Twin DCOE 40's on a 1760 crossflowflow

In article , snipped-for-privacy@NOSPAMvoodoosystems.freeserve.co.uk spouted forth into uk.rec.cars.modifications...

That sounds like a full competition spec engine.

And it sounds maybe like a paddle clutch too.

They aren't mean;t to be street driveable. A know of a guy with a a 120bhp Skoda Estelle, with a tuned 120L (1.2 litre) engine rather than the more popular 1.3 choice.

His car won't idle below 3k. It revs through to 8k, instead of 5.5k. It is like shit of a shovel.

For the Danish MOT, he swaps out the engine for a standard ish one to pass emmisions, then puts the lump back in afterwards.

that would be normal for a modified engine due to the cam, can be a bastard to drive in traffic ;-)

Before blaming the carbs check the distributer advance centrafugal mechanism isn't sticking, as the symptoms you descube fit exactly. If you have a "Lotus Twincam" type Lucas 23d distributer this is quite common.

As for the carbs. Check the accelerator pumps are actually working, easiest to do with the carbs off -- the pump jets are very prone bocking on DCOE carbs and the pump pistons stick. Also check the pistons in the cold start mechanism are free and seating properly -- they MUST be used/moved ever now and again even if they are not used to start the car or else they corrode and stick --- which can cause trouble when a basckfire lifts them off thier seats. Next you want to check the jet and choke sizes are sensible, it could be the idle jets are too small or too large --- a lot depends on the airfilter used.

Check the condition of the manifold "O" rings and put the carbs back on and check the gaps on the double spring washers on the mounting bolts are equal at around 0.5mm. Next you have to balance the carbs, on cars with one choke percylinder I usually do a compression check first (and of course check the points and ignition advance). I find balancing twin 40s by ear much easier thanbalancing say a pair of SUs but if you have the right tool use it. Getting the idle mixtures set is the next stage -- a Colour Tune plug works well.

Flowed head, high lift cam, twin DCOE, doubtless lightened flywheel and heavy duty clutch.

Yup, sounds about right. Does it kick you in the head above 5000rpm?

My old Mini was a bit like that. Ticked over smoothly at about 1200rpm, but needed a feather touch on the throttle around town, had a clutch like a lightswitch, albeit a lightswitch that weighed half a ton :) but went like stink. That had a 1.75" SU, modded head, flyweight flywheel, heavy duty clutch and a power delivery that made me grin like a loon.

Welcome to modified engines. It is worth getting it checked for return to idle, but the rest sounds perfectly normal. Adapt your driving style and enjoy :)

snip The float levels are checked by removing the lid of the carbs and placing bit of round bar under the the float hinge strips -- can't remember the correct size of bar 5/8" would be my guess from hazy memory -- anybody know ?.

The distributer sounds like a Lotus unit, in standard form they only had 10 degrees of advance built in you can confirm this by looking underneath the base plate you should se a "10" stamped adjacent to one of the advance stops -- this may or may not have been increased by removing metel from the advance stop. with this distributer if the advance is set for max power you may find the timing is over advanced at low crank speeds you may also find the engine hard to start because of this.

Interesting. The ignition systems looks quite old for an electronic setup, so your probably right about its origins. I don't think this is the problem though, I'm sure it's something to do with the carbs, in particular the idle circuits. My only real issue is the way it doesn't always return to Idle. The difficulties of driving at low revs would get a little easier when this problem gets sorted because I'm sure they're related. I realise this isn't going to be a smooth town car, afterall I bought it for the sound it makes as well as the way it goes and looks. I wasn't around when they were in production, but I've always had a soft spot for a RWD Escort, this is my third one so far, and hopefully not the last.

Ben.

Weber DCOE carbs can have a problem with the throttle spindle twisting, this can be caused by an excess of pedal movement resulting puling the cable too tight. Normally it isn't a problem with Fords where cable normally connects to the front carb between the two carbs using a Lotus spec throttle quadrant parts but it can be if after market or home made parts are used. The movement in the throttle cable should not exceed the movement available at the carbs -- ie the when the the throttle pedal is fully down the carb throttle quadrant shouldn't be forced hard against its stop but a few "thou" clear

Just a thought have you got a servo on the brakes as this is prob on no 1 Cyl and can give you gip on setting up the 40s but don't expect to much smooth running below 3000 rpm if it is full race / stage 4, what cam do you have ?

Pete

suggestions

There's no servo, but that's no problem as I don't like 'em too much anyway. There is however a bit of rubber tubing blocking of the servo connection point on the manifold, I'll make sure it's properly sealed. I don't know which cam is fitted, but to manage 138bhp it's got to be at least a mild race cam. I had a look at some cam specs on the kent cams web page, most of the power bands start above 2000 and some don't kick in until 4000rpm for the full blown race ones. A 1760cc doesn't usually rev all that high, no where near the 8000rpm mark of the full race cams, so depending on the crank I'm probably looking at a max rpm of 6500 to 7000. Also because it idles happily at 950rpm, the cam cannot be as wild as it could be.

I'm not expecting a miracle, just a bit more smother running. It feels like it wants to pull from 2000rpm, but it cuts out when you put your foot down. The powers there for an second or so, then it kangaroos a bit until 3000 comes up then you get shoved into the seat proper. The rolling road session may be the only solution. It'll defiantly answer the question of whether or not it should run better under 3k. Just hope I can solve the return to idle problem before I go.

Fingers crossed,

Ben.

Humm How about your fuel pump I Know it's go the power @ the top end but I had a xflow 1762 cc 85mm bore, piper 285 cam, st3 big valve head, 40s, Steel valve gear, luinition etc got over 160 bhp (yes no bull) @7500+rpm very good on the road the pump went belly up (mitsuba electronic) & gave me all sorts of gip @ low to mid rev range.but full chat was OK fitted A facet solid state & comp filter king fuel regulator & all was back to normal.but only 15 miles to the gallon. Hope this is of some help Pete

It's got a Lucas electric diaphragm pump and a swirl pot high volume filter. I can't say I've ever noticed the swirl pot being empty or low, so I think the fuel pump is working well. The engine you described sounds very similar to what I have, I think the cam isn't as wild, hence the lower bhp figure, and I'm pretty certain it's got a standard crank that's been balanced so

7500rpm is unreachable. It does manage something like 20-25mpg on a decent run which isn't too bad considering. It makes the 40 litre petrol tank seam very small though.

I getting somewhere with it though. I took one of the carbs off at the weekend, the throttle spindle had been twisted, which meant the throttle wasn't closing fully on one side.I've rectified this and given it a good clean. I'm going to take the other carb off this weekend and give it a similar clean. I think something is getting jammed open a bit, probably a dirty throttle barrel or something to do with the pump jets. I've also sorted out a bad earth connection on the battery, and fitted a thermostat which was missing altogether. It's now maintaining a better running temperature which seams to help with the overall smoothness. I'm also getting used to driving with a light right foot when I need to, so things are defiantly getting better.

Thanks again for all the suggestions, keep them coming I'm finding them very useful.

Ben.

electronic)

Never heard of a Lucas fuel pumps apart from high presure for fuel injection -- begs the question is the fuel pressure too high and causing problems. With this spec of engine the standard fittement Fomoc or AC mechanical pump should be more than up to the job.

I'll look for a product name and part number and report back. It looks like it's of a similar age as the electronic ignition, so it might be of Lotus decent as well. If the fuel pressure was too high, fuel would probably be dripping or even pouring out of the air filters when the ignitions turned on but the car not running, i.e. the needle valves were being forced open and overflowing the float chambers. I think I would have noticed this by now. It does drive like it's flooding a bit a low revs, so I won't dismiss this totally just yet. I've got no choice but to use the Lucas one at the minute, because the mechanical fuel pump isn't fitted. There's just a metal plate covering up were it would have been fitted.

I've just cleaned and re-oiled the K&N air filters because they were looking a bit dry and dirty, maybe this will help things a bit.

Ben.

The lucas pumps were fitted to old layland/ BMC motors the best one to use is the one from an old Jag, the OEM crosflow one is of no use on full chat !!!!! as i know it cost me a set of powermax pistons back in the 80s sob sob are you any where near north Kent ? pjj

Combination of fuel injection, and smaller port sizes keeping gas velocity up. Good torque at low to medium revs but then the small port begins to restrict gas flow higher up.

Tim..

w00t, I'm in Scarborough too !

Got it all together again, balanced the carbs, set the mixtures and checked the ignition timing. It now runs like I suspected it should do, there's not much going on below 2500rpm but the power comes in much smoother. The only remaining issue is a minor one, when travelling at say 50mph in 4th gear if my foots off the peddle it runs smoothly. When accelerating hard it runs smoothly, but at the point where there's just enough force on the accelerator peddle to just start accelerating the engine sort of misfires a bit, and if kept there it can pink a bit as well. This problem is noticeable during other driving conditions, it just most noticeable when at cruising speed.

Am I running too little or too much advance or are my mixture settings too lean or too rich? Just for reference I'm balencing the carbs by listening to them with a bit of rubber tube to make sure they're making the same sound. I was shown this trick when working on an MGB with twin SU's by a friend.

Ben.

Sound weak mix to me, balenceing carbs that way all ways worked for me get it setup on a roller !! Have fun pete

I just found a guide to set the float levels properly, both carbs were around 3mm too low. I'll find out tommorow if this has done the trick and got rid of the weak spot. I'm going to book a session on the roller for next weekend, really looking forward to it now.

Ben.