How to tune/sync a Honda twin?? CM400

Tommy2 · 05-07-2009, 01:47 PM

Cant seem to get the carbs dialed in properly. The bike seems to run fine.. Good acceleration, etc.. but I have zero idea how to sync the carbs.
The Clymer manual does not even mention carb syncing.

Im assuming they need to be sync'd because one of the mufflers has a lot more exhaust flowing from it than the other.

I played with the mixture screws..Little difference.. Then I found a screw which I thought had something to do with the sync.. but I think its just an additional idle screw, as far as I can tell thats all it affected when I adjusted it.

Any clue how to make this adjustment??

Sorry to post this.. but Ive been googling constantly the last couple days and cant turn up much detail for Honda twins.

Tommy2 · 05-07-2009, 01:59 PM

Wait a sec.. Apparently there is a synchronization procedure in the Clymer book. Its in the tune-up section, not the carb section.

Looks like I was turning the right screw..

And there is a place to hook up a vacuum gauge.. A screw by the carbs on each cylinder head is apparently a vacuum tap.

Tommy2 · 05-07-2009, 02:46 PM

Ha!

Youre gonna get a kick out of this...

THE MUFFLER WAS CLOGGED!

Decided to pull the muffler off just in case.. Some big chunk lodged in it...

Rattled it out.

Put it back on.

Bike runs even better! Sounds much better too!

That explains why that spark plug was fouled when I got the bike...

The throttle is much more responsive now..

Both mufflers seem to be flowing equally as far as I can tell..

Guess I should still sync the carbs up though..

Sorry for all the posts..sometimes it helps to just talk out loud

bullfrog · 05-07-2009, 04:39 PM

wow.

problem solved in 59 minutes.

good job.

typing it out does help in diagnosing the problem..

05-07-2009, 01:47 PM	#1
Tommy2 ^OP Gnarly Adventurer Joined: Apr 2009 Oddometer: 232	How to tune/sync a Honda twin?? CM400 Cant seem to get the carbs dialed in properly. The bike seems to run fine.. Good acceleration, etc.. but I have zero idea how to sync the carbs. The Clymer manual does not even mention carb syncing. Im assuming they need to be sync'd because one of the mufflers has a lot more exhaust flowing from it than the other. I played with the mixture screws..Little difference.. Then I found a screw which I thought had something to do with the sync.. but I think its just an additional idle screw, as far as I can tell thats all it affected when I adjusted it. Any clue how to make this adjustment?? Sorry to post this.. but Ive been googling constantly the last couple days and cant turn up much detail for Honda twins.

05-07-2009, 04:39 PM	#4
bullfrog Dismember Joined: Apr 2006 Location: Armpit of Texas Oddometer: 591	wow. problem solved in 59 minutes. good job. typing it out does help in diagnosing the problem.. __________________ R1200GS Adv, R1150GS Hacked, Speed Triple 1050

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05-07-2009, 01:59 PM	#2
Tommy2 ^OP Gnarly Adventurer Joined: Apr 2009 Oddometer: 232	Wait a sec.. Apparently there is a synchronization procedure in the Clymer book. Its in the tune-up section, not the carb section. Looks like I was turning the right screw.. And there is a place to hook up a vacuum gauge.. A screw by the carbs on each cylinder head is apparently a vacuum tap.

05-07-2009, 02:46 PM	#3
Tommy2 ^OP Gnarly Adventurer Joined: Apr 2009 Oddometer: 232	Ha! Youre gonna get a kick out of this... THE MUFFLER WAS CLOGGED! Decided to pull the muffler off just in case.. Some big chunk lodged in it... Rattled it out. Put it back on. Bike runs even better! Sounds much better too! That explains why that spark plug was fouled when I got the bike... The throttle is much more responsive now.. Both mufflers seem to be flowing equally as far as I can tell.. Guess I should still sync the carbs up though.. Sorry for all the posts..sometimes it helps to just talk out loud