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2007 VTX 1300c - Unable to accelerate without backfire

4835 Views 9 Replies 4 Participants Last post by  spryguy
Bought the bike in 2009 with 2400 miles, now have about 19k and kept up with routine maintenance every 4k at reputable dealer (Team Powersports in Garner, NC).

*About three years ago drilled out pipes (loved the results!), added K&N filter for extra air flow.
*Started getting backfire on deceleration this Spring (2015), read through the posts here on VTX Cafe which pointed to lean A/F mixture. Picked up permanent mount A/F screw from Glens VTX Garage in June. Problem solved!
*Two days ago, was changing lanes and bike hesitated and then backfired while trying to accelerate. Worrying, but it drove the rest of the way home OK.
*Yesterday, hesitation and backfiring started getting worse, couldn't accelerate to highway speeds. Barely made it to work (10 miles from home) and almost didn't make it home, spitting and sputtering the entire way on back roads.

I have more than 1/4 tank of fuel, tried reserve position just in case, no change.
Tried riching out the A/F 1/4 turn, didn't help.
Tried driving with the choke out a bit, no change.
Starts and idles just fine, only have issue when accelerating.

Any ideas? It's got to be a fuel flow problem, right? I'm confident I have the basic skills to pull the carb and clean it up, but due to how sudden this was, I'm completely baffled as to what the root cause could be.
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You may have one or more of several issues...
The Vacuum line or internal Diaphram in Petcock are bad (low gas flow).....
The accelerator pump in carb.....
Diaphram in Needle valve.....
Have even heard of mouse nest in Air cleaner blocking air flow or dirty/clogged air Filter..

But it does sound like a low fuel (lean) mixture issue....

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Thanks for replying so quickly! I may try some exploratory work this weekend to see if I can find anything obvious. This really sucks because we've had a brutally hot and humid Summer (since May really) and we are just now seeing mid-70's with 50% humidity! Perfect riding weather!
I got a hold of the VTX1300 Service manual for the 03-04 models, and under the Fuel System (section 5) is says: Backfiring or misfiring during acceleration could be lean mixture or fault ignition system (section 17). Could this be a faulty throttle sensor?
Agree with Frank, check the vacuum line at the petcock. Needs vacuum to let the fuel flow. Also check the vent line at the right rear/bottom of the tank -- need that vent so fuel will flow.
Check the easy stuff first (like vacuum lines). Next remove the seat and check the green and black wires going into the ECM on top of the battery. Been known to break from engine vibration and cause misfiring.
Thanks, fellas, I think I "accidentally" figured out what's wrong. The service manual pointed to an ignition problem. Since I'm more comfortable around an ohm meter than a carburetor, I decided to test the resistance of the throttle position sensor from the 22P wiring harness at the ECM under the seat. I was a little discouraged when I was seeing correct readings (4.7 kilo ohms), which meant there wasn't anything wrong with the sensor. However, when I re-attached the 22P harness, I noticed one black/gray stripe wire was broken! Sure enough, the bike wouldn't start, so I bridged the gap with alligator clips and the bike started right up! The way the wire broke inside the harness assembly, there wasn't anything to grab on to so it took me a while to get the pin socket out so that I could try and solder it back. Presto! The bike is back and running good as ever. I haven't been able to figure out what this wire belongs to (for example I know the yellow/red, red/yellow, and blue/green belong to the throttle position sensor), but it's purring like a kitten again!

I'll include a picture so you can see what I am talking about. The wire is partially stripped so I could get an alligator clip on it. When I found it, it had simply snapped off.

Wire Electrical wiring Electronics Technology Cable
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Oh, and to prevent any movement of the ECM in the future, I stuck a couple of squares of velcro underneath. I figure it was rattling around there under the seat and that little bit of shaking eventually broke the wire.
Oh, and to prevent any movement of the ECM in the future, I stuck a couple of squares of velcro underneath. I figure it was rattling around there under the seat and that little bit of shaking eventually broke the wire.
I use Shoo Goo silicone (can get it at Walmart) and coat the wires at the plug. Stops the vibration that breaks them thin lil wires.
Could be a pain in the butt should I ever have to get at the clips inside but of all the bikes I have Gooed no one has ever come back with a broken wire.
That's a great idea! Thanks!
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