retarded timing i guess.

 

[OakBehringer]

Or a plug not firing consistently.

 

[marvintheminnow]

first, set the mixture screw using dead cylinder method. if you change pilots do it again. popping on decel could be a lean pilot jet or a leak in the exhaust.

if flames shoot out it is too rich, that's unburned fuel leaving the cylinder in the exhaust stroke and exploding in the pipes. you need to set the mixture screw, put the needle back to the middle, clean all holes everywhere, until carb cleaner flows easily..

ride it and check the plugs, they'll tell you whats up

Or a plug not firing consistently.

the plugs were pretty black because i had the needle clip above the plastic washer and they were just blowing out causing the bike to run extremely rich. I cleaned them up with carb cleaner snd a wire brush. is it possible they got fouled? there really clean now and producing spark.

 

[marvintheminnow]

there is also the possibilty of an air leak where the exhaust flange meets the motor. Ive notice that they look like their not sitting in all the way but i dont want to over tighten and snap the stud. can i spray starter fluid or carb cleaner in this ares to detect a leak?

 

[Pandorasglocks]

For the sake of conversation, what would it have implied if he was going from WOT to mid throttle?

To be honest, I don't know if it would even be possible to have a carb related issue with this symptom. It would have to mean that the mixture created by the high air flow and the needle/needle jet circuit is too lean to ignite at the high rpms of sustained WOT. But if this was the case I don't see how you could even get to WOT, the machine would just fall on its face right after 1/8-1/4 throttle.

Just a random thought of mine lol.

If it is ignition system related it would most likely be very loud and noticeable and accompanied by a loss of power.

Have you checked for air leaks around the header->motor and header->muffler yet? I have yet to encounter one of these leaks but a mechanic buddy of mine said that you can use a stethoscope around suspected exhaust leaks and it will be pretty obvious if there is one.

 

[pamcopete]

marvin....,

The dead cylinder sync method requires you to kill each cylinder, one at a time. Most writeups will tell you to pull a spark plug wire to kill the cylinder.

DO NOT PULL A SPARK PLUG WIRE TO KILL THE CYLINDER!

With a dual output coil, both plug wires must be connected to a spark plug AT ALL TIMES. Pulling a plug wire will potentially fry the coil and the ignition system.

If you have vacuum barbs, then you can kill the cylinder by pulling the vacuum hose or blind plug off of the barb, leaving the plug wires alone.

If you do not have vacuum barbs, then you will have to connect the plug wire to a spare plug that is grounded to the engine, leaving the other plug still in the engine. This method requires that you stop and start the engine on one cylinder at a time.

However, a much simpler sync method, if you have dual exhausts, is to just adjust the center sync screw until both exhausts sound the same.

 

[nj1639]

there is also the possibilty of an air leak where the exhaust flange meets the motor. Ive notice that they look like their not sitting in all the way but i dont want to over tighten and snap the stud. can i spray starter fluid or carb cleaner in this ares to detect a leak?

A half handfull of baby powder will show a leak, just toss it on the flange area where you suspect while the engine is running. It'll spray like smoke it there's a leak.
The flanges on mine don't sit flush, 1/8" or so gap.
If there's a leak just loosen the mounting hardware while the pipes are cool, re-adjust, snug up and try again. You don't need to crank the dog shit out of yer flange nuts.

 

[marvintheminnow]

took it for a ride yesterday and pulled the plugs when i returned. plugs look rich. Im one over on the pilot and have the stock pilot jet on order. im going to wait until it shows up before i mess with it anymore. i may just be to rich on the pilot. I will however start it up and try this powder test on the exhaust.