Engine Leans Out At Cruising / Light Throttle

[Charlie Brown]

A bit of backround. 1962 413, very mild cam. Over the winter I pulled the engine to re-seal the engine. Removed the heads and had them reconditioned. There was quite a bit of oil fowling in the head chambers and on the top of the pistons. I re-assembled the engine with all new seals. The only change was to use Fel Pro Blue .039 head gaskets to replace the factory .022 steel units.
The engine ran perfect before tear down. After re-assembly the engine would surge at all speeds. I did rebuild the 1405 Eddy carb that is on the engine.
The first thing I did was to advance the initial timing from 10 degrees to 16. I also installed larger primary jets in the carb, using the Eldebrock tuning chart as a guideline. Went from #98 jet to #101. These two changes helped quite a bit, but the lean cruise condition still exists.
I'm not sure why I'm having this issue. Except for the different head gasket thickness, I didn't change anything. When leaning into the gas pedal, the engine smooths out and has plenty of power.
I checked the following. Engine vaccuum at idle (800 rpm) is 15 degrees, but at 1000 rpm, it's 18 degrees. Initial timing is set at 16 degrees at 800 rpm and is all in at 37 degrees at 2800 rpm.
The vacuum canister begins to move / engauge at 12 degrees vacuum. Stamping on canister arm is L9 and is an adjustable unit. Not sure how much advance is built into this canister.
I'm posting a couple of pics of my plugs. To me they still read lean.

Not sure what my next step should be. Perhaps go the next step up in jetting or reduce the amount of vacuum advance at cruise or?

 

[68-500]

Did the intake seal properly when reinstalled? Sounds like a vacuum leak from here. If it ran well before.

 

[pnora]

Did you rebuild the carb before or after the running problem started? Did you replace the timing chain?

 

[Orig69]

The spark plug gap on number 7 doesn't look right maybe it's just the picture, other than that the spark plugs look good.

 

[66 Sat]

Did the intake seal properly when reinstalled? Sounds like a vacuum leak from here. If it ran well before.

If it was a vacuum leak would that not show up on the vacuum gauge i.e. unsteady needle?
I know when my intake had a slight internal oil leak into 1 cylinder the needle had a slight rapid flutter. After I replaced the intake gasket and fixed the leak the needle was rock solid.

 

[Charlie Brown]

Did the intake seal properly when reinstalled? Sounds like a vacuum leak from here. If it ran well before.

Pretty sure it's installed correctly, but I'll check it again.

 

[Charlie Brown]

Did you rebuild the carb before or after the running problem started? Did you replace the timing chain?

Carb rebuild was done at the same time as the engine re-seal. Timing chain was still good.

 

[Charlie Brown]

If it was a vacuum leak would that not show up on the vacuum gauge i.e. unsteady needle?
I know when my intake had a slight internal oil leak into 1 cylinder the needle had a slight rapid flutter. After I replaced the intake gasket and fixed the leak the needle was rock solid.

Vacuum gauge reads steady so I think there is no leak, but I will double check.

 

[Some Car Guy]

That is the 600 eddy, right? I recall that one being an economy carb and that would make me think it’s set up on the lean side. Might just need a rod swap to work better with your cam.

 

[Charlie Brown]

That is the 600 eddy, right? I recall that one being an economy carb and that would make me think it’s set up on the lean side. Might just need a rod swap to work better with your cam.

It is a 600. A rod / jet change is my next step.

 

[furious70]

The oil fouling may have been masking lean before. Is your spray carb cleaner around the intake and there's no idle change then it just wants to be richened up it seems.
My experience has been all eddy carbs were lean out of the box

 

[pnora]

Carb rebuild was done at the same time as the engine re-seal. Timing chain was still good.

I would try a different known good carb.

 

[gtxrt]

600 cfm carb on a 413 is too small. bigger than stock cam besides. even if it is not your problem a 750 cfm would give you a lot more performance.

 

[furious70]

600 cfm carb on a 413 is too small. bigger than stock cam besides. even if it is not your problem a 750 cfm would give you a lot more performance.

While I agree that's not making it lean.

 

[gtxrt]

While I agree that's not making it lean.

no but adding 6 degrees of timing will. the stock jet size in a 1405 is 100 so you went back to near stock. the metering rods should be 70-47 you can change it to a 68-47 or 68-42. put the 98 jet in the secondaries which should be 95 stock.

 

[Texas97]

If it was a vacuum leak would that not show up on the vacuum gauge i.e. unsteady needle?
I know when my intake had a slight internal oil leak into 1 cylinder the needle had a slight rapid flutter. After I replaced the intake gasket and fixed the leak the needle was rock solid.

is this gospel on vacuum gauge? if so, then ive got a leak as my vac gauge bounces some. guess i need to start spraying carb cleaner

 

[BSB67]

is this gospel on vacuum gauge? if so, then ive got a leak as my vac gauge bounces some. guess i need to start spraying carb cleaner

No don’t spray cab cleaner. That method maybe work 50% of the time. Simply cup your hand over the carb a listen carefully to how the engine rpm changes. It takes practice. A leak will cause a slight rpm increase before it dies.

Did you ever say why you think it’s lean?

 

[Charlie Brown]

I think it's lean because because it surges at light throttle. Just checked for vacuum leaks using propane. Seems OK. I did determine that the distributor advance pod was pilling plus 18 degrees advance. This puts me at 55 degrees total advance cruising. I dialed back the vac advance 5 degrees, but that made no difference, maybe a little worse. I'm going back to play with the jets / metering rods.

 

[Charlie Brown]

no but adding 6 degrees of timing will. the stock jet size in a 1405 is 100 so you went back to near stock. the metering rods should be 70-47 you can change it to a 68-47 or 68-42. put the 98 jet in the secondaries which should be 95 stock.

Current jet / rod combo is 101 / .068 x .042. Think I'm going to try 104 / .073 x .052

 

[furious70]

That is enough cruise timing to induce lean surge in my experience. If it likes the initial and mechanical timing where it's at right now I'd back off more of the vacuum advance.
A quick test is to plug the vac advance and see if the surge is gone.