Problem starting motor

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

atheras29

Member
Joined
Apr 26, 2011
Messages
18
Reaction score
0
Hello, I'm new to the forum and please be patient because English is not my first language. My son wrote this out. Haha. Thank you.

I made a scratch built 4-cycle motor for an rc boat. It is water cooled and 10cc. I used the carb that I had handy. It is a Super Tigre LXFW08. Cylinder compression and timing seem to be okay. However I can't start the motor. Can anyone help me make the proper carburator with the proper ID dimensions?

IMG_5837.JPG


IMG_5841.JPG
 
Nice engine ;)

What are you using as an ignition source?

I cant see a spark plug hole anywhere? :-*
 
Looks like a hogged out Whittle 10cc, nice...

No spark plug? :eek:
 
Very nice little engine that, from what i can see the spark plug is in the cylinder wall, pointing upwards on the opposite side of the engine from the manifolds. Of course it could be a diesel?!
 
Chaffe said:
from what i can see the spark plug is in the cylinder wall, pointing upwards on the opposite side of the engine from the manifolds. Of course it could be a diesel?!

I see what you are seeing, there's an inclined section on the cylinder opp the manifolds..

Wouldnt have thought the ideal place for a plug?

Diesel? mebbeeeee...... :)
 
John Rudd said:
Nice engine ;)

What are you using as an ignition source?

I cant see a spark plug hole anywhere? :-*

Thanks John

I start it as diesel engine an i realise that the chamber ratio is only 6:1
I modified two different cylinder head in order to convert it to a petrole engine with a (cdi) RCEXL ignitions


IMG_5921.JPG


IMG_5920.JPG


IMG_5919.JPG
 
John Rudd said:
I see what you are seeing, there's an inclined section on the cylinder opp the manifolds..

Wouldnt have thought the ideal place for a plug?

Diesel? mebbeeeee...... :)

John the best place for the spark plug is on the side because the motor is to be used for an RC boat and it is a problem with the boats' deck

scratch.gif i wish it wash diesel!!!!!!

IMG_5801.JPG
 
BillC said:
Looks like a hogged out Whittle 10cc, nice...

No spark plug? :eek:

Thanks

It is a Whippet 10cc medium-performance liquid cooled petrol engine
(spark plug on the side....#10-32 thread)

IMG_5900.JPG


IMG_5901.JPG
 
Atheras29,
Just looking at the proportions of your carb to the engine and the intake valve size, I would say the throat of your carb is probably too large. Small engines just can't draw fuel very well through large throat carbs. A much smaller carb with a throat dia. of about .100" should work better. Unfortunately, the small carbs usually have to be made by the builder as few this size were available from RC engine builders. None are currently available to my knowledge. Bob Shores has a nice little carb design available. You can make the throat size to your needs. Always start the engine initially from a near closed throttle to get the best fuel draw.

You can also install a restrictor plate in the inlet to your present carb starting with a hole size in the .085"-.100" range. This might work temporarily to get the engine started, but is not the ideal solution. Good luck. Keep us posted on your progress.

Jeff



 
If you're sure that the timing is right (cam, valves & ignition), I would expect it to make a pop or two from time to time when trying to start it - is there any such signs ?
 
What strikes me is the 'depth' that the sparking plug is recessed into the cylinder head. It may, or at least should not, make a difference one would think, but to me the end of the plug should at least be visible in the combustion chamber. Where it is situated now I would think that the spark generated is shrouded from the fuel intake charge. Along with the others comments regarding the carburetors ability to not draw fuel as efficiently as it could, I think the engine is a beauty.

BC1
Jim
 
bearcar1 said:
What strikes me is the 'depth' that the sparking plug is recessed into the cylinder head. It may, or at least should not, make a difference one would think, but to me the end of the plug should at least be visible in the combustion chamber. Where it is situated now I would think that the spark generated is shrouded from the fuel intake charge. Along with the others comments regarding the carburetors ability to not draw fuel as efficiently as it could, I think the engine is a beauty.

BC1
Jim
Hello Jim
I start it as diesel engine an i realise that the chamber ratio is only 6:1 (should be 20/22:1)
I modified two different cylinder head in order to convert it to a petrole engine with a cdi ignition and be able to start it
photo#5917 with 1/4-32 spark plug thread on top of cylinder head
photo#5901 spark plug thread on the side
With both set-ups i was not able to start it


IMG_5917.JPG


IMG_5901.JPG
 
Admiral_dk said:
If you're sure that the timing is right (cam, valves & ignition), I would expect it to make a pop or two from time to time when trying to start it - is there any such signs ?

Yes Admiral_dk the timing is right
It pops a lot but can't keep up rpms. It floods, too.

With diesel fuel sounds better, more promise
 
If it cant generate enough power to run it could be leaking compression. Maybe the valves aren't seating or maybe the piston fit is not as good as it needs to be.
 
jpeter said:
If it cant generate enough power to run it could be leaking compression. Maybe the valves aren't seating or maybe the piston fit is not as good as it needs to be.

Hi Jim
I compressed air through the cylinder head and noticed a little leak from the breather (timing cover). Valves are OK. I must test it again with a pressure gauge. Do you know what numbers I have to look at for the size of the motor?

Thanks again
 
Crankcase cover leaking - the rings are not seated yet. New engines suffer from this and is a major problem to overcome at start-up. You will probably notice oil fouling the spark plug due to the rings. Spinning that engine by the flywheel, you should feel good resistance to compression - if not it will be very hard to start.

You can set the engine up on your lathe and without the spark plug installed, spin it for considerable time to seat the rings. The engine will become quite warm to the touch while it is being run-in. Then clean out and refill the oil.... Reinstall the plug and note the difference in the resistance to rotation by hand....

just another 2¢ ;D

Oh yes, Whippet, not Whittle....I have a new untouched casting set for one... I also built its big brother the Wallaby. Westbury designs are fine! I had to build a windage tray for the Wallaby and an oil relief due to so much oil thrown up on the cylinder walls. It did much better after the rings seated. I now use it to proof new carburetors.

BillC
 
i agree with billc. i had the same proplem with my jerry howell powerhouse, i ran it with a set up with an electric drill. it went from no bounce to good bounce on the piston.i would also relap the valves with some real fine clover lapping compound.good luck jonesie
 
Good advice from BillC. It's often hard to start a new engine, but once run in, the compression improves, the valve seating also improves.

Remember the big issues:

1) Fuel/Air
2) Compression
3) Ignition

If you have these,t he engine will at least run for a second or two. That verifies that you have compression and ignition. For sustained running, the fuel/air mix becomes critical.

You should be able to remove the carburetor, add a few drops of petrol to the intake port, and get a second or so of running.

Using glow carburetors for petrol can be tricky. Glow fuel has different vaporization and viscosity than gasoline, and the needle valve becomes hyper-sensitive. With a glow engine, you can often adjust the needle more than one full turn, and the engine still runs, but with gasoline, I've found that even 3 clicks of the needle valve can take it to too rich, or too lean.

Visually, your carb seems a tad large to me. I'd suggest keep trying, incrementally adjusting the needle valve, starting from closed and going towards open. Try 1/2 a turn each attempt. Once she coughs/sputters, try 1/4 turn either direction. Narrow it down.

If all that fails, consider a smaller carb. You need air velocity to vaporize the petrol, and if the throat is too large, it won't run well.

Remember too that without a float valve, the fuel will gravity feed (siphon) and flood the engine. Keep the fuel level (for now) a cm or so below the carb needle, and count on vacuum to draw needed fuel. You'll also find with this sort of setup that, with the needle being super-sensitive, the mixture will CHANGE as the fuel in the tank goes down. It'll go lean on you, not enough fuel. This is why a float valve helps, but that is for the future.

Hope this helps,

Swede
 

Latest posts

Back
Top