Posted by Al Evangelista on September 24, 2000 at 10:57:18:
Folks,
This problem has been dogging me for the past few days.
My normally well behaved 230 has recently been difficult to keep running when cold
(50 degrees F). It requires about 2/3 choke to start and keep running for the first 4-5 minutes.
For the first 15 - 20 minutes it will backfire through the carb and stutter under acceleration.
During the warm-up period if I use about half choke it will diminish but not alleviate the problem.
With the engine fully warmed it runs almost as well as it did originally.
I recently did some internal engine work (rings, ex. valves), replaced a cracked exhaust mainfold and adjusted the valves which may have contributed to this problem.
The problem persists over a range of ignition timing settings.
Intake manifold vacuum reads steady at 15.
Formerly, the idle mixture adjustment could be set too rich to keep the engine running, now it can't be set too rich.
I checked for vacuum leaks by using oil around each of the three intake ports. I also removed and plugged both the crankcase vent fitting and the manifold to vacuum pump fitting - this made no difference in vacuum reading or performance. I eventually reseated the intake manifold, also with no change in results.
I believe that the fact that it runs better when fully warmed tends to rule out intake valves being set too far open.
It sounds like the engine is starved for fuel. I bypassed the aftermarket fuel filter with no results.
I suspected that the carb had a clogged passage and opened it for a quick inspection, I found a tiny piece of soft black plastic in the step-up jet and the step-up jet piston gasket was twirled around the piston spring. I fixed these items fully expecting to have solved the problem but no luck.
Any help would be greatly appreciated - we have our fall trail ride in less than a week and I hate to take a sick truck...
...That briggs and stratton conversion kit is looking better with each passing day.
-Al