View Full Version : Odd sportster problem, please help! (running on one cylinder)

04-09-2014, 8:37 PM
I know there is a sportster question thread, but nobody seems to look at it enough to get anything answered. so please bear with me here guys.

OK so i have a 2001 sportster XL1200C.

it ran flawlessly before it was put away. here's what is happening.

it starts, and idles. it has NO power it seems. i have recently done a TON of work to the bike but the parts that are being used are either new or were fine last fall.

The front cylinder gets hot, the pipe gets fairly hot, but the front cylinder is blowing cold air. the rear is all normal and firing and giving me hot air.

the coil is stock, the wiring to it is stock. the ignition module is stock as far as i know. never touched them. the coil was relocated, but the wiring was not changed. I added screamin' eagle wires and put new plugs in just now. doing the hillbilly spark test, i have spark on both sides of the coil.

I have a carb "kit" installed from previous owner, the jetting was spot on and it was snappy and fast especially for a "stock" 1200c. i took the carb apart and made sure the accellerator pump was clean, both jets, and checked the air/fuel screw. it is at 2 turns, where i "think" it was.

i added breather bolts for the intake and took out the pancake. there was one hole in the carb flange that i saw and the moon intake i put on had a hole for it so there should be no problem with orfices on the carb. HOWEVER, when i lift up the slide the needle moves up in it a ways. as if there is nothing keeping it all the way down. the plugs dont come out wet so its not sticking open btw. with the choke on or off, it will idle higher but i still get no heat from the front cylinder.

i did add a ripple top from biltwell for the carb. is there any chance i messed something up? (i am fluent in working on shit) the slide does not move up on its own when i rev it in neutral (should it?)

i got a few seconds of hot exhaust out of the front cylinder when i put my hand over the pipe completely and then back to cold. made no sense to me.

it is a stock exhaust with some aftermarket slip ons (brand unknown) do you think something got in my pipes? or did i fuck my carb up on the diaphram portion with the ripple carb top?

kinda at a loss. i havent done a compression check but the thing ripped last year and i guess i dont know if lifters collapse over the winter or something. starting to think maybe something got in my pipes, but i havent had any critter problems in my garage to date. help!

04-09-2014, 9:16 PM
update: ok so i put plugs in it and went by the dynojet specs on the mixture screw, and i had to go in (they say 3 1/2 turns, seems like a ways out) to about 2.5 which is where it liked it. i held my hand over the front pipe for about 20 seconds and it started talking back to me and it hit and got warm. i got out on the road quick and gave er' and it was a pooch for a bit then it came on hard. did it again same thing. seems like it is opening the slide way late like there is a vaccum leak or something so i am going to pull that ripple top off and make sure everything is ok with the slide. but when i get on it, its like the delayed reaction but NO bog. like it either isnt advancing the timing or like the slide is staying shut for too long. any input 33'ers?

04-09-2014, 9:29 PM
pulled the ripple carb top off to find that the diaphram moved on me and there was a tiny pinched crack in it and it wasnt seated properly into its groove. looks like i found it, but ill reply once i replace it. the thing seems like it opens, but it opens too late. i wonder if that little hole was enough.

04-10-2014, 4:18 AM
Yes even a tiny hole or not sealing at the carb top can cause the diaphragm to not operate properly. As for the needle moving....it has to move. It's being pulled up by the slide. Set your air/fuel screw once you get the bike up to temp (after a ride). There's good info on nightrider.com about how to do that. I don't put much stock into feeling the air temp of the exhaust being much of an indicator of anything. I t sounds like you're on the right track with the diaphragm.

04-10-2014, 5:58 AM
Yes, bike will run like poop if you pinch the diaphram. Tp test the action of the slide, lightly blow air (from a compressor) into the oblong hole at the carb inlet top. Slide should rise and then fall smoothly when you remove the air. Replacement vacuum pistons/diaphrams are available from Drag Specialties at a reasonable price and are good quality.

04-10-2014, 7:31 AM
You can also blow into the oblong hole using your mouth. (Think of it as horizontal robot pussy.)

"Feeling" exhaust air temp ain't shit, but a fine old shop trick is to grab the spray bottle of dish soap/water you use for mounting tires and squirt both pipes, or multiple pipes on rice rockets, near where they exit the cylinder head.

Differences will be readily apparent.

I do compression checks on a "need it or not" basis. That way I KNOW what's up. Your engine is likely fine, but compression checks are free.

04-10-2014, 3:27 PM
thanks guys. i got a new diaphram and installed it properly this time, after i do some errands ill be running it again.

also i realize that the needle is fixed to the slide and it moves with it, i meant that i could push the needle up in the slide as if it were not fixed to the slide solid like it should be, but once i got it apart i realized it is held down by spring tension (by design) just a style i havent worked with before. anywho thanks for the info guys and ill be sure to get on here and let u know how it goes.

04-11-2014, 2:18 PM
new diaphram fixed the problem immediately. its crazy how much one little pinch in the thing can screw the whole works up. glad to be back to normal.

also an old school buddy of mine told me that with the stock exhaust headers with a crossover pipe, feeling the exhaust temp on the tips of the mufflers is useless because at an idle it could be scavenging the hot air through the crossover to the other pipe, so the only way to "feel" if something is burning and firing is to start it cold and tap the exhaust up at the flanges and make sure they both rise in temperature evenly. makes a bit of sense to me

04-11-2014, 8:15 PM
Glad you got it !