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Old 05-10-2011, 10:50 PM   #1 (permalink)
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stage 1 tc88 low speed jetting problems

Ive got a stage 1 tc88 in my 2000 fxdl on the factory cv carb and i cant seem to get the low end straightened out. Ive already checked for intake leaks and there are none.

My question is should a mildly modded tc88 require a 48 pilot jet under any circumstances? Carburetor is clean as it should be as I went through it about 2 months ago yet i still get it spitting back through the carb at low speeds rolling on the throttle.

It had a 40 in it when i first pulled it apart and I was under the impression they had 42s stock in them. Right now I am running a 45 slow jet with the screw almost 4 turns out and still get popping when its under 80 degrees ambient. I just wanted to know if this sounded strange to anyone else, or if I should just stick the 48 in it and be happy. Elevation is about 800-1500 above sea level depending on whether I'm home or not.
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Old 05-10-2011, 11:28 PM   #2 (permalink)
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Need more info...
Has it done this since day 1 or is this carb new to your bike?
What exhaust are you running?
Where is your timing?
What do your plugs look like?
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Old 05-10-2011, 11:31 PM   #3 (permalink)
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kehin makes a jet kit and it comes with a new needle it the needle thats the the problem it comes with e few slow jets and a few main jets and a fool proof guide just go down the list of mod combos and find your and it tells you what to do did my wifes sporty and it was perfect
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Old 05-11-2011, 12:36 AM   #4 (permalink)
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Quote:
Originally Posted by BandidoLenny View Post
Need more info...
Has it done this since day 1 or is this carb new to your bike?
What exhaust are you running?
Where is your timing?
What do your plugs look like?
carb is original to the bike, started doing it this year, moreso after putting the k&n intake on. I also went to the 45 pilot at the same time, and have checked for leaks several times.

v&h bigshots, that have been on it since i got it.

Im somewhat new to harleys, I was under the impression the timing was locked down on these?

New plugs, dont show majorly lean, but it still pops when i roll on it softly. Wont do it past about 3000 rpm though.

I still come up with nothing, but due to the lack of harley tuning experience i have, seems to me it should be getting plenty of fuel now. Just wanted to make sure I should be jetting it up more, and Im not just covering up an existing problem.
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Old 05-11-2011, 12:47 AM   #5 (permalink)
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Do you mean a K&N "air cleaner" or "intake manifold"?
If all you changed was the air cleaner then yes... you will need to richen up the carb. Keep reading your plugs to make sure that you are not going too rich.
If re-jetting does not solve your problem then you may look into the above mentioned slide needle modification.
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Old 05-11-2011, 01:01 AM   #6 (permalink)
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Quote:
Originally Posted by BandidoLenny View Post
Do you mean a K&N "air cleaner" or "intake manifold"?
If all you changed was the air cleaner then yes... you will need to richen up the carb. Keep reading your plugs to make sure that you are not going too rich.
If re-jetting does not solve your problem then you may look into the above mentioned slide needle modification.
Im beginning to think i may need to do something with the needle. The k&n unit im running is the rk-3910, with the backing plate and velocity stack and whatnot. I didnt think it would make THAT much of a difference airflow wise which is why i went to the 45, but Ill shim the needle and see what happens, if that doesnt work ill step up to the 48.
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Old 05-11-2011, 01:12 AM   #7 (permalink)
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Shimming the needle should help the drivability so it's a mod that you would want to do anyway.
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Old 05-11-2011, 01:13 AM   #8 (permalink)
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Quote:
Originally Posted by BandidoLenny View Post
Shimming the needle should help the drivability so it's a mod that you would want to do anyway.
Don't forget that your slow jet needs attention too... that's the circuit where your carb is popping on when revving up off idle.
Yeah being 4 turns out i think i need to go up one whether i shim the needle or not. Guess ill head to the hardware store in town tomorrow.
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Old 05-11-2011, 01:34 AM   #9 (permalink)
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Jor Minton has written about this problem in American rider a couple of times. His solution is to remain with the stock high speed jet for mild mods but to chang to the 1200 sportster needle which hgives a smoother transition, while eliminating popping on decel and it still maintains your mileage. Have shared with friends, most very happy with this simple solution. Also have watched Dr Dyno shim the needle and return to near stock jetting to resolve an A/F mixture issue.
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Old 05-11-2011, 07:13 AM   #10 (permalink)
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efb,

Did you buy this bike new or used? Sounds like you got it used being that it had a 40 slow jet in it. Are you sure that nothing else has been done to it, for instance, someone messed with drilling out the hole in the slide or put a different needle in it or a different spring?? I'd stay away from CV carb kits and follow the suggestions in the article below. You also didn't mention what exhaust you have. Depending on what's on there, that could also make a big difference, for instance, straight drag pipes.

I'm not positive on Dyna's but on 2000 touring carbed bikes, a 45 slow jet was stock. 1999 (1st year TC), the touring bikes had a 42 as stock. I don't think TC's ever had a 40 as stock slow jet.

If you don't have a HD service manual for the bike, I'd strongly suggest you get one. Lots of good info there including stock jet setup.

Here's some info from Joe Minton that someone else mentioned. Might help you.
Taken in part from a tech article by Joe Minton in July 02 issue of American Rider.
Carbureted evo, twin Cam and Sportster engines can have their air/fuel mixtures corrected with one part - a stock Harley part - the needle from a 1988 or '89 1200 Sportster (HD part #27094-88). There's no need for an elaborate kit or to make extensive modifications to the stock Keihin CV carb.

Even with the Screamin' Eagle or other hi-flow air cleaner and a set of free flowing mufflers, the stock main and slow jets are correct. You do not need to change the main jet when you fit a set of say, Cycle Shack slip-ons and a free-flowing air cleaner. Just install the new needle, remove the aluminum plug over the mixture screw and adjust it outward for best idle.

With these two simple modifications, your Twin Cam, Evo or Sportster motor becomes the civilized and responsive powerplant it can and should be.
Why is the solution so simple, you ask? Because the only area in the throttle range where stock Harley engines are lean is in the first quarter of throttle slide movement. That is where government controls require such lean mixtures. The straight-diameter part of the needle, together with the needle jet it fits into, controls mixture in this throttle range. When the needle's straight part is smaller in diameter - which the early Sportster needle is - and the mixture gets richer, the engine runs better.

The stock main and slow jets are OK for two reasons. The mixture screw controls the slow jet's fuel delivery into the engine at idle and very low speed, and it is a simple adjustment. The main jet doesn't figure into emissions testing. Harley, like most manufacturers, fits a slightly large main jet to make sure the mixtures do not become too lean at full throttle with free-flowing air cleaners and exhausts. Therefore, when you fit that combination of free-flowing air cleaner and mufflers, the main jet becomes correct (AT OR NEAR SEA LEVEL). The slow jet is the right size in the first place. It simply needs to have its delivery volume increased with the mixture screw.
END OF ARTICLE

The stock needle can also be shimmed in lieu of using the 1988 sportster needle.
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Old 05-11-2011, 09:03 AM   #11 (permalink)
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4 turns out is to much, 45 slow jet is probably to much.

Leave the needle alone, unless you go to the sportster needle.

Spend 18.05 at your harley dealer and get a new accellerator pump diaphram.

The problem you are most likely having is when you give that lil rev at a stop sighn or light while waiting to go. You probably have that lil pop and some times while warm that pop stalls it.

I have been finding this alot in the 99 thru 04 carbed 88's.
Most, if not all are the same thing. It seems thru repo's and other reasons I do not know of that we have a generation of machines that are being bought by dealers from Auctions.
I'm not sure of why they are at auction but they all seem to be developing the same problems a bike that has been sitting up in warehouses or something with no gas in them. I have been finding these accellerator pump diaphrams to be perfect on the back (air) side but to be pretty britle to the worst I have ever seen on the front (gas) side.

Look at the machanical linkage of the carb with the bike off. Simmulate that lil throttle movement that you make when it pops, you will see it is rite when the accellerator pump first starts to stroke.

Try it out for $18.05 I believe you will find it's an easy fix.

Set that A/F mixture screw back to 2 to 2 1/2 turns and set your idle rite again. By the time July comes around you may want to find that 42 slow jet and get her back in there too. The slow jet will have no affect on that popping.
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Old 05-11-2011, 09:26 AM   #12 (permalink)
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A trick that has worked well for me with tuning CV carbs. Inexpensive and easy to do, go to Radio Shack and buy some precision washers, about 1/32" thick, 1/4" in diameter, with a hole about the same size as the jet needle. Remove the top cover off the carb and carefully pull out the diaphram/slide/needle. Remove the needle and place 3 washers on it as to raise the needle height. This will richen the mixture evenly across the whole rpm range. If the motor is still stumbling or flat, add 1 washer at a time until it runs smooth.
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Old 05-12-2011, 11:41 PM   #13 (permalink)
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Well after taking the carb apart again and pulling the needle to shim it, I saw that the previous owner had put shims in there.
Of course, he just carefully set them on TOP of the needle. Guess he doesnt understand how a carb works.
I figured they would probably work better underneath, so thats where i stuck em. Havent had a chance to play with it yet since its raining, but i suspect thatll do it.
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