Ryobi 31cc, Zama C1U carb (8mm), CDI ignition.

I can't seem to get it leaned out. If I turn the high end needle in (have to turn it in almost till it stops) to get it to stop 'four cycling', it starves the rest of the throttle settings and leans out and dies when returning the throttle to idle. According to the parts diagram for this and other C1U and C1Q carbs, there is a device on the side of the carb called a 'governor assembly'. Can anyone please explain how it works and why it's there? Thank,

-Tommy

I had a similar problem with a walbro carb. Turns out when I did some work on the throttle butterfly, I put it back on backwards. Had it opening the wrong way. Engine would not idle at all. When the butterfly opens the wrong way, the low speed ports are blocked off. Dont know it the same holds true on a Zama but you might want to check it. On the walbro carb there are three holes in the side. The two lower ones are for the low speed and the last one is for the high speed. The butterfly should close against the side with the holes. When closed the lower one will be below the butterfly and the other two will be above.

Just a suggestion.

Jim

Thanks Jim, I looked it over and it appears to be correct and similar to your Walbro. I didn't disassemble that part of the carb before the conversion, so it should have been okay anyway, but thanks for the suggestion, I've tried everything I can think of.

I'm taking a beating in another thread, so here are a few pics and a link to the runup video:

http://www.youtube.com/watch?v=nW3-xGS9XUc

can't see where the sensor is to the mag.........

Racin im not trying to beat you up. sorry if you feel that way and sorry if i offended somehow. Lets agree to not let this go any further. I am sure we are two intelligent highly skilled people so lets put our heads together and solve this.

Pictures are worth a thousand words

What line do you have hooked up to the port where the needle valves are? is it the fuel line from the tank or is it the primmer line?

Yeah, in the pic it's on the other side, away from the camera. It's a small 3/16 x 1/8 magnet counter-bored into the prop hub and JB Welded in place. I have it timed at 28deg BTDC. I've tried it retarded, and up to 32deg. It actually ran better when I advanced it, but the rich condition persisted. Some friends have suggested altering the float lever position, which I did earlier, that I will try again along with another cleaning of the jets to maybe free up the float needle.

The inlet with the bend in it feeds the pump side, which is the one without fuel tubing attached in the right hand pic. The line hooked up to the needle side inlet is actually a piece of fuel tubing with a fuel plug in it, originally equipped with a primer. You can actually just barely see the plug (screw) in the line in the center pic.

Ok that sounds right then on the lines. When you cleaned your carb did you use compressed air? I have before using compressed air blown the needle seat out of the housing and clean across the shop. I would not even have seen it if it hadent been for the pop when it came out and the ping it made on the shop tin lol. Anyhow cheak your needle seat real good it may be damaged and or missing from cleaning. use a piece of fuel tubing and blow in it and see if it shuts off the flow properly. other than that im up against a wall to without seeing it. I think your pump is ok as to much fuel is the problem so something has to be suppling the fuel. it definatly sounds like a meetering problem. Timming maybee I dont know. i know mine didnt run worth a darn when i interchanged the different mags with different coils as it changed timming drasticly like from 29 deg to 60 degree advanced.

Are you sure the diaphragm is very supple? This trips a lot of people up. It can't be stiff at all or it won't work right. Also, I am not real well versed in the function of the governor, but I seem to remember reading somewhere that it "governed" by messing with the mixture. (Making it rich to slow the engine down.) I would probably put a good, two needle, 11mm Walbro on it if it were me....

AV8TOR

yea im not sure about this govenor to. I noticed i have a zama carb on the engine pile i got maybee i need to pull one apart. i would like to see parts explosion of this carb to.

AV8TOR, that is exactly what I was wondering. I actually took it off the carb (the governor) and it's so small, I had to look at it under a mag. glass (getting old), but it has a tiny check ball in it along with a spring and an orifice that lines up with an orifice that meets up with what I would call the float cavity. Perhaps once a certain pressure diff. is reached, it opens the check ball and floods the cavity with fuel? The engine actually seems like it kinda spools up really well, but once it reaches a certain point, the same point every time, it just goes suddenly rich and slobbery. You can hear it (and see it in the exhaust) in the video.

The diaphragm is new, but when I had it out multiple times today, it still seemed soft and pliable.

I have a Walbro 9.5mm two needle job I'll try if I can't get this one going. I was really hoping to get a solid base with the stock carb, so I could see any appreciable gain with a bigger carb.

Combat, I have run into that problem before (blowing pieces across the shop with compressed air) so I try not to use that anymore. I also try not to use pieces of music wire or welding electrodes to clean out various orifices anymore either (my wife appreciates that). I'll double check the seat tomorrow. I don't have the necessary tools to change the seat should it be a problem, but the needle itself is new.

Great information here...

http://www.zamacarb.com/pdfs/TechGuide_2007.pdf

Excellent information for adjusting the float lever. I may have mis-adjusted mine, according to the information there.

Again i am unfamilliar with the zamas but is the needles the same size on both the low and hi? is it possible to get then in the wrong spots? just a thought

The low side needle is bit longer in reach than the high side. It even states that in the Zama information above. No information on the governor assembly, though.

Here is the parts diagram for the C1U that is on mine.

http://www.m-and-d.com/pdfs/zama/C1U_PARTS_LIST.pdf

ok my wife is peved i ran out to the shop and grabbed a zama carb. Im disassembling it on the couch right now. what is this part you guys are describing as the govenor?

It's the screw sticking out under the fuel inlet (pump side) opposite the needles in the pic on the left above.

huh neither of mine have this so i cant see how this will affect this carb circuit. darn im gona have to hunt one up

man i hate this dial up its excritiating I may have to wait to go to the library to download the diagrams.

Ok i got the diagram. what is the #35 plunger and what is its purpose? it looks like its in the passage that supplys fuel to the needle valve from the pump.

More and more i think about it its got to be the needle isnt seating properly.

Man i wish i could see it.

I dunno what #35 does, my carb doesn't have it.

So I tried the new lever position and nothing changed. I also checked the needle, the seat, and all the other orifices with a mag. glass and couldn't find anything plugged or sticky. The Walbro's going on it now, as I'm not sure where to go next.

Just in case that doesn't work.....

I was just remembering a strange problem I had with my brother's Ryobi some time ago. It had similar symptoms. It sounded exactly as if it were four stroking from a too rich mixture, and was nearly impossible to lean out. What I finally found was a bad reed valve seating area. The backplate had a crack in it, running near and through the reed valve area and the reed couldn't seat properly. I repaired this problem, and the engine ran perfectly.

AV8TOR

I'll give that area some close attention, as I now have the engine apart, again. The reed stop should be adjusted so it's about 1/8" off the backplate, right?

I put the Walbro on and things were progressing well with the tuning, then the vibrations loosened the backplate and wore clean through the backplate gasket, so testing is again on hold 'til I get a new gasket and some lockwashers.

This motor shakes a lot. Is it normal for these single cylinder gasssers to do this? It smooths out at a few rpm points, but really shakes, especially when it's 'four stroking'. I can see I'll really have to isolate the radio equipment in the plane it's going in. I balanced the prop, but I'll recheck it later.

Sounds like you've got a very unbalanced engine. It shouldn't vibrate that much. See here: http://www.rcuniverse.com/forum/m_8313441/tm.htm

AV8TOR