Need advice: engine spit/cough @ throttle-up

[twins4life]

I'm ready to sell it but I love riding it.

2002 Sportster 1200, dealer installed Screaming Eagle intake & ex. #45 low speed jet, tried a #48 but fouled the plugs. With the idle mixture screw in it is worse, with the idle mixture screw almost falling out it is *better*. Even with the #48 running over rich it still spit. I've almost wore the mixture screw out from adjusting it.

It can go all day and run 100% then spit on throttle up 4 times in a row. Never misses at idle or under load always when trying to accelerate from stop. Carb is clean, tried different octane/brands of fuel.

Was told by one dealer that this 'problem' is normal for Sportsters. Is that true? Supposedly the spiting is due the the ignition system design, i.e., firing both plugs at the same time. I have crossed the plug wires and it ran so this must be true, but is this the cause of the spit?

Faulty carb?

Help!

[choppers4life]

I would check for a air leak at the intake to heads,and the carb.

[slickone]

You can get a #46 slow, they make that size. I think J&Pcycles has it. Could be air leak. I don't think it is the dual fire ignition.

[SKUNKY]

The guys are right ...you might have a intake air leak...also ...if this starts to happen again...pull the choke out @ 1/2...if it stops spitting after that then you have a fuel problem somewhere...maybe in the diaphram or acc pump...Exxon fuel works best in mine....

[twins4life]

Ok I'll check for an air intake leak. Aside from that what next? Cant be burnt valves or bad lifter because it runs idles and pulls perfect right?

Could a problem with the breather (umbrella valves) cause this?

It was suggested that I advance the timing (CW or CCW on the plate???) 2* and run only 93 octane might help, any comments?

Also, I assume this is not a 'normal' thing (spitting back), right?

Glad to hear it's not a dual fire problem.

[twins4life]

Update:

Did the spray oil thing and the idle speed dropped when I sprayed the y pipe / flange area. I used Rem Oil instead of WD-40. I expected an increase in idle speed if leaking???

Guess this indicates an air leak.

[Cadiero]

If the Idle speed definately changed while you sprayed any type of aerosol on the gaskets you do have an air leak. If you can, pull the intake off and check those two rubber gaskets for cracking. you most likely will find the problem visibly if the bike runs that poor

[twins4life]

I replaced all 3 seals. The manifold seals seemed to have melted edges, the carb slid had a lot of carbon on it, the bike must have been doing this for a long time.


Result: Went to dinner on the bike, 25 miles, no problem then spit twice while moving around the yard. Time to sell it I'm out of things to try except for a new carb.

[DyNasty]

Accelertator pump, or the air bleed jet in the mouth of the venturi.
Mine did the same thing.
A Mikuni HSR42 seemed to fix it for good though.

[twins4life]

Interesting, what did you do to the air bleed jet? My accelerator pump is functioning fine, checked that first.

[DyNasty]

Originally Posted by twins4life

Interesting, what did you do to the air bleed jet? My accelerator pump is functioning fine, checked that first.

Replaced it. It was not entirely plugged, but there was some crud in it that would not clear.
It picked up the idle quality somewhat, but in the end, I replaced the carb with the Mikuni. I got it from USA Twins for something like 250.00.
The performance gains were amazing! Very crisp throttle response and better power throughout the power curve. I did have to change the needle jet to the next size richer and I moved the clip on th eneedle from the middle position to the next step richer. It came with 2 main jets- A 155 and 160. I used the 160.

[MuddyJEEP]

hope this helps...I know its book long, but it is what I emailed another lister in need .....here ya go:

its very easy really...the dealer wouldn't help me and they kept wanting to sell me the dynojet kit and some dyno time......
I have the 04 1200...stock it has a 42 low jet and a 180 high......after 2 weeks of playing around with different jets, I ended up with the same set of stock jets installed and used the 88 model needle and shimmed it with a very thin brass washer....go to the hardware store and buy some really small washers, open the top of the carb up and look at how the needle goes into the plastic piece holding the diaphragm..this will tell you what size washers you need, as in diameter so they will fit.....you can take out the stock needle and look at it to understand what it looks like....kinda like a nail and as it sits, it closes up the orifice of the high jet,......my problems were solved when I realized that the carb uses the high jet also at low speeds....as in, vacuum pulls fuel through it also...that's when I discovered the use of the needle and its value for no farts......so, after going to a 45 low jet, I could feel the bike felt richer and a smidgen sluggish.....most important to pay attention to how it responds with each change......this was done with the stock needle installed.....it felt sluggish......I changed to a 48 low for grins because I still had pops and figured what the heck......it felt really fat and sluggish and still popped and farted some.....and the plugs showed the same, black and rich...the exhaust pipes even had a soot layer you could wipe with your finger....so back to square one.....re-installed the 42 low and still had the stock 180 high.....so I started looking at the carb when it was running and you could see the fuel is coming through the high jet at part throttle or when "blipped"...so I wizened up and started playing with the needle......I went and bought the 88 needle because it is supposed to be the "thinnest" needle they made....that alone should help a bit more fuel pass by and stop the farts....and it did, but still had an occasional fart and pop.......so I shimmed with a rubber O ring I had laying around from a box of RC car parts....it helped a lot but felt way rich when I did it....no more farts at all....so I went and bought some thin washers and started shimming down from the fat size of the o ring I had used to lift the needle or shim the needle......all in all, I ended up with the stock 180 main and the stock 42 low and a shimmed 88 needle and it is responsive as all get out...you can blip the throttle and it sounds extra crisp and responsive, it never ever farts or pops and after riding 4 k miles and buying new plugs for datas sake every 1 k miles, I have tuned it via the shims to have the plugs reading perfectly gray....I have it actually just a smidgen rich per the plugs so it is safe.......as in, plenty of fuel so it doesn't run lean, but lean enough where it is responsive and runs beautifully.......to make sure the 180 main was what was needed, I bought a couple of extra jets like a 165 and a 175...and the way to test the high side is at full throttle in 3rd or 4th gear and it will fall on its face or run out of power when the throttle is opened up all the way, if you can back off the throttle a bit and it perks up, you know you need more fuel, IE; a bigger jet....the 180 seemed perfect.....also I have found that no bike is the same as another, even though you have the same motor...weird I know.....so, when you start all of this, buy a new set of plugs so you will have a blank slate to start reading so to speak.....read the plugs after each change, but mostly, you can "feel" the difference you make...if you try a smaller main jet, be aware of what you are doing, as in you know you are providing less fuel at WOT (wide open throttle) and do the throttle tests to see if it feels like it drops in power at wot and then picks up when the throttle is backed off a bit, like a 1/4 turn......doing the needle shims, pay attention to the bike and how it feels...read the plugs for a black sooty rich condition or a sandy grayish brown color for leaner conditions...white is not good as in to lean.......pay attention and use new plugs through out your testing because they are cheap and its good to know for datas sake..........
I hope I helped and if you should have any questions, please don't hesitate to call my cell phone, I'll help in anyway I can. 281-830-2532
Good luck to you...its easier than it sounds....also, change the screws on the top and bottom of the carb and use Allen head screws, that way you can make all the changes needed without having to remove the air cleaner , carb, or basically anything...just the covers is all :-)

[twins4life]

OK, I'm with you. I'll stay with the OEM high speed and my 45 slow. I'll order a 88 needle tomorrow

My needle has two lower and two higher grooves in it so I can raise (and lower) the needle without shims. What is the OEM needle? According to the book I have a 170/195 Main jet. Is the 170 the needle size?


Thanks, I appreciate your informative response!!! (I may be calling you if I run into problems.

[HDMD88]

Originally Posted by MuddyJEEP

hope this helps...I know its book long, but it is what I emailed another lister in need .....here ya go:

its very easy really...the dealer wouldn't help me and they kept wanting to sell me the dynojet kit and some dyno time......
I have the 04 1200...stock it has a 42 low jet and a 180 high......after 2 weeks of playing around with different jets, I ended up with the same set of stock jets installed and used the 88 model needle and shimmed it with a very thin brass washer....go to the hardware store and buy some really small washers, open the top of the carb up and look at how the needle goes into the plastic piece holding the diaphragm..this will tell you what size washers you need, as in diameter so they will fit.....you can take out the stock needle and look at it to understand what it looks like....kinda like a nail and as it sits, it closes up the orifice of the high jet,......my problems were solved when I realized that the carb uses the high jet also at low speeds....as in, vacuum pulls fuel through it also...that's when I discovered the use of the needle and its value for no farts......so, after going to a 45 low jet, I could feel the bike felt richer and a smidgen sluggish.....most important to pay attention to how it responds with each change......this was done with the stock needle installed.....it felt sluggish......I changed to a 48 low for grins because I still had pops and figured what the heck......it felt really fat and sluggish and still popped and farted some.....and the plugs showed the same, black and rich...the exhaust pipes even had a soot layer you could wipe with your finger....so back to square one.....re-installed the 42 low and still had the stock 180 high.....so I started looking at the carb when it was running and you could see the fuel is coming through the high jet at part throttle or when "blipped"...so I wizened up and started playing with the needle......I went and bought the 88 needle because it is supposed to be the "thinnest" needle they made....that alone should help a bit more fuel pass by and stop the farts....and it did, but still had an occasional fart and pop.......so I shimmed with a rubber O ring I had laying around from a box of RC car parts....it helped a lot but felt way rich when I did it....no more farts at all....so I went and bought some thin washers and started shimming down from the fat size of the o ring I had used to lift the needle or shim the needle......all in all, I ended up with the stock 180 main and the stock 42 low and a shimmed 88 needle and it is responsive as all get out...you can blip the throttle and it sounds extra crisp and responsive, it never ever farts or pops and after riding 4 k miles and buying new plugs for datas sake every 1 k miles, I have tuned it via the shims to have the plugs reading perfectly gray....I have it actually just a smidgen rich per the plugs so it is safe.......as in, plenty of fuel so it doesn't run lean, but lean enough where it is responsive and runs beautifully.......to make sure the 180 main was what was needed, I bought a couple of extra jets like a 165 and a 175...and the way to test the high side is at full throttle in 3rd or 4th gear and it will fall on its face or run out of power when the throttle is opened up all the way, if you can back off the throttle a bit and it perks up, you know you need more fuel, IE; a bigger jet....the 180 seemed perfect.....also I have found that no bike is the same as another, even though you have the same motor...weird I know.....so, when you start all of this, buy a new set of plugs so you will have a blank slate to start reading so to speak.....read the plugs after each change, but mostly, you can "feel" the difference you make...if you try a smaller main jet, be aware of what you are doing, as in you know you are providing less fuel at WOT (wide open throttle) and do the throttle tests to see if it feels like it drops in power at wot and then picks up when the throttle is backed off a bit, like a 1/4 turn......doing the needle shims, pay attention to the bike and how it feels...read the plugs for a black sooty rich condition or a sandy grayish brown color for leaner conditions...white is not good as in to lean.......pay attention and use new plugs through out your testing because they are cheap and its good to know for datas sake..........
I hope I helped and if you should have any questions, please don't hesitate to call my cell phone, I'll help in anyway I can. 281-830-2532
Good luck to you...its easier than it sounds....also, change the screws on the top and bottom of the carb and use Allen head screws, that way you can make all the changes needed without having to remove the air cleaner , carb, or basically anything...just the covers is all :-)

That all sounds great but one thing a disagree with ..... the plug should be WHITE .... grey is too rich, the color on the plug is telling you that you are not burning everything in the combustion chamber. Plus you have a COMPLETELY different motor than Twinie...you have bigger cams, heads, valves, and lighter flywheels in the 04 model. Also everyone is missing the fact that the Dealer put on a S/E 44mm manifold....why would they do that without doing cams and head work? That slows down the velocity in the intake runner because its bigger than the carb throat and bigger than 85% of the intake valve face. If the velocity is slowing down then there is fuel sitting in that manifold driping into the combustion chamber which will pop and be unadjustable, thats why when you changed jets things went too rich or too lean. When you went through all you did you put more fuel into the pipes in midrange and it cooled the pipes so they wouldn't pop and it worked for you but it had to put a dent in your gas milage. Think about this, when does decell popping happed? It happens when the throttle plate is closed....when the plate is closed the needle jet is NOT in operation...put the pilot jet is and its fueling the Idle mixture. The idle mixture is the ONLY fuel the carb is giving at closed throttle. In my opinion, which comes from over 35 years in this field, The manifold has to go and I'd install a dynojet kit with a 45 pilot jet....put it on the dyno to dial in the A/F ratio to 13.7:1. As long as there isn't a intake leak OR an exhaust leak, OR retarded timing, the popping will be gone and gas milage will be good....... Muddy Jeep you fixed your problem and you proved with out a doubt that you can think things through and get results, but it can be better by attacking the problem....not putting a bandaid over it. I hope you see what I've tried to show you all here....I have watched this thread for a couple of days now to see if any one would catch the larger than life manifold.
Good Luck

[twins4life]

Tried 3 shims under the needle, no difference. I'm thinking it's not carb related.

It has been suggested to me that the dual fire ignition system is causing the spits. Any ideas about this? Seems reasonable.

Is this the answer: http://www.dragspecialties.com/fatbo...roductID=40057

My son (BMW rider) is having a field day with my problem, is he right that HD just sucks??? I'm trying real hard to prove him wrong.