intermittant carb problem

1990 softail CV carb. bike was running fine, then it started coughing a bit just off idle at steady speed coasting and just off idle in traffic, and I do mean "just" off idle. I have completely disassembled the carb 3 times now, cleaned thourghly in the parts washer, with compressed air, and carb cleaner, and am positive none of the passages are obstructed. I have also closely inspected the slide diaphram and accelerater pump diaphram by placeing them in front of a bright l.e.d. flashlight while gently stretching each of them to reveal any pinholes that may be present. no pinholes or cracks were revealed. The fuel tanks were removed and rattled with ball bearings and alcohol, thourghly washed with hot soapy water then rinsed with an ocean full of fresh water, then alcohol again, and finally rinsed with fresh fuel, emptied and left overnight to dry. Everything reassembled without incident, i.e. the diaphrams seated correctly, and nothing pinched or bound in anyway. This carb has been modified previously, idle screw has been uncoverd, and I belive the slide drilled out to 1/8". In an attempt to tune it after this cleaning I followed the proceedure of turning idle screw to lightly seated then backed it off 2 turns to establish a base line for fine tuning. brought the bike to operating temp by riding it a bit, then attempted fine adjustment by idleing at aprx 950-1000 rpm turned idle screw in till the engine began to idle roughly then backed out the idle screw 1/4 turn. All this helped, that is untill I tried to ride it again. repeated the entire process several times, turning the idle screw in increments of apx 1/8th of a turn first richening the mix then leaning out some, everytime I think it is right it will run fine for awhile, sometimes I cant make it cough through the exhaust no matter how hard I try, and then the next time I try and ride it the whole thing starts all over again. The carb to manifold seal seems to be fine, not mis-shapen, loose, torn or damaged visably, and seating the carb into this seal requires a bit of effort due to the snug fit. The manifold to head seals show no signs of leaking, and I am not getting any backfires through the air filter, just through the exhaust, which makes me think an overly rich situation, and leaning the idle mix doesnt seem to help much when following the above mentioned proceedure. the part that has be baffled is it ran fine for over 3500 miles before this all started so I dont think re-jetting is the issue. Any one got any ideas, and sorry bout being so long winded I just wante to put out a comprehensive explaination of what is happening and what I have done. I guess the next step is a rebuild kit and new intake seals, barring some help here . thanx in advance

Re: Intermitant carb problem

I forgot to mention that I can avoid the exhaust popping by driving through the rough spot, i.e. bringing the revs up to about 2000 rpm and slipping the clutch but who wants to have to ride like that eh ? Mid range and top end are fine, and it idles smoothly, its this issue just off idle thats killin me. I have also added some Berrymans chemtool carb and injecter cleaner to the fuel and run almost a tank full of premium fuel through, just to be sure there was no residue in any of the carb passages.

Re: Intermitant carb problem

actually I havent tried that although the thought did occur to me the other day, dont remember why I didnt follow through on it, I'll give that a shot in the morning. I just want to come up with a correct diagnosis before I start throwing parts at it . thanx for the reply, I'll post the solution or further frustration as the case may be.

Re: Intermitant carb problem

OK tried the leak finding thing. it was running sort of OK last night when I quit, this morning tried to warm it up and played hell keeping it running, so again I turn the idle screw to lightly seated back it off 2 turns and try to warm it up some more and its seems even worse today...... think I'll get the gun and shoot it or me, this is killin me here!

Re: Intermitant carb problem

OK heres the deal...... it pays to be absolutely sure what you are dealing with....yes the carb was absolutely full of rust sediment and all sorts of crap, as were the fuel tanks. So after the thorough cleaning of the carb and tanks, and all of the tuning efforts, the more I worked with it the worse the problem got. To the point I couldnt even get it to run even slightly OK. The clue that sent me in a different direction was the tach started bounceing wildly. Conclusion, the problem has to be electrical in nature. Long story short (oooops to late) I start swapping out parts I have laying around the shop, coil, ignition switch, then the ignition module Hit the starter button the motor fires, stumbles for 2 or 3 seconds and EUREKA!!! smooths right out, take it out for a test ride and it runs smooth as silk. Conclusion, the Screamin Eagle ignition module was bad. I dont know if this is common for that unit or not. The problem presented itself in slow degradation of performance, I would have thought it would have been more of an , on or off situation, meaning it either works or doesnt work, obviously I couldnt have been more wrong. I guess my long winded point here is pay attention to the finest of details, and attack things with a systematic approach, and keep track of all that you do. And take a break once in awhile and come back with fresh eyes.

glad you got her fixed....always good idea to have a beer...and relax and take a good look at the problem.....