Can't find air leak?

[Slade]

Hi all,

So I bought a Revo 3.3 a few months back and put a gallon of 33% nitro fuel through it before it started overheating viciously. I could get the running temps down to the 260-280 F range, but only if the mixture was so rich that it didn't even have enough power to make 2nd gear on a long flat surface. I noticed fuel accumulation on my back 2 shocks, and assumed it was the front bearing starting to leak, as I read they seem to go out on the TRX 3.3's fairly early.

So I bought an OS 21TM (I know I could have changed the bearing on the trx, but I wanted the OS anyway so I figured I'd just go for it) I took the OS out of the box and sealed the base of the carb with black high temp silicone RTV just to be on the safe side.

I started the break-in for the OS with byron's gen2 25% nitro, 11% lubrication fuel, and the glowplug that was included. After about 10 minutes of idling I noticed there wasn't much smoke coming out of the exhaust. I thought that was strange so I checked the temperature: 411 F! I killed it right away, it shut off almost as soon as I pinched the fuel hose.

The manual states that it comes with factory set needle settings for breaking it in, so I never messed with them.

I did a leak check on the tank, it seems to hold pressure fine. No bubbles underwater. So I installed all new fuel lines and zip tied the bases in place.
After letting it sit overnight I tried to run it again. It climbed to 300 in a matter of minutes, so I shut it off again. I noticed when I was trying to start it that the engine seemed to be having trouble pulling fuel through the hose. I had to place my finger over the exhaust and turn it with the easystart for a good 10 seconds just to get the fuel to the carb.

I'm at a loss for what to do next. Thanks for any advice.

 

[sur3fir3]

since you switched motors and have the same issue its must be with exhaust, tank or lines. you tested the tank, switched the lines, so that leaves 2 things either the new motor needs to be sealed, or its an issue with your exhaust. I did some reading (as I dont own a revo) and some people were reporting they needed to use a big block side pipe with that engine, not the stock pipe that comes with your revo. Do you happen to have a spare exhaust around? or a LHS that might have one you can test with?

 

[Slade]

What other areas of the engine could I seal? The exhaust manifold on this engine slides over a rubber boot of sorts, so I'm not sure I could seal it. It did come with a large spring that I can't seem to find a use for. Possibly the back plate where the easy start attaches?

That's an interesting idea about the exhaust pipe, I'll have to look in to that. Possibly the pipe isn't producing enough back pressure resulting in a weak fuel flow to the carb? That would cause it to run lean and overheat I suppose? Annoying, as they market the 21TM as a direct drop-in for the Revo.

Thanks for your help!

---------- Post added at 6:40 PM ---------- Previous post was at 6:32 PM ----------

I also read that the exhaust manifold that comes with the OS 21TM doesn't seal that well with a rear exhaust (as is stock on a revo)

Maybe some new exhaust gaskets? if so which ones?

 

[sur3fir3]

you dont have the spring hooked up to your exhaust?

the spring need to be on as so

 

[davidac49]

Yea the spring stretches around the engine to go into the two holes on the manifold. I would recommend some needle nose pliers to stretch it around.

 

[WinnersCircle]

What other areas of the engine could I seal? The exhaust manifold on this engine slides over a rubber boot of sorts, so I'm not sure I could seal it. It did come with a large spring that I can't seem to find a use for. Possibly the back plate where the easy start attaches?

That's an interesting idea about the exhaust pipe, I'll have to look in to that. Possibly the pipe isn't producing enough back pressure resulting in a weak fuel flow to the carb? That would cause it to run lean and overheat I suppose? Annoying, as they market the 21TM as a direct drop-in for the Revo.

Thanks for your help!

---------- Post added at 6:40 PM ---------- Previous post was at 6:32 PM ----------

I also read that the exhaust manifold that comes with the OS 21TM doesn't seal that well with a rear exhaust (as is stock on a revo)

Maybe some new exhaust gaskets? if so which ones?

BUKU makes front bearing crankcase caps to seal air leaks that are common from front bearings. These work great! They can make an engine that is impossible to tune easy to tune.

Lee
Winner's Circle