Another thought is to use viton tubing as there is less flex in the tube walls so pulse is not absorbed by the tubing.
Glenn

earlwb: I am trying to suggest there may be another possibility.

Originally Posted by earlwb

I am now running a 15:1 oil ratio instead of the 20:1 oil ratio they suggest.

Perhaps the increased oil mixture has improved the engines ability to draw fuel into
the engine, and / or decreased friction? This used to be a great argument for increased
oil percentages for motocross bikes.

Originally Posted by gravityking

Starts at about post 797 & on. Not better carbination but better fuel pump action feeding the carbinator!

The function of the fuel pump is only to provide fuel to the needle and seat only. Its function
is no different than gravity supplying fuel to the carb on a Harley. You never want a fuel pump
to effect the needle and seats ability to properly meter the fuel supply, and thereby effect the
carburetors performance. That is why Walbro WT carbs have a 50 psi pop-off.

Was the engine starving for fuel before? if so, did engine rpm increase after changing the nipple size?

Did engine idle rpm decrease?


Bill M.

I would, without further testing, believe my rod failure was due to fuel starvation at WOT. Of course fuel starvation equals lubrication starvation.

That may be true, but fuel starvation could have been caused by something other
than the fuel pump.



Bill M.

Originally Posted by Capt. Quirk

That may be true, but fuel starvation could have been caused by something other
than the fuel pump.



Bill M.

That is always a given .
Earl has brought his actual experimentation and findings to the table .We have reasoned as to possible causes behind the results . It appears the needle and seat are now getting an ample supply of fuel . The Walbro also seemed to have no fuel supply issues .

What else do you have ?

You still ignore that at WOT there is nearly no suction to make atmosphere pressure open the needle from seat to make pump to be able to feed carb.
At glow application, that no suction line fed by pressurized tank,not spray bar suction.So Gravity King s case was as expected.
At Walbro, there is venturi suction to make regulator needle open the fuel pump line to feed the engine at WOT.

Originally Posted by Capt. Quirk

earlwb: I am trying to suggest there may be another possibility. ...snip...

Was the engine starving for fuel before? if so, did engine rpm increase after changing the nipple size?

Did engine idle rpm decrease?

Bill M.

Well I can agree there is always something else that could affect it. Such as having the regulator cover exposed to the wind speed behind the prop. Where the atmospheric pressure could change the reference side of the regulator diaphragn. A sticky needle and seat in the regulator or diaphragm that didn't work right.

But yes I am always thinking about whether something else could be causing it too.

Yes engine power went up with the larger fittings for the pump. The engine could now pull the test stand over, before it couldn't as it had to be left running more on the rich side. Performance is better, it is more like running a K&B pumped glow engine now, where you can set the engine near peak RPMs and leave it there, no richening it up to compensate for the fuel tank emptying out. The carb is now working well with a decent mid range to it as well.

Engine idle improved too, it now idles down about 2.2k rpm and no surging either. before I couldn't get it below 2.5k but it surged about 500 rpm doing it.

The real tests happen this weekend when I go test flying it. Then I'll see if something else or different happens too.

Turk , (If your comment was directed to me ) ; I don't believe that I am "ignoring" anything . I am simply addressing the improvement that Earl has noted in fuel delivery . The NGH system seems to be functioning far better in that respect at present . If there is no fuel at the the needle/seat , all is moot . It seems that the fuel delivery is much better .

Originally Posted by Capt. Quirk

You never want a fuel pump
to effect the needle and seats ability to properly meter the fuel supply, and thereby effect the carburetors performance. That is why Walbro WT carbs have a 50 psi pop-off.

Fuel supply pressure in a Walbro will always influence the resulting mixture. Fuel pressure over the orifice area of the needle will have an impact on the required diaphragm pressure differential to lift the needle. I've observed this by varying fuel pressure with a Cline setup. The Walbro WT service manual only says pop off pressure should be greater than 10PSI, because the pump makes 5-7PSI. The narrow range for fuel pressure helps keep things in tune. If, in this case, there was a lack of fuel pressure the carb would go lean.

Greg

Originally Posted by gkamysz

Fuel supply pressure in a Walbro will always influence the resulting mixture. Fuel pressure over the orifice area of the needle will have an impact on the required diaphragm pressure differential to lift the needle. I've observed this by varying fuel pressure with a Cline setup. The Walbro WT service manual only says pop off pressure should be greater than 10PSI, because the pump makes 5-7PSI. The narrow range for fuel pressure helps keep things in tune. If, in this case, there was a lack of fuel pressure the carb would go lean.

Greg

Exactly

Originally Posted by jmaderoy

Hi everyone

I actually bought the NGH fuel delivery system to use it for a glow engine. On the first test (Saito FA 45S) the engine flooded and stopped in 15 seconds. I opened the pump and regulator, wich was full of white crud. The needle was stuck open, wich caused the engine to flood. I cleanded out the whole unit, and the second test run was more successful, the engine kept running until I shut it down. However it had a tendency to run lean at WOT.

After that I mounted it on my CG Super Chipmunk (Saito FA 80) This setup also had the tendency to run lean and erratic at WOT. I tuned the engine a little on the rich side (HSN 5 turns open, far more than with exhaust pressure). LSN did not need any adjustment, engine could idle for long without loading up.
I made two flights, both without deadstick. However I was not really happy with the WOT performance.

After reading more on Walbro carbs, especially on pop-off pressure, I tried to measure it with a bike pump, I pumped it up to 50 psi, but it did'nt pop. I understand that a high pop-off pressure is equal to a low float level, and lean mixtures.

Has anyone of you measured the pop-off pressure of your NGH-pump? And a Cline regulator (I can't test it since I don't have one). It seems to me that the problem might be in a 50 cent spring. I am not giving it up yet, I believe this can be worked out!

Best regards,

The Fuel System is manufactured by Walbro, it uses standard Walbro parts. I
tested one of my Walbro WT carbs, and the pop-off was also 50 psi.


Bill M.

Originally Posted by turk1

You still ignore that at WOT there is nearly no suction to make atmosphere pressure open the needle from seat to make pump to be able to feed carb.
At glow application, that no suction line fed by pressurized tank,not spray bar suction.So Gravity King s case was as expected.
At Walbro, there is venturi suction to make regulator needle open the fuel pump line to feed the engine at WOT.

The engine does run at WOT, so negative pressure inside the venturi does exist.

But a WT style carb has 4 ports that supply negative pressure to the float diaphragm, and
the pop - off is 50 psi. NGH carb has only one port.

The WYK series is a barrel valve carb, and has only 1 port that supplies negative pressure
to the float diaphragm, it has a really small main jet (aprox. .018" dia.) and the pop - off is 30 psi.

I have mentioned before that a balance is required between float diaphragm and the carburetor.
Changing the spring rate may assist that balance, but I don't believe it is the only thing that needs to
be changed.


Bill M.

Hi everyone,

Originally Posted by Capt. Quirk

The Fuel System is manufactured by Walbro, it uses standard Walbro parts. I
tested one of my Walbro WT carbs, and the pop-off was also 50 psi.


Bill M.

Thanks Bill.

I tried fitting a restrictor at the end of the crancase vent line to obtain a stronger pump pulse, but that didn't help much. Then I grabbed my bike pump again and connected it to the engines crankcase nipple, I pumped and watched the pressure gauge, the pressure dropped very quickly.

After the Saito 80, I also tested my other engines, the Saito 45 and one of the two 56 showed the same fast pressure drop. The second 56 held its pressure perfectly, no drop at all.
But when turning over the engine I could not feel air coming from the crankcase vent.

The first three engines had their bearings replaced a few years ago, all open rear bearings, and shielded (ZZ) front bearings.
The last one was bought used, oiled up and shelved. I opened it up and , both bearings were sealed (2RS), and the cam area was bone dry. I decided to give that engine a new set of bearings, open rear and sealed front (2RS). After assembly I could feel a healthy pulse and the engine passed the bike pump test, the pressure dropped a lot slower .

I decided to give the Saito 80 a new sealed (2RS) front bearing, I pulled the prop driver, did the bike pump test again. I could feel the air flow though the front bearing , this must be the cause of the problems!!

I already replaced the old ZZ bearing with the new 2RS, but the engine isn't reassembled yet. I also drilled the engines crankcase vent nipple from 2.0 mm to 2.4 mm to impove airflow. I also changed the NGH fuel system's original 1.3 mm nipples to dual barbed 1.5 mm nipples, that was aleady done before all the testing, the fuel lines just fell off the old nipples. I use 2.5 mm ID fuel line, also for the crankcase vent and pulse line.

This might also be important for Perry VP 30 users on fourstroke engines.

Best regards

Originally Posted by gkamysz

Fuel supply pressure in a Walbro will always influence the resulting mixture. Fuel pressure over the orifice area of the needle will have an impact on the required diaphragm pressure differential to lift the needle. I've observed this by varying fuel pressure with a Cline setup. The Walbro WT service manual only says pop off pressure should be greater than 10PSI, because the pump makes 5-7PSI. The narrow range for fuel pressure helps keep things in tune. If, in this case, there was a lack of fuel pressure the carb would go lean.

Greg

I believe Gary Cee already knows, so what the heck!

I have tested the output of the fuel pump, and it 5 to 7psi between mid-range
and WOT. The pop-off pressure is 50 psi, and the amount of vacuum it requires
to open the needle and seat is very small, about 1" of mercury. I am working on
a more definitive measurement,but I need a inline needle valve to dampen the
pressure oscillations inside the venturi.



Bill M.

Originally Posted by Capt. Quirk

I believe Gary Cee already knows, so what the heck!


Bill M.

Not certain what you mean by that or why but , yes I agree with what Greg said in response to Turk's comment .