422 vaporlock

[maujer422]

I had problems with my 422 in May, it seemed like vapor lock it wouldn't run the mower. I replaced the fuel filter, chcked the gas lines, put in a new air cleaner, and had good fuel flow that didn't help. I talked to the Robin dealer, he told me that the gas we buy around here was junk, so I tried something I put about an ounce of car injector cleaner and a little gas dry in the tank, still ran bad 1/2 round mowing then picked up full power just like flipping a switch, been running great ever since. I mow about 3 acres every week.

 

[ClintBlake]

I had similar problems with my 422 Robin. After running for a while it would starve for fuel unless I added about 1/3 choke. I finally pulled the fuel solenoid on the carburetor and found a little piece of what looked like filter element in it that would block the jet. Since cleaning that out I have had no more problems.

 

[Charlie_Iliff]

David:
Although certainly the posts regarding the fuel lines, heat & blockage, may hold the answer, you've already listed having done the fixes (except the tank outlet elbow?). Your problem, however, is similar to what I see with the 1845 diesel in hard mowing when the engine cooler plugs. I don't know how exactly your engine is cooled, but it sounds as if the engine is overheating. Any chance there is some blockage in an air passage or a fan that isn't working correctly?
422/425 owners - any experience?

 

[Piedmont3]

I used to have a 14 HP riding mower that would do this on very hot days. I tried everything I could think of to fix it.
Finally took it to a friend of mine that was a small engine wizard and he changed the mechanism that splashed oil up into the engine, and it solved the problem.
My point is maybe it is related to the engine over heating instead of purely a fuel problem, like Charlie said.

 

[BobRip]

I believe you have it backwards. The hydraulic cooler does not cool the tram fluid (which is somewhat isolated), but the other fluids.
At least that is the way I see it. According to PT the mower is the biggest load.

Bob Rip

 

[SnowRidge]

<font color="green"> Okay, I think I have tried many things and none have worked. I have been suffering the vapor lock blues on a 425 I think.

I have replaced the tygon tubing with std 1/4" hose, replaced fuel filter, and moved the filter closer to the tank. I have also routed hose so it is not touching hyd lines.

All that and tried to mow for about 25-30 minutes in 85' weather and the engine just stalls. I can usually re-start but can not put full load back on the engine until it cools down a bit.

This problem never occurs when it is cold start-up. It will always run for 25-30 minutes at full throttle with no problems. Once things get very warm it stalls.

One note of interest.... My machine only has 47.5 hours on it and at 25 hours I checked the oil level and found that it was just below the low mark on the stick. At that point I added almost a full quart. I checked it this morning cold, and it was just at the full mark. Not a bit over full. Just full. I have read many posts that warn that too high of engine oil level will cause pump problems... Any thoughts </font>

Vapor lock -- Vibration helps induce vapor lock. Check to make sure that none of the fuel system components are rubbing against something they shouldn't and are properly mounted. Been there, done that, etc.

High oil consumption -- New engines tend to use some oil because the rings are not yet seated. Clogged or partially clogged air filters cause high oil consumption with the Kohlers, and may do so with the Robins. This is particularly true with new engines. Again, this is from experience. One mowing alone can require filter service under some conditions.

 

[BobRip]

Measure your fuel pump pressure. It should be about 2 PSI. If it is low look for oil in vacuum inlet, or did you check this?

Bob Rip

 

[SnowRidge]

Bob, was your reply intended for me? My problem was one-time-only, and it was vibration: the fuel tank coming into direct contact with with the engine cover due to a misaligned mount. That's how I discovered that vibration induces vapor lock.

When it was cold, it was fine. Once it heated up, bubbles formed in the line between the tank and the pump. Adjusting the tank mounting bracket so that the tank did not contact the cover fixed it.

 

[BobRip]

I guess it was aimed at the Bigheadedkid, and I missed. Sorry

Bob Rip

 

[SnowRidge]

Not a problem, Bob. I just wasn't sure.