1600 DP driving me nuts...

What kind of carburetor? Can you hook up a vaccum gauge at idle with the timing set back around 5-7 degrees to see what it reads? Have you tried spraying carb cleaner around the ends of the throttle shaft at idle?

I had two bad 'brand new' carbs in a row with similar problems to yours. If it is a pierburg 34pict-3 you should probably check the fit of the throttle shaft in the casting. The new ones I've handled have been worse than a well-worn bocar in this regard.

Chris

Did this engine run properly at one time? I mean, with the new cam?

On the off-chance that it has never run right, the cam could be installed one tooth off .

Speedy Jim

Chris: I've had 2 carbs - one good Solex, one new Pierburg, both 34Pict3, with little/no change.

I can adjust the volume screw on carb up/down and the idle mixture screw in to "starve" the motor or out to richen it - it reacts just like a normal engine, but all the while the exhaust is eye-watering rich and the idle very lumpy (at best).

Jim:The motor ran better, but has always stumbled off of idle to midrange, no matter where the accel. pump arm is set. I didn't build the motor. Question: Would anyone ever intentionally jump the cam by a tooth for midrange/upper range performance gains? Seems like a no-brainer when you're building a motor to check the cam/crank gear relationship. Thanks, Bill.

Oh, it can happen quite by accident (cam gear)!

Is it possible that the eye-watering richness is due to mis-fire rather than rich mixture? It wouldn't have to be mis-firing on every stroke to produce raw fuel effect.

On the stumble off-idle, try this test: Engine warmed up and idling, out of gear. Very, very slowly pull the throttle arm off idle. Revs should come up evenly without dropping off or (worst case) trying to stall.

If it fails this test, look for clogging in the 4 idle ports just above the throttle plate. The trasition between them is supposed to occur seamlessly.

Speedy Jim

"Chris: I've had 2 carbs - one good Solex, one new Pierburg, both 34Pict3, with little/no change.

I can adjust the volume screw on carb up/down and the idle mixture screw in to "starve" the motor or out to richen it - it reacts just like a normal engine, but all the while the exhaust is eye-watering rich and the idle very lumpy (at best). "

A while back I had a 1915 engine that was doing this, and it was an overly restrictive exhaust that was partially to blame. Idle was always rich, HC's were off the chart..and I could not get the idle leaned down. I took the baffle out of the stinger..and whala, it cleaned up considerably. Going on a few assumptions here...if you have a stock exhaust, are the peashooters pushed all the way into the muffler by any chance?

I'd still like to know how much vacuum you are drawing at idle and to know what happens to the vac gauge as you slowly advance the throttle. As you leave idle it should momentarily lose vacuum and then come back equal to or slightly higher than the idle reading. Continue to about

3000rpm. Progressively decreasing vacuum could mean an exhaust restriction.

If your idle vacuum readings are very low then things lend themselves more easily to the cam possibly being installed incorrectly. If the needle is bouncing around at idle we need to know how much it is moving in terms of inches of mercury on the gauge to make a guess as to what is wrong. The fact that you need 20 degrees of advance at idle to keep it running is probably a bad sign. If you return the timing closer to stock and see the vacuum drop off with it sounds like a cam timing problem.

Chris

Checked the vacuum: 30" steady at 2500-3000; Idle is a different story - severe bouncing from 0 to 15 - 0", etc. The engine will sometimes idle well, then just won't hold an idle. Put new plugs in, new wires, double checked carb, blew-out jets, passages, etc. and it ran a little better, but once driving (especially after running at 3000 rpm and coming to a stop) the motor wants to die. I even checked my engine ground. Also, I removed the rear section of the exhaust, but no improvement. The car is very "jerky" on acceleration - bucks a lot unless I jump the idle up and richen it to the point where it's almost dumping raw gas out the pipe. Hard to explain, but when idling "well", motor sounds lumpy; when idling "bad" it sounds like a motor that's flooding and eventually dies, but the needle valve isn't stuck and the float bowl isn't overflowing. Thanks, Bill.

Forgot to mention: Vacuum readings were taken from the "bus vacuum brake port" on the intake below the carb. Plugs are NGK B7hs @ .024. Thanks, Bill.

With the needle bouncing as severely as it is at idle I think a compression check is warranted. Hopefully that will let you narrow it down to a specific cylinder and/or head. Your problem might be a bent valve that is intermittently sticking.

Chris

I've decided to pull the motor & tear it down....I'll let you know what I find in there. Bill.