Give Gas At Startup?

[Gretz]

New-to-me 82 SC. The previous owner of my 82 SC told me that you should never give it gas during startup. Doing that, he blew the airbox (no pop-off valve at the time) and had it replaced with a pop-off valve installed. The car is having some starting issues and it seems a little gas would help to get it started (I'm working on diagnosing those issues).

Can I give it some gas during startup now that a pop-off valve is installed?

[gazzerr]

I think it's more of a risk with the earlier cars (pre 81?) that don't have the metal spider in the airbox. You risk putting extra unburnt fuel into the intake chamber that all the runners connect to so there's a chance you could flash it off and blow up the airbox. A CIS that's working properly doesn't need you to touch the pedal to start it. If the CIS is not functioning properly then there's always the risk of a backfire that could toast the airbox. I've read here that the pop valve can actually leak from a previous backfire cause a lean condition and then cause another backfire which can blow up the airbox too!

The fix begins with checking fuel pressures to determine the condition of your warm up regulator (WUR) and checking for vacuum leaks. After 30 years the glue holding the airbox together fails and they leak, causing what you describe as well. It's quite possible your car has had a backfire or two in its history and the airbox is leaking from that. Search for "CIS for Dummies". It's the go to thread for re-conditioning your CIS.

[Coastr]

As stated, A correctly set up cis car doesn't need any pedal to start. Should start after a few turns.

If it's not doing that troubleshoot until it does. They aren't a big carb.

[SCadaddle]

Typical start up with my 82SC is foot just above gas pedal, hit the starter and she lights right off, then a little dancing of the foot on the gas pedal to bring it on to a stable 1200 cold start rpm then it is fine. Is that the way it is supposed to work? Probably not. But then again I only drive the car maybe once every 2 weeks. Rarely have I ever had the pop off valve do it's thing while starting the car like this.

[RSBob]

Never pump the gas with the ignition on, starter not engaged yet, on a CIS car. I did it once, like I used to do on my MFI car, and blew the air box. As stated above, if everything is set up correctly, just hit the key and it should start. You can give it gas after it has started to clear the crap out.

[SCadaddle]

I don't think that working the accelerator pedal on a CIS 911 does any more than opening the throttle body. It's not like a carburetor where you are injecting fuel into the intake manifold by working the pedal, running or not. What it would do shortly after cranking and start up would be to put the engine in a lean mixture situation and that is what creates the backfire/air box explosion/pop off valve operation. Am I wrong?

[Gretz]

I look forward to the answer to SCadaddle’s question above. Seems correct to me.

An update on my situation: There’s definitely some troubleshooting that I need to do and that will be happening in short order. I am plunging into CIS For Dummies and the CIS Primer. After my fuel lines were replaced recently the mechanic told me I’d need to come back for a mixture adjustment. That’ll be very soon. I just wanted to make sure I could get the car started in some manner. Today when cold the engine was starting and then dying. Then when got it going again I gave it some gas and kept it up around 1200. After it warmed up for 3-5 mins it seemed fine. I went to drive it with no issues. Came back and parked. Started it warm and it fired right up perfectly. I’ll check the cold start again tomorrow. But at least I know now that with a little gas I can at least get it going and get it to my mechanic for the mixture adjustment or troubleshooting if I can’t figure it out myself. Thanks for all the help folks.

[SCadaddle]

I think a lot of folks have used this technique to get the mixture "pretty close".

[Gretz]

Great video. Very worthwhile to see it in action. I stumbled across some of the same info in the CIS Primer. Might be helpful to others to see it explained in print: 911 CIS Primer - Testing: Mixtures

It seems like in the video he’s going back and forth adjusting the mixture and the idle. Is that correct? Seems like you’d adjust the mixture and once it seemed correct you’d adjust the idle.

Also, my mechanic mentioned he needed to check/adjust the mixture both from a cold and warm start. But the instructions I’ve read discuss setting the mixture from a warm start only. Do I simply set it warm and then check/adjust the following day from a cold start?

[RSBob]

There are differences in early and late CIS systems in terms of fuel handling and perhaps proclivity to airbox detonation. All I know is that my 82 box blew after two pumps on a cold engine.

[gazzerr]

The worst thing to do is to mess with the mixture before you know the CIS is functioning correctly. You just end up masking issues and making the problem worse and more difficult to diagnose. Once you are sure you are free of air leaks (remove the oil tank cap and if your rpm's drop then you know you don't have a significant leak) and your timing is right, WUR, AAR, AAV, deceleration valve, O2 sensor, frequency valve, micro switch, throttle position switch, TTS, OXS relay, dizzy vacuum pod, temp sensor, injectors, spark plugs, ignition wires, fuel distributor, accumulator, throttle body and sensor plate (phew - I'm sure I've left something out) are working correctly and in spec, then you can set the mixture. There's the method above in the video which puts you in the ballpark, then there's the measured ways i.e. the frequency valve duty cycle signal method from the test pin in the engine bay and the factory adjustment using a gas analyzer. The "dummies" thread goes through all of this. It's a really good read.

There are lots of real experts here like boyt911sc (Tony) that love this stuff and are always ready to jump in and help. He helped me immensely.

I spent a lot of time going right through mine and it now works really well and it's very reliable. If the car has not been sitting it fires up right boom right off the key warm or cold. If it's been sitting it needs to crank for a couple of seconds to build the fuel pressure back and it fires. I still have an issue where in warmer weather the AAR tends to close a bit too quickly and I need to give it a bit of throttle to help it warm up (or just drive off) but it's a 40 year old fuel injection system so I feel like it's never going to be like a modern system. One day Santa will bring me a digital ITB setup like Mr. Kosmal's ... one day ...

[Gretz]

Very good points. I am planning on picking up a gauge to check fuel pressures. Vacuum leaks are more difficult because I’m not a fan of spraying carb cleaner in my engine bay. I wish someone in the area had one of the smoke machines I could use/borrow. I’ll start with the oil cap test you mentioned and go from there. Thanks again guys.

[SCadaddle]

Ha! I've watched that video a few times, but just now noticed the "wildlife" in the background just before the 3:00 minute mark.

[gazzerr]

Nice turtle! You don't need to use carb cleaner. Search for boyt911sc's positive pressure test where he uses a vacuum cleaner and some soapy water in a spray bottle to look for leaks (safest). You can pressurize it through the exhaust pipe and put a rubber glove over the throttle body.

There is also the cigar test but I'm not a smoker . Guys have also made smokers out of a paint can, an air tank and air hoses/fittings, some wire, 12V and a bit of mineral oil. I don't want to set myself on fire though.

[Bob Kontak]

Originally Posted by Gretz

Very good points. I am planning on picking up a gauge to check fuel pressures. Vacuum leaks are more difficult because I’m not a fan of spraying carb cleaner in my engine bay. I wish someone in the area had one of the smoke machines I could use/borrow. I’ll start with the oil cap test you mentioned and go from there. Thanks again guys.

When I have done the spray test, brake cleaner works. Not as volatile.

However, I have started this stuff on fire on a Ford Taurus with the FWD sideways mounted six. The rear passenger side plug was cracked and had absolutely no problem setting the fluid off. On the downside it is not as volatile so burns longer.

Hope this sets you at ease.

[fred cook]

I don't have to use the throttle to start my SC, even after it has not been used for several days.

[Gretz]

Neither did I prior to my mechanic replacing the fuel lines. I think somewhere during that process a vacuum leak or fuel issue developed. Going to start troubleshooting soon.

[gazzerr]

If he's pulled a bunch of stuff apart to make room to replace those lines then that's very possible.