Tried to sync carbs.... failed

[kyxon]

I have a 1984 vt700c that I got 2 months ago. For the most part it runs pretty well but Ive been having an issue with idle rpms (bouncing from ~900 to 3k) lately.

This evening in particular I did not experience the problem. I got a new (old) chrome throttle cable cover and since I started having the problem after installing that piece I removed it tonight.

I intended to sync the carbs anyhow since I don't know when it was done last and the service manual recommend it being done periodically and Carbs Synched - big thanx!!! (w/some pix) made it sound easy.

So I built the manometer but couldn't find 1/8" line and used about 18' of 1/4" line. Made my own vacuum ports with 3/16" copper tubing and threaded it using M5 nuts. Used oil in the manometer as recommended in case it got sucked in.

Drove the bike around to warm it up. Futzed with the idle set screw a little since I felt it may have been off before but didn't experience the problem that started the whole endeavor.

Shut off the bike, took out the vacuum screws and hooked it all up. Started fine and watched as the oil in the manometer started sucking to one side pretty significantly. I let it take 28" or more of movement before I got the feeling it just wasn't going to stop. Tried making small adjustments but never saw a change.

If the carbs are way out of sync, won't the bike run like crap? I would be surprised if the carbs are really this far off, I am suspecting that my sync equipment must be crummy.

Turning the screw clockwise increases vacuum at which port? Trial and error?

[luisr320]

Since you have the tank off and you haveaccess to the carburetors, why not pull them out and try to visually adjust them to match each other butterfly to open at the same time. Then it will be a small tweak either way. It's like tuning a guitar first by ear and hooking up a tuner. If the strings are way off, you won't have a ground level to start with.

[kyxon]

Well, I didn't actually take the tank off, and I didn't want to buy rebuild kits for the carbs so I was trying to avoid taking them apart. I am assuming if I pull apart the carbs in any way, the o-rings and such will break.

After reading more about the sync process, I realized I needed to use a line restrictor so will find something for that for the next attempt.

[John Hopkins]

Look this is not going to please you but you are wasting time and effort trying to sync faulty carbs, the rebuild kits are about $20 for each carb, you also have to check the diaphragms for pinholes or splits..You don't sync carbs until after you have cleaned them and fitted new repair kits.

John.

[luisr320]

My carb sync comes with those air taps that you use on an aquarium ( fish tank ?) and you can buy those at any pet shop.
Like this:


But I have to agree with John. Rebuild the carbs and sync them after. Cheap and easy. Just make sure you have all the required parts before you start.

[Scrapdog2grand]

Originally Posted by luisr320

Since you have the tank off and you haveaccess to the carburetors, why not pull them out and try to visually adjust them to match each other butterfly to open at the same time. Then it will be a small tweak either way. It's like tuning a guitar first by ear and hooking up a tuner. If the strings are way off, you won't have a ground level to start with.

Originally Posted by kyxon

Well, I didn't actually take the tank off, and I didn't want to buy rebuild kits for the carbs so I was trying to avoid taking them apart. I am assuming if I pull apart the carbs in any way, the o-rings and such will break.

After reading more about the sync process, I realized I needed to use a line restrictor so will find something for that for the next attempt.

What he is saying, does not mean you have to pull the carbs apart, you are going to the set the the sync screw by eyeballing the butterflies . then re-sync with the guage.

as John stated you may have to pull them apart for cleaning. may be needed.

[95shadow1099]

Originally Posted by kyxon

After reading more about the sync process, I realized I needed to use a line restrictor so will find something for that for the next attempt.

^^^^^ This was your problem, stuff 1" of a #2 pencil up each tube...or a couple of those colored plastic b.b's.

[adlowe]

Originally Posted by kyxon

After reading more about the sync process, I realized I needed to use a line restrictor so will find something for that for the next attempt.

About $1.50/each in an auto parts store last time I went looking. Get 2 and splice one into each end of the line a few inches downstream from your homebuilt adapters. So what if it doubles the cost of the manometer?