Small engine help needed

[racerone3]

Ok, I'm usually pretty good with small engines but this one has me stumped so I turn to my friends here at 6x6 world.

Background:
A few weeks ago, I picked up a Bobcat 610 skid steer loader. Wisconsin V4HD engine (4 cylinder gas engine with a carb and distributor). Previous owner thought it "was blowing up, cause it smokes real bad" looking it over at his place, I noticed that the choke was stuck fully closed and the smoke was black and smelled of fuel so I went ahead with the trade.

Problem: Once I freed the choke, she fired up and ran great (tons of power) for about 15 minutes, then it would sputter and die. It would refire, but with a miss and no power. If I let it cool for 15 min, It would fire up and run great for another 15........ I've tried everything I can think of and the problem persists. It is still running rich and the carb has a non-adjustable main jet... sometimes when it dies out, one of the spark plugs is wet.

What I've tried/ checked:
rebuilt carb (float level is correct)
new air filter (also oil and filter... not that it should effect this)
plugs, wires, cap and rotor (has been converted to a pertronix so no points/ condensor)
new coil
fuel lines wrapped with insulation (vapor lock???)
New fuel pump and lines
fuel pickup is clean
gas cap vent is working fine
exhaust checked for blockage
jumper wire run straight from battery+ to coil+ (to eliminate a possible bad oil pressure switch)
compression is good
I'm sure there are other things I'm forgetting....

Anyone have any ideas for me????

[azz7772]

what is the fuel line rubber or metal I would run a temp. Bypass line to see if there may be a pin hole sucking air and starving the carb. Or a collapsing line restricting the fuel.

[racerone3]

what is the fuel line rubber or metal I would run a temp. Bypass line to see if there may be a pin hole sucking air and starving the carb. Or a collapsing line restricting the fuel.

lines are rubber, and have been replaced

[LarryW]

Everything I could think of you already mentioned. Is it air cooled or liquid? Are you sure its not overheating?

I googled and found out its air cooled.

[LarryW]

After more searching around looks like the coil would do that but you said you replaced it. I wonder if the new one is bad?

[marshgunner]

It to me sounds more of a ignition problem than a fuel related problem to me. Maybe pickup coil in the distributor or worn out bushings in the main shaft? Is their any type of engine control brain box hooked up to the distributor? Is it always the same plug that is wet?

[Toys4Me]

My old 2 stroke was having that same type of problem and it was because the piston rings were shot. After if would warm up and everything would expand I would loose compression until it cooled and it would run great again for a bit.

[Bazooo guy]

When its hot check for spark at the plugs. Sounds like the coil could be overheating.....
Is it mounted in a hot area on the engine? Wet plug means no fire
Try running it in the dark and look for spark leaking to ground.

[racerone3]

After more searching around looks like the coil would do that but you said you replaced it. I wonder if the new one is bad?

Swiped the coil off my Bronco, just to try it out... same issue

It to me sounds more of a ignition problem than a fuel related problem to me. Maybe pickup coil in the distributor or worn out bushings in the main shaft? Is their any type of engine control brain box hooked up to the distributor? Is it always the same plug that is wet?

I keep going back and forth between ignition and fuel.... Distributor bearings seem ok (no play at the top when you grab it where the rotor mounts). No "brain" on the distributor. this is a mid 70's machine, just the basic coil and distributor. It had points, but those were eliminated with a pertronix unit (suppose it could be going bad???) The wet plug issue seems to move about randomly.

When its hot check for spark at the plugs. Sounds like the coil could be overheating.....
Is it mounted in a hot area on the engine? Wet plug means no fire
Try running it in the dark and look for spark leaking to ground.

The coil is pretty far from any major heat source, and does not feel hot to the touch after the engine shuts it's self down. I ran it for a little bit tonight once it was dark and didn't see any sparks.

I'm wondering if the pickup tube in the tank has some pinholes in it. Tonight I took a spare fuel cap, drilled a hole in it and welded in a long piece of 3/8 od steel tube which will reach the bottom of the tank (with an angle on the bottom of the tube to keep it from sealing it's self off). the tube sticks up about 2 inches above the top of the gas cap. Fuel line is now hooked to that tube to eliminate the stock pickup. I also installed a low pressure electric pump (1-3 PSI) and have the stock mechanical pump bypassed. I only drove it long enough to pull it out of the shop, and then ran it another few minutes to look for spark leaks, so I will have to report back tomorrow as to weather this was the solution. The exhaust didn't smell nearly as rich this time. Perhaps the stock pump was building too much pressure and forcing the float needle open

[Bazooo guy]

Could it have sticky valves from sitting?
Did you do a compression test?
Is there a fuel filter in the carb?

[racerone3]

Could it have sticky valves from sitting?
Did you do a compression test?
Is there a fuel filter in the carb?

Valves don't seem to be sticking, but some seafoam in the oil can't hurt.
haven't done a hot compression test yet.... dropped my tester and broke it. Need to pick up a new one tonight.
no filter or screen in the carb.

[racerone3]

Still need to replace the broken compression tester, but not for the Bobcat... she seems to be fixed. I ran it hard for about 20 min today, and it was in the 80's, by far the hottest day I've tried it on. Now I will have to figure out what the actual problem was (or it will drive me nuts ). It either has to be the fuel pickup, or the pump so it shouldn't be too hard to figure out! My best guess would be pump as there isn't a cloud of extreme rich exhaust anymore when I'm running it. I ran out of time, so I haven't pulled plugs to see for sure that it is leaned out.