another GF45i problem
 

Hi guys,

Here is my problem with my GF45i. I have had the engine for a few months now, and had it running fine, then about 2 weeks ago, I apparently set it to lean and dead stick in a very bad spot. I tore the Landing gear and the firewall of my Edge and had some building to do. Now the plane is on its feet again, and I ran the engine again this Weekend.
It started right up, Idle was fine, but as soon as I opened the throttle the engine would surge at high revs and run rich. As I close the high end this goes away, and the engine revs up very nicely. Now my low end is a bit lean, so I open the low end then the surging is back. I then close the high end again, and it seams to become a lot better, to the point where it is gone. But as soon as the plane leaves the ground its back, it surges only at full throttle. The plane has no Cowl on it, so I thought that it would be ram air. I put a velocity stack on the engine, but no change. The problem seams to be that I can not close the low end far enough to get it run lean enough in the top end, If I close the top end then there is no transition, and the engine wants to die if I open the throttle.

Here are my thoughts: If I hold my hand in front of the Carb at full throttle, preventing ram air to enter the Carb, the engine goes rich! to the point where it looses a lot of power.

Do I have to put a Cowl on to fly????
Is my prop to small? (18X10 MAS, only balanced prop I had there at the time, giving steady 8200RPM at WOT)
Is my fuel mixture wrong 32/1 Klotz 310 and 95 octane unleaded?
Do I have to run a line from the diaphragm hole to the inside of the plane? (the diaphragm is pointing backwards on this engine, so!! no ram air on it????)

What are your thoughts?

RE: another GF45i problem
 

I think you answered your own question.
The diaphragm hole is backward, and created a vacuum at high speed, that is why the engine goes rich when you hold your hand between prop blast and carb.
By all means fit a line, and connect it to an in-fuse balsa box.

RE: another GF45i problem
 

Hi Pe,

Thank you for the quick answers, I am always impressed by your, know how.
I have been to your Internet pages, and have seen that you are willing to ship worldwide, dose this include Namibia? I'm asking because the price that you have for a MVVS 116 is allot cheaper than the guys here sell for, do your prices include VAT (GST) or is that the nett export price?

I hope that I am not going against RCU's policies here by asking these questions.

Groete
Dries

RE: another GF45i problem
 

I sent you a PM

RE: another GF45i problem
 

Hi Guys,

Here we go again, after taking Pe's advise, I soldered a tube to the diaphragm cover and ran a line inside the fuse, this is about 20 inches long, and at a spot that I thought would be in still air.
The out come is that the engine behaves a before, no change??? On an 18X10 Prop it is very bad, and can hardly be set. I put a 22X8 Menz prop on and the problem goes away. This prop is however a bit large for the engine and only turns at 5900RPM WoT. Yesterday, we had a holyday and a big fly in at the field, I decided to put the Cowl on the plane and fit the Velocity stack, just because the guys said that that would help. I even cut a hole in the Cowl for the velocity stack. I was hoping that this would do it. I started the engine (it was hard to start) It ran very rich, Max RPM on a new 20X8 Menz was 4000RPM. I thought that it was the cowl that made it run rich so I took it off. It was infact the Velocity stack that made it run rich.
I set the high needle, and it pick up to 7250RPM WOT running very strong and clean, good transition and huge power good idle. So I went to fly. As soon as the plane speeded up there was the surging again, only at full throttle though, I flew a while and landed. I reset the high a bit leaner and flew, the same thing, this time the high end was to lean and it would sag at WOT. I then set it very rich almost 1000RPM below full power, and set the low a bit leaner. The transition got even better, and it now barks at you when you blip the throttle. In the air although no change, it surges at WOT. I landed and set the low as lean as it would go, this improved the transition even further (it's a bit scary now, this thing really barks at the slightest blip of the throttle) and now the high end was clean also at 7200RPM (massive power on a 12lbs plane) In the air, the same surging appears again.
I am at my whites end with this thing, I don’t know what to do.
The engine runs great on the ground, and as soon as I fly a vertical line up, I can actually open the throttle and the surging will go away. At half to 3/4 throttle it performs great in the air and like I said the transition is down right scary. What else can I do??????

Prop Is a Menz S 20X8 well balanced!
Fuel is 95 octane unleaded at 40 to 1 Klotz synth!
Altitude is 6800ft ASL
Engine starts easy, runs very well on the ground, no vibration, idle at 1800RPM and WOT 7200RPM very clean transition.

PLEASE HELP................

RE: another GF45i problem
 

I've noticed that a lot of these piston-port side-mounted carby engines have problems with surging when in the air.

There's a *lot* of turbulence going on in and around the carby once that plane is flying so getting a constant pressure on the diaphram and at the venturi opening is very hard work.

RE: another GF45i problem
 

You can make a velocity stack with an angled mouth and flange as separate pieces such that you can rotate the mouth. Drill a hole in the carb between the choke valve and the venturi, and fit (locktite) a brass tube therein. Connect that brass tube to the regulator membrane cover.
Now your reference pressure equals the pressure at the venturi entrance, and you can re-adjust the carb mouth direction for best results.

RE: another GF45i problem
 

Hi Pe,

Thanks again for the reply. I seem to be a bit daft, I sort of know what you are saying, but I can't imagine where I should drill this hole????? Could you please elaborate a bit on where precisely I must drill to set this piece of tubing. (Pictures would help).
Thank you
Regards

Dries

RE: another GF45i problem
 

look at the picture. Make sure the entry hole ends above the closed choke, or you will not be able to choke the engine.

RE: another GF45i problem
 

Thanks Pe,

I am a bit scared to try what you have suggested, so I went out on Saturday to try the GF45 as it was. The result is a smashed up Edge! The engine Surged as before, and no amount of tweaking the needle made a difference!
On of my club mates suggested I use a bigger prop, so I put on a 22X8 Menz S and retuned. The Transition was not as fast, probably due to the extra load, but it ran well. I took the Edge up and you will not believe me, the surging was gone. It flies beautifully. I was happy. Then on the next flight, dead stick, the plane was only about 15meters up, and as luck would have it, as I got the Dead stick a club mate flew past and I did not even realise it was dead. It stalled trying to turn it back to the runway.

After I got home I tried to find out what had happened, I connected the Ignition and could not hear a spark inside the cylinder, strange? I took out the sparkplug, and to my amazement the electrode gap was almost closed???? I had taken the plug out before the days flying, inspected it and replaced it, could I have been uncarefull and baged against something while replacing it?

And then I looked inside the plughole! I think I have now seen everything????? The Plug actually touched the Piston, and yes it is at such an angle that the electrode gap would be closed by the contact! It is not much, that it is touching, just barely, not enough to damage the piston, but touch it did.

Any suggestions?????

Regards
Dries

RE: another GF45i problem
 

The old G23 would do that if a BPMR spark plug was used, it took a BMR...
The 10mm CM6 spark plug has short threads, the RZ7C and CMR 7 are long...A long thread plug in a short thread cylinder will do what yours did, check to see which plug it needs...
sparkplugs.com has the specs and pictures of all the different spark plugs...

RE: another GF45i problem
 

Hi Ralph,

The question is, why did it only do it now?? The engine has about 2 Gallons through is allready?

regards
Dries

RE: another GF45i problem
 

It is important to note that if the metal earthing ring on the 45 is not fitted under the spark plug, or of that ring (or the sealing washer) is compressed even a small amount -- the piston *will* hit the spark plug. I have observed that the plug-washer *will* compact by quite a bit (and possibly cause piston/plug contact) after being removed/retightened several times.

I encountered this when evaluating these engines for potential use on our UAVs -- the first plug actually fouled the piston before the engine was even run.

It is also important that you don't use a version of the spark plug that has a tapered seat rather than a washer.

RE: another GF45i problem
 

Thanks Xjet,

The plug is the original one, but as you have noted, it had been takin out and retightend several times.

Mabey I will put a new headgasket in that is a bit thicker? What do you think.

regards
Dries

RE: another GF45i problem
 

You are right to be careful. The mod itself is simple, but you may have to play with angled pipe ends like in a spraybar until you have the carb behaving like you want. The setup in the picture produced a lean carb setting. Rotating the tube 180 degrees restored the H-needle to two turns open.
Just bringing the reference pressure out of harms way (out of the prop blast region) mostly solves the problem as well with less issues.
I hope you get the engine running once the spark is strong again ;)

RE: another GF45i problem
 

A thicker cylinder gasket will also raise the ports slightly and reduce the compression-ratio (since there's no "head" as such and the gasket is at the bottom of the cylinder instead). This could reduce power so the option is to use an extra washer on the plug -- you might find a suitable copper washer at your local auto-parts store -- perhaps one designed for a sump-plug.

RE: another GF45i problem
 

I had a problem similar to this and it was caused from running a 4.8V pack instead of a 6.0V pack. As soon as I switched packs the high end surging went away.