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Discussion Starter #1
I bought a 1999 FXDX twin cam 88, about two weeks ago with only 2810 miles. It is now at about 3300 miles. I know the miles are low, and the bike is in perfect shape, still looks new, but the age probabally means some things are just aged.

Anyways, It has begun to backfire through the carb quite loud and results in a sudden losss of power. Seems to be at around 2000-3000 rpm's when it hppens and worse when it is really cold.

I have adjusted the idle mixture to about 2-1/4 turns(ides at 1000rpm now), was at at 2 and it still does it when cold, but not as often. For reference, I have the stage 1 intake and exhaust.

My other thoughts are maybe an intake leak? Manifold or carb. Maybe the diaphram in the carb.

Maybe clogged jet or needs to be rejetted? But with the low miles I don't see this as the problem unless age as effected the jets?

Any other ideas?? How about a partial vaccum in the tank? I have read the OEM gas caps may cause this and drilling a small hole in the cap can help?

Since it is about 7 years old now, and sat in a garage for quite some time, I assume this is all alge related. Thanks in advance for any suggestions and advice. This is my first harley and I want to take care of it!!
 

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If it SPITS through the carb its a sign of a lean condition, cleaning the carb out and installing one size larger pilot jet will help ( pilot jet #46 for a 88'' and a 48 for a 95'') I say to clean it out because its been sitting so long.
If its BACKFIRING through the carb try changing the plugs and inspect the wires for dry rought. This is a starting point.....good luck
 

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Discussion Starter #3
Ok, I checked for manifold leaks using Kroil and it doesn't seem to have any.

I looked at the plugs and the look OK and are gapped properly, .040 right?

The lug wires do not appear to ave dry rought. the connectors to the ignition have a ring on the outside of the inner ring connetion that looks like it is to hold it in place. however, on the rear cylinders wire that connects to the ignition, the second outer ring is missing and it slides on and off much easier than the other bottom wire.

I also adjusted the mixture screw all the way in and it did not idle any differently than when 2 turns out. I have it now back out to 2-1/4.

It also hass a stock cap and is a california bike. Should I drill a small hole??

I am going to get carb cleaner this weakend and try that, but it looks clean, as I pulled the filter and clean it as well last weekend.
 

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Dragon_MD said:
Ok, I checked for manifold leaks using Kroil and it doesn't seem to have any.

I looked at the plugs and the look OK and are gapped properly, .040 right?

The lug wires do not appear to ave dry rought. the connectors to the ignition have a ring on the outside of the inner ring connetion that looks like it is to hold it in place. however, on the rear cylinders wire that connects to the ignition, the second outer ring is missing and it slides on and off much easier than the other bottom wire.

I also adjusted the mixture screw all the way in and it did not idle any differently than when 2 turns out. I have it now back out to 2-1/4.

It also hass a stock cap and is a california bike. Should I drill a small hole??

I am going to get carb cleaner this weakend and try that, but it looks clean, as I pulled the filter and clean it as well last weekend.
You said the plugs look good....give me your defination of good.
The plug wire fitting lose in the coil not good...it needs to be replaced.
 

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Discussion Starter #5
Plugs look in good shape, white coated.

Give me you definition of good as well please, as I am new HD's. And street bikes in general.
 

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Just as a matter of interest, the 99 TC's came with a stock 42 slow jet.
 

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Did you try the "run the bike in total darkness test"? Look for flash over or leaking spark by running the bike in a dark place (plenty of ventilation)

Usually, needle valves run about 1 1/4 to 1 1/2 turns out, check the needle to see if it has a groove from over tightening.

back fire = slower burning of a lean mixture. (most times)

Are you sure you have good compression? sometimes a bad intake valve can make noises in the induction system. You will usually hear a compression problem when the engine is cranking over. The cylinder with a problem turns faster due to less Resistance.

You did the induction spray test and did not find leaks....are you sure?

Forgot to say: the new gas really sucks and does not last long. They took the MTBE out and now use a sort of alcohol base that actually breaks down and looses many of it's combustion friendly qualities needed. Many boats have had big fuel system head aches over it. How old is your gas?
 

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Ed Y said:
Just as a matter of interest, the 99 TC's came with a stock 42 slow jet.
Did they ED??? I thought all 88'' TC came with 45s....oh well getting older by the minute:whatever:

Dragon if the pilot is a 42 install a 45 or a 46 pilot.
 

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Just a couple of thoughts. When this occurs, are you rolling on or opening the throttle quickly... gradually as in maintaining speed on a hill... or holding the throttle steady??. If it occurs with a quick opening..then it is most likely fuel related and is too lean. If it happens on a very slow opening , gradually increasing load or steady opening....it is a secondary ignition concern. Wires, plugs or a bad ignition coil..in that order.
Unless at a steady speed with the throttle barely open at all...you are not on the idle circuit at those rpms and you can forget about the pilot or idle jet and it's adjustment. If it pops on a quick throttle opening say accelerating up from 2500 rpm...then the float level is either too low or the needle is too lean.
You mentioned the idle speed didnt change when you closed the air bleed screw all the way....that is not good..the only way it was getting fuel was through the enrichner circuit. so make sure that first there is about 1/8th to 3/16ths play in the choke knob as you pull it out before you feel resistance..(to assure it's fully off when pushed in) and be
sure it is pushed all the way in and the motor is good and warm when making adjustments.
 

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hdmd88 said:
Did they ED??? I thought all 88'' TC came with 45s....oh well getting older by the minute:whatever:

Dragon if the pilot is a 42 install a 45 or a 46 pilot.
I've had good luck putting in a 44 in place of the 42 on '99 model years.
 

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Discussion Starter #12
Wow, thanks, let me go through and try to answer all of these questions to get this straightend out.


It is a pretty loud pop, from the carb. I would not call it spitting.

I have not done a dark check, I'll try that this weekend. Nor have I done a compression check. I am also pretty sure there are no mainfold leaks. I spreayed a ton of kroil and idle never changed.

It seems to happen when I lightly roll throttle back. Example, right after I swtich gears and roll back lightly it occurs. Going wide open or quick throttles are fine. Or, when I am cruising in lower rpm ranges 2000-2500 or so and lightly open throttle. If I keep the RPMs high when shifting it does not happen. SO I think 2500 and up is fine.

I'll check the choke. Also, ,when I bought the bike it had a half a tank of gas and I don't know how old it was. I have since filled up 4 times I think.

So it sounds to me like I should do the cheapest things first. Change plugs, wires, and go to a a #45 pilot jet. Sound good?
 

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Back Fire

Well, two things I would suggest, first you can take a 1/4 inch bolt, weld a washer on it and install it about 1 inch from the end of each exhaust pipe, this will most often resolve the back fire issue.

A better choice is to throw the CV carb away and install a Mikuni HSR 42 MM flat slide carb. You can buy the HSR42 EZ kit from JIREH, and it will cost $275.00, increase your HP by about 20%, and you will be very pleased with the results, also install the high flow air cleaner kit.

Good Luck,
Ray
Willow Creek Cycle:beer:
 

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Ray galetti said:
Well, two things I would suggest, first you can take a 1/4 inch bolt, weld a washer on it and install it about 1 inch from the end of each exhaust pipe, this will most often resolve the back fire issue.

A better choice is to throw the CV carb away and install a Mikuni HSR 42 MM flat slide carb. You can buy the HSR42 EZ kit from JIREH, and it will cost $275.00, increase your HP by about 20%, and you will be very pleased with the results, also install the high flow air cleaner kit.

Good Luck,
Ray
Willow Creek Cycle:beer:
Sorry but I disagree with both points you made, first off your putting a bandaid on the problem and not fixing it....throwing away the C/V for a 42 mikuni isn't going to help if his timing is off, plus I never in my day seen a 20% gain in power from a carb change.
 

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Discussion Starter #15
OK, I threw in 2 new NGK plugs. When I pulled the other two out, they were all black. They were not that before I messed with the idle. So I out it back to 2 full turns out.

Also, ,The choke has no play at all. It has resistance form the begining. Should that be adjusted??

My biggest concern is that when I close the idle jet completely it does not change the idle much is still idles at about 900rpm. That can't be good.

I took a short ride with the new plugs and checked them and they had just a slight white coating. .
 

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Dragon_MD said:
OK, I threw in 2 new NGK plugs. When I pulled the other two out, they were all black. They were not that before I messed with the idle. So I out it back to 2 full turns out.

Also, ,The choke has no play at all. It has resistance form the begining. Should that be adjusted??

My biggest concern is that when I close the idle jet completely it does not change the idle much is still idles at about 900rpm. That can't be good.

I took a short ride with the new plugs and checked them and they had just a slight white coating. .
Yes ..you need to adjust the enrichner cable...the black knurled part on the outside of the mounting bracket..the enrichner is on all the time....being held out....hence no change when you bottom out the air bleed screw for the pilot jet..and the reason for the black plugs. The pop is cause its so rich on throttle roll off ..most guys get it in the exhaust...And I hear this B.S about leaking exhaust seals letting excess air in the pipes...pops are from fuel..you gotta simply make them too lean to pop or too rich to pop...in your case ..leaner will fix it. I would guess you mileage is pretty poor.
 

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Discussion Starter #17
Checked the plugs again and hey are a slight tan.

AS for the choke, how exactly do I adjust it? I can loosen the knurled screw, but all that does is pull the choke back in when it is pulled out. The choke still only goes in so far.
 

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Dragon_MD said:
Checked the plugs again and hey are a slight tan.

AS for the choke, how exactly do I adjust it? I can loosen the knurled screw, but all that does is pull the choke back in when it is pulled out. The choke still only goes in so far.
With the knurled nut loose the friction is releaced off the enrichner rod, at this point the enrichner knob should have a 1/16'' or so of free play before it pulls against the spring pressure off the plunger. If this free play is not there then the plunger is not seating in the bore. To regain the friction so the enrichner will stay out tightned the knurled knob back up with your fingers.
 

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hdmd88 said:
With the knurled nut loose the friction is releaced off the enrichner rod, at this point the enrichner knob should have a 1/16'' or so of free play before it pulls against the spring pressure off the plunger. If this free play is not there then the plunger is not seating in the bore. To regain the friction so the enrichner will stay out tightned the knurled knob back up with your fingers.
Thanks DOC ! I forgot to tell him HOW to adjust. DUH !!!
 

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Discussion Starter #20
Alright, I adjusted the choke. I went riding for a few hours and it did not pop once. I hope it worked. I'll see ffor sure when I ride home from work monday night and it is 40 degrees!!
 
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