My brothers 18ss engine keeps revving up and down and up and down while on idle, its definatly not a radio problem.

When the engine is 'pulsing' up and down the carb is not moving at all?!

Could this be air in the fuels lines maybe?

I really have no ideas on this one, anyone?

you are sure the servo is not glitching right?
check the cooling head bolts
check the fuel lines for a little hole
there shouldnt be that much air in the line

Definatly not the servo as it still does it when the servo is disconected, will check the cooling head bolts and the fuel pipes.

Thanks.

also how long does it take to start idling bad
check his needle settings

Usually does it after 5 - 10mins of running.

Low speed needle is at factory settings (HPI recomend leaving it there)

High Speed Needle is about 3/4 clockwise of factory settings (about the same as my truck, which is fine)

It never stalls by the way, its just dam annoying. As the fluctuation in idle sometimes makes the truck drive forward then stop and so on. While its supposed to be stood still on idle.

it sounds like your clutch is engaging when it shouldnt
does it do it when you keep it running and refuel it
might be running out of gas

Clutch, thats interesting, i will look at that. It does it wether its full of fuel or not.

is there alot of air bubbles in the fuel line when this is going on?

No []

well then check all the things i said [&:]

what tempeture is the engine at
what fuel do you have
also if you have another glow plug try that

Don't know about the temp.

Can't remember the name of the fuel (15 or 16%), but its the same fuel we all use, and all the other cars are fine.

Will try another glow plug tomorrow. (as its 10:30pm here!)

how many gallons have the motor been through?

Engine has done about 2 or 3 gallons i think.

wow didnt think it was that late
5:00 here

start it up no one will care (j/k)

I would but i can't be bothered to go out to the car to get it!

I will finish work at 2pm (9am your time!) tomorrow so i'll try all the things you guys have suggested, then post back my progress here.

Thanks for the input.

no problem

Turn the idle down a bit and see if that helps. Same thing happened to a friend of mine... Turns out it was simply idling too high, problem went away when I turned the idle down on his truck.

how did that work?
idle settings is idle setting it shouldnt make a diffrence

I can't turn the idle down anymore as it is low anyway... i'm sure it will stall?

Thanks for the thought though.

when it starts acting up place your glow plug igniter on the glow plug like you were going to starting
if it quits acting up then you need to get another glow plug

This is what i've done this afternoon:

Clutch springs changed for stiffer ones.
New glow plug installed (Warm weather)
Idle reduced as much as possible.
New fuel lines installed.

Gave it a run around the garden and all seems fine so far, will be taking it on a proper bash tomorrow afternoon.
Will report back any progress.

What color should the top of the piston be after about 4 weeks of hard bashing, ie: about 20 hours of use? Cause i just checked and its dark brown [X(]
Is this bad, i mean will it get worse if so what will heppen?

Thanks again.

The stuff on the piston is probably carbon build up... You don't generally get that in only four weeks if you have been treating your engine correctly. I have been running one of my engines for over a year and still doesn't have any..

you use after run oil right?
this is my fantom .15 before rebuild i had about 6 gallons on her
she didnt have any compression left