Posted by joe csuti on June 15, 2013 at 03:36:43 from (220.127.116.11):
In Reply to: JD 318 posted by Jonak on June 14, 2013 at 19:06:55:
The most common cause for this mod eng to surge is intake manifold leaking/sucking air at split in same,idle passages in carb plugged/restricted due to dirt or high/low speed needles mis-adjusted.
Check that manifold tight on block & gaskets good,if mounting ok,clean off intake manifold & carefully inspect for loose/broken rivets that hold manifold together & also check for hairline cracks in castings,if no loose/broken rivets or hairline cracks found in manifold,get a spray can of carb cleaner with plastic ext tube.
With eng running at slightly above idle & with ext tube installed in spray can nozzle slowly spray all the way around manifold where halfs joint,if eng speed changes while doing this either one/more rivets loose or gasket bad at joint.If you can pinpoint air leak & it's a small area try sealing same with red rtv sealer,if manifold leaking in several spots,either replace manifold OR drill out rivets & seperate manifold halfs,clean out joint & pack with red rtv sealer,reassemble manifold useing screws,lockwashers & nuts.IF no bad rivets/ air leaks found in manifold consider removing/disassembling carb & cleaning out/blowing out all passages in carb body & possibly rebuilding carb at same time.
Other possible causes of surgeing,problem in fuel delivery system(weak pump,plugged/restricted filter,bad fuel lines between tank/carb,dirt in tank plugging outlet,plugged vent hole in tank cap or cap bad)problem in ign system(coil may be going bad & dropping 1 cyl)internal eng wear or mech problem(worn cyl/rings,sticking valves/worn valve guides,leaking head gasket(s),hairline cracks in block/heads.
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