Carb problems

[ldabe]

Hey guys,
I need some help on what the problem is with my PT.

When I start it up (with full choke, and 1/2 throttle) it starts fine.
Then I back off the choke as anyone normally would.
I take the throttle up all the way to full speed.

From here everything is going good (sitting and running this way or working it under loads).

Here is the problem...
when I back the throttle back down to slow (say to get off to pick up some trash or a stick, but leaving it running) then when I get back on to throttle back up to full, the engine starts 'popping' real bad!

I cleaned the air filter, and the plugs were fine.

I repeated the same proceedure above after letting it set awhile, but this time I left the air filter and cover off to be able to see what was going on in the Carb.

When it was 'popping' I could see fire inside the Carb.

Does anyone have any suggestions as to why this would be doing this, and of course what the remedy might be?

I didn't take it out of the garage after checking it with the air filter and cover off. I was afraid it could die on me out in the field, or even worse ruin the engine.

Thanks in advance for any comments, suggestions, or remedies.
Abe.

 

[catsco]

A grim possibility is a broken or sticking intake valve. To check that, removed the valve covers (after disconnecting the fuel line) and crank the engine WITH THE SPARK PLUG WIRED DISCONNECTED OR THE PLUGS REMOVED to see that all four rockers arms and valves move correctly.

BUT FIRST! - -
It's more likely that the carburetor float is sticking. I had the same thing happen two different times (PT-425 w/Kohler engine, 500+ hours).

The first time the plugs were very wet; I removed them, let them dry, cranked the engine while the plugs were out (blowing some unvaporized fuel out), reinstalled, and managed to get the PT started after WAY too much cranking. It worked fine for about two days.

Then, it quit again with much popping and carrying on, and I was out in the woods where there was no possibility of towing the machine back.

So, I removed the air filter entirely, including the bottom plate which is attached to the carb by four bolts.

Then, I removed the top of the carburetor (after carefully cleaning everything as well as can be done in the woods). If you do this, be careful when detaching the linkage by rotating the carb top various directions to get it off the cable end.

Obviously, be very careful to not lose the needle valve or clip.

The float level appeared to be OK, as did the needle valve and seat, BUT, there was quite a bit of debris in the bottom of the float bowl. I emptied the fuel from the bowl (sort of mopped it out with clean rags), and carefully cleaned out the debris. I'm not sure how it got in there, as I have always used a good fuel filter, but apparently some can get through, or was already in there when I bought the PT new.

After reassembling everything, the tractor started easily and has run perfectly for the last 20 hours.

The first symptoms of the problem were the occasional popping, hard starting, and inability to idle at anything less than 1/2 throttle.

If your PT has a Robin rather than a Kohler engine, I assume that the procedure would be similar.

Hope this helps.

Regards,
Mark H.

 

[cqaigy2]

I had a similar problem. I removed the carb and removed a bunch of crap from where the fuel goes into float valve. While i was at it, i cleaned out the gunk in the bottom of the bowl.

 

[ldabe]

Thanks guys!
I will try to take it apart and clean it up, and hopefully all will be well.

I will let you know when I finish.

Thanks again,
Abe.

 

[ldabe]

A grim possibility is a broken or sticking intake valve. To check that, removed the valve covers (after disconnecting the fuel line) and crank the engine WITH THE SPARK PLUG WIRED DISCONNECTED OR THE PLUGS REMOVED to see that all four rockers arms and valves move correctly.


Well, it looks like I will have to try checking the valves :~(

I cleaned the carb with no success. It really looked pretty clean anyway.
But, I went ahead and cleaned it, but it is still "popping".

It might be a few days before I can check the valves...so if anybody else has anything to add, please do.

Thanks.

 

[J_J]

I had a similar problem on a 25 hp Kohler engine, I fixed my problem by cleaning out the fuel shut off solenoid. It should be on the bottom of the carb bowl.

 

[Barryh]

A grim possibility is a broken or sticking intake valve. To check that, removed the valve covers (after disconnecting the fuel line) and crank the engine WITH THE SPARK PLUG WIRED DISCONNECTED OR THE PLUGS REMOVED to see that all four rockers arms and valves move correctly.


Well, it looks like I will have to try checking the valves :~(

I cleaned the carb with no success. It really looked pretty clean anyway.
But, I went ahead and cleaned it, but it is still "popping".

It might be a few days before I can check the valves...so if anybody else has anything to add, please do.

Thanks.

Last fall my 18 hp Robin was running pretty rough, so per J.J.’s suggestion I cleaned the fuel shut off solenoid. Made a big difference. Engine runs much smoother now. You may want to at least give it a try before moving on.

 

[ldabe]

I had a similar problem on a 25 hp Kohler engine, I fixed my problem by cleaning out the fuel shut off solenoid. It should be on the bottom of the carb bowl.

Thanks JJ & Barryh,
I will try cleaning out the fuel shut off solenoid as suggested.
Probably will not get to it until this weekend, to many other irons in the fire for Thursday and Friday.

Thanks again, and if anyone has anything else, please jump right in.

 

[ldabe]

Thought I would bring this up to date.

I was drowning in other projects/businesses (that bring in money) so I figured I would just take it in and let someone else who has the time/place/tools and knowledge to work on this.
I went to the Robin site to find someone to service the engine in my area...8 miles down the road...so far so good.
Service man said approx. $200 to find/fix the popping problem, change eng. oil, hydro oil, hydro oil tank gasket, fix a broken zerk fitting. I supplied the eng. oil filter & hydro oil filter.

One full month later (after 3-4 calls...part on back order...ignition coil) and $400 dollars above the quote, I have the PT-422 back.

Labor: $180
Material: $413.56
Tax: 24.81
Total: 618.37

Majority of price for parts/material was for 2 ignition coils at $116.88 each.
There was a few other material/parts not mentioned that came to approx. $35-40 bucks (no big deal).

The 1 month wait, was what bothered me the most.
The parts/materials I can understand.

But now...
I was not able to use it for about a week went brought home because of other priorities.

So I went out today to do some much needed mowing. Hooked up the deck and let the grass fly for about 25-35 minutes, with an outside temp of approx. 92 degrees, and humidity at approx. 85.

I looked over my shoulder and notice the hydro cooler fan was not operating!
Headed back to garage, turned off engine and let cool down for about 30 min.

Went out to see if I could find problem after looking at PT's "Power Trac Wiring Diagram".

The diagram has a wire going from the cooler fan to a cooler fan "thermal relay" connection. Then on the other side it has another connection that is 'suppose' to have a wire (white) what looks like a harness (SO #14-5).

I don't have any wire connected to this other side of the "thermal relay" and don't remember if there was one (don't see any wire hanging with that type of connector) before I took it in for service.

SOS ... need help!

Anybody understand this mess, or have any suggestions? Please ;~)

Thanks in advance,
Abe.

Edit: 'suppose' to have a wire (white) what looks like a harness (SO #14-5).
Should be: wire (white) what looks like it goes to a harness (SO #14-5).

 

[BobRip]

Abe, I looked at my unit and this white wire goes into a cable harness which was lying against the left hand side of the engine compartment. It is almost straight to the left from the "thermal relay. It looks like it's inside a tygon (clear plastic) tube. The cable harness is hiden under the lip of the engine compartment. You can reach under that lip and find it, if your unit is just like mine. There is a big piece of heat shrink around the cable there and the white wire comes out of the heat shrink tube, runs forward a few inches, and then backward and up to the "thermal relay". If this does not help I can take a picture.