boosted180

My Feedback: (8)

i have a saito .72 with almost a gallon of 15% powermaster fuel through it running a 13x6 apc prop. it doesnt have as much power as i'd expected or hoped for for my 6 lb. edge. it seems very "tempermental". on the "good days", it'll have fairly good vertical performance and hover at around 3/4 throttle. on the "bad days" like today, the power is way down and it wont even hover at full throttle. also, the rpms drop after i remove the glow starter. it seems to do this less after i've had a few flights for the day. i'm using the saito plug that came with the engine. it's taching at 9,900 max and i backed it out to 9,400 for flying. the last time i was out, it tached at 10,400 max.

while it's idling, the rpm also doesnt stay constant. after i rev up the engine, it'll idle differently than after it's been idling for awhile (while i taxi out to the runway) or right after starting up.

i was considering gettting the .82 but wanted to find out first if what i'm experiencing is "normal". why is my .72 so "tempermental"? any suggestions?

one more thing: i'm running some tubing (about 5 inches) from the muffler to deflect the exhaust. is this too long and maybe decreasing power? would i get more power if i removed the muffler? (i'd tap a new hole for the pressure line)

thanks,
brian

w8ye

My Feedback: (16)

The exhaust extension is not th problem

You have tank problems

Your fuel is foaming or the engine is inverted and the tank is too high

daveopam

My Feedback: (9)

It could also be sucking air around the intake tube. Check your "O" ring on the head side. Sometimes the throttle linkage will flex the carb mount enough to give you trouble. I ran a zip tie around the base of the intake tube and cylinder head on the first one I had. It gave me trouble and I had to order a new tube washer and "O" ring. The other two I have don't have a problem. Other than that. Try leaning out the low end a little at a time. I would also suggest you try a 13X4W APC.


David

Flylow

I agree with Daveopam. My 72 had a split oring where the intake tube meets the head. The symptoms were similar to yours.

w8ye

My Feedback: (16)

I forgot that I had to replace the backplate and intake O-rings on my 72 last year.

boosted180

My Feedback: (8)

thanks for all your inputs. i've noticed since running the engine for the first time that near the carb and back plate area, it gets all oily after the engine runs. i wasnt sure if there was a leak somewhere in that area or some fuel is just coming out from the carb. but i got a bit suspicious b/c the oil was black. i took the engine off the mounts and noticed that the 2 screws that were holding the carb onto the rest of the engine were not completely tight and it was leaking from there a bit. since i've tightened it up, it's stayed dry at that area but still a lot of oil near the backplate area. the engine still is not running right (although a bit better than before).

i'll pull the engine out of the plane again today and check everything over carefully to see if anything's out of the ordinary.

i just didnt really think about leaks or worn out o-rings, etc. b/c it's a brand new engine!

my tank and lines are fine.

thanks,
brian

daveopam

My Feedback: (9)

Brian if those screws were loose I'll bet the "O" ring is bad. I wouls order one from Horizon before I pulled it out of the plane. I think it also comes with the metal ring that holds the "O" ring in place. For anybody else reading this. If you need to flip your carb around. Pull those two screws and swival the carb toward the side then turn the carb. Try not to pull the intake tube out of the head to do your carb flipping. This is what caused my problems on the first one.

David

Ernie Misner

In the Saito Club thread there is a lot of info on the 72. For some reason that engine seems to be more prone to carb/intake vibrating and o-ring problems than the 82. Saito came out with a stronger backplate a couple of years ago to help solve the problem. Your engine is new though, or just now running it?

The o-ring in the head is a tougher one than the one in the carb end I believe. You can purchase them locally (might have to get a whole gasket set from Horizon....). Take your old one in, but I think it is an 8mm x 1.5mm Viton type o-ring. The "Viton" is a type that stands up better to chemicals and heat, where it is mostly needed in the head, so specify that rather than a standard o-ring.

Ernie

MJD

My Feedback: (1)

Apart from the leak problems, you mention rpms dropping when you pull glow heat, and that you have the Saito plug in the engine that came with it. Might want to swap out the plug.. If you've seen black stuff near the carb you may have pulled some fine metal particles in, and at the very least that is hard on the plug element - a sure sign of plug deterioration is rpm dropping when plug heat is pulled, assuming other factors are within reason such as the fuel and the typeopf plug you're using in the first place. I've had the happiest times on my .72 with the OS F plug.

Mine needed tappet adjustment after maybe 2 gallons of fuel, and power came up noticably and manners also improved. Check that if you do everything else and power still is down. Pretty simple job with the supplied tools, at least I thought so.

Yeah your rpm are low for that prop.

MJD

boosted180

My Feedback: (8)

thanks mjd. would you mind giving me some pointers on adjusting the tappets? the instructions are not clear at all and there's no diagrams or pictures. this is my first 4 stroke and i just wanna do it right.

i checked over all the bolts and everything's nice and tight.

the black screw (with the spring) at the carb shouldnt need any adjusting, correct?

i'll also change the glow plug to an o.s. F and see if that helps.

i have a suspicion that it's the valves or the glow plug since everything else checks out fine. i'm sure there are no leaks in my lines, there's no fuel foaming and tank positioning, etc. is good and i'm sure that my needles are not that far off.

brian

Ernie Misner

Run the piston up to TDC on the compression stroke and leave it there. Check the clearance between the rocker arm and the end of the valve stem with the supplied feeler guage. It is about .004", but the engine will be even happier at about .0015 or .002. (these engines do not loose the clearance when they get up to operating temp like automotive engines) The easiest way to do that with the supplied guage is to set them so that there is a tiny bit of drag on that guage, but the make sure there is still some clearance when it is removed.

Ernie

blw

My Feedback: (3)

I had the opposite things happen with APC 13x4w and 13x6. Mine was a dog with the 13x4w and flies well with the 13x6. I'm pretty sure that I'm under 6 lbs on the plane.

I had all of these problems and it was to the point where I was really getting tired of it. I used RTV around the o ring area a few times. The engine was still tempermental. The fix seems to be when I used epoxy in the backplate threads on the crankcase. I let it dry overnight before putting the bolts back in. Bingo! The problems are now gone and it has been flying steadily and predictably ever since. I really don't touch the hs needle valve any longer unless we go through a drastic change in temp and humidity down here. The .72 just flies well every time. I've just about forgotten all about the trials and tribulations that me and W8YE went through with this engine. I strongly suggest using a generous amount of epoxy in each hole like I did. It doesn't hurt a thing, and is heat and fuel proof. You can back the bolts out whenever you need to. It isn't permanent.

rclement

My Feedback: (1)

Thanks blw, I think I'll try that. I put the RTV around the intake months ago but haven't run it since. I don't have a plane to put the 72 into.

Ernie Misner

>>> The fix seems to be when I used epoxy in the backplate threads on the crankcase. I let it dry overnight before putting the bolts back in >>>

BLW, you've lost me. Did you put epoxy in the aluminum threads in the crankcase, or in the plastic threads in the backplate where the carb bolts on, or? Or did you mean you put high temp RTV (rather than epoxy) in the aluminum crankcase threads?

Thanks,

Ernie

snowball

I have a 72 saito with a 12x6 prop on an lt40 .I never weighed the combo but it will hover with pull out power left. I USE 30 % HELI FUEL AND AN OS TYPE Fglow plug.Keep trying to get yours set up right,its a great engine.Good luck

MJD

My Feedback: (1)

Sounds like Ernie has you covered on that question. Heck, I can't even remember what I did, it was only once, and I just followed instructions. However, I was glad I did because the engine improved very noticably, it was running a bit doggy before and picked right back up with all its power afterwards. I am somewhat guessing at the 2 gallons of fuel figure, I didn't really keep track, but I may have gone longer than I should before checking clearances. I could fill a dumptruck with my collection of 2 strokes, but the .72 was my first 4 stroke. And I had far less problems than I ever thought I would, it has run very well for me and so far everything makes sense. I notice it is sensitive to plugs - I have run OS F and Hangar 9 4 stroke plugs and it runs far better on the F - mostly I notice improvement in idle reliability and transition, top end seems the same. Typically I run 15% - 20% nitromethane.

I currently run mine in a Pizazz, and like the performance with a 13-7 APC best.

MJD

blw

My Feedback: (3)

I swabbed epoxy into the threaded holes on the crankcase itself. I let it dry overnight, so no epoxy got on the plastic backplate. The dried epoxy doesn't really dry completely hard, but it is more than enough to grip the threads and hold a bolt tight. The threads on the bolt chews it up a little to make a better grip. I experimented with it, tightening and then taking the bolts out to see what happens.

Epoxy works well on 2 stroke muffler bolts that tend to vibrate loose. It will usually fix the problem for good if you use it in the threaded holes of the muffler manifold extension.

I forgot to mention that I added 3 small washers under the bolt heads for the backplate. These aren't as small as the Saito washers and I couldn't fit on under the carb mounting bracket.

boosted180

My Feedback: (8)

i checked the valves last night and the there was just a tad bit too much clearance. i also switched to an os type f plug. i went out today to see if these changes make a difference.

but at the field today, i discovered that there was another much more obvious problem. it's leaking BIG TIME from the intake tube where it mates with the carb. i'd suspected some leaking there before but it was never enough to make it obvious. i'd just see droplets in this area after landing but today i looked carefully at the engine while throttling up and i can visibly see fuel spurting out from the intake tube/ carb interface!

this is a brand new engine! i'm getting a bit frustrated.....

i checked the o-ring in the carb and it appears ok. i called horizon and they said just to send it in. i really want to avoid down-time so i've just used some rtv silicone gasket maker to seal this area. i'm going out again tomorrow and hopefully this will take care of it. if not i guess i will have to send it in. i just have such bad luck with engines!

brian

Flylow

boosted 180-
I suspect you are seeing condensation on the tube. I have noticed this many times on my Saito engines. Condensation is normal and is caused by temp differences. Do you fly with anyone who might be able to help? For the most part, Saitos are very trouble free. Don't give up!

If you haven't already removed the line extending off your exhaust, I suggest that you do. Get it running great, then put it back on.

boosted180

My Feedback: (8)

flylow, condensation is also what i thought it was. the last few times i was out, i looked very carefully and couldnt see any leaks anywhere both while idling and throttle on. but after landing i would notice droplets on the intake tube and just dismissed it as condensation.

but this morning, it was definitely leaking fuel. during idle, i couldnt notice anything (other than the "usual" erratic idle). but when i throttle up, fuel was definitely coming out at the carb/ intake tube junction. it was very obvious.

is this just a bad design? i mean the very first time i looked at the engine and had to rotate the carb around (to get the high speed adjustment screw where i wanted it), i thought to myself, "there's nothing really holding the tube to the carb. the rubber o-ring is the only thing that's keeping these two parts together and making a seal??"

anyway, i'll let you guys know how it goes tomorrow. the tech guy at horizon hobby said that i may just have a poorly machined carb or intake tube. they'll replace/ repair for me if that was the case.

MJD

My Feedback: (1)

So.. any progress? I'm curious to see how this all pans out!

MJD

skiman762

I gallon is hardly broke in
The plug was a good idea you should always put in a new plug after break-in and the rpm drop is a sure sign it's going bad
Have you adjusted the low speed screw yet saito has them out quite a bit for break-in

blw

My Feedback: (3)

The manifold is held in place by both the backplate to the crankcase, and the carb mount which uses two screws. This forces the manifold into the cylinder, which is also helped along by that flat washer that you can see right where the manifold enters the cylinder. It is fairly secure when everything is tightened down.

Can you look at your backplate and see if it has reinforcements molded in the plastic? There have been 2 versions of backplates for the .72.

The .72 has been known to have problems with the top part of the manifold not sealing correctly. There are a couple of causes. There are some fixes listed in the Club Saito thread. I had my engine on a test stand and saw where the backplate bolts were coming loose after every run. My fix was to swab epoxy into the holes in the crankcase where the backplate bolts on. I let it dry overnight. This has fixed the problem which was bad on my engine.

Most people use RTV under that silver washer on the upper manifold to help the seal.

boosted180

My Feedback: (8)

ok, after using some rtv gasket maker to seal the carb/ intake tube interface, i test ran it for about 10 minutes on the ground and there was no leaks at all. it stayed nice and dry. there was quite a bit of condensatio on the outside of the tube (which is normal due to the cool manifold compared to the adjacent hot cylinder).

on my lunch break yesterday i flew it once and it seemed to be fine. the idle was much more consistent, although sitll high. i cannot get it to run lower than about 2800rpm at idle. power was also considerably better but still not quite as good as i'd hoped for (it would slow down quite a bit towards the end of long vertical uplines. enough to hover but barely enough to pull out with any authority.)

tomorrow will be the real test when i bring it to the field. i may play with the low end a bit to see if i can get it to idle lower but i think i'm close to as good as i'll get it. hopefully it'll be more "broken in" and perform better with about another 1/2 gallon of fuel.

by the way, should i even mess with the idle adjustment screw? (the black one near the carb with the spring)

i'll keep you guys posted......

w8ye

My Feedback: (16)

The screw with the spring around it is the idle SPEED adjustment screw. This should be backed off just enough that you can cut the engine off by closing the throttle with the radio. This screw also holds the throttle barrel in the carb body so don't back it out any more than necessary.