422 vaporlock

[Phils]

In reading years worth of posts before buying my 422, I did see menion of vaporlock problems/solutions....

Happened to me last week while mowing. I could see the bubbles forming in the gas at the lowest point in the clear fuel line before the filter. I use 91 octane gas (the highest available here) but it's happened altogether 3 times now. The last time, while I had the "hood" up letting everything cool, I was moving some concrete lawn ornaments and discovered a nylon tie in the dirt underneath one. Must've been a "message from above" and I used it to pull the fuel line away from the [hot] hydraulic hoses that were in contact with the gas hose.

Didn't have the problem again that day (nor since) but the outside temps were only in the low 80's. It's typically in the 90's and 100's during summer and I'm guessing this could be a recurring problem unless I do something else in addition to not letting the fuel line be in contact with the hydraulic lines.

Any suggestions from other's experiences?

Phil

 

[MossRoad]

Just a question... why do you use high octane fuel?

We've run everything(chainsaws, mowers, cars, trucks, 2 stroke/4 stroke, etc...) on 87 octane for as long as I can remember.

 

[Phils]

Hi, MR.

I use hi-octane because

1) I thought it said that in the manual (but I could have some failing memory cells here too)

2) I have occasional 'run-on' or a backfire after shutting down the PT after use. I was hoping the higher octane might help in those situations, and can't say for sure whether it does or not. I still get the occasional run-on or backfire, but would it be worse if I used a lower octane fuel? Maybe I'll get a can or two of 87 octane one of these times and see.

Phil

 

[NJBill]

Phils
I'm don't think I ever thanked you for your input on generators. I was holding off all winter, and thank goodness we did not have any signs of emergencies. I did listen with both ears and planted the Honda 3000eu firmly in my mind, even found a source here in NJ ready for a quick call. Again , Thank you.
On the posible, suspected vapor lock, I think routing the hose as clear as possible from any heat, with the lowest part being at the entry to the carb. Do away with the hanging trap.
I like your choice of fuel. We have 93 in this part of the world, and like you for as long as I have been in this country I have used nothing else for ANY gasoline engine. I have reccomended
the same to all my customers, with the cheapy weepys I asked them to try premium for every third tankful. Going out on cold winter mornings to start some of these cheapies, I always armed myself with a squirt can, full of one step higher than premium, thats laquer thinner of course, beats startying fluid anytime. If you ever have to take one of your engines apart, you will find the benefits of using premium - clean.

I'm going onto tire leaks next ! ! ! ? ! ! ! ?
Bill

 

[BobRip]

Just a silly thought, if the outlet of the fuel tank is restricted the pressure would be reduced in the fuel line and this might cause vapor lock. I had some early problems where the silicon caulking compound that PT used to seal around the gas cap inlet had gotten into the fuel tank outlet. I did not see any bubbles, but the engine had little power.

Bob Rip

 

[MossRoad]

The reason I asked about higher octane fuel is that doesn't it make the engine run hotter and isn't heat in the fuel lines the main cause of vapor lock?

Our Kohler had run on at shut down, but I have pretty much eliminated it by throttling down to 1/3 for about 30 seconds, then throttle down all the way for 5-10 seconds and shut it off.

I'd say try the 87 for a while this summer and see how it acts. If it acts any different, then you have a good test. If it acts the same, save yourself some money and use the lower octane gas. I would suspect the engine will last longer because it is subject to less heat over its lifetime.

 

[Charlie_Iliff]

<font color="red"> doesn't it make the engine run hotter </font>

I'm not sure you'd notice any difference in operating temperature, but if there is one, the lower octane would probably run a little hotter. Higher octane burns more slowly, so allows higher compression ratios and more spark advance, so more power. In the same engine, with the same c/r and timing, it may even be that the lower octane gives a bit more power because it burns faster, but the particular engine has to be set up to take advantage of that. I'm not sure I know of one which truly does. As a result of the faster burn, however, you may get a little higher combustion chamber temperature (but for shorter time?)
My bet is that the only observable difference between regular and premium in the 22 or 25 hp PTs will be in the resulting net weight of the owner's wallet. /forums/images/graemlins/smirk.gif

 

[PTRich]

I run my kohler with the throttle all the way down at idle for a minute before turning the motor off. This should eliminate your problem. MY gator says to do so in the manual to eliminate back fires wich can realy do some damage to your exhaust.

 

[Phils]

I've tried letting the engine idle for a few minutes before shutting it down, and noticed very little difference in the "run-on" and "backfire" problems. Maybe a little. But it'll still do both after idling a couple of minutes. If I let it idle for five or ten minutes before shutting down it doesn't do either, but that seems a little excessive [but maybe necessary] on the fuel usage and hour meter advancing.

I agree that re-routing the fuel line so that it doesn't dip down so low may help more than anything. At least the PT is easy to work on. Can't say the same thing about our Toyota.

Phil

 

[J_J]

Does your Kohler have a solenoid valve in the carb bowl? If it does, and a little trash gets under the seat of the solenoid. It will let some fuel through as you shut down, maybe causing the engine to run after you turn the key off. The purpose of the fuel shut off solenoid is to do just that.

At least take it out and look at it and clean as necessary.