mxrider42

I have an HPI RS4 3. It will crank and run good. But after it warms up it will stop and will crank and run for about 5 more minutes. Then it cuts off and will not run again till it cools down. I have ran the body off of the car thinking that it was over heating, but that hasn't helped and it will only runs about ten minutes at a time. Any help or suggestions will be a big help.
Thanks
Trey

hpi apollo

how hot is it running? how many gallons has the engine been run through? sounds like vaporlock from the hot carb

mxrider42

I haven't checked the temps. I just went out and got a temp gun today and haven't run it yet. I just took the body of for better air flow. I bought it off of ebay so I have no idea how much fuel it has been run through it. How do I solve the vapor lock problem?
Thanks for your help
Trey

hpi apollo

well for the engine, reset the needles to factory settings and work from there, tune the hsn then the lsn, and vaporlock is when your hot engine cuts off and you try to prime the carb, its so hot it makes the fuel evaportate and push the fuel outta your line, all you can do is let it cool

mxrider42

I will try that tomorrow. Thanks for your help!
Trey

jeremy12

hey try to run you car really rich then lean it out bit by bit

millerracer

I've experienced vapor lock too - it sucks as once you have a good run in - and shut it off, then it won't start again. You can actually HEAR the fuel burn off in the carb before it even gets in the motor...lol.

Not sure how to fix this problem other than increase airflow to the head and carb.... as I am not running the motor too lean.

Hey apollo - I bought an OS 10E carb - this should happen a lot less with that carb correct?

hpi apollo

really the acrb doesnt effect it much unless it is composite, which only high doallar engines have usually, the only reason vapor lock happens is heat in the carb, to be honest, and im not trying to be rude, if people would break down the reason why things are happening, they could find the solution

millerracer

My thought is - with high speed and low speed needles, the carb will effectively feed the motor the proper amount of fuel at low and high RPMS - rather than just one end of the spectrum - the increased and more efficient fuel flow (which is both cooling and lubrication for 2-stroke engines) will keep the motor running at a more consistent and cooler temp therefore reducing the chances for vapor-lock.

Other than that - airflow to the engine is the only thing that can keep your engine cooler unless it is water cooled. I have pretty good ducting to my motor, and I still will get vapor lock - that is why I assumed it might be something besides airflow.

hpi apollo

no, keepign the carb cool is the main part, more fuel flow would just mean you are running rich which would effect performance, all you can do sometimes is let it cool off, or pour a little bit of fuel on the sides of the carb

millerracer

got it - i need better ducting

hpi apollo

no no, you are thinking "i need as much airflow as possible" dont do that

too much airflow will make your engine run cool, while you may think "hey cooler is better" no, if you are one who tunes by temp, then it could say 200 degrees while you are running lean, same thing happens when running in the winter

millerracer

I don't tune by temp - I tune by carb.... and if I get the carb perfect and it vapor locks - then is that just something I need to deal with then?

hpi apollo

tune to performance, if it is running hot yet performing how i should, you need more airflow, vaporlock is something that will happen, unless you get a composite carb, and i doubt they make them for engines like those

millerracer

just the info I was looking for - glad I am doing the right things.

By the way - the os 18 should be showing up any day then it is "accessory shopping"