LXhoweller Posted October 17, 2020 Share Posted October 17, 2020 Hello. So I am kind of new to this hobby, had a nitro car when I was younger and had great fun but got too busy with life to continue it. Now I have had a bit of time I decided to try to rebuild my old car. It hasn't ran in 10 years so I completely stripped the engine and cleaned and re oiled it. I just tried starting it for the first time and it was going fine, sat at idle for about 5 mins then all of a sudden the revs started to increase, I tried to stop it by blocking the exhaust but the revs just kept climbing, the car couldn't be stopped I just had to wait for it to run out of fuel. In a car I think this is called a runaway. When this had finished the engine just sat smoking from all of the heat build up. My question is what could cause this and how to I avoid it again? Fortunately it had no wheels so didn't go crashing through my fence. Sorry if this sounds stupid. Quote Link to comment Share on other sites More sharing options...
Smartstots Posted October 17, 2020 Share Posted October 17, 2020 Hi, next time, take off the air filter and starve it of air, it will soon stop then. Did it have a lot of fuel left in the tank, was the carb closed when it ran away? It could be a leaking bearing or an air leak from somewhere else,, if an engine pulls in air then it will idle erratic or won’t start, leaking front bearing by flywheel is quite common, or carb not sealing correctly against body of car, what engine is it, what fuel are you using? Nitro is fiddly but fun when they run right. Mart Quote Link to comment Share on other sites More sharing options...
LXhoweller Posted October 17, 2020 Author Share Posted October 17, 2020 8 minutes ago, Smartstots said: Hi, next time, take off the air filter and starve it of air, it will soon stop then. Did it have a lot of fuel left in the tank, was the carb closed when it ran away? It could be a leaking bearing or an air leak from somewhere else,, if an engine pulls in air then it will idle erratic or won’t start, leaking front bearing by flywheel is quite common, or carb not sealing correctly against body of car, what engine is it, what fuel are you using? Nitro is fiddly but fun when they run right. Mart Okay I will try stopping with the carb next time. Fortunately I only quarter filled it for first start and alot if it was gone. It only ran for about 20-30 seconds, the carb was in its idle position with about 1mm gap. Not sure what engine it is sorry, but the car is a thundertiger tomahawk st. For fuel I am using a brand new bottle of 25% nitro. I remember it being fiddly before but I've never experienced this before. Can I fix a bearing leak or would I have to replace it. Thanks Alex Quote Link to comment Share on other sites More sharing options...
LXhoweller Posted October 17, 2020 Author Share Posted October 17, 2020 I will also add that on inspection after it had cooled there was alot of greasy residue, I believe from the fuel, around the base of the engine and on the pull start. I don't know if this is from a leak or just from me spilling some fuel Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted October 17, 2020 Share Posted October 17, 2020 so in essence it was about to run out of fuel ? how long did runaway effect last ? if you havnt already i would put a bit silicone tubing over exhaust outlet about 1/4 inch past the metal plastic outlet that way you wont burn finger as bad trying to stop engine with finger over exhaust Quote Link to comment Share on other sites More sharing options...
LXhoweller Posted October 17, 2020 Author Share Posted October 17, 2020 6 minutes ago, Stormbringer said: so in essence it was about to run out of fuel ? how long did runaway effect last ? if you havnt already i would put a bit silicone tubing over exhaust outlet about 1/4 inch past the metal plastic outlet that way you wont burn finger as bad trying to stop engine with finger over exhaust That tube idea is a good one never thought about that. It was about to run out of fuel but that was only convenient, it could have done it with a full tank I think. I hope what I am trying to say makes sense. If you youtube diesel runaway that is essentially what happened to my RC car. The runaway only lasted 20-30 seconds but that's just because it ran out of fuel, if it had more fuel it would have lasted longer. I did try to cover the exhaust to stop it but that wouldn't stop it, the pressure from the runaway was so high it just pushed my finger off Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted October 18, 2020 Share Posted October 18, 2020 It is kind of normal when a nitro starts to run out of fuel and it starts drawing air bubbles into the carb to run away and they can rev their nuts off till mixtures to lean to run I am going to suggest you run it again and see how it behaves but instead of finger over exhaust to stop it try pinching fuel line to stop it if it races again If its ok and only races when about to run out of fuel thats normal Quote Link to comment Share on other sites More sharing options...
LXhoweller Posted October 18, 2020 Author Share Posted October 18, 2020 28 minutes ago, Stormbringer said: It is kind of normal when a nitro starts to run out of fuel and it starts drawing air bubbles into the carb to run away and they can rev their nuts off till mixtures to lean to run I am going to suggest you run it again and see how it behaves but instead of finger over exhaust to stop it try pinching fuel line to stop it if it races again If its ok and only races when about to run out of fuel thats normal Okay I'll try again later when I have chance. I know that can rev higher when running out of fuel but this was more than that. I genuinely thought it was about to explode by the screaming noise it made Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted October 18, 2020 Share Posted October 18, 2020 I take it the throttle servo is working correctly ? Quote Link to comment Share on other sites More sharing options...
LXhoweller Posted October 18, 2020 Author Share Posted October 18, 2020 10 minutes ago, Stormbringer said: I take it the throttle servo is working correctly ? Yeah working perfectly. I think I may have worked out a possible cause. The seal between the exhaust and the engine has split, I found part of it outside, I can shine a light straight through. I think it's possible that when this broke the engine just kept pulling air in making it jump in revs. Thats the only issue i found with it so far mechanically Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted October 18, 2020 Share Posted October 18, 2020 thats a possibility do you have spare seals ? Quote Link to comment Share on other sites More sharing options...
LXhoweller Posted October 18, 2020 Author Share Posted October 18, 2020 43 minutes ago, Stormbringer said: thats a possibility do you have spare seals ? I have ordered some, they should be here Tuesday. Thanks for all the help by the way Quote Link to comment Share on other sites More sharing options...
Stormbringer Posted October 18, 2020 Share Posted October 18, 2020 no probs mate just hope you get it sorted out 🍻 Quote Link to comment Share on other sites More sharing options...
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