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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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  #1  
Old 20th August 2012
Peanut Peanut is offline
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Default Still coughing through carb along with other problems.

This weekend I went back through the carb replacing the fuel pump diaphram and installed the ez-tune mixture screw recommended by Hogmania. Great product Hogmania, thank you for the advise. I took the two inch drag pipes off and put the stock exhaust back on. I also replaced the spark plugs and gapped the plugs at 40. I found an exhaust leak on the right boot behind the carb. The bike is still coughing through the carb every once in a while. It also back fires a little when de-accelerating. It is accelerating much better but stills seems a little sluggish.

Any thoughts on what to do next would be greatly appreciated.
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  #2  
Old 21st August 2012
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Two things cause carb farts: lean low speed mixture and overly retarded spark at idle.

What kind of carb do you have?
If it is the stocker, you most probably need larger low speed jet. Something like an 80.
You probably need a bigger than stock main jet too.

The other cause of carb farts can be a worn out auto-advance unit in the ignition allowing too much retard at idle/low speeds.

If you look in the Tech Stickies Index in red near the top of the Ironhead forum page, there are threads in there on tuning the Keihin carb.

A third possibility is your pushrod clearances need adjusting. There is a video on this in the stickies too.
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  #3  
Old 21st August 2012
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glad you liked the EZ tune mixture screw, it really makes it alot easier to tune the carb, follow Hopper's advice you'll get it going good soon I bet. Keep up updated.
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  #4  
Old 21st August 2012
Peanut Peanut is offline
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It is a stock Keihin carb. I believe the main set was a 178 and the slow jet was a 77. The bike has 21K miles on it.
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Old 22nd August 2012
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sounds like someone played with the jetting before, those aren't stock sizes for a 81
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  #6  
Old 22nd August 2012
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For 1981 stock jest are main 160, slow 68. You could go to main 170, slow 75. Best to follow correct re-jetting procedure. For the slow jet follow the pilot screw setting Sticky.
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Old 18th September 2012
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Default Still have the Carb Farting

Quote:
Originally Posted by IronMick View Post
For 1981 stock jest are main 160, slow 68. You could go to main 170, slow 75. Best to follow correct re-jetting procedure. For the slow jet follow the pilot screw setting Sticky.
I ordered and installed the correct stock jets and a new set of intake clamps. The bike is still coughing. At one point it coughed and gas came out of the carb and flashed on the exauhst. For some reason I can't open the linkes on the carb tuning in the stickey's. Im about ready to push this thing to the curb.. Im going to look at the spray pattern in the carb and adjust if need be. Then Im going to adjust the push rods. Am I on the right track?
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Old 19th September 2012
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You are right about those links, they are no longer working.

Checking/adjusting the pushrods and checking/setting the ignition timing are definitely the right track.

I have no direct experience with carb backfires so others will have to comment.
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  #9  
Old 24th September 2012
Peanut Peanut is offline
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Update: I got a day off and worked on the bike. I adjusted the push rods and inspected the spray pattern in the carb. I did not find anything wrong with either of the two. The bike is still backfiring out of the carb. I was going check to timing next. Or have I missed something?
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  #10  
Old 24th September 2012
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Timing is your next step. A helper speeds things up considerably.
Pull your spark plugs and front push rod covers and timing plug and rotate motor, [Easiest way is rear tire in the air, 4th gear], till you reach Top Dead Center of the forward piston compression stroke. You'll know this when the piston is as high as it can get and both pushrod tappets are as low as they can get.

You are doing this because thru the years, someone may have had to replace your flywheel with a different year or aftermarket brand. If so post back.

At TDC you should see a straight line. That is your timing mark for the front cylinder. The double dots to the right of the line is the timing mark for the rear cylinder. You want the line mark. Once found, replace pushrod covers and spark plugs.

Put bike in neutral, Start and increase RPM to approx. 2000RPM.
Note; Your bike is going to spray a fine oil mist all over you ,the timing light and the dog. Clear screw in timing plugs are out there or just shove in some hose just short of rubbing on the flywheel.

Rev bike to 2000RPM, hold it there and stobe the flywheel. Rotate your ignition or points plate till single line is centered in the timing hole. Tighten plate and re-check timing. If good, button her back up and see if you still have a blow back problem. If so there are a few other things we can try.

You may want to check recent threads, [last few days], on reinstalling timing plug. There is no need to torque it to till it strips the threads out. It was a JBGOOD thread if I remember correctly.
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