The case of the unstartable engine

[allwheeldrive]

Hi all, so I have been trying my hardest to get the Harbor freight Predator 420 engine to start in my Scrambler project, and to no avail, perhaps the more experienced internal combustion experts on here may have some foresight I lack.

The breakdown:

A few months ago bought this action age 1970-74 scrambler. Re-welded one rear hub. Became very familiar with the centrifugal clutch and all the other friction clutches throughout the drive train as I got everything running relatively smoothly while rewiring and re-cabling the rest of the rig.

The Day I had finally finished the last calibration to the steering clutches on my maiden test drive I nearly creamed my car in the drive way as the engine was sent into a runaway. A last second full strength right turn sent me skidding out of danger where I had the time to pull the kill switch coming to a sputtering stop in the neighbor’s yard. We rolled the 6wheeler back to my yard where it spent the next night. The next morning we started it up, the moment I pulled the lever on the choke the engine blistered back to full speed runaway with no control from the gas pedal. Again the 6wheeler was brought to a halt in my yard via kill switch.

My father and I put it up on cinderblocks to see what the issue with the runaway was. We came to the conclusion that the throttle’s return spring had simple been over stretched and no longer had the tension to return the gas to close.

Here’s the dilemma:

While testing to see what the cause of the runaway was the Predator 420 (only a year or so old and in good shape) started idling oddly and eventually cutting out. From that point on each time we started the unit over the next 5 min the engine ran for shorter and shorter amounts of time before cutting out. Giving it a little gas seemed to prolong the cut off momentarily but than with about the 6th time starting it 5 min later the engine immediately cut out and would not start again. It is still resting on the cinderblocks in the middle of my yard weeks later, nothing we try can get it started again.

Things we have checked and noted:

-There was very little oil in the engine. So will topped it off with some new oil
We are getting spark

-The air filter is unobscured and clean.

-With the air box removed and only the carborator installed we still get no start

-Battery is fully charged

-Electric Starter spins at full power

-Pull cord feels like there is full compression when pulled

-All gasoline removed and tank cleaned, replaced with fresh gas and then added some sea foam additive

-Gas lines are clear

-Carborator removed and fully cleaned

-Float bowl and all jets fully cleaned

-Exhaust is not blocked and free flowing

-Valves are in good condition and clean

-Tried starter fluid

Have tried choke off / On / half way

Tried full throttle / No throttle / half throttle and everywhere between with all combinations of choke above

Disconnected kill switch (though we have sparks so this shouldn’t have been a problem anyways)

Only thing we haven’t done is replace the sparkplug, but since it sparks and worked before we figured it should be fine.

Any idea guys?

Thanks,

[Rudy_Magnum]

Replace the spark plugs. Sometimes they will fire when you have them out, but when under pressure will short out internally. A buddy of mine had a generator that did this. I chased it around for a few hours, after he chased it for days. It had only run 20 mins. New plug, ran like a champ.

[Dozerlarry]

^^^^^^ I had a spark plug tester that you put air pressure to the plug and hit a button that put fire to the plug. I was amazed how many plugs would fire till you put the air to them---and then nothing.

[Paul219]

Spray the starting fluid directly into the cylinder, if it starts briefly, your carb is messed up.

[Tomo]

HI
by spraying starter fluid u also check the pump ,assuming the carb is clean & ok

tomo

[allwheeldrive]

Thanks, guys, will try a new spark plug. Ill report back on what happens.

[racerone3]

Sounds to me like a sheared flywheel key. Each time you started it, the timing got further and further off till it wouldn't run but still has spark.... Just not at the right time. The runaway could have been from an internal governor failure either the possible cause or effect of a sheared key.

[allwheeldrive]

Well installed a brand new spark plug no luck, nothing changed. Raceone3 how could I check something like this? (also like your sig)

[racerone3]

pull the sheet metal cover off over the flywheel, then remove the nut that tightens the flywheel to the crank. usually you can see the keyway in both the crank and flywheel. if they are not in perfect alignment, then the key is sheared