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Newly rebuilt original 2.0 with balanced Webbers. Idle smooth at 1000 rpm. Timing at 30 deg BTDC at 4500 rpm. Very rough off idle to about 2000 rpm, hesitation off line like loading up, wants to stall. Runs best above 2500 rpm with increasing throttle. Any suggestions appreciated.
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Have you been able to adjust mixture screws for each cylinder and found they could shut off fuel and then when re-opened the engine resumes running on that cylinder? If this is not possible then I suspect the fuel galleries feeding the mixture screws are partially clogged thereby limiting fuel flow for the low speed running. Once you open the throttles up you will begin to have main circuit fuel supply which is why the 2500+ RPM operation seems normal.
Hi Paul this is Duffield in NC, one of your old customers. I put the Webbers on that you redid for me recently and used your air and fuel settings and at 1000 rpm had all barrels drawing 4.7 on the synchrometer with good throttle response. After the hesitation below 2000 rpm, I pulled the plugs and nos 1 and 6 were black and I assumed they were not firing. Found some minor issues with the rotor and wires, so replaced cap, rotor and wires. Did the test drive with same results below 2000. Pulled the plugs and with the same result. Nos 1 and 6 are black. Reving the engine without load does not produce the hesitation. I am using MSD with the Tac adapter that is probably 10 yrs old. The old "is it electrical or fuel" issue. This is a new rebuild and I am having some bad thoughts! Thanks for your input.
Checked for plugged idle jets. Very common problem in my experience.
Sorry to hear of your troubles.
I recommend performing Lean Best idle mixture screw adjustment for all six cylinders. With engine warmed up and after air flows are balanced, perform Lean Best in this fashion:
- Remove air cleaner assembly
- Start with cylinder #1 and turn idle mixture screw clockwise 1/4 turn
- Wait 5 seconds and carefully listen to engine to see if it changes idle speed or running smoothness, by carefully I mean get your ear down close to the engine and really listen
- If there is no discernable change in engine running then turn mixture screw another 1/4 turn clockwise, wait 5 seconds and listen
- Once engine reacts to the mixture screw adjustment then open that screw 1/2 turn
- Repeat for remaining 5 cylinders
A couple of comments:
- If engine RPM increases during this procedure then use throttle stop screws (mounted at end of carb and touch the throttle lever arms) to re-adjust idle speed to 900 RPM
- If your first 1/4 turn mixture screw adjustment causes engine running smoothness to falter then open 1/2 turn
- Lean Best tuning is completed once you can adjust each mixture screw closed by two 1/4 turn increments with a resulting change in engine running smoothness
- It may be a bit easier to perform this tuning at 1100 RPM but be careful to not activate the mechanical advance at 1300 RPM or so which will rev the engine beyond idle tuning RPM region
Performing the Lean Test procedure will ferret out a rich or lean running cylinder.
Thank You Thank You That advice has worked and I think I have a car back. What a great organization of people helping people. Did I say thankyou?
Sometimes the magic works.