WOT problems with my new Fastech .15

[Mikeshobby]

Hi, I got the boat at a local hobby store and it's a fun little boat just to toy around with. I read the break in instructions very carefully and did the process at a local pond. When I was ready for the big lake, I took it down to the big lake to see what it could do.
The boat ran fine for a while under Wide Open Throtte (WOT). After a couple of cool downs and a tank later, all of the sudden WOT RPM would slowly start to drop almost to where the boat was barely moving. When I let off the throttle, it seemed to recover for a little bit but when I got back on it the same thing happened. I brought it to shore and noticed the fitting for the return line on the maniofold was loose so I tightened it and sealed it.
I took it out the other day again and same thing. It runs fine under WOT for a minute or two and then starts to get lazy again.

Here's what I did:
I figured it was too lean and or getting hot so I made sure it was cooling properly by observing the water from the head cooler spraying out the side. Then, I started backing off the high speed needle to run it richer. That didn't really help much. I have to run it so rich that it keeps stalling. Then I swapped out the glow plug to no avail. It still does the same thing. Like I stated before, during and after the break in process it ran fine. This is a sudden problem. Iv'e had this problem with some Nitro cars Iv'e owned in the past as well. Should I try a diffeent fuel? I'm using "MONSTER" Trinity 20% blend.

Sorry about the long story and thanks in advance for any any advice,
Mike

[Kmot]

You're on the right track. It definitely sounds like it is dropping power due to lean overheating.

I would double check the tightness of the back plate on the engine, and the carb pinch boat. Also check the fuel lines for pinholes. If the engine can suck air from any of those spots it will go lean.

[Mikeshobby]

Thanks, there's a thread like this on another forum and someone suggested it could be a worn out motor/cylinder causing low compression when warmed up. I hope I don't have a bad motor already. :eek:

Hopefully it just needs a little fine tuning...

[Mikeshobby]

I guess I was running it too lean. It seized on me while I was trying to start it. I took it apart and the clyinder sleeve has a shiny ring worn in it near the top. I have a new sleeve and cylinder on order from Horizon Hobby.

The funny thing is, the high speed needle was set at the factory setting for break in which should have been rich. I guess I'll have to be a little more carefull during break in with the new rebuild....

[Mikeshobby]

Here's a pic of the damage. It's a little hard to see but if you click on it and look close you can see where the sleeve is worn by the shiny area:

[Kmot]

I would hone it and try it again. Might at least be good for a spare piston/liner set.

[drakonis]

honing such a small cylinder wont do any good. they are a compression fit. my question is: is there a groove in the cylinder wall? can you push the piston thru the cylinder and how far? (im an ex nitro head and know lots about them) if you can push all the way thru its done. if you can only push up to about a 1/16 of more from the top it still might be ok. hows the con rod bushing at the bottom look? alot of slop? if the cylinder is ok reassemble and turn the top needle out 3 full turns from bottomed out and close the barrel on teh carb with the idle screw and adjust the lowend needle all the way in till bottomed dont force. then unscrew 1 1/4 turns then use a 1mm allen and adjust the idle screw till the allen fits with out force. you might need to open slightly to get a decent idle. this is a good starting point to break in. let me know on the cylinder and piston fit. doug.

[Mikeshobby]

The sleeve is spent. The piston locks up in it about 3/4 of the way up to TDC. A new piston and sleeve kit was only $34. it's kind of dissapointing thought becuase it's brand new and I only had it out twice.

That's good advice on the break in Drakonis. The factory setting for break in was only two turns out and it seemed to be kind of lean to me. I actutally remember double checking it. I'll get back to you on the fit.

[Kmot]

The piston locks up in it about 3/4 of the way up to TDC.

Actually, that is good. An ABC constructed engine relies on "pinch" at the top of the cylinder. When the engine comes up to normal operating temperature, the cylinder expands slightly and the piston fits easier, but the compression is maintained by the pinch.

I would still break the 'glaze' off the cylinder. That is why you could hone it. Or use some WD-40 and some very fine sand paper to put a slight cross-hatch in it. Even though it is not a ringed engine, breaking the glaze will renew the cylinder and allow the piston to mate with it again. Then keep the parts as a spare set. Been there, done that.

http://www.mecoa.com/faq/carb/needle_marine.htm

[Mikeshobby]

Actually, that is good. An ABC constructed engine relies on "pinch" at the top of the cylinder. When the engine comes up to normal operating temperature, the cylinder expands slightly and the piston fits easier, but the compression is maintained by the pinch.

I would still break the 'glaze' off the cylinder. That is why you could hone it. Or use some WD-40 and some very fine sand paper to put a slight cross-hatch in it. Even though it is not a ringed engine, breaking the glaze will renew the cylinder and allow the piston to mate with it again. Then keep the parts as a spare set. Been there, done that.

http://www.mecoa.com/faq/carb/needle_marine.htm
Sounds about right. However, I think for what I paid for a new kit, I'll just use the new parts and keep the old one as spare.

[drakonis]

The sleeve is spent. The piston locks up in it about 3/4 of the way up to TDC. A new piston and sleeve kit was only $34. it's kind of dissapointing thought becuase it's brand new and I only had it out twice.

That's good advice on the break in Drakonis. The factory setting for break in was only two turns out and it seemed to be kind of lean to me. I actutally remember double checking it. I'll get back to you on the fit.
no problem, glad to help. ive wore out many os engines. air and car. mainly .12 engines and used to mod my own for more power. thats the basic break in for OS engines. as for the fit on the origional parts 3/4 up is good. but is there any scarring or grooves on teh piston and cyl? good to keep as a back up. break in the minum of 3 tanks befor wot. and lean up 1/4 turn afgter each tank. after about 5 tanks you should be ok to let er rip and lean it up so it runs "on song" :D

[Mikeshobby]

O.K. I got it back together and running again. Iv'e run a few tanks through it and I'm still kind of having the same problem. I can run it around the lake at WOT for a minute or two just fine but eventually it starts to slow down. It stalled once on me and I thought I was back in the same boat again (pun intended). I have the high speed needle set at three turns out which should be pretty rich.
I guess it must be getting hot. There's not much ventiliation in the hull where the engine sits however the head is water cooled. I'm thinking heat is building up in the hull and causing it to over heat. Any ideas?

[Mikeshobby]

Eh scratch that. It's still too lean. I had it out today and had to fatten it up even more. The richer I make it, the better it runs, The factory setting is WAY off with only two turns out. :eek: I'm almost 3 1/2 turns out and it's still too lean.

The instructions say when you pinch the fuel line, RPM should pick up for about 4 seconds before shutting off. I have it so it picks up for about 2 seconds and shuts off. I'm guessing I'm somehwere in the ball bark.

[green-boat]

The factory setting is WAY off with only two turns out. :eek: I'm almost 3 1/2 turns out and it's still too lean.


The instructions IMO are only a guide to go by. There are many variables that go into machining an engine. Yours could have something different with the carb that makes it the way it is.

[Mikeshobby]

The instructions IMO are only a guide to go by. There are many variables that go into machining an engine. Yours could have something different with the carb that makes it the way it is.
Yeah, I'm finding that out the hard way, lol. The instructions also say you should see a thin trail of blue smoke out the exhaust and all I can see is water. I figure as long as it doesn't get hot and try to shut down, I'm in the ball bark of how it should run.