H5606

I don't have a lot of experience with four stroke engines. I have a ThunderTiger .54 mounted in a Sig Rascal .40 turning an APC 11X5. I do not have any tach numbers. I replaced the air bleed carb with the newer twin needle carb and find I'm using very little of the barrel travel to achieve "normal" operation from idle to what I think is full throttle. Full throttle "sounds" like it is producing full power... Throttle operation is not linear and uses quite a bit of expo to operate at what I consider normal for a two stroke. The airplane will loop from level flight but can't hold verticals for very long. Can anybody tell me if there is a problem based on what I'm seeing or is this considered normal performance?

Hobbsy

My Feedback: (102)

An 11x5 is not nearly enough prop, a 12x6 would be much more appropriate. Of course I'm judging by Saito .56 experience but the ,54 should be in the same power range.

Rudolph Hart

My first saito engine was a 62 and i struggled to get a reasonable tune(read bad)on a 12x6 mas

Hobbsy

My Feedback: (102)

Pete, I run of your Bolly 13.5x6's on my .62, it's just right.

mike109

G'day

My Saito 56 has run for years on a 12 x 6. I am just now putting it back in a VMAR Apache trainer and it will be getting a 12 x 6 again. Might be a RAM or an APC. If I still had any Bolly 12.5 x 6 props I would try one of them.

I have had both the Thunder Tiger 54 with the airbleed and the twin needle and I liked the airbleed better. I did find the twin needle harder to tune. The air bleed was mounted inverted in a Ryan STA and worked perfectly. I think it had a 12 x 6 too.

Mike in Oz

H5606

Thanks for the feedback.

I made the mods I have seen in these forums: i.e. opening up the air bleed port and filing a notch in the carb barrel to allow more air at idle but perhaps went too far. After extensive tinkering, I replaced the air bleed carb with the "new" twin needle carb. The engine never seemed happy with more than a Zinger or APC 11X5 although I never tried more prop with the new carburetor. Now, I can achieve a low reliable idle and transition smoothly to what seems like full power however, the carb is not fully open. If I move further towards aligning the barrel opening with the carb opening, it goes lean and quits - like it's getting too much air - is this condition normal for most four strokes?

Hobbsy

My Feedback: (102)

It could be that your idle is too good, meaning that the LS needle is too lean, this will make the HS needle ineffective; creating the exact condition you're describing. Try backing the LS needle out about one half turn then bring the HS needle to absolute peak and then set the LS again.

H5606

It makes sense as I vaguely remember encountering the interaction of both needles when I set it all up. Thanks for your advice - I'll try it - although the low, reliable idle may be hard to part with on this airplane...

So then, the carb barrel of a four stroke should be able to align perfectly with the carb opening at full power?

Hobbsy

My Feedback: (102)

Yes sir.

H5606

Okay, thanks.

blw

My Feedback: (3)

+1

jaka

Hi!
11x5 is too small prop for that engine! As has been said prevously use a 12x6 APC ,RAM or Graupner "Sonic" prop, those are the best!
Aim for around 9000-10000 rpm.

H5606

The TT operating manual suggests an 11X5 for break-in so I stuck with it but I'll try a 12X6 again. As if I'm a glutton for punishment, I may try the air-bleed carb again too. Excuse my ignorance regarding props - what is RAM and are they available in the U.S.?

AMB

THE apache is very happy with ANY engine turning 12X6 in the 9 to 10K range I have powered mine with an Irvine 40 diesel in that rev range that is an equiv. to a 52-56 4 strk glow in power martin

Hobbsy

My Feedback: (102)

http://www.modelshopleeds.co.uk/cata...105_106_51_156
Here is a place in the UK that sells the RAM props.

cordell staker

My first question would be is this a new engine? If not how was it put away (if you put it away for the winter) How are the bearings? What % on fuel? How old is the fuel? Try a 12x8 that's what I use on Saito 56. I think you are too lean. Test your tank and fuel line for an air leak.

SkyPilot101

Peak you high speed, then at idle pinch your fuel line at the carb...What happens? If it speeds up your idle is too rich, if It dies with no RPM increase its too lean. Perfect idle will gain a few RPM before it dies

jeffie8696

Iuse the Master Airscrew 11X7.5 on my 50 size four strokes with great sucess.

H5606

This comment got me thinking - something crossed my mind as I was laying in bed this morning: the engine is installed inverted in this airplane and a stringer runs right over top of what I believe is a breather port (fitting) on the "bottom" of the crankcase; perhaps this is the source of some power restrictions...?
Nice to learn something new and that there are alternatives to try out.
This is an engine I bought new ~18 years ago and have been flying over the last ~6 years or so; just run dry each session. The rear bearing race is brown but the engine turns over smoothly. I've used 10 and 15% Omega and Cool Power, 15% CP 4 Cycle w/ a smidge of Sig castor added , and 30% heli fuel at one time or another all various ages. I'm using an OS #F. It flew with plenty of power on the 30% heli but created other problems.

Just to reiterate: this engine runs and transitions well from idle to full power and back and flies the airplane adequately. So, I guess most would say: "What's the problem?" It just seems that a two stroke .40-45 would pull it further in up-lines... So I agree with what is said about turning a 12X higher pitch at 9K should be possible; however, from what I remember I don't think I saw much more than 6,7,8K rpm? with a 12X6.

BTW, comments about air leaks reminds me that I'm using the suggested Du-Bro Quick-Fill re-fueling valve on the Rascal .40 that I remember once vowing never to use again from previous unsatisfactory experiences on other airplanes. I had the tank out w/in the past year and it showed no bubbles anywhere when pinching one line shut and blowing 'till I was blue in the face while holding the tank submereged in a sink full of water...

jeffie8696

My 4 stroke 50 size engines typically run the MA11X7.5 in the 10,000 rpm static range. It is desireable to keep the rpms down to this level with prop selection to prevent overrevving and damaging the valvetrain.

wcmorrison

My Feedback: (2)

Definitely use a TACH  on the engine.  I had friend who thought his TT two stroke was right on.  It was 1500 below max after he used a TACH.  I can not hear so well as to determine max RPM on a four stroke.  So use a TACH to set up the HSN, the check out the LSN.

the Wasp

My Feedback: (1)

if this helps, if your not using an OS F4 you should, I have no faith in the Tiger 4st plug

Jim

H5606

Update 7/30/13:

I finally got out to fly this past weekend. I removed the 11X5 and installed a balanced, APC 12X6. I reset the ATV on the TX to achieve max open and absolute closed. To the best of my knowledge, I opened the LS needle 1/2~1 turn. I also opened the HS needle a bit. While setting up my glow driver, I blew the damn plug and I had all my spare OS type F's safely in a drawer at home. So, I stuck what I had on hand in and that was an old K&B long with idle bar...

To make a long story short, after baking myself in the hot sun screwing with needles and successive restarts through a tank of fuel, I just wanted to fly and am back where I was before: total throttle throw using ATV's is just 3/16" - tach read 3400 rpm at the low end and 8600 rpm at the high end. I put in one flight and called it a day. Airplane my have flown marginally better? Note: I may have been getting a lower idle in flight...

jeffie8696

Idle bar plugs are not normally used in 4 stroke engines. I would try opening up the low speed needle quite a bit and make sure you get the high speed needle right first.

1QwkSport2.5r

My Enya 60-40C came with a Fox idle bar plug in it of which ran really well. In fact, it ran better than the OS F did. I broke it in on the idle bar plug as well as ran it for some time with it until I got a handful of Enya #3's.

So I personally wouldn't be bothered using an I/B plug in a 4-stroke. Enya 3's run as well as OS F plugs do and cost half as much. Fox plugs are cheaper yet.