Carb syncing - Printable Version

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Carb syncing - lostinflorida - 04-04-2008

I've made myself the homemade carb sync tool with the flexible lines and fluid in it. I've got the
basics down and understand that you sync everything to match #4.
I've looked for the thread that had the hook up pattern and can't find it. Should I hook it up 1 to 2 and 3 to 4 then cross the setup to balance all four. Or should I hook 1 to 3 and so on.
I guess what I'm asking is balance first across the engine or each side then to #4?

Re: Carb syncing - Guest - 04-04-2008

It's great that you were able to make your own manometer. Do you only have two hoses?
If so, you may just be wasting your time. Every adjustment you make has an effect on the rest. Generally speaking, you'd balance one bank, then the other, then balance side to side. This will be a very tedious process if you don't have four sight glasses. After you're through with the idle sync, you need to raise the rpm's to around 3000 rpm and check for even syncronization. Next to impossible to check four carbs with two hoses.

Re: Carb syncing - lostinflorida - 04-04-2008

I can't take credit for the manometer. It's on a thread either here or on Steve Saunders and I just can't find the exact thread. You can guess how many threads there are on carbs on both these great forums.
It's really simple, two pieces of flexible clear tubing about 10' long each. You make a loop at the bottom and at the bottom is a few inches of MMO or ATF to be easily seen.
Each end of the loop hooks to a carb. The stronger carb pulls more than the weaker carb. The fluid is higher on that side of the loop. Adjust till you get the fluids even.


Re: Carb syncing - William_86 - 04-04-2008

i have done the same home-made sync tool for my carbs, i did two hoses, for 4 carbs, after a lot of trying i realized it was really hard, since there is no vaccum reading, just a balance.,

your carb can be like

1 to 3 connected and 2 to 4

1 to 3 are synchronized to each other, but they are lets say a number (too big) 10% and 10% open while the fluid on the fluid is balanced on the tube

and 2 and 4 are 20% but balanced to each other. once you switch to 1 to 2 and 3 to 4, the gauge will go crazy you know what i mean?

the best way i found is to mechanically sync the carb first, then use the gauge for a fine tune

Re: Carb syncing - HarrysToy - 04-05-2008

Personely I find it much easier to do with four vacuum, gauges.
I just use valves for fish tank air lines to slow down the pulse's........... 8)

Re: Carb syncing - William_86 - 04-05-2008

no doubt :p

Re: Carb syncing - cooter - 04-26-2008

I also use the 4 vacuum gauge method, very accurate,fast and reliable. I also snug up the "cruise control" on the twistgrip to hold engine about 1500 RPM while the carbs are being balanced. Also I use a flat screwdriver to turn the adjusting screws. This allows small tweaks to made without having to apply any pressure on the screws as needed on philips screws. The adjusting screws conveniently accept both types of drivers. After all are balanced in the proper order, release "cruise control" and blip the throttle slightly and recheck all is balanced at 1200-1500-1800 just by twisting the throttle. Note that the balancing is not done with the throttle at idle (not sitting on idle stop). As long as the individual idle mixtures are set correctly the idle will be perfect. This is probably not the way that is described in the manuals but has worked for me for many years.
cheers Cooter Smile

Re: Carb syncing - Satch - 07-03-2008

Just for the record and speaking with experience, forget the homemade manometer and buy one or take it to a shop. I spent hours making one for four carbs. Checked my bike and it was off so i started to adjust got better than not. This went on & on. Finally I took the bike to the shop and $50 dollars latter it runs like a new Gl1200 and the homemade Manometer is on the way to the landfill. Believe me if ya want to do it yourself than buy one its only another $50

Re: Carb syncing - MikeM - 07-03-2008

I always blip the throttle after EVERY adjustment made so everything "takes a seat" where it should be. Some times nothing changes after a blip, some times there is a big enough change to need another adjustment.

Re: Carb syncing - Guest - 08-21-2008

I'm a new owner of a 85, 1200I and was doing what any concientious new owner would do .... bring the maintenance on the new bike up to a level I am comfortable with. Just so happens that carb syncing was high on the list, however my Clymer Service Manual seems to lack anything on the subject. I'm interested in pursuing the 4 vaccuum gauge approach (that was referenced in this message thread) but need a list of materials and instructions. Can anybody help me out ?

Also concerning the carbs: The 85 GL1200I's and possibly several other flavors had a problem with sputtering and power dropouts when the bike was even moderately cold. Honda provided a "fix" for the problem in ... Honda Service Bulletin # 9 June 1985 (covers bikes with serials 2500001 thru 2509296) California bikes use a different Bulletin (go figure). Anyway, does anybody have a copy of this bulletin that I can lay my hands on ? I'd appreciate any info available.

Thanks In Advance (TIA)


Re: Carb syncing - Feetup - 08-21-2008

I made a rig years ago with four analog vacuum gauges and small needle valves that I used on my old CB 750 and later on my 75 GL 1000. I was never really happy with it, and last month when I got my 1200 I was in the Honda shop and saw a true manometer for a ridiculous price. Being somewhat susceptible to such blackmail I paid my dollars and took it home.
I am very happy I did. I have never been able to sync carbs so accurately before. If I go over it twice, at at least two different throttle settings the resulting smoothness in the engine is wonderful.
I paid 130 bucks Cdn. for it which was a crime considering the cost it would take to manufacture, but I still feel like it was a bargain after all those years with a less than accurate setup. The analog gauges did not have jewelled movements and would not react to the subtle changes. The result was over adjusting then bringing it back down. Very frustrating and less than satisfactory.
I usually buy the best tools I can find and this is one more case of getting what you pay for. You just can't get quality results from cheap tools.


Re: Carb syncing - Guest - 08-21-2008

I would stay away from the homemade deals and go with a good manometer. After researching I settled on a Morgan Carbtune. Nicely made, and works fantastic. You can order direct from them in England via their website and you'll have it within a week to 10 days. $128.00 comes with 5 and 6 mm adapter and a very nice case. about $20.00 without the case. You won't be sorry, it's a great tool and very nice people.

Re: Carb syncing - Satch - 08-22-2008

How often do you need to balance your carbs? WHy have the head ack. Take it in and have it done every 3-4 years

Re: Carb syncing - Guest - 08-22-2008

Only takes 15-20 min. to do yourself with a quality tool. If you ride your bike often ,doing them once or twice a year is worth the improvement in driveability. Why hand someone else $80-$100.00 for a few minutes work.

Re: Carb syncing - Feetup - 08-22-2008

These bikes are over 20 years old. The throttle shaft bushings and carb linkages are just as old and will not hold a setting perfectly any more, if they ever did. Balancing the carbs twice a season is not unreasonable, and once a season is minimum IMHO. If you like to fuss with your bike this is a very satisfying and enjoyable way to fuss, and the results are just as tangable as a good wash and wax. It is a bit of an art but one that is learned quickly, and if you have a friend or two with multi carbs you can share the tool, or even do a "group fuss" and see how close you can get the balance. It's fun to do over a cold one.