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Still no vacuum fon # 3 and #4


KAWoodworth

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I thought I had cylinder #1 not firing because it was cold. I pulled the plug and turned the bike over and there was spark. As I went to pull #1 plug it was completely loose. Checked all the rest they were loose also. Thought that might be the reason for no vacuum. Tightened them all up and put things back together but still no vacuum form 3 and 4. I pulled the carbs off. Checking the vacuum pistons #3 springs back really quickly all three of the others are real sluggish. Could that have any thing do do with the no vacuum on #3 and 4? I'm going to check the jets next to see if any are clogged. I'm about at my whits end! I was really hoping to get things straightened out before the WNY rally.

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My guess would be that the throttle plates in carbs 3 &4 are more open than the ones in 1 & 2. A larger hole in the vacuum passage= less vacuum. If you still have the carbs off, measure the clearance of each throttle plate to carb throat. You can also shine a light from the bottom of carbs and see if one throttle plate is more open than the others.

 

Earl

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No vacuum= broken piston rings, valve stuck open, blown head gasket, cracked head, hole in piston, bad seal between intake manifold and heads bad seal between carbs and intake manifold, broken vacuum lines or just not connected and probably a couple of things I have forgotten over the years.Now with that said, go back to before you pull carbs and set your valve clearance. did the bike run ok? If so then you know the problem has something to do with the reinstall of everything you removed. I still say the carbs on that side of the motor were not fully seated in the intake boots. the jets can be plugged, the carbs can be way out of sinc and you will still have vacuum. the problem is an air leak.

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When you say cylinders 3&4 I'm assuming you are referring to the cyl's on the left side of the bike? Keep in mind all 4 cyl's and all four carb's are separate from each other, so the only thing that can effect 2 cyl's at the same time has to be something that is common two both cyl's, that can only be the intake boots or a common vacuum line.

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When you say cylinders 3&4 I'm assuming you are referring to the cyl's on the left side of the bike? Keep in mind all 4 cyl's and all four carb's are separate from each other, so the only thing that can effect 2 cyl's at the same time has to be something that is common two both cyl's, that can only be the intake boots or a common vacuum line.

 

As you sit on the bike, 3&4 are on the right side. Now which ones exactly are the issue, it makes a difference on the diagnosis.

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I'd check the compression on each jug with a compression gauge long before I started rippin er down to rebuild er because of vac loss if it were mine.. A cracked hose or two or a line off somewhere can cause a complete loss of vacuum really easily... Wonder if somehow the screw that controls the sync match between 3/4 and 1/2 somehow got screwed in and its holding the throttle plates open on the right side.. That make sense,,, probably not,,, worth asking about though I guess so I will leave it on here..

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I'd check the compression on each jug with a compression gauge long before I started rippin er down to rebuild er because of vac loss if it were mine.. A cracked hose or two or a line off somewhere can cause a complete loss of vacuum really easily... Wonder if somehow the screw that controls the sync match between 3/4 and 1/2 somehow got screwed in and its holding the throttle plates open on the right side.. That make sense,,, probably not,,, worth asking about though I guess so I will leave it on here..

 

Um it makes alot of sense to me as I barely had vacuum on one side and had to back the screw out to start getting vaccuum on the one side but anyways I am tired.... May be talking in circles, But do you just take Cat naps there Clark?

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Um it makes alot of sense to me as I barely had vacuum on one side and had to back the screw out to start getting vaccuum on the one side but anyways I am tired.... May be talking in circles, But do you just take Cat naps there Clark?

Yep,, they grabbed a bunch of my bladder when they yanked the cancer out me back in January and now I am a 2 oz pee er.. Not so bad but gotta get up frequently to go pee pee - not that much fun but better then pushin up daisies and not being able to give you guys a hard time :rasberry:

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Sitting on the bike the right side 2 cylinders. I pulled the carbs and #3 and 4 butterfly were sightly open @1 and 2 were completely closed. Turning the sync screws I got all 4 completely closed. I'll check the vacuum lines and see if I see any cracks and make sure I have everything back together correctly. Is there a special compression tool for our bikes. The spark plug holes are so far in, it seems you would need a compression gauge just for the second gen cylinders. One more question. Setting the float levels was supposed to improve the gas mileage. Was that due to setting the floats to close sooner so less gas gets in the chamber?

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You need to sync the carbs after messing with the screws. I had no vacuum on 3&4 after rebuilding the carbs and syncing them brought all back in line.

 

:farmer:

 

Sitting on the bike the right side 2 cylinders. I pulled the carbs and #3 and 4 butterfly were sightly open @1 and 2 were completely closed. Turning the sync screws I got all 4 completely closed. I'll check the vacuum lines and see if I see any cracks and make sure I have everything back together correctly. Is there a special compression tool for our bikes. The spark plug holes are so far in, it seems you would need a compression gauge just for the second gen cylinders. One more question. Setting the float levels was supposed to improve the gas mileage. Was that due to setting the floats to close sooner so less gas gets in the chamber?
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At this point, you should run a compression test, bench sync the carbs and check and recheck all the rubber bits and hoses for cracks and proper connection.

 

The Harbor Freight compression tester is good enough to find any major issue and should reach all four cylinders.

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Keep it simple, start with the sync. Sounds to me that would be the major if not all of your problem. You will need a proper gauge though, it can't be done by ear, I mean, it can't be done by ear, which means that listening to it won't get you very far, you'll need eyes to do it even close to right.

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Thanks guys. After fooling with carb sync I finally got vacuum out of #3 and 4. #3 is much higher than 4 but I could not get them to match. #1 and 2 seem to be just fine. I'll try some more after work today. I added some Tecron fuel cleaner and hope that it would help #4 . Maybe something gummed up.

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