bradjones

Hi I bought a second hand hyper 8 with a xtm 457 nitro engine and cannot get full throttle out of it with out the engine cutting out, tryed all simple things tuning back to factory settings and tryed new fuel line, new air filter, new glow plug, but still having same issue.

Symptoms are engine cuts out at wot from low range to high range, running 25% nitro

Also I can see that there is air coming from the fuel tank and quite abit of it too.

I have posted a video up on youtube (hobao hyper 8.5 engine issue) by brad jones..

If anyone as had same issue or can help I would be most grateful.

It is a bump start engine and cannot be addressed with tuning as I have tryed every tune. Also getting good idle and good smoke engine isnt over heating or too rich? Have checked hsn valve is in correct position on carb.

Thinking I could have a air leak in fuel tank but cannot see any signs of fuel on chassis for this to be the problem?

Also I have another rc car that I am going to take fuel tank off tomorrow afternoon and another carb from a thunder tiger. 21 engine if it fits I will try.

nitroexpress

http://www.rcuniverse.com/forum/car-...s-engines-269/

Ybenjulkay2x

you are running lean due to air leak on fuel line or tank it self, try to do bubble test on both tank and line.
use a gal container filled with water, dip you tank with one fuel line connected, plug other end of tank, blow fuel line, and check bubble
for any sign of bubble, if the is that's where the leak will be, tank or line.
also have you seen any bubble coming from the carb side fuel line?, you might have also problem with the main shaft.

bradjones

Ive changed the tank and fuel line but with same issue then I tryed my fiends xtm .25/6 & it worked fine? ,?,?

I got hold of another carb which fits on not sure what it is And the glow plug worked first of all then it was running hot so I let it cool down,
When I went to start it up again it would start on bump start with glow starter on but when I lift the glow starter off it shutS down? and I tryed starting It several times with no luck, the plug is a fire power f5 medium heat.

And yes on the old xtm carb I did have bubbles of air from the carb side, I changed carbs and didnt notice the bubble after?

Can I put pictures up onto here?

nitroexpress

Replace glow plug.

bradjones

The glow plug was brand new when I first got it running the other day went good ( tunning wasnt best) for about half tank then it wouldnt idle without glow starter atttached, would stall soon as removed,

nitroexpress

Which indicates a bad plug. Plugs can fail at any time due to a bad tune (usually too lean) or defect.

bradjones

Agh right ok ill try new plug then, I checked for air leaks and had one on hsn, refitted it with new washer and no leak now, I also had a air leak on the carb seating screw which connects it to the engine anyone no a good cheap sealant so I can seal it up and have no more problems, used ptfe tape havent tryed it to see if still leaking, does engine need to be fully air tight to have it running properly or can it have small air leaks still and have it run ok still?

bradjones

Quick update, carb was leaking air on bubble test so ive sealed it up and no leaks, now I have noticed that I have bubbles coming from the front bearing where pinion gear sits on what can I do about this, will I need a new one and are they interchangable, engine is a xtm 457 .28

nitroexpress

A small amount of leakage is normal.

bradjones

Okay cool,

I noticed aswell that the carb is moving where it gets retained and the carb retainer screw was air leaking :l.

Is there a engine sealant which would be good for this?

Anthoop

If the carb. is loose then there is a fault with the pinch bolt...either loose or missing collets/stripped.
You can use RTV sealer to seal but the carb. should be held solidly by the pinch bolt.....seal around the pinch bolt also when you have fixed the issue.

bradjones

Ye thats what im thinking of doing as its not an expensive engine so if it works after ill be happy, tryed it to day but with no luck, it is idiling quite high and then when I go to drive it off the starter box it just dies like its running to lean, which I take it the air leaks fault. Also without weight (on the starter box) it will rev up freely.

Im just in process of taking engine out because I have found the retaining bolt is threaded but may beable to get grips on bolt edge hopefully.