Hi,
A club member has a thunder tigre 70 something 4 stroke that will not run at more than 1/2 throttle. It has about 24oz fuel through it, all at 1/2 or below. We have adjusted both the hsn and lsn all over the place. To get it to run at even 1/2 throttle you have to have the hsn turned out about 3-1/2 turns. I took the hsn out and flushed the carb. Adjusted the push-rods, one was about 15mm. I normally am pretty good with tuning engines but this sucker has me baffled. It is a new engine and seems the LHS doesn't seem to want to do anything about it. I think he is at the point where a hammer looks like a good fix. Any help would be appreciated.[][][]

Hi GoIrish,

I had similar problems with a four stroke once, they can really test you! I found that you REALLY need to lean out your lsn to a point where you barely think it will run, and work back to a reliable tick over. Leave your hsn wide open during tis stage.

Now move on to your hsn, starting at the factory reccomendations, or just try 3 turns out, then gradually lean until you get a good rpm.

Hope this helps, though you'e probably tried all this already!

Nixer.
Up the Déise!

The usual precedure quoted on here is to back the low speed needle out to the factory setting or if that is not know to back it out at least a whole turn

Then set the high speed needle to lean peak

Come back and adjust the low speed needle <u>in 1/8 turn at a time</u> until you get to the point that the engine wants to quit instead of accelerating

Open the low speed needle back out 1/8 turn

Reset your high speed needle two or three clicks on the rich side of peak.

I have high hopes for the Thunder Tiger line of 4 strokes after my dismal experiences with Magnums.

Isn't that strange. I have 9 magnum 4 strokes 52's,70's,91's and 180 and wouldn't trade any of them.

Yep. Also I picked up a Thunder Tiger .91 FS a few years ago cheap. It wouldn't run right. I installed the the O-ring kit for the carb and it ran super. Sold it at a nice profit.

There's something wrong with the TT .70.

CR

I have a Thunder Tiger .75 4-stroke and, for me, it has been a great engine. I did break it in on the bench. For the first couple of runs, I left the glow ignitor on since I was running righ at full throttle. I ran a half gallon through it for the bench break-in. It has since been in two planes and has never missed a beat. It idles well, turns up good and hides in a radial cowl due to its low height. I have not had any overheating problems, either.

I was turning over 10,000 rpm with a 13-6 prop, and I don't like to over speed a 4-stroke, so I went to a 13-7 for a sport plane. Now that it's on a scale plane with a radial cowl, I'm running a 14-6 Zinger wood. The engine till runs good.

It is my policy to never mess with the low end needle before I have run several tanks through the engine and have the ring seated. Messing with the low end needle, which is factory set, causes people more trouble than not.

I also have several Magnum 4-strokes: 2-.30s, 2-.52s, .70, .80, .91, 1.20. All except the 30s have been great engines. I also have several Saitos and an OS .70. If I get another .70 class engine, it'll be a second TT .75. The price is right and they run very well. They do not, however, break-in as quickly as an OS. Of course, Saitos and Magnums don't either.

Thanks Ed.

WE did mess with the lsn because it would never run more than 1/2 throttle.

Just put a gap of about 1mm between the spray bar and the low needle
High speed needle on mine needed about 4 turns when new. maybe your high speed is too closed??? I've set my low speed needle to get a good transition...when the athmospheric conditions change, if I see that the engine dies when accelerating..I just open the high speed and don't mess with the LS, it is quite easy to set the engine on the lean side because you don't hear a big difference. Anyway 24Oz seems too little time on it.

My engine also didn't like full synthetic oil, I've tryied cool power and Graupner sx-12, and results were not promising...and then I've mixed my own with 10% nitro, 3% castor 15% Molsyn 150k synthetic, and so far is the best thing to it, now that after about 10 liters of fuel seems to be fully broken in, I would like to try the same fuel but with 5% nitro ($$$$)

The engine (TT F-75s) runs great, and I love it

Irish, what happens when you go past 1/2 throttle? Does it bog down, cut out...?

Just quits- tops out at about 5100 rpm's anything above that and it quits like it is lean. Problems is, that it is slobbering rich. Really has me stumped.

May you have tank problems? pressure problems?

when you said that the pushrods were 15mm, you mean 1.5mm gap??

What prop, fuel and plug are you using?

Check the basics...

tank, tank lines (look for pinholes), tank isolation with foam...

Tell us more about the setup

Put a new tank and lines on. 12/8 prop. Cool power 15%. OS-8 Plug. the gauge for the push rodsgo and no go. I think they are .03 and .10. The no-go would slide through very easy. Adjusted to the .03 would slide in but not the no-go one. I don't have the engine here with me so I am not 100% sure what the size of the go and no go gages were. What ever was recommended for that engine. When we first started working with it, idle was the only thing it would do. I did start the hsn and lsn at 2 turns out. One post said lsn only 1 turn out. We had to turn the hsn out approx 3 turns to get it to run. Then we still had to prime it every time before we could get it to run at all.

Ok

You are running a wrong glow plug, you are not going to get good results with a that plug on a 4 stroke engine...buy a 4 stroke plug!! first change the plug, and then, try the following

As I said, I hadn't good results with coolpower, so I switched the gallon of fuel...

Another thing that you may want to check is the cam timing..

take te cam cover, there is a TDC mark on the thrust washer, the timing mark should align with the pushrods, you may have one tooth off, or two or three.

Then reset needles..1mm gap for the lsn and 3.5 turns for the hsn.

Saludos,

Jorge

Hi!
You cannot use a OS 8 plug!!!
The OS F plug is for four strokes!

I have a tt four stroke and I gave up on it. Mine has the exact same symptoms that you describe. I have changed tanks....ran it on the bench
checked valve lash...used every trick on the motor I know as far as carb adjustment and enlisted the aid of all my knowledgeable friends and
this motor will not run right. It acts like it is over heating. One thing that I will try now that someone has mentioned it is checking the cam timing.
I had this motor installed in a u-can do and because the motor is shorter than an o.s. or a magnum I had to put a half inch playwoood shim behind
the motor mount to get the prop in the right spot. These engines are just not worth the trouble because they are no cheaper than a magnum. I luv all
my magnum engines.....they are basically a set um and forget em. The only thing I have to do is check the valve lash from time to time.

Jorge,
Did you relate a dry bearing problem to us a week or so ago on this same engine? Could this be the issue here?</p>

Yes, there is an active thread about it.

But the engine runs indeed good despite this problem. After i solved the problem the engine ran better, but it was running good


To Rodestar99,
you can't blame an engine just because it doesn't work for you, mine runs very well, and it has run very well to other people. You may have gotten as well a lemon or an engine with really something bad. How much fuel does it have run, what is your setup, what fuel are you using? Check the cam timing (the dot should align with the pushrods at TDC). Is it well run in?? After about 10 litres of fuel my engine came to life.... post some pictures and what you have there, maybe we could help you.


Saludos,

Jorge

If I could just break in and ask what the low speed needle setting is for a new thunder tiger F-75S is? cant find any reference and its not stated in the manual at all. I have it at 3 turns out, is that about correct..

not to sound dumb but how do you measure 1mm out on the lsn michael

It would be okay to look closely at the screw and guess at 1mm.

If it cranks okay, then think in terms of 1/16 and 1/8 turns either way.

so you screw it in all the way and back it out 1/16 to 1/8 turn is that right michael

Mine is set about 1.5mm from the spraybar...

It won't be difficult to find the right spot.

Visual Low Speed Needle setting:
Open throttle all the way.
Look inside the venturi at the spray bar.
Turn the LSN so that the tip of it is ~1mm out of the spray bar.
(When the throttle is closed the spray bar is twisted onto the LSN effectively closing off all fuel flow. When the throttle is being opened past around half throttle the LSN no longer has much if any affect on fuel flow - it's all HSN.)

For an engine that will not run past half throttle there may be a fuel draw problem. Put a piece of fuel tubing over the needle valve where it meets/enters the carb assembly (getting it under the needle-keeper spring may be test your patience). Works wonders. I won't run an engine without it.

Definitely check the cam timing. It is a likely cause of a poorly running 4S above half throttle. My TT91 came with the cam out of place.

If your cam is set right and there is no fuel leek around the HSN, check the O-ring that fits between the carb and the intake manifold.

A fourstroke plug is mandatory.

Good luck!!