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Keihin Carb Issue

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Old 05-22-2011, 11:37 PM
stevenlisa stevenlisa is offline
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Default Keihin Carb Issue

Well, my top end rebuild on my 80 XL is complete. It started right up for me and sounds great. However, after a minute of running, it stalled. I couldnt get it to restart unless I choked it. After pushing the choke back in it wants to die out again. That is the only way to keep it running. Choke on/Choke off. I have a few different ideas but wanted to check here first. I have tried adjusting the air/fuel mixture screw and the idle screw but nothing changes as far as it wanting to stay running. Is it fuel starvation? I'm listening and you have my undivided attention. This is not a CV carb. Just a standard stock Keihin.
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Old 05-23-2011, 01:06 AM
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sepixlh sepixlh is offline
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Check filter inside of petcock, clogged intermedia jet... did intermedia jet had rubberplug ?
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Old 05-23-2011, 07:33 AM
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Try this ...

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 ...

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.
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Old 05-23-2011, 09:37 AM
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Before tearing down the carb, or making any other random adjustments, I would consider the rule of thumb that when the bike only runs with the choke on there is an air leak in the intake.
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Old 05-23-2011, 10:40 AM
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Sounds like either too much air or not enough gas. In addition to checking for trash in the carb and manifold air leaks, make sure the petcock isn't stopped up and check the gas cap vent. The easiest way to check if the cap is the problem is to start the bike with the cap off (or loose) and see if it idles OK. Also, flip the petcock to reserve and see if that makes any difference.
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Old 05-23-2011, 12:08 PM
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shepdog shepdog is offline
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for sure too much air,it would have be a pretty big intake leak, with a fresh top end there is a good chance the intake is leaking with the choke on it will run so get it running and turn the air screw all the way in and see if it shuts off if not take the intakes back off and re seal
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Old 05-23-2011, 07:02 PM
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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 definetly 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 huge 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.
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1979, 40, accelerator, cable, carb, carburetor, choke, clean, cv, davidson, harley, keihin, leak, leaking, passage, pump, wd40

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