Author Topic: Needle valve option for Evo36 (Read 4069 times)

Larrys4227 · « **on:** April 22, 2009, 05:53:56 AM »

I was having inconsistent runs and surging in flite with my Evo36 and after no change with a tank swap, I decided to get rid of the remote needle valve. I drilled out the large venturi and installed the OS 20-25FP spraybar/needle. The spraybar fits snugly in the threaded half of the venturi, so no issues there. Have almost a dozen runs on it now, and it runs superb. Needle changes are not sensitive at all, and I'm getting steady runs until the last minute of flight. It seems to have plenty of power to pull my 38Special (41oz, 520sq. in.) and my flight times have increased from 4.5 minutes to over 6 minutes with the same 3.5 oz. of fuel. I'm not getting the fuel spray out of the venturi like I was with the sprinkler bar, it was all over the front of the motor and down the fuse side .... maybe I was loosing more fuel than I thought.

Its worth a try if your looking to experiment with your Evo36 .... I'm very satisfied with this change!

FlySafe! Larry (Larrys4227)

ray copeland · « **Reply #1 on:** April 22, 2009, 07:51:12 AM »

Hey Larry, thanks for the tip!! I hope to mount an evo .36 on my Twister next week and if runs are not good i will definitely try this.. Ray

john e. holliday · « **Reply #2 on:** April 22, 2009, 08:03:37 AM »

Thanks for the tip. May try that to see if it helps the starting of mine. DOC Holliday

Steve Helmick · « **Reply #3 on:** April 23, 2009, 07:02:57 PM »

Can someone please post the ID size of all three venturis for the Evo .36? We have a few in our club, and results have not (yet) been wunnerful. This info would help, I think.

FWIW, my Magnum XLS .36 has a .272" venturi with a .156" spray and a Bruline Coarse air filter, but if I need more range, then I can change to a fine filter, or if I need to burn more fuel, I can run with no filter. This ought to be close for the Evo....ballpark, anyway.

Steve

Ralph Wenzel (d) · « **Reply #4 on:** April 23, 2009, 07:11:24 PM »

If memory serves, Steve, the venturi sizes are 6mm, 5mm and 4.5mm - -

For those observing a marked difference in fuel consumption, note that the 6mm venturi is almost 50% larger than the 5mm venturi in choke area. (Actually, it's 44% larger in choke area, but counting the spray bar, it's over 50%.) That's significant!

Dan McEntee · « **Reply #5 on:** April 24, 2009, 02:23:40 AM »

I experienced similar problems with mine on my Hanger 9 PT-19. Like I couldn't get the engine to run rich enough unless it was on pressure. I drilled out the large venturi also, but for a St.51 needle valve assembly. I got more control over the needle settings also, and could run it with out muffler pressure also. I think the problem is in the needle valve and seat. The needle valve is the same as the one used of the OS LA series it looks like, and I've chucked one of those up in a lathe and worked it down to a point. Next time out, I'm going to hook the rear needle valve back up and see if this modification helps. I'm thinking it will.
The engine does seem to make lots of power. Mine might need to be broken in some more, and then I might retro fit it into another model for more testing, or just buy another one. Maybe recent production engines have had the problem resolved.
TYype at you later,
Dan McEntee

tom hampshire · « **Reply #6 on:** April 24, 2009, 04:44:13 AM »

I don't own one, but the venturi looks too short to me. Unless the flow past the NVA is up to speed, there is too little manifold vacuum to pull the mixture droplets into the case. Side mounted, the fuel could be lost outboard. Anybody who has one mounted either upright or inverted would not experience the problem. The solution is a new and longer venturi. This same thing happened to a bathtub Fox 29 in about 1957. These had a very low profile oval shaped venturi. Couldn't get it to continue to run in flight, ran fine on the ground. That was solved with a tinplate addition to the venturi to lengthen it. Tom H.

Larrys4227 · « **Reply #7 on:** April 24, 2009, 05:18:17 AM »

Quote from: Steve Helmick on April 23, 2009, 07:02:57 PM

Can someone please post the ID size of all three venturis for the Evo .36? We have a few in our club, and results have not (yet) been wunnerful. This info would help, I think.

.226
.236
.265

FlySafe! Larry (Larrys4227)

Larrys4227 · « **Reply #8 on:** April 24, 2009, 05:30:59 AM »

Quote from: tom hampshire on April 24, 2009, 04:44:13 AM

I don't own one, but the venturi looks too short to me. Unless the flow past the NVA is up to speed, there is too little manifold vacuum to pull the mixture droplets into the case. Side mounted, the fuel could be lost outboard. Anybody who has one mounted either upright or inverted would not experience the problem. The solution is a new and longer venturi. This same thing happened to a bathtub Fox 29 in about 1957. These had a very low profile oval shaped venturi. Couldn't get it to continue to run in flight, ran fine on the ground. That was solved with a tinplate addition to the venturi to lengthen it. Tom H.

Tom, The height is the shortest on the large ID venturi, and using the OS spraybar, I haven't had much fuel covering the motor. Using the stock sprinkler and the medium venturi (alittle taller), the whole front of the engine needed to be wiped down after every run. Even with the large venturi being as short as it is (with the OS spraybar) fuel waste is now at a minimum. I've picked up over a minute and half of run time, and I'm guessing this is why.

At first, I had the OS spraybar hole pointing directly at the crank and after reading that it really shouldn't be, I rotated aft about 20degrees. Didnt notice any difference, but I've left it that way.

FlySafe! Larry (Larrys4227)

Warren Leadbeatter · « **Reply #9 on:** April 24, 2009, 06:10:41 AM »

Gday all

I was having the same problems as Larry with my Evo 36 on my 38 Special. I did the same thing Larry did ie put an OS NVA in the short, large diameter venturi and now my worries are over. She flies/runs like a dream and lasts 6 mins on a 3.5oz Tank with an 11x4.5 TT prop. Definitely heaps better than what it was with the remote NVA.

Regards,

Larrys4227 · « **Reply #10 on:** April 24, 2009, 06:39:55 AM »

Warren, It was good to work with you over PM's to get these lil' issues worked out. Your a half-world away, but felt like you were next door. :-) I think its pretty cool that we have the exact plane/motor combo, same prop (which the motor really seems to like), and the same venturi mods .... and are both pleased as punch.

Did you ever go back to adding abit of oil to your fuel? I didn't .... seems to be real happy with fuel(10%/18%oil) straight from the jug.

Oh yeah, the other change that was helpful was a hotter glow plug (OS #8 for me)

FlySafe! Larry (Larrys4227)

FLOYD CARTER · « **Reply #11 on:** April 24, 2009, 09:19:44 AM »

Maybe I got a defective Evo 36, but mine runs great with the remote N.V.A. Consistent runs and good control. Only difference I note is a slight delay between a N.V. adjust and engine response. Besides, it keeps fingers away from the prop.

Floyd

Balsa Butcher · « **Reply #12 on:** April 24, 2009, 04:28:58 PM »

Mine might be defective also (runs great, smallest venturi, stock NV) but I'm wondering if the fuel splatter might be a centrifugal force thing when Evos are mounted with the cylinder pointing to the the outside of the circle, profile style. It is nice to know there is a viable alternative to the stock set-up.

Dave Adamisin · « **Reply #13 on:** April 25, 2009, 11:18:16 AM »

Quote from: Pete Cunha on April 24, 2009, 04:28:58 PM

Mine might be defective also (runs great, smallest venturi, stock NV) but I'm wondering if the fuel splatter might be a centrifugal force thing when Evos are mounted with the cylinder pointing to the the outside of the circle, profile style. It is nice to know there is a viable alternative to the stock set-up.

The fuel splatter is caused by blow back from the crankcase before the rotary valve closes. The longer vents may have a small effect but the answer is to make the vent flow better in than out. The spray bar going through the vent is a good obstacle for the fuel that's getting rejected at the end of the intake cycle. I've been meaning to make a new vent with a flat bottom (instead of the chamfered one currently) that would cause a good shearing effect to the fuel in the blow back. Tell me to do it and stop talking about it.......

Mark Scarborough · « **Reply #14 on:** April 25, 2009, 01:58:11 PM »

Dave,
quit talking about it already and do it,,

there ya been told,, if that doesnt work give me the little ladies phone number I am sure SHE could get you moving,, grin,,,

Leester · « **Reply #15 on:** April 25, 2009, 02:23:44 PM »

Mine worked great (inverted) in an ARF Nobler, only needed some fuel tube on the needle to keep it from vibrating in or out. It ran great till I planted it or lawn darted as I was told by one of my flying buddies. It only had the normal amount of fuel on the plane, but our electric flyer Crist complained about it

.

Warren Leadbeatter · « **Reply #16 on:** April 25, 2009, 07:32:11 PM »

Quote from: Larrys4227 on April 24, 2009, 06:39:55 AM

Did you ever go back to adding abit of oil to your fuel? I didn't .... seems to be real happy with fuel(10%/18%oil) straight from the jug.

Larry

I tried yesterday afternoon with 10% Nitro Buggy Fuel (10% syn/5% castor oil) and managed to squeeze just over 6 mins in a wet 2 cycle. Changing back to 22% 50/50 oil in a wet 2 could only get 5.5 mins.

The runs are very consistent though now, much better than before with the remote needle. I'm still going to keep playing around with the setup to try to get a better(longer) run.

Cheers

Dave Adamisin · « **Reply #17 on:** April 26, 2009, 10:17:55 AM »

Quote from: Mark Scarborough on April 25, 2009, 01:58:11 PM

Dave,
quit talking about it already and do it,,

there ya been told,, if that doesnt work give me the little ladies phone number I am sure SHE could get you moving,, grin,,,

Thanks Mark. Chips will fly this afternoon. Gonna make one for the 52 too...... tooo tooo?

Howard Rush · « **Reply #18 on:** April 27, 2009, 12:29:32 AM »

How much does an Evo .36 weigh?

Warren Leadbeatter · « **Reply #19 on:** April 27, 2009, 12:45:51 AM »

From the Horizon Hobby web site:

Evo 36 Specs
Type:2-stroke
Displacement:.36 cu in (5.71cc)
Bore:.81 in
Stroke:.70 in
Cylinders:Single
Engine (Only) Weight:9.30 oz
Muffler Weight:Tongue muffler 0.5 oz (14 g); cast muffler 2.118 oz
Crankshaft Threads:1/4 x 28 in
Prop Range:9x5 - 12x5
RPM Range:9,300 to 17,000
Fuel:5% - 15% Nitro
Mounting Dimensions:38mm x 15mm
Muffler Type:Tongue (machined) - Std expansion-type - cast
Cylinder Type:ABC
Carb Type:venturi sizes - .225"(5.7mm), .235"(6.0mm), .275"(7.0mm)
Experience Level:Beginner

Dennis Moritz · « **Reply #20 on:** April 27, 2009, 01:02:09 AM »

Usually in Philly, we swap out the remote needles and use through the crankcase alternatives. Hanging the needle out there on a stalk can enhance bad harmonics. On profiles vibes are frequently an issue. I've had remote needle set ups that worked, others that have worked for a while and then gone weird. I think the 90 degree bend in remote needles is a potential clog point for debris, also harder to flush. Having the pointer finger on my left hand hacked up by a prop while adjusting a needle, had me trying remote needles. But I'm back with the near the prop slice and dice mounting. Just seem to work better. Needle settings on profiles can be an art. Some of my best performing profiles sound awful on the ground, surging, uneven, one consistently good running plane (in flight), is launched in a run run runaway mode. After a quarter of a lap the bird settles into a very satisfying and usable 2x2 break. Needles have to be set for how the profile mounted engine performs in flight. Perhaps a similar anomaly is effecting your bird.

Howard Rush · « **Reply #21 on:** April 27, 2009, 01:33:16 AM »

Thanks, Warren.

Author Topic: Needle valve option for Evo36 (Read 4069 times)

Dave Adamisin

Dave Adamisin