nitro coffee

Hey guys, need some help here. I have a very well maintained and nice condition GRP Tuned .28. It was
broke in properly and not rushed. It's still not fully broke in but almost. Its under a gallon of fuel. Has a lot
of compression and everything is factory on it. The only things I have changed here and there are carbs
and plugs. Lately it has been running worse than ever!! Its so frustrating because its a great engine
and runs well when it wants to apparently. It idles fine, and revs fine, but if I rev it past half throttle
the engine sticks at what ever rpm I let off the trigger at!!! This is on the box mind you without wheels/tires.
The clutch is fine, I tested it in another car/engine a couple days ago. So its not the clutch, not the exhaust.
Its using factory head and shims. I noticed the GRP plug Im using that came with the engine doesn't sit flush
with the combustion chamber. It sits a bit higher up .5mm or so. Come to think of it, it must be the plug. FUNNY
as it is the manufacturer plug for goodness sake! When I first wsa breaking the engine in I was using OS plugs
and it ran very well and tuned pretty well. It never stuck at high revs like this. Was also using the Novaroos carb then too.
he tank and lines are fine and the throttle servo and linkage are set up well and fully returning to idle. Its so crazy to see a nitro engine stick at revs
after the throttle has been fully closed!! That's pretty scary to think that can happen. I really don't see what the mechanical issue would be if there was one.
The engine internals are fine, all is smooth and operational internally. There are no mechanical defects externally either. Could it hang at
high revs due to a defective plug or it not seating flush? I haven't checked the button and piston since this. I will tho.
The only possible thing I can think of (that hasn't caused this issue or any issues before) is Im using a Novarossi carb without the
carb o'ring so it seats fully all the way down in the crank case. Could there be an air leak there at the base of carb without the oring?

Bud

Sounds like an air leak to me. Can you seal the carb with silicone?

1995 Monster T

Sound like you have blockage stuck inside the carb needle. This will cause engine to rev high and not stop until you close the carb. The solution is clean out the carb set back to factory settings and install a fuel filter. Check to make sure you throttle linkage isn't binding and opening and closing carb. You may have to readjust the throttle linkage. Check rx battery for good power.

Bud

It happens after the carb has closed. He has an air leak. The motor's leaning out.

petersen114

As stated, it sounds like an air leak. If that o-ring is not installed air will defiantly will get through.

Derr429

iTrader: (3)

Don’t most tanks come with a clunk aka stone filter already installed? Why would you want to add another filter? Seems to me just another spot for issues when you start adding things.

Roelof

I believe it uses a turbo plug? If so and the current plug is not sitting flush then there is your air leak.

Matt Piva

iTrader: (25)

If I was you I would do what I ALWAYSdo, tear down the engine clean it and use a wd40 and qtip soaked of it to put it back together. If there’s an issue you will see it. I even tear down my carbs cause I can see where the needles are by sight and pictures and it makes the world or difference. My opinion is you just have a dirty engine and you need to go threw it and make sure no orings are split.

nitro coffee

I did tear the engine down fully and cleaned it entirely!! I always do. Thats why Im baffled. Some good response here guys thanks. Running without the carb throat oring in the past hasn't caused this issue. Although it may have been there before just to a much less degree.
That could be why I could never get a truley dialed tune on it. I always thought about not having that 1 little oring on carb throat can lead to issues or not?

So its either the oring on carb throat not being there or the factory plug not seating flush in the combustion chamber, is what we have so far. These were my thoughts as well. Ok time to go back to an OS plug (which was what I was going to try anyway) and the stock carb I will try.
I want to use the Novarossi carb of course with the throat oring but its doesnt seat all the way in the block with the oring. That's the only reason why Im not using it.

1995 Monster T

NO!

1995 Monster T

Tearing down an engine completely. every time you run is the worst thing you can do, You can lose parts, damage threads or worse??. That o-ring for the carb throat is important. That is causing an air leak and over time will get worse causing problems later. A loose glow plug won't cause the problems you're having. It will just start easier and vibrate looser and loser until it pops out and engine will stop. Swapping carbs from one brand isn't such a good idea either?

nitro coffee

Ill be testing the engine very soon again. I will have a base o ring on it even tho I hate how it doesn't fully seat with that. I always thought that would be prone to an air leak. I think its more the plug not fully seating in the head.
Ill try an OS plug and report back.

fyrstormer

iTrader: (1)

Has the throat of the carburetor been deformed AT ALL by the clamp that holds the carb in-place? I don't think I've ever seen one that hasn't been deformed at least a little over time. Without rubber O-rings at the top and bottom of the throat, air leaks past the gaps caused by that deformation will get worse and worse each time you disassemble the engine for servicing.

nitro coffee

I know! its damned if ya do damned if you dont. Unless you oil the rings each time, which I dont. I use residual oil around the carb or engine and rub it on but dont bust out the oil can each carb install. I dont think most do.
I need to stop swapping carbs! lol Im trying to find out why the grp carb isnt tuning as well as the Nova carb. There may have been a leak somewhere at the time as well, may not have even been the grp carb giving running issues.
The one thing I hate about nitro is the fact that you need to check 8 different things to find the cause of 1 issue. I think I have an air leak at the head currently, not the carb. Ill resolve this with a better fitting plug hopefully. But the carb issue, I really want to love the grp carb on the grp engine but Im just not at all
confident in it so far. I ran the carb twice and didnt like how it ran both times. Couldn't dial in a tune, extremely sensitive to small needle changes. The last time I ran the grp carb was before this thread started and this thread issue.
When I ran the grp carb there was no throttle sticking. Everything was good then except the carb was so sensitive to tune, extremely. Not any fun at all. I heard grp tune well and easy. I haven't seen that yet.
The engine isnt fully broke in tho either. under half gallon on it.

1995 Monster T

It's NOT the plug!!!!!!