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Webster IC Engine build log.
lordedmond:
Chris
reading your reply and Doug's post
I am 99% sure that its the fuel tract I think its not getting fuel into the cylinder constantly
When ( many year ago ) I played with IC engine's I developed a pressurised fuel system with a flat slide throttle body for a 3 1/2 cc glow motor these ran on 95% nitro :) at 30 k rpm, to set these thing up as the pressure for the ann was from the exhaust they could not pull fuel at crank so a quick squirt done the air intake would run the motor for about 30 sec I used these on 1/8 scale racing cars ,ring life ( dykes ) was 1 hour :( , but they won me a few cups for the mantle shelf
back to the issue to hand have you tried disconnecting the vapour tank set up , open the inlet valve and squirted some lighter fuel ( that I believe you have ) ? and see if it will start up most times using this method ,if it does then the problem may lie in the bit you have disconnected
Stuart
NickG:
Chris,
A better way to check the air tightness of the system is to just take the piston out and try blowing into the end of the cylinder with the valves shut. Even better, if you could take the cylinder / valve block assembly off with spark plug, everything in place, submerge it in water, blow into the end of the cylinder and look for where any bubbles come from.
Nick
raynerd:
Hi guys, thanks for the continued advice. I`m at work today so will be trying your suggestions this evening and will reply as to how I get on.
Nick - this is what is confusing me! I have actually removed the spark plug and blown as hard as I can into the cylinder, nothing comes through the valves. They seem sealed - yet there is definately air coming back out the intake when I tried before work this morning with the plug back in the place and the piston creating the pressure and vacuum. :palm: :loco: That being said, it is also "sucking" as it should through the intake on the piston back stroke.
I`ve removed the valve block and can blow as hard as I can through the port and the valve is sealed! Yet on the engine it clearly isn`t.
Also, the fact that air is moving through the valve block, all be it the wrong way, I`m confident that the seal is good between valve block and cylinder head.
NickG:
Chris, It is pretty strange and frustrating. I'm wondering if the blow test isn't sufficient then. I think the webster has a compression ratio of 5 or 6 to 1, so the pressure will be around 75psi+ at the top of the compression stroke, whereas you can probably only produce 1 or 2 psi with your lungs.
If the engine gives sufficient 'kick back' when you spin it past the top of the compression stroke, I think you can rule that out anyway. Following Doug's action plan would give it the best chance. Taking the o ring off (providing the kick back is still there with it off) will eliminate the possibility of it being a friction problem.
If the valves are free sliding in their guides, use the lightest spring possible on the intake valve to make sure it's opening. Make sure the exhaust spring is strong enough so that it wouldn't bounce at speed, and as others said, that it shuts before TDC prior to the inlet stroke. There's nothing more you can do then with the vapour carb. The only thing left is ignition timing, if that's set to fire around TDC on compression stroke it should work!
What was your piston made from again? If it's aluminium and it's too close, it could be binding in the cylinder. It expands a lot faster than cast iron.
Hoping you get some luck tonight.
Nick
raynerd:
Yes that is what I was thinking but the fact that I`m having it kicking back on the compression stroke, even if it is leaking a bit, then the seal still seems good enough.
Doug, I`m going to try and get an ignition timing light but they seem expensive at £40 a pop when I search the internet - I just can`t afford that!! I`ll see if I can borrow one.
Chris
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