DCOE setup help request

[Marsu]

Yesterday was initially rewarding but then frustrating. A typical Triumph motoring experience - the full experience being contradictory. [:0]

After ~60klm on the test run, using mostly very mild throttle, I stopped and fitted the 175 Air Corrector Jets on the F16 Emulsion Tubes. Inspecting the new plugs I thought the mixture looked lean, more so on No 1 & 2 than 3 & 4, so I enriched the mixture screws 1/4 turn on the front carb and 1/8 turn on the rears.

On restart it seemed improved as the bottom end bog was reduced/less prevalent. But on full throttle take off it now had a hesitation and "flutter", most noticable in third gear. It seems like fuel starvation, which I don't understand as the 175 air correctors should have enriched the mixture. Perhaps the fuel pump is not keeping up with demand? I doubt this though as I'm sure I would have experienced the same thing with the other air jets.

I did another 160klm, mosly mild throttle with the odd power take off. When I pulled the plugs No 1 & 2 looked way too rich. No 3 looked a quite lean, No 4 looked a little rich. The discrepancy between No 3 and 4 is confusing as I am confident both were adjusted equally previously. I leaned out (tightened) No 1 & 2 a 1/4 turn (to where they were before), loosened No 3 an 1/4 to enrich and tightend No 4 an 1/8 to lean further.
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I fabricated a new bracket for the throttle return spring end points, hoping this would provide a better solution to the idle issue. I think there is a problem with the shaft bearings as even with 3 springs stretched way beyond what seems right the tangs are not returning to stop against the idle speed screws when it is hot unless I physically push them up (yet it is now good when cold). Further, their is now so much tension on the accelator it is not so nice to drive. More work required here!


The drive home (another 60klm) was pretty ordinary. [:(]

The low end bog and fast acceleration flutterng had both seemed to have got worse after the mixture changes. [:(!]

I think I need to reset all mixtures and balance again. I'm inclined to order some 180 Air Corrector Jets and fit them as they are between the other two.

Troy, I'm curious about trying the F7 emulsion tubes. Would you recommend changes to the main or air corrector jet to use these?

I'm going to have a closer look at the accel pump next weekend so would value suggestions as to how to check its operation.
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Something else I'd value advice on is how the crankcase breathing tube from the top rear of the timing cover should be rigged for DCOE setup. With SUs this was plumbed in to ports on the carbs, and hence I assume received a vacuum. On advice from a club member I have run this to the charcoal canister as the Webers did not provide an equivalent pickup. Since doing this I have a small discharge of oil around the Sprint sump dip stick, not major, but suggesting some ring blow by. Opinions welcome.

[Troy ODoherty]

Hi Marsu
You really must do things in the correct sequence or you are going to make your life ell.
Set the idle balance and the mixture screws. Now LEAVE them alone.
They have no useful influence on the mixture at any point other than at idle.
If you change one mixture screw 1/4 turn you must adjust all the others the same amount. Logic and attention to detail will win everytime with Webers.
If there is a mixture problem some where else in the rev range then you must adjust the correct components to fix it.
If there is still a flst spot in the mid range then a slightly larger fuel jet may help. It is just a likely that a change to a set of F7s will help to. If it is there when you open the throttle gently then it is probably an emolsion tube issue. If it is worse with more rapid throttle openings I would be checking the Accel curcuit.
It appears that you have too much spring on the throttle shaft.Find out which one is the master throttle.IE which side of the balancer pushes the throttle home with a solid pin not the spring loaded side.

I think it is the front carby looking at the pic. Make the springs work on that side of the balance only. this way the springs wont upset the balance.
I have to go I will post some more possible issues with the thottle return later

Cheers Troy

[Troy ODoherty]

Back again.[:)]If you are still having idle return issues, try this.
Disconect all the external springs. Remove the top covers from the carbies. the 5 screws on top. Carefully remove the top covers and floats. Open the throttles and see if they are smooth in their action. Now lift the top of the accel plungers and feel the difference in the action of the throttles.You should notice that the throttle feels as if it drags slightly when the accels are operating normally. When you hold them up they should feel slightly lighter.

Now that you know how they feel, the nuts on the end of the throttle shafts that hold the end covers one may be too tight.Bend the tangs up and carefully loosen the nuts, say 1/4 turn now feel the throttle action and check to see if they return better.

Sometimes the washer rubs against the end of the carby body. Sometimes you can leave the nuts a little loose. It is also possible to place a very thin shim washer under the covers., and then retighten them. They dont need to be very tight, as the lock tab will retain the nut. DONT use excessive force on them either doing them up or undoing them as this is when most shafts get twisted.

Have a look at the washers as you take them of. Check for shiney marks were they have been rubbing on the bodies.

Now retighten them one at a time. If the throttles dont close after each one is tightened then that is where your problem is.Even my brand new 45s and 48s dragged a little.

Cheers Troy

[Marsu]

Thanks again Troy.

I've learnt my lesson regarding adjusting the idle mixture screws based on visual inspection of the plugs after driving on a range of throttles. In future I'll only make consistent adjustments across all mixture screws. Though, I assume the plug inspection approach could be used if the car sat idling for 15 to 20 mins on new plugs to confirm idle mixture setting?

I'll follow your suggestions for checking and adjusting the throttle return, fit a spring directly to the master throttle lever (it is the front carb and only the rear carb levers were connected to springs before) and reduce the spring tensions.

When I first fitted the F16 emulsion tubes (and then subsequently fitted the 175 air jets) the flat spot seemed reduced under very gentle throttle, but not changed much with more rapid throttle openings. Hence, I'll have a look at the accel curcuit next.

I greatly appreciate the advice.

[Marsu]

I had a closer look at the accel pump, throttle shafts and levers last night. The action on the front carb is not smooth with either the accel plunger raised or in normal position.

The levers and shafts seem to come to rest closed, but a slight further pressure on the front lever causes it to "snick" back further. It's hard to describe, but it seems like the shaft bearings may have a worn spot to which the shafts naturally come to rest and it takes additional pressure to force them past this so that the throttle plates are fully closed, or the lever shifts on the shaft flat with the same effect.

Due to the lever's balance bar arrangement it is not possible to remove them (and the underlying washers) without removing the carbs from the manifold - for which I did not have time. The shafts are also missing lock tabs for the nuts.


Given that carbs and inlet manifold need to be removed to fix the oil leak from the water pump I stopped at this point. [V]
[edit]
The pic above is shot from the left hand side of the car - the front carb is on the left

[Troy ODoherty]

Hi Marsu
You may not agree at the moment but this is good news. You now know the most probable cause of you problems. If the lock tabs are missing it is almost certain that the throttle nuts are too tight.

When you remove the carbies, you will be abel to inspect the washers for marks to show they were touching. It is extremely likely that this is the problem with the lack of return. I would be very surprised if you have a bearing issue.

As you are now going to remove the carbies, it is a good time to check that the action is smooth and consistent. Check that they return properly with the nuts loosened. Also check that the throttle plates are centered in the bore. It is possible to loosen the brass screws and allow the throttle plate to center itself. then retighten the screws with a drop of loctite to make sure they dont come loose.

You can try loosening the nuts that you can get to and see if that helps.

Cheers Troy

[Marsu]

blah - see below

[Marsu]

Hi Troy,

I'm waiting on a water pump kit to arrive from the UK so thought I would continue trying to get a reasonable tune from the DCOEs while they're still on the car. I've disconnected the crank case breathing tube from the charcoal canister and the oil leak from the water pump has reduced to being trivial - I'm checking the level each time I stop.

I forgot to mention in my last that I had slackened the throttle shaft nuts and this did (sort of) help with the idle problem. It now struggles to idle when cold, requiring some throttle at first and then the odd jab on the accelerator to keep it running. When it first warms up it begins to hold a correct idle, but after running for some time the idle gets up to ~1300rpm or higher, particularly if I have been a little heavy with the right foot.

With the engine hot I've now run it round a test circuit on the local roads using the four combinations I have of emulsion tubes and air jets (F15/F16 and 175/185). The F16 with 175 are most tractable but have a flat spot as it progresses from the idle to the main circuit. This is more noticable with the 185 air jets. With the 175 jets I can alleviate the flat spot by dabbing the throttle once (to engage the accel pump circuit) and then push smoothly on the throttle through the flat spot.

Hence, I think if I go for an air jet that helps enrich the progression further, say 165 or 170, I may have a something that works really well.

But the budget may permit me to try another emulsion tube with say two alts for main and air jets. The emulsion candidates seem to be F2, F7 or F11, with appropriate jets.

Would value opinions on which tube and jets I should try!

[Troy ODoherty]

Interesting stuff Marsu. I am a bit short of time untill tomorrow night , but the air correctors should have little influence , except at high revs. I would try slightly larger fuel jets, Probably one or two sizes and try slightly richer setting on the idle mixture screws to help the cold idle.

If you then still have problems i would try an F7 tube. I may be coming to Sydney in a couple of weeks and might have time to catch up. I so I can lend you some fuel jets and tubes to try as I have a good assortment.

Cheers Troy

[Marsu]

Hi Troy,

Yesterday I fitted some second hand F7 emulsion tubes with my 135 main jets and some new 195 air jets.

It's another fastastic call! [:D]

With very light throttle (`1/8) there is *almost* no flat spot on progression from idle to main circuit.

With slightly more throttle (<1/4) there is a *very mild* flat spot on progression, but much less than what I had with the F16 and I can gently push through it.

With mid throttle (~1/2) it bogs momentarily and then takes off. The bog is shorter in duration than with the F16 on progression.
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I'm so amazed at the difference in the bottom and mid rpm range. [8D]

The car has more bottom end torque than it's ever had before, including with the 1.75" SUs.

Before, with the F15 & F16, it felt sluggish in the low and mid range, a bit like a car feels when the timing is off.

Now it is transformed in this part of the range: much sharper in response, gaining revs much faster.

It also runs a little hotter on the gauge, smells richer and is louder, much louder in fact!
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Unfortunately it's not quite right using wide open throttle, having a major hesitation and makes a strange sort of sound, so the 195 air jets are obviously not the right size.

I'll do some sustained wide open throttle test runs over the weekend and take plug cuts in the hope I can see if it is rich or lean.

I've bought some new 205 air jets so can go another step leaner, or back the other way using the 175 or 185 if it needs enrichment.

I'll let you know how I get on.

Thanks again for all your help so far.
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ps - do let me know when you're coming to town - I'll buy you beer or two.

[Troy ODoherty]

Hi Marsu
Good to hear that it is responding to logic[:D] I would try changing fuel jets and see what that does for you . The fuel jets govern the mixture right thru the main circuit, the air jets only work on the top end. From what you are saying I would increase the fuel jets by one or two sizes and try that . If it fixes the flat spot on progression and you still have an issue on the top end, then I would decrease the air jets.
The larger the fuel jets the richer the mixture becomes. The larger the air jets then the leaner the top end becomes.

I will be in Sydney on Friday night and am busy with my young bloke on Saturday. He has a state chess tournement on all day and i have to go to an AGM for the NSW Classic rally car association on Saturday night. If the young bloke does well on Saturday then he has to play again on Sunday. If not I might be able to catch up on Sunday morning.
Where abouts in Sydney are you?

Cheers Troy

[Marsu]

So very close now!

This morning I swapped the 135 main and 195 air jets on the F7 emulsion tubes for 140 main and 185 air jets to make it richer. I also fitted the dash vent fresh air plenum as I was hoping this was the *final* jet change.

It wasn't easy to start and after it did and warmed up I took off and it was apparent that things were vastly different and not in a good way! I stopped and removed the fresh air plenum. On restart the car began behaving more normally again so it is obvious that the rear carb is not getting the air it needs with the plenum in place.

With the richer jets the hesitation when using wide open throttle was gone, but so was the low range torque and super throttle response in the mid range. It felt sluggish again!

I pulled the plugs when I got to the workshop (55klm) and they were reasonably consistent across all pots but I found them difficult to read with confidence regarding mixture in comparision to how the plugs looked after running under SUs. There is a lot more soot around the rim and the electrode is sooty on the open side and clean on the side under the foot. The foot looked on the lean side of normal, but this is hard to see in the following pic:


I fitted the 135 main and 175 air jets for the return trip home. This improved the bottom end torque and mid range responsivness, The wide open throttle is also ok but not yet right
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I'm going to get some 130 & 125 main and 170 & 165 air jets to see if there is any improvement.

I'm also tempted to try variations on the 50F9 idle jet to see if that helps solve hte minor bog on transition.

Input welcome!