K&B 7.5 questions

[Mike]

K&B 7.5 questions

I just recently bought my second rc tunnel rig. My first rig is a 3.5 tunnel with thunder tiger .21 ob. Motor runs great. I noticed that the fly wheel and prop both turn counter clockwise. On my 2nd rig my k&b 7,5 the prop turns counter but the fly turns clockwise. My starter turns the fly wheel in the opposite direction making the motor start in reverse thus screwing up my flex cable.(that's all I hope). This only happened once for a second before I realised something wasn't right. I reversed the pos/neg on my stater and the boat took off like the rocket that it should . (Is something not right with this picture). I ran the needle at 4 turns out on only 10% nitro to start. What is the leanest you can run this engine?. It was a little choppy and the motor was stalling at idle in the corners, is this caused from the rough conditions. Any help would be appreciated. Mike..

 

[Eric Bourlet]

Re:K&B 7.5 questions

Well Your right the Thunder Tiger starts backwards from a K&B because it uses a gear in the drive train. You say that your K&B dies in the corners. Does the motor sound clean? Or is it gurgling like it's rich. My suggestion is to richen it and see if that helps. Also make sure that after every run you take the power head off and wash the PTO and motor with a good after run oil.

 

[Jerry Dunlap]

Re:K&B 7.5 questions

On some of the K&B 7.5 OB carbs there is a disc to adjust the low speed idle. If the motor is quitting at slow speeds, you might try moving the disc to richen the mixture at low speed.

Jerry Dunlap

 

[mike]

Re:K&B 7.5 questions

Thanks for the help guys. I'll play with the low idle mixture and see if that's it.

 

[Mike]

Re:K&B 7.5 questions

We'll had my second run with the 7.5 and it was better than the first but not up to snuff yet. Boat ran well for a couple of minutes on 3 1/2 to 4 turns out on main needle. (rich) with low speed out where you can just barly see the back end of set screw . The boat suddenly just died after several runs . The leaner I went the faster It died. I dont think 3 1/2 turns to too lean.

Here is the variables I have. Only 10% nitro . mc9 plug . full tank of fuel running on straight 8 pipe out of the back of the engine. Is my plug not right for that % of nitro. Plug to hot to cold for the nitro I'm using or visa versa. Any more help vets would be appreciated. All water cooling was running good.

 

[TimD]

Re:K&B 7.5 questions

Mike,

i would say that the Mccoy no.9 is too cold for your fuel / motor combination. If your idle drops as soon as you remove the igniter then this is most likely the cause. go to a hotter plug. Also, check that the brass tubes inside your tank for fine cracks, as this can cause problems with leaning out when the fuel level changes.

Tim.