My recent barn find '81 Ironhead is spitting fuel out the carb, enough that it drips from the butterfly.

I cleaned the Khein butterfly carb, new gasket kit, set the float spot on, new air fuel mix needle, new OEM jets (68/160), rebuilt accelerator pump. She's just way too rich.

What am I not getting?

Thanks!

 

Spitting fuel from the carb may indicate that the intake valve is open during an exhaust cycle. Check the cam timing...

Note 1: If you have not yet had the cam [gearcase] cover off wait for additional information before proceeding with this procedure.

Note 2: Setting the cam "timing" has no correspondence whatsoever to ignition timing. Do not refer to the ignition timing hole mark at all during this process.

Note 3: The idea that installing cam gears is difficult or risky or to be feared is an internet myth. It may be based on installing cam gear #1 first simply because it is #1. It is important to start with #2 so that it and the pinion gear can be lined up before installing any other cam gears.

The procedure to re-install the cams may be a bit tedious, but it is simple and easy to do. Proceed as follows ...

1. Position the pinion gear mark at approximately the 11:00 position by rotating the engine. Use either the rear wheel or the kicker
2. Install cam #2 so that the mark lines up with the pinion gear mark. This may require moving the pinion gear mark a bit so they match perfectly
3. Temporarily, partially uninstall #2 while you install #1
4. Install #3, then #4 and finally the generator idler gear

When checking for the marks matching get down low and look straight on. Looking down at an angle may result in marks appearing to be correctly aligned when they are not.

 

Thank you Ironmick. I was rolling the engine without the pushrods installed while installing a new head gasket. I certainly have them offset as a result.

I bought this bike as a project to learn about older VTwins. Looks like I'll be getting a lesson in cam timing...

Thank you for helping.

 

Rolling the engine without the pushrods installed will not change the cam timing. Before doing a re-install of the cams I would investigate what other things would cause backfire thru the carb. See what others say - perhaps it could be ignition timing?

What ignition is in the bike? - the original electronic ignition? points ignition? modern electronic ignition? If you are uncertain post a pic of whatever is behind the round ignition module cover on the cam cover.

 

Ironmick,

Oddly, it is a points ignition. I expected an electronic setup but many of these early ones were switched back to points back in the day. Checking ignition timing is my next step but I can't get her to idle strong enough to get a sighting!

The points themselves are clean, square and true. Looks like someone installed a "new" set recently. They spark mildly. The ignition cam lobe is a loose fitting sleeve, that sort of surprised me. It rotates a few degrees on it's shaft. The condenser is, well, a condenser. Not tested. I have not tested the advance yet, but it shouldn't come into play at idle speeds.

It's most certainly something I did in either refreshing the carb, changing pipes from 1.75 to 2.00 drags, or removing/replacing the front head/valve cover gaskets.

In seeking a carburetion solution I was looking for the OEM specs for the Pilot jet. I saw references to later series 1980's Keihin butterfly carbs using a pilot in the low 50 range. Mine had a 68 in it as found. The step up was probably due to the unbaffled drag pipes. Could I possibly be getting that much fuel out the carb from just an incorrect jet? I was trying low 70's to cure a lean pipe condition when I ran into this over rich situation...

I should note that it will not run at all with the aftermarket 6" round Uni filter foam air cleaner on (cleaned and oiled) Again, wildly rich... It will rough idle with it off. Tellingly, too, the Air/fuel screw (new) has no effect whatsoever. Not surprising since theres another, larger, fuel mixture problem.

i was really liking the cam timing idea because of what looks like fuel reversion out the carb. Could I have otherwise messed up the valve train somehow? The pushrods went in smoothly just like the shop manual says...

Black smoke, lots of it, a "wet" carb and backfiring out the carb are my symptoms.

I'll go back to thinking its a carburetion or ignition timing issue.

Thank you so much for helping!


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Well, it was valve timing, in a way. I went back over my prior work and found that the #1 exhaust pushrod was wildly out of adjustment. The lock nut had worked loose and the tappet spun down. A rough readjust and she fired up clean.

​​​​​​The tappet winding down explains the way the problem crept up on me, getting worse as I was messing with jets. It took me time and advice to finally realize that the problem was way beyond carburetion.

Now I can start over and dial in the carburetor. Thanks Ironmick for the lead...
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Awesome! I was in the midst of preparing a long, detailed process to find the fault. I gave up knowing that I did not know any more. I logged on again hoping that someone would have nailed it. I am happy that it was yourself

Here are some of my notes, which may still be useful...

It is well known that any drag pipes are not good for performance on a street bike. They are only good literally for drag racing [high RPMs for short times]. Some guys like the noise Also well known is that 2" drags are decidedly worse than 1-7/8. Drag pipes typically have a flat spot around 3000 RPM.

It is very common for new points setups to be bad right out of the box.

It is natural for the pilot screw to be ineffective when the fuel mixture is way too rich.

The correct spark plug for IronHead with points ignition is NGK B6L or equivalent. I have always used NGK plugs as I have never heard any negative comments about them and they have always worked well for me.

The stock jet sizes are on page 4-1 of the Factory Service Manual, part number 99484-85. It covers 1979 to 1985. Search eBay and Google for the part number. You should be able to find one.

For 1981 they are main jet 160, slow jet 68. It is common to run larger jets - 165 or 170 main, and 70 or larger slow depending on the need. Here is a process to follow...

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: Some carbs, noteably 1966 to 1978 Sportster carbs, do not have the o-ring and washer in the pilot screw passage.

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. I usually go for a half hour or so ride outside the city, then ride home with the last 10 minutes at city riding speeds [so that it is on the "idle port", not the "idle transfer ports", the "mid range port", or the "main jet" [see carb diagrams in FSM]]. 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, an hour or so] before i can trust that the new results are reliable.

 

Thanks Ironmick for the tutorial, I'll be on to that process next.

I bought the 2" drag pipes simply to replace the rusted 1.75" set on it from the PO. I wanted muffled fishtails but none were to be found at the time... I was aware of the drag pipe reputation and have wondered why they are almost universal. Maybe I'm not understanding, are all staggered shorty pipes "drag" pipes? Perhaps some have internal mufflers or baffles that make them not-drag? I installed little 4" baffles to create some back pressure. Are mine no longer drag pipes as a result? Am I just over thinking this?

Why does the Keihin butterfly carb have a bad reputation? It seems to be a simple setup. I have an Evo chopper with a Keihin CV carburetor and it seems much more complex and potentially prone to air leaks, etc. Maybe the butterfly is too crude for extra fine tuning?

I rebuild 2 stroke jet ski Keihin and Mikuni carbs as a hobby job. They are MUCH more complex. Many tiny passages, mysterious internal flappers, springs with "pop off " pressures to adjust, multiple flat gaskets and O rings, filters, etc. They even have self contained fuel pumps in them!

When I started on HD carbs and English AMAL carbs I was pleased at how simple they are. It's easier to be successful with these, I think.

Thanks again for the help, I'm enjoying my first ironhead...

 

I believe that drag pipes are so popular because they are LOUD, and guys love the sound. Some [many?] think they are powerful too. Oh well, ...

They are drag pipes if they have a uniform diameter for the entire length and no baffles. The inclusion of the baffles will make them much better.

I do not have personal experience with drag pipes so I cannot be scientific about them.

I used the Keihin butterfly carbs in my IronHeads for about 10 years, then switched to Mikuni VM38-9, which I believe are the very best bar none [my opinion ]. I think the bad rep is based on collective opinions rather than on science.

My Keihin carb cleaning notes [perhaps not needed given your extensive experience with carbs]...

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: This setup works better than putting the carb directly into the vice ...



EDIT: angle metal works even better than the flat stock

3. I am very careful handling the float so as to not change the level. I use the official specs for setting the level as in the FM, and check it, every time i 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. I prefer to clean each individual part rather than soak or boil the whole carb in carb cleaner. But either way is good. 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.

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.

EDIT: Some carbs, noteably 1966 to 1978 Sportster carbs, do not have the o-ring and washer in the pilot screw passage.

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.

 

Thanks for the write up IronMike! I needed that too.