Pony motor dying out under load

[Flannery]

Hello brethren

Got a 00 gmc bucket truck with a tweed xt55

Kubota w742 pony motor

Motor is dying out under load from the boom after about 5 minutes of use

Idles and high and low rpm just fine no problems it will just run but once it’s under load it will eventually bog out

Hydros make a whine when the controls are in use
Upper and lower
Engine revs down under load then revs back as you let off the controls
Normal I assume

But after 5 mins she will die down. Just started this

Cap, plugs, wires, filter, fuel pump, carb, all done

Thinking it my be hydraulic related but not sure. Like I said idles high and low no problem
Firing correctly doesn’t skip

Plugs came out a little ashy and a bit of back fire every now and again

Fiddled with the tune on the carb but no difference

Hoping it’s not a new motor deal

The pistons do look a little gunky on the inside with a bore scope

Going to be uploading pics and vids tomorrow

Hours reads 4.9k and I don’t know if it’s original or not

Any help would be appreciated

Jonathan Thorland Flannery II
View attachment IMG_2093.MOV

 

[grizz55chev]

Hello brethren

Got a 00 gmc bucket truck with a tweed xt55

Kubota w742 pony motor

Motor is dying out under load from the boom after about 5 minutes of use

Idles and high and low rpm just fine no problems it will just run but once it’s under load it will eventually bog out

Hydros make a whine when the controls are in use
Upper and lower
Engine revs down under load then revs back as you let off the controls
Normal I assume

But after 5 mins she will die down. Just started this

Cap, plugs, wires, filter, fuel pump, carb, all done

Thinking it my be hydraulic related but not sure. Like I said idles high and low no problem
Firing correctly doesn’t skip

Plugs came out a little ashy and a bit of back fire every now and again

Fiddled with the tune on the carb but no difference

Hoping it’s not a new motor deal

The pistons do look a little gunky on the inside with a bore scope

Going to be uploading pics and vids tomorrow

Hours reads 4.9k and I don’t know if it’s original or not

Any help would be appreciated

Jonathan Thorland Flannery II
View attachment 993024

Compression test and or a leak down test might shed some light on the problem, and maybe a valve adjustment? Not familiar with your parti ultra motor, but these are pretty basic diagnostic steps for most 4 stroke engines. Hope this helps.

 

[Flannery]

Yeah couldn’t find my compression tester but that is next. I’ll look up a leak down test.

Valve adjustment meaning hydraulic valve?
Just looked into that so going to give that a shot in the morning as well

Definitely helps thanks for the info

 

[northmanlogging]

whining hydrualic functions indicate a problem with the pump, either the pump is dying/dead, or the bypass valve is janky. Once the hydro fluid warms up things start to show themselves. If the lines are hot to the touch after 5 minutes, something is wrong. A cheapo parts store "laser" temp sensor (star trek phaser looking thang) makes a cheap diagnostic tool, lets you find the really hot spot in a hurry

 

[grizz55chev]

Leakdown test will narrow down the loss of comp from either the rings or the valves, a very useful test for accurate diagnosis of the problem. Y TUBE will lead you in the right direction.

 

[Flannery]

whining hydrualic functions indicate a problem with the pump, either the pump is dying/dead, or the bypass valve is janky. Once the hydro fluid warms up things start to show themselves. If the lines are hot to the touch after 5 minutes, something is wrong. A cheapo parts store "laser" temp sensor (star trek phaser looking thang) makes a cheap diagnostic tool, lets you find the really hot spot in a hurry

Yeah I was thinking hydro. It also whines like a bastard when the truck pto is engaging the boom. Screeches.

Pony motor screeches at first then smoothed out and after 5 minutes bogs out and dies.

I’ll try and post video of both issues today

After I get done climbing

 

[Flannery]

Leakdown test will narrow down the loss of comp from either the rings or the valves, a very useful test for accurate diagnosis of the problem. Y TUBE will lead you in the right direction.

Ordered both of amazon
Should be in tomorrow going to have a look

 

[Flannery]

Also upper boom from the bucket is slow to get moving while below a 90 degree angle
Gives a whine when engaged

 

[Flannery]

Video of what it’s doing

No lines are hot. Pump isn’t hot. Adjusting the valve doesn’t fix the issue

 

[Flannery]

Only running on 2 cylinders

Thanks everyone for the input

 

[Captain Bruce]

Hello brethren

Got a 00 gmc bucket truck with a tweed xt55

Kubota w742 pony motor

Motor is dying out under load from the boom after about 5 minutes of use

Idles and high and low rpm just fine no problems it will just run but once it’s under load it will eventually bog out

Hydros make a whine when the controls are in use
Upper and lower
Engine revs down under load then revs back as you let off the controls
Normal I assume

But after 5 mins she will die down. Just started this

Cap, plugs, wires, filter, fuel pump, carb, all done

Thinking it my be hydraulic related but not sure. Like I said idles high and low no problem
Firing correctly doesn’t skip

Plugs came out a little ashy and a bit of back fire every now and again

Fiddled with the tune on the carb but no difference

Hoping it’s not a new motor deal

The pistons do look a little gunky on the inside with a bore scope

Going to be uploading pics and vids tomorrow

Hours reads 4.9k and I don’t know if it’s original or not

Any help would be appreciated

Jonathan Thorland Flannery II
View attachment 993024

Hoping it’s not a new motor deal.....Hope in 1 hand, and spit in the other...and clap. Why buy tune-up parts for an engine with a clear mechancial issue......even if its simply worn out???? Start with a compression test? Engines don't falter under load unless that load exceeds the torque provided to the load.

 

[Aknutter]

Only running on 2 cylinders

Thanks everyone for the input

You can use the laser temperature thermometer to get temps on exhaust manifold at each cylinder. This will tell which cylinder is firing.

The valve adjustment that griz was talking about are the intake and exhaust valves of the engine. Some engines require periodic adjustment at certain intervals.