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Old 08-05-2008, 07:01 AM   #1 (permalink)
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Backfire - Carb and Pipes

I have several problems that I think are related.

I follow the 3 min, 3 mile warm up faithfully with my ride. (1998 FXSTS) Lately and it's happening more and more, I am getting backfires on acceleration (only after I close (push in) the enrichener), on deceleration and at times just in normal cruising.

The acceleration backfire is coming from the carb and rarely is heard in the pipes.

The deceleration is for sure in the pipes.

In normal cruising at times it is just like a major cough... almost like it's getting no fuel for a minute. I also get this sensation at times that I'm not firing on both cylinders.

Under major acceleration however, it doesn't backfire once I get to the power curve (don't know how else to explain that). At least if it does it's very rare.

Also including the acceleration backfire it is constant at take offs from stand still unless I up the revs prior to releasing the cluthc. (Sure don't like doing that!)

I have cleaned the plugs... then installed new ones day before yesterday gapped at 40.

I have read something about working with the carb but don't know how to do that. I believe the air/fuel mixing screw is sealed with an alluminum cap. Would like to know how to do this if it is practical.

My ride is a 1998 FXSTS with just over 11,000 miles. I bought it second hand in China (that's where I live and ride so dealers are hard to come by. To my knowledge there is only one in Beijing with a branch in Shanghai. I live far from both of those places.) so I am not sure if the carburetor is stock or not. Nor do I know how to tell. It does look like what is in my service manual though.

My pipes look normal but I know they have nothing inside. This ride is loud!

I have been wanting to check my timing thinking that may be part of the problem since the bike rides "hot". I feel it is much to hot at the end of a ride... but then I have read that could be caused by to lean a mixture at the carb. I have tried and tried to both find and/or make a sight glass for the timing hole but no luck so far.

I have also read a person can test for leaks with carburetor cleaner. Don't have any and sure don't know where to get any here. Is there something else a person can use?

I know this is rather lengthy but I would sure like to get this delima taken care of. I fear this backfiring is not doing much good to my ride!

Since buying this machine I have changed the fluids, adjusted the clutch, installed a new clutch cable I waited for one month to receive from the States, adjusted the primary chain to 3/4" play and loosest point, adjusted the hex bearing retainer and the fall away on the front wheel/fork, checked the oil pump with a clear flexiline to make sure oil was pumping into the tank and torqued all nuts and bolts to service manual specs. I think I get around fairly good with the maintenance as long as it's not major overhaul so if anyone can point me in the right direction with this back fine issue I would be most greatful!

Thank You and cheers!
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1998 FXSTS Springer Softail
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Life is not about waiting for the storm to pass....
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Old 08-05-2008, 08:15 AM   #2 (permalink)
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claydbal is reading this now saying WTF is this?
oowf, your fart , belch, hiccups and loud pipes are directly related.

search for a how to remove the seal on the idle mixture screw, and look into ordering a 46 pilot jet. the mix screw may fix ya, but for a few bucks it would be nice to have the pilot in hand in case thats what it takes. timing cant be checked or changed unless you buy a unit like the DTT.

good luck.

BTW, a set of baffles may cure ya also, certainly wouldnt hurt-------do angry chines police still kill people?
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Old 08-05-2008, 11:21 AM   #3 (permalink)
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oowf take a look here http://www.nightrider.com/biketech/hd_cv_mods.htm
that will tell you how to remove the plug on the idle mix screw and alot of other info about your carb .

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Old 08-07-2008, 02:56 AM   #4 (permalink)
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Thanks Claydbal and LoneEagle964 for your replies.

First of all (sorry for my lack of knowledge) what is a DTT? And as far as the baffles are concerned, I have yet to find an outlet that is willing to ship to me here in China. If anyone knows of one that sells HD parts and/or after market that will ship internationally I would sure appreciate their name. I have looked extensively... filled out several on line orders just to be told they won't ship to me here in China.

My service manual is very clear on how to adjust the timing. I have the proper timing light but so much oil mist spews out without that sight glass it is impossible (along with my old eyes) to see what is going on. I'm currently trying to make on, by the way.

This afternoon I'm going to purge flush my bowl and adjust the mixture screw. Thanks to everyone who has offered information I found a lot of articles on how to do that...

OH.. and by the way... the police don't try to kill ya.. but they all want to ride your bike! (NO WAY JOSE!) and get a little uptight when they hear the negative answer... so I just tell them they are used to riding a bike that weights 200 lbs... this one weighs almost 800 and while there's is a 250 CC this one is close to 1,400... so they need special training and then I will be happy to let them ride it! <grin>

Thank you again!
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The Oowf

1998 FXSTS Springer Softail
17,950 Kilometer - 11,153 Miles
I think everything is stock.

Life is not about waiting for the storm to pass....
It's about learning to dance in the rain!

Last edited by oowf; 08-07-2008 at 03:06 AM. Reason: Correct Spelling
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Old 08-07-2008, 03:07 AM   #5 (permalink)
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Quote:
Originally Posted by claydbal View Post
oowf, your fart , belch, hiccups and loud pipes are directly related.

search for a how to remove the seal on the idle mixture screw, and look into ordering a 46 pilot jet. the mix screw may fix ya, but for a few bucks it would be nice to have the pilot in hand in case thats what it takes. timing cant be checked or changed unless you buy a unit like the DTT.

good luck.

BTW, a set of baffles may cure ya also, certainly wouldnt hurt-------do angry chines police still kill people?
This bike is an Evo. Sounds to me like you're offering advice for a TC??????????????

oowf,

Popping on decel is probably due to the exhaust system. Make sure the intake manifold is sealed tight at the heads and that the carb is seated in the throat of the manifold properly. Also make sure you have no exhaust leaks.
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Last edited by Ed Y; 08-07-2008 at 03:12 AM.
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Old 08-07-2008, 06:36 AM   #6 (permalink)
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Yes, this bike is an Evo.

Well, today I flushed the carburetor bowl by backing out the purge screw and working it back and forth. The first time around I flushed through about two ounces of gas and it had a lot of minscule black objects like dirt. So I repeated the process about ten time with the last time dumping through about eight ounces of gas. Still dirty but not as bad.

I also removed the tank filter screen at the pit cock, blew it clean (didn't appear to be dirty in the first place) and put it back.

So... I ran out of time but decided to make sure my throtle and idle cables were adjusted correctly before getting into messing with the mixture screw. I couldn't do it.

According to the service manual I am supposed to loosen both cables to zero adjustment then made sure the handlebars were straight ahead and open the throttle wide open. Then lengthen the cable until the throttle cam just touches the cam stop.

I can't do that. I run out of thread on the cable adjuster before the cam gets to the cam stop. It's about 1/4" short of touching the cam stop.

Since I can't get that part set right I'm wondering if I'm doing things in the incorrect order here. Maybe I need to figure out why the cables don't adjust properly.

Ed Y's comment is surely appreciated. I will do everything you suggested tomorrow but I am quite sure these pipes have nothing in them. Would that contribute to the popping on decel?

I guess this is the bain for buying a used bike...not knowing what is stock and what is not and what the last guy/gal did... although it is sure fun working at getting everything
tuned just right.

This evening after I flushed the bowl and cleaned the pit cock screen I took her for a ride and it ran worse than it has before... actually it seemed the idle I had set about three days ago was way, way down now so I guess I need to adjust that tomorrow as well and I don't guess... I know I'm a little confused right now...

One stupid question. (I think I'm allowed one a day... <grin>) It seems to me it's going to be rather difficult to adjust the mixing screw with the bike running. Is there a special trick to that and also with the air box removed will I get a true tune?

Cheers and Thanks!
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The Oowf

1998 FXSTS Springer Softail
17,950 Kilometer - 11,153 Miles
I think everything is stock.

Life is not about waiting for the storm to pass....
It's about learning to dance in the rain!
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Old 08-07-2008, 07:45 AM   #7 (permalink)
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claydbal is reading this now saying WTF is this?
yep, i notice the 1998 now. sorry!

oowf, you dont need to have parts shipped to you-----you are in china, thats where all harley parts are made!
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Old 08-07-2008, 08:18 AM   #8 (permalink)
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Based on your explanation, it sounds like you don't have the right cables on the bike. All things being equal, that's the only reason I can think of that would make you run out of threads before the cam hits the stop.

Your best bet would be to remove the carb and check the whole out on the work bench. And yes, the mixture screw can be adjusted with the bike running. Before doing the final adjustment, make sure the bike is up to normal operating temp (at least 20 mile run). Take off the air cleaner cover and use a short or shortened screwdriver that fits. Generally speaking, you could probably just set the mixture at about 2 1/4 turns out and be pretty close.

And pipes with nothing in them (drag pipes) will almost always cause popping on decel. It's not a bad thing just annoying. It's the spitting thru the carb that's the problem.
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Old 08-07-2008, 08:41 AM   #9 (permalink)
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Ha.. Claydbal... You are probably right about their being made in China... but I can't get my hands on them.

There is one Harley dealer that I know of in China and it is in Beijing with a small branch office in Shanghai. They told me it would take four weeks to get a #46 Pilot Jet and a #185 because it had to come from Milwaukee... go figure!

And Ed Y your last comment leads me to a question I've been wanting to ask for some time now. Can a person shorten his own cables?

I just received a new clutch cable (works great too) I ordered about a month ago. The reason for the replacement is the clutch cable on the bike when I bought it looped up above the handle bars about ten inches. I assume at one time someone had some mod handle bars on here thus the long clutch cable.

If I could have I would have shortened it myself. Is that ever done? Can common soldering hold the nub in place on the end of the cable if one does that?

Ok.. it's late here in China town... I'm going to sleep and try all of this stuff tomorrow!

Thanks and cheer!

P.S. I seem to remember reading a few weeks back about welding some washers inside the pipes toward the tail end. Have you ever heard of that? I can't for the life of me remember where I read it but they were talking about how making sure the washer hole was centered in the pipe. Is that some type of baffle?
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The Oowf

1998 FXSTS Springer Softail
17,950 Kilometer - 11,153 Miles
I think everything is stock.

Life is not about waiting for the storm to pass....
It's about learning to dance in the rain!

Last edited by oowf; 08-07-2008 at 08:44 AM. Reason: To add one more question!
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Old 08-07-2008, 11:06 PM   #10 (permalink)
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Gentlemen.... Claydbal, LoneEagle964 and Ed Y,

I did everything I set out to do this morning here in China... benched the carb, cleaned it all up, set the mixture screw to 2 3/4 out from light seat, added 3/32" of washers to the Jet Needle, tightened the intakes at the heads (two screws were loose) put her all back together and now I can tell it's an evolution engine... smooth as silk... goodness... I am literally thrilled.... it is the smoothest running Harley I've ever ridden...

Thanks so much for you sound advice! It all worked great!

Cheers!
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1998 FXSTS Springer Softail
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I think everything is stock.

Life is not about waiting for the storm to pass....
It's about learning to dance in the rain!
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Old 08-08-2008, 06:30 AM   #11 (permalink)
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What was the problem with adjusting the cables???

Operator error?????
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Old 08-08-2008, 07:33 AM   #12 (permalink)
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You know, I just don't know. Since I can't come up with a reason it must have been operator error...

All I know is on re-assembly everything fit just nicely. Well, almost. The idle return cable is still a tad long. It is adjusted to the Max and barely qualifies... but it works OK. No tension on the idle cable at all except at idle... as it should be from what I understand.

Got in two hours of ride time this evening... totally enjoyable!
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The Oowf

1998 FXSTS Springer Softail
17,950 Kilometer - 11,153 Miles
I think everything is stock.

Life is not about waiting for the storm to pass....
It's about learning to dance in the rain!
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Old 08-08-2008, 08:00 AM   #13 (permalink)
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claydbal is reading this now saying WTF is this?
oowf, i can apreciate what you are doiiing. back in the day, we had to do what you are doing now. adapt, overcome and make do!!! no internet, no parts, dealer was only place to get parts and they would usually have to order.

being in china, you are like we were 30-40-50 years ago. you sir are a pioneer in effect!!

keep the shiny side up!
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Old 08-08-2008, 09:37 AM   #14 (permalink)
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oowf I have not tried but have been told that other bikes , honda and others also use the same carbs and you can get jets from those dealers you may want to check that avenue if you do indeed need other jets for your carb.

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Old 08-08-2008, 12:24 PM   #15 (permalink)
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Some Kawasaki's for sure use a CV carb.
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