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JD 70 issing under load

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Mike C.

12-09-2001 06:48:42

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My 70 gas is missing under load,it idles fine but as soon as it needs power it starts to miss BAD.i have changed plug,points ,condensor and fiddled with the timing a little with no noticable change.Can anybody tell me whats the problem? Thanks, Mike

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Clooney

12-09-2001 08:59:25

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Re: JD 70 issing under load in reply to Mike C., 12-09-2001 06:48:42

Mike, it sounds like you are going a little lean under load. You have a (DLTX Duplex Carburetor) Start buy adjusting the "metering screw" it's the bigger & shorter of the 3 on the bottom of the carb. Start at 2 1/4 turns out from seated & open from there until it pulls clean under load. If it still misses under load pull the drain plug from the bottom of the float bowl & make sure you have a pencil sized stream of fuel for at least 30 seconds, if not clean the fuel strainers in the sediment bowl & under the big nut at the fuel inlet on the top of the carb. If all ok there look for a bad or incorrect ignition coil or plugged air cleaner.

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jack

12-10-2001 09:32:48

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Re: Re: JD 70 issing under load in reply to Clooney, 12-09-2001 08:59:25

Hey Clooney my 70 does not miss but it has only 43 hp on the dyno and thats at full throttle and 45 at half throttle.I have a good supply all the way down to the strainer on the top of the carb and I have even unhooked the oilbath and added a paper element and no change.What could I do to get more fuel into the cylinders?I have adjusted the metering screw while on the dynometer to get the best its got and have never seen the first sign of black smoke while loaded.Thanks

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Pat

12-12-2001 09:37:31

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Re: Re: Re: JD 70 issing under load in reply to jack, 12-10-2001 09:32:48

Jack,

On your 70 with the lower hp at full thottle-

The problem may be in the flow after the carb. I know too much carb is is worse than just enough. If your tractor has more power with the throttle plates partly closed, then it is usally one two things. 1) The cam is allowing more flow than the heads/manifold can flow. This means porting, three angle valve job, bigger valves, ect... will help. 2) Carb is too big, above remedies should also help.

If it were me I would do nothing to the carb, but would do a little head/manifold work. Most vehicle manufacturers used about 100cfm larger carbs than necc., I would imagine tractor manufacturers also used larger than necc. carbs as well.

As far as Black Smoke, it is just unburned fuel that is busy fouling spark plugs-be glad you don't have any!

Hope this helps, LATER

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joe

12-09-2001 08:26:29

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Re: JD 70 issing under load in reply to Mike C., 12-09-2001 06:48:42

try tuning up the carboretor. put the throttle at 3/4 and turn the load needle(on back far side) counter clock wise till it runs smoother.

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