Topic: CB400F Dies after warms up

[darius_tii]

So I just got a 75 CB400F a month ago, and it just started giving me some problems.
I'm hoping someone on this forum will be able to help me diagnose what the problem may be.

It is running, ONLY until the bike is warmed up and riding, and then looses power and dies.

Here's some background on the bike:
Got it in a non running condition.
Cleaned out the carbs and bench synched them; Adjusting float levels, and all that stuff.
After doing the carbs, cleaning up some of the wiring, and some new gas it started up and ran good.

I decided to take of the muffler to see how it sounded, and I ended up running without it for the last couple weeks. (only riding the bike for a couple miles here and there, every couple of days)

Went for a ride last weekend, and forgot to turn the petcock on after filling up the tank. 
Ran for maybe half of a mile, until it started sputtering and all that. Instantly I realized what happened and turned the gas back on. 
The bike ended up dying after coming to a stop, so I let it cool down.

It started back up, and I rode it for another 30 miles or so, and then on the freeway, then the bike started loosing power and eventually died.

After letting it cool for like 10 min, it started up again and I ran it another 10 miles until it did the same thing.

Lost power while riding, then died.

Ever since it has been doing the same thing.

I will run it for a little while, and it will ride fine. Then once the engine warms up it will just die.


I changed the spark plugs when I first bought it. and just before this happened I changed the oil. (which is now causing oil to slowly leak from the engine


I guessed that I had blew the engine or something, but after doing a compression test (engine was cold though) all of them were within 3-5psi.
So I don't think compression is a prob.


What do you guys think the problem is?  I am sort of stumped..




Any help is greatly appreciated.

[TwoTired]

Air filter new?  They can only be "cleaned" so many times.  Then replacement is needed to stop from choking the engine.
Anyway, pull the plugs and look at the tips.  Black fluffy soot deposits can short out the spark.

Look for rust in the gas tank, a "compromised" fuel filter, and possibly some renewed pilot jet blockage.

Reserve position drains fuel from the bottom of the tank, where all the crud/sediment settles.

Cheers,

[darius_tii]

Thanks for the quick reply!
you live in Milpitas? I live right on the border of milpitas and San Jose.


I went through the air filter, and it doesn't look to bad actually.
After riding it again and messing with it, it seems like as long as I say on the throttle it will continue to run, its just when it comes to idling it dies automatically...


Its super strange..

may have to end up taking the carbs out again and seeing what may be causing it.

Still not sure if its a gas problem or electrical...