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Old Mar 17, 2012, 12:12 PM
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Canada, MB, Winnipeg
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Originally Posted by Boostoman View Post
gravityking, bubble are coming from the carb to the pump which is strange i have never seen that before. thus effects the fuel flow. i have reopend the fuel pump to make sure all the diaphrams are in place plus the plate screws tighten. can you guys share with me the needle starting points low and high.
The bubbles are caused by the valves in the pump, outlet valve actually. I have circled the valves in the attached photo. I know the type of material used for the valves and it's not very good, it is usually rubberized cloth. The problem with this material is that once it gets wet, it swells and must stay wet to stay flat. If it dries it will shrink around the edges and bulge in the center. Once this happens it starts to leak and when the pump sucks in it will also suck from the carb and you get bubbles. The engine if it starts will run leaner. I have tried in the past to reflatten the valves but, I had no luck and ended up replacing the valve/gasket. I know some manufacturers changed thier material to a plastized fiber type that lasted much longer. I'm not sure but, maybe you can place the valve material between some books or something to reflatten it. But the valves must be PERFECTLY FLAT to work. This is a common problem with all fuel pumps using this type of material.

As for the needle settings, you should be able to find something in this thread somewhere. Somewhere in this thread I read that the low speed needle is factory set and I would try 1.5 turns out on the high speed to start.

Ray
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Old Mar 17, 2012, 02:07 PM
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Oman, Masqat
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ray,thanks for all the info. i opened up the pump and redid the rubber gasket. when i blew into the outlet of the pump the air didnt go through so i think i managed to get it sealed. i hope my issue has been resolved.

regarding the needles the problem i played with the LS needle so i now need to find the factory settings. the manual mentions 3.5-4 turns but im not sure if thats correct
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Old Mar 17, 2012, 02:51 PM
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Originally Posted by Boostoman View Post
ray,thanks for all the info. i opened up the pump and redid the rubber gasket. when i blew into the outlet of the pump the air didnt go through so i think i managed to get it sealed. i hope my issue has been resolved.

regarding the needles the problem i played with the LS needle so i now need to find the factory settings. the manual mentions 3.5-4 turns but im not sure if thats correct
Well then I would adjust the carb in this order:
1. Idle speed around 2000 - 2500 rpm.
2. LS for highest rpm , readjust idle screw to keep it around 2000 - 2500 rpm.
3. HS max rpm and a little rich.
4. Reset the LS for the best transition from idle to high rpm. I do this by constantly going from idle to full throttle, adjust LS, and do idle to full again, keep doing this until you get the best transition.
5. Readjust HS for highest RPM and then make it a little rich. A 500 - 1000 RPM drop (rich) should be fine. If you really want to get exact, check the spark plug colour by running at full throttle for 30 sec. to 1 minute, then shut the throttle and ignition off, do not let it idle. Remove the spark plug, plug center electrode (white porcelen should be just starting to turn brown to dark brown. This is best done with a used plug to gain experience.
6. Adjust idle RPM for a smooth/steady idle, do NOT Readjust the LS needle.
7. Get a pen/pencil and paper, scew in the HS, LS, and idle screws and count how many turns in each screw took. Write these numbers down and save the paper somewhere safe. Turn the screws back out the number of turns you recorded and make sure the motor still runs the way you had it set.

Ray
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Old Mar 17, 2012, 03:00 PM
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thanks for the info again ray. I will try to start up the engine tomorrow and see how it goes. figures crossed my pump is sorted
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Old Mar 17, 2012, 05:36 PM
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Pleasant Valley Modelport
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Walbro makes that plasti-fiber gasket for their carbs now. Maybe they will sell blank material. If it's that important. I have seen the bubble problem on several weed eaters.
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Old Mar 17, 2012, 09:25 PM
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Don't know if you can still get them but I used to make them from the diaphrams in the Mikuni double carb fuel pumps. These were the round pumps about 2 1/2 or 3 in. dia. used to be used on snow machines when I worked on them. Same cloth/ plastic material. Seen some weedwacker oddball carbs with clear plastic for diaphrams.

Gord.
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Old Mar 18, 2012, 10:38 AM
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Quote:
Originally Posted by Boostoman View Post
gravityking, bubble are coming from the carb to the pump which is strange i have never seen that before. thus effects the fuel flow. i have reopend the fuel pump to make sure all the diaphrams are in place plus the plate screws tighten. can you guys share with me the needle starting points low and high.
I motor is thus regulated to 4 turns needle low
1 turn needle high
carburetor open until almost the middle

the only way I managed to function
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Old Mar 18, 2012, 02:13 PM
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alright guys i thought i might make a vid since it would be alot easier to explain to everyone my issues with my engine. they are three main issues im having

1) bubbles coming out of the carb when starting up which is causing issues when starting
2) engine cutting up at full throttle
3) alot of fuel residue and blue smoke coming out of the exhaust. which I think it's due to having too much fuel: oil mix (i''m using 20:1) which i will try to use my normal 32:1 fuel that I use on all other planes to see if it makes a difference.

my setup 11x7 prop. with 4.8v on the ignition


NGH 9cc engine tuning issues (1 min 50 sec)
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Old Mar 18, 2012, 02:16 PM
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Quote:
Originally Posted by flavinn View Post
I motor is thus regulated to 4 turns needle low
1 turn needle high
carburetor open until almost the middle

the only way I managed to function
'thanks for the info flav. thats the same setting i was using. plus i was surprised to see how big the carb opening was to get the engine started. it's alot smaller on nitro engines. maybe these gas engine need alot more air to ignite
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Old Mar 18, 2012, 02:31 PM
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There is no way it will ever run right till you find out where the air bubbles are actually coming from. It's very difficult without having the system in ones hot little hand. The air bubbles are really screwing up the proper mixture through the throttle range. From the looks of it, full throttle is running lean,,,, sometimes. Gets some fuel, then a snoot full of air, making it slow down, then more fuel to make it rev up. Anything less than full throttle and it runs too rich, causing the smoke and rough running. One runs into the same problem with any plane with a pinhole in the fuel line. Really messes up the mixture. Won't run right till there's solid fuel coming through the line.


Gord.
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Old Mar 18, 2012, 03:16 PM
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gird,
so should I just ask Himodel to send me a new fuel pump?
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Old Mar 18, 2012, 03:41 PM
Fly'em like you Stole'em
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Get a felt clunk in your tank .
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Old Mar 18, 2012, 03:56 PM
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Couple of things to check first to find out where the air is coming from. There should be no air coming up from the tank to the pump, just solid fuel. If there is air bubbles run a new line from the tank to the pump. If it is solid fuel to the tank, it has to be getting in from the crankcase line. Could be a hole in the diaphram or a warped case. You might put the pump in a pot of gas or kerosene. If the case were leaking, it would draw kero or gas from the pot and solid fuel would show in the line. Then you can order a pump and tell them what happened. I don't know what's on the other side of the pump without seeing it, where there is normally a metering diaphram. Need to see a breakdown of the inside of the pump.

Gord.
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Old Mar 18, 2012, 09:43 PM
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Joined Jan 2012
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Today I flew GT9 - First flight of 10 minutes and all normal - suddenly shut down with less than 3 minutes

Something called me a note, and she turned a propeller loose ... had no compression - a propeller spun free - How was no spark
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Old Mar 18, 2012, 11:02 PM
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Wheres Mr Chow when you need him ? I hope hes not busy making his next line of engines . Cheers the pope
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