Rough running for the first 30 min.

[Rick_Powers]

Hello friends,

I have a recently rebuilt A-4 and I love it.

My observation is that in the first 30 minutes of running it, it runs rough (surging), without full power.

After about 30 minutes it cranks hard and well, and leaves a big wake (Catalina 27 doing 6.4 knots).

I have emptied the fuel tank, changed the fuel filter, etc.

I have installed the electronic points in the distributor.

Is it normal to have early rough running (sounds like skipping firing) ?

Is this typical?

[Kaselehlia]

My motor likes to be warmed up well before it runs smooth, accelerates fast and idles flawless.

[tenders]

Rick, what you have sounds to me like a sticking valve that eventually unsticks itself. Are you using Moyer's recommended mix of Marvel Mystery Oil in your fuel?

[msauntry]

Sounds like a carb adjustment issue. It should settle right in after its warmed up, but I think a half hour is a little long. Does it run a little better in that first half hour if you give it a little choke? What do the plugs look like? That can give you a clue as to what's going on in the combustion chambers.

[Rick_Powers]

Reply to the above

The plugs are new. Marvel Mystery oil is in the fuel. Not sure about the choke, but will try that next time out.

Regarding carborator adjustment, what do you mean by that? What should/can I adjust?

Thanks!

[msauntry]

The carb can be adjusted for idle speed and Don sells an adjustable main jet on his site, but the stock one is fixed. This enables you to enrichen or lean out the fuel mixture as appropriate. Do a search on this site for more info on his main jet.

I was guessing it might be a clogged idle jet or main jet that could give you a little bit of rough running, but I reserve the right to be barking up the wrong tree

You can drain the fuel bowl and see if there is any debris that has settled there. Compressed air can also clean out any bits of junk in your passageways.

[msauntry]

Next time you have the problem, play around with various levels of choke and see if that helps the problem. If so, you are enrichening the mixture by choking it and you might be running lean without it. Fix it by cleaning the carb, increasing the main jet size, or adding Don's adjustable jet.

[rigspelt]

You might want to search the archives for posts about surging. This symptoms has been discussed in several threads (called different things), and Don and others have posted some useful comments before.

I don't think switching to the adjustable main jet would necessarily fix a surging problem, but I'm no mechanic.

[Rick_Powers]

Interesting observation

Ok, yesterday I had early warm-up surging.

Today I took it out, and had fine running from the get-go.

Maybe it is no problem, or accumulating something for a week of sitting.

Obsession? Maybe yes...

Thanks for all your great help.

-Rick