Hesitation while in gear

[Clucas]

My late model RWC A4 is in very good to excellent condition. Did some work last spring which included the following:
- Rebuilt carb
- New Racor and polishing filter elements
- Indigo PCV valve
- New plugs, points, rotor, condenser and spark plug wires
- New hot section, mixing tee and anti-siphon valve
- New manifold gasket
- Oil change

Starts right up and runs at normal engine temp. Here’s what has me stumped… While in neutral, the engine responds immediately to any throttle adjustments – increasing or decreasing rpms without hesitation. While in gear though, the response to an advance in throttle is very sluggish – eventually the rpms catch up, but it will take sometimes 5 seconds (or more). Throttling down while in gear is immediate. This is a new behavior this year. Prop (2-blade folding Martec) is clean but feels like I have less power this year. I can turn the shaft easily by hand -- it is not bound in any way.

After installing the PCV valve, I adjusted the idle jet per Tom Stevens' instructions. I’ve purchased, but haven’t yet installed, an adjustable main jet, but don’t hold much confidence that will be the solution. New hot section is almost identical configuration to what I replaced (mixing tee is different).

Thanks in advance for any thoughts.

[hanleyclifford]

Your narrative suggests a vacuum leak or other leaning condition. Try turning the idle adjusting screw in by 1/4 turn stages.

[smosher]

Sounds like it runs rich, I would turn out the idle mixture

Steve

[Dave Neptune]

I'll bie the carb!

Clucas, what you are describing sounds like a classic main jet a bit dirty IE idles fine but sluggish responce under load. If it isn't that it could be you are loosing fuel preassure although a bit less likely as when the F/P drops there is usually a point at which it just won't run as you advance the throttle slowly.
It isn't that big a deal to pull or blow out the main jet to clean with the carb still inplace. I suggest starting it and then running it out of fuel to minimize the fuel to be let out of the carb. Do catch what comes out to inspect.

Dave Neptune

[Dromo]

check the firing order of the spark plugs ,you might have some wires crossed
Rick

[Clucas]

Diagnosing Vac Leak & Exhaust Steam

My trusty A4 experienced some hesitation issues this summer -- found it to be running a bit rich, but still felt I was missing power that I had last season. Ran fine in neutral but under load would hesitate and then surge. I'm thinking it may be the main jet, but open to other ideas.

Another wrinkle... as the engine would warm up, I would get some steam in the exhaust. No water in the oil, engine temp is fine and never overheats. I replaced the hot section last spring -- had the manifold off and replaced the gasket. Also added an Indigo PCV valve.

Possible causes? Here's what I'm chasing down:

a) Did an acid flush after she was hauled (amazing what came out). Exhaust flow was acceptable prior and even better afterwards.

b) Replacing exhaust hose this winter. Reason to believe it's ancient and wonder if the inner wall is partially collapsed which might cause steam from partially trapped water. (??)

c) Possible bad seal between manifold and block resulting in power loss? Planning to loosen, support from underneath and re-tighten (in case it wasn't seated properly).

d) Testing PCV valve - possible bad valve?

Feel like I'm chasing a ghost or two here -- would welcome any thoughts or suggestions. On the power loss front, a vacuum leak was suggested -- best way to test?

Thanks in advance for any insight.

Chris

[Antibes]

Remove the pcv and tape over hose, or fill hole in spacer as a diagnostic to rule out pcv as your source of problem.

[Dave Neptune]

Surging

Chris what type of fuel pump are you using?

Dave Neptune

[Clucas]

Chris what type of fuel pump are you using?

Dave Neptune

I have a mechanical fuel pump which I'm considering rebuilding over the winter. Noticed this summer that if I adjust the idle way down, the engine will rhythmically increase in rpm every :05-:10 - not a big surge, just a slight increase in rpm which I attribute to the fuel pump.

Engine runs great in neutral - quiet and smooth.

Going to rule out PCV valve as suggested above.

[Clucas]

Remove the pcv and tape over hose, or fill hole in spacer as a diagnostic to rule out pcv as your source of problem.

Thanks, good idea. Would love it to be as simple as that.

[Dave Neptune]

Easy check!!!!

Chris, a common symptom of the mech. fuel pump going out is surging often at idle however it can happen at almost any RPM range. The carb draws a bit more fuel than the pump can deliver so the engine begins to slow and the fuel pump catches up then runs back out again. You can easily check this by pumping the bail on the pump when the symptoms start. This will progressively get worse until it can't catch back up.
Why were you planning on the rebuild? Do you have any other symptoms regarding the F/P that led you to a rebuild other than the surging?

Dave Neptune

[dvd]

Dave

I was just going to refer this issue to your most recent post on my last surging idle post. I think you may be right about the fuel pump thing.

dvd

[Clucas]

Chris, a common symptom of the mech. fuel pump going out is surging often at idle however it can happen at almost any RPM range. The carb draws a bit more fuel than the pump can deliver so the engine begins to slow and the fuel pump catches up then runs back out again. You can easily check this by pumping the bail on the pump when the symptoms start. This will progressively get worse until it can't catch back up.
Why were you planning on the rebuild? Do you have any other symptoms regarding the F/P that led you to a rebuild other than the surging?

Dave Neptune

No other reason for the rebuild other than age (of the F/P... ) and the fact that it's probably about time. Would rather do it in the off season and on the hard than lose time sailing time in the spring. I don't think this has anything to do with the hesitation issue I've reported while in gear as the engine throttles up and down smoothly while in neutral.

[Clucas]

Dave

I was just going to refer this issue to your most recent post on my last surging idle post. I think you may be right about the fuel pump thing.

dvd

Yup. Already on it. Thanks!