gr8johnson3

well i got the tach. i regapped the valves. i did not have the supplied gages for gaps. but it must have been close. i will confirm gap tomorrow when i get my feeler gages from work. i also got the manual from the great folks from Ace hobbies. i adjusted the needle valve as suggested. i cant get more than 9,200- 9,300 rpm. and the transition is not that smooth. any suggestions guys. or did i buy a lemon. i am going to take it to the club when i get a chance to see if someone can help me.

Mighty Mouse-RCU

My Feedback: (145)

Your RPMs are pretty close. What altitude you flying? What fuel? What prop size?
Your transition may be a problem with idle setting. What does it do when you transition?
Is this a new engine or has it been run a while.

Sport_Pilot

If he is running the fuel and prop I think he said in his last post then he is running almost 1000 RPM shy. I think it was a used engine, and thus no telling if it is broke in or not. Good idea to refresh our memory on the prop, fuel, and plug you are using.

DarZeelon

Tim,


How are you adjusting the valves?

To adjust each valve properly, the lifter/cam-follower must be on the base circle ot the cam.
To find the correct point of adjustment, turn the prop with the valve cover(s) removed, until the valve that you want to adjust, is at what looks like the maximum lift.

Note this point and turn the prop one complete turn exactly. This will turn the camshaft one half turn and place the lifter, diametrically opposite the cam peak, on the base circle.
Without moving the prop, the appropriate feeler gauge must fit between the valve tip and the rocker; with neither free-play, or lash. Adjust the lash if this is not so.

Repeat for the other valve with its appropriate feeler gauge.


With excessive valve lash, or open valve(s), you will not get close to maximum power.
The low end mixture adjustment (the idle needle) seems too rich also, but first get the valve lash properly adjusted.

If it is a .91, or a .54, it should get 10,000-10,500 on the recommended prop sizes.

gr8johnson3

ok sorry i didnt put in the info. yes it is used. it has a 13-8 master air screw prop. 15% Omega nitro. the transition seems slow. it hesitates before going to full power( 9,200-9,300 rpm. when i had it at full power i turned the needle out until it sounded like it was at its highest power. than i tried turning it and out to get the best power. just never got what i thought was max power. i did get my feeler gages at work. i looked at the one the manual says to use and i do have the valves gapped too much. boy that feeler is thin. i will try it again when i get home from work. that for any help gang.

pikebishop

do you have the choke installed? these need the venturi effect to aid fuel draw.

gr8johnson3

no. it did not come with the choke. the carb is open always. where do i get one? the manual did not mention a choke. it is a 91 size by the way.

Sport_Pilot

It won't run right without the venturi, though mine ran fine on the ground without one, it would lean out and die in the air. Fraid you will have to go back to the owner, or buy a new one from TT.

Frag

I have a .91 FS as well and am currently finding the correct settings. I did gap the valves first and found that they were too open from the factory. Then, at the field we set the high speed needle first to max rpm minus 500. This was about 9300 rpm. We then set the low speed needle by letting the engine idle for a few seconds then try transitioning to full rpm. If it was trying to die and put out plenty of smoke when given full throttle then we leaned in the slow speed needle. We got it to a pretty slow idle (~2400) with pretty good transition, noit too much smoke and little lag. The only thing is that the idle is still a bit unreliable. The engine is mounted at 45 degrees with the head aimed downward.
Would a hotter plug than the O.S. F plug help?

Sport_Pilot

Yes, but the only one I know of is the Thunderbolt plug. Did you break it in? That will help with an inverted engine more than anything.

Frag

Its probably had a gallon through it, so I'd say its broken in. The other thing I noticed is that after running in the air for say 6-7 minutes that the engine doesn't seem to have the same pick up or rpms that it had at the beginning of the flight. Could that be from getting too hot in my cowled Sukhoi-31? Its got a great big opening in the front and a fairly good sized outlet underneath.
I'll read up on the Thunderbolt plugs-thanks

Sport_Pilot

Yes, but it could also be that you set it up slightly too lean, then the tank empties and it get leaner.

pikebishop

although off topic I believe cowl exit size has got to be more than inlet area, otherwise an air daming effect occurs. also the increase in air pressure within the cowl can effect mixture leaning it slightly. the theory is higher air pressure impedes fuel flow at the spray bar.

Frag

I will richen the high end a bit more and see if it helps- thanks for the input

Sport_Pilot

If you don't have the venturi installed you are going to have to run that so rich it will barely get off the ground! I understand that a pump will eliminate the need for a venturi, so if you have one hanging around you could try that.

DarZeelon

Tim,

If the venturi/choke parts are missing, don't let Thunder Tiger get away with it, until your engine can be made to run properly.
And it all must be done at their expense, not at yours.

If they give you lousy service, tell us about it.

Sport_Pilot

He bought it used Dar.

DarZeelon

Sorry, Hugh.

I did not see Tim wrote that (now I do).

Well, he must contact the person from which it was purchased and obtain the missing parts.
Most chokes only facilitate starting, but in this engine it is necessary for simply running it.

This engine is a pretty good one; it would be a shame to see it wasted so.

Sport_Pilot

Dar,
Actually you may have made a correct reply! This tread was started by gr8johnson3, you were replying to Frag. I suspect that they have been running the engine slightly lean from the start. Although I could richen my TT 91 enough on the ground another poster here could not, I think he squeezed his tank and the engine spead up! It just won't run right without the choke/venturi.

DarZeelon

Hugh,

You were right. I was replying to Tim, who started the thread.
Tim wrote in post No. 5 that he bought it used.

Anyway, even if you buy something use, it must include everything, or the seller must notify you if something is missing, so you can obtain it elsewhere.

Did the Thunder Tiger .91 four-stroke always include the choke, or is the current model an improvement on an older one?

Sport_Pilot

Yes Dar the choke is included, it is longer than most and the bore is smaller than most. I failed to note that the instructions said that the choke should be installed before starting. But it didn't say it in a way that indicated it had to be installed. I think it said it should be installed prior to mounting the engine. This kinda sounds like it should be installed now rather than later, not that it had to be installed.

gr8johnson3

i spoke to the guys at Ace ( very good service) and he said i dont need the choke. now i have seen 4 strokers with a venturi and some with a choke. do i need both or just the choke? thanks.

jaka

Hi!
Of course you don't need a choke! It's good to have but it's only helping you start the engine it has nothing to do with how the engine performs...
But you need the venturi (if it has one.... which I doubt it has as the TT is an OS clone and OS has never had a separate venturi on their engines. The only one who has is SAITO.


Regards!
Jan K
Sweden

Sport_Pilot

The guys at Ace are a bunch of lazy hacks! Very bad service, the only bad thing about TT.

Jake,
Magnum is a clone TT is not, it is a differant engine altogether. It is only similar because it is designed by the same engineer who designed the first OS surpass series. It is the engine OS would have made if he has stayed with them.

It won't run right without the choke! I have had two and ran the first one without it I should know.

stegl

I disagree with any of the stements that you need the choke on the TT 91 . Ran mine for several years without the choke and started/ran just fine (perfect). One problem when using the mechanical choke is you can over choke the engine if left too long closed. I ran my engines dry after every flying session but used the soft choke method at the start of the next flying day and never had a problem with a great running engine. For those that do not know what a soft choke start is :::: cover the exhaust opening ( good for both 2 and 4 cycyle) with your finger and let muffler pressure, pressurize your fuel tank and send the fuel to the carb. Works like a hot dam and never a flodded engine. Have to use an electric starter though as hand flipping the prop not fast enough. Sounds like needle valve settings and or fuel tank level. If it is used may be dirt in carb and like with any engine doesn't take much. Don't run too lean as that seems to a problem with a lot of flyers. Try different plugs . One I used was Webra's four cycle plug if still available ; I hear enya makes a great 4 cycle plug or they did ; I belive.