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Old 03 May 2012, 13:47   #1
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Carb question

I have a 1999 carbed Yamaha F100 and I need to strip and clean them because of a lumpy idle.

The question is do we need a setting for the carb vacuums or is it a matter of balancing them equally regardless of what the vacuum is?

May sound a stupid question but I can't find the answer anywhere.

thanks
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Old 03 May 2012, 14:20   #2
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I'm pretty certain that to do it properly you need a carb balancer.
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Old 03 May 2012, 14:28   #3
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Sorry. Didn't make myself clear. We have a carb balancer but I'm not sure of what the settings should be. Do we need to adjust to a set number across all four or pick one of the carbs and balance the others to that number. If it's a set number, where do I get those set up numbers from??
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Old 03 May 2012, 14:57   #4
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Should be in this:

YAMAHA OUTBOARD SERVICE MANUALS 1995 - 2006 ALL MODELS | eBay
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Old 03 May 2012, 15:21   #5
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If the engine is anything like any motorbike engine, then I think you simply balance them evenly. But it has been a few years since I've done it so best to get the manual or wait for more people to reply
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Old 03 May 2012, 16:02   #6
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Quote:
Originally Posted by Portholme View Post
Sorry. Didn't make myself clear. We have a carb balancer but I'm not sure of what the settings should be. Do we need to adjust to a set number across all four or pick one of the carbs and balance the others to that number. If it's a set number, where do I get those set up numbers from??
The lower carb has no adjustment screw and you syncronize the remaining 3 carbs to the specs of the lower one . This one is the reference for all other carbs .
Instead of using the standard "vibrating" 4x balance gauges you can take a few meters of transparent hoses which you nail as a loop on a 2m wooden plank . Then you fill them partially with oil - red ATF for instance and put the plank upright next to the engine .
One open end you connect to the lower carb , the second open end to the carb above . Then start the motor in low idle .
Due to vacuum differences between 1st and 2nd carb the oil level in one hose will go up while the other side goes down . The trick is to turn the sync screw in a way that the oil level on both sides is on THE SAME LEVEL = means in both carbs is EXACTLY the same vacuum .
This way you can syncronize then also the 3rd + 4th carb with the lower reference carb .
Have just done this to my F100 and it runs great .
Tomorrow I could post some pictures if some´body is interested ..
Regards - Jürgen
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Old 03 May 2012, 16:14   #7
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The lower carb has no adjustment screw and you syncronize the remaining 3 carbs to the specs of the lower one . This one is the reference for all other carbs .
Instead of using the standard "vibrating" 4x balance gauges you can take a few meters of transparent hoses which you nail as a loop on a 2m wooden plank . Then you fill them partially with oil - red ATF for instance and put the plank upright next to the engine .
One open end you connect to the lower carb , the second open end to the carb above . Then start the motor in low idle .
Due to vacuum differences between 1st and 2nd carb the oil level in one hose will go up while the other side goes down . The trick is to turn the sync screw in a way that the oil level on both sides is on THE SAME LEVEL = means in both carbs is EXACTLY the same vacuum .
This way you can syncronize then also the 3rd + 4th carb with the lower reference carb .
Have just done this to my F100 and it runs great .
Tomorrow I could post some pictures if some´body is interested ..
Regards - Jürgen
I love it, Genius idea !
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Old 03 May 2012, 16:23   #8
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Brilliant idea. Would love to see a photo.
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Old 04 May 2012, 01:14   #9
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Hi ,
Here we go with the pictures :
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Old 04 May 2012, 03:56   #10
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Thanks guys appreciate the help. I'm feeling confident with this now and have ordered the service manual on eBay for the princely sum of £4.44.

My dad just got charged an arm and a leg to have a cam belt done on a five year old yam f150 and the thought of involving dealers just makes my blood curdle!!!
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