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I recently replaced my stock carb (99 superglide) with a stock carb from a 96 custom soft tail. ( checked with Harley to make sure that it was compatible to be sure) However, I still have a prlblem at idle.

What started this whole thing was the installation of a new screamin' eagle air cleaner assembly. The only jet that needed replaced according to Harley was the slow speed jet, which I went from a 42 to a 50. I screwed up the float mount on the original carb during the replacement of the jet, and when I put it back together, the idle was very erratic. It appeared that the idle mixture was too rich due to the look of the plugs. (this only began after the installation of the new air cleaner kit-it ran fine before) I then replaced the carb, swapped both the low speed jet, and main jet from the original carb, and I am having the same problem as before. According to my buddy who owned the new carb, it worked well prior to him removing it, and Harley said that I should just be able to swap carbs/jets, and go.
I am beginning to think that the new low speed jet may be causing part of the problem due to it being the only thing changed from stock.
The "idle problem" that I refer to is this.. The bike starts idling ok, then after a few seconds/minutes, the RPMs drop to more of a "pop pop......pop pop....pop pop...." then stall.
Could the new low speed jet be causing my problem?

 

[Ed Y]

You got some very bad info from someone. Put in a 45 and adjust the mixture screw. You may also have to shim the stock needle with a free flowing exhaust and the SE air cleaner setup. For a better streetable approach, put the 42 back in (45 was stock from 00 on), put in a 1988 XLH needle (HD part # 27094-88) and adjust the mixture screw. I've done a bunch of 99, 00 and 01 bikes with this setup and it works good. Once in a while on 99's, have to put in a 44 slow to eliminate carb farts at very low speed..

 

[FXDeanX]

Start with the mixture screw. That controls the idle.

Dean

 

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Thanks guys. This helps out alot. I replaced the low speed jet, and ureka! There is still a slight hesitation changing from slow speed (in town) to more throttle (going from idling down a street to picking up speed), however, I am definately on my way.

 

[Ed Y]

What slow jet do you put in? Did you adjust the idle speed and then the mixture screw after warming the bike up real good?

 

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I actually went to the Harly Dealer to ask for some "expert advice", and they installed a 48 slow jet, and adjusted the idle mixture, and idle speed for me. The mechanic seemed to know what he was doing, and was willing to spend some time explaining things. According to the mechanic, there is a Yos power tube in the carb as well. He suggested that if I still notice anything strange, to replace the power tube with the stock venturi (spelling) tube, needle, and jet. According to Harley, the stock main jet for my year is a 180, and I believe the stock slow speed was a 42. The mechanic suggested with my SE air cleaner, and straight pipes, that the 48 slow speed should do it. I do have a 45 slow jet I can try if I think it is still rich. He didn't suggest that I change the main, unless I had trouble at upper end, or the plugs show fouling. The main needle that is in the carb has a small stop (looks like a washer, or clip) that limits the travel into the power tube. I am assuming this is part of the "yos" design. The mechanic thought that due to that "stop", the main needle may be "fluttering" at lower idle, causing gas to spit into the manifold at times. I'm wondering if that is where I am noticing my hesitation. One other thing that I noticed was that when I am idling through town (not really at idle, just slow, constant RPMs with no load on the engine) there is some surging. Not alot, just enough to be annoying. This is not noticable when increasing speed, or cruising, at say 60 MPH.

 

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Just took another ride, and noticed something new.. When I am at the "no load" condition as stated above, meaning going roughly 30 or 40MPH, and not increasing/decreasing speed, when I go to give it a little throttle, I notice hesitation, and at times, it backfires through the carb. Could the idle mixture have something to do with this? This is with a size 48 slow jet, and 180 main.

 

[Ed Y]

I still think the 48 is too rich. The CV carb was stock with a 42 thru 99. Some kind of change was made in 00 and stock slow jet was changed to a 45 along with a higher main jet (something about air bleeds, etc). The carb you have now, I believe from what you said, was off a pre 00 bike. Increasing from a 42 to a 48 is too much, I think. Still think 44 or 45 would be better.

With the symptoms you describe, it sounds like the transition from slow jet to needle is too rich. Doubt if the mixture screw would have that much effect there. I'm not familiar with the Yost at all so can't help there.

 

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Well, I believe I am getting much closer. I changed out the main needle and venturi tube as a result of the suggestion by the Harley mechanic (see above). Now everything in the carb is stock, with the exception of the slow speed jet. My surging went away, as did my hesitation that I noticed transitioning from slow speed to initially giving throttle to pick up speed. It seems to be running much better. As far as the 48 slow jet, I will keep a close eye on the plugs to see if I still have fouling. I have a 45 that can be easily changed if the problem persists. One thing that I am cautios of is running too lean, as I understand that this can cause major motor damage. I still get a "burp" in the carb every once in a while when sitting at idle, and goosing the throttle. I wonder if this is the idle jet, or the slow speed jet...

 

[Ed Y]

Your carb burp is either the rich 48 slow jet, the needle when you move into the transition range from slow jet to needle or the mixture screw. Did you reset the idle and re-adjust the mixture screw when you changed the emulsion tube and main jet?? Also keep the idle up to 950-1050 RPM's. If it's too low, it will cause a burp not to mention poor oil circulation and drain on the charging system.

You mentioned an idle jet. There is none. Only slow speed jet, needle and main jet. There is also a needle jet that the needle slides in and out of, but it has been the same since the accelerator version of the CV carb came out. Plug reads are very hard except at the very rich end or the very lean end due to todays gasoline additives.