dyno run on my old +2

[rgh0]

One worry I had was that the power seems to start dropping over 5500 rpm. Is this usual?
Cheers
Tim

Tim

The losses on the rolling road dyno go up roughly linearly with transmission and wheel speed. As you reach the maximum point in the power curve the losses are actually increasing faster than the power output of the engine is increasing. Thus the rear wheel measured power output peaks slightly earlier than the actual engine flywheel power.

After multiple dyno runs on multiple engines I have estimated the loss for my Elan and +2 at around 4 kw per 1000 rpm. This will vary somewhat depending on the types of tyres you run, oil used in the transmission, etc.

I usually see about a 500 rpm difference between the actaul engine peak power and the rolling road rear wheel peak power. The peak power in a big valve sprint twin cam is between 6000 and 6500 rpm so for the rolling road dyno to show it at 5500 rpm is not unexpected.

regards
Rohan

[tdafforn]

When I say flat spot I mean that it if the car is running between 1.5K and 2.5K RPM and I push hard on the gas, the car hesitates and then takes off..
Keith, is this what you mean?
Cheers
Tim

[type26owner]

That's a bog. Look at the accelerator pumps in that case. A bog that lasts about a second can be from going too fat or lean and/or the duration is not matched for your engine. You'll have to figure out which. With a fast wideband O2 sensor the shot AFR can be easily seen and the fault condition corrected with the least amount of fuss and bother. Your tuner guy should have done this before your car was put on the dyno.

[tdafforn]

Just checked my pumpjets on the Dels and they are 45, which is correct according to elan books..
However the books on dell ortos that I have suggest 35-40, so I wonder whether it is bogging due to running rich.
May be time to buy some new jets.
Cheers
Tim
(I agree with you about the tuner, I did mention that I thought that perhaps the pump jets were at fault, but I bet he didn't have any..! Sad really, he was recomended by some single seater hill climbers that hold records at some of the hills 'round here)

[type26owner]

Tim,
Without the right diagnostic tool you're just guessing what to do. It's a hopeless situation really which will soon be frustrating and expensive. If this stuff were easy any tuner would be able to rectify all these faults pronto. Most don't have a clue.

I predict in the next couple of years the folks that posted technical articles on how to do this or that will be horrfied to find they didn't know diddily squat afterall. There is huge surge of understanding of how a carbie really works with the recent introduction of the ultra-fast wideband O2 sensor technology. Even the carburetor manufacturers didn't understand it completely. They just trial and errored it until they got it to work. The real research to understand it is done later in academia.

[tdafforn]

I am currently working with some maths guys and a chem engineer that use PIV to look at single and two phase flow. I'm just a biologist, but I can understand the compliexities of the problem. In fact I asked them whether they would pop a dellorto into one of their systems when they have some spare computational/PIV time. They looked horrified..
I know what you mean by "just guessing what to do"...
My intuition would be to do plots of everything, throttle position, rpm, mixture (%CO?), ignition advance. Then look at changing each parameter in a systematic form to get some data sets that I could at least model using some of the empirical methods we use in the lab..
For instance, some plots of just mixture vs throttle position vs rpm (or power) for a wide range of idle, idle air corrector, main, emulsion tube would be interesting..
I have never understood why books don't have this sort of data. It would surely be easy to collect and if done with a close to standard twinc it would have implications for most people with twincs.
My guess (and I could be way off with this) would be that in such a complex parameter space there are probably a range of close to correct settings.
Anyhow, have to stop ranting..
Thanks for the help, without a high tech mixture read out I will have to stick with my standard %CO probe. It seems to show a spike in %CO to 8-9 which followed the bogging..
Cheers
Tim

[Dave-M]

Tim,
Don't change the jets, look for the fault elswhere. If the jets are not blocked and the rubber o rings are present you will need to remove the carbs and check further. I suspect that this is why your rolling road man glossed over the problem. Dismantling the carbs and doing a re-furb is not a quick job.
The acceleration circuit in dellorto and weber carbs is quite complex and cannot be sorted in 2 minuits.
I don't doubt he would have been able to do it but would you have been able to have left your car for a day or two while he sorted it?
Lotus did not sell cars that did not run correctly just as they did not sell cars where the headlights drooped or the water pump faild after 10k miles.
All these problems occur through user neglect / ignorance.
Keith,
Are you really saying that lotus, ferrari, porsche et al did their carb tuning by guesswork / trial and error, I think not. Thier carbs were set up very carefully to accomodate all the variables their cars would encounter.
It's all very well critisising 1960's technology with the benefit of 2005 technology (innovate/ tech edge wide band lambdas) but for their time these cars were cutting edge and did their job very well. If you can improve your car using this technology that's great but please dont say that lotus did not know what they were doing in respect of weber / dellortos. I seem to recall they were world F1 champions and won Indianapolis. It is perfectly possible to have a sweet running engine with standard factory setting without all the esoteric solutions to problems caused by neglect or abuse.
I well remember in the late 60's seeing a lotus engine (fitted in a cortina)
which had been rebuilt by a company by the name of Broadspeed. They were well known in england for their racing saloon cars. The engine was all standard and at idle you could balance a coin on edge on the cam cover.
It can be done!
Even with the wide band lambda technology I think massive gains are not there to be had but subtle individual improvements can be made with careful thought.
110-130 BHP from 1600cc in the 1960's is exceptional accept it and enjoy it as crude as it is when compared to modern EFI equipped engines
Regards
Dave

[type26owner]

If you've got a Gunson CO meter it's not suppose to be that sensitive, that quickly. IIRC, they tell you in the instructions to hold the rpms steady for 30 seconds to get a reliable reading. Better than nothing though. You ought to be able to spy a black puff of smoke come out of the exhaust too. At least someone following you should be able to see it.

Having come up to speed on the O2 sensor stuff all you really need as the bare essentials for doing the tuning is a throttle position sensor and the AFR meter. The testing procedure is done the same way over and over so you don't need to know the rpms. It's nice but not necessary. The AFR meter records the time streaming along automatically.

The Dello has a diaphram accelerator pump, I think. If so, the flowrate is determined by the spring tension. There are normally at least three different spring types available for the weber. You should check to see if the Dello has a similiar setup. The reason is the springs are quite cheap and have a big impact on the behavoir of the pump shot. Messing with the jets is expensive and the affect happens slowly. If it's too fat then you'll want to slowdown the shot. It will actually be wet-fouling the plugs for a moment and that's the bog you feel.

I'm just a biologist, but I can understand the compliexities of the problem.

My son is home for the holidays from graduate school and it's a delight to have him as a soundboard for discussing some of my most recent observations on the Webers. He's going for a phd in bio-physics. That's an exploding field and he's getting into it at just the right time when there's lots of funding becoming available.

[type26owner]

Hi Dave,

Thier carbs were set up very carefully to accomodate all the variables their cars would encounter.

Please direct me to the text that supports your claims. I've been guessing and surmising by comparing it to the direct evidence of the tuning work I've been doing. From the published jet sizes I've come to the conclusion they had glass belly buttons. I can't speak about any other marque since I don't own one of those. Pointing out the racing success as a reason to blindly believe their engineering was faultless is a joke. That's the funniest argument I've heard recently. I also own a Lotus 41. Would you like to know how stupid they can be with a racecar? The front oiltank is held in with a bungee cord. They drilled two holes in the frame tubing to hook the cord into. They didn't think to provide drain holes for the water that gets in there to run back out. Well it eventually rusts through to the oil lines which run through the bottom frame tubes. Bad things happened as a result!

I suggest you first read John Passinis' books and the Weber Tuning Manual. I would love to debate the subject in fine detail. I think clearly John P. will point out it was done by trial and error guesswork.

I'm trying to simplify the tasks and do away with the bullshit so everyone can have a perfectly tuned induction system. Before going off on me may I suggest you try what I'm saying first and see for yourself if it's bullshit or not. Advising Tim to tear into the carbies looking for some unspecified fault is not really helpful. What is it he's going to check exactly?

I've had it watching them make decisions about stuff they don't understand. I was told recently it's a great honor to have another laboratory copy my kickass x-ray optics design. Well it turns out just last week I found out they threw out the hamburger and ate the paper wrapper so to speak instead. Wouldn't ya think they would at the very least ask why I did it a particular way before changing it????

but please dont say that lotus did not know what they were doing in respect of weber / dellortos.

Why, when the facts clearly support my contention? I wish it was not true too. I'm not the only one that could not get the stock configured carbies to run correctly.

[tdafforn]

Hi Keith et al..
I tore the carbs down last year. o-rings had the consistancy of tar! Car ran better after. Tested the pump jets and they all seem to be firing approximately the same amount for the the same time the same distance.
With respect to possible puffs of smoke at acceleration. You hit the nail on the head!
I travelled with friends in convoy over the summer and one of the chaps took me aside and said the car kept puffing smoke, and that I should perhaps sell it and by an MX5 (Miatta) as the engine had obviously had it!!! I obviously didn't take his advice, but did assume that I was burning some oil (the engine is probably due for a rebuild, mind you a compression test showed no signs of detioration?). Anyhow, on the way back form the tuners (dark night) I watched through my mirrors as I pulled away from the many traffic lights. The lights from the car behind beautifully lit up puffs of smoke on take off. There also seemed to be some when I was accelerating from about 2000 rpm steady...
So perhaps it is pump jets..

I do have a Gunsen CO meter (probably worth the 15 pounds from EBAY), and it probably explains why the tuner reconed that the car was in pretty good tune. However I do have an eye on your set up keith. I wonder whether some of the other guys from the UK on the list would chip in so we could share one!

Thanks for the help
Cheers
Tim
PS Good luck to your son, Keith, I am a biophysicist with a particular interest in polarised optics.

[Dave-M]

Tim
You have just saved me a load of typing with your last post.
I will just have to do the end bit now.
Assuming the situation with your pump jets is still the same, ie clear and squirting equally, The following may be of help.
By changing the pump jets to a larger or smaller size will not change the amount of fuel discharged through the jet it will only extend or shorten the duration of the squirt.
Assuming the correct jet is fitted you can vary the amount of fuel discharged by altering the adjustment on the rod which connects the throttle spindle to the diaphragm pump arm. By screwing the nut upwards you will increase the amount of fuel discharged and vice versa.
A typical starting point is to have around 3mm of thread exposed below the lock nut and work your way from there.
Unfortunatly you will have to remove the carbs to do this but while they ore off at least you can give the distributor the once over.
Let us know how you get on.

Keith if you read this I will get back to you tonight

Regards
Dave

[type26owner]

Hey Dave,

Keith if you read this I will get back to you tonight

Great! However, I don't want to fight with you over this stuff. That nasty behavoir stuff goes on over on the mailing list and it can stay there. This forum is for the polite folks that just want to get on with it and resolve the problems they are having. You obviously have much more hands on experience with the Dellortos so let's join forces to understand the issues.

I've posted a ton of stuff on the carbies here and it would be good if you reviewed it and would give me feedback and your insights. I know I've made many mistakes but that's the only way I know to learn such a complex subject like this turns out to be.

Let me point something I became aware of recently. John Passini blows past explaining the emulsion tubes like it was voodoo magic. He didn't understand them it's safe to assume or he would not have done that. The Weber Tuning Manual is also quite vague. Why is this? Webers' emulsion tubes have been around for over forty years now and as far as I know no one has provided a simple way to deal with choosing them or tweaking them to alter their effect. This is basis of my claim Weber does not know exactly how they work either. The simple reverse engineering stuff I've been doing has revealed some fruitful results. I'm keeping this stuff to myself for the time being though.

I don't have a copy of the Dellorto Tuning Manual and I'm curious as to whether they have any in-depth info on the emulsion tubes.

[steveww]

I am in the UK and I have already purchased the same wide band lambda sensor set up as Keith. If you are looking to buy your own I would suggest you check the prices carefully. I order mine direct from the USA and saved over ?100 against the likes of Demon Tweeks etc..

I back up what Keith says totally, with out one of these gadgets you are just making a wild guess as to what is happening with the AFR.

[tdafforn]

Hi Steve,
thanks for the heads up on the prices. I had noticed the discrepency...
Did you by direct from the company? Were they happy to send it to the UK?
Cheers
tim

[steveww]

Yes, placed my order direct with innovate motorsports and they were happy to ship anywhere in the world. They shipped by UPS and you have to remember there is some duty to pay when it arrived in the UK.