Need help on 420 engine

[JohnDeereJimOhio]

I have a 420c that recently quit running. We pulled it apart and it was a stuck valve and bent push rod. I got it tore down and all the new parts, and had the carb rebuilt. We got it back together and it wasn"t running right.. It would run then spit and sputter.. So took a break from it and read the book. I thought it was a timing issue and times it according to the book. I have great spark but still not running. The only thing I have now is backfiring out of carb, but only if choke is pulled... I am completely out of ideas what to do with this thing. Valves are also in spec per the book. Anyone got an idea what to do?

 

[johndear720]

A compression check would verify if the valves are set correctly. Is the only way it will run is with the choke closed? Spitting back through the carb sounds like intake valves too tight or running way to lean or fuel starvation. Open the drain on the bottom of the carb or remove the plug with the fuel turned on. You should have a good pencil size flow of fuel that doesnt diminish for 30 seconds. If not you have a restriction between the tank and needle and seat in carb. If you have a good flow of fuel has the carb been adjusted? 2 turns out from seat on low and high speed adjustment as a starting point. I don"t know who "rebuilt" your carb but it may still have something plugging the high speed circuit. Carb cleaner doesn"t really work on cast iron carbs. requires removing drill passage screws or steel balls and running a drill bit through passage.

I"m willing to bet you have a fuel issue.

 

[rick deere]

change the spark plug wires at the distributor cap

 

[Mike Aylward]

Jim, did you check the rocker arm that had the bent push rod? Quite often when this happens the rocker will develop cracks which will cause the valve clearance to be erratic. This can cause the symptoms you describe. It's good practice to examine and even better practice to replace a rocker once this happens. Mike

 

[JohnDeereJimOhio]

New rocker arm and new pushrod.

 

[JohnDeereJimOhio]

replaced rocker arm assembly with a new used one, as well as push rod...

 

[JohnDeereJimOhio]

I have great spark

 

[JohnDeereJimOhio]

Vales are set correct, it wont run at all, only back fires out carb when choke is on. have good fuel flow through line. Carb has just been rebuilt by this site. Also have set it per book and cleaned it with carb cleaner as well.

 

[johndear720]

Any chance the timing is 180 out? Remove front plug and roll motor over until you feel compression. You can then continue to turn motor until TDC mark on flywheel shows in timing window. Make sure rotor button is pointed towards number one post on cap.

If timing is correct have you tried removing plugs and putting a little squirt of gas in each cylinder then putting in plugs and trying to start? If it starts and dies you have a fuel / carb issue.

Will it run on ether?

Is points, condesnor, rotor, cap, n plugs new? You say you have good fire but sometimes a good spark outside the cylinder isn"t so good under compression. Might try a different set of plugs.

I generally start with compression. If 100+ then it should at least run. Verify timing and good spark. Then the carb is all that is left to blame.

 

[JohnDeereJimOhio]

Johndear720,
I think timing is my problem. I timed it per what the book says and had it at TDC on comp stroke but still no fire. I tried either and got nothing. All electrical components are new. However when I timed it the cap and distributor was almost 180 degrees away from where it originally was. Im confused by it. Its at my dads so I guess I need to start from scratch next weekend and time it again..

 

[johndear720]

You can pull front plug, take off cap and mark where number one was on body of distributor, stick finger over plug hole and spin the starter to see real quick if rotor is pointed at number one when your finger is blown off the hole. If it is pointed the wrong way re-time it. Hope that is your problem as it will be an easy fix. Good luck!

 

[CPeter]

I am pretty sure you have a timing problem. I have seen one of mine run with the distributor cap off. Not well, but it did run by crossfiring inside the cap and firing to both plugs at the same time. It is possible, though not easy to get the distributer in 180º out. There is an offset in the key, but you can put in in the wrong way around. Also you can get the wire on the wrong term. Front wire to front cylinder. Timing is best set with a light. "-Spark-" should show in the window at high idle (+/- 2025 rpm).

CPeter

 

[JOHN DEERE 70]

Points gaped right or need changing ? Sounds like my 60 when points and condenser are bad

 

[JD Tim]

Jim,
I'm assuming that you had the motor completely tore down. When I rebuilt mine the distributor was 180 out which is driven off of the oil pump. You may have to drop the pan and reinstall the pump in the right position to get your timing right on the distributor. I'm just taking a stab at your problem but that's what was up with mine.