Author Topic: Bruce Macbeth Engine, European Version  (Read 58848 times)

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #645 on: January 21, 2022, 07:35:24 AM »
That was a very interesting little tidbit Roger - do you have any reference, or was it just told verbaly to you ?

Per

I found this by a number of routes. L C Mason refers to a carb with two butterflies, one before the jet and one after and the relationship between them. I have a couple of commercial carbs that I have modified for my engines and noted that the air intake bore was bigger that the bore in the barrel and the engine side bore. If you go to the extreme and make the inlet side bore bigger than the air intake side you will end up drawing neat fuel and no air. For a high volume production finding the optimal bore can be done by experiment. For a one off as soon as you open the air intake past the optimum you have to make a new body  ::)


Hi Roger,
a very interesting discussion.
May be also the reason, why I have  avoid it so far, to make a carb by myself.
There are so much different information available, all in relationship to very special applications.
The first idea was always to follow a recommendation and to use a carb of the shelf where somebody else has done the approval already.
Now I feel it is time to go deeper and try to understand the contex a bit better.
Good to know that there is some information in the book of L C Mason, I do have it and will try to find the part about the carbs in there.
Just seen, that Malcolm Stride also has a chapter about carbs in his book, also something to read very soon again.


In then meantime R&D was busy too yesterday.
Coolant was given into the system and surprise no leakage so far, also not later with 90░C.
And also this morning after resting a night it seems to be fine.
The main intention was get the cooling working to make a longer running stint possible.
I have started with the 3 mm carb same as has been used so far for running.
Same behavior, running with fully open throttle only no chance for and control of the revs.
By the way, next thing to do, to fix a small piece of reflector tape at one flywheel, so a measurement of the revs will be possible.
The adapter with the O.S. 2A carb was prepared some days ago has find its way to the intake manifold now.
The bore in the barrel is 4,5 mm. See pictures below.
By try and error the best coolant level has to be find, because if the engine stalled, some fluid comes back from the engine into the reservoir.
The water jacket in the heads is much higher than the coolant reservoir.
Generally it was checked if the coolant circle does work as it should be.
A lot of different effects are coming together now.
With every minute run time, the engine seems to go smoother
It is reacting to the barrel position now a bit.
Over all I could write something about 5 minutes run time into the records.
Here are nearly 50 sec of run time captured by another video with steaming coolant.
Max temperature measured was 90░ C, when the fuel cell was empty.
I took this as a sign to stop it for that day and make a plan for further experiments.
So it seems we are going into the right direction now.
The to do list shows now:
To start the engine with half open throttle and to find the right nozzle jet position for it, if possible.
To measure the revs in accordance to the throttle.
As Jeff suggested, to measure the intake and exhaust timing.
Generally to get more run time for better evaluation.
« Last Edit: January 21, 2022, 09:15:17 AM by fumopuc »
Kind Regards
Achim

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #646 on: January 22, 2022, 08:19:47 AM »
Hi everybody,
yesterday was another successful day at the R&D department.
The engine is running now with approximately half open throttle.
It is going better and better.
It is reacting to any adjustment of the needle.
I am running it much leaner now than at the very first beginning.
The revs are down to less than 1000 rev/min and adjustable.
That means a stint will be longer until the coolant will get 95░C, max temp to switch it of.
Overall all run time now is 35 minutes.
:pinkelephant:





Kind Regards
Achim

Offline RReid

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Re: Bruce Macbeth Engine, European Version
« Reply #647 on: January 22, 2022, 08:33:53 PM »
You now have that running every bit as well as it looks. Congratulations!  :ThumbsUp: :ThumbsUp: :cheers:
Regards,
Ron

Offline Johnmcc69

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Re: Bruce Macbeth Engine, European Version
« Reply #648 on: January 22, 2022, 11:43:31 PM »
 :cartwheel:
 Fantastic job Achim!
 I'm glad you got it all sorted, she's a beauty of an engine & your additional touches really show the level of skill you've reached.

 congratulations! Looking forward to whats's next!

 John

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #649 on: January 27, 2022, 07:45:30 AM »
Ron, John thanks.


Earlier at this posting I have mentioned to build a carb by myself.
This experiment has started also now.
It is the Lynx carb designed by Malcolm Stride, with a 4 mm Venturi instead of the original 7 mm Venturi.
Kind Regards
Achim

Online Roger B

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Re: Bruce Macbeth Engine, European Version
« Reply #650 on: January 27, 2022, 08:10:45 PM »
Hi Achim,

I had a look at my 'go to' carb. It works on the 3 cc single, the 12 cc twin and the 25 cc single. The barrel bore is 4.2mm, the air inlet side bore is 5.9mm and the engine side bore is 5mm. The jet protrudes about 0.5mm into the barrel and has a 0.5 mm hole and a fine tapered needle valve.

It shows a good response, although this is not what you may need with this engine  :)

Best regards

Roger

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #651 on: January 28, 2022, 07:17:37 AM »
Hi Roger,
thanks for measuring and showing the values here.
Very similar to my 4,5 mm Venturi O.S. carb and to one I am making here.
Here the progress.
Housing is nearly finished, missing the main bore.
I would like to do this in one go with the barrel.
So next we do need, the side plates and the barrel.
Kind Regards
Achim

Offline kvom

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Re: Bruce Macbeth Engine, European Version
« Reply #652 on: January 28, 2022, 12:30:41 PM »
Time for a new project.   :ThumbsUp:

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #653 on: January 29, 2022, 07:06:29 AM »
Kirk, thanks for popping in.


In the meantime the barrel is made and assembled first time.
The main port drilled at the lathe.
Kind Regards
Achim

Online Roger B

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Re: Bruce Macbeth Engine, European Version
« Reply #654 on: January 29, 2022, 07:22:19 AM »
That's a neat little boring bar in Vergaser 20  :)

You may find you will need to increase the size of the bore on the air inlet side otherwise the mixture will get too rich as you close the throttle.
Best regards

Roger

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #655 on: January 29, 2022, 07:43:52 AM »
That's a neat little boring bar in Vergaser 20  :)

You may find you will need to increase the size of the bore on the air inlet side otherwise the mixture will get too rich as you close the throttle.


Hi Roger, that is as a Horn Super Mini.
https://www.hornusa.com/horn-solutions/turning/
I have had the luck some time ago, to get a used set for very low price.


I`am curios about it, if the function of this carb is usable.


There are some other idea/wishes in my head in the meantime.
If it will really work, I could make it with a smaller body and barrel or this configuration, it will be more suitable for the BME than.
Also bolts could be changed from M 2 to M1,6 mm.
The needel vale will be the same.
This prototype may be will increased to a 5 mm main bore/venturi.
At the end I will have a collection of carbs with different bores for any kind of R&D work.
The small 3 mm Chinese RC carb, may be better sealed as proposed by Jeff.
The here mentioned 4 mm carb with the smaller housing, specially to be made for the BME.
My currently used 4,5 mm O.S. carb at the BME.
And the here in the pictures shown self made prototype, increased to a 5 mm bore.
May by a nice collection for future application work and yes, dreams of a retired person with some time to really do it. 
« Last Edit: January 29, 2022, 07:50:09 AM by fumopuc »
Kind Regards
Achim

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #656 on: January 30, 2022, 08:13:59 AM »
Going ahead with my first ever build carb.
One challenge for me, the 0,8 mm hole in the spray bar.
Normaly I do not make holes smaller than 1 mm, so no stock of drill bits.
There was a little red box under the bench, coming with my used Proxxon drill press many years ago.
Inside drill bits smaller than 1 mm and by luck there was one with 0,8 mm diameter, exactly what I was looking for here. But only one.
There have been two possibilities to chuck it. One time very long to start with and one time very short in this tiny Chinese chuck.
At the end the hole was done and the drill bit in one piece still.
The hex made at the mill in a collet block and chucked again at the lathe for machining the barrel side of the spray bar.
Next to do the  fuel needle.
To be safe with the curing process, I have left it at the table for one night untouched.
Kind Regards
Achim

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #657 on: January 31, 2022, 06:40:02 AM »
I have left the carb for curing one night untouched at the table.
Going to bed with the quiet hope, that all the epoxy glue will stay where it should be and will not flow at places where it has not to be.
The barrel will need a lever also.
And last the little fuel tube was made and soft soldered into the spray bar.
Last picture an assembly at the engine with the air filter.
Kind Regards
Achim

Offline Admiral_dk

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Re: Bruce Macbeth Engine, European Version
« Reply #658 on: January 31, 2022, 11:52:18 AM »
Fits nicely - have you tried it ?

Offline fumopuc

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Re: Bruce Macbeth Engine, European Version
« Reply #659 on: February 01, 2022, 07:01:28 AM »
Fits nicely - have you tried it ?


Hi Per, yes.
There is a positive report from the R&D department.
The test session has been started with the 4.5 mm O.S. carb first.
Firing with the first crank rotations.
So immediately I have swapped the O.S. carb against my DIY one.
And pure surprise, also her pop┤s with the very first movement of the crank.
So far it is the best configuration for this engine, there is a good reaction to the throttle and to the needle adjustment.
Full throttle means nearly 2.000 U/min, revs around 1.000 U/min and less are also possible.
All this has encourage me now to make the smaller brother of it, as mentioned earlier.
The hosing will be smaller and I will try change the thread at the needle vom M3 (standard M3x0.5) to the finer version M3x0.35.
The set of tap and die is ordered.
Hopefully this modification will increase the sensitivity of the fuel mixture again.
Kind Regards
Achim