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fuel mixture issues. stuart 400 replica build.

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rickhann

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so, it fires and hits next compression and bounces at this point. I think maybe it's just fuel /air mixture, but I have no control over what goes in the cylinder.
the big question, is, what would you all do? should I give up on gas and fit a bubble or surface carb? or should i keep looking for better gas control and fit a carb with a needle for propane? someone here will know. unfortunately, there's not much written or published about this engine anywhere. the few pictures I've found on the net are mostly carburettor and spark, so I'm very glad I didn't make it the original hot tube ignition. would appreciate some feedback.
I would take a hard look at the timing. Seems to me that the first ignition should be enough to carry it through to the next firing cycle. How can it run if the second ignition point is not reached because of bounce back. Sounds like you have more than enough compression, maybe too much. These old engines were low compression. Just my two cents. Rick
 

Canyonman

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Jason, Do you have anymore information on the 1/2 scale Robinson X?? My name is Ken Robinson.
I have found Robinson Wrenches and would sure love to put that engine to the collection!

PS Wow I am finding alot of info and YouTube vids no plans. Found a set of castings but it was 2015, bummer.
 
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Jasonb

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My Robinson was built from a mixture of old reject castings and those that were not available were cut from solid. The rejects were ones that Alyn Foundry still had that had been sitting around since the owner stopped producing them due to a combination of loss of the Foundry that he used and ill health. I did have it down as one I was going to build from scratch but when the castings came up at a good price it was easier to work around the defects than start from nothing.

Graham at Alyn Foundry will probably still sell you a set of drawings but his stash of rejects is quite depleted and after not getting particularly good castings back from a batch he had done a couple of years ago ( from which the Allman came) he is unlikely to be casting anything for sale at the moment. Though I have recently just finished some pattern making for him for some parts of a 1/3rd scale Brayton engine. There is a thread about the reject Robinsons on this site that includes mine and also a scratch built one. Also some history of the "Chippy" engine.

 

Jasonb

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Emma, I saw on a couple of your videos you were not sure how well the rings were sealing, you could consider replacing the lower ring with a Viton one that is just lightly squashed, both the engines in the videos I posted use a single Viton ring.

Also you were talking about the strength of the inlet valve spring, these do need to be as weak as possible to get a good length of open time, this is the Robinson's valve opening as I turn it over by hand.

But doing that mixture test with the flame would still be my first suggestion.

 

Rustkolector

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A propane fuel system for a hit & miss engine is one of the simplest fuel systems in use and lots of good suggestions here. But it depends on whether you are trying to duplicate the "original" fuel system for this Stuart engine or just want to get it running for now. I cannot help you with anything close to the original 400 fuel system.

If you want to just get it running follow TonyM's advice on the demand regulator, also known as a zero governor. Jerry Howell's plans for that regulator valve are excellent. This device simplifies a propane fuel system while adding a highly recommended safety feature. Most propane fuel users I know use this design demand regulator. If using a simple 1 lb propane bottle you can get a Weber "Go Anywhere" gas grill pressure regulator which gives you an adequate 4" water column pressure. Connect the demand regulator to the fuel line coming from the pressure regulator, turn on the gas and test it according to the JH plan instructions. If it works, connect it to a simple fuel mixer on the engine with a venturi or restriction and needle valve for fuel mix adjustment. Try the fuel mixer suggestions and venturi proportions suggested by LAS. Crank the engine over with a drill motor while adjusting the fuel needle valve and you should have it running in minutes.
Jeff
 

Jasonb

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Should just point out that the 400 was not hit and miss governed, speed would have been set partly by control of the amount of fuel (gas) and also by altering the position where the burner heated the hot tube as this will retard or advance the timing. As you are now running as a sparker you will need to advance/retard the timing by however you have mounted the contacts.
 

Rustkolector

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Jasonb
I assumed the 400 was H&M due to the first plan publication of the 1915 era and the hot tube ignition. With spark ignition it just means the fuel mixer can be changed to a simple carburetor with a throttle for speed control. Preferably a self compensated RC carb that maintains a relatively constant fuel/air ratio from idle to full throttle/load. However, the self compensation feature may be of little use with a narrow speed range engine. The only other issue with a throttle is that a different type governor (if any) would be needed. Did the 800 use a throttle fuel system?
Jeff
 

miss_emma_jade

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thanks, everybody. Tecumseh parts on order, so the first thing will be to make a gas valve. the 400 was very very basic compared to the 600 and the 800, or even the 1/2hp or Sandhurst. I made a spark timer as per the instructions, but I believe the instructions for the gas hookup just weren't included. I looked at about 5 very early English model designs, some quite advanced, before I started this. WS Farrens little vertical engine, the ME gas engine from 1898, and a couple of others I had information about. this one was the only one that had even SOME information about the fuel system. obviously Stuart changed that by the time the 800 came along, because if that paragraph was in the 400 instructions, then I believe I would have had it running, Jasonb thankyou.

The Stuart 800 was a much fancier, better-designed side shaft engine with flyball governor. I believe a whole lot more of those were built.
 

Jasonb

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The 800 used a vertical flyball governor driven by bevel gears off the end of the side shaft that moved a small valve to alter gas volume, there was a separate cam operated inlet valve.
 

L98fiero

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miss_emma_jade

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ok, I'm about 90% into Jerry H's demand valve. there are some design issues that don't work. I hope I have the right needle and seat.
I machined it all and put it together, then realised the needle sits way too high, to the point that when I sit the diaphragm on, then the valve is pushed in and opens without any suction on it. I thought I got the right part number Tecumseh part, but it seems way too high. it also won't seat particularly well, so I wonder if i did get the right part. has anyone made this who could give some feedback?

EMMA
 

miss_emma_jade

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OK>.. so dumb blonde mistake there, girl. there's a lil rubber seat that's supposed to go inside the needle seat body and that fixes everything. oops.
 

LAS

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ok, I'm about 90% into Jerry H's demand valve. there are some design issues that don't work. I hope I have the right needle and seat.
I machined it all and put it together, then realised the needle sits way too high, to the point that when I sit the diaphragm on, then the valve is pushed in and opens without any suction on it. I thought I got the right part number Tecumseh part, but it seems way too high. it also won't seat particularly well, so I wonder if i did get the right part. has anyone made this who could give some feedback?

EMMA
The Tecumseh part numbers for the ones I made are;
630932A - Carb kit (needle & seat)
630978 - Diaphram

An aftermarket supplier ( Rotary) part numbers are;
22-1430 - needle valve kit
22-1427- diaphram
 

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