RCGF 30 twin won't start - RCCanada - Canada Radio Controlled Hobby Forum
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Old 07-14-2016, 08:11 AM   #1
grosbeak
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RCGF 30 twin won't start


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This is not so much a cry for help as a way of laying out my experiences so far and what I plan to do next. Of course, advice is always welcome.

I installed this engine on my AMR 26 and since it's so pretty I'm leaving it cowl-less for now.



I first set it up in the back yard and tried to start it a couple of days ago with no luck. It's sporting a prop nut since the shaft is too short for a spinner and backplate.




I flipped by hand (paint roller) with the choke on and the choke off and tried with a starter. No luck, and gas was dripping out of the carb. I checked the plugs - both clean and dry. Then I checked for spark... none that I could see outside in the daylight.

I charged the 2500 mAh A123 ignition battery - it charged for two minutes and change and 31 mAh went back in, so that wasn't the problem. I found an excellent resource for ignition troubleshooting and I followed the steps in the shop with the ignition connected directly to the battery as directed. Turns out I did have spark. I put everything back together, though I did remove the voltage regulator from the loop because it's not needed for this ignition. Another test and all was good. Only one change that I noticed... the ignition LED, which used to go dark immediately when I hit the kill switch, now takes almost a second to fade out. Curious, that.

I got the plane outside today. With the starter and the choke closed it will burp and quit (as expected) - over and over again if I want - but it will not start with the choke open. And the carb still drips a little gas when I open the choke.

I guess the next step is to check that the fuel lines aren't leaking air. If I don't find the problem there I will remove the carburetor and reed block and lap the mating surfaces.
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Old 07-14-2016, 09:11 AM   #2
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Re: RCGF 30 twin won't start

I should add that I have not checked the timing and that the needles are open 1-1/8 turns (low) and 1-1/2 turns (high).
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Old 07-14-2016, 09:35 AM   #3
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Re: RCGF 30 twin won't start

Yeah, sounds like the spark is ok. Timing is supposed to be 28 degrees before top dead center. If you had the plug out, you could just put a length of 1/4 dowel in the cylinder
and use a protractor to check. I never trusted those insulator blocks either. I assume you would lap it on a piece of glass. not sure if using a high temp sealant from Permatex is a good idea. others will have suggestions.
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Old 07-14-2016, 10:19 AM   #4
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Re: RCGF 30 twin won't start

open the low more and try it before ripping it apart. id say at least to 1 1/2 - 1 3/4
Just based on my limited experience with my gas engines i find if i am lean on the low it will pop with choke then mabye pop once without then just will not fire at all until i open the low up.
Especially with the hot weather.
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Old 07-14-2016, 10:56 AM   #5
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Re: RCGF 30 twin won't start

Quote:
Originally Posted by cassat View Post
Yeah, sounds like the spark is ok. Timing is supposed to be 28 degrees before top dead center. If you had the plug out, you could just put a length of 1/4 dowel in the cylinder
and use a protractor to check. I never trusted those insulator blocks either. I assume you would lap it on a piece of glass. not sure if using a high temp sealant from Permatex is a good idea. others will have suggestions.
Yeah... but which cylinder?

As for the lapping, 600 grit on glass... I've done it with all my other Chinese gassers so I guess I ought to do this one too in any case. My method (shown on a DLE 20): http://www.grosbeakrc.ca/engines/dle20/lapping.html

Quote:
Originally Posted by jtsmash View Post
open the low more and try it before ripping it apart. id say at least to 1 1/2 - 1 3/4
Just based on my limited experience with my gas engines i find if i am lean on the low it will pop with choke then mabye pop once without then just will not fire at all until i open the low up.
Especially with the hot weather.
Duly noted... thank you.

It's also been suggested to me that the plug wires might be connected to the wrong plugs. Although the manual makes no reference to which connection is correct, I found this illustration...



... and my setup is indeed the opposite.

My only other experience with multi-cylinder gas engines is with cars, and I know that hooking up the wire to the wrong plug in that case causes all sorts of problems. I would assume that's the same with this engine - please correct me if I'm wrong.
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Old 07-14-2016, 11:36 AM   #6
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Re: RCGF 30 twin won't start

It shouldn't matter where the plug leads go. Both cyls fire at the same time.
Try opening the low to 1-1/2 turns out.
As mentioned, make sure there are no air leaks around the carb base and reed valve block.

Also, make sure that the carb pump "flapper" valves are not stuck to the carb. If the engine has never run before or if it has sat for a long time, these little flappers can stick to the carb body. Just lift the edges a little a put a little gas on them. They are under the cover with the single central screw.
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Old 07-14-2016, 03:08 PM   #7
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Re: RCGF 30 twin won't start

Quote:
Originally Posted by mogman View Post
It shouldn't matter where the plug leads go. Both cyls fire at the same time.
Of course they do. I knew that. Didn't I?

Quote:
Try opening the low to 1-1/2 turns out.
As mentioned, make sure there are no air leaks around the carb base and reed valve block.

Also, make sure that the carb pump "flapper" valves are not stuck to the carb. If the engine has never run before or if it has sat for a long time, these little flappers can stick to the carb body. Just lift the edges a little a put a little gas on them. They are under the cover with the single central screw.
Will do on all of the above... thank you.
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Last edited by grosbeak; 07-14-2016 at 03:47 PM.
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Old 07-14-2016, 10:59 PM   #8
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Re: RCGF 30 twin won't start

This evening I took the carb off the engine for a look.

I removed the fuel pump cover to make sure the rubber plate wasn't sticking. No problems there!




I removed the needles for a look.

The low was reinstalled at 1-3/4 turns open.




The high was opened 2-1/2 turns.



Time to lap the carb and reed block mating surfaces. The carb was especially rough.

Before...



Lapping



After




One reed wasn't seating properly either.




All the mating surfaces were lapped except for the crankcase. The gasket appeared to be adhered so I left it alone.




Next - the timing. This is the position of the sensor relative to the magnet at 28 BTDC. I don't know enough about these things to tell whether the sensor is correctly positioned for 28 but it looks pretty close.




It was dark by the time I finished so no test start tonight. Tomorrow...
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Old 07-15-2016, 01:45 AM   #9
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Re: RCGF 30 twin won't start

Just looking this over here, originally you said the cylinders were dry and no go. After looking at the picture it appears that both needles look very close to the same, any chance they at the factory put the two needles in the wrong holes? It could be a new person put it together and they are backwards. I would go there myself they make an excellent engine.
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Old 07-15-2016, 11:05 AM   #10
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Re: RCGF 30 twin won't start

Quote:
Originally Posted by Jimmy P View Post
Just looking this over here, originally you said the cylinders were dry and no go. After looking at the picture it appears that both needles look very close to the same, any chance they at the factory put the two needles in the wrong holes? It could be a new person put it together and they are backwards. I would go there myself they make an excellent engine.
Having just read this I would tend to agree, though this is not a Walbro carb per se - the logo on the fuel pump cover appears to read, "HLIC" and I'm pretty sure it's model Mc16a10 (bottom left corner). Nothing further I could find on the needles though.
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