Rear Cylinder not running unless Carb Intake 90% covered

ejohn90472

I have a 2002 Sportster 883 with 728 miles on it. The bike starts with the enrichment cable pulled all the way out. However. once the bike starts it will only run above 2500 to 3000 RPM with the back cylinder kicking in occasionally. As I try to drop the idle the bike wantz to die with the rear cylinder not running correctly and staying cold.

I checked the spark on both the front and rear cylinders – the front plug fires straight across the spark plug while the rear cylinder appears to be sparking in all directions. I changed the plugs and that still didn’t change the rear cylinders performance nor correct the problem.

What did work is when I removed the air cleaner assembly and placed my hand over approximately 90% of the carburetor intake. The bike then appeared to run fine. I was able to push in the enrichment cable while maintaining my hand 90% over the Carb intake. I’m not sure what this could mean and was hoping that the Harley Guru’s here could HELP!

Any recommendations would be appreciated. Thanks


ejohn90472
2002 Sportster

Bluesssman

I would be looking for a possible intake leak. Putting your hand over the carb intake is enriching up the mixture. That would be my first thing to try. Other questions, how long has it been sitting? Was any gas stabilizer used? A 2002 bike with only 728 miles... wow! It must be stored quite a bit.

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glider

If the bike has been sitting a while stored, sounds like the low speed jet is clogged or you have an intake leak, possibly on the rear cylinder. Drop the float bowl if you can handle this and clean the carb/jet out.

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bikermonkey

I don't know how reccomended it is,,,,,but I have found intake leaks by spraying ether around the intake boot area,, the idle will increase if a leak is present. I'd more likely suspect a clogged jet.

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67hat34c

Eather is way too dangerous for this. Use wd40 or simply put your fingers around the area, you can feel the air movement.

glider

What's dangerous about a squirt of WD40 around the boots to check for a leak. Most times a small intake leak cannot be felt with the hands, it's not like a leak where air is pushed out.

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Zamadan

Think he meant to say ether is to dangerous, use WD40 instead.

glider

OOPS, You're right there .I missed the "ether" part. For sure you would get a bang out of that.

Have to learn to read slower but I swear that post read differently when I replied to it.

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cansel kansu

Spraying water will do the same. if there is a leak, water will be sucked in and idle will also increase. this is very common way of finding intake leaks at most of the engine repair workshops.
I had pretty much the same problem till yesterday.
I first changed the places and then replaced the spark plugs with new ones, no help!
First changed the places of spark plug wires connection points on the induction coil end and then replaced with new ones, no help!
I got my compression ratio measured, 9 bars both cylinders, no prob...
Tried to tune the ignition angle by rotating the igniton module, no help. (I was the first one unscrewing the fixing screws of the ignition module plate, there was no screw tightening mark on any other place before I started to tune) then did the static tuning before closing the cower.
I was just hopeless about finding a solution and started to check ebay for buying a single fire igniton kit or a complete upgraded carburator yesterday then I wanted to give a try for tuning the carburator. I took the carb out and set the idle mixture adjustment screw only 1 turn off from the max in position. now I can hear that both cylinders are firing. the new problem is, idle rpm increases as the engine warms up, up to 15-20 minutes. when I adjust the idle after 20 mins, then cold running will be too low. this is not annoying me as much as loosing the back cylinder so I consider my back cylinder problem solved.
any suggestions for the idle fluctuation issue is wellcomed.

glider

You may try adjusting the idle mixture fully warmed up to the highest and steadiest setting. Too many people think the 1 turn open is the place to be when it's not at all. It's an "adjustment" that will return a good running motor when it is done properly as long as other areas are not causing a problem.

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