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Old 05-05-2013   #1
AnswerMeister
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Really loud backfire

OK here is the second problem with my sonís 96 carbureted 1500 v-twin. He bought it from my brother and it seemed to have worked fine for years. It has 2 into 1 roadhouse pipes and a after market exposed air cleaner. My brother says that he followed the tips on the Vulcan board when he switched it over and put in the recommended jets for the carb after the changes. Gas mileage has always been awful, in the low 20s never anywhere near the 40s that he should be getting.

Anyway in the last week once warmed up, as soon as you try to hold a speed or roll off the throttle you will get a loud backfire. Iím sure that any packing that was in the roadhouse pipes has been blown out. Should I be looking for an intake leak that is causing this? With it running do I shoot some starting fluid around the intakes to the heads to see if the RPM jumps up?
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Old 05-05-2013   #2
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Re: Really loud backfire

Backfiring usually means unburnt gas in the header(s). Could be overly rich from 1) improper jetting; 2) improper float level or stuck/leaking/saturated float. Could also be either an ignition- or a cam-timing issue. Also potentially a tight or burnt valve. I'd look to the over-rich fuel problem first--it's cheaper and simpler and more likely.
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Old 05-05-2013   #3
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Re: Really loud backfire

Last years stale gas still in it?
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Old 05-05-2013   #4
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Re: Really loud backfire

Whenever I get these issues I run a couple of tanks of fresh gas loaded up with sea foam before i do anything else. It has saved my bacon on more than one occasion.
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Old 05-06-2013   #5
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Re: Really loud backfire

Quote:
Originally Posted by dualsport View Post
Last years stale gas still in it?
Nope I know for a fact at bike week we ran 4 or 5 tanks through it. What is in there is maybe 30 days old. But itís empty now so it will get fresh Ohio gas lol


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Whenever I get these issues I run a couple of tanks of fresh gas loaded up with sea foam before i do anything else. It has saved my bacon on more than one occasion.
When he called me about this last week I asked him to put in seafoam. He never got the chance or wanted to wait for Dad to buy it and do it. Needless to say that will be one of the first things to be done
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Old 05-06-2013   #6
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Re: Really loud backfire

turn air/fuel screw out 1/2 turn...
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Old 05-07-2013   #7
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Re: Really loud backfire

Gas, even unburned gas, needs oxygen to burn. You should be looking for an exhaust leak-- not an intake leak (unless it's spitting back through the carb).
Check the pipe joints or for any way air could be getting into the exhaust system. Throw in an overly rich mix and the problem is compounded.
20MPG? Are you sure it isn't a Super Hawk?
One more question-- is it a constant velocity style carb?
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Old 05-07-2013   #8
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Re: Really loud backfire

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Originally Posted by WOZERD View Post
One more question-- is it a constant velocity style carb?
Maybe these will help



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Old 05-07-2013   #9
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Re: Really loud backfire

Many of the big Kawasaki cruisers, as well as some H-D models, use the Keihin CV carb. I found a link to a pretty basic primer on the theory, function and tuning of the carb:

http://www.gadgetjq.com/keihin_carb.htm

Not sure if the one on your bike is the same model, but the thing should work the same. Find your bike schematic online and check out the part numbers for your specific year/model.
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Old 05-07-2013   #10
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Re: Really loud backfire

I have a 1/4 bottle of seafoam in it and a fresh tank of gas, we'll see what a couple of days of riding produce. As of this afternoon the back fire is only there between shifts below 45 MPH.
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Old 05-07-2013   #11
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Re: Really loud backfire

Muffler bearing going bad?
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Old 05-08-2013   #12
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Re: Really loud backfire

Quote:
Originally Posted by AnswerMeister View Post
I have a 1/4 bottle of seafoam in it and a fresh tank of gas, we'll see what a couple of days of riding produce. As of this afternoon the back fire is only there between shifts below 45 MPH.
When I had my 2004 Vulcan 1500 Classic (carb) bike, I took it down to Bike Barn. Allen cleaned and adjusted the carb on the Vulcan where it ran like a new bike with lots of power. The gas mileage was good too. He revived the Vulcan and we rode it until reach mid 70,000 miles (I bought the bike when it had around 3200 miles on it).

Bike Barn is out on KY 36 near Jonesville, a good ride to the place.
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Old 05-08-2013   #13
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Re: Really loud backfire

I have a couple of guys a little closer but it's good to know there is an expert that close.
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Old 08-17-2013   #14
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Re: Really loud backfire

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Originally Posted by WOZERD View Post
Gas, even unburned gas, needs oxygen to burn. You should be looking for an exhaust leak-- not an intake leak
So I took the exhaust off and the flanged header pipe for the back jug was bad. The flange pulled away. I had that welded and put in some new crush gaskets and we got rid of the back-fireing and popping.
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Old 08-18-2013   #15
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Re: Really loud backfire

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Originally Posted by AnswerMeister View Post
So I took the exhaust off and the flanged header pipe for the back jug was bad. The flange pulled away. I had that welded and put in some new crush gaskets and we got rid of the back-fireing and popping.
Good to hear (or-- should I say-- NOT hear!)
I meant to say PARTLY burned (instead of unburned).
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