Not sure what to call it bogging, hesitation, sputtering, but my 65 xlch ironhead has this issue when accelerating in each gear. If I accelerate slowly, it's okay. But a normal to aggresive "throttle" causes what feels exactly like I'm running out of gas.

The first time it happened I was low on gas and going uphill. I believe the angle of the chooper frame, with hill, literally caught me out of gas. But then it started happening intermittently for the past 3 weeks.

My bike starts on the first kick almost every time. (thank you God) I'm looking for something in the fuel area. I thought I had it licked yesterday when I thought about a vapor lock in the tank. I was bogging on every acceleration, I stopped and removed the gas cap and put it back on and for the next mile, no bogging. Nice. I thought that was it. No breathing back into the tank. So, I proceeded to enlarge the holes in the cap every so slightly to ensure breathing. Didn't work. I then thought about the glass fuel filter perhaps not allowing enuf gas to pass. So today I replaced the tank to carb hose/filter with a new hose only, no filter. Didn't help. (I'll put the filter back)

Any ideas on where to look next? Your help and ideas sure would be appreciated.

IN summary: 65 ironhead, sputtering on normal to heavy acceleration (but not on slow accelration); not a vapor lock or filter problem (or so I think).

thanks much...Kevin

 

Remove, disassemble, and clean the carb.

 

check the level of the float

 

Two things immediately come to mind. Float level in the carb too low, and slow jet too small. What carb? What jets? How many turns out on the pilot screw? Here are some notes. These are written for Keihin butterfly style carbs but the principles are the same for others.

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.

3. You must be very careful handling the float so as to not change the level. You must 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. Ignore any advice that says to soak or boil the whole carb in carb cleaner. Rather, 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.

Setting The Pilot Screw on Your IronHead

If the carb is old and dirty the pilot screw passage may be gummed up such that you will not be able to "gently seat" the pilot screw reliably. If this is the case remove the carb from the bike and clean it up. Some guys try to do carb work with the carb in the bike. IMO this is a very bad idea.

In the pilot screw passage there should be, in this sequence: screw, spring, washer, o-ring. [Often POs have installed these parts in the wrong sequence; remember that the purpose of the washer is to protect the o-ring from being damaged by the spring]. The screw usually comes out easily. The other parts may require some work. The best technique is to stick a pipe cleaner in the hole, twist it around, and, like magic, out come the other parts on the end of the pipe cleaner.

EDIT: The above info on the pilot screw applies to 1979 and newer carbs. For 77 and older there is nothing in the passage except the screw itself.

1. You need to have easy access to the pilot screw, easy enough to reliably judge "screw it in until gently seated". Loosen the front fuel tank mount bolt; remove the rear fuel tank mount bolt; prop the rear of the fuel tank up on a piece of 2X4; on some bikes this will not be necessary.

2. With the engine cold [so you do not burn your fingers] turn the pilot screw in clockwise until it is gently seated. Count the number of 1/4 turns as you do it; write the number down. Back it out to the original setting. You may need to return reliably to this setting after experimenting.

The "normal" starting point for this process is 1,1/4 [according to the 79 - 85 FM] or 1,1/2 [according to usual practice] turns out.

EDIT: An old HotXL magazine article recommends for Keihin butterfly carbs between 1/4 and 1,1/4 turns out. My experience is that this works best. If you are more than 1,1/4 turns out your pilot jet is too small.

3. The engine must be at full warm up. It will have very hot parts; to avoid burned fingers have a well lighted, comfy place to work.

4. Set the engine idling at about 1000 RPM. You want it to be idling at the slowest speed that is consistent with a smooth idle so that you can hear or feel slight changes.

5. Turn the pilot screw in clockwise until the engine idle becomes worse; tending to stall. Count the number of 1/4 turns as you do this. Then turn the pilot screw out counter clockwise until the engine idle gets good, then becomes worse, tending to stall. Count the number of 1/4 turns as you do this.

6. The best setting for your bike will be somewhere between these two settings. The FM says to use the leanest setting [most screwed in] consistent with a good idle quality. Some guys say to go between the two settings.

It should be between 1/2 and 1,1/2 turns out from gently seated. If it is not within this range you should change the slow jet.

EDIT: I follow the advice from the old HotXL mag article - set it between 1/2 and 1,1/4 turns out.

7. You may have to adjust the idle speed.

8. Make sure that the spark plugs are clean, then ride the bike around your neighborhood for 10 minutes. Keep it under about 15 MPH so that you are on the "idle port", not the "idle transfer ports", the "mid range port", or the "main jet" [see carb diagrams in FM]. Hopefully the plugs will come out a nice medium gray or tan color. If they are too dark you can screw it in another 1/4 turn; too light screw it out 1/4 turn, and try the ride again.

9. If they are really light or really dark the problem is not with the pilot screw setting. For example, too light might mean an intake or exhaust leak, and too dark might mean the pilot jet is too large [among other possibilities].

10. My experience with this process is that after making a change i have to clean the plugs and go for a good ride [say, a half hour or more] before i can trust that the new results are reliable.

 

Thanks much jamesroadking, shepdog, and ironmike: the gascap "fix" sure was easier! ;-) but a good carb clean will get me to dive into this beast head first and learn a bunch more.
As always, I sure do appreciate your kind help. Semper Fidelis...Kevin

 

Hello again: I just remembered that when I purchased the bike, the previous owner had just put a new Zenith carb on it. From the outside, the carb does appear to be brand new. Before I tear into a carb pull-apart, what "external" adjustments might I check first? Sorry I forgot to mention the carb "newness". thanks much...Kevin

 

There is a "O" ring in the carb that can deteriorate,if it is,in Your Zenith,it will have these same symptoms.Hopefully Mr. P.G. will chime in with the procedure.

 

thanks 70weight for your help.... I'll start reading up on the Zenith and see what's what. Sure do appreciate your help...Kevin

 

Always it's good to check that filter inside of petcock isn't clogged....

 

Hmmm, filter in the petcock? Sounds like it's time to pull that tank and carb and clean it all out...thanks sepixlh...Semper Fidelis...Kevin