On a cold start I have to nurse the accelerator for 2-3 minutes until the engine warms up to prevent it from dying – even with the engine fully choked. The engine was recently rebuilt and runs great once it is warmed up. I’m running a Weber carb and have tried re-jetting the main idle jet (from 45 to 75) to no effect. Any ideas?
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Runs Rough When Cold
- Thread starter johnd
- Start date
John, there should be a fast idle cam on the carb, actuated by the choke, that opens the throttle more than the normal idle stop when the choke is fully choked. Is there such on your carb?
Tom
On the Weber it may not be a cam.
Here's a link to an assembly dwg for the Weber 32/36DGV 5A:
http://www.webercarbsdirect.com/v/vspfiles/weber_carburetor_schematics/3236DGV.pdf
But the part number descriptions are incomplete. See items 55 and 60, they are the Fast idle control rod and Fast Idle loose lever. At full choke they should move the primary throttle to a higher position than the normal idle stop. Not sure how it works but that rod should move when fully choked.
Tom
On the Weber it may not be a cam.
Here's a link to an assembly dwg for the Weber 32/36DGV 5A:
http://www.webercarbsdirect.com/v/vspfiles/weber_carburetor_schematics/3236DGV.pdf
But the part number descriptions are incomplete. See items 55 and 60, they are the Fast idle control rod and Fast Idle loose lever. At full choke they should move the primary throttle to a higher position than the normal idle stop. Not sure how it works but that rod should move when fully choked.
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Key question, Can you see the throttle move off the idle stop at full choke? If not, then there's the problem. My Weber is converted from an automatic choke and does not have a Fast idle lever so I do exactly like you for the first 3-5 minutes. If full choke does not move the throttle enough to get fast idle you have to move it with the accelerator pedal instead. On the electric choke versions there is actually a Fast Idle adjustment screw, but I can find no info on how to adjust the fast idle speed on a manual version. Maybe you need to bend that control rod (#55) more.
Tom
Tom
Thanks Tom - there is still some room for the fast idle cam to move before it hits the stop. I'll try bending the rod some more.
Its been a while since I've looked at a Weber, but isn't there an adjustment screw that contacts the stop?
Bill
Bill, the electric choke version has an idle adjust screw acting against a cam. But I assume John has a manual DGV type. Instead of an adjust screw and cam it has what they call a "Fast Idle Loose lever". See the dwg I linked above. From the dwg I cannot understand how it works. But I have a paper copy of this dwg that has a more complete description of each part. #55 is the "Fast Idle Control Rod" . It pulls up on #60, the "Fast Idle Loose lever". #59, 61, 62, 67, and 64 are all part of the "Loose lever assembly. Note that all these levers have round holes, so they float "loose" on the throttle shaft. So I do not see how they can rotate the throttle shaft to increase idle speed. Unless maybe the wavy washer , #61, creates enough friction against washers #59 (with flat holes keyed to the shaft) to move the throttle. I have found nothing on line to describe how to adjust fast idle on a DGV manual choke version.
I am 90% sure that John's problem is that the "fast idle lever", is either not moving the throttle shaft at all or not rotating it far enough to get the idle speed up. But I do not know how it is supposed to work. If I am correct about the wavy washer and friction, maybe he has no wavy washer or maybe the assembly is too well oiled and has no friction.
Tom
I am 90% sure that John's problem is that the "fast idle lever", is either not moving the throttle shaft at all or not rotating it far enough to get the idle speed up. But I do not know how it is supposed to work. If I am correct about the wavy washer and friction, maybe he has no wavy washer or maybe the assembly is too well oiled and has no friction.
Tom