Rough Idling

[kevin the chicken]

Hi all,

 

Yesterday after months of messing around with little and annoying jobs, most of which should have been done properly the first time by previous custodians of my S7 redtop, it was time for the mot. Naturally it failed to start, just firing up when the starter was engaged and then dying as soon as the button was released. Cue major panic, check plugs two dry, two wet! (Thats where the bell should have rung) Clean replace and try again.Nope. Check fuel thats ok, spark ok. Nothing. Should have said it has a pair of webers on it. Engaged services of mechanic from garage as it is now one hour to mot. He did the same as me but pulled the leads off the engine one by one and found very little was happening at the front carb at idle.although above idle it seemed to run ok. A couple of turns of something or other improved things enough to be able to get the car to the mot but he was the first to admit that he didn't know enough about them to want to do any more than that. Car ran rough until I got it on the road and gave it more throttle and then it was ok (well it seemed very fast with your bum on the ground). Amazingly it got an mot so that made up for the earlier stress!

It was always my plan to take it to a local rolling road to get it properly tuned anyway but my question is should I trailer it there or would it be ok to drive?. I have a trailer so it wouldn't be a problem if there was a risk of damaging the engine. Please let me know what you think.

Regards

Kevin

[nicko]

I'd say trailer it 'cos if it goes bang on the rolling road it'll be easier to get it home. Plus, sounds like it'd be difficult if stuck in traffic. HTH, Nick

[speedtripledan]

Trailer every time dynos can exaggerate pre existing problems before the car gets set up...

[kevin the chicken]

Hi,

Thanks guys, obvious really but I hadn't thought of that. The rolling road I am going to use is only about 4 or 5 miles away but I will trailer it for the reasons you have all pointed out, especially as the engine is of unknown origin. Typically with my luck I could have had a slot on the rolling road today but had to do the school run and go into school for a reading lesson with my four year old son. My wife has gone to Bosnia for a week for work and left me in charge, Interestingly for those of you are dithering about where to go on holiday, although it is a beautiful place the government advice is to not step on any grassy areas and verges outside of public parks as they may not have been cleared of landmines. I can't imagine taking my two there as they never go where they are told.

When I get on the rolling road I will post the results, it may be of use to someone like me or help me find a new engine!

 

Regards

Kevin

[Bob Tucker]

Sounds like the balance bar between the front & rear carb needs adjusting.

Best tool is a vacuum meter.....they can be very simple, just a lenght of tube, a plate to go over the carb throat & a free running bead inside a plastic graduated tube.

Or a lenght of pipe placed in the carb throat & the other end pleced near an ear.....adjust until identical hissing can be heard.

[kevin the chicken]

That sounds highly probable Bob. I'll have a look tomorrow as I think I still have one of those vacuum meters somewhere. The trouble is that this car has obviously been taken apart and then thrown back together in a hurry by somebody. But it does run reasonably well at larger throttle openings so I don't think it is far away. I just need to be able to run it for a few laps around town to sort out a couple of things before it goes to the rolling road i.e slight coolant leak and a temp gauge that reads max all the time.

[Guest Ian & Carole]

http://www.redlineweber.com/html/Tech/dcoe_adjustment_layout_typical_i.htm

 

Have a read of this, easier than trying to explain, but like Bob says make sure both are pulling the same air in or you will never get a smooth tick over.

Mine ticks over at 800rpm as steady as a rock.

Once set don't fiddle, just recheck once a year.

One other thing ......... make sure you are not pulling any air throught the 4 flexi couplings between carbs and manifold or again you will never get a smooth tick over.

Gently lift carbs and press down on them to see if tick over changes.

HTHs

[kevin the chicken]

The problem was adjustment of the balance bar between the two carbs but as usual there were two problems, the first being that the spindle nut on the rear carb (from the front of the car ) was loose allowing the linkage to wobble around making balancing the two impossible. Once this was tightened I got a good idle. Strange because you would have thought that if you put it back together and bothered to bend the locktab over then you would make sure it was tight. I know I haven't had it apart! Right of fto the electrics forum now to see if anyone can shed light on some other issues.