CBR Forum - Enthusiast forums for Honda CBR Owners

- CBR 900RR (https://cbrforum.com/forum/cbr-900rr-19/)

- - Carb Sync (https://cbrforum.com/forum/cbr-900rr-19/carb-sync-19902/)

When I rebuilt my carbs, I think I may have knocked my carbs out of sync. Is syncing carbs something that I can do at home or do I need to take it to the dealer? If I go to the dealer, how much can I expect to pay? If I can do it myself, what tools do I need? Has anyone ever documented how to sync carbs?

--Thanks, Chris

You can easily do it at home.

You can either buy/borrow a 4 cylander manometer - or - make a home brew one.

Take the tank off - set it aside. Hang a gas jug from the ceiling with a length of hose, or put a long hose on the tank and lift it upto a nearby bench.

I've not sync'ed a 900rr but generally - If you have a 4 port manometer it is easier - plug each port into a cylander - don't cross the hoses over because that will make it harder ;) If you only have a two port you will have to sync 1 to 2, 3 to 4 and then 1-2 to 3-4. It takes a bit longer but still is possible.

The principle of it is you want the same vacuum from each carb. Homemade tools measure the vacuum relative to each carb - ie - 1 vs 2. The stronger vacuum moves the fluid to the stronger side. Turn the adjustment screw to balance these carbs so that they have the same vacuum.

To make a homemade manometer?

Some people just use a slug of oil in a long hose. That works, but I find some people have problems having the oil slug sucked into one carb because the sync is way off or they were too slow. My personal preference is the two-bottle manometer.

Find two bottles that are the same size. Put some food coloured water on each side - say 1.5". Run a short hose ~18" from the bottom of one bottle to the bottom of the other bottle. Run a longer hose out of the top of each bottle to a carb. Say you attached left bottle to carb 1 and Right bottle to carb 2 for example. Seal both bottles - it is important to get a good seal. I have in the past used 1/4" hose, and drilled two 3/8 holes in the top of mayo bottle lids. Inserted and positioned the hoses, and filled around the hoses with poster putty or glue.

IF carb 1 is stronger the fluid will move from the right bottle through the short hose to the left bottle.

If you make two home built units you can get 1-2 and 3-4 done at the same time... I personally found that faster. I have not figured out how to build a home 4 port tool - you'd have to use a different principle.

If you have access to a colour tune plug get it. As you change your sync the mixture can change. As you change your mixture the vacuum changes. Small changes but if the carbs are way off it can take a bit of time to get them setup perfectly.

Woot.

How much at a dealer? Probably at least 2 hours... it doesn't take that long if they aren't way off, but they usually only charge full hours. To make it cheaper ride the bike there - strip it in the parking lot so they don't have to.

Dude, you built a car. You can handle this for sure.

Synchronizing the carbs is easy as eating pancakes. But you do need to sack up and buy the vacuum measuring doodad. Just get a 4-tuber so you're not constantly switching back and forth between the carbs. It comes complete with a bottle of mercury. Pour the bottle into the container that the end of the lines are resting in, and watch the vacuum signals for each carb. There are 3 screws to turn to adjust the angles of the butterflies and in turn the vacuum signal. It is incredibly simple. And the engine runs MUCH smoother when you're done. The idle will be nice and steady and the transition from idle to part throttle is seamless.

If you don't have a service manual, there is one on www.rrzone.com in the downloads section.

got a picture of that manometer thingy?

Me?

One second - I have a picture of a friends.

Also see:
http://www.carbtune.com/ ( My preference - no mercury - this same site also has the colortune which I really like)
http://www.motionpro.com/motorcycle/...omy_carb_tuner
http://www.busters-accessories.co.uk...l.asp?prod=EVG
http://www.ibmwr.org/prodreview/twinmax.html

[IMG]local://upfiles/9650/567071C4F15A47D6AD2A9E4D17E97A06.jpg[/IMG]

Thanks for all the good info. After looking at the manual--which I did not have before; thanks!--it does seem pretty easy. I'll order the tool and have a go at it.

--Chris

Make sure you get the one that reads all four carbs. It's a little bit more expensive, but it'll make things so much easier than having to swap back and forth.

I'll do that; thanks. All the tools looked to be under $100, so it might as well buy a good one. I kinda like the look of the 4 individual round vacuum gauges. That seems like it would be the easiest to use.

--Thanks, Chris