Yet Another Webster Begins

[johwen]

When you spin it over with your electric drill and then take out the spark plug is it wet? should be. If not your not getting fuel into the engine this says valves. timing, fuel/carb possibly the problem. If you have a ball valve in the inlet of the fuel line maybe the ball is to heavy for a weak suction to lift it from its seat. If the plug is wet I would be looking at the ignition The spark should be blue and if not change your condenser, Check also that there are no High tension leaks under compression. Tick of each one of the following one at a time and stay with each until you are sure before moving fore ward
1. compression/valve seating
2. timing of valves affects above compression
3. fuel supply can you flood the carb by choking it.
4. spark timing at or just be before TDC compression stroke
5 quality of the spark under compression.
My suggestion in that order don't move on from each until you are satisfied each is up to scratch.

 

[Brian Rupnow]

On the issues of the points sticking.-The hole which takes the #10 bolt is marginally undersize. Run an electric drill 3/16" diameter thru it. That should fix the points sticking issue

 

[CFLBob]

now next i will say that i appolgize for blowing up your build with so many replies

No need to apologize at all! I appreciate all the suggestions. I have to notice that some of the tips seem to be opposites of each other, but that's fine, too.

Roy seems to say that the CDI ignition will work with either the points opening or closing to set the spark. I remember he told me the ignition cam should have rounded shoulders and but didn't really talk about what kind of radius makes them rounded. I rounded mine over a little (barely visible in the pictures). I've watched the points firing with the spark plug lying next to the engine and looked closely at my points. I think I've seen them cause a spark both closing and opening.

As for retirement, I'm coming up on being retired five years. Tomorrow is my five year anniversary of my last day at work. I recommend it to everyone.

 

[CFLBob]

Yesterday, I removed the valve block assembly and while I was experimenting with adding a gasket between that block and the engine, I noticed something funny. I had disconnected the fuel line and stood the tank up so that the tubes were sticking upward out of the top. I noticed that the metal piece that came on the fuel line was no longer in the fuel line, but just lying on the bottom.

I didn't round up a glass bottle to pour the Coleman fuel into until a little while ago, and when I went to take off the top to pour out the fuel, found the plastics inside the bottle had come apart. Badly.

That black plastic thing, now in two pieces was used to seal the bottle by tightening that Phillips screw in the lid. That's not sealing again. The light blue fuel line on the brass tube and the much larger diameter tube underneath and behind it were the same piece when I got it. That tubing swelled in size until the metal piece fell off. I suppose if I left it lying on its side much longer, it would have started leaking.

Obviously these plastics aren't compatible with the Coleman fuel!

This was a model aircraft tank from Tower Hobbies, and I got it mostly to save the work of making a gas tank from parts I don't have, figuring it's hard to beat the $5 tank with some extra fuel line.

I need a replacement but don't know where to turn. I guess RC model engine supplies are out. Can anyone point me to a source? Any ideas? Is this repairable somehow?

 

[Brian Rupnow]

#1--No, you can't repair it. #2--why are there 2 lines coming out of the black rubber plug? There should only be one line running up to the carburetor and an air vent to let air into the tank to keep the tank from vacuum locking as the fuel level goes down.

 

[CFLBob]

... #2--why are there 2 lines coming out of the black rubber plug? ...

The line with the short piece of tubing on it is the air vent into the tank. The dark blue tubing is the fuel output line.

 

[Longboy]

I find that cloudy looking silicon fuel lines swell in Coleman. The weed wacker/lawn mower red vinyl fuel lines are very stiff. Clear vinyl tubing works well and can bend to tight radius. You can order some Delrin round stock for the cap if your fuel bottle is up right or cap the ends of a tube with aluminum round stock epoxied in place and make a filler neck and line feed outlet for a horizontal tank. Clear PVC tubing looks cool for a fuel tank too! Just walking thru a grocery/ drug store looking at containers with screw or snap lids might give you ready made solutions also.

 

[Ghosty]

The bung with the fuel lines is for "GLOW" fuel, you need the bung for "PETROL"(gas) and the problem will be fixed. Both Sullivan and Dubro make the gas bungs. Dubro Cat No. 400, Gas Conversion Stopper, also you should use Tygon fuel tube(yellow)
.
Cheers
Andrew

 

[CFLBob]

The bung with the fuel lines is for "GLOW" fuel, you need the bung for "PETROL"(gas) and the problem will be fixed. Both Sullivan and Dubro make the gas bungs. Dubro Cat No. 400, Gas Conversion Stopper, also you should use Tygon fuel tube(yellow)

Thanks, Andrew!

The same hobby store chain I bought the other from had these. Checking to be sure they'll fit.

 

[Ghosty]

Yep, they fit, I use them in my boats, the latest one, custom step up counter rotating gear box and dog drive.

Cheers
Andrew

 

[CFLBob]

Well, I was thinking of the fuel tank I have and if the stopper will fit. It's just about 17.5mm across and I haven't found dimensions for the #400 stopper.

The hobby store online (Tower Hobbies, if you know) has the Tygon tubing but 5/32 inch. That's 0.156 inch, 3.96mm and the tubing that fits well on the carburetor is 2.5mm, .098" That doesn't sound like it's going to work.

Meant to say that's a wicked fast looking boat!

 

[johwen]

With Hit and Miss engines you generally need a one way valve in the fuel line to prevent drain back of the fuel on Miss cycles particularly if the fuel tank has any depth and lower speed other wise the engine may stop. johwen

 

[CFLBob]

With Hit and Miss engines you generally need a one way valve in the fuel line to prevent drain back of the fuel on Miss cycles particularly if the fuel tank has any depth and lower speed other wise the engine may stop. johwen

This engine has nothing like that. I built my holder for the tank with the idea that mounting the tank too high was worse than too low because the fuel would run freely into it and flood the engine, so I might need to put some shims under it to ensure fuel flow.

As an update to my previous remarks, I found that Dubro says the gas stopper will fit anything from their 2 oz to their 50 oz tanks. Mine is 4. The tubing that Tower Hobbies had was 5/32 ID, but Dubro does make 3/32 ID, like that darker blue tubing in the picture (and fits the Traxxas carburetor well).

Both of those are on order but from RC hobby shops on eBay. Given the Christmas rush in shipping aren't like to be here until Christmas or later.

 

[awake]

In terms of the gas line, I used some from the auto parts store, as best I recall - I think it was made for a weed whacker.

 

[CFLBob]

My fuel stopper arrived today - the email advising it shipped said it should be here tomorrow through next Monday. My Tygon fuel line says next Tuesday through next Thursday. It wouldn't offend me by being here sooner.

What I've been up to is examining the valve assembly to see what I can do about making it work better.

I tried something I'd never thought to try before. I disassembled the valve stack and held the intake side with its valve up to my mouth and did my best to suck on the part without interfering with motion (like getting a lip in the way). The valve wouldn't open. I could open the valve with my fingertip and then the air flow was enormous, but if the valve was closed I couldn't open it. The valve slides easily by light fingertip pressure but I sure couldn't move it by suction.

When I made the parts, I dismissed something in the specs as being nice but not necessary. What I ignored was that the top of the part had a 5 degree (included angle) taper on it. I now think that was wrong to dismiss. When I looked at mine, every turn on the spring was motionless except for the one or two turns beyond the end of the valve guide. In watching other guys' videos on YouTube the spring moved more and the valve opened a lot more than I ever saw mine open.

I thought I should put that taper on the guide, and it seemed the only way to do that would be to put in the 4-jaw chuck on the Sherline lathe. That is, the only way besides pushing the guide out of the aluminum block and running the risk of ruining it. There was an immediate problem: I had bonded the carburetor adapter into this piece with LocTite 680. I tried fitting it into the 4-jaw without removing that adapter, and it could be done, but the adapter was too thin and collapsed. So I pulled the adapter out, zeroed the valve guide on the 4-jaw and put the taper on it with the Sherline compound.

The spring now looks much better on the valve guide.

Making another adapter for the Traxxas carb shouldn't take long, so I want to do everything I can do to the valve assembly to ensure that it will open. I think if the problem was that the valves weren't lapped well the problem wouldn't be that they wouldn't open, it would be that they never sealed right. They seem sealed too well.

I'd appreciate suggestions on what to look for in these simple parts. The valve guide is reamed to .094. I don't have a .001" oversized reamer, but I could drill it with a #41 bit, which is .002 oversized - at best.

 

[Brian Rupnow]

Bob---that is known as the "Blow yer guts out" test.---Brian

 

[minh-thanh]

CFLBob !
With a valve and a valve seat is airtight, the valve will open automatically when there is suction force in the cylinder (spring is suitable, of course).
my engine's valve guide and valve body were very loose but I believe the engine is still run

 

[CFLBob]

Bob---that is known as the "Blow yer guts out" test.---Brian

Brian, I assume when I suck on the assembly, the valve should open. The valve is an easy sliding fit in the valve guide, so I don't really see any sense in drilling the hole bigger. Is there a way to test this and get useful numbers?

 

[awake]

Bob, is it still not opening with the revised valve cage? It shouldn't take much "suck" to get that valve to move. If it feels like it moves easily, I wouldn't drill the guide larger; I'd think about a lighter spring. But take my thoughts with a grain of salt - I have only a smidgeon of experience, where Brian and others are the masters!

 

[Brian Rupnow]

Bob, I have used the old "blow yer guts out" method to check a lot of engine related things. Another way to check for leaking valves or rings is to sacrifice a sparkplug, knock all the ceramic out of it and solder a stub of 0.175" diameter tube to the part that sticks outside the cylinder where the porcelain used to. Screw the plug into the cylinder head and torque it down to spec. Then rotate the engine to top dead center, on the intake stroke so that in theory both valves should be completely closed. Now connect your air-line to the stub of 0.170" diameter material welded to the sparkplug and give it about 25 psi. This will give a clear indication of any leaks in the combustion chamber. Be warned though, you need to block the crankshaft so it can't rotate, because with 25 psi behind it the piston will take off like a rocket ship if it gets the least bit beyond top dead center.