vacuum leaks?

[mikeyd]

Im having a hard time getting my b400 to stay running under 3k rpm. What is the best way to check carbs for possible vacuum leaks, I know they definately need syncd but its kinda hard to do if the bike wont run at a normal idle

[Lone Rider]

I've heard it suggested that spraying carb cleaner (and various other fluids) around the manifolds and sealing points while the bike is at idle can identify an intake leak...rpms temporarily increase.

[Nigel Marx]

What's a B400? I may be able to offer some advice if I know.

Regards

Nigel in NZ

[lecap]

Nigel: Bandit 400

I also would recomend the spray intake rubbers method. Best stuff to use is cold start aid spray from the automotive dealer or ether from the pharmacist (working ingredience is the same, decide what's easier to get. The cold start spray is available everywhere in cold and arctic climates. The pharmacist might ask questions )

[Nigel Marx]

After I posted that, I figured as much. I'm wondering if it might be more than an air leak. As a four cylinder, the chances are it is unlikely that more than one inlet manifold would spontaneously have a leak, unless someone has not assembled the carbs properly. I would expect it to idle at better than it is. It is possible, but I would start looking elsewhere first. What sort of carbs does the B400 have? CV or what? If you can get the airbox off and see down the throats (a mirror helps) sometimes you can get a rough sync by getting someone to open the throttle and see if the sliders start moving together.
Here in NZ, we can buy a brand of cold-start that has about the most descriptive name of any product I have seen. It's called "Start, Ya Bastard"!!!
http://www.horizonsunlimited.com/hub...ilies/rofl.gif


Regards

Nigel in NZ

[mikeyd]

the slides are all working together it seems, perhaps they may need thoroughly cleaned would that cause said problem?

[Nigel Marx]

I have yet to see a problem caused by unclean slides. That would most likely make them stick open and cause reving. Has the bike been left for a period of time unused? Say for 6 months or more? If so, then some fuels can evaporate in the carb float bowls and leave a varnish-like residue that can block off the tiny fuel galleries that feed the idle fuel circuits. Dismantling, and blowing out with compressed air can fix it but if it really badly blocked, using a fuel additive like Seafoam or heating the carb in a 50/50 mix of water and Yamaha carb cleaner for 20 minutes then washing in water and blowing with air will almost always do the trick.

Regards

Nigel in NZ