2002 Dyna missfire

[FLDL02]

Hello again,

I posted about some trouble I was having with an intermittent miss fire on my 02 FXDL(carbureted). I think the problem is solved now thanks to research I have done on this forum. Thanks to all who wrote about their problems so that others could benefit from their experiences.

My symptoms:
Single engine miss fire after slight hesitation.

Occured:
During cruise with light engine load all gears when releasing throttle then easing it back on in the first 1/4 throttle range only.

Occasionally when shifting up a gear under light acceleration and low speed.

At high rpm(3000) in 1st to 4th gear. Rarely in 5th gear at high speeds.

Bike mods:
SE stage one breather with a 48 pilot and 190 main jet(stock is 45/190).

Things I checked first:
Electrical(regulators, ignition module, spark plugs and wires, battery connections, etc.)
Fuel(petcock, lines, tank contents, carb crud, octanes, enricher etc.)
Exhaust/Intake leaks, none but changed flanges and gaskets or seals anyway.
Lean/Rich, bike has normal mixture indications on the plugs.
MAP sensor, didn't change it but it seems ok.
No codes, all clr when checking with both methods( blinking light/ odo reset)
Carb float level/condition.

The only things that helped were:
Running with enricher partially pulled out, or running at high elevations and hot temperatures (southwest desert in June). I live at sea level in Vancouver, BC. It missed worst in cool damp weather.

My conclusions:
After research on this site I decided it was a lean fuel mixture condition causing the miss fire under certain conditions. Why the lean condition is present is still unknown to me. I think it is because the SE stage one kit allows more air into the carb and the PO did not have it tuned properly after installation.

Solution:
Acting on advice from this site I have made the following carb adjustments:
45 pilot, 190 main jets(both stock), needle shimmed with two #4 washers, IMS out 3 turns.
Mileage is 44mpg(combined) using 87 octane, idle is 1000 rpm.
The bike runs great, pulls enough for me and never misses now.

I experimented with the 45 and 48 pilot jet but found that with the 45 and no shim washers the bike surged and hesitated at high (2500 to 3500) rpms.
Trying 1, 2 and 3 washers, I found that 2 was the best choice. This alone completely eliminates the miss fire. The washers also eliminate the surge/hesitation that the 45 jet produces. Should I use the Sportster needle that the HD tech recommended? What about mileage?
Using the 48 jet with or without washers there was a lot of decel pop that was very hard to reduce with IMS adjustments. The pop is there because I am running with a 2 into 1 header with no muffler on. With muffler it never pops. I didn't notice any significant performance improvement using the 48 pilot jet.
By the way the exhaust never made a difference with the missing whether the stock pipes were on or the 2 into 1 with/without muffler was on.

So I have cured the symptom(the miss fire) but not the disease(the lean mixture). If any one has a suggestion about curing the lean condition without sacrificing mileage I am happy to read further.

I hope this helps others who have similar carburetor issues.

Thanks again to Glider and the rest for your insights and experience.

Pauly

 

[glider]

Pauly

I would suggest going to a #46 low jet instead of the #45 with washers. The washers raise the fuel metering rod and all the fuel circuits in the carb have to "blend" together as you accelerate otherwise there will not be a smooth transition when acceleration which will result in hesitations or surges. (lean or rich). After replacing the low jet, readjust your idle mixture to the highest and steadiest setting after fully warmed up, usually about 2 1/2-3 turns open. Set your idle speed then to 1000 RPM +/- and you should be OK unless there's an intake leak.

 

[FLDL02]

Thanks for the tip Glider.

I think I will get a 46 jet online. They are not readily available at HD dealerships unless you get a kit full of other stuff too$$.
The tech recommended the Sportster needle. What do you think?

 

[glider]

I don't like going to the sporty needle. That needle comes from a carb without an accelerator pump and when you use it in a carb WITH an accelerator pump, you run too rich and the MPG goes south. Too much fuel.

 

[fin_676]

I am with glider on the don't use the sportster needle the taper will be too steep when used with an accelerator pump and I did not work that well without the accelerator pump as that design was dropped after a couple of years
I do not understand why you think you are still lean as with a 190 main and 45 pilot you should be good if lean would backfire miss and cough back through the carb
When you go to a 46 pilot jet the you may need to remove a washer or both from the slide needle
By putting washers under the needle seat it raises the needle and opens up the main jet by approximately 1 so you are now running equivalent of a 192 main jet so when the pilot is larger the main needs to go down to maintain the correct balance of fuel delivery
The main jet supplies fuel all the time but the amount of fuel is restricted by the needle the needle is tapered so that the higher it is raised the less it restricts the main jet
But always be aware that a carb is always a compromise it is just that you need to find the best compromise for your needs you may already be at the best compromise and further fiddling may not be as good as you are now
If a carb is set up for a good wide open throttle it may have a surge or flat spot at some point or it may give a smooth power delivery through the revs but be lean or rich at wide open throttle
I think from what you have stated that you are fairly close to a good setup and only try small changes from now on

Brian

 

[HDDon]

Great explanation Brian. I think you're spot on with your observation and the OP is about as close as you can get with a carb.

 

[glider]

Pauly

This may help you understand how the fuel delivery works with the different circuits in the carb.

 

[FLDL02]

The engine missfire is a carb cough. It only happens within the 1st 1/8 to 1/4 throttle open position after coasting then applying throttle again gently in all but 5th gear. It is occasional when bike is fully warm(after 15 miles of riding) but very frequent when cold(the first 10 miles or so). That is with a 48 pilot and no washers.
With 2 washers there is no miss/cough any time.
With the 45 pilot and no washers it coughs and surges/hesitates at cruise in all gears. When I add 2 washers, no cough, surge nor hesitation with the 45 pilot or the 48 pilot.

Given that, would a 46 pilot really be any good without washers since the 48 pilot still coughs without washers?

The problem seems to be with fuel delivery in the transition from idle to 1/4 throttle. That is the needle region mainly right? So the washers are helping add fuel to eliminate the miss.

I have a 195 main jet I could try without washers but I worry about too rich a mixture and sluggish top end performance.

As far as the even/balanced transition, how would I notice an uneven transition or unbalanced condition?

Pauly

 

[FLDL02]

I forgot to add, the only 2 things that eliminate the cough are running with enricher out a bit or the two washers. The symptom is like when the main tank runs out of gas (bowl becomes empty) you get a couple of misses or coughs then she dies. I flip over to the reserve and she starts back up. Its like those single coughs just before she dies. That says fuel starvation(lean) right?

Pauly

 

[glider]

Two things I would like you to check before going any further...

1. the accelerator pump diaphragm for holes and the position of the discharge nozzle and verify that you are getting a healthy squirt from it when you twist the throttle.

2. The diaphragm in the top of the carb to be sure there are no tears or holes in it which would also give you the problem you are having. While you're in there make sure the jet is tight and installed correctly and not upside down.

Also verify the main jet needle for a part number and make sure it's the correct one for your carb.
While you're checking, make sure there are no intake leaks at the seals on the head and carb.