ORIGINAL: SJN

Hi Guys.

I can not figure out whats up with my old 91 4 sroke.
I cant get it to idle without the glow atatched.
Even if it is runniong at about 1/3 throttle, and I remove the glow, it will imidiatly drop rpm, and finaly quit.
But at half throttle and up, then it will run.


I bought this engine used recently, and had to replace both bearings, and a cracked con-rod.
The engine was pretty gummed up with old castor, but I got it all cleaned up, and looking nice again.

Removed the valves, and cleaned them up completly, and also cleaned out the intake and exhaust ports.

The cylinder lining looks great, and the piston and ring also looks good and is free, and the compression is fine.

Cam timing dot is in line with the pushrods, and the valve overlap on both rockers are exactly equaly depressed on TDC.

I have tried to set the valve clearance tight and loose, and does not make a difference.

Tried 2 new F glow plugs.

No leaks around the glow plug, or the cylinder hed, nor the intake tube.

the breather is free, and oil is comming out of it.

I have adjusted the idle screw for a few hours, and easily found the sweet spot, and leaned it until it wont start, and richened it to the point where you realy had to open up the throttle alot to get it running at all.

I installed an ASP carb on it, and it does the same exact thing.

I took the tank apart, inspected it, leak checked it, and put it back together.

removed my fuel filter, just to see if that helped.

Fresh 5 % nitro caster/synth blend. Also tried allmost fresh 20% nitro full synth fuel.
It does run better on th 20%, but still dies slowly as before

Tried rinnung it without a muffler installed at all. Also without tank pressure, and it still does the same.

Last thing i did was disassembe the head completly again, and check the valve springs, and the valve stems again, and could not find anything wrong. No sticking valves, and no eccesive wear in the guides.


I have never had this problem with a 4 stroke before, and Im at a dead end.

What am i missing?