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Tuning an engine from scratch. Advice needed


jamiepeers

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Hi Guys. I've been missing for a good few weeks off here, mainly as i haven't had the time to give the car a decent amount of time over the Xmas period and all.

I had a few issues regarding coils/spark etc found in my last thread here.

http://club.triumph.org.uk/cgi-bin/forum10/Blah.pl?m-1319998163/s-0/

If thats too long a read, the basic background is my 1300 Spitty hasn't been turned over in about 2 years and i have inherited it in this state, also with the carbs in need of a rebuild. I have now rebuilt the carbs using a Rimmer Bros kit, and opints, condenser, coil, leads and plugs are new

Yesterday having previously set the timing statically and also setting the points, i tried to start the car and lo and behold, after a little persuasion and using easy start for the first 3 or so times, she eventually fired up and ran on her own steam.

Now, although the car idles of a sorts, its really only on full choke (as expected as it was stone cold) and this is at around 3500RPM or just in excess of that.

I know this is way too high, and i have been looking and i think i am familiar with how to set the carbs up etc etc, i also have a timing light.

However, given the nature of all thats been done, i.e points, static timing, carb rebuild, i am looking for pointers as to how to set the car up from scratch, as in which order to do things to make my job the easiest.

I can't really set carbs up with it racing away, and a few of you guys must have done extensive work on these engines to have a setup guide so i was hoping you could point me to it. In a nutshell, a chronological set up list.


Many thanks

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The easiest way to do the job would be from the manual. That way you can do it step-by-step with quick reference as you're going. If you haven't got one, get one as it'll come in handy for all the other jobs you'll have to do at some point.

Until then, Jame's site may be useful to you;
http://www.mintylamb.co.uk/?page=sutune.htm

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Hi ferny.

I have the Haynes, and also the Haynes  manualon SU carbs. I know what i should be doing (hopefully!) with reference to each task, but i was wondering if anyone had some tips regarding which order to carry them out in.

For example, when setting the timing, it always assumes in the manual that everything else is set ok, such as points, carbs etc, and vice versa. I was hoping some of you guys had a sort of checklist when starting from scratch, which should be set first to make the whole job easier

Cheers

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Jamie,

I personally would do it so.

New plugs, (gaps set correctly)
New distributor cap, condenser.
Set static timing.
Set points gap.
Set dwell angle.
Start her up and set carb's, tick over, (obviously once warm) then mixture.

Do a timing check (one with advance/retard)
I also find it's good to go back and check them all again, as you can fidle with carb/timing and it will throw the other out.

Hope that helps.
Cheers
Shaun

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Hi Jamie,


The dwell angle is the number of degrees of rotation of the cam/distributor during which the points are closed. During each rotation of the cam/distributor, the points must open and close once for each cylinder. The points must stay closed long enough to allow the coil primary current to reach an acceptable value, and open long enough to discharge and produce a spark.


I will now tell you how to set it, but I'm going to cheat, because I'm lazy and don't want to type so much, so I'm going to copy and paste it for you.

Cheers
Shaun

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Are you ready.

- Pull out the old points, condenser and rotor. Check for smooth movement of the vacuum advance plate, preferably by sucking on the vacuum hose. Mount the new points on the plate along with the condenser (on some cars the condenser mounts on the coil). Loosen the distributor's hold-down screw just enough to allow movement, and rotate the distributor until the wiper arm on the points is at the top of one of the shaft's actuating cam lobes. Tighten the hold-down screw and adjust the points for proper mechanical gap, according to your engine manual. Use your feeler gauge properly and take your time, because you are mechanically setting the proper dwell angle*. Install the rotor and cap
*Automotive coils generally have secondary-to-primary ratios of 200 to 1. Therefore, a 12-volt input to a coil's primary windings will result in a 24,000-volt output from the secondary winding. That's where the spark plugs get their electricity. Inductance isn't perpetual motion, nor is it "free energy." There are many "howevers" and other considerations to worry about. The biggest one is the coil's inability to hold the induced voltage once it's been built up. In a very short time the voltage will "bleed of," leading to weak spark. Also, the coil takes a finite amount of time to build the charge up. That's the dwell time, normally defined as the degrees of rotation of the camshaft during which the points are closed. Too little dwell and the coil doesn't have time to charge up fully. Too much dwell and the coil has bled off some charge, causing a weak spark. Hesitation, low power, misfiring, pinging and a number of other conditions are symptoms of incorrect dwell.

- Gap the new plugs and install them, being careful not to over tighten the threads into the block. Place the plug wires onto them while noting the firing order. Make sure the wires are seated into the distributor cap and coil.

- Get out the dwell meter and connect it. The red lead goes to the points side of the coil (negative terminal) and the black clamps onto any good ground point on the engine. Start the engine and measure the dwell angle. If it isn't in the middle of the allowable range (say, 24 degrees when the range is 20-26 degrees) stop the engine and move the point gap closer to raise the dwell or farther apart to lower it. Keep doing so until the dwell is correct. Dwell angle has always been set by properly adjusting the ignition point gap. Your car's
points gap was derived by engineers to approximate the dwell angle, but individual point sets can vary considerably in their mechanical and electrical characteristics. The only way to properly set up ignition points is with a dwell meter.

- Get out the timing light, the most overused engine maintenance tool. Why is it overused? Well, because the engine's internal components only wear miniscule amounts over time, which means timing chains or gears don't "jump" or get loose between tune-ups. The reason
an engine's timing changes is because the dwell angle is changing as the wiper on the points wears down.

Why? Since dwell is measured by camshaft rotation and the camshaft runs at twice the speed of the crankshaft, for every two degrees of dwell an ignition is off from its proper setting, the engine's timing will be off one degree! If an engine needs to be re-timed when it's periodically checked, the points have worn down (thereby increasing dwell). The timing chain hasn't slipped, as so many believe. Conversely, if you set the points correctly at every tune-up you will find that the timing never changes!

(thankfully I didn't have to type all that,)
Hope after that it's a bit clearer, I have a auto test meter you could borrow, but I'm a little far away from you!
Ask around someone local may have one.

Cheers
Shaun

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Thanks Shaun.

The only meter i have is a standard multimeter which i take is not correct for measuring dwell??

I have an Accuspark Electronic ignition conversion to put on the car, but wanted to get it all set up using the points first, rather than swapping everything out at once all over the shop.

Do you think rather than investing in a dwell meter, i'd simply be better setting the points gap with feelers (already done), then assume the dwell angle is ballpark for tuning.

Tune the car, swap over to the accuspark, then re time and retune as necessary as i'll be very close to optimum tune by then??

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Hello Jamie,

setting new points carefully will give good results, it's once they are worn a bit that it becomes harder to set them with feeler gauges. You only need to time the engine statically to begin with then adjust the carburettors to optimum mixture. Now you can fine tune the timing (If you time with incorrect mixture it will be wrong when you correct the mixture as the burn time in the cylinders will be different). The best way to set the timing is by road testing, advancing the timing bit by bit until it pinks then back off just a shade so it just doesn't pink.

Alec

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Many thanks chaps.

Unfortunately i can't time on the road as yet as its a work in progress with no MOT etc etc, but if i can get it timed dynamically on the light then follow your lead regarding road timing that'll do nicely.

Shaun, yeah i'll run it up on points first then as soon as i'm happy swap over to the Accuspark.

As a final note regarding road test timing, is there any particualr gear and speed i should be at before burying the throttly to load the engine up, or is say 30mph in top gear loaded enough?

Cheers

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With the engine running at normal temp', turn the slightly slackened dizzy slowly in the opposite direction it rotates to advance the ignition till the engine goes off, runs rough etc, then turn the dizzy back a bit till it runs smoothest again. Tighten dizzy and the timing will near enough.

Did mine this way when I changed to Accuspark.

8)

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That's ok for setting one up roughly, but when under load (driving, accelerating hard etc) the engine does change (wear in the system, fuel mixture under load etc etc)

The best thing is to go to a rolling road, they test and set it up all through the range, I had an old beetle, that I thought I set up perfect, and it ran really well, then we went to a rolling road session, the settings were not good under load, timing slightly retard at higher revs/loads, the guy adjusted it all, set the fueling, I can't remember off hand how much bhp I gained with the session.
when I drove it after he finished, bloody he'll it felt like someone had given the bug a go go faster pill!
Well worth the money. But if you do it, go once you fit the electronic ignition.
But go to a good one, who has good feedback.

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Tuned for the most part, my bloody timing light doesn't work, brand new too. Grrr. So i had to "assume" the timing was ball park enough to tune the carbs.

Had to richen both sides up considerably in order to get her to tickover once warm with no choke.

Set the carb mixture using the various youtube guides and lifting the lift pin to hear the carb rev a little then settle back down.

Balanced both carbs using my balancer, then reduced tickover, however i could only get the car ticking over at about 1100rpm with the idle screws backed right off.

The only way i could get the tickover down was by retarding timing. Once this was done i could then set my idle using the screws. Not sure exactly where abouts my timing is now though which is a pain at the moment.

I need to sort a working timing light out then retune, then swap over to accuspark and retime.

Does everything else sound about OK?

Oh, and a last point, now found that i don't have any electrics as in lights or wipers so more fault finding needed there.

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