DCOE setup help request

[Troy ODoherty]

Ah yes you are not the first person driven to drink by a TR and I am sure you wont be the last[:D]

When you set the balance do so with the center screw and then turn the front carbys idle speed screw in a turn or so . This will make it idle. Then adjust the balance screw untill it is right. Now set the idle speed screw and adjust mixtures and adjust idle speed again. Repeat untill it is happy. Do not re adjust the balance screw unless you are sure this has moved.

As you said then wind the other idle speed screw in untill it just takes up. This will reduce the load on the throttle shafts when they are closed.

The emollsion tubes are not so much richer or leaner, more it is about when they make the progression from idle to main cuircut.

One other thing that is vitally important and has caused many of people lots of grief is the choke retaining screws that are underneath the carbies. They must be in place and they must be lock wired , NO EXCEPTIONS. if one of these come loose or fall out the auxillary venturi will turn in its bore and stop the flow of fuel into the barrel. This will cause the car to drop a cylinder. Some times intermitantly.

Dont worry to much about the emolsion tube yet. I am using F16s in the V8. They are really expensive and should only be changed when you are sure they are an issue. Or you have nothing better to do than mess with things that work.[:)]

Cheers Troy

[Marsu]

I took the morning off from work as getting the wedge to work seemed more important - this sort of reflects my OCD and wedge addiction. [:I]

Frustrating was that the intermitent no spark condition had gone away again! I replaced the ballast resistor anyway so if it returns it can now only be a faulty lumenition unit and the spare dissy is in the boot.

With more knowledge (thanks Troy) what became immediately obvious was that the throttle return springs have stretched and are now too long the pull the tangs on the shaft back against the end of the front carb idle speed screw.

I rang all local suppliers but found that none had a short enough spring (<60mm) so had to reshape the hook at one end of each spring to get it to (sort of) return fully. This mod is not really satisfactory so I'll have to mod the setup to suit the available 75mm springs - this can wait a bit.
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First up I set all idle mixture screws to a 1/2 turn from closed. It didn't like starting nor idling, but eventually did with manual operation of chokes and throttle. As it warmed up it became more willing to idle (sounding a bit like a smoker trying to clutch start a diesel tractor) and some tweaks on the front carb idle speed screw got it hrrumphing regularly.

I then attempted to balance by just using the meter on the front/leading throat of each carb and it was much easier. I took secondary readings from the trailing throats, making minor adjustments to the central balance screw to dial the rear carb down, and then returning to measure the leading throat and adjusting front carb upwards (ie, tighten) marginally if the front throats were imbalanced. Overall this was a much quicker and methodical method that what I used before.

Given it was running I tried to check for vacuum leaks. Unfortunately my carb cleaner rattle can had mysteriously emptied itself of propellant and the only other aerosol I had was WD40. Application around the gasket interfaces did not make any change to the idle characteristics. Should I get more carb cleaner and check again or is no change with WD40 likely to be a good enough test?

I suspect not given the problems I encounted in getting a consistent idle.

As the engine warms idle speed increases. The return springs evidently are not strong enough to pull the throttle shafts back against their stops. But it is also obvious that jets are too rich on the idle circuit as it is only with less than a 1/2 turn on the idle mixture screws is there any reduction in idle rpm.

I'd be grateful for more advice as to what to change!!!!

On a more positive not, the car was more drivable on less than 1/2 throttle than last time, but still is not practicable.

[Troy ODoherty]

It sounds like you have made some excellent progress.

You need to sort out the idle return before you can make to much progress. Repco should stock GJ grab kits which have throttle springs. They often sell them in blister packs of 4. If not try an industrial supplier. Is it possible to bend the mount for the spring slightly?

Dont be too quick to think the idle jets are wrong as 50F9 should be very close. If they are it will only be by 1 size Ie 45F9 or possibly 50F8. You are going to end up knowing all sorts of stuff that you didnt know you needed to know.

As you have a set of F16 you could try them and see what diffrence they make. F16 are one of the very common tubes and F15 is only one step away. Leaner in the mid range and increasing throttle respone if memory serves. When you change them do not grab the tubes with pliers or put them in a vice. the outside diameter is critical they must not be damaged. You can grab the fuel jets or the air corrector if need be.

Once you are sure that the throttle is operating correctly, check that both carbies are getting full throttle, and that the spark is good you should now be able to check the jets.

See how that goes for you and if it still needs work I will run thru the check for the idle jets. Looking at the jetting that is in it it sould be close enough to drive reasonable well. The biggest gain will probably be in changing the emolsion tubes or checking that the accelorator pump is workin properly. When you say that it doent respond well with less that 1/2 throttle, are you accelerating gently or with large throttle opening? If it responds to gentle opening but not fast opening then you have a accl pump problem.

If the other way around then it is probably an emolsion tube problem.

Cheers Troy

[Marsu]

I had another play this afternoon, bending the end point for the springs outwards, but it wasn't enough. The original springs are knackered.


I bought some springs but all are too long and I can't get the idle < 1500 rpm using either the old or any of the new. The setup requires a short tension distance from eye to eye of ~60mm. New proper carb return springs are >=72mm. The cheat springs I bought (meaning not of good quality) are 65mm. Neither have enough tension to pull the tang against the front carb idle speed screw.

I'm going to have to fabricate a longer bracket for the spring end point connection. The other problem with this set up is that both springs act on the rear carb lever which pushes against a short spring pin fixed to the front carb lever. Hence, neither act directly to bring the throttle plate fully home on the front carb.

My plan is to drill a hole in the front carb lever and make provision for 3 springs at the end points. This will mean different lengths and tensions - opinions welcome.
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Troy, regarding your question on throttle usage - the car does not respond well usung very gentle or moderate throttle. But if I floor it, it hiccups a couple of times and then responds very well.

I'm getting a misfire on more moderate throttles. Not a backfire, but a hiss and hiccup that is pushing out the carbs I think. More effort and analysis required to describe this properly.

I do want to know if I have done the right or wrong thing in plugging the dissy vacuum advance. There was no obvious place to connect to and something I read suggested blocking it off was the way to go. Opinions please.

[Hasbeen]

Marsu, On the vacuum advance. You should do a modified advance curve when you remove it, there were a number of people who did modified springs, & bob weights back in the old days, but finding someone who knows now is doubtful. The vacuum advance only works up to around 2000 RPM anyway, so if it will idle, don't worry about it.

Still, my 4.6L in the 8 had a ruptured diaphragm on the disy, & you would never have known it. It still did everything beautifully, as it was tuned with it ruptured.

Your hiccup sounds like excess fuel pressure, giving just a little flooding. Those things don’t like more than 2 PSI when driven gently. Check it with a pressure gauge, or remove the air filters, & look for wet throats. We used to run 45s at 2 PSI on 160BHP, 8,000RPM twin cam Cosworth Fords with out supply problems.

Some people used to bump the pressure up, & the things would flood, every time you had a big braking effort, & then take ages, [probably a second or so] to come clean when you put your foot down. You would see them running around the pits, with petrol running out of the inlet trumpets.

As for a little miss; when did you last check the valve clearances? A riding, tight, [less than 3 thou clearance] or sticking valve will cause your symptoms, if I understand them correctly, particularly if spitting back at low revs, gentle throttle. The problem seems to go away at higher revs, high throttle, but you can easily burn out valves.

Also check all the light wiring in the ignition system, particularly around the coil, if the wiring is old. They can look OK, but have poor contact, small breaks, or loss of voltage problems.

Hasbeen

[Marsu]

Thanks Hasbeen.

Once I have the throttle return sorted I'll be able to decide whether a mod to the dissy advance is needed to compensate for no vacuum advance. I recently read some testimonials on a company called [url="http://www.performanceignition.com.au"]Performance Ignition Services[/url] whom Greg Tunstall apparently uses, so I might give them a try if need be. There are located in Victoria but seem to offer a quick turn around.

I'll fit a pressure regulator next as I've noticed that the throats can leak fuel, particularly if the mixture screw is set too rich. Most of the doco I've read suggests DCOE need 3.5psi at a high volume, so I'll start there and dial pressure down if I continue to see fuel out of any of the throats at idle.

It's nearly 3 years (but less than 8,000 klm) since I checked the valve clearances. Time to do again methinks - thanks for the suggestion. I'd like to know how often BL expected this to be checked but can't find a listing in the ROM. Does anyone know or have a recommendation?

I'm 100% confident about the condition of the ignition wiring as I have renewed all crimped connectors and any cable which had tired insulation. I'm hoping that the intermitent no spark condition was caused by a faulty balance resistor that I've just replaced. Fingers crossed. [8]

[Hasbeen]

Marsu, I have been unpleasantly surprised at how short a time/mileage it can take for the valve clearances to close up somewhat on a 7.

I had expected an old fully beaded in OHC system to hold its settings much better. The car had been idle for couple of years, but that shouldn’t make too much difference.

Some of [about 3 I think] the valves in my current 7 had to be adjusted 3 times in the first 6,000Km of use, after her recommissioning.

With more & constant driving the settings are now holding for over 10,000Km, with just a couple of thou variation on a valve or two.

I do find that just a couple of thou tight will cause quite a large loss of power in these things.

I also found that light oxidisation, [not showing as corrosion] of the tangs on the coil gave me a very slight, but most annoying hesitancy at low revs, low throttle. I spent weeks chasing it.

I don’t know which part of the bayonet connector system was at fault, as after everything in that area was totally cleaned that the annoyance stopped, but I have a feeling it was the actual contact area on the coil, where the tangs bolt on that was the problem.

Hasbeen

[Cobber]

<font size="2"><font face="Comic Sans MS">Marsu, I use Performance Ignition Services they've always done right by me.</font id="Comic Sans MS"></font id="size2">

80'Triumph TR7, , 73'Land Rover (Ford 351. V8),
'89 Ford Fairlane
85'Alfa 90, 69'Ford F250.
76' Ford F100

[Troy ODoherty]

Just quickly, coughing back thru the inlet can be a sign of a lean mixture. Backfiring out the exhaust is due to a rich mixture.[:D]

Cheers Troy

[Marsu]

Thanks again Troy.

I enriched the mixture and that improved things on very mild throttle. I have the idle mixture screws now set about full turn from (lightly) closed.

This has made it almost drivable on very mild throttle (<1/4) but between there and 1/2 throttle it still coughs, spits and sometimes backfires! (It does have a mild backfire on overrun too.)

Trying to push gently through this bad running doesn't seem to work, but stomping on the pedal it bogs for a second and then takes off nicely. [8D] It does seem to have less torque in the lower rev range than it did with the SUs.

The idle is still too high when the engine gets to temp (~1400 rpm). I'm going to have to fabricate a better solution for the return springs as I think the angle they are at is not pulling tangentially to the lever's arc.

Based on some advice from someone in the club I haven't connected the chokes, but it is a bugger to cold start without them. Has anyone else out there fitted chokes?
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I'm slowly getting there. [:p]
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Oh BTW, forgot to mention that I do have the lockwires on the bottom of the carbs you mentioned and glad I now understand what they are there for.

[Troy ODoherty]

At this point I would be changing the emolsion tubes and trying that. It is such a simple job and will cost nothing.

To check the if the idle jets are correct follow this proceedure.

1 warm engine up

2 ensure that the balance is good and the engine is idling well

3 increase the idle speed using the front idle speed screw. Do this slowly listening for a change in the engine behaviour. Approx 300-500 rpm above idle it should start to run on the idle jets only. If it becomes ruff stop.

4 Now adjust the mixture screws evenly approx 1/4 turn at a time. If you turn them out you have richened the mixture. if the engine smooths out it indicates that the idle jets are too lean and need to be increased in size.

If no noticable change then return them to there previous point. Now screw them in. If the engine is now smoother the jets are to large and need to be smaller, as you have leaned the mixture out.

Whilst it is true that the mixture screws are only there to set the idle mixtures, this test shows that they have a small influence right across the whole operating range.

Still they are not to be used to try and adjust the mixtures at any point other than the idle setting.

Idle jets main jets and air correctors are cheap and if you are careful you can get pretty close using what you have so then you can narrow down what you may need to order.

Hope this helps[:)]

Cheers Troy

[Troy ODoherty]

I forgot to mention. Dont bother with the chokes. I have never seen a car in AUS need them. To start the car cold give it a couple of pumps of throttle and crank it over. If it doesnt fire stop and give it a couple more and try again.

They are all just a little different. My sprint needs this done a few times as i rarely drive it. It will sit for weeks at a time as I have not finished setting the webers up on it.Tommorrow could be the day as it is raining here again[:(]

The V8 with its quad 48s needs 6 or 7 full strokes on the throttle before it will start cold. it rarely fires up first time and the second or third time i give it 3 or 4 pumps. This is after I let the fuel pumps run for a bit to prime the bowls.

Once it is warm it starts without touching the throttle at all. It is also easier to start after it has done a rally, and then gets harder to start progresively untill it does the next event.

Cheers Troy

[Troy ODoherty]

One other quick thought. Check the wiring around the igition switch if you have any more spark issues.Also check the connections in the fuse box.[:)]

Cheers Troy

[Marsu]

Hi Troy,

Your suggestion to change to the F16 emulsion tubes was a great call!!!!

I fitted them with the 185 Air Corrector Jets that were already attached, made a amall balance adjustment and took the car for a test run. It is totally transformed. [:D]

I have low end torque again and all the hiccupping, coughing and backfires have ceased. It also feels crisper in the top end.

I still have a bit of a bog in the middle throttle range and a hestitation for a second when stomping on the pedal but I can at least drive with confidence now.
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I used your procedure to check the idle jets and it seems that they are ok. The idle does not get smoother when enriching or leaning out the mixture screws. Oh, it also idles and starts better now too. [:)].

I've just fitted new plugs (again) and will take it for a couple of 100ks run on the freeway tomorrow and then examine them to see if my mixture setting is truly right - I am a little concerned I may be too lean as the exhaust never looked and smelt so clean when on SUs.
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Only bummer is that the tacho suddenly stopped working on the test run. The coil connection is fine so it looks like the instrument might have died from shock of hearing the little Sprint revso wonderfully. [;)]

I love the sound the Webers make - there is now this fantastic burble/gurgle at lows revs and when the throats open the sucking sound is almost like singing.

Fitting them seems like the best decision I have made with the car so far![}:)]

[Troy ODoherty]

Ah another convert to the world of Webers.[8D]. I would be interested to know how it went with a set of F7 emolsion tubes in it. They are slightly richer in the mid range and may fix your remaining problems. It could also be that the accel pump is not quite right.

Be aware that the larger air corrector jets that you fitted with the F16s will lean the top end out. They have no real influence at any other point in the rev range. I would take the other airs with you on the drive and change them at some point to see what effect they have on things.

Good to see that it is all coming together.

Cheers Troy