Hello

I have recently bought an HPI RS4 RTR 3+ Evo with RotoStart. I have 20% HPI racing fuel. I first got the car, and i filled it up with nitro fuel, and primed it, and started it. It started fine, and i drove it around the driveway a few times. I first noticed that even when giving it full throttle, it was veryyyy slow, going only a few mph. After running for a minute or so, it got alot better. One thing i noticed was that when i would brake, and hold the car steady for a second or so, it would stall. (Possibly needs to be tuned?). After stalling and restarting a couple times, i decided to start the break in procedure. I propped it up on a brick (as stated in the manual). I did not prime the engine, i put in the rotostarter, pushed the rotostart button, and after a second or so, the little teeth on the end of the rotostart shaft broke off. I figured that the engine had somehow gotten flooded (I am not sure how, because i hadn't primed it, because it was running just a couple seconds before) I ordered a replacement shaft, and now, a week later, i got it, and when i was priming the engine, i didn't see fuel flowing into the carb. I thought fuel was maybe already in the tube, so i took the tube off and sure enough, fuel came out. I put the tube back on, pumped the air bubbles i had created out, and put the RotoStart shaft into the socket on the car, and MANUALLY turned it. It turned maybe once or twice easily then it became alot harder. Because i did not turn it manually before the first shaft broke, i don't know if this is abnormal.

Basically, i think that the engine somehow got flooded, and was still flooded a week later. Is this possible? Wouldn't the fuel have just evaporated? Was i supposed to do something to clean out the excess fuel out of the lines after running?


Thanks for your help!

You really shouldn't store the car with fuel in it.

It can do bad things to the engine over time.

That said, just remove the glow plug, turn the car upside down and rotate the engine a few times to get all the excess fuel out.

Re-install glow plug and try again.

When you say dont store it with fuel in it, do you mean fuel in the tank, or fuel in the tubes?

WOT? Nice job!

I think it most likely flooded when you last tried it and didn't think fuel was flowing into the carb and maybe it was, and when you got the air bubbles clear maybe more. regardless of when it happened it's pretty easy to flood a nitro. (sometimes called "hydrolock") take the plug out as was mentioned to clear it out. what i do in order to prevent more fuel from going into the carb when upright or upside down is take the fuel line off the carb and put it on the tank pressure outlet..this way you have a closed loop and fuel wont exit the tank.

you may want to turn the idle needle up higher to help keep it from stalling out. after you make some progress with running/breakin you can adjust it back down to where it should normally be, but up high helps it from stalling on a new engine.

Instead of raising the idle, you would want to lean the LSN for a better idle. I NEVER move the idle up or down just because it idles too high or stalls. You tune the LSN then counteract with the idle. So the leaner you go on LSN, you would want to turn the idle out.

No, instead of using the LSN to change idle the LSN should be adjusted for what it is designed and intended to do - to fine tune the transition from idle to 1/4 - ½ throttle where the HSN then takes over. The LSN is not there to adjust or modify idle speed. The LSN adjusts the transition from idle to about 1/4 throttle and above.

Some simple engines only have a HSN. The LSN was created because the engine has different fuel requirements throughout the throttle range - which a single needle cannot accommodate very well.


The HSN should be adjusted before the LSN. Fuel enters the carb through the High Speed Needle first and it directly affects the amount of fuel that goes on to the LSN. The HSN is the first needle to get adjusted, then the LSN is adjusted to get a clean and snappy transition to about 1/4 or half throttle, after which the HSN takes control.

My suggestion to a newb to leave the idle high is that it will help prevent stalling out so that they can get the 2 needles sorted out with less stalling - after all higher rpm requires more fuel and thus a very low idle is easier to ‘drown out’ if the needles are too rich while they are being fine tuned.

ShoestringRacer, Read my tuning thread, [link]http://www.rcuniverse.com/forum/m_8831801/anchors_8831801/mpage_1/key_/anchor/tm.htm#8831801[/link].

Anyways, I disagree. I always reccomend tuning your LSN for break in just so it gets a steady idle. LSN effects idle and throttle responsiveness. If ypu dont believe me, richen the LSN 1 full turn. Will the engine idle? No, if you had it tuned perfectly before. Now lean it 1 turn and it will idle again.

the engines that only have a HSN are crappy RTR engines, and the only one I can think of that only has a HSn is an old Traxxas engine. Some race engines have a MSN too.....

Read my thread and try my tuning method out. I assure you you will get great performance.

Every engine I have owned was super rich from the factory, some of them wouldn't even start so I had to lean the LSN to get them to start. And when trying to get started, the idle won't effect anything because you are blipping the throttle from WOT to idle quickly if the engine won't start. And if your LSN is still blubbery rich, you will need a very high idle for the engine to even run, and that will cause the clutch to engage. On my engines, my tires don't turn off the ground at all as I try to get the lowest possible idle. Also, your LSN has a big effect on temps and fuel mileage.

good answer

When starting a new engine or during break in: back the glow plug off 1/4 turn. This releases the presure and alows the engine to start easier. After it has warmed up: tighten the glow plug. After awhile you won't have to do to this as the piston should have broken in properly.

Chris RC and Shoestring Racer:

Before you guys get too bent out of shape (there's already a bad thread going on in this forum...one's enough......chuckle), when I read your posts, you don't seem to be disagreeing, just miscommunicating.

Chris said:

"Instead of raising the idle, you would want to lean the LSN for a better idle. I NEVER move the idle up or down just because it idles too high or stalls. You tune the LSN then counteract with the idle."

Shoestring said:

"the LSN should be adjusted for what it is designed and intended to do - to fine tune the transition from idle to 1/4 - ½ throttle where the HSN then takes over. The LSN is not there to adjust or modify idle speed."

To me, you are both saying the same thing...."make sure the LSN is adjusted properly first, then adjust the idle set screw if required"

However, there is one issue.

Chris said:

"Every engine I have owned was super rich from the factory, some of them wouldn't even start so I had to lean the LSN to get them to start."

while Shoestring said:

"The HSN should be adjusted before the LSN. Fuel enters the carb through the High Speed Needle first and it directly affects the amount of fuel that goes on to the LSN."

I agree with Chris on that one as I don't think the normal range of the HSN will have any affect on the very limiting setting of the LSN. However, this is one where a lot of people disagree, so it's not worth getting into wihtout proof. I tried to do some experimenting where I check fuel flow with a gravity feed set-up to see if the HSN would acutally affect the LSN (at a typical normal setting), but without suction from the engine, the LSN wouldn't drip fuel consistently so I gave up the experiment. BUt basically, I do as he says....first adjust the LSN so the engine won't keep stalling.

So to be fair to Shoestring, his advice below also works fine:

"My suggestion to a newb to leave the idle high is that it will help prevent stalling out so that they can get the 2 needles sorted out with less stalling"

Oh....I've tried that glowplug loosening thing several times, and I could never get any benifit out of it. Too touchy....either too loose, so not enough compression to fire, or to tight so it didn't make a difference. Oh well...............

Also if you have a turbo plug engine, you can only loosten it 1/2> turn or the threads will strip on the head button.

Works fine for me. check to make sure your plug is burning yellow/orange if not that is where you start.