thielepr

Ok I have a 12 bridge ported with a dellorto 48. Whit the hooley"blue" fuel pump. The thing is I got the car yesterday from the mechanic because I broke it in a Solo event.

A few months ago a went to a dyno jet an a got 144whp (I was looking for 160) with 12.6 in Air/fuel ratio at the pick. But when I was in the SOLO event it was making a lean sound at high rpm. After three times of the "lean" sound the inevitable happen. kabummmm.

Now I have the car back (in break-in) and I have the fear to get the same "lean" sound. The only thing that change is that the day before the SOLO event we clean the Dellorto. But it was the same setup. Also when the car start to get problems we open the gasoline jets but nothing diferent happen.

My question is: Is there a common setup for dellorto? Air jets gasoline jets, fuel pump, fuel line ect

t_g_farrell

iTrader: (1)

Take a look in this link: http://www.gruntled.com/Dellorto

Theres some info on jetting for street ports there. You'd have to extrapolate that to a bridge port.

DriveFast7

iTrader: (1)

Which intake manifold do you have? Does the carb sit on top of the motor or on the side of the motor, right above the headers?

I can help with jetting either way but need toknow the manifold layout as it makes a big difference.

thielepr

side draft, on the top of the engine

thielepr

I put 2 1/2 turns of fuel and have the same lean. Put the car back to only 2 turns and no problems. I need a better fuel pump? I need to replace the fuel line?

Siraniko

iTrader: (13)

typically, when you go out more than 1.5 times (from seated position), the idle jet is too small.

t_g_farrell

iTrader: (1)

I'd start with the street port jetting from the link I posted earlier and work from there. Also there some good books on tuning Weber/Dells you could look in.

thielepr

Looking to solve my problem I notice that I open this thread about three years ago and now I still have the same problem. The engine hasn't broken again (a miracle when you see the dyno chart) and we have reaced in track days for this three years. The only difference in the engine between 2008 and now 2011 is MSD ignition on the car.

The problem that we still have is that engine turns very lean after reaching 7,000 rpm and logically stops procuding more power.

The car is a 84 12A bridgeported with MSD ignition and Dellorto 48 carb. I don't have many experience working on jets and Dellorto carb. I just want to know what should be the dellorto setup, find the parts and try the dyno again.

Here is the dyno chart. Thanks for looking

rwatson5651

iTrader: (5)

I think you need a smaller air corrector jet, that will help richen it up some in the upper rpms.

thielepr

I have found this link in another old thread. It's for webber on triumph but the explain about the air correttor jet
http://www.tjwakeman.net/TR/WeberDCOEinfo.htm#idle

j9fd3s

iTrader: (3)

what needle and seat are you running?

81WideMariah

iTrader: (8)

You need to read up on your carb set-up and how to tune them. You've been given several recommendations and you are ignoring them because of your lack of knowledge.

Air bleeds or correctors control the amount of vacuum allowed to bleed off of the emulsion tube, which directly affects air/fuel mixture in the upper RPM range. Additionally, your floats could be improperly set and you're emptying the float bowl. You could also have a fuel delivery issue. Possibly a clogged fuel filter... poor voltage to the pump... clogged lines... the list goes on and on.

You need to stop looking at the carb as a PART and more of a fuel management system. If we were dealing with fuel injection here would you think that you could take the computer/injectors/sensors from a Mustang and bolt them to your car and it will magically work?? I think not.... and a carb is no different. It replaces all of those injectors and fancy sensors with mechanical linkages and jets..... and replaces the computer with YOU.

You have 2 choices here..... educate yourself, or pay someone to do it for you. There are no free rides.

Or just keep beating on your engine and drop another $1k into a rebuild, and keep doing that until your wallet empties out....

snivley whiplash

iTrader: (4)

buy the how to tune the webber/delarto carb book. it wll be your bible. as 81wide mariah said, the fuel delivery is VERY important, look outside the box at the whole picture.
I have been tuning my dell on a 13b six port now for a few months. Granted it is a daily driver I seek to make it perfect..........WRONG answer. you can get it close but remember, It will change running charistics with weather changes. Just the nature of the dells. Find a happy medium and run with it.

As for the wot a/r ratio, It will change engine to engine, imo 12.5 is too lean at wot. some say this is ok, not me sorry just my opinion. I am at 11.7 wot and very happy. No smoke pulls hard and plug readings are just slightly dark.

As for jets, I use a 80 primary and a 180 main, you will need to start changing e tubes and air correctors from that point to get where you want to be. I have done so many changes in the last few weeks I don't remember what is in my set up now. Just know I have hundreds of dollars in jets and e tubes, some of which I got when I purchased the car and more I have purchased in the last three weeks.

Keep at it, you will get there. stop making full throttle pulls till you get the low speed sorted out first then work up from there. Also use stock ignition timing to start with, get the fuel correct then start to power tune, this will save you any more engine problems. Also if you are at hard pull and hear what sounds like pop corn popping....get off the throttle, it is predetonating and surley to pop an engine.

Hope this help you to get your tune better, just remember more fuel is better that lean.

Joe

and btw I am running 40mm chokes right now and looking to go bigger soon

PercentSevenC

It's pretty hard to get an NA rotary to knock. You'd have to be running some pretty crazy ignition timing. Run it at whatever AFR it likes to make the most power. Every engine and every carb is different here, so what someone else's setup likes might not be what yours wants.

The air correctors are the first place I'd look (you want to go much smaller than whatever you're running now), followed by the needle valve and/or float level and/or fuel pressure (it might be running the bowl dry at high RPM).

thielepr

You have some strongs words in your post . But they are very true. My lack of knowledge is the big problem.

I decide it to choose both options. I have been reading a lot on how to tune the webber/dellorto and also find a good mechanic with a lot experience in webber setups.

His name is "loquito Killer" you can search it on youtube. He's have some very good numbers in the 1/4. Obviously using microtech but he came from the webber times. He verified everything fuel pressure, pump, leaks, temp, fuel ine, and every inch of the dellorto. The time was retard. After the check the car still runs lean on high rpm.

He explains me how work and whats are the jets. I'm ruuning 230 on air correction jet and 250 on needle valve.

I just ordered 150,170, 190 air corretion jets and a 350 needle valve plus the gasket kit.

Also he found that the alternator wasn't working at 100%. I'm addressing that untl the jets arrive.

Thanks everyone for your comments and suggestions

thielepr

Thanks to all your inputs. After some self study I ordered the needle valve and the air correction jets. Here is the new dyno. Comparing to the old one where the air/fuel ration went to 16 after 7,000rpm ths one stays on 12.3 at 8,500 rpm.

thielepr

j9fd3s

iTrader: (3)

much safer AFR curve! now if you run it on a cold day, or the fuel filter isn't 100% you have some margin...

interesting that the HP didn't change at all

DriveFast7

iTrader: (1)

Larger chokes, go up a few mm. You should make more than that. That manifold and I'd assume the 39mm chokes that came with the carb from Racing Beat runs out of breath at 7000rpms anyways. Above that the motor is just spinning and not making any more HP.

t_g_farrell

iTrader: (1)

+1

I think I've read that a bridged 12a gets around 240 or so crank hp so you should
see around 210 rwhp or in that range. Hopefully the engine was built to do this
with hardened stat gears and oil mods and extra pressure. It will need to spin
up to 8-9K I think to get this power. Also, the longer intake runners for the Dell
(assuming the RB 2 piece intake here) will tend to keep the torque curve and
power lower in the rpms than an IDA or other short intake runner setup.

thielepr

Yes you're right. 39mm RB manifold here. But first we are going to correct an oil leak before the engine gets some damage