Hi folks...

Just returned from a 4000km trip on my 1988 FXRS-SP and on the way back I started getting some intermittent puffing noises coming from my carb.

The notion of fiddling with my carb is a bit intimidating, since my experience there is virtually non-existent. So before I start taking anything apart, I wanted to post this for some troubleshooting help. Any advice would be appreciated!

Here's a couple factors I've deduced might have contributed to the issue:

1) I ran my tank pretty low during one stretch of the trip. The following day is when I started getting the puffing sounds, so I'm wondering if some gunk might have made it's way into the carb from the tank. It's worth noting there wasn't an in-line filter on the fuel line.

2) This same day that I started getting the puffing sounds, I hit a pretty ugly patch of weather. About 250km of steady heavy rain. Is it possible that some moisture might have found its way into the fuel system because of this? Maybe a dumb question, but figured I'd ask.

At first I thought the issue might have been that I got some bad fuel somewhere along the way, but I've since ran about 5 tanks worth premium fuel through it and the problem persists.

I've pulled the plugs to make sure I wasn't running lean, and the fuel mixture seems right... the plug tips are a nice light brown.

Since the problem started I've cleaned the K&N air filter and just today I installed an in-line fuel filter.

Also as of today, I'm running a tank of fuel with some Sea Foam added to see if that helps clear things up.

The puffing seems to happen most frequently (but not exclusively) when slowly accelerating after a period of idling. And it seems to be more prone to the puffing at lower RPMs.

For the most part, the puffs are quite small but in two instances I did notice some white smoke coming from the air filter after a larger-than-usual puff. I read here: https://www.hdforums.com/forum/engin...moke-mist.html that this could be a potential valve/lifter issue? I've only had the bike for a couple seasons, and it's my first Harley, so I can't say whether or not the valve train noise is excessive. There's currently just over 43 thousand kilometers on the bike.

If the sea foam and fuel filter don't fix the problem, I'm wondering what the next troubleshooting step would be.

Like I said, any input would be appreciated!

 

Could be water in the fuel. Take the carby off and blow through the passages with carby cleaner. You could try some methylated spirits in your gas as that absorbs water but doing the job properly is best.

 

I would check the Accelerator pump action.

Remove the air cleaner and look into the carb while twisting the throttle open slowly and see if gas is being squirted into the throat of the carb. Recommend the engine be shut down. Just in case of a backfire, wouldn't want to loose your eye brows/lashes.

If not then pull the pump and concentrate you efforts there.

Also make sure the push/pull throttle cables are properly set and the pump is actually be actuated when throttle is applied. Related: make sure that full throttle is full throttle, this will "set" the proper timing of throttle vs demand.

The filter you added must be of a motorcycle gravity feed type, a normal automobile type is pressure feed from a fuel pump. That is why most people remove them because they install the wrong one to start with and run into all kinds of problems. Don't forget that there is a filter on the petcock inside the tank, this one may be clogged also.

Try running on reserve to see if it improves or worsens, reserve pulls fuel from the bottom of the tank and may give and indication of gunk in the tank.

 

Thanks Spanners... if it is water, I'm hoping the sea foam remedies that problem. I just added it to the fuel today, so I'll take it for a long rip tomorrow to work that through the system. Hopefully it's as simple as that.

 

Thanks for the advice. I checked and yes, I'm getting fuel squirted into the throat of the carb. Throttle action seems fine. And yes, the filter is gravity fed... specifically a 5/16 Russell in-line filter.

Can you elaborate on your comment about making sure full throttle is full throttle? Like I said... not much experience with carbs, so you might have to talk to me like I'm in kindergarten.

 

Sounds like you low speed circuit is gunked up. You can try fuel additives, but in the end, it would be best to pull the carb and clean it.

"Can you elaborate on your comment about making sure full throttle is full throttle?"

Reference to proper adjustment of the throttle and the idler cables. They do stretch, and need periodic adjustments. Get a factory service manual, it is invaluable for working on your bike.

 

If there is water in the float chamber, I'm not sure that a foam will remove it, whereas it is very easy to do so, by taking off the float chamber! That will also show if you have anything else undesirable in there, such as rust from your gas tank. I had a BMW flat twin for many years and that routinely collected water in the carbs. I came to recognise the symptoms and it took a few minutes to clean them both out. Let us know what you find!

 

You don't need an inline filter...the one in the tank is just fine....and the first thing I check with any carb related problems.

 

When at full throttle on the handle bar grip the butterfly tang(both on right/front of carb when looking at the carb) must make contact with the stop on the body of the carb. Not hard contact but contact none the less.

This is not a difficult procedure, but must be done in a sequenced procedure. Starting with putting in all the slack in the cables.

Follow Hackd advice and get a manual to follow the procedure step by step, it will also have pictures so you can identify the proper components. The last step when you set the spring tension at the carb (cable with spring on it) is the one that I find matters the least, this is a good thing because it is hard to tell when it is set properly. Don't worry close is close enough at this stage and then you will be finished anyway.

Someone here may have a suggestion how to get it exactly, I just go for close.

1) Take all the tension out of the cables at the adjusters. (near twist grip)
2) Make sure the front wheel is pointed straight ahead. (close is close enough)
3) While holding throttle wide open, start taking up slack on the pull cable until the butter fly tang contacts the body tang. (just touch, doesn't have to be tight)
4) Release the throttle and then take-up slack in push cable until the spring seats in the throttle horn.
5) Now to test your work start the engine and make sure the RPM's don't change while moving the front wheel from stop to stop; Left and right.
If the RPM's change it is because the "push spring" is to tight. That is what the little spring is far; to allow enough slack in the throttle cables to allow for movement in the handlebars.
6) If everything functions to your satisfaction, you are done.

Hope this helps, sorry I don't have any picture to show you, I'm on a dial-up connections and you will have bought a new bike in the time it takes me to up load pictures. LOL

 

+1 On the slow speed circuit.
...."The puffing seems to happen most frequently (but not exclusively) when slowly accelerating after a period of idling. And it seems to be more prone to the puffing at lower RPMs."....

Stop! Before you do anything and possible ad to the problem. What kind of carb do you have?