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Beginner Questions about carbs, tickover, choke

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Re: Beginner Questions about carbs, tickover, chok

I think it's just opposite, Jack. It lights off well when 'cold' without choke but stumbles on rapid throttle app. As it warms up seems to be running a little better. That would seem to be a lean condition. Funny bit is: choke making no difference.

Julian:
Try gapping the plugs at .028", air filters off, watch the pistons as you apply throttle and see if the pistons rise in unison. Looking for an indication of balance/out-of-balance here. It's not the best way but indicative. If you see one rise ahead of the other, they need to be synchronised more closely. And with the filters off you can access the mixture adjusting nuts more easily, too. Does it "POP" at the carb throats when you give the throttle a jab? That's a lean indicator too.

And can you check that the mechanical timing advance is working correctly (timing light is best for this)?

Just had a thought: You have those little "poppet-valve" thingies in the throttle plates? You may consider pulling the carbs back off and soldering those shut.

...random babbling now. Speculating without the beast in front of me. /ubbthreads/images/graemlins/wink.gif
 
Re: Beginner Questions about carbs, tickover, chok

Well Doc, as you said kinda hard from a distance. But you don't think it starts rather easly just because idle is so high. I think he said it would not go lower??
 
Re: Beginner Questions about carbs, tickover, chok

Just for grins, the needle in the carbs should be a #5 with the jet about .050" down. I use ATF in the dampners, it's ligther than the 20/50. I also find 8 out of 10 used HS4s to need throttle shaft work, the .010" over sized shaft is the best way to go.
 
Re: Beginner Questions about carbs, tickover, chok

Dr Entropy - If an SU piston leaps rapidly upward, you'll get a very over-lean mixture, not over-rich. Even though the needle is at the fine end, you lose depression over the choke and that more than compensates.
 
Re: Beginner Questions about carbs, tickover, chok

Have you determined the status of the throttle shafts yet? Trying to "tune" a carb pair with ovaled throttle shaft bores is all but impossible. You will waste endless hours trying to get it to run right, and it never will.

Lots of reputable rebuilders here: Hap, Lawrie Alexander, Joe Curto...
 
Re: Beginner Questions about carbs, tickover, chok

[ QUOTE ]
Have you determined the status of the throttle shafts yet? Trying to "tune" a carb pair with ovaled throttle shaft bores is all but impossible. You will waste endless hours trying to get it to run right, and it never will.

Lots of reputable rebuilders here: Hap, Lawrie Alexander, Joe Curto...

[/ QUOTE ]

I'm absorbing all the advice, and will make a plan of attack for the weekend. Sounds like the shafts are high on the check list!
 
Re: Beginner Questions about carbs, tickover, chok

Yo, Roger!::::

My post: [ QUOTE ]
As it warms up seems to be running a little better. That would seem to be a lean condition.

[/ QUOTE ]


FYI, FWIW.
 
Re: Beginner Questions about carbs, tickover, chok

/ubbthreads/images/graemlins/iagree.gif
 
Re: Beginner Questions about carbs, tickover, chok

I took a look again at the tickover/throttle problem. I've still not got to the bottom of it. Here's what I did:

1) re-gapped the plugs to 0.028" as per Doc' suggestion
2) while doing this I noticed that the two plugs at the front of the engine were quite sooty ... the pair at the rear, less so
3) I saw why the pistons weren't rising in unison when applying throttle: the rear carb's lever and pin were slightly differently positioned, so the front carb's piston would start rising before the rear's. I fixed this by adjusting the position of the lever (loosened the bolt and twisted it round a tad).
4) After running the engine for a while, I stopped it and took a look in both float chambers, and they were about half full each of gas.

My interpretation of the sooty plugs is too rich a mixture. But why would the front cylinders be worse than the rear?
 
Re: Beginner Questions about carbs, tickover, chok

[ QUOTE ]
I took a look again at the tickover/throttle problem. I've still not got to the bottom of it. Here's what I did:

1) re-gapped the plugs to 0.028" as per Doc' suggestion
2) while doing this I noticed that the two plugs at the front of the engine were quite sooty ... the pair at the rear, less so
3) I saw why the pistons weren't rising in unison when applying throttle: the rear carb's lever and pin were slightly differently positioned, so the front carb's piston would start rising before the rear's. I fixed this by adjusting the position of the lever (loosened the bolt and twisted it round a tad).
4) After running the engine for a while, I stopped it and took a look in both float chambers, and they were about half full each of gas.

My interpretation of the sooty plugs is too rich a mixture. But why would the front cylinders be worse than the rear?

[/ QUOTE ]

Excellent observations!

Your carbs are out of sync, and out of tune.

The reason the front cylinder plugs are black is because the front carb is running richer than the rear.

The reason the pistons are rising at a different rate is because the carbs aren't synchronised.

I would explain how to do this, but there are articles in several places that are written with much more eloquence and authority than I could muster. The good news is that you can do it yourself. Relax and enjoy the process, and you'll be an old pro in no time.

Some may disagree with me, but I would personally recommend you invest in a carb synch tool of some sort. They're worth the $30, and kind of cool to impress your friends with anyway. 8)

Wish I oould be there to help.....
 
Re: Beginner Questions about carbs, tickover, chok

Eric's got it in one... as stated before, the carbs are outta synch. You're "sneakin' up on it" fer sure. A "listenin' pipe" can be your first try, but a "Uni-Syn" tool is really the best bet. It doesn't indicate mixture but it allows you to set the draw between the carbs equally. The trial-and-error "lift-pin" proceedure outlined in the Bentley book will allow you to get the mixture balanced closely.
 
Re: Beginner Questions about carbs, tickover, chok

[ QUOTE ]
Eric's got it in one... as stated before, the carbs are outta synch. You're "sneakin' up on it" fer sure. A "listenin' pipe" can be your first try, but a "Uni-Syn" tool is really the best bet. It doesn't indicate mixture but it allows you to set the draw between the carbs equally. The trial-and-error "lift-pin" proceedure outlined in the Bentley book will allow you to get the mixture balanced closely.

[/ QUOTE ]

I made a little progress on matching the carbs, using a length of tubing and listening to the draw. However, just as I was about to start adjusting the mixture nuts, I ran out of gas!

What was unclear to me is whether "clockwise" rotation of the mixture nut refers to the direction when viewing from the top of the carb, or from the bottom? The Chilton manual wasn't clear. I suspect it means the direction of rotation when viewed from the bottom of the carb, looking skywards, right?

I felt I should take a look at the timing as well. Again referring to the Chilton book (which is excellent, BTW), it talks about turning the engine over by hand or by the starter solenoid. This puzzles me:

1) How can I turn the engine over "by hand"? That's going to be hard with the plugs installed, and besides, how do I get sufficient grip on the crankshaft? I dimly remember doing this on my Renault 4, but that had a starter handle!

2) If using the starter motor, isn't that going to wear the battery down very rapidly, and how precisely can the engine be turned anyway, using this method?

Apologies for these really very basic questions :smile:
 
Re: Beginner Questions about carbs, tickover, chok

No apology necessary!

Turning the jet adjusters clockwise looking from underneath (up at 'em) leans the mix. One flat can make a difference BTW, so take your time, be sure to "clear" it after the pin rise and fall by a short 'blip' on the throtle after each "test".

You can turn the engine by hand, but it IS easier with plugs out... and safer (Make certain the ignition is OFF anyhow!)then with some tension applied to the fan belt and grabbing the fan by the HUB (plastic fan will break if you try to use a blade) to turn it... This is for setting static timing or valve adjustment purposes. In either circumstance the plugs out won't matter to the task and makes it much easier. Trying to do this with the starter is an exercise in frustration.

Some will say put the car in third gear and roll it around to the mark, but that means you gotta "chase the car" around. Plugs out, turn it by hand.
 
Re: Beginner Questions about carbs, tickover, chok

Many thanks Doc! Much appreciated advice. I'll let you know how I get on :smile:
 
Re: Beginner Questions about carbs, tickover, chok

Yep Doc, He be running rich. Also if the shafts are worn they will wiggle in the carb bodies if you check them by hand.---Keoke
 
Re: Beginner Questions about carbs, tickover, chok

are you turning the eninge over by hand to set the timing by the "static timing" method?

I would really suggest getting a timing light. They're cheap, and you won't lose sleep second-guessing yourself about whether you got the thing set correctly.

As for turning the engine, there is a nut down on the crankshaft pulley that you can fit either a wrench or a socket on to turn the engine.

Also - personally I like to set points with a dwell meter. accuracy when setting point gap / dwell isn't critical, but measuring dwell with a meter is a bit more precise than setting point gap with a feeler gauge. And you don't have to turn the engine by hand. 8)

my $10 harbor freight meter measures volts, ohms, dwell, and current. Sooner or later, you're gonna need a voltmeter anyway.

Just some thoughts.
 
Re: Beginner Questions about carbs, tickover, chok

NO, since I consider timing to be a critical issue I use a high quality dwell meter followd by a Snapon timing light to get things spot on.---Keoke
 
Re: Beginner Questions about carbs, tickover, chok

I have a dwell meter coming. I considered using one of my portable 'scopes (it would just be a matter of looking at the waveform and calculating the mark/space ratio I 'spose), but figured a purpose built device was probably best.

In the meantime I have adjusted the tappets today. Interestingly the rear four were pretty much spot on, but the front four gaps were too small.
 
Re: Beginner Questions about carbs, tickover, chok

It'll be a 'bit' more portable than your O'scope, too!

...and you ~may~ have found the reason the front two plugs were more 'sooty' than the back two! Well done!
 
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