400E with weird rolling idle.

[Guest]

The carbs have been stripped and dipped twice, new o-rings, bench and dynamic synched and idle set around 1200 rpm.The carbs have stock jets and needle setting and stock airbox. The tank has been cleaned and sealed and there is an inline filter. It ran fine the first couple of tanks full now its acting up with a rolling idle.

It will run strongly but coming down to a stop the idle will rise to around 3000 rpm, hold for 10 seconds or so and drop back down to 1200 or so only to repeat the cycle in another 10 or 15 seconds and so on ad infinitem.

Blipping the throttle doesn't drop the idle but, and here's the strange thing, pulling the choke knob and immediately letting it go does drop it back to 1200. The cycle will repeat itself.

I have never experienced anything like this before and can't find any information on anything like this.

Does anyone have any thoughts? Its a baffler for sure.

Cheers,
Spyug

[Nessism]

Does that model bike have intake boot O-rings and if so, have you changed them? Where are the pilot screws set and have you vacuum synced the carbs?

[spyug]

Ed,

I pulled and checked the intake boot o-rings and they appeared good so I didn't replace. The airscrews are about 2 out and I did vacuum synch ( dynamic synch).

The weird thing is that I started it up after supper and idled it for 15 minutes with absolutely no rise from the 1200 rpm level. Blipping and it comes back down.

I'm stumped. I guess I'll change the o-rings anyway. The only other thing i thought about is that silly inline fuel filter. I wonder if it is a case of it filling and emptying every few minutes causing too much then too little fuel getting to the carbs or something along that line.

I'll pull that filter and try it with it off and see if that changes anything. I usually don't run filters but this one seemed "oversize" so I thought the flow would be adequate. Who knows.

Thanks for the input and I'll let you know what I find out.

cheers,
spyug

[don]

In general, the symptom you are describing is called " hunting ". The idle is continually hunting for a nice place to be. In my experience, hunting is caused by a verry slight air leak or a slightly obstructed fuel passage.

Air leak
The motor runs at the correct idle for a moment then the mixture is leaned out via introduced air. The lower rpms draw less air which " plugs" the slight air leak with fuel. Then the motor returns to normal idle until the coating of gas is drawn into the motor. Then.......all over again.

Fuel clog
The motor runs at the correct idle while the fuel supply, (through the pilot tube for example), can keep up. The motor "uses up" the available fuel and leans out. The idle starts to drop. The fuel catches up. Then the idle will go higher, (like when the choke is opened up), with the exess of fuel. Then the cycle starts over.

I see you have dipped and dipped the carbs, as I have done several times. I also have experienced carbs that didn't quite run correctly after mili-dips but worked perfectly after a good soak in an ultrasonic cleaner with the correct solvent in it. The guy I know with the ultrasonic cleaning machine only charges me $25.00. But I only bring him the stripped carb bodies and the jets. I do all the work for him. He simply " cooks" them for me.

Wether it applies to your issue, I don't know for sure, this is simply my experience with a " hunting " idle.

Hope it helps.............

[Nessism]

Replace the intake O-rings for heaven sakes and adjust the pilot screws to three turns.

[spyug]

No need to shout Ed, I heard you the first time That will be first on the list then and I'll twiddle the airscrews too.

I did like what Don said too as that fits with what I'm thinking about the silly filter i.e. lots of fuel then not enough fuel thus the "hunting". Thanks Don.

I'll bet its a combo of things guys.

I'll report back tomorrow.

Cheers and thanks,
Spyug