Spark plugs for two cylinders

mdross1 · Dec 3, 2015

Could not find any topics using search. Spent the summer breaking in and using 70 at pulls and plow days using a set of Autolite 3116's. Thinking next season might try a set of Autolite 388's one step hotter, anyone here use these?

buickanddeere · Dec 3, 2015

Run the coolant at 195 and lean the air fuel mixture back to where it's supposed to be .

RickB · Dec 3, 2015

388's are a pretty hot plug. Not sure they are needed or appropriate for a fresh engine.

mdross1 · Dec 5, 2015

Thanks for the input this spring will hook up to a dyno and play. Want to see what the difference is between muffler and straight pipe. When plowing the muffler has to be on the tractor at the pulls some say why not a straight pipe then we can hear you. We will see same goes for plugs and fuel mix. Already have the 195 stat. This tractor also has K&N air filter,propane exhaust manifold and 2.0 roller rockers.

buickanddeere · Dec 6, 2015

The straight pipe may or may not lean the mixture to some degree.

mdross1 · Dec 7, 2015

How do you check the fuel mix. I have been tuning carbs for a lot of years on muscle cars and Harleys these duplexes do not have a lot to play with and I'm new to them.
Mike

buickanddeere · Dec 7, 2015

There is a vast selection of nozzles and jets for the duplex carb's . The all fuel 70 main's flow more than the gas 70. The all fuel metering for the 720/730 are a size larger yet again.

mdross1 · Dec 8, 2015

Now you have peeked my interest I would very much like to know all there is to know about these carbs. First off how do you judge the mix other than being hooked to a dyno? These engines being low compression and all reading the plugs is next to impossible. My first instinct is too lean the mix out a little where the plugs are so dark.

Mike

buickanddeere · Dec 8, 2015

Weld a bung or drill and tap into the exhaust manifold just prior to the flange where the pipe to the stack bolts on. Thread in a wide range O2 sensor and read the voltage .
Summit racing has them on the shelf. Needs a 12V neg electrical system .

mdross1 · Dec 9, 2015

Appreciate the input but do not want to drill into the manifold nor convert to neg ground. I will just have to wing it

Mike

buickanddeere · Dec 9, 2015

mdross1 said:
Appreciate the input but do not want to drill into the manifold nor convert to neg ground. I will just have to wing it

Mike

It would only take 1/2 an hour for conversion to (-) chassis , drill and tap the manifold.

pmsmechanic · Dec 10, 2015

Ok so here are my thoughts. Why not purchase a second manifold to drill and tap for the wide band 02 sensor. When you test use the modified manifold and when your showing your tractor just put the original manifold back on. If you spray Pam on the gasket's they can easily be reused. For testing it would also be easy to just set up a separate battery to run the 02 test. Then there is no need to change to a (-) chassis.

mdross1 · Dec 10, 2015

Good food for thought have all winter to think about it. What kind of A/F ratio would work best on these engines?

RickB · Dec 10, 2015

I'd find a dyno and tune it that way.
I bet one of your pulling or plow day buddies has one.
Might even be an enjoyable day/afternoon.

The whole hobby is about common interests and having a good time.

buickanddeere · Dec 10, 2015

Depending on the engine , somewhere around 13.5 to 1 for max power. 15 to 1 or so for max efficiency .

mdross1 · Dec 11, 2015

Already have a dyno to back up to and plan to warm it up this spring.
Have a question buickandeere what kind of A/F does the stock jetting on the DLTX carbs give? My 70 carb is freshly rebuilt with stock jetting.

Mike

buickanddeere · Dec 11, 2015

Depends if the fuel enrichment screw is dialed out , altitude and fuel density . Set for max power it will be on the rich side of 14.7 to 1. I would be guessing what the ratio would be leaned out.
Back in that era and on Nebraska tests. The gasser's tended to be on the rich side of 14.7 to 1 as max HP was a priority . Fuel economy was secondary and emissions were unheard of.

buickanddeere · Dec 11, 2015

Depends if the fuel enrichment screw is dialed out , altitude and fuel density . Set for max power it will be on the rich side of 14.7 to 1. I would be guessing what the ratio would be leaned out.
Back in that era and on Nebraska tests. The gasser's tended to be on the rich side of 14.7 to 1 as max HP was a priority . Fuel economy was secondary and emissions were unheard of.

mdross1 · Dec 12, 2015

Without the O2 check I guess my gauge will have to be the dyno this spring. Max power is my focus also want to see what difference a straight pipe makes over a muffler. It would seem that when hooked to a sled with throttle wide open the straight pipe would be the way to go given the right fuel mix.
Makes me wish I had a dyno parked in my shop.

buickanddeere · Dec 13, 2015

I would not place any faith that a straight pipe on a 70 will give it the power of a 720. Just more noise. Why more noise is a benefit is beyond me. If you want to tinker with the exhaust system. The 720/730 oval muffler from Deere is a legitimate update.