Hi All, My first post on here, I have tried searching for an answer, but forgive me if this is a stupid question! I have a problem with as it doesnt just drop back to idle quickly, it keeps high revs and slowly comes back. The idle was too fast when it came back from a rebuild at a specialist guy but it sat around for a while and when I went back to it it wouldnt start. I diagnosed this as no fuel, I have cleaned out and cleaned out all the jets and used the birdmans process to set and balance up the carbs. They are all balanced nicely with the meter. The problem I have is birdman says go 3 turns out on the idle mixture screws, but if I do this I cant get it to idle much less than 1800 rpm. So I wound them in to get to 2 turns out from closed and it will then idle at around 700, so I can then use the throttle stops to set the idle to 900 ish, as per birdmand process. That is all ok but when you blip the throttle it doesnt return crisply to idle, but very slowly. It seemed to get worse as it got warmer. The idle jets are 50 I read various articles and came across some stuff about the fast idle spring / setup. I had a look at that and seems it is disconnected (the adjustment screw had been removed). So I am not sure what to do next, does anyone have any ideas on what might be the cause of my idle problem. Its just the idle - the pickup and acceleration is really nice, if it would to idle and not feel like the throttle is sticking it would be great Thanks Roger
This is not the best way to do it. When you go to 2 turns you are probably just causing some cylinders to miss and not contribute at idle. You need to reduce the airflows by closing the throttle plates more. Also, make sure the air bypass screws are as closed as possible -- either both should be fully closed on each carb, or one should be closed and the other opened just enough to get the same airflow in both barrels. When you are at 1000 RPM warn idle, the airflow in each barrel should be something like 3.5 Kg/hr.
Have you checked whether the throttle is indeed sticking or not? You are making carburetor adjustments which do not seem to be helping the problem. I would take a look at the throttle linkage at the accelerator pedal and at the carbs and check for any binding. It has been noted in some prior posts that occasionally the floor mat will interfere with the accelerator pedal and create problems. When you mention that on blipping the throttle the engine does not crisply return to idle, are you blipping the throttle with the pedal or by hand while standing at the back of the car? If blipping the throttle by hand results in a crisp return to idle, this may point to some binding at the pedal or in the cable. I guess what I am saying is check the simplest, most obvious possibilities first. Hopefully the solution is a simple one. Keep us updated.
+1 I was having the same problem with my '79, but was able to identify the sticky throttle linkage right away. I've yet to dismantle my linkage as I wanted to study-up on all the monkey motion first, unfortunately work has had other ideas lately. Good luck and let us know what you find. - Dave
No 308 but 328. During the first days that I had the car same problem. Slow returning idle and too high idle speed. Simplest things first ...... yes it was the (double) floor mat. This placed a bit further back and fastened and since 2 years no problem anymore.
Hi All, Thanks for the replies - Sorry I should have said I did check the floor mats and I have all the air by pass screws closed, I am mostly blipping the throttle at the engine end anyway. I also removed the fast idle cam completely as I wanted to be sure that wasn't interfering with the throttle adjustment. After the posts above I had renewed enthusiasm to have another go. So I set all the idle mixtures to 3 turns from closed, checked all air by passes are closed. I still have good synchronisation between the carbs. I backed of the throttle stops to get it to run at a good idle but it still doesnt return to idle properly. This is where I got to in this video, when I rev it it comes back to a fast idle at about 1600, and then it slowly (after about 30 seconds comes back to my idle at 800 or so, and eventually dies as I have the idles set a bit low at the moment - which is obviously fixable!. I hope you can see the video - I push on the throttle in eth middle to show that its not linkage related and it is back to its stop 20250423_093917.mp4 When I can get it to idle at about 900 for a bit I am seeing about 5 or 6 on my meter, which is a lot up on the 3.5, so maybe there is a clue there? Cheers Roger
Yes, some cylinders not actually contributing at idle (so the others that are working at idle need more air to make enough torque to run the engine at 900 RPM). In that state, just close the mixture screw on each cylinder one-at-a-time -- if no change in engine RPM/sound = that cylinder is not contributing at idle; if it does change, just unscrew the mixture screw slowly until the cylinder does start running (lean cutout) then maybe go 1/4~1/2 turn more rich.
Hi Steve, Thanks again, can I just clarify - if I get no change at idle when I screw in the idle mixture screw, you say that the cylinder is not contributing, so I would expect that it means that I should unscrew it until the revs start changing and then plus another 1/4 turn The way I read your message it says if the revs do change I unscrew the mixture screw which doesnt seem right! Cheers Roger
Maybe I said that confusingly, but I think it's accurate. The bottom line is that you should be able to (deliberately) cause each cylinder to go from running at warm idle to not running at warm idle and back-and forth by using the mixture screw -- if you can't do that either something is wrong with the carb for that cylinder or the ignition for that cylinder. (I.e., if you are at warm idle, and think everything is working, and then close the mixture screw = that cylinder should stop contributing and you should note a change in the engine operation/sound. If there is no change = that cylinder wasn't/isn't actually working at idle.)
Thanks Steve thats great - success!. Rather counter-intuitively (in my head) winding the idle mixtures out makes it idle better and not overun. I ended up taking them all out to 4 turns from closed and got a nice idle at 900 and about 3.5 on the meter and having a nice crisp return to the idle which is brilliant. I'll take it for a spin tomorrow and see how it drives but I think it should be good. I dont know if I should now try to get the hot idle cam thing working?, do other people use them or is it normally deleted?
I adjusted it to be ineffective -- and most do IMO (and just use the acc pedal to squirt extra fuel and add extra air as needed for the first ~30 seconds after cold start-up before gently driving off). The problem is that that fast idle device mostly only adds extra air for cold-running so you'd also need to use the choke to add extra fuel, and the choke on the DCNF can stick open (regardless of where the choke lever is inside the passenger cabin). Not a serious problem on a non-cat car as you'd just foul a spark plug if the choke spool does stick open, but on the cat-equipped cars is a serious fire risk.
Thanks Steve, I have removed it. Took it for a drive today and it is going great and very pleased, thanks for your help!
Very glad that you've got it sorted -- we can't any F not running right . The others gave some good suggestions for other possible causes for a high idle, but your description of "it keeps high revs and slowly comes back" is very indicative of cylinders working at large throttle openings (because the idle adjustment doesn't have much effect at large throttle openings) but not working at idle (and the high 5~6 Kg/hr at warm idle is another clue in that direction). I've often found that after following instructions that say "Do X to make things right", it can be more useful to then have instructions that say "OK, you think everything is good, now do Y = things should get bad (or different in a certain way), and, if they don't, everything wasn't good" -- often applies to the K/KE-Jet injected F models as well.
