OS.12cvr engine tuning help

[j4roe]

I have an OS.12cvr engine and all the gaskets are brand new. I was having trouble with the engine not running correctly and I realized I had a small leak on the gas tank. I read that proper pressure is needed to run these engines so I bought a brand new tank. That seemed to help with the pressure situation, however the engine is still not running correctly. I believe I have the bottom end and top end adjustments in the correct positions and the truck will start up fine with no problems. I run the truck for 2 minutes and everytime its the same issue, when I let off the gas the engine just stalls out. I cant figure it out, and when I richen it a couple of clicks more on the bottom end the truck doesnt idle properly and will stall. Will these engine shut off if they get too hot? Other then overheating I cant figure out why it runs perfect for 2 minutes and then you can hear the idle start to get weaker and weaker up until the engine dies out when you let off the throttle... and help would be greatly appreciated. Once again, all gaskets are new and the head is screwed on properly tight and flush and the gas tank and fuel line are brand new. I dont believe I have an air leak whatsoever. Thanks for the help... if you need pics of my truck to analyze the engine that I have there are some pics of my truck in the rc10 truck forum, sc10gt is the thread...

[Charlie don't surf]

Start at the baseline for tuning, high speed needle adjustment should be flush with the adjustment bbl, and the low end should choke out 3 sec after pinching the fuel line shut. But, the nitro fuel, nitro content and the humidity plus your glow plug temp, plus the idle screw also have to be right.

[lpddpd]

I would put a new glow plug in, sometimes that makes all the difference.

[Brandon G]

Check your carb opening with the filter removed. With the engine not running and the servo at neutral position, hit the brakes. You should NOT see any closing of the barrel in the carb. If it closes even the slightest, simply tighten the idle adjustment screw until you just start to see the barrel move.

Are you using one of those aluminum pre filters? If so, get rid of it. I have never had any luck or seen hardly anyone else use those and it not cause problems.

Did you seal around the base of the carb AND the carb pinch bolt? If not, do so.

Is your fuel fresh?

Like the other guys stated, check your glow plug, or just replace with new.

Check your exhaust gaskets and make absolutely sure that they do not leak. Exhaust leaks can make tuning impossible.

And last bot not least, how much run time does this engine have on it? The way it's acting, it sounds a bit like it is done. How much compression does it have when cold and hot. If it is really loose when it is hot, you may be screwed.

[Brandon G]

Ron Paris tuning tips, good info, hopefully it can be read.

[j4roe]

Ok, thanks guys. I have been wondering myself if the engine is done, but I dont want to just replace the sleeve and piston head at $60 when a whole engine costs $100. It feels like it still has good compression when it is cold. It does seem like when it gets hot it starts to act up and I dont think Im running lean. If I had to guess Id say the engine needs replaced, I just think Im in denial wondering if it could be something else... Basically everything you guys have mentioned is a check and in good working condition... frustrating!

[j4roe]

Ok, I think Im getting a little closer but still not sure. I sealed everything that I could with the silicone and the pressure seems to be fine, good compression and the bottom end is dialed in. The engine is accelerating good and I just let it idle to see how long it would go, 10 min + just sat there idling, so Im positive the bottom end needle is good, however the truck is still cutting out when you let loose with it. It goes well at high speed for maybe a minute and then when you bring it back down to an idle the idle is low and it cuts out. Its similar to the hypothetical situation #2 in the above tuning tips. The bottom end is loading up with a false rich setting because the idle is high. I dont think its that because I have the idle screw good and the bottom end leaned out and Im confident that I have the bottom needle on point. Is it possible that Im too rich on the top end?

[Charlie don't surf]

Yes it is possible, and it is also possible that you are too lean on top- how many seconds does it run when the fuel supply line is pinched out?

[Jay Dub]

Get a brushless...

[adam lancia]

Check to see that the sclutch shoes aren't hanging up, that can stall the engine too.

[Brandon G]

10 minutes idling? If it does that when hot, I would guess that the engine is probably in good condition. However, these racing engines (like your CVR) were really not designed to be run that long at idle. I'm happy with mine if I can get 20 seconds of straight idling without blipping the throttle. Might be your low end is a shade lean. Check your clutch shoes as mentioned above, and also check your clutch bearings. If they drag, they will cause it to cut out.

If you idle for long periods and punch it, most of the time the engine will load up a little at idle. Then you whack the throttle open and it floods the engine. I guess what I'm trying to say is that tuning your engine to run long periods at idle may hinder the tune when not idling.

Are you getting smoke out of the pipe when run at 25% throttle and higher? That is the most important thing. Smoke=lubrication

It is really hard to forum tune an engine. Sound and sight plays such a large factor. Keep at it though. Through the whole process you will learn lots about tuning these little bastards.

[j4roe]

I have visible smoke at 25% throttle and good response. Thats why I believe Im either right on or very near +-2 clicks on the bottom end. What you're saying makes sense about having to blip the throttle and thats why I pry do have it a couple of clicks lean because I was having to blip it so I leaned it out 1 or 2 clicks. I will go 1 to 2 clicks richer on the bottom and get the idle to come down to running around 30 sec or whatever. I believe when this whole problem started I was having the load up scenario where my truck was giving the false low idle because the carb barrel was open quite a bit so Im guessing I had the bottom end way to rich to compensate for the rich air setting. I adjusted that after reading the pdf above that you put on here. I now have that small .2mm gap that I believe they recommend and the bottom end has been leaned out to the correct position. Like I said, I believe the bottom end is very near good, within 2 clicks and Im not having the load up issue anymore. However the truck still basically shuts off. The problem ISNT when you let the truck idle and then punch it. Its when you have it idling fine and then you punch it full throttle up to full speed for 60ft slow down make a turn come back same thing, good acceleration, visible smoke as you open up the throttle, full speed for 40 feet or whatever, let off the throttle and within 5 seconds truck stalls out. Its always after you run it full speed for a minute. Thats what I dont understand, I feel like this engine is tuned pretty good, truck rips for 30 sec or a minute till the dreaded stall out that happens every single time. MY TRUCK IS A ONE MINUTE SENSATION, absolutely the most frustrating issue Ive dealt with in a while... I hope at this point Im not just rambling and some of this actually makes sense or hopefully Im getting the point across. Like I said, it idles wonderfully and I will go 1 or 2 clicks richer to get a more rich idle but after that the truck runs great for about 1 MINUTE and then right after you let off of a full throttle straight away and let the engine come down to an idle, STALL,................ THANKS AGAIN FOR YOUR HELP.

[uzzi]

What sort of fuel are you running? Those OS engines run like clockwork but they do like plenty of lubrication. Also what percentage nitro? small block engines do not like fuel with high nitro content (15% max i would say) What pipe are you running? Have you check the nipple there? How old is the engine? Have you pulled it apart to inspect the rod and bearings? is the combustion chamber clean?

Basic rule of thumb for engine tuning, run it to temperature (about 3 minutes min at low to med speeds) stop the car and count to 10.....accelerate to max throttle. Your car should launch cleanly without hesitation, accelerate with a nice stream of smoke coming from the exaust. If it gurgle and bogs then takes off...its too rich. If it launches hard then hesitates or stalls...its too lean. Remember also your top end needle adjusts the overall amount of air and fuel going into the engine. The bottom end needle fine tunes within the range set by your top end needle.

Hope this has helped

[Brandon G]

Your car should launch cleanly without hesitation, accelerate with a nice stream of smoke coming from the exaust. If it gurgle and bogs then takes off...its too rich. If it launches hard then hesitates or stalls...its too lean.

I agree 100%. After your last post it seems like your engine is starving for fuel on the top end.

Also, what air filter are you using? If it's stock, then keep it that way. Don't ever use those K&N type air filters they sell touting better performance. They will kill an engine faster than you can say "damn it just killed my engine"