420 sputtering and backfireing

Tomriker · Post by **Tomriker** » Sat Oct 27, 2012 9:40 pm

before we brought our new crawler home it purred like a kitten, now.. not so much it just sputters and spits and backfires... the only thing that changed was it was in the high desert and we hauled it 300 miles to the valley floor. now like i said it backfires like crazy and only runs with the choke on, we had the carb rebuilt thinking that was the problem. but it still doesn't want to run right. could somthing have come loose while hauling it home? distributor cap is what we're thinking to replace next, maybe plugs?
thanks for any info in advance

Post by **Lavoy** » Sat Oct 27, 2012 10:06 pm

If it only runs with the choke on, it is lean for some reason. Did you set the load jet after you rebuilt the carb?
Lavoy

Willyr · Post by **Willyr** » Sun Oct 28, 2012 2:15 am

You have a vacuum leak some where as a possibility as well. Easiest way to check for vacuum leak. After it has started, use some wd-40 or some form of aerosol lubricant. Spray around the gasket surfaces. If the engine rpm changes while spraying in a area you have found your leak.

I did have something on my 60 that bothered my tractor as well. It backfired up a storm comming down a hill when using it for a people mover. On mine on of the valve adjusters had broken and I had a 0.250" clearance on a exhaust valve. Just a thought to check. Once it was back to the correct setting my tractor no longer even rumbles.

Only other item is heat. On the desert it may have been warmer than down on the valley floor. Castings may have made for tighter joints. Again it would be a vacuum leak.

gregjo1948 · Post by **gregjo1948** » Sun Oct 28, 2012 6:24 am

Too much air--not enough fuel. But why the backfiring? I'd check ignition timing, check for fuel flow ubstuction, then adjust carb. Greg

Tomriker · Post by **Tomriker** » Mon Oct 29, 2012 12:36 pm

Thanks for the tips, we could find a vacuum leak, but we pulled the plugs and they are pretty much shot, also goin to file the points a little to see if that helps... How do you guys feel about putting an electronic ignition on it? Pros/cons?

TR

Post by **Lavoy** » Mon Oct 29, 2012 2:21 pm

Done it on 6 volts, would never do it again, way to irratating to start. On 12, would not be an issue.
Lavoy

Tomriker · Post by **Tomriker** » Mon Oct 29, 2012 2:51 pm

Any idea why it made it tougher to start? We put new plugs and sharpened the points and it purrs like a kitten again

Howard Yoder · Post by **Howard Yoder** » Mon Oct 29, 2012 3:15 pm

is there any possibility that you left the switch on that could have burned the points

Willyr · Post by **Willyr** » Mon Oct 29, 2012 8:54 pm

I used the electronic points on my 420. Loved it for certain. Cost is high, but you can guaranty ignition.

If I had the money again I would get a set for my 60

Gil · Post by **Gil** » Wed Oct 31, 2012 6:26 pm

I have three gas JD440s with original design 6 volt ignition components that I run every month. One revolution of the engine and they all start immediately. My point is that there is nothing wrong with the original design. You can change to 12 volts, or move to electronic ignition, or make other modifications that suit you; but don't do it because you think that somehow the old 6 volt system never worked well. Gil

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