Cleaning carbs....I think I wanna do it!

[GooseMan]

I think I post this like once every few months...but I think I really want to try to clean my carbs! Bikes gonna be sitting around for the next few months anyway, and I figure its a good time to clean the carbs. If I screw up, at least I have a few months to figure it out! And you know me....I usually screw something up! 

I've looked over the diagrams from the manual, and it seems pretty straightforward. I figure if I take my time and be patient, I can do it right.

My ONLY concern is getting the carbs back to the factory settings when putting them back together. When I take out all the mixture screws, how do I know how to put them back to factory specs? It only says "1 1/2 turns back" for the pilot screw...what about the others? I just wanna make sure my carbs are back to normal when I put them back together...

[pmackie]

Hey GooseMan

Don't get too concerned. Most of the carb circuits are NOT adjustable, you actually need to change jets to adjust. A couple of things to watch for:

1. Air Screws - check them first by turning them all the way IN (gently) while counting how far they turn until they just bottom out. Write this down for each carb.

2. Float height - you actually have to "bend" the tab on the float mount that contacts the float needle to adjust, so unless you are really rough, nothing will change. You should check this height when apart however. Check the distance between the float bracket and the carb base when the float just makes contact with the float needle.

3. Watch for O-Rings. It is useful to have your camera, and take pictures as you dismantle things, to help you remember, or have a good manual with pictures/diagrams.

Otherwise, take you time and you'll be fine.

However, why do you want to take them apart? Are you having some problems? I'm not familiar with the 400's carbs, but you can usually drain the float bowls without removing the carbs. If you capture the fuel and look for any crud, and everything looks clean and runs well, you might just want to leave it.

[GooseMan]

OK cool! Just wanna make sure its all set back to stock when re-assembling.

Basically, I want to clean them because its an older bike with 60,000 km on it, and I really have NO IDEA when the last time the carbs were cleaned. I just like having my stuff running in top condition, and I honestly dont know if it is at the moment.

The bike runs well, but it does have a few issues starting. There have been a few instances where the bike will start right up one day, I'll ride around for a few hours, and then wont start up again after a 30 min break. I'll have to start it up and keep the throttle at about 2500 rpm to keep the engine from dying.

Other times, it just wont start for whatever reason. It'll turn over, fire a bit, but wont run. I'll either have to give it some throttle, or it'll just die :( The next day, it'll start RIGHT UP.

I'm gonna guess it has something to do with the carbs, and/or the starting system of the carbs or low RPM fuel delivery.

[Boom-Boom]

A couple more tidbits about the b400 carbs...

The starter pipe (which is the copper tube on the outside of the carb that provides extra fuel when the choke is on) is very easy to break when trying to remove or re-install the carbs.  Make sure not to bend/break it while pushing the carbs back onto the manifold.  I did this and it's a pain to fix.

Lubricate the rubber gaskets to make it easier to slip the carbs back onto the manifold.

I replaced all the #2 philips screws w/ socket cap hex screws to make them easier to service in the future.  There is 8 per carb.

Loosen the throttle cable at the hand control to make it easier to remove from the carbs.  You'll have to readjust the throttle cable tension once you get the carbs back together.  Turn your bars all the way left and then all the way right while the bike is idling in neutral to make sure the cable tension doesn't affect throttle response.

Use a carb balancer.  It's easier to do w/ a 4 carb balancer, but you can do it w/ a 2 carb balancer.  You'll need a temporary fuel bottle (I make one out of a soda bottle and the correct sized hose barb) and you'll need a flexible shaft screwdriver to get to the air/fuel mixture screws while the bike is running.

If your carbs are clean, you're getting good spark from your plugs and coils, and your air filter is clean, but you are still getting weird ignition and running behavior, start looking at the CDI.

[GooseMan]

cool..thanks!

Is this a good resource for cleaning carbs? http://faq.f650.com/FAQs/Carb_Clean.htm#Enough%20of%20the%20Preamble,%20How%20do%20I%20actually%20Clean%20&%20Replace%20Carb%20Parts. It seems the BMW F650 has similar carbs (Mikuni BST 36mm), so is it safe to assume most of this is true for our carbs?

[gsxr400 racer]

there is great info on here about cleaning carbs do a search

[Forde]

Hey man if the bike is runnin fine dont get into the carbs just throw some fuel system treatment in the tank.  If it aint broke dont fix it.

Do something that needs done to satisfy your urge to tinker!

[GooseMan]

Well, I've already run two cans of Seafoam last season, and she still acts up sometimes!

I'm thinking maybe I should wait till the season starts, and see how she goes. The battery will be nice and fuly charged (left on a Yuasa charger all winter), fresh oil and filter, cleaned air filter, and maybe I'll change the plugs. If shes still bitchy after all that, its carb time!

[PitterB4]

There's some great info and tips in this thread.  Nice job fellas!   

As someone who has had B4 carbs off and apart literally dozens and dozens of times...  I'll highlight a few and add a couple...

First, that starter tube is EASY to bust and a PAIN to fix.  You don't want to break it.  When you pull the carbs with the throttle cable attached, you'll be tempted to rest the carbs on it (far right side of carb #4) while you're working.  Be really careful with it. 

All 3 of Pmackie's tips are right-on.  Be careful when you take the black tops off.  There's a little tiny o-ring under each one.  Don't loose it!  I always pulled the tops and diaphram/slide/needle/spring before removing the carbs from the intake so it had less chance to go rolling away.  Still, my kids and I spend hours cumulatively searching for the damned things a couple times.  Taking some good photos any time you dismantle something for the first time is a great idea.  Hell I even did it the first time I pulled the tank so I'd remember where the hoses go...

If you're going to take the time to tear into them, get an o-ring kit and replace every damned one of them.  If they're not bad now, they will be and this will save you going back in there.

Here's the Pitter method for getting everthing clean.  Keep in mind, YMMV...  Once you get everything pulled apart, hit everything with some carb cleaner.  Using the straw on the can, force it through ever hole and passage.  When you squirt it in somewhere, you should see it coming out somewhere else.  WEAR EYE PROTECTION when you're doing this.  I would ususally run a strand of wire through the pilot jet to be sure it was clean.  Then, replace the o-rings and fit all the internal stuff back together.  Check your float height (float height tool is very useful here) and put the a/f screws back to their earlier setting.  Put the bowls back on (yeah, replacing those shitty screws with hex screws is a great idea!).  Using some lube (I'd spray wd40 on a rag and wipe it on), very carefully (for the love of God, don't break that starter pipe now!) replace the bank on the intake.  Then, drop the diaphram/slide/needle/spring assembly back in.  Put the tiny o-ring back in it's place and then very carfully replace the cap making sure not to lose or move that o-ring. 

Like Jay said, there's tons of info here and that site you linked looked good too.  Everything I said above is here somewhere but I'm completely burned out at work and needed a break!     Good luck!