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Discussion Starter · #1 · (Edited)
I know this has been discussed many times. The last task on the CB400T II is to balance the carbs. I have done this many times
but today I failed to get it right. Using the clear plastic tubing with Marvel Mystery Oil for the indicator. I have used this set up several
times but today I could not make it work for me. When I cranked the bike the left cylinder pulled more vacuum than the right side.
Should be simple to adjust the screw and balance the vacuum. I finally got the carbs so far out the bike would not
start so I fiddled with the balance screw until the bike ran well and quit for now. I may try again tomorrow or just ride it the
way it is. Starts and runs fine, are the carbs synced, not sure. What was I doing wrong???
 

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I had too many problems with the homebuilt manometers so I bought a carbtune a few years ago, it works great but then I found a digisync and I love it. It also has a built in tach that works off of the engine pulses so no tach wire hookup and is VERY accurate.

You probably have a vacuum leak either on the bike or your manometer set up.
 

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Discussion Starter · #3 ·
I balance carbs about one set a year so I need to do it on the cheap.
Would vacuum gauges work for me???
 

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Vacuum gauges is what we are talking about. Balancing the carbs is so each carb sucks the same as the other. Maybe just make sure you don't have a vacuum leak in your setup.
 

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On the carbs for my 400A after the rebuild I put the carbs on the bench with a bright lite source behind them. Then set the carbs to open and close at the same time. Worked great.

Wouldnt work with them mounted buts it not that big a deal to take them on and off and a whole lot cheaper. I have a manometer But such a pain to use I only use it when I have no other choice.
 

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On the carbs for my 400A after the rebuild I put the carbs on the bench with a bright lite source behind them. Then set the carbs to open and close at the same time. Worked great.

Wouldnt work with them mounted buts it not that big a deal to take them on and off and a whole lot cheaper. I have a manometer But such a pain to use I only use it when I have no other choice.
When I sync carbs they are synced at idle using the throttle screws, they are then synced at 3000 rpm using the cable adjusters. Do the 400's link the carbs together and do not have a split cable? I only sync at idle on my nighthawk and Sabre since the carbs are linked together and have one throttle cable.
 

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The 400a carbs are linked together with push pull cable to open and close. Set everything by the manual when rebuilding the carbs, set and mounted them . Bike fired right and a little adjustment to the idle and she ran fine. Operating temp on heads were within 2-3 degrees of each other . On other bikes that carbs are not linked I use a 1/64 inch drill bit to set each one . Have not worked on anything larger than the 400 so dont know about them.

Bill
 

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The cheap way to go about this is by setting each carb independently so that the idle speed is the same for each.

1. Take the plug off one cylinder and fire up the bike
2. Adjust the throttle screw to control the idle speed of the one firing cylinder so that it idles without stalling (e.g 2000 rpm or so)
3. Now turn off the bike, and do the same to test for the other cylinder.
4. Make sure the idling rpm is about the same.
5. Fire up both cylinders and turn the throttle screws of both carbs the same number of turns until the idle speed is where you want it to be.


Otherwise just pony up the $33.50 and get yourself a vacuum gauge. It will pay for itself in no time.

https://www.walmart.com/ip/Honda-To...9172&wl11=online&wl12=545615985&wl13=&veh=sem
 

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Discussion Starter · #10 ·
What you describe may not work on a CB400T. I think I will order the Wal-Mart gauge
for $33.00 or so. Much simpler. I am going to try my home made system 1 more timebefore
I buy the gauges.
 
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I just checked out the digisync ..$119 for a 2 cyl. I would pop for the 4 cyl. one and see if a buddy will go in half...maybe worth it.. especially if you have friends that share the same interest....
 

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The SOHC's have linked carbs meaning that the left and right carb have an interlocking linkage. There is one idle speed screw and there is one balance adjust screw.
"Old Okie" try to look at the balance screw portion. There are 2 washers plus the spring on the link, the washers are supposed to be one on either side of the linkage. 201_4644-002.JPG
 

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I know this has been discussed many times. The last task on the CB400T II is to balance the carbs. I have done this many times
but today I failed to get it right. Using the clear plastic tubing with Marvel Mystery Oil for the indicator. I have used this set up several
times but today I could not make it work for me. When I cranked the bike the left cylinder pulled more vacuum than the right side.
Should be simple to adjust the screw and balance the vacuum. I finally got the carbs so far out the bike would not
start so I fiddled with the balance screw until the bike ran well and quit for now. I may try again tomorrow or just ride it the
way it is. Starts and runs fine, are the carbs synced, not sure. What was I doing wrong???
We just went by exhaust pressure on a twin. Just feel the exhaust pressure exiting the mufflers, adjust until they feel the same.

Sent from my SM-J320V using Tapatalk
 

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Carb sync makes very little difference when throttle is opened, only matters at idle . And it doesn't matter if it's SOHC , DOHC or pushrod.

Sent from my SM-J320V using Tapatalk
Completely wrong. On linked carbs the sync is only set at idle since the throttle linkages are connected together. On split throttle cables the sync is done at idle and at 3000rpm. At 3000rpm, the cables are adjusted to sync so that both carbs are opening the same.

I drilled and added vacuum ports to my 450K6, after syncing it was like a different bike.
 

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Discussion Starter · #20 ·
I ordered the sync gauges from Wal-Mart for $33.50.
I synced the carbs by the was the motor ran until
I get the gauges. With the carbs being linked together
this whole process is really simple. Screw in the nipples,
hook up the gauges, start her up and adjust by turning 1 screw.
The carb bowls probably have enough gas in them to complete the process,
no auxiliary tank needed. Currently the bike starts instantly and settles
into a nice idle. We will see what changes when she is properly synced.
 
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