Help.......Thunder Tiger 25......Starting problems

Hello Guys,

I got a couple of Thunder Tiger 25 NIB off ebay. Both look really good. Sold one to a Friend and kept one. My Friend has his mounted on a profile. I ran mine upright on a test stand to break it in.

The Problem: Both engines seem very hard to start. My friend's mounted sideways on the profile seems to need to be really wet to get it started. I mean like fuel running out of the venturi wet. Then it still takes considerable cranking to get it to light off. He's running muffler pressure. With the pressure, he gets a wet two cycle with the stock needle valve about a turn and a half out.

Mine, uprgiht on a test stand, seems to flood extremely easiley. I mean I choke it just enough to bring the fuel up to the spray bar and that's it and it will flood and won't start until I disconnect the fuel line, crank it until it runs the fuel in the crankcase out, then I hook the fuel line back up and it will start with no choking at all. With no pressure, I have the needle set at about two and a half turns out to get a similar run in a wet two cycle.

The needle seems to be extremely sensitive on pressure. Without, it seems not so sensitive. Both engines now have about six or so runs on them. Still breaking in????

I am wondering if replacing the NVA with a ST NVA would help and which way does the hole in the spray go, if I do replace it with the ST.

Any advice, help would be appreciated. Thanks very much in advance.

Ole DOC here in KC, when you get your engines broke in they should start easier. I have had engines I never did think would start. But, eventually they got broke in and each time would start easier. If you think yours floods easy, try a Brodak 40 during breakin. Almost took my hand off a couple of times. You've seen us start Foxes in racing after they are thoroughtly broke in. Later, DOC

Hey Doc,

I think you are correct. After I posted, I put a ST NVA in it and took it back up to the circle. Got it started easier this time. With ST NVA it required about 3.5 turns out. Ran in a wet 2 cycle, pinching the fuel line every now and then to drive it into a hard 2 cycle. I am using Sig 10% nitro 50/50 oil with enough caster to make it 23% total oil. OS #8 plug. Seems to run really nice once it's going. Didn't let it cool all the way down this time and got 1-2 fiip re-starts. I really think you are right, Doc, more break in time.

Thanks for you input!!

Regards,

Hi John, I have 4 of the Thunder Tiger 25's and they are really fine motors. I bought them originally for SLC and have run them all on bladders but as of late, I am using them for sport flying. On a bladder, the stock TT nva will not stop the fuel flow when run all the way in so I replaced them with ST nva's. They provide a bit finer adjustment over the stock assembly too. No suprise there. However, for sport flying (on uniflow) the stock needle valves work just fine. Because it is a true venturi, the hole in the spray bar must be facing forward, parallel with the crank (if it is indeed stock) and not straight down, otherwise it won't run worth a flip.

The NIB one has got a good fit and is tight and new. The other is about standard and just a little worn. Treated right both will last a long time, your NIB one will be easeier to start in about 20 runs.

Thanks Jim and WR for the input.

I decided to take the stock NVA out and discovered the grove cut in the venturi. I positioned the hole in the spray bar pointing into the center of the grove. Seemed to work fine. As noted above, had a little trouble getting it to start cold with the ST NVA, but 1-2 flips starts when I just let it cool down a little and tried to restart. It's turning about 10-11,000 rpm in a soft 2 cycle with a 9 x 4.6 Zinger.

WR: Paul has the other one. I think his just needs more time on it too. Thanks and Ya'all take care.

Cheers,

I don't know about 25s, but I have a Thunder Tiger 15 that needs the needle almost entirely closed to run decently.

One thing that hasn't been mentioned, if these are stock engines, the factory venturi is too large for a good stunt run on suction. Actualy, it is too large for a run on suction period. This, like a lot of manufacturers these days, is designated as a CL venturi, not a CL Stunt venturi. If you replace the venturi with a properly sized smaller one, it will run better. It will also start better. It will also needle better.

Also, with the needle in front of the venturi, you need to face the hole in the needle towards the rear of the engine, into the venturi. The stock venturi has a ring groove all the way around it. There are then multiple holes in this groove, and it will run better if one of these is facing forward. The onces we make have a slot in them and can only fit one way.

On your test stand, where is the tank mounted. It sounds as if the tank is a bit high for the needle location and this might be contributing to your flooding problem, especially if the needle doesn't shut off all the way. But otherwise, these should be very easy engines to start as they are simply a clone of the FP with the exception of the style of venturi that they use.

Hi Leonard,

Appreciate you input. You may have a point on the tank location. The bottom of the tank is about 3/4" above the height of the NVA. Not been a problem before with other engines on the test stand, but perhaps this one is a little more sensitive to that.

I did point the hole in the spray bar into the grove cut into the venturi. Once I got it apart, that seemed like the obvious way to orient it to get fuel into the engine.

Have you got a venturu size recommendation and do you have them in stock?

Regards,

The tank height is your problem.

>Hi Leonard,
(Snip)
>Have you got a venturu size recommendation and do you have
>them in stock?
>
>Regards,

The factory venturi on these is a .173 for a .0235 choke area.
I would suggest a .125 or .129 which is about half the size. Big difference. But fuel draw will be much better and it will needle much better, not to mention run much better.

And yes, I do have these in stock.