My Zen 260 is stalling,when I let off the throttle,after running down the straight away and "lifting" to go into a corner. Infact it will die on the straight away if you lift much more than 2/3 throttle. I tried to set the LS needle richer,but the motor "loads up" at launch,or low speed. It's running great as long as you hold it WOT. It also launches well,accelerating up to top speed,but you can't back out of the throttle,once you are at top RPM ?:? Any advice will be greatly appreciated. Ron

What type of Hull ?

What type of Fuel tank system ?

What Carb you using ?

Sounds like a fuel feed problem--post info Scott asked for---

Pro Boat Miss Elam Hydro 1/8 scale. IV Bag 1000ml,Wabro 644 carb> Ron

rocket ron wrote:
I would suspect low needle leanness for starters ...

* When running richer on the low needle setting, forget the loading up at start and while milling .... DOES the starving for fuel when backing off from WOT still happen ?

Yes it does,Scott! I have the LS set at 1 1/2 turns out. If I set it at 1 3/4 out the motor really struggles to clean out,and sometimes,it won't. Also (I don't know allot about these carbs) I've been told that the LS needle set's the overall fuel mixture,and the HS needle sets the air mixture. Is this true? Thanks Ron

No ... both needles control fuel flow.

I would suspect a BAD carb, or one in need of fresh diaphragms.

having a high speed lean out when SHUTTING down the throttle is not a typical problem and actually quite rare.

Suggest trying another carb on engine and isolate the issue this way. Carbs like a 257/771/813 pumper are all better carbs than the 644 in most applications.

Thats about all we can do talking about it, you have a real odd one :dash:


rocket ron wrote:

Thanks,Scott! I'll order another one! Ron

If you want to test with another 644 I probably have some new ones here...I could send you one (free) if you don't mind waiting for it to get to you. Let me know.

The ETHANOL additive in most pump gas creates many problems in the small motor carbs , The best fuel additive I've found is Marine Stabil which is Blue colored... Without it I was repairing carbs monthly. The other approach is to use Coleman fuel or other Naptha based camp fuel..Works great in Zen engines ,DON"T USE IT IN STIHL CHAIN SAWS,EVEN A PARTIAL TANK (don't ask how I know) getting hard to find in gallon cans locally and price increases are passing inflation rates...