backfires thorugh exhaust when accelerating, WHY?

[burlybiker]

i just picked up my first bike about two weeks ago and it backfires through the exhaust when i accelerate. why?

also, if my charging system isnt working right, could it cause this by lack of voltage? if i rev it with a multimeter on the regulator, it will drop the voltage to about 11.5 volts. thats when it back fires.

any ideas? my wifes car is broken so she drives my truck and this is what i use to get back and forth to work.

:usa:

[ryno18000]

Welcome from Indiana. We will need some info on your bike. What is it? What year, make, model. Is it carburated or fuel injected.

Ryno

[burlybiker]

its supposedly a 98 soft tail with a carb. the harley CV carb.... i think its an older model (96 or 97) with an aftermarket frame. it has straight pipes. heres a pic

http://viewmorepics.myspace.com/index.cfm?fuseaction=viewImage&friendID=119686262&albumID=1197136&imageID=29227299

i snugged up the exhaust, checked the intake for leaks with carb cleaner and changed the plugs.

[old skool]

good lookin ride, welcome from fl, the exhaust popin sounds like ya need to re-jet yr carb, have you checked the plugs? not sure about yr charging problem but i think a drop from 12 to 11.5 sounds reasonable

[burlybiker]

thanks....

the guy i bought the bike from said that it ran great. he let it sit for a bit and then it started running like this. its got fresh 93 in it, so its not the gas.

i just dont want to have to take it to the dealer if i can fix it myself.

so how would i start to rejet my carb? i have already taken it apart and cleaned it up.

i am a car guy and bikes are a whole new concept to me.

[ryno18000]

good lookin ride, welcome from fl, the exhaust popin sounds like ya need to re-jet yr carb, have you checked the plugs? not sure about yr charging problem but i think a drop from 12 to 11.5 sounds reasonable

+1

If you are running straight pipes, you have no back pressure. This causes engines to backfire. You can install some torque cones or some baffles. Rejetting will help too. Where are you measuring your voltage at exactly?

Ryno

[burlybiker]

i measured it at the wire leaving the voltage regulator. the battery stays the same. i have had trouble with the electrical lately, so thats why i asked if that could be causing it.

backfire as in when it pops, i get a nice flame?

[old skool]

yeah ryno is right on about the drag pipes, you should really think about baffles or something for backpressure if your gonna make it a daily rider. if yr a car guy and you already pulled apart the carb and felt ok doing that, putting new jets in will be like fillin up the tank with gas for ya (easy if ya didn't get my stupid analogy) first thing first, do yourself a favor and get the HD manual for yr scoot, not a knock off but the HD one, you wont regret it. second did you check the plugs? you need to know whether yr running rich or lean so you can see if yr going up or down in jet size. i would probly get the baffles first and see how that works out, you don't need something to quiet yr motor just something for backpressure so you could make them or do what i did and but some 4 inch baffles (there cheap) and chop the actual baffle off so you just have a small cones for back pressure then you can weld them in.

[burlybiker]

i was checking out the torq cones. do they cause any problems, like lower HP? i am running rich because the plugs are a little too black. i played with the carb and took it for a spin and it ran like a raped ape, so maybe thats all it needed?

i will see tomorrow when i take it to work...

thanks for your help guys

[shovelhead73]

Welcome to the forum. Just so you know, there are a lot of evos running around without baffles in their pipes and they don't pop on acceleration.. What they will do ,is backfire when you decelerate. But on acceleration, it sounds like you have a plugged up main jet. It just depends on whether it does it when you give it heavy throttle or just normal acceleration. Just make sure your jets are clean,and I would bet that would be your problem. No baffles will make your bike kind of sputter and pop when you decelerate, but never when you accelerate. Those appear to be 1 3/4" pipes wjich should give you some back pressure anyway. If you get a look at your jets, see how far apart they are in size. The closer together you can get them the better it will run. But, that's just my thinkin.

[old skool]

torque cones are good but i personaly believe ya need a little more back pressure than that, that is a good start though. let us know how it goes tommorow

[old skool]

Those appear to be 1 3/4" pipes wjich should give you some back pressure anyway. If you get a look at your jets, see how far apart they are in size. The closer together you can get them the better it will run. But, that's just my thinkin.

really good point shovel

[shovelhead73]

I used to run nothing but 1 3/4" pipes until someone sold me a set of 2" and asked me to try them. I put them on ,and all that bike did was pop and sputter when I let off the throttle. I hate that too. Went back to the 1 3/4" the next day.

[old skool]

i'm runin 2inch in mine but i got some back pressure plates that i welded in because thats a big pipe for a 1200 but with the back pressure she runs great

[shovelhead73]

Yeah , dude , your pipes sounded real good.

[freeriderogur]

What about your voltage drop?
Unplug your regulator, and put a multimeter on the leads to the stator. Double check with your manual, it should read on AC voltage over like 20 or something, while running. With the engine shut off, ohm each lead to ground and it should come up .000. Again check your manual and ohm lead to lead on the stator, to see if it is within specs. Rub the pins of the regulator across the cylinder fins, if it sparks the regulator is bad. If these two things prove good, the battery is lunched.

[shovelhead73]

You're right on that. Your voltage should not be dropping when you accel;erate. It should actually be going up to maybe 13-13.5 volts.

[burlybiker]

well, its been two days and the first day everything was great. today i got a bit of sputtering cruising at about 70. i feel that its a fuel related issue, but i have already pulled the carb apart and cleaned it thoroghly.

i guess this weekend it comes apart again and maybe i need to do a better job.....

[old skool]

was that tank sittin a while before the guy ran it for ya? have you pulled the petc0ck out to see if there is a bunch of rust or just crap pluggin up the filter? maybe time to instal an inline fuel filter, i did and i'm really greatfull i did

[burlybiker]

well, i filled it up with 93 and stuck a new battery in it and everything is a ok. thanks for the help, and yes, i am going to install an inline fuel filter.

thanks,

[fanopalot]

ignition module under the seat thats your prob ??