Need help with modifying a flathead engine

Good evening everyone,

I'm new here. First and foremost, what a great forum for engine lovers!
Anyway, I'm an engineering student in Portugal and am currently working in a project where I have to modify two flathead engines to compare the performance between stock and opposed piston engine configuration.
Due to the unique configuration and flathead engines not being readily available, I ended up buying two B&S 124T engines.
I've been preparing all the parts for modifying but I lack the experience and would deeply appreciate all your experience regarding a few issues I have.
- I wanted to use the stock carburetors (reference 799866). I disassembled the entire engine so that I will keep the stock exhaust, disable the governor and move the intake so that the carburetor will end up above the flywheel and starter, thorugh the ventilation case. The idea was to use a single throttle cable for both carbs but it's not as easy to adapt the stock carburater. I'm considering replacing the stock carb with a PZ19 or PZ20, however, these seem to be for up to 125cc engines, not 190cc such as this engine. The idea here is not to get the best performance but to compare the performance gains, therefore I do not need the best carb but it sbould be compatible with the engine and not limit its performance. I can either install a similarly sized carb or adapt the intake to a 30mm carb, but somehow, and after reading some threads, it seems that for these low power engines, the PZ19 should be enough. Could you shed some light?
- Also, I read here that some people complain about the exhaust muffler. I can delete the muffler and use a 90º bend and straight pipe. It even would be useful in the long run once a turbocharger and electronic injection system are installed. Will it reduce performance, increase or not have any significant impact?
- Any more advice, questions, suggestions?

I can share some pictures of the project as it will go along if you are interered.

Thank you all for the help,
Best regards,

Alexandre

PS: The engine models are similar to the 124T engine. The shaft output will be horizontal, the exhaust will probably be kept stock (one pointing to the bottom and the other to the top) and for the intake, I am to make an adapter to remove the 90º bend and go straight to the back.
 

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My main issue is the carburetor. The idea is to make a modification similar to this one. At the end, the carburetor will be installed. Initially, I intended to use the stock carb. However, it would be easier to purchase a carb such as a PZ19 or PZ20. That way, I could easily use a throttle cable without having the trouble of modifying the stock carb to control the throttle and the choke. However, both PZ19 and PZ20 are rated to be used in engines up to 125cc. Only PZ30 (or 30mm carbs) are rated for 200cc+ engines. Nevertheless, the stock carb is a 19mm carb, which makes me believe that the suitable carb for a 124T Briggs engine is around 20mm since it is only a 3.5-4HP engine, even though it's a 190cc.
By the way, the petrol to be used is 95 octane (it's the standard rating in my country). Also, I can always make an adapter for a larger carburator and reduce the ID to the 19-20mm at the engine intake but I feel that I won't have any gains by installing a larger carb and furthermore, I can actually reduce the throttle response reaching full RPM at reduced throttle.
 

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Hey that's pretty neat! Old design not many picked up on. Less moving parts and gobs of compression in that design but has a pipey 2stroke like power curve so a supercharger is used for low end and turbo pick the top end. Ford is playing with an opposed piston engine.
 
Hey that's pretty neat! Old design not many picked up on. Less moving parts and gobs of compression in that design but has a pipey 2stroke like power curve so a supercharger is used for low end and turbo pick the top end. Ford is playing with an opposed piston engine.
Thanks! It's actually a quite complex but interesting project. The idea is to test new configurations never tested before to understand the possible gains. It will not stop at opposed piston engine. That is just the first stage. My problem is that I lack the experience in some details. The carburetor is really giving me headaches! On one hand, I think I'd be better off keeping the stock carb. However, it would make my life easier installing a clone carb and not having ot modify anything. Furthermore, I could even improve performance a little and get better throttle response. As far as the exhaust goes, my professor says that it's better to keep the stock muffler arguing that the engine runs better with it due to back pressure. My goal is to compare the performance between several different configurations, not achieve the best performance possible. However, I don't want the engine to be limited by the carburetor, of course. But it seems that the limitation of this engine is not in its displacement but rather on the valve ports' diameter.
If you want, I can share some pictures and even videos if there are people curious about these modifications.
 
Carb size twin clones could work twin pz 19 would be easier to do twin cble operation . Port configurations are a limit .
Decreasing the combustion chaber size should be a design goal .
 

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I don't know if you found this reference.

I thought it would be here in the flathead section.

https://4cycle.com/karting/forums/building-a-flathead-jimmy-glenn.94/

Pretty good reference for stock model 13 flattys used in the 'stock' form.
Thanks a lot! Very good material for reading!

Carb size twin clones could work twin pz 19 would be easier to do twin cble operation . Port configurations are a limit .
Decreasing the combustion chaber size should be a design goal .
That's what I thought. I may end up sticking to the PZ19 or PZ20 carb.
I doubt the OEM carb is really optimized to take advantage of 20mm diameter of the intake to maximize the airflow, since the 124T engines are for low power applications and lawnmowers. Therefore, the PZ19 or PZ20 should be in the same performance range than the stock carb. However, I may take a few pictures of the engine ports and carb once I get to the University.
Also, the volume of the combustion chamber is kept the same, by considering a 6:1 compression ratio which seems to be the stock value for Briggs stock flatheads.
 
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Okay , think on this ; left over residual spent air space .
I think I get what you mean.
However, if the goal was to increase the performance to the maximum, I totally agree with increasing compression ratio (decreasing the combustion chamber volume).
But the goal of the project is to basically dyno bench the stock engine (which I need to modify since it's a vertical shaft engine) and get a baseline.
Then, I will mount to engines opposed to each other and compare the performance gains (or not. The idea is to see if the peak internal pressure increases, if the peak torque and power more than doubled or not, what is the fuel consumption, etc.)

Having said that, I need to make the least modifications possible in order to better compare the impact of the modifications which I want to evaluate.

I'm sorry if you were not taking about the increased scaveging and lower exhaust gases being trapped in the cylinder. That's what I understood.
 
@flattop1
Can you, by any chance, give me some advice regarding the carburetor? I have to purchase the carbs tomorrow, probably, and I'm still not sure which ones to buy.
 
As your doing a comparison , whichever is simpler to mount and operate .
Cost not withstanding the 19 mm should be more than adequate .
The clone carbs are .615 vs .750 of the 19 mm .
If cost is a concern the less expensive option .
 
As your doing a comparison , whichever is simpler to mount and operate .
Cost not withstanding the 19 mm should be more than adequate .
The clone carbs are .615 vs .750 of the 19 mm .
If cost is a concern the less expensive option .
Thank you very much for your advice. I didn't really understand the .615 vs .750. Do you mean the ID of the intake side?

As far as jets, I wanted to buy a set of different sized main jets, but it's not easy to find them here for the PZ carb. Ideally, those 2 stroke carbs that clamp on would be great for me to install, however since they are 2-stroke, I'm not sure they would work good here.

One more thing I noticed in the meantime - I found some users talking about the Tecumseh HS50 engine (which has similar displacement and power) and one user argued that the PZ16 is actually a very good carb for stock operation and both 19/22mm are suitable though needing some rejetting and mainly for slightly modded engines.

Have you ever heard any of this?


LINK for the tecumseh information:
http://www.pinrepair.com/minibikes/tecumsehmb.htm#carb2

CARBS (some links to carbs I'm taking into consideration):
https://www.banggood.com/19mm-Carb-...-1563414.html?cur_warehouse=UK&rmmds=category
https://www.amazon.es/-/pt/gp/product/B00T1DHZLE/ref=ox_sc_act_title_12?smid=A2JZB4OT9LNGYP&psc=1
https://www.amazon.es/-/pt/dp/B075C...1821&replacementKeywords=mm+carburador&sr=8-4

more or less along these options.
 
Nice link on the tecumseh .engine . actually have one of the red engines , though it has a diaphragm carb .

Actually like the middle one better . the first has what looks like an electric choke .
The third has an enricher circut so it would be fine as well if you want 20 mm.
 
A couple of issues I can see.

Converting to horizontal shaft will require a rethink of the oiling and crankcase vent systems.

A dipper will work on the half with the camshaft above the crank.
The other side, if paired as shown, will be more difficult, as the oil level will need to be higher.
Also, the crankcase vent is the cover over the valve springs, which will be submerged in oil. Venting elsewhere will be fine, but, the valve stem seals may be problematic.

Unless you are only using the valvetrain in upper position.

If that is the case, the porting and valve size will be limiter as you are doubling displacement.

Keeping the engine in the vertical position will eliminate the crankcase problems, as can be used as designed.
If using both valve train, no problems there either.
Is the reason for converting to horizontal simply to facilitate dynoing?

Where are you placing the spark plug?

PS I think I see now where the spark plugs will go.
 
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If can be run vertical, with both valvetrain and carbs, simply use the original carb and exhaust setup to make proof of concept a much simpler task.

A 90 degree gearbox comes to mind for dyno comparison.

Flywheels are another concern.
If these were mower engines, they were intended to have mower blades attached to add flywheel weight.
The lightweight aluminum flywheel could cause kickback, maybe causing a broken wrist. Ask me how I know.

A cast iron flywheel, at the least, from a horizontal engine may be in order.
Maybe 2?

Sounds fun and challenging.
 
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