Wish I knew more stuff

[n5lp]

My airplane has a carburated O-360. Once in a while, in the last few months, there is an issue after the first start of the day. The fuel pressure goes high, around 7 or 8 PSI, and the engine runs very rough at idle. I think it would die, but I can keep it going by leaning to near idle-cut-off.

During and after the run-up things are much better and the engine always runs great at higher power settings. For the rest of the day there is no further problem.

I'm thinking this is a mechanical fuel pump problem but I don't know how the pump regulates pressure. This weekend, at a fly-in breakfast, I asked two different mechanics about the issue and they didn't seem to have any idea.

Do I just need to replace the pump or is there something else I can do? I have checked that the vent line is clear.

[N941WR]

Larry,

Make sure when you test run your engine as you work through this problem to keep an eye on your CHT's so you don't glaze your cylinders.

Your carb should have been flow (bench) tested and the mixture should be set correctly. If this is not the case, check with the company you got the carb from.

It is possible that you need to have the thing adjusted. Worse case, it is around $600 to have it overhauled.

[n5lp]

Originally Posted by N941WR

Larry,

Make sure when you test run your engine as you work through this problem to keep an eye on your CHT's so you don't glaze your cylinders.

Your carb should have been flow (bench) tested and the mixture should be set correctly. If this is not the case, check with the company you got the carb from.

It is possible that you need to have the thing adjusted. Worse case, it is around $600 to have it overhauled.

I should have mentioned that this engine has about 1,000 hours on it, all in this installation. CHT is not an issue as this only happens after a cold start and only while at idle or near idle. This is an occasional problem only, which makes me think it has nothing to do with adjustments; wear, maybe.

[mannanj]

Larry:

Check your PM's

[Walt]

If 8 psi is flooding the carb then it's time to rebuild it, needle/seat/float assy replacement should do it. Check the new SB out on these so you get the latest and greatest parts for it. The fuel pump sounds ok to me, 8 psi is within limits.

[N941WR]

Originally Posted by Walt

If 8 psi is flooding the carb then it's time to rebuild it, needle/seat/float assy replacement should do it. Check the new SB out on these so you get the latest and greatest parts for it. The fuel pump sounds ok to me, 8 psi is within limits.

I just checked my notes. The OH for my MA3 was $700 in December of 2005 and it was done by AVstar.

The thing was bolted on and worked as expected. 200+ hours now and no issues.

[az_gila]

Originally Posted by Walt

If 8 psi is flooding the carb then it's time to rebuild it, needle/seat/float assy replacement should do it. Check the new SB out on these so you get the latest and greatest parts for it. The fuel pump sounds ok to me, 8 psi is within limits.

...the usual specification is 0.5 psi to 8 psi at the carb. inlet. So the 8 psi is exactly at the upper limit.

If the guages are not very well calibrated, this could easily be above the limits....

However, at 1000 hrs, a new seat/valve assy would certainly do no harm...

[n5lp]

It seems the consensus is that I need to do some carburetor work. Now I have to decide whether to learn about it and do it myself or send it off to a good shop.

Apparently the mechanical pump doesn't really have a regulator but by design should only be able to put out so much pressure?

[Dennis Fox]

Try looking on this site.

http://www.sacskyranch.com/eng.htm

[Geico266]

Originally Posted by n5lp

It seems the consensus is that I need to do some carburetor work. Now I have to decide whether to learn about it and do it myself or send it off to a good shop.

Larry, unless you have a flow bench to test the carb you should send it in.