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John deere G compression/ignition help

A

Anonymous-0

Well-known Member
In a post awhile back that I aquired a G that had the pistons lengthened and pushed out to the end of the block, I finally found the fuel it likes to prevent spark knock. My next question is, when you put a heavy load on it, it cuts out suddenly with a light black whisp of smoke. There is no fuel blockages and I have opened the load needle more than most tractors in the past to get it to the point it is, which is the best its run at the moment. Carb has been completely cleaned (and yes I know all the passages etc) The tractor has a wico C mag, which seems to supply a decent spark. It also is hard starting, it will hit quite a bit but wont take off and run like it should. Does this sound like an ignition problem? With that setup do I need to reduce plug gap from .030? would that aid with the cutting out? Does this tractor necessarily need the delco dist? it seems to be getting enough fuel at idle and quickbumps of opening the throttle.. any ideas would be appreciated. Thank you.
 
Just a thought. Do you think you're getting enough flow through the needle/seat? Is it simply running out of fuel after a long, hard pull?
 
I can check that but we are talking about riding the brakes putting it under load.. hasnt been hooked to a sled yet
 
A distributor would be a good start. Mags have a tendency to break down under high compression and the compression will blow the fire out. Depends on what your compression ratio is if it is a stock stroke and stock bore. And we run JD LP distributors on all our pullers with MSD.
 
- I"d start with a compression check.
- I"d also ditch that POS Wico C mag and replace with a Distributor with Pertronix (Some hate them, I"ve had good luck with them), make sure you get the right resistor. Or a Wico X.
- Make sure the cap and rotor are in good shape and not sloppy or cracked.
- Check the timing (use a gun, "retarded" is pretty vaugue). If the compression is as high as it might be, you may need to move the governor a tooth. If you do that, make sure you pull the mag off before putting the side cover on the governor housing or you"ll break the bushing inside the mag
- RPM"s ???
- Cam timing?
- Fuel - you said you found somehting better, what are you actually using?
 
Mag has been retarded turned toward front of tractor as much as possible
Factory Rpms
190 lbs at cranking speed
Factory F900 cam timed factory
Seems to run the best on 100 LL aviation
 
Get a timing light. Be careful and pay attention to your base timing. I broke the nose off the starter on my 70 with too much base timing (advance seized up at full timing. Next time I tried to start it it kicked back).

Not saying ignition is why its stalling, but you may have another problem with your timing now not helping things.

With 190 psi and a stock cam, you may want to try better fuel than 100LL as you start addind timing.
 
Another easy thing to try is close the spark plug gap, I got a b with lots of compression and a mag did the same thing under a hard load closed the gap fixed the problem
 
Throw away the mag. You need more ignition. The mag cannot keep up with that high of comp.
Go to a racing gas fuel 110 octane. And take about 3/4 of an inch off the pistons. Leave the long rods. Also you might hear a chirping noise. That's comp. going past the valves.
Hope this helps.
 
I'm guessing you are stock bore and stroke... Guessing you are running M&W style pistons with a sytled head... (I don't remember the thread.) you should be fine with your compression... I agree with the others.. go do a different ignition system..

How far do you have the load jet open? Stock 51 carb? Just a shot in the dark.. but try closing the load jet some.. (I had one that would do the same.. and it was getting too much fuel..) but your's doesn't sound that is the issue.. but worth a try..
 
whats the best way to time these tractors and what is the right degree for timing. Every book you look in seems to have different specs. I read a post before of setting engine on TDC, then turning distributor till spark occured;that it was timed. Is this accurate?

Which way is advanced, rolling distribotor or mag towards front of tractor?
 
I have found that with higher compresson you need heavier valve springs If you use a Mag be sure it's HOT or get a delco with pertronics
 
4010,

No set RIGHT way to know where to set it without a dyno.

As you roll it forward, it RETARDS it.

Depending on compression and fuel, somewhere between 18-28 degrees works good. if he"s high compression, you will have to move the governor gear a tooth to get the mag to work.

Nice thing about a mag is you can set cranking and runnng sparks independantly. You"d have to get someone to change the guts in the distributor to do that.

Never had to have stiffer springs due to compression, just RPM"s.

My mag worked fine at 11+ compression.
 
Mine would never run on a stock magneto so I just put a distrib on it and high output automotive coils are cheap later went to electronic ign and never had any problems
 
Is this a good general rule for stock or just for higher compression engines? 18-28* advance is good? That is with engine at TDC and distributor rolled counter clockwise?
 
Get a set of sparkplug adapters to run 14mm plugs like in cars I been using them in my 2 G's and B for years here's the website www.sparkplugadapters.com , R.E.A.M 989-743-9148 I run high compression engines also and had the same problem you are.
 

It really would help you if you could put the tractor on a Belt..feed-grinder, Prony-brake or Fan..
Lets you work on it as it is working..
I would suggest pulling the inlet air tube to the Carb (from the air-cleaner), to eliminate other problems and verify that the choke is staying Open..
As JDB Puller said, the ignition may be letting the Fire go out..
be sure the engine is warmed-up before you try it and see if it is better..
Ron..
 
Ron is right about setting the timing under load, however I would sugest you find a dyno. If you are going to use a belt, BE VERY CAREFUL when you are reaching over it to adjust the distributor/mag.
 
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