Power Loss & Shotgun Backfire
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1st Gear
Joined: Apr 2015
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From: Conshohocken
Power Loss & Shotgun Backfire
This is my first forum ever. My bike won't stop backfiring, losing power, or stalling out when you get on it. It seems to work ok when the engine is ice cold or when you don't get on it hard. I have a 99 sportster 883...I know I know...that my buddy and I have been tearing apart and putting back together. I bought it two years ago with 3900 miles on it. Now, it only has 6200. Here's what we done so far:
- replaced both sets of rocket gaskets to fix there oil and air leaks
- Cleaned the carb and jets out
- dumped the fuel
- gleaned out the fuel filter
- fresh premium gas (all I run it it since I've owned it)
- replaced the fuel line from the petcock
- replaced a vacuum like going to the carb
- tuned the airflow/fgas mixture screw to factory
- new plugs
- gave it a good wipe down and gleaned the leak oil off the bike
No more oil leaks! It still backfiring through the carb and the pipes. We don't know what else to do! I just want to ride it and upgrade soon! I thought maybe we could figure something out through a forum...
- replaced both sets of rocket gaskets to fix there oil and air leaks
- Cleaned the carb and jets out
- dumped the fuel
- gleaned out the fuel filter
- fresh premium gas (all I run it it since I've owned it)
- replaced the fuel line from the petcock
- replaced a vacuum like going to the carb
- tuned the airflow/fgas mixture screw to factory
- new plugs
- gave it a good wipe down and gleaned the leak oil off the bike
No more oil leaks! It still backfiring through the carb and the pipes. We don't know what else to do! I just want to ride it and upgrade soon! I thought maybe we could figure something out through a forum...
Road Captain
Joined: Apr 2013
Posts: 600
Likes: 10
From: Rochester, NY
Sounds like a timing issue to me.
Three things in your list can cause timing issues:
1. The vacuum hose going to the carb. This vacuum hose helps advance the spark at higher RPM's. Make sure it is not leaking. Take it off, plug one end with your finger, and suck the other end like a straw to see if it holds suction. Also make sure the hose does not collapse. If it does get a hose that is specifically rated for vacuum.
2. Air/Fuel mixture. If your air/fuel mixture is incorrect it can cause the compressed mixture to combust without the assistance of the spark. Turning the set screw to the factory position may have worked when the engine was brand new but is most likely not the case now. If you have no way to analyse the exhaust gases you should bring the bike to a Harley shop and have them adjust it for you.
3. Premium Gas. Your stock 1999 Sportster is most likely not rated for premium gas (93+ Octane). My stock 2011 Street Bob is only rated for 91 octane fuel. 93+ octane is usually used on high-performance engines. It can in some cases help with backfiring though because it burns hotter, clearing out all the combustible air/fuel mixture. Premium fuel is most likely not your issue though.
Three things in your list can cause timing issues:
1. The vacuum hose going to the carb. This vacuum hose helps advance the spark at higher RPM's. Make sure it is not leaking. Take it off, plug one end with your finger, and suck the other end like a straw to see if it holds suction. Also make sure the hose does not collapse. If it does get a hose that is specifically rated for vacuum.
2. Air/Fuel mixture. If your air/fuel mixture is incorrect it can cause the compressed mixture to combust without the assistance of the spark. Turning the set screw to the factory position may have worked when the engine was brand new but is most likely not the case now. If you have no way to analyse the exhaust gases you should bring the bike to a Harley shop and have them adjust it for you.
3. Premium Gas. Your stock 1999 Sportster is most likely not rated for premium gas (93+ Octane). My stock 2011 Street Bob is only rated for 91 octane fuel. 93+ octane is usually used on high-performance engines. It can in some cases help with backfiring though because it burns hotter, clearing out all the combustible air/fuel mixture. Premium fuel is most likely not your issue though.
when you replaced the plugs did you make sure they were gapped correctly. I made that mistake on my old bmw and after fixing them it ran fine. Also the plug wires themselves?
Last edited by DMWyant; Apr 17, 2015 at 07:52 PM.
Thread Starter
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1st Gear
Joined: Apr 2015
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From: Conshohocken
New Plugs and Wire
I just ordered new plug wires and new plugs. I did put fresh plugs and made sure they were gapped correctly. I am going to order a new set as well just in case. Any recommendations?
2nd Gear
Joined: Apr 2015
Posts: 6
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From: central califonia
I had a sportster do that years ago, had no idea what was happening, starts when cold but backfires in 2 or three minutes then stalls then wont start till tommorrow morning....my problem turned out to be the intake manifold that the carb bolts too, got a new one (and a couple of orings it seems like), doesnt look like a part like that would ever go bad but I was told vibration, and years of wear and tear wears out the tight fit, anyway ran perfect afterwards
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Thread Starter
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1st Gear
Joined: Apr 2015
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From: Conshohocken
Gapping and plugs
Can't find anything in the service manual on gapping specs. Replaced the wires yesterday. Upgraded them and it's running better. Runs good unless you lean it, sounds its starving for gas, then it picks up again. Still runs like a top till it warms up. Trying to figure it out and not have to take it in anywhere.
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