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Hello to all,

When my Speedster (CMC-2110) has been sitting for a few days and I go to start it, it takes several try's to get it to fire-up. When it does fire-up it revs at a high RPM for a few seconds and goes down to around 1000 RPM. On some occasions it will stay at a high RPM until I goose the accelerator and then it revs down to 1000 RPM (is something sticking?) I am not hitting the accelerator at all when I turn the engine on. Please advise if there is something that I am doing wrong or if there may be technical problem....all opinions are welcome......Thanks!

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Yeah, it's OK. There's some relearning things that you forgot, and a few more things that are unique to dual carbs on a flat 4.

I strongly suspect your fuel bowls are drying up when the car sits. This is pretty common with Dellortos and Webers. It's a super-good reason to have an electric fuel pump. If you don't, you need to crank and crank to fill the bowls with the mechanical pump. If you don't have an electric pump, I'd get one. There are other good reasons to do it, but this one keeps you from needing to crank the car for 15 seconds to fill the bowls.

If you do already have an electric pump, the cold-start process is as follows:

Turn on the switch. Wait 10 or 15 seconds until the pump tone changes (you can hear it), indicating the bowls are filled. Pump the accelerator while cranking - it'll take several pumps to squirt fuel down the throats. The engine should catch and start.

Once it does, you'll likely need to "clear out" the fuel you just shot down the throats, so I blip the throttle two or three times, before allowing the accelerator to "snap" back - I don't try to ease the throttle back to idle, I allow the return springs to close the butterflies with their pull force (a spring doesn't have as much force when it's nearly returned).

It'll probably barely idle, and maybe not at all. If not, blip the throttle a few times, allowing it to return to idle until it will stay running. If you are timed and jetted right, it'll probably idle at just over 750 RPM when cold and closer to 1100 or so when warm. You can dial it down further, but it may not stay running when cold if you do.

Every engine behaves differently. Webers and Dells don't have chokes - it doesn't take very long at all for the intake manifolds on a dual carb setup to warm up, as they are sitting right on the heads.

If my 40mm Dellortos are any indication, I would be surprised if it idled faster than what your normal idle rpm is on a cold start.  

If anything, I would expect it to try to idle lower with a bunch of coughing and puking until it warms up enough to sustain an idle (slightly lower than normal).  That should take 20-30 seconds at least and a minute at most.

You also said that if you rev it once or twice it'll drop down from the fast idle to something more normal.  That, to me, sounds like something's sticking somewhere - Either that, or you have mechanical choke plates on your carbs with a fast-idle cam that gets knocked down when you tap the gas.  I have not seen such a thing on either Webers or Dellortos, but that doesn't mean they don't exist.


I've got Webers, not Dels, but the two should have similar cold start characteristics.

I'm with Gordon. I've never seen a car with either of these carbs 'race' on cold start - it's usually just the opposite. And the most obvious explanation (there will be others) is that something is 'sticking somewhere', as Gordon suggests.

Here's a simple thing to check. Find the idle stops on your carbs. On each one, there will be an adjustable screw that holds the shaft of the carburetor open just a bit at idle. (This is how you normally set the idle speed.) You should see how the shaft comes to rest against the screw. Make sure the fitting on the shaft that's supposed to contact the screw is actually doing that for both carbs when the throttle is released.

You can check this with the engine off. The shafts of both carbs should return all the way 'home' (against the idle stop screw) after the throttle is opened, slowly or hard, and released.

It could be something inside the carbs that's hanging up (or something completely different), but this is a simple thing to check for starters.

The shafts on both carbs should move freely, with no binding, through their whole range of motion. With Webers (I don't know about Dels), depending on what type of throttle linkage you have, sometimes the internal springs of the carbs aren't strong enough to close the butterflies reliably at idle, and external springs must be added. It's possible that one or more of your return springs may have broken or come loose.


Last edited by Sacto Mitch

It is unlikely, but altogether possible for this "high idle/surge" to be something else.

It may NOT be the carbs at all. It could possibly be the breaker plate in the distributor is hanging up or the advance spring(s) is shot or missing. That would do it as well. It's also possible that the distributor turned a bit, and idle advance is higher than it's supposed to be. This would increase the speed, enough to be getting into the advance curve which adds even more advance. Throttle plate closed, eventually the engine starves a bit and the speed slows.

90% of carburetor problems actually ARE ignition problems. Check there first before messing with carbs, other than verifying throttle return/linkage sticky-ness.

As everyone mentioned: Accel pump vs choke, requires a few pumps.

My ritual is like Lane’s: Turn on ignition and let fuel pump run for 5-6 seconds, pump the accelerator 2-3 times, hit starter. Depending on how recently I’ve driven it, it will either idle about 800 rpm or die. 1 more pump and hit the starter again, and gently run the run the revs between 1-2K for about 10 seconds then it will idle.

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