CATA

I have a JC 28 cc engine that has been running fine until recently. The engine starts and has good transition. Lately the engine will surge and sometimes tries to quit at full throttle until the engine warms up well it then runs fine on the ground. Now the surging is getting worst with the motor running poorly above 3/4 throttle. I cleaned the internal screen no improvement. Could the high end be too lean causing this problem? Ignition problem? Anyone have this problem, suggestions to fix this welcomed.

Thanks
Charles

ahicks

My Feedback: (2)

Surging is usually lean. So yes, it could be your high speed adjustment. Have you checked the rest of you fuel intake system - like the pick up tube in the tank?

skip1320

Check for air/fuel bubble,s around all gaskets,cylinder base,CC halve,s,mine was blowing bubbles at cc halve,s a dab of rtv orange did the trick,you will se it by bumping it on compression if wet,good luck!

aussiesteve

All suggestions given so far are correct
If they find nothing, get yourself a carb kit (D10), a can of carb cleaner, a bottle of red blue loctite and a tube of red Silicon (I use Permatex Ultracopper). Take the carb off, Take the carb covers, needles and diaphragms off. Spray the carb very clean with the spray cleaner (Including therough the orifices) and reassemble it with the blue (or Tan) pump diaphragm. Check the reeds haven't cracked. Reassemble the reeds back on, smear a little of the selaer ont he carb mounting gasket and apply a drop of the loctite to each bolt. Tighten it all back up but do not overtighten it - if you see the "rubber" gasket / holder for the reeds squeezing out of the joint, you are too tight and wil be creating an air leak.

The carb cleaner is a very handy thing to have around - you can use it to find air leaks by spraying it (using the tube supplied with the can) on the joints while the engine is running - the note will change if you spray it at an air leak. WD 40 / CRC 5-56 also is useful for this application.

skip1320

http://www.youtube.com/watch?v=nqSGRnFdtq4 ,clean area before using rtv,this video was supposed to go to Henry,forget if i ever sent it,ran good after ,think i found it by eye,not running condition,good luck!

aussiesteve

Hey Skip - Yep - that sure is a leak and a half. Was it from new or close to new or did it develop it after a while? Reason I ask is I have had a couple of people contact me from various points of the globe recently with running issues on these and their issues have developed after a while - It could be another specific area for me to point them to look at.
Gotta admit, I love the European made 28cc engines that I fly now - never had any such issues with those. But that is off track for this thread.

The cleaning of the area before using the RTV that you mention - another good use for the Carb Cleaner and a scouring pad.

Mr67Stang

Just watched your video. Counter on you tube said I was the first Anyway, I assume that was fuel/oil mix in the crank case pumping out at the gasket seal of the case halves as you turned the crank by hand? Was engine surging the sympton of this leak?

skip1320

It was under half a gallon,I dont think it was runnig bad,honestly can,t remember,like I said,cleaned w/alchol and smutzed on some rtv orange,the last two owners never had a problem,ran strong,would buy a dl 30 instead now though. http://www.youtube.com/watch?v=p4xHw0E-CTw

CATA

Thanks for all the good advice. I checked over all the fuel system for leakes and the motor gaskets. i changed the plug and richen the high end just a little. This seemed to get rid of the high end surging. I will try this and fly it.

Thanks
Charles

karolh

Aussiesteve,

Please tell, which 28ccc are you referring to.

Karol

aussiesteve

Hi karolh
The European one to which I refer is a 3W - , not everybodys cup of tea in the purchase price but worth every cent of it to me.

Charles
Let us know how it went. It is possible the engne has simply "leaned a bit" due to it running in but I have often found that when an engine tune changes quickly, something else has contributed to it.

karolh

I figured as much. I'm still kicking myself as I had the opportunity of buying a 3W 24i some time ago and made it slip by.... silly me.

Karol

CATA

I had a chance to fly today. The motor started fine and ran fine with only a small amout of surging on the first start. It smoothed out after it warmed up. I may still have a minor problem once the cowl is inplace so I may ritchen it a little more with the cowl on and retry.
Charles

JVB

My Feedback: (2)

My JC 28 may have developed the same problem. I've been running it for a little over a year. Not a huge amount of run time, but it has run flawlessly until last weekend. Last weekend it died a couple of minutes into the flight. Tried it again with the same result. I thought it might be the ignition. Started it on the ground last night. At somewhere between 1/2 and 3/4 throttle, it was surging. If I went to wide open, it would die. I opened the high speed needle in quarter turn increments. The surging went away and it ran at WOT. I am now sitting at 3+ turns open and it doesn't seem to want to run rich. I don't know what suddenly changed, but I think it is most likely a carb issue.

aussiesteve

CATA
If the cowl makes a big difference to the way the engine runs, you have one of (or both) the following issues.

A - The effective Inlet area is bigger than the effective outlet area and you are building pressure in the cowl. That pressure will change depending on a few factors but especially related to airspeed. To overcome this, you may want to look at cowl entrance baffling and/or cowl exit baffles.

B - Because of pressure fluctuations in the cowl, the carb ambient pressure reference will get an incorrect reading. To correct this you may want to run a tube form the reference point (the little hole on the cover with 4 screws on it - most solder a tube in there) to a static pressure area such as the fuselage or outside the cowl via a rear facing tube.

aussiesteve

JVB
Something definitely changed on yours and it is more than likely something such as the carb or reeds reaching the preset hour limit. Sort that out (most likely with a carb kit) and don't worry too much about the engine not going rich even at 3 turns out.
The JC 28 has an oversized carb on it (WT805) that is used on some of the larger capacity engines. It allows the enigne to develop good top RPM (which is how too many engines are sold) but there is a cost to doing that. I have yet to see a JC 28 that will allow the high speed needle open far enough for the RPM to drop due to a rich condition (The only RPM drop I have seen was when the needle came right out - it dropped to zero).These carbs can not get adequate airflow through them for that carb to go rich on the high speed.

The sad part about it is the original carbs on them (the 793) were a good size match but due to a lowering of manufacturing cost, they were jsut too hard for the assemblers to get them working.

JVB

My Feedback: (2)

Thanks AussieSteve!

JVB

My Feedback: (2)

Regarding carb kit D10, is D10-WAT the correct one? That's the only one I can find. The one's I've seen don't have replacement gaskets for the carb to reed block to engine and carb to reed block. Is it ok to reuse the old ones?

Thanks.