Poor Idle / Zenith 40 Tins

Barry · Post by **Barry** » Sun Oct 31, 2004 5:43 pm

Picture this: freshly built engine (2.4E) running on 40 Tins - a combination I have seen running on other cars with the Tins on 'T' type jets. Pulls fine, plenty of power for a new engine BUT it has a very unreliable idle. you set carbs as per Zentith / Porsche manual (thanks Phil), but after driving engine revs surge and don't die down / or surge then die down to sputtery halt. There is some spitting back through carbs, and some exaust pop on over-run. As far as I'm aware, all symptoms of air leaks or poor inlet valve seating. Currently idle jets are nearly four 1/2 turns out (!) which gives best idle.

I suspect throttle spindle wear as all usual suspects have been dealt with (I think). There is some present, but really not much (you could probably move the throttle link end .75mm if that). Anyone know how much play in spindle will start to affect idle, has anybody done this job / had it done??

impmad2000 · Post by **impmad2000** » Mon Nov 01, 2004 8:45 am

When I was trying to diagnose throttle spindle wear on another car, I was told to run some oil down the spindle . this will make a very temporary seal, but should give a clue if it is the cause of your trouble.

HTH

domo1977 · Post by **domo1977** » Tue Nov 02, 2004 8:55 am

I've got 40TINs on my 2.2T engine that has been standing for a couple of years, so I've been reading up about these carbs in preparation for some grief when I try to get mine running!

I've found penty of Zenith info on the Pelican Tech Forums, and have read most of it! not very busy at work last week

So my 2 pennys worth if it's any help would be first to check and clean the idle circuit fuel passages as you shouldn't need to open the idle valve that far. From what I've read it's a fairly common fault for these to be blocked, the engine then gets it's fuel at idle from the transition (part throttle) circuit which leads to these surges in revs and odd/lean mixture at idle that causes the popping.
Might also be worth checking the fuel pressure going into the carb think it should be around 3 to 4psi, if this is too high from an incorrect or faulty pump the float needle wont seal at times of low fuel demand (idle) and again you will get an uncontrolled mixture.
This is general stuff applicable to most carbs of this type (webber, dellorto etc) that I've picked up over the years.

hope this helps

Barry · Post by **Barry** » Tue Nov 02, 2004 5:22 pm

Thanks Tim /Domo. The carbs are currently back off. I did clean then through with carb cleaner initially, and I have to admit that if the cleaner came through, I assumed that the passage must be clear - had I known how it would run I would of been more thorough! Someone has now generously lent me some carbs (known to be good) to try, which will help to track down the fault. Watch this space.

Robster · Post by **Robster** » Thu Nov 04, 2004 5:36 pm

Hi Guys,

with your idle (mixture?) screws wound out so far, you will be seriously running a rich mixture, which will either cause the car to rev, or foul your spark plugs,i.e too much fuel at low revs will stifle the engine.

Trying each screw in turn, wind the mixture screw in until you get the engine stumbling, and then back it out. You will actually find that as you lean off an over rich mixture, that the engine will increase it's revs as it reaches the optimum airflow, mixture ratio. Not sure on Zeniths, but on webers, approx 2.5 turns from completely closed on the mixture screws gets it in the ball park....

Of course if you have an airleak, you must get that sorted first or you will never get them dialled in.

Hope that helps,
Robster

Barry · Post by **Barry** » Fri Nov 05, 2004 4:34 pm

Thanks, Robster, good thought, I initially set the carbs on the factory setup of 2 1/2 turns, and went out from there. I did not get the impression of it running rich (exhaust very clean etc) but well worth trying. The current situation is that I removed my carbs, plus the maifolds. De-studded the manifolds, and re-faced both surfaces (all very slighly off) replaced manifolds with new gaskets. Just fitted these other carbs which recently came off a well running car. Literally about to try these in a few minutes - if the symptoms disapear, then it can't be throttle spindles, as these have a fraction more play than mine.... In fact if they do disappear I have been offered these at a fair price so they can stay on, whilst I investigate the originals.

Barry · Post by **Barry** » Sat Nov 06, 2004 9:08 pm

Right, sorted.

Speaking to a ex-mechanic and race engine builder, who suggested the same faults could be due to wear in the distributer - particularly the advance/retard parts (affecting idle speed etc) Upon checking, the adance/retard was indeed a bit tardy, and now the engine has run for a few miles, general wear was in the main shaft inself. A swap to a spare dizzy (as new) but with original carbs improved things by miles: enough to think that ignition was 80% of problem. However putting on borrowed set of carbs really had it running well. Random sucking/blowing of original carbs revealed vacuum take-off to be blocked

, therefore can only imagine, dispite blowing cleaner through everywhere, there must still be a blockage I've missed. Now buying these (good) carbs, and will go through originals over winter. Thanks for all the advice, folks, its been emotional!