engine idle to fast...cant slow it down? help!

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
hi guys,

big post..sorry!..

im just after fitting new front cable brakes to my marder/beetle. i bought a new servo for the job, hi-tec hs645-mg which runs the throttle, front cables and rear diff brake.
i set it all up, and all was well.

i took the car for a run yesterday and it ran fine for about 10 mins..first, i thought i was getting interference a couple of times as the throttle did not respond to commands for a second on two occasions....

aside this, all was fine and it ran for around 10 mins more as a mate was blasting around the tarmac with it, shredding my new tyres for me for, donuts and the like.

he ran off the tarmac on to the grass, and the car ran away...out of control..

i quickly took the radio from him and switched it off.... so the failsafe kicks in and applies the brakes. the car comes to a stop, grounded on top of a mole hill, the engine still running, brakes fully applied..(thanks to the failsafe!), but the wheels are still going.

i approached the car and turned the radio back on, the brakes release and the engine revving around 1/3 throttle, the wheels are spinning pretty fast. i cannot brake/stop them...no rear brake power.

i shut the engine down and take the lid off. i notice the throttle/brake servo arm has snapped clean off, on the rear brake side. the other side that controls throttle and front brakes is intact.

me, thinking i can still drive the car with the front brakes and throttle..i starts the engine, and it's revving high on idle..around 1/3 throttle, and, the servo no longer reponds.

ok..shut down..back home.

i removed the new servo and took it back to the LHS where it was purchased the day before, the guy stripped it down to find the motor in the servo had burnt out. luckily, he had a brand new servo, same model which had a stripped gear, so he switched the motors for me..and the servo was wroking again..i was happy, considering he told me they have no warranty.(?).

anyways, i installs my new servo, replaces the snapped servo arm and heads out again.

upon start up, the engine is revving high, around 1/3 throttle. the carb/throttle is closed...i make sure by releasing the throttle rod collet and going throught he normal routine of adjustments of the rods and servo arm....still, no difference..

still idling at a third throttle. i have tried adjusting the idle screw, no difference. i can slow the engine by closing the choke, but then when i try and accelerate, the engine cuts out.

i did recently install a samba pipe, but run a couple of times with no probs..so i guess it;s not the mixture that's at fault, but i reset the LSN back to factory (1 and 1/4 turns out) and i still have over revving problem..

can anybody help??

background info if it helps..

29cc CY engine, samba pipe, k&n filter.

i guess the servo arm snapped because of the force created when the engine was running fast and the brakes were fully applied..which caused the run away. so the over revving problem occured unnoticed just seconds before the run away (described above)

any ideas whats wrong with my engine?
I'll offer what I can - are you sure the the engine revving high is not a lean mixture, since it slows a bit when you close the choke (making it richer)? What happens when you richen the LSN more? Can you see the Unless there throttle actually close, when the linkage is in the idle position.

About the servo, Hitec has a 2 year warranty, at least that's what their site says...

Sorry if that wasn't too helpful, but I'm sure an expert will read up here soon...

thanks fabiano..

if i richen the LSN it cuts out when i accelerate..so i don't think its the mixture..

somebody els on another forum suggested an air leak..i will investigate that..
Did you check the idle screw and make sure it is not too far tightened? Was the idle perfect before the servo horn snapped?
Most servos if left in a failsafe setting with heavy load will burn out or get damaged - This is not under warranty, it is a user error. I recommend to set your failsafe with a medium setting on brake as to not put major stress on the servo for a long period of time. Eventually you will get a 2nd servo just for the front brakes and the adjustments will get better.
I would also recommend using a alloy servo arm. If the throttle part of the servo is what snapped the throttle should of snapped back to idle? If it did not and your saying the idle changed since the accident then you may have an air leak and might want to check it with some WD40 spray and see if the idle changes when spraying it around the intake areas.:)
Where you running out of fuel at the time?
no...it was the rear brake side of the the horn that broke..(the engine running fast, the rear brake was under big pressure, so it snapped at the weakest point...the plastic servo horn)

i was checking it again today, i tightened everything up around the carb and the airfilter (the bolts that hold the carb on, 1 was actually loose). i replaced the perished looking black fuel line with a new one. i also noticed there was no gasket on the engine side of the carb, so i put one on it (i had a spare ).

i went out to give it another go..

it is running a little better (?), but is still revving pretty high (even under full brake).

with the LSN set to factory, i can slow the engine and stop the wheels spinning by turning the LSN anti clockwise, but when i try accelerate the engine bogs and cuts..obviously too much fuel...so i lean it up again to the stage that it can accelerate freely, but the engine speeds up accordingly and the wheels are spinning fast/engine idling too high.....and, with the idle screw almost completley out (anti clockwise) the engine is still far too fast.

i will try the wd40 spray test a little later..

any other ideas?
yep get a copper head gasket next time .. there a much better sealing gasket aswell .. i always use even alittle bit of gasket sealeny aswell .

I've read a couple people having problems with them sealing or staying sealed, have you had any go bad? Are they thicker cause that will mess with the performance.
i use the copper head gaskets with gasket sealant without any issues at all .. and .020 thickness gasket and i never reuse them , but thats what i prefferr .. other swear by paper which is kool also .. people try and get the most knowlegde from other users and make the best choices thats whats so good about forums :)
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock    No Thanks