I bought this 73 XLCH a couple weeks ago, was told the engine was rebuilt 10 years or so ago, Morris Magneto, S&S Super E carb. Previous owner seemed to have maintained it well, but wasn't riding it so much anymore. I had to ride it home about 100miles home after I bought it, everything was great for the first 60-70 miles, then it started to bog down as if I wasn't getting enough fuel then it backfired when I applied more throttle, pulled off at the next rest stop and found plenty of gas in the tank. I kept on my way to make it to work, found around 65mph or so in 4th gear it started chugging losing power, same thing around 55mph in 3rd so I stayed out of that zone for the ride home. Next day off I replaced the plugs, checked the gap on the points, checked the static timing and still have the problem....even tried advancing and retarding the timing to see if that helped, no luck. I put some gas treatment to get rid of water, no change...
So as this is only an issue with the bike moving....it's got to be an air/fuel issue correct? If I open the throttle up it seems fine, or if I'm going slow, but right where I tend to need to be for traffic it's running terrible. I have a day off ahead finally and want to get it fixed, gonna clean the carb and start there. Any ideas on things to look for would be appreciated. Thanks

 

I would agree that the problem is probably crud in the fuel system ...

I would drain the fuel tank and look inside with a flashlight. Rusty or clear? If rusty consider either fixing it yourself with RedKote or POR, or as i do take it to an auto radiator shop to be cleaned and lined. The local shop here uses the RedKote product. Avoid the Kreme product.

Remove the in-tank fuel filter, clean it and re-install it.

Then clean the carb. I wrote the following notes for the Keihin carbs but the procedure is much the same for any carb ...

Cleaning a Carb

1. Removing it from the bike should be straight forward. First thing when it is out is to check the pilot screw setting. Turn it all the way in until gently seated counting the number of 1/4 turns; then write this number down; then reset it.

2. I put mine in a vice to remove the screws, and for much of the following work. Wrap in a shop towel; close the vice gently taking extra care with the choke and throttle linkages. The vice is a needed extra pair of hands.

EDIT: A better choice than a plain vice ...


Better one ...



3. You must be very careful handling the float so as to not change the level. You should have the official specs for setting the level as in the FM, and check it, every time you dismantle the carb, as the last thing before putting it back together.

4. The jets are made of brass, a soft metal that is easily damaged. Use an exact correct size screwdriver. I ground a medium flat blade screwdriver down to exact size on my bench grinder to access the slow jet.

5. The general appearance of the inside of the carb is not necessarily a good indication of its condition. It can look spotless and have clogged jets, or look cruddy and have clear jets.

6. Clean each individual part. Do not allow any solvents to contact any rubber parts [tip of needle, o-ring seal for bowl]

7. Make a list of all of the jets and passages for your carb using the carb manual or the FM for the bike. Then ensure that you can blow either compressed air or carb cleaner thru each one.

8. Remove the pilot screw and clean the parts and the passage. The passage contains in this sequence: pilot screw, spring, washer, o-ring. These are very small parts, especially the washer and o-ring. Usually the spring will easily fall out. One time i thought the spring was not in there because it would not fall out; i obtained a new spring and could not get it in! The technique for removing the washer and o-ring is to use a pipe cleaner: stick it in the hole, twist it around, remove it - you should see the washer and o-ring on the end of the pipe cleaner.

EDIT: the washer and o-ring are part of the pilot screw assembly for 1979 on. They are not in the 1978 and earlier Keihin carbs.

Remember that the purpose of the washer is to protect the o-ring from the spring and you will always get them back in in the correct sequence.

9. Dismantle the accelerator pump assembly noting carefully the sequence and orientation of the parts. Clean and inspect the parts. Replace the diaphragm if it is cracked.

10. Check the float level then carefully put it back together. I personally find it very confusing trying to decide which way to bend the tang if it is not correct. If the fuel level is low is the float high or low? Do i need to bend the tang up or down? On the bench the carb is usually upside down, adding to the confusion. Sort all this out before making an adjustment.

Best to replace the original Phillips screws for the bowl with stainless steel socket head screws.