Tunning Help

[Nitroz28]

I just broke in my RS4 rtr 3 with the hpi .15fe motor . when i start it up when its cool and on full tank it runs good have it tuned good. but whenthe tanks becomes half empty it starts acting up. it start to act sluggish and no low end speed and revs up and down in idle and when i accelrate. i see the fuel line moveing when it does these too. i installed a fuel filter . and also when i prime it i see air bubles in the fuel line.but there is no leaks in fuel line.

also when it stalls on half tank i have to prime it to get it to start up again. and some times it will start up then stall right away until i get alot fuel in the carb by primeing it . please help out if u know whats wrong .

i thinks its starving for gas and i see bubles in line also i put the fuel filter very close to the carb and the fuel tube is kind of short. ill take pics tommrow and show u all... thanks

 

[Nitroaddict]

if u r getting excessive bubbles (a lil bubbling is normal), and you are having variations at idle, these are classic signes of an air leak. You say that u checked the fuel line, but most of the time, u will not be able to see the leaks. REPLACE all the fuel line, it will only cost you a buck or two. while you are doing this, remove the fuel tank, and submurge it in a sink full of water. see any air bubbles? if so, then u have a leak in your tank. if the tank is okay, then replace it along with the fuel line, and try to run the car. if it runs fine, then it was the fuel line, and you are good to go. if it still has problems, then u have now narrowed the problem down to the carb.

if it is the carburetor that is leaking, the first and easiest step will be to take some gasket sealant, and lightly spread a small amount around the part of the carb that connects to the engine block. do this with the carb off the engine. replace the carb, and let it dry for a few hours. if you are still having a problem, then u may be leaking out of the needle valves, and we will get to that if needed. try these things out first, shouldnt cost u more than a couple bucks, ,and report back to us!

 

[Nitroz28]

well i havnt replaced the fuel line yet havnt had a chance to go buy some fuel line. But when its idling it starts to rev up and down also the fuel line moves too at same time pulling down likes its trying hard to drawl up the fuel. Also theres alot of dirt collecting by the gasket where the fuel line goes into the neddle. and thers no dirt no where else on the carb . could this be the LEAK ?


here's a pic is the fuel filter too close? :help:

 

[Nitroaddict]

while i normally whould put the filter that close, i dont think it is causing the problem u are having. You really need to follow the steps i indicated in my last post. it should either narrow your problem down to the carb, or solve it altogether, and it wont cost u but a couple of bucks

 

[gthang]

when i had the same problem, it turns out that the rotary carb guide screw went missing, send the carb back to hpi to get replaced.

 

[Nitroz28]

i replaced the line and checked the tanks they are fine. it was to be the carb . where is the carb guide screw so i could check if its gone . i look at the carb no screws missing . what should i do call hpi first ?

 

[gthang]

if you take the carb out and stare at it so that the High Speed Needle is to your left, the screw should be near the bottom right. Look at the instructions, there's a giant parts list, including engine parts. Since i have the Nitro Star 12R SS engine, (i got the Type SS), i don't know if the carb is the same or not. but still...

Also, the same time my rotary carb guide screw came off, the nut that is near the HSN (turn the carb CCW to find it easier), the HSN is/should be the long cylindrical object into which the fuel line plumbs into. the nut that is there came off on mine, and contributed to my starting problem. If you don't see this nut or the guide screw, call HPI asking about their replacing of the carb for free if your car is still under warranty.

If you have any more questions, let me know.

 

[Nitroz28]

UPDATE !!!:mobile:


FIXED IT, It was Two things. FIRST the throttle return spirng was the issue with it not being able to restart it. theres a cheap plactic arm on the carb and i had a throttle return spring attached behind the ball. and when the servo was in idle it missaligned the carb ..so when i pushed back on the servo to make sure it was all the way back the carb completly closed.And it could not go to WOT either. so that was why it would stall and not start back up b/c this is after i hit the brakes.:yes: sliding the carb in full closed. SOLUTION . took it off For now and the carb moves nice now and can get WOT now. QUESTION ? should the trottle be able to move back and forth a little i can slide it in and out like 1 mm back and forth maybe almost a mm theres some play in it ?


SECOND, i had it too lean. when it hit 1/2 tank it was soo lean it would rev up and down and strave for gas and die. when it was a full tank it was getting gas but as u know the tanks leans out when it gets lower so when it hit 1/2 it was just straving for gas. so i riching it up and it's running good now it will run trew a full tank of gas with no problems. and i finally got to see it at WOT .
:ahh: thanks for all ur input .

 

[HPIdriver046]

Toprevnt the air bubbles i would replac and re-route the fuel line and make sure your hose connections to the tank carb and fuel fiter are tight.