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88 venture carb sync question


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I just bought an 88 venture which the previous owner said only sat for a month. Well, when the bike would only run on chock, i took of the carbs to clean them. Needless to say they were interesting inside. Now that I have them cleaned out, was curious to know what I should set the sync screws at so I can at least get it started and sync them properly. Any inout is greatly appreciated.

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You want all the butterflies open pretty close to the same amount. There are a number of ways to accomplish that.

 

I like to sight through them at a light and judge the crescent of light showing through them.

 

Others like to use some sort of gauge to feel them. A thin piece of wire (like a small paper clip) or a narrow strip of business card are supposed to work. Because of the shape I think a piece of thin wire is probably the most reliable for this method.

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If you still have carbs off the bike you can get them close. Place a bright light under the carbs and adjust the sync screws until the throttle plate just closes in venturi. At this point the light shining up from bottom will dim considerably, you will see the difference. Adjust the carbs by the procedure that is used when running.

 

OK Carl, you beat me this time !!

 

Gary

Edited by dingy
Micarl won
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Hey Shawn,

First off, welcome to the VR.ORG Forum! With a "new to you" First Gen., this might be the best $12.00 you spend on your bike! Now, about those Idle Mixture Screws.

Below each of the four Carb. Diaphragm Caps, there may or may not be a brass plug that covers the Idle Mixture Screws. If there is a brass plug, drill them out with a 3/16" drill to expose the screw head. I use PB Blaster on the screws BEFORE I try to move them. Once that is done, LIGHTLY bottom out each screw, (if you get "Heavy Handed" here, you will destroy the Carb. Body, making that Carb. useless) and then turn them out 21/2 turns. This should get the bike running. I would then use a clamp on digital tach. (or an Exhaust Gas Analyzer) to fine tune the Mixture Screws.

As far as the Carb. Sync. Screws go, if you didn't move them when you removed the Carb. Rack, then start there. You will need to connect a Manometer to the four Vacuum Ports on the Carb. Intakes, then adjust the screws to "Balance" the vacuum between the four Carbs. If you did move them, turn each screw in three turns, and try to start the bike. There will be two Sync. Screws on the right side of the bike, one for front cylinder to rear cylinder balance, and the other for right side to left side balance. On the left side of the bike, there will be one Sync. screw for front cylinder to rear cylinder balance. Make small adjustments, blip the throttle after each adjustment. It is not as important what the reading on the Manometer is for each cylinder as it is for all four cylinders to read the same.

Stick around, you may actually enjoy yourself!:thumbsup2:

Earl

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Thanks for all the input from everyone. I will be finishing the last 2 carbs tomorrow and will see what happens. I will let everyone know once I get them back on. One question, When I turn the sync screws in 3 turns...what is the starting point...im pretty sure the previous owner messed around with them.

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Thanks for all the input from everyone. I will be finishing the last 2 carbs tomorrow and will see what happens. I will let everyone know once I get them back on. One question, When I turn the sync screws in 3 turns...what is the starting point...im pretty sure the previous owner messed around with them.

 

I am confused, I think you are referring to the idle mixture screw when you say you turned it in 3 turns. The idle mixture screw are on each carb body, just below diaphragm cover. The sync screws are on the throttle linkage between the 4 carbs.

 

Gary

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If carbs are still off bike look at post # 2 or 3.

 

You start with #1 carb, #2 carb is fixed, #2 is the reference point that others are synched to. #2 is set with the idle speed screw, between #1 & #2, under cross bar.

 

Not sure of the order between #3 & 4, having computer issues, I'm on my laptop without access to all my reference material.

 

Gary

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ok, got the carbs finished and back on bike. I can now get the bike to stay off choke and run. Still runs like garbage and cant throttle up on it. I am hoping that the carbs just need to be synced. I am going to try and see if a friend has the carb sync tool, if not, I guess ill have to order one and see what happens. Ill check back after I attempt to do the carb sync. Keep your fingers crossed. I know I am. Thanks again for all the help.

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ok...put the air box on, still running like crap. I cant give it any type of throttle without it stalling out. Does this sound like carbs out of sync or a problem with the one of the carbs itself?

 

Not likely sync. Probably more than one carb not properly cleaned.

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Did you remove the small aluminum block inside each carb, then remove the two jets under the rubber plugs? If not you may have wasted your time the first time you tore em apart. Those jets stop up and cause alot of the problem. They are very small.

 

I tore my 85 carbs apart 3 times before realizing the problem there.

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When I first got the bike, it would only run on choke. Now i can take the choke off and it will stay running, but I cant open the throttle with out it stalling. I am pretty sure the previous owner screwed around with the sync screws... the ones on the right side of the carbs nect to each other and the one on the other side by itself. These screws are located in between the carbs on each side. My question is, if the carbs are out of sync, will the bike idle, but have trouble running when opening the throttle.

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Probably should run better than that.

 

Could be a fuel feed problem, fuel filters, or pump issue. There are three filters. 1st is in fuel tank, screens around pickup tubes. 2nd is traditional filter near pump. 3rd is a screen in each carb just before float valve.

 

How many turns are the carb idle mixture screws set at?

 

Is air cleaner seated on carbs fully with air filter in and top on?

 

Gary

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It could be just out of sync. I just went thru the same issue. At first my problem was one cylinder was not firing, but once I got that worked out, the bike would run like yours. It would run with choke and idle without choke, but as soon as you gave it some gas, it would die. I could only get a reading on the Carbtune from one cylinder at that point. It turned out that it was just way out of sync, and once I got that in line, it runs fine. Good luck.

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ok, got the carbs finished and back on bike. I can now get the bike to stay off choke and run. Still runs like garbage and cant throttle up on it. I am hoping that the carbs just need to be synced. I am going to try and see if a friend has the carb sync tool, if not, I guess ill have to order one and see what happens. Ill check back after I attempt to do the carb sync. Keep your fingers crossed. I know I am. Thanks again for all the help.

 

There is more going on here than just a sync issue.

 

Sure, a set of carbs that are way out will cause some idling and throttling issues, but not like this.

 

When mine did exactly what yours is doing it was because of two main reasons .... The carbs were dirty and some of those pilot passages are small, but the main cause was that the diaphragms were shredded. All four had holes, some worse than others.

 

A couple of the air shut-offs were bad too, but that doesn't cause this problem.

 

Replacing the diaphragms and a good clean, followed by careful setting up has resolved the problems.

 

ps ... Syncing the carbs is harder to describe than it is to do ... it's an easy procedure, but a waste of time unless the valves are in spec AND the carbs are working correctly.

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The filter has been changed. Where are the idle mixture screws? I didnt see any ones on the carbs themselves, unless there is a plug that has to be removed to get to them.

 

Idle mixture screws are just below diaphragm cover on each carb. If never adjusted, these will have a brass cap over them, about 1/4" dia. and flush with carb body. Drill small hole (about 1/8", depends on screw size used next) in brass cap to allow a small sheet metal screw to just start in brass cap, then remove brass cap with pliers. Do not allow drill to go in more than a 1/2", idle mixture screws are then under the removed cap.

 

Initial setting for screws is about 2 turns out, after gently seating them. It will take a narrow head, flat blade screwdriver. Get biggest one you got that will just fit in hole. Do not force them, if tight, spray with penetrating lube.

 

What procedure did you do to clean carbs?

 

Did you pull jet block off in behind float bowl cover? (This one is important)

 

Did you replace 2 fiber gaskets & 6 o-rings ?

You need to look at each diaphragm with a bright light behind it and see if there are ANY pin holes in it around outer edge (or any where).

Do all 4 diaphragm sliders snap back all the way when pulled open with your finger, or do the hang up?

 

Gary

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When I first got the bike, it would only run on choke. Now i can take the choke off and it will stay running, but I cant open the throttle with out it stalling. I am pretty sure the previous owner screwed around with the sync screws... the ones on the right side of the carbs nect to each other and the one on the other side by itself. These screws are located in between the carbs on each side. My question is, if the carbs are out of sync, will the bike idle, but have trouble running when opening the throttle.

 

Do you have a air leak like the carb boots are not seated both top and bottom of carb?

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