Vapor lock problem - please help
 

Hi, I just started breaking in a Novarossi Mephisto .12. During my first take of the break in I noticed that when the engine stalls, I can't prime it or restart it because the carb rejects the fuel. The hottest the engine got was about 216 degrees F. Once the engine's temperature goes down to about 140 degrees it primes no problem and restarts. Does anyone know of any solutions? Any suggestions would be greatly appreciated.

Hello tc3thatflys7,

I would say that if there is a Vapour Lock then the engine is at Over Heat state. One think that You should consider to check if Your Temperature Probe is still has a correct temperature reading.

And You might also consider to Richen Your High Needle while conducting Your Break-In Process.. Vapour Lock at Break-In Process is not good at all..

Cheers.. :)

Thank you. I used my back up temp guage and that was also giving the same temperature reading plus or minus 5 degrees. As for the needle settings l, it is on the recommended needle settings. The engine is brand new and hasn't gone beyond 220. Is there another reason this could be happening?

Do you think it could be the carburetor? For some reason the mephisto I bought came with an aluminum carb out of the box instead on the composit carb shown in the stock Novarossi photos.

What fuel are you using and which glowplug?

I'm running Team Losi 20% and am using a novarossi No. 6 plug that came with it.

With 20% on a (tight) 16% configured engine I would say to add a headshim

Thank you. I will try that.

It might also be worth checking the following;

• your pressure fitting on the pipe isn't blocked or there is a small cut or split in the fuel tubing
• your fuel tank is sealing airtight (submerge the tank under water, pinch off the outlet tube and blow air into the inlet, look for bubbles),
• that the fuel drains out of the fuel line when it is held lower than the tank itself.

All quick, easy checks that could save you a hard time whilst needing a rich tune for break-in. Might not be the root cause of your issue but its good peace of mind after checking.

Thank you for that! I'll try those tests out.

I pressure tested the fuel lines and fuel tank and there are no leaks. I also switched out the pipe to a new pipe to make sure the pressure line is not clogged and it is still showing the same vapour lock symptoms.

There may be an air leak in the fuel path. Make sure the inlet (high speed needle housing) is sealed properly. Make sure the fuel pickup is in tact and not sucking air. I take it that you are quoting your temps in F and not C? I had a similar issue with one of my O.S. .12 engines that had a leak at the HS needle housing as they can be a little delicate when tightening.

Probably have to make this bigger to read it. It talks about a hot carb. A little out of focus but it's readable.
https://cimg3.ibsrv.net/gimg/www.rct...0817b99ae4.jpg

Thank you for those comments. I checked the HSN and it is well sealed and I didn't see any signs of air leaks. I also looked at the front bearing and the crankshaft and didn't see any signs of wear or overheating. I ran a few more tanks through it and the highest temperature I reached was 220 F plus or minus 5 degrees. I also took the tempurature of the carburetor and noticed that it is reaching about 150 F. I'm not sure why my mephisto came with an aluminum carburetor, but I noticed that it should come with the composite carburetor. I ordered the composit carburetor and will give that a run when it arrives. Do you have a preference on carburetors aluminum vs. composite/plastic?

As you discovered, you can't infer the temperature in the carburetor based on the temperature on top of the glowplug. Most Novarossi engines have all-metal carburetors which absorb more heat from the crankcase and will cause the fuel to boil more easily. I always prefer composite carburetors when the option exists, but if there is no composite carburetor for one of my engines, I can just tune the carburetor ever-so-slightly richer to make sure the carburetor never gets hot enough to boil the fuel.