Dellorto DRLA 40 B. What jetting for a 2110cc Type 1 engine?

No, because you had two trips after that? One of them might have re-jetted? Or as you say what's written on the jets might not be the truth. I just thought it interesting that the first one upped the airs from "the DRLA STD" (and mains to keep the ratio) so I wondered why and found the bit I quoted. If the quote is good info, he upped the airs because your afr got richer with revs above peak torque. If ALL THIS IS TRUE, sounds like your first RR guy knew what he was doing.
There's only one way to find out - measure your jets. Top Tip - don't buy a set of cheap jet drills from ebay - I did and they supplied random sizes, 3 of one size, 6 of another etc - laughable, not a set at all even if the container was marked as if they were. Ha.

 

Have a quick re read as i've just posted the other graphs and added in what the receipts say etc.

The first rolling rd figures i posted (before i found the graphs) were from my notes and mainly relate to the first rolling rd visit. Then the 2nd torque figure was from the 2nd rolling road visit, (see the 2nd graph).

As far as i know the only jet change happened at the first trip to the rolling road which only has one graph and one set off figures. It doesn't have figures before jets were changed and figures after jets were changed. I don't know what the jet sizes i wrote down in 2013 relate to!


Rolling rd visit number 2 doesn't give any additional info about changing jets or what size they are. Same bloke and machine as number 1 visit as far as i know.

Rolling rd 3 adds nothing at all to what we know!

Last weeks jet sizes are what i read off the jets in the couple of minutes one long stack was out the carb.
A photo was taken at the same time, when we zoomed in later we saw 32 for the vents.

So what the jes have stamped on them seem to have no relationship with the figures i wrote down in 2013.

Im easily confused though

 

Graphs much of a muchness, I wonder what causes the dip at 2,600 rpm. I think I'd find that annoying as often driving around those revs. Can you feel it when you're driving?

 

I’m just sticking my head in as I was tagged, but to be honest, I’m way out of my depth with all this grown up talk!

For what it’s worth though, if funds allow, I think I would look for a left carb with a vac take off, so you could fit a vac dissy. You could then sell the other one on?

 

No idea what causes the graph(s) dip at 2,600 rpm.
I've never noticed a dip when driving or accelerating in real life.
I'm not even sure im reading the graphs correctly. Thin line power/hp. Bold line lb/ft torque?

 

I'll do more digging into the jet sizes but reading my notes back I now think
Prior to 2013's rolling rd i had Main jet 160, Air correctors 215. Idle 55
My note to the Rolling rd mentions poor mpg and possibility of smaller jets. Invoice says re jet carbs

May 2022: my jets stamps show Main Jet 145, Air Correctors 175.
So i assume this is what they were changed to by the rolling rd.

Alternative option seems less likely: that the jet stamps are wrong & wern't scratched off and i'm now on Main Jet 160, Air Corrector 215.

 

I don't really understand what benefit id get from a vac dissy, except slightly better mpg.
I also don't fancy buying an unknown second hand Carb (with vac take off) £350+? & a new vac dissy £+.
Surely the cash would be better spent on a programable 123 dissy (without vac) £360 ish

My Twin 40b's were bought brand new and the right one slightly modified at the time. They were bought as a set and I know the history off them and how many miles they have done and what they have been exposed to (including the air filter stud down the carb!)

I'll add some pics of my slightly different carbs

 

Fair enough.

If a 123 can indeed mimic a vacuum then that does sound like a plan. I’m just a doddery old git that likes an old fashioned dissy, with a vac can that you can see working.

I don’t know your driving style, but if you like the lower end of the rev range, you will find a vac dissy / 123, a much nicer drive.

 

Other way round, power (rev dependant) climbs steadily - torque is measurement of engine efficiency - ideally for a nice drive it would climb fast initially and then be flat. Where it peaks is broadly cam dependant.

For a race motor you want a cam that peaks the torque at high revs because HP is roughly torque x revs - max torque at max revs is the max power you could get. The downside of course is lack of low rev torque x low revs = almost no HP.

For a well mannered camper engine you want a cam that peaks at lower revs so that you have power over a broad rev band. Mine is handy as an extreme version of that as it peaks at about 2,000rpm and stays fairly high to almost 4,000 rpm. So, I have 50HP at 1600rpm - that's as much as a 1600 at full chat. The torque then slowly drops off but as the revs are rising the power slowly increases, it's a very nice balance for "driving about".


Your Torque peaks higher so you need more revs (2,350) for that 50HP but that ain't bad at all. Also you don't get your peak 100 HP until 5,000 rpm+ and as you say you only rev it to 4,000rpm - you never use it, though as your cam is nevertheless quite mild, you do get 90HP of it. Compare to mine - I get my max 100HP between 3,400 and almost 4,000 and where your 90HP I have from 2,750. In a nutshell, that's why I like mine - it's no race car but has plenty power over a wide range of rpm and peak power at rpm I actually use a lot - motorway hills for example.

If I can be bothered, I might try and plot yours and mine on the same graph - not fair because I have more cc's, but more to see the difference of where our power is. Power is ultimately what we're interested in - just that peak power is somewhat irrelevant.
You put your foot down at 1500rpm and have to wait for the revs to climb - mine goes straight away.

 

I don’t know where aircooled.net got the info that the valve train will only last 5k miles and in retrospect I shouldn’t have cut and paste what they said. However, just looking at the cam spec you can see that a Web 111 cam has 0.476” lift and 272° duration, that’s a lot of lift and that means the valve accelerates and decelerates quickly, therefore it needs stiff valve springs to keep the cam followers on the cam.

The rockers don’t just go up and down, they wipe across the top of the valve stem, and the stiffer the valve spring is the more pressure there is on the valve stem and the more sideways force there is. And the higher the lift the more the rocker slides on the stem.

The Web 111 has the highest lift with 272° duration that they make and if there were no disadvantages all engine builders would use it but having said all that if your happy with it obviously keep it. Even if you changed it the cost would never be recovered by improved economy.

Circa 20mpg seems good to me but to reduce fuel consumption the ignition needs to advance when the engine is under light load and there is no point in fitting a 123 unless there is a signal to tell it how much engine load there is. If you can’t use ported use manifold vacuum, they’re the same as soon as the throttle is opened anyway.

 

It's at idle where you need to tell the distributor to ignore the vac advance, I have an idea you can do that with a programmable 123 - I'm orf to check.

[edit] yes you can - you can set a start rpm for the vacuum curve. Then you can see the vacuum you get on the app and adjust the curve to use your actual vacuum specific to your engine. It's a good bit of kit for anyone with odd ball engines and aftermarket carbs.

 

Odd balls ?

 

I don’t think I’ll get involved in ported v manifold vacuum discussion; I’ve probably said too much already.

 

Like you said - same thing as far as we care, apart from having vacuum at idle and that can be programmed out with any programmable ignition - a 123 is a really cheap way to get basic programmable - I know it won't do everything, but it does do the basics.

 

No problem with you posting the aircooled.net info.

Ive just received a very nice reply from John at aircooled net who has confirmed what it says on his site is correct in his opinion.

I have this CAM as it was what the engine builder fitted. I put my faith in him and he chose the bits he was happy with and had experience of. I have been happy with my engine and how it drives.

Now I know what i know, Im not happy I have this CAM, but its what I have. I dont have the skills to whip the engine out & replace the CAM & i havent got the funds to pay someone else to do it for me. So its a bridge i shall only be crosssing when the engine has to come apart for another reason. Which hopefully wont be for a long long time.

I'll never actually know if my, valve seat problem & loose valve guides were caused by the violence of the CAM or because mofoco didnt put the valve guides in tight enough in the first place. Or a combination of the two, or overheating or something else.

It's been a learning experience for me, but id rather it hadnt happened as it cost a lot of money and i missed a few camping opportunities.

This thread was originally about carb jets & i now know a bit more than i did before.

I hope for simple answers/solutions but there never seen to be any, just more things i should buy or change from what i currently have.

Still smiling, still trying to improve my knowledge.

My manifolds don't currently have any pipe take offs either. (Think they are the big silver tube things under the carbs that bolt onto the heads).

 

He's very conservative in is opinions and does his best to describe what he's selling without pulling any punches. He also kind of assumes the worst of his customer's skills and I think I'd rather have him warning that you can't just slap that cam in without careful consideration of the whole valve train that just selling it with no comment. He definitely means well but he sells a lot of things. He's probably had customer feed back on that cam that indicated that it's hard to live with but you know the yanks - light to light racing revving the nuts is the order of the day.

 

I have found John to be very helpful over the years.
Reckon he has been helping me since the 90's.
Would rather have his opinions that some of the others that sell any old stuff.

I will say, admittedly years ago, Mofoco didn't have the best reputation for their heads.
Reckon the loose guides is just one of those things and you have fixed it.

 

Even manifold vacuum is some indication the engine is under light or heavy load - the lower pressure at a given RPM the more the throttle plate is closed.
That high vacuum area is not explored fully on a simple pull on a rolling road.
If you can shut off the advance by using RPM as well as vaccum then you can use manifold vacuum and stabilise the idle using a 123tune's tables. Not perfect but better than a 009..
Normal carbs use the throttle plate closing the vacuum port as a proxy for idle speed selection.

Also have a read on why different rolling roads give different readings for the same engine with the same tune. Its not really valid to compare small tuning changes at different RR locations.

I have a tuning hill for WOT in 4th. If I can stay in 4th by the top, still doing 32mph .. its goood.

 

If you have a dial indicator and a degree pulley, you will find the specs of your cam and compare them with Webcam cam cards.
That's will be a accurate answer to one of your question.

Could it be possible to tap and die a vacuum port directly on a manifold?

Using this ;

https://weber-carbs.co.uk/shop/product/vacuum-take-off-union-0-8mm-bore-weber-dcoe-dellorto-dhla/

 

Thanks for tagging me Paul @paulcalf. I'm not sure what I can add to what's already been said. You've probably not noticed the torque dip as it would be most obvious at full bore, WOT, acceleration. Nevertheless, it suggests to me that there's a slight mismatch in the cam, intake size and length and the exhaust primary lengths. Maybe a quick fix might be longer intake trumpets, if they'll fit.
I'm slightly puzzled over the lack of vacuum signal as I thought I saw some ports on one of your photos. My 45's have one ported vacuum take off per barrel and one manifold take off per body. I think, but could be wrong, if yours don't have them they can be drilled as the boss is there in the carb body.