Club 80-90 Forums

With a cold engine, when the start position is pre-set by pressing/releasing the throttle, should the highest fast idle cam position always be set? 

I'm really struggling to work out why my van refuses to idle as the choke starts to come off and I noticed that every time I try from cold, the fast idle screw doesn't latch on the highest setting, but the second one.  Even with the automatic choke twisted as far clockwise as possible it won't latch on the highest cam.  I can get it to latch on the highest position by holding the throttle open and pushing the cam round a bit further with my finger but it won't do it "naturally".  Is that normal?  

I know temperatures aren't that cold yet (in fact it's very mild for the time of year) but I'm wondering if there's something not right about the automatic choke.

When I stripped, cleaned and refurbished the carb, two of the three screws that hold half the choke housing to the carb wouldn't budge. I cleaned up best I could without dismantling the choke linkages, so it should still all be assembled correctly.  It moves pretty freely with only light finger pressure on the lever that goes into the choke spring, but it's not "sloppy"... second question, is it normal or is the choke spring so weak that the mechanism needs to be really loose for it to work? 

The choke spring seems to be working, when the engine starts up after a couple of minutes the choke flap starts to open as you'd expect, but it does seem to open fairly quickly.  Not timed it, but feels like maybe 3-4 minutes (although during this time as soon as the choke starts opening I can't keep it idling without throttle)

I'm probably clutching at straws here with the choke because although I've not got it really hot, it refuses to idle properly even when things have warmed up, but I'm wondering if perhaps the choke is coming off too quick and not helping matters.





 

I seem to remember that from fully cold to completely off the choke takes 7 or 8 mins
Have you checked that vacuum section is all good, the pull down unit is a common issue , with the diaphragm often being weak

It's a bit colder this morning, just tried pushing/releasing the throttle and this time the choke moved to fully closed with the cam set at the highest position.   So maybe that rules this one out, I was just looking when things weren't quite cold enough.

E D I T actually just answered my own question:
"(NOTE HOWEVER : If the ambient temperature IS greater than 10 Degrees C the choke flap will not close fully and the initial start up speed will not be the very high rpm as would correctly occur with cold temperatures)"

The vacuum should all be good, new pull down unit, new distributor advance unit (both seem ok along with the 2nd stage vac unit), new hoses, airbox tube disconnected and blanked off at the carb, servo hose/NRV seem to hold vacuum and tested previously with them disconnected and blanked off at the manifold.  But I'm going to test all this stuff again next I think.



 

Tried it one more time from cold with the electric choke heater wire disconnected.  This had an obvious effect and it took a lot longer to come fully off choke, over 10 minutes, but it did stay running the whole time and a high idle, around 1500-2000.

When the fast idle cam finally switched off it was struggling so I quickly upped the idle speed setting a few turns and left it for a few more minutes until it was fully warmed up, but I couldn't get a smooth idle below about 1100/1200.  Below 1000 it tends to die, adjusting the idle mixture screw a couple of turns either side of my starting point (about 4 turns out) didn't seem to make a lot of difference.


 

I had another thought about this, I might be barking up the wrong tree entirely.

Months ago, while I was waiting for parts to arrive for the carb overhaul, I replaced the full set of pushrod tubes.  This all went well enough, and I was careful (I think) to ensure that all the rods went back in the right order.  I didn't touch the tappet adjusters as I figured I hadn't actually changed anything, but looking at Haynes now (I didn't read it at the time!) it says they should always be adjusted if the rocker arms are removed.

When I finally got the engine started again (with fresh oil) it was noisy for a while but settled down so I didn't really suspect anything.

So could this be the reason behind my poor idling issues? Valves just slightly out of timing? Perhaps nothing to do with the carb?! 
 

Adjusted all the lifters to 1.5 turns from contact.  Some of them did seem to be a bit out previously; one was over 3 turns in from the contact point  It definitely runs better.  Start from cold is great, fires up instantly and ticks over nicely for 2-3 minutes.  But it's still not happy as the choke starts to come off, and won't idle properly under about 1100/1200 when warm. 

So the search continues!