Poor idling/running - in what order do I do this?

#1
Hi everyone.

I have problems with the way the car runs. I have got the idle speed set at about 1,000 revs (based on dash tachometer which I understand may be inaccurate) because below this level the car hesitates and splutters when accelerating from rest. Car currently accelerates fine, but then trying to cruise at say 30 m.p.h. the car is " jerky" rather than smooth running. Before touching the carbs advice seems to be check plugs, points & timing. However, just watched an MSD video on YouTube about setting the timing and those cheery chaps said that you adjust timing at idle and that it then changes as you accelerate (you will have guessed by now I'm pretty "green" when it comes to things mechanical!). So..does it make sense to check the timing at the current excessive tick over rate as part of my elimination of causes other than the carbs? I have also read that mysterious "weights" start to deploy above the normal idle speed so again is it correct to set the timing when those things are doing their stuff? All advice greatly appreciated as today is yet another in the glorious long hot summer we're having here so I'm keen to crack on with trying to improve matters. Thks.
 

harveyp6

Well-Known Member
#2
You can do a compression check first of all, then if that's OK start with the points if you have them, followed by checking the plugs, cap and leads, air filter etc. All the normal service items. You will need to reduce the idle speed to set the timing, (don't rely on the in-car tacho, it's not accurate enough) but as long as it runs at the correct speed to do that you don't have to be to careful about you achieve it. Once the timing is set then you can move back to the carb and set that properly. It can involve a bit of juggling, but providing you follow the basic order of making sure the points are set first, followed by the timing, (even if you have to roughly reduce the idle speed to set it) then the carb you can then check the advance weights using the timing light while revving the engine.
 
#3
Hi HarveyP6

Thanks for your reply. I don't have any equipment to do a compression check but the engine was only rebuilt a few thousand miles ago so I'm hoping I can discount that from the investigation. I replaced the distributor cap & rotor arm last weekend. Points look pretty new but no harm checking the gap while I have the plugs out and the engine can be turned easily by hand. How do I check the operation of the weights?
 

harveyp6

Well-Known Member
#4
roll said:
I replaced the distributor cap & rotor arm last weekend.
Don't discount them as the problem just because they're new. There are a lot of very poor quality new ignition parts about.

roll said:
How do I check the operation of the weights?
You can check that the mechanism isn't seized by twisting the rotor arm in the direction of rotation and making sure it springs back, and then when you have the timing light on it, rev the engine and watch the timing marks advance up.
 
#5
Tried to slow down idle to 700 ish using proper tachometer but best I could do was get it into a range of 900 ish to "almost stalling" below 600. On this basis I can say that the timing traverses the 6 degree mark but as I can't get the idle to settle below a much higher rev rate I'm unable to get a proper fix on timing. Today I"ll have a look at plugs, weights and points gap but after that Is the next step to have a think about the carbs? Interestingly, when trying to slow down the idle speed I was able to completely back off the idle screw on the rear carb without any effect on idle speed so that would suggest that it might be one of my problems. Will also check linkages today to make sure they are working freely. I have two rebuild kits on the way from SU so if I don't find anything today I might need to go down the carb track next week. Don't suppose there is anybody in or around Lower Hutt that has rebuilt carbs if I need a second opinion on anything during that process?
 

JVY

Active Member
#6
TCs have a bit of a reputation for poor idling if the carb's aren't balanced. Could be that making sure the idle mixture is set correctly and same on both and they are balanced properly at idle (using the idle speed adjustment screws you mentioned) will get it idling smoothly enough to set up the timing?

My car certainly idled very unevenly until I sorted the carb balancing and mixture out.

Another common reason for 4 pots idling roughly is the valve gaps. Even if your engine has been rebuilt, it may be worth checking this too?

Getting the carb overhaul kits is probably a good idea. There are various things that can wear and affect idling that the kit might cure. Another common problem is leaks on the inlet manifold (e.g. the big rubber o-rings that sit between the carbs and the manifold).

Just another thought (and sorry if you already know) - assume that you disconnected the vaccum advance tube from the dizzy before trying to set the timing?
 
#7
HarveyP6 is on the money.

I've found that once the basic timing and ignition are spot on, it becomes a case of faffing around with the carbs to get smooth running. In my experience TC carbs are incredibly sensitive to even small adjustments to both idling and mixture as well as the lost-motion setting on the accelerator actuation linkage - you'll get there eventually and have a smooth running unit: in my case when the Moon miraculously aligned with Mars in the Summer Solstice of '10 - or thereabouts. :D

The dashboard tacho is a joke for this work. Mine shows idling at 1200 rpm which translates into circa 900 in the real world: baring in mind that, depending on fuel quality, ULP tends to require a slightly higher than workshop manual setting for easy idling.
 
#8
roll said:
Interestingly, when trying to slow down the idle speed I was able to completely back off the idle screw on the rear carb without any effect on idle speed so that would suggest that it might be one of my problems.
That sounds like an air leak on your rear carb. I had that problem, and I could see that the manifold gasket on the inlet manifold had blown out allowing air in there. I had attempted to tune it quite a few times with no success. Took the manifold off, made a new gasket out of gasket paper, then reinstalled. I could also be the o rings already mentioned.

James.
 

chrisyork

Active Member
#9
To check for air leaks on the induction side, spray WD40 or similar over the potential leak areas. You'll be able to see it being sucked into the joint if there is a leak.

Not my tip - James Rumney showed me that one - incredibly effective.

Chris
 
#10
Thanks for your ideas everyone - looks like another rovering weekend coming up (sunshine promised once again!). Must admit I'm beginning to wonder about air leaks myself so will try chasing those down as suggested - still nervous about applying my novice skills to carb dismantling when I don't have any experience in this department. Didn't disconnect the vacuum advance tube when trying to check the timing so thanks for pointing that out!

Best thing I did at the weekend was replace all 3 choke cables with beautiful NOS items from WINS. Action is "smoooth as" and the shaft even locks when you pull it out - ideal when you use the choke to manage the idling speed on an on-going basis!
 
#12
I feel like I am teeing myself up for a sage one liner from Harvey here but...

I thought when setting the timing the car had to be idling below 800rpm, so the centrifugal advance was inoperative and with the vac pipe disconnected so the vac advance was inoperative and the pipe was plugged so there was no vac leak.

..go on Harvey do your worst !
 

harveyp6

Well-Known Member
#13
pat180269 said:
I thought when setting the timing the car had to be idling below 800rpm, so the centrifugal advance was inoperative
Right so far...

pat180269 said:
and with the vac pipe disconnected so the vac advance was inoperative and the pipe was plugged so there was no vac leak.
.... but as a little exercise go out and check your timing with the vac pipe in place, and then while still looking at the timing marks with the light, disconnect the vac pipe and plug it and make a note of how many degrees of alteration it makes to the timing....
 
#14
Thought I'd update progress as play has been curtailed by rain (hopefully the case with the cricket as well given the thumping that the Black Caps are getting from England!)

Have replaced plugs, points and distributor cap with no noticeable effect. Ordered a new set of leads last week from "Super Cheap Auto" and a set of Bosch leads duly arrived yesterday, but the degree of assembly required and the rather obscure instructions for cutting the leads and clamping the ends made me reconsider and reject this option, so will place an order with Wins today for the proper kit. That said, I think the leads look ok not sure this is going to make much difference.

Took off the top cover to have a look at the valve clearances as recommended. On the positive side I was able to take the opportunity to check the timing given my inability to establish a consistent idle below 1,000 rpm. Was able to determine that at 8deg the points were not open whereas at 6 deg they were so I think I've now ticked that box (?). Interestingly I noticed the points sparking as I hand turned the engine while doing this - is that normal?

On the negative side the valve gaps were 6 thou and 11 to 12 thou which seems well below the tolerances. Given that the engine was rebuilt last year this has obviously been done deliberately, and the car was running fine when first delivered back, so not sure what to make of this. I will be emailing the engine shop next to ask them why they did this.

More worryingly, the "nut securing chain wheel to bracket" is not present (will attach photo if I can). No idea if this is cosmetic or important. I assume that if it was present it has tumbled down into some harmless place (?). Again - a question for the engine shop.

My rebuild kit from SU has still not shown up but I'm in no rush to pull anything apart at present (still got air leaks to check for before that).

All good fun!
 

harveyp6

Well-Known Member
#16
roll said:
More worryingly, the "nut securing chain wheel to bracket" is not present (will attach photo if I can). No idea if this is cosmetic or important. I assume that if it was present it has tumbled down into some harmless place (?). Again - a question for the engine shop.
If you mean what I think you do, the nut is only used to hold the chainwheel in place while it's removed from the camshaft.
 
#17
Hi Harvey P6

Thanks for your reply. Have just looked at the forum post "Sick 2000TC" which has a photo of the "smiley slot" I am referring to and Chrisyork has confirmed that it is normal for there to be no nut present.

Tried to upload a photo but got the message "Sorry, the board attachment quota has been reached".

Rgds

Peter
 

redrover

Active Member
#18
Hi Peter,

Yes, it is normal for no nut to be present. The chainwheel rotates clockwise, so it would probably encourage a nut to become looser over time with potentially disastrous consequences!

In the meantime, you can use one of the nuts from the steering idler box bracket securing bolts. They are the same thread. There are four so removing one isn't going to harm anything for the time being. It's probably worth tightening these up anyway as they seem to work loose over time creating a vagueness and clunkiness in the steering, so extra reason to take a spanner to them! They're 9/16", but the nuts are a touch soft, so I use 14mm which really grips them tight without damage.

Michael
 
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