RBean

I have a G-38 I got used. It was in a crash. Crank is ok. It needed a new insulator block for the carb. Has Walbro WT 338 carb. This is the old magneto version. Starts ok (as long as you don't flood it).
Idle and midrange is ok but at full throttle it sags. Opening up high needle does nothing. Can't get it to run rich or four cycle wide open. When holding plane up it sags more and sometime quits. It is obviously starving for fuel wide open. I have taken carb apart shot carb cleaner through all the passages I can get to, especially the high speed needle and jet. Screen was clean. I replaced the pump membrane and the diafram while I had it apart. Same problem. I'm using 3/16" fuel line and a Walbro 125-527 in tank filter. Is this fuel line and filter too small for this 38cc engine? This is the largest engine I have. Same set up works ok on a DLE 30.

I went through the tank and fuel lines to make sure nothing is kinked or pinched.

Do I need to throw in the towel and order a new carb or find someone who knows what he's doing to overhaul this one? Or increase the size of the fuel line and filter? Or something else? Stumped.

MTK

The gas line size is fine; if anything, it is larger than necessary. You may have a probl;em with the carb so if you have another known good carb, use it for comparison....a carb from a DLE 30 should work. BTW, do you see any air bubbles in the gas line? That's a big no-no

Are you bench running it with engine completely open or is it in the plane all cowled in? If it's in the plane, then you may not have enough airflow over the fins and the thing is overheating. You will need to install proper ducting around the cylinder. Also, no other air entries to the cowl allowed which will tend to blind the cooling air to the cylinders. Air flow always follows the path of least resistance.

Make sure the ducting forces air through the fins and feeds the exiting holes undisturbed. One thing we have found very effective is to place a short dam in front of the exit holes, maybe 1/4" tall, so that outside air actually deflects away. This will actually create a negative pressure condition at the exit and would suck the hot air out. Some guys use louvers on the exits; some guys use hooded exits. You don't necessarily need a 1:3-4 hole size ratio, entry to exit area if you make your exiting holes more effective by using the small dam, louver or hood. Good luck

RBean

MTK, thanks for the reply. The fuel line is 3/32" not 3/16 with 1/8" brass tubing. I have been told this should be plenty. The engine is on a plane, but I have been running it on the ground with the cowl off. Has problem right away. It is inconsistent. Got one good flight out of plane and engine, then next time I started, it acted up again. I had changed nothing. Increase fuel line to 5/32" and eliminated in tank filter, still same problem. I've ordered a new carb and will install and see what happens.

w8ye

My Feedback: (16)

The old WT-6A carb has a jet in the high speed circuit that limits the maximum flow at high speed. The HS needle can farther limit this if screwed down tighter.

It probably worked fine with straight gasoline? But with the gas we have today - who knows?

Scota4570

Crud on the filter screen in the carb? Metering diaphram is stiff? I got a junker G-38 in a trade deal. After replacing the crank and ring I replaced the carb with a regular Walbro type. WT-542 if I recall right. I retained the magneto. It is in a Fokker D-7 so, I needed weight anyway. It is a sweet running engine.

13 mm carb http://www.ebay.com/itm/Walbro-WT529...item232e1a434e

13 mm carb http://www.ebay.com/itm/Walbro-WT542...item232e1a5a2e

It would be easier and probably comprable cost to replace the carb rather than trouble shoot it. That is, unles you are good at that kind of thing and like doing it.

thepamster

When you say opening up the hs needle it does nothing, did you try closing it?
I know my 20 year old G38, which runs great, the hs needle is "almost", but not quite, all the way closed.
I have heard this is normal with this engine and the old carb.
If I had to guess I would say that mine is set between 1/4 and 1/2 turn open and not the typical 1 1/2 turns or so.
After rebuilding the carb 3 years ago it works fine on ethanol gas.

RBean

UPS brought the new Walbro 338 carb. I installed it, primed the engine and it started in a few flips. Warmed up ran wide open ok. Idle good. Good response and mid range. Ran good with the airplane held up vertically and also inverted etc. Have not flown it but I think it is fixed. Obviously a carb problem. Now that I have it fixed I'll take the old carb apart all the way including the ferrel? plugs and see if I can tell what is wrong. 18-10 Xoar two blade wood prop turns about 7,250 - 7,300 rpm. I think this is in the ball park as to what I should expect. I tried an Xoar three blade 18-8. It only turned 6,800 rpm. Not sure of the power curve of the G-38. Where does it produce max power. I think unloaded there will be about 1,000 rpm increase so should be ok at least with the two blade and I'll see about the 3 Blade. The three blade looks good on the ESM Hellcat.

RBean

According to Horizon Hobby the bench mark prop is 18-10 at 7,300 rpm, so looks like engine is producing the expected power.

thepamster

Glad you gotter going. Engine problems can be fun to troubleshoot but also a pain in the rear.
Let us know what you find with the old carb.
I used to run a 18x6-10 back in he 90s and still earlier this year, the same actual prop until I broke it. Now I run an Xoar 18x8.
Never tried a 18x10.

RBean

It turns out I didn't have her fixed. I thought it was ok. Started up, good response, good idle, good top end. Held airplane vertical at full throttle. Seemed ok. The not long after take off it started surging again. I was able to land ok. The without shutting down engine held vertical at full throttle, it started surging and died. Took off cowl. Ran on bench. No bubbles in fuel line but could not richen up at full throttle. Engine is getting fuel. I think the crank case drawing air through the seals. I finally took engine off and dissembled. It seems to me the front and rear seals were not very tight. They easily side off the crank with out resistance. I have ordered new seals and bearings while I'm at it, although the old ones seem ok. More distressing, I found a crack in the fly wheel radiating out from the mounting hole. I've ordered a new flywheel. Wouldn't want that thing to come apart at 7-8,000 rpm.

RBean

I installed new seals and bearings. Engine is running normally. Had two flights today with no problems. It was leaking air through the old seals and leaning out when wide open. Now I guess I have a spare carb.

speedracerntrixie

My Feedback: (29)

Not sure if a Mag ignition would be the same but at one time the DA 150 had issues with hub cracks and this would mess up the timing enough to make the engine run like poop.