Increasing idle

[Eric Corwin]

Hi,

Sorry to keep asking what are probably very simple questions but this is all pretty new to me and I want to understand what I'm doing. So:

This is in regards to my '69 1600. I've now got the cooling system under control and I adjusted the idle on the carbs (probably poorly) acording to the service manual and the car seems to idle nicely at a fairly low rpm (the tach cable is messed up and the replacement too short, more about that in another post). After I rev the engine soon after turning the car back on it comes right back to idle perfectly. However, as the engine gets hotter (about 5 mins) the idle won't come all the way back unless I really spike the throttle. After about ten minutes even this doesn't work and the engine is now idling at (I'm guessing) around 3-4000 rpm. At this point when I turn the car off the engine shakes around a few times and then backfires and then stops (probably because something is still trying to feed it lots of fuel?). However, if I step out of the car and manually push down on the throttle I can get the idle to return to normal.

I replaced the throttle return springs (which were a bit worn) with stronger ones and this helped the problem a little, giving me about 15 minutes until I can't get the idle back down. So it seems that something is expanding as it gets warmer and sticking to something and providing too much resistance for the throttle return springs to do their job. Searching for other reports of similar problems I saw a suggestion to spray carb cleaner around the carbs to check for leaks but I couldn't find any. So it seems that it's probably something mechanical (and dirty). However, I'm more than a little reticent to start taking things apart on the carbs and trying to clean them without some kind of guidance as to what needs to be done. So, any advice on what could be sticking?

Also, are there any roadster clubs around the Chicago area? I think I could really benifit by having a couple of knowledgeable people look over things with me.

I hope I get it fixed soon 'cause I was driving around at dusk last night testing out the problem and it was so much fun.

Thanks,
Eric

[spl310]

First, remove the stronger throttle return springs unless you want to spend money to replace the throttle shafts. The heavy springs cause excessive wear.

Second, this is a simple fix that will make sense. Loosen the throttle cable at the linkage "drum" and have a little slack in it. What is happening is that at idle, the cable is adjusted properly. As the engine compartment heat rises, the cable outer sheath expands a little, and the cable does not want to return to the idle location. If you have some slack in it, then it will not be fighting itself and will return to idle normally.

I hope that this helps!

[Minh]

I just learned something the other day while talking to Mike Kerr.

Old SUs tend to, when they get old, suck air through the shaft hole in the throttle body. It is becuase the gasket is made of paper. So, when you finally adjust for idle while the butterfly is closed the moment throttle opens up your mixture is automatically set to be rich.

I don't know how true this is or if he was trying say I will be better off in the long run with the ball SU throttle body.

Hope this helps...