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Old Nov 07, 2012, 09:19 AM
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Originally Posted by augustomoura View Post
The problem is that I changed this third screw. Nothing is working now, even after doing all the step by steps you indicated.

The LSN is inside the throttle arm?

Augusto.
Yes the LSN is inside the throttle arm there in the center.

I'll am not sure how sensitive the carb is to moving that third set screw. It might have changed something I don't know about. Other than what Turk1 stated it does. The setr screw does protrude a few turns out though. I'll see if I can get some close up pics of it tonight when I get home.
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Old Nov 07, 2012, 09:42 AM
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Originally Posted by turk1 View Post
The mysterious 3rd needle is to adjust spray bar length(posiiton of spraybar mouth )So no need to play unless feel unproper placing of spraybar mouth.
Now I am just wildly guessing: the airspeed in a venturi is not uniform, but higher in the middle and slower closer to the walls. Higher velocity means higher fuel draw (the fuel pump/regulator just keeps the pressure at before the needles constant, the fuel is still drawn in by pressure differences in the venturi, as in any carburettor). Maybe that principle is used to influence the linearity and transition of the carburettor a bit. If that is true, it would make sense that a centered spraybar richens midrange, and a withdrawn spraybar leans it out. I remember on some old Enya's the spraybar could also be screwed in or out (although that was never the designers intention I guess) and turning that in or out could improve transition a bit.

Just guessing....

Brgds, Bert
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Old Nov 07, 2012, 04:44 PM
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Originally Posted by earlwb View Post
Yes the LSN is inside the throttle arm there in the center.

I'll am not sure how sensitive the carb is to moving that third set screw. It might have changed something I don't know about. Other than what Turk1 stated it does. The setr screw does protrude a few turns out though. I'll see if I can get some close up pics of it tonight when I get home.
I think my carb condemned. Now I can not find the correct setting.

A photo can show the position the third screw. I think.

The engine is in a Piper J3 Cub.

Tks. Augusto.
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Old Nov 07, 2012, 04:51 PM
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The membrane carburetor was replaced too?

This membrane I did not find to buy.

Augusto.
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Old Nov 07, 2012, 04:58 PM
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Himodel.com sells the parts for the engines. They have been pretty quick on getting backorders filled too. I ordered some spare parts from them. Just in case.
If you bought from a higher tier dealer they should be able to get parts too.
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Old Nov 07, 2012, 09:39 PM
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Originally Posted by ahicks View Post

Any thrust estimates? The 12x6 MA prop at close to 10k? Is that in the range of what I might expect? Target rpm to prop for, regarding good performance vs. reliability? 20:1 oil, correct?

Thanks, -Al
The planes I am using do well with a 11x7 prop, but when I did some RPM checks with different props, propping for a 11x7, 11x7.5, 11x7.75 or a 11x8 seems to work quite well with the engine. the 12x6 might be pushing it, but if the engine is broken in good, it'll likely work OK. They had mentioned that the engine developed 0.8 HP so the power figures are about correct too.
Pretty close for honest advertising from a engine company.


A 12x6 prop at 10,000 RPMs develops about 5.5 pounds of thrust and about 56 mph speed. HP is about 0.789 HP with that prop too.

Pe Reivers on his website offers the Prop-Power Calculator as a spreadsheet you can download. MVVS-NL.com
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Old Nov 08, 2012, 12:28 AM
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Originally Posted by Brutus1967 View Post
Higher velocity means higher fuel draw (the fuel pump/regulator just keeps the pressure at before the needles constant, the fuel is still drawn in by pressure differences in the venturi, as in any carburettor). Maybe that principle is used to influence the linearity and transition of the carburettor a bit. If that is true, it would make sense that a centered spraybar richens midrange, and a withdrawn spraybar leans it out.

Just guessing....

Brgds, Bert
Hi Bert my opinion,on this engine unfortunately pump/regulator system cant supply constant pressure before carb only because carb is glow style.What does that mean?Regulator needle reacting against pressure (vacuum) differences but at carb.like you said ,not at pump. In a glow carb max vacuum occurring at idle and near position.So reg. needle opens full to drown carb.When pilot adjusting the HSN,LSN according to this situation,then same adjustment begins not able to supply at WOT only because reg. needle restricting fuel supply now,because lower vacuum than before(idle position).So user must find a way to keep fuel supply constant before carb.Then engine is a champion.with a little header tank before carb.and removing spring and reg. needle and leaving only pump maybe means another solution.
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Old Nov 08, 2012, 12:59 AM
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I don't think that is what is happening....

Don't get me wrong: I do not own one of these engines, so I am just "experimenting in the brain" here.
Fuel draw is not effected by vacuum in the carb throttle, but based on the bernouilli-effect (increase of local velocity is decrease in local pressure). This is the same effect that carries paint from an atmspheric container upwards to the nozzle of a paint gun, even if the air pressure is way over atmospheric.

The mixture strenght SHOULD be effected by the needles and the bernouilli effect, and the function of the regulator should be only to keep the pressure before the needle at a very constant level. The pump/regulator has exactly the same function as the float&bowl in a conventional carburettor: to maintain a very constant pressure regardless of fuel flow (the float does that by maintaining an exact liquid level, as liquid level=column pressure).

If that regulator cannot supply a constant pressure, than you will never get that engine to run good. it is just as simple as that. But if the pressure regulator is OK, even a glow-style carb should do the trick, maybe the needle profile needs to be adapted to the fuel (similar to for example Lötterle Carburettors having different needle shapes for every Nitro content or oil content).
For example look in this thread, where people have managed to run glow engines on gas, with just a glow carburettor: http://www.rcgroups.com/forums/showthread.php?t=1476259
So, a glow carb can work with gas, it is just way more pressure sensitive....

I really think, that adjusting the location of the spraybar will influence the whole behaviour of the carb, but I think, that with adjustment of the spraybar location, both high and low speed needles need to be readjusted due the changed fuel draw.

Brgds, Bert

Come to think of fuel pressure: with the big gassers, propwash entering the atmospheric hole of the fuel regulator has many times caused engines to run irregular. Can that be an issue with this engine with its loose fuel pressure regulator????
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Old Nov 08, 2012, 09:54 AM
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Hi Bert you miss a big factor that spray bar mouth( jet) is under the barrel.Not over the butterfly.I am repetaedly mentioning this.So fuel jet(spray bar) cant match any bernoulli law.It is directly under changing vacuum but unfortunately just reverse of Butterfly/venturi type carb.(Walbro).Make an analogy please ,how it can be if main jet was under the butterfly instead over it in a Walbro carb?Just same here because of barrel/Glow type carb.So regulator needle gets crazy to supply.
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Old Nov 09, 2012, 12:04 AM
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Hmmmm.... that is indeed a very strange and unlogic design, and it changes things a bit....
I was thrown off by the statement "glow style carb" so I assumed the spray bar was in the centre of the drum.
I would say, that the vacuum under the valve then has to be supplied to the pressure regulator, in order to keep fuel pressure equal to vacuum. Maybe it needs an equalizing chamber in the line to prevent pulsing.

For example Ducati does this on their older SuperSport models: there they fit two plastic chambers connected with hoses to the carbs, that seem not to do anything, but if you take them out, or if a hose starts leaking, carburation will be impossible to set-up.
These chambers somehow control the pressure in the float bowls and match it to the intake manifold pressure.

Once fuel pressure and intake manifold pressure are matched, bernouilli should take over once more again....

Brgds, Bert
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Old Nov 09, 2012, 04:51 AM
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Hi Bert I saw many times that on a glow type carb,glow engine , vacuum at the spray bar at idling position is so high that even LSN blocks the spray bar mouth,the o ring (sealing the spray bar stock) was leaking to feed the engine to run at idle.Same situation here is affecting adjustment nearly impossible for WOT because regulator needle and LSN.(I dont mean leaking o ring,I mean high vacuum and LSN position accordingly.)
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Old Nov 09, 2012, 06:08 AM
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Not saying it is impossible, but I have in 33 years never observed what you describe.... so I cannot say anything about that.

Brgds. Bert
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Old Nov 09, 2012, 07:35 AM
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Bert, be sure that the spray bar of the NGH9 is, in fact, centered in the barrel as we expect it to be.

Greg
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Old Nov 09, 2012, 08:04 AM
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Originally Posted by Brutus1967 View Post
Not saying it is impossible, but I have in 33 years never observed what you describe.... so I cannot say anything about that.

Brgds. Bert
Are you sure?No need to see o ring problem but, Didnt you meet any Chinese glow carb which impossible to adjust.When adjusting LSN accordingly ,impossible to keep it from stopping when about take off?I still have to handle them by changing LSN profile.Some others I know try to redrill the fuel inlet holes on spraybar stock.All because very high idle vacuum.
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Originally Posted by gkamysz View Post
Bert, be sure that the spray bar of the NGH9 is, in fact, centered in the barrel as we expect it to be.

Greg
Sure but pls. think about spray bar mouth open to cranckcase vacuum but limited atmosphere all I was meaning.
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Old Nov 09, 2012, 09:33 AM
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If the spray bar is centered in the drum, my original statement is valid....

The placement is intended to separate the spraybar from the crankcase vacuum, and subject it "more or less" ony to a changing air velocity and thus the bernouilli effect.

Then adjusting the spraybar in or out should more or less adjust the linearity of the carb. It is not a very effective adjustment, but it does influence things a bit.
Like I said, I expect adjustment inwards fattens up midrange, and adjustment out leans out midrange, but most likely, unless other forms of midrange adjustment, shifting position of the spraybar first necessitates readjustment of the main and LS needle....

Brgds, Bert
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