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Mechanics 101 Can't get it to run right? Find a trick to add HP?
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Old 12-17-2017, 10:45 PM   #1
ryan5685
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Default I'm failing at syncing my carbs

I built a homemade manometer using snapple bottles, vinyl tubing, some rubber stoppers and oil. I've been trying to sync my carburetors by doing the following:

1. Attach hoses to carbs
2. When looking at the carbs from engine intake side, adjust left screw first (carbs 1+2), right screw second (3+4), middle screw last (2+3)

The problem I'm running into is minor adjustments cause the rpms to skyrocket (I'd guess 6,000 rpm but I just installed a new tach and I must have missed something when plugging it in)

I have adjusted the idle screw all the way down to where it isn't even touching the throttle assembly and I don't understand why my rpm is so high.

Wouldn't better synchronized carbs run at higher rpm? When I started I couldn't idle and now I'm idling at 6000 rpm. Carburetors are fun (:
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Old 12-18-2017, 10:45 AM   #2
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Sounds like you have a vacuum leak. When you're doing 1 and 2, are 3/4 called off? When going 3/4, are 1/2 called off? Same for when doing 2/3.
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Old 12-18-2017, 12:33 PM   #3
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Your way off. Back the sync screws out till they just touch, turn them in 1.5 turns and try again.
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Old 12-20-2017, 01:10 AM   #4
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I bought a couple of vacuum gauges from Harbor Freight and I know they aren't the best quality but I really don't want to drop a bunch of money on a nice carb tuning tool when I may have a vacuum leak.

I got the bike a bit better; when I tried riding it on Tuesday I could barely accelerate. I don't have the things to attach that keep the needles steady because I couldn't remember what they are called. My dad told me I could achieve the same effect by putting clamps around the tubing so I'll try that tomorrow.

If I understand correctly, the only place I could have a leak is the engine intake boots, correct? One of them was giving me trouble before and I'm not sure if I fixed it by reseating it.

My bike was pretty decent until I started messing with this so I'm pretty frustrated. I only had bogging when the engine was cold and now I can barely start the engine. I really appreciate your help as this is pretty stressful knowing I'm the reason my bike won't work the way I want it to.
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Old 12-20-2017, 01:58 AM   #5
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You really need a sync tool haha.. you need restrictors, an old main or pilot jet would work for that. A vac leak wouldn’t generally keep the bike from starting. Have you pulled the plugs and check them. Black and or wet isn’t good. Once running check the header down tube temps, they should be the same temp. A cool/cooler pipe would indicate a non operating carb.
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Old 12-23-2017, 10:19 PM   #6
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You say you reseated the carb boot. As in removed it from the head and re-attached it? You probably need a new oring. The intake boots have an oring between them and the head and they flatten out. If your boots arent visually cracked to shit, it's a good chance you need new orings. Get it running and spray some carb cleaner at them, if the idle increases, they leak

Also, +1 on a sync tool u can get one on eBay for $40.00. For what it's worth, if you intend on maintaining a lengthy motorcycle riding career, you will use them again. I bought the Morgan carb tune for $100.00. They are great.
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Old 12-24-2017, 01:58 PM   #7
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Also, that's far from the only place you could have an air leak. Head to carb boots, carb to air box boots, any of the vacuum lines, the sync ports, the carbs themselves, etc
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Old 12-25-2017, 12:41 PM   #8
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Quote:
Originally Posted by shpielers View Post
Also, that's far from the only place you could have an air leak. Head to carb boots, carb to air box boots, any of the vacuum lines, the sync ports, the carbs themselves, etc
The carbs themselves? How?
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Old 12-25-2017, 12:47 PM   #9
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Diaphragm and cap.
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Old 12-25-2017, 03:29 PM   #10
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I had vacuum problems but it was only related to the old nipple cover on cylinders 1, 2, and 3.

The statement about using a clamp on the hose is correct. I have done this with just a vice-grips. Old school.

You might be so far off, you can see one butterfly is off compared to the others. Sync on the bench is what I call it, before the carbs are even installed.
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Last edited by AR-15; 12-25-2017 at 03:29 PM.. Reason: Automerged Doublepost
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