Ok, so now it is running good at closed to 1/4 and good after 1/ 2 to WFO. But beween 1/4 and 1/2..it has a bad hesitation. And thats about the cruise speed...it back fires.if i let off...and barely roll it, its good..if i crack it, its good.this carb is driving me nuts...been trying to get it set right all weekend.

 

and I'm trying to figure out what the missing cap does...this is a picture of the top of my keihin carb..doble butterfly..one for choke, other for throttle. my father-in-law decided to mess with it and before i noticed, he had drilled the cap off thinking there was a screw under it...and theres not..not its left me wondering what the purpose for it was. and could that be a reason for my carb acting funny at about 1/3 throttle? i dont have the cash to buy a new carb. he tried putting silicone in it to plug it and it didnt seem to effect it..and i pulled the silicone out..and again, didnt seem to effect it. i have messed with the float level cause of the previouse problem i had with it..i figured id try to see if that was the problem..but alls it did was make it overflow out the line...so i bent it back down down a little bit. it looks like its parallel to the rim of the carb bowl mating surface.but like i said its got a bad hesitation at about 1/3 throttle.

 

Yes, it is a stock keihin butterfly carb. What year is your bike? The screw that father-in-law was looking for is the pilot screw - it is visible in the tower, top-back of the carb, top-center of the pic.

The cap that father-in-law removed was installed at the factory as part of the manufacturing process. Not intended to be removed. It should be OK to simply clean up the area, check any exposed parts, and seal it off with silicone - ensuring that the silicone does not interfere with any passages.

Post a very clear pic of the area after it is cleaned up. Do not use a flash; use indirect light - to ensure there are no washed out areas and all parts show up clearly.

The Factory Service Manual shows how to set the float height. The distance from the float to the edge of the carb should be 15mm to 17mm. A pic in the manual shows how to hold the carb and do the measurement. The needle should be just seated in the seat.

The function of the cap has to be replaced and the float height set exactly precisely before proceeding.

Next step after that is to set the pilot screw. Then test ride and see where it is at. Good luck with this ...

Setting Slow Jet and 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. Occasionally 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.

EDIT: In my experience you cannot properly warm up the engine in the shop. Take it for a half hour ride mostly away from city traffic.

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 a few times during this process.

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 5 or 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 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 so] before i can trust that the new results are reliable.

 

its driving me nuts....i have it dialed in..but it missing between 1/4 and 1/2 throttle...if i just roll the throttle from closed to WOT, its good till that spot then it cuts out, but as i roll it more it opens back up. if i can keep it running in that spot..and i have to flutter the throttle to keep it running at the spot...it just sputters and back fires.

 

I can think of two possibilities ...

1. Intake or exhaust leaks messing with the fuel mixture

2. Drag/straight pipes with no baffles, as these are well known to result in tuning issues in the 3000 RPM range - altho perhaps not as dramatic as whay you are describing

May be more than one issue causing this.

Intake And Exhaust Leaks Tests

You cannot get a good tuneup if there are intake leaks or exhaust leaks.

1. Check for Intake Leaks

With the engine idling spray propane gas or WD-40 around the carb/intake/cylinder head joints. Propane is best because it leaves no mess, and is most easily sucked in thru leaks. WD-40 is said to work well because it has very fine spray droplets. Be careful to not allow any of either to get sucked in thru the A/C as this will invalidate the results.

Any change in engine RPM is a leak which must be fixed.

EDIT: Experience is that this procedure will identify larger intake leaks, but it may miss very small leaks that also must be fixed. And that propane is the better choice.

EDIT: You have to do a lot of spraying to detect a small leak. Propane will be really clean. Anything else like WD-40, carb cleaner, etc will make a mess.

2. Check for Exhaust Leaks

Pour about 1/2 ounce of oil into each cylinder thru the spark plug holes. Run the engine at idle. You will get lots of smoke for about 5 minutes.

All smoke should come from the ends of the exhaust pipes/mufflers. Any other is a leak which must be fixed, especially at the cylinder heads.

 

Have you removed the slow and main jets for cleaning? And cleaned the passages from whence they came out? Best is to blow compressed air or carb cleaner thru these parts.

 

I have the float at the right spec...just measured it, .015
i have the bike idling right and its not coughing as much as it was...its actually got the potato potato potato sound. I dont have propane to spray..but i do have WD40 and carb cleaner..Id rather use the carb cleaner...(preference). Ive sprayed it around the manifold and no difference in RPM. Now, I have seen some smoke come out of the front exhaust at the head, without using oil....but its not billowing smoke out. its only when i pin it...and i understand i need to tighten that up.
I have cleaned the carb and cleaned out that missing cap passage...i found the cap that he removed..so i flattened it and siliconed it back on.
And its still not hitting at that 3000 RPM range. ive got the air filter off and was watching it when i hit the throttle. the accel pump also isnt squirting at the same range..it squirts up to it..and afterwards.

 

now looking at the front of the carb...the accel pump jet, at that speed, its sucking the fule into that passage behind it. and its cause it to flood out. i had it idling and took the carb cleaner and sprayed it into that passage and it did the same thing..at idling. maybe if i took the bowl off and adjusted that accel pump jet..?

 

So ive now realised thats the air jet to the main jet... And i believe thats where my problem is. What would cause the main jet not to kick in when it should?i watched the main jet start to kick in, then stop, then blast alot of fuel in...ive taken it out and looked at it..even cleaned it again..its clean. Theres a lack of something somewhere. No matter which way or how far i adjust the accel jet...its still doing the same thing..and it deals with the air jet and the main jet.

 

Regarding the aim of the accelerator pump jet ...

If you close the choke plate you will notice a cutout at about the 1:00 o'clock position. When the choke plate is fully open, the acc pump jet should spray fuel up thru the exact center of that cutout. The fuel spray will then pass over the air jets and hit just to the "left" [your left as the viewer] of the divide in the manifold for the front and rear cylinders.

The way to adjust the aim of the acc pump jet is to use a 1/4" drive, ?mm metric socket. Sorry i forget the exact size. I know it is an odd number. I think 9mm.

The best way to do the adjustment is with the carb on a stand, like this but with the carb top side up ...



I do it with the bowl loosely attached, no gasket, spills a little fuel but so what, gotta get it done easily.

I made my most recent version of that stand using angle aluminum instead of flat steel stock - more stable and easier to drill the holes.