Short amount of info: Brand New Thunder Tiger 91 4 stroke..Mounted on a Topflite Thunderbolt goldkit.. Head points down to 7 O'clock position..Tank is a little higher than the spray bar on the carb/intake on purpose to help with fuel draw..Propeller is a MAS "K" series 13X8 with a Flat alum Thin nut against the prop backed up by a Hub Nut (Scale look) Making it a double nut set up...PROBLEM::: hand starting or starter spun, the motor likes to kick the prop off on start up AND ... Dies when glow driver is removed...WAIT ! ! We have tried two NEW "F" type plugs and a Fox Miracle plug in the head.. Three types of fuel...( Wiches brew 4 stroke fuel, Wild Cat 4 stroke 15% and Power master 15% fuel,,, ALL three fresh and new bottles. using large silicone fuel line through and through....This motor started this problem right out of the box. I followed up by doing a break down inspection.. the cam is timed at the right position according to the manufactures info (Straight up key way and dot on cam at the top) I re-set the valve lash which was way off on the exhaust rocker, it had no lash originally...Motor has the choke flange on the intake ( It is recommended for better draw) Tank is a three line set up with muffler pressure to tank... what have you seen or what am I overlooking? Thanks for the help! Terry

Check the cam and follower closely on the ex side. Mine ate the cam up after 6-8 tanks of fuel. Had a sealed bearing in back, keeping the oil from getting to the cam. I oil the top end / cam of all my 4 strokes every time before going to the field. Popping the prop off? Check your mixture.

Once I got my engine rebuilt (warranty), it runs great.

G'day

I had the same engine mounted in a similar way. Mine used to dead stick. What it needed was quite a lot of running in and then it was fine.

Suggest you pull it out of the model, put it in a test stand and run it for at least half an hour in short runs then try again.

The prop throwing suggests a lean mixture when you are starting it.

Mike in Oz

Suggest lowering the tank, it should not need the tank set higher after running in.  I had a similar setup on the plane in my avitar and found it ran better on all synthetic oil, low nitro and a Thunderbolt four stroke plug (hotter than OS F).  It got much better as it ran.  But I only had some ground running time and about 12 flights (no deadsticks on the last 10 flights) before the full flying rudder fell off and it spun in.  It is repairable and have repairs half completed when I stopped RC due to fhe lack of funds because of college tuition.

Well i made some progress today. invested 5 hours of time though..The Cam was set as per owner's manual but I went in and retarded the cam anyway and MUCH Better.. It will idle when I take the plug driver off now and it does run up but has just a tad of lean on top end with needle out 3-4 turns. (Should be 2-2.5 out) I think at this time I am just gonna run it mid throttle and tie it up to run a few tanks full through it. Not willing to risk 5 months of building time on a questionable engine run....any input is helpful...thanks Terry b.

G'day

This probably does not help you but it might inform you. I had 5 Thunder Tiger engines. I sold all of them. I have 14 Saitos. I have only ever sold one and I was talked out of it. Does this tell you anything?

I have also had quite a few ASP/Magnum four strokes. I now have only one and I bought it to get the plane it was in. It runs OK but not nearly as well as my other four strokes. (Satio, Laser, Enya and OS). It also has a leaky exhaust valve which has resisted all attempts to get it to seal by lapping.

I have sold quite a few OS engines but usually because they were not needed at the time. They ran OK.

Mike in Oz

Try opening your low speed needle a little to gain the effectiveness of your high speed needle

AFter the cam shaft timing change the motor was ALOT better but not well enough for me to risk the new p-47 but I am going to remove the motor from the fus and bench run it for a while until it learns to behave... I do find it odd that the cam had to be retarded to run right...... Makes me wonder if the cam is marked wrong or possiably the wrong camshaft all together.. but... We will see how it goes. As far as brands go: I know Satio is a killer motor but I have nothing but good things to say about the Magnum motors.. all the ones I have had any contact with have been good reliable engines..Maybe not the most powerful engine but worth the money for sure.. I have 5+ Gallons of fuel through my 52-4 stroke over 6 years with just valve adjustments...I like mine alot!
I have the 120 in the stearman.. a good match for me...Thanks for the intrest.. I will follow up with a report later on as It goes...Have a good day flying!

Ibelieve my TT 91 FS is an early one, it required a carb change to settle down and run right, it was binding really bad and was taken care of under warranty. Ihope to mount it up and really test it some day .
My Magnum 52 RFS took about a gallon of flying to settle down and behave. However my first Mag 52 RFS had to be completely replaced under warranty.
My Saito 52 was easy peezy right from the start and got even better after the first gallon.

Do as W8ye said.  Opne the low speed needle.  Start with a 1/2 turn.