My apologies if this has already been asked and answered. I am new to the group and I did search the forum I might have missed this discussion.

I just bought a PA24-250, carbureted.

On climb if I turn off the fuel pump on the left main tank the engine sputters and dies unless I am in level flight. The right main does not appear to exhibit the same behavior but to be honest I haven't done a lot of testing. I do not relish being a test pilot.

Any ideas on this? I saw a Mooney discussion that indicated the vent may be blocked.

I am taking it to a mechanic on Friday but would like to be able to give him something to work with before this repair costs more than the plane. I seem to be burning an awful lot of fuel based on my two flights in the aircraft so far. This is something else I may need advice on later after I get this issue addressed.

On the possibly stupid question side. The checklist says to use the fuel pump to prime the engine. I am not sure if the checklist is correct or not given the age of the checklist and changes made to the plane over the years. The plane has a primer. Wouldn't I use the primer since it is a carbureted engine and not fuel injected?

I have a few other anomalies which I will leave for a future post.

Oh, and one day after buying the plane the AI gave up the ghost. Seems to last for about 30 minutes of flight then slowly goes nose low till it hits the stops then flops over and dies. Except strangely it comes back to life when I reduce power.

Oh the joys of plane ownership.

Thanks

Richard,

Welcome to the ICS Forum.

Sorry to hear you are having problems. I know this has been discussed in the past but I couldn't find it either. Does the person who did the pre-buy have any advice?

If I were in your shoes, I'd go read the section pertinent to this in the Service Manual - go to the Home Page under the Tech Tab and be sure to take the plane to someone knowledgeable in Comanches.

Also the Killough POH is available and will have the proper checklist for your aircraft.

While I fly an injected Twin, after an annual, I turned off the fuel pump and the engine ran so rough, I turned them back on REAL fast and landed. Injectors were clogged.

Perhaps some 250 owners will chime in.

I too have a carbureted 250. Sounds like you have two main tanks, no aux. the plumbing for the 250 works such that when you turn on the aux pump it will bypass the mechanical fuel pump. This leaves fuel not moving in that line, which is of course close to the muffler . The heat generated from the muffler can evaporate the fuel in the line. Thus when you turn off the fuel pump you can get some sputtering or rough running due to vapor lock or air in the line.The solution is to use the aux pump for take off and landing only. I usually turn it on when I'm cleared for takeoff and off when I'm 1500agl. If you get a rough engine when u turn it off, just turn it back on for a few maybe 10 sec or so, then off, repeat as necessary, and eventually you will purge any air in the line to the mechanical pump. The 0-540 only needs .5 psi fuel pressure to operate.
Aviation performance products makes an upgraded stc exhaust system for the 250 that is great.
For starting I go mixture rich, fuel pump on to verify its working,ie fuel pressure up and u can hear the two pumps clicking, fuel pump off, I pump the throttle 2 times like an old Chevy , crack the throttle maybe just a tad in and start. i try to keep rpm at min untill oil pressure comes up then 1000rpm. I am in a warm climate so I never have to use the primer for starting.
Your engine should definitely not stop running. Could be a vent line, or fuel selector issue. Good luck . Youv've come to a good source for troubleshooting. There are a lot of knowledgeable folks here. Try the delphi site as well.
Hope this helps
Andrew
7533P

Thanks. I actually have two tip tanks as well but I was told to always take off and land on the mains.

I will have to listen more closely to the boost pump. I haven't really discerned that two are running though I know the aircraft has two boost pumps or at least is supposed to have them.

You will have to help me with the Delphi site. I am not familiar with it.

I operate in a warm clime as well, south Florida.

So much to learn. Thanks again.

It's called the Airworthy Comanche Forum, just google delphi forums, then search for airworthy comanche forum. Its free, and very helpfull.
Matt kurke is in southern florida as well. ComancheGear.com. He is a great resource, especially for gear related issues. Webco are the go to guys for parts and advice.
Others will chime in here. The best advice after 14 years of ownership is try to find a A&P who is familiar with Comanches. If your at all mechanicaly inclined comanches are simple machines and you can save a lot of time, money and agrevation by learning about your aircraft.. If your not, then it's vitlal to find someone who is familiar with Comanche's. Otherwise you pay for the learning curve. The level of experience you can get here and at Delphi is very valuable. Good luck and keep us posted

When u turn on the fuel pumps, no engine running, headsets off you should hear a clicking type sound. The pumps should be located on the right, lower left side of the firewall, open the cowling and you'll see two clylidrical objects. That's the pumps. You can have someoneelse turn them on, if you put your hand on them you should feel them operating. Both pumps must work.

Andrew

A few years back I had a similar problem. When I had climb power the engine would vibrates and cylinders two and four would cut out on me. If I would back off on the power they would kick back in. After getting my injectors cleaned a second time the problem moved to the right side of the engine, cylinders one and three. The only thing that had changed was the location of the injectors. I bought a new set of gami injectors and have been running smoothly since. At least until today. See my next post