I'm having trouble getting my Dell'Orto in tune. My main troubles are throttle response and idle after the engine reaches operating temperature.
First, the throttle response issues. I'm running the Carter pump and Holley regulator ... the gauge registers 4.5 psi and as far as I can tell, it maintains the pressure under load. The car accelerates with spunk, but it's just that it sputters when I'm moving from a dead stop and it lurches when I'm in the lower end of the rev range. In my experience that point to flooding (possibly the pressure is too high? - don't know) but I'm keeping the 4.5 psi (per Racing Beat). I'm thinking maybe I got the wrong regulator, I got one that goes from 4.0 psi to 9.0 psi (because if I can get a Holley system, then I will - I'm really not liking the Dell)
Second, the car idles fine when it's cold and heating up. It is a pretty solid 1,000 RPM. However, when it gets hot, I've noticed that the throttle is not returning to the stopper screw all the time (unless I stab the pedal a few times, VIOLENTLY!!!!) I've chopped about an inch of the return spring, hoping that the increased tension will make it return. I've cleaned the linkage several times (even though the carb is practically brand new - it sat in my room since 1995) Nothing seems to work and the thing idles at 2000 to 3500 RPM when I'm at a light, because sometimes stabbing the throttle doesn't even work.
Frankly, I'm running out of ideas and I need to get this thing to behave better because now it's my daily driver. The only thing I can think of is maybe the exhaust is choking it up, because I have not put my exhaust system on yet (I need to figure out which mufflers I want to run) - but that's all I can think of ...
Anybody out there with a $0.10 cent opinion ?????
Thanks!

 

my guess owuld be is that its runnign to rich, but i really dont know much about that kinda stuff.. just a guess.

 

If you're in southern california bring it by my house in Redondo Beach. I'm a dellorto expert.

Crummy off idle throttle response is due to big 39mm chokes creating low velocity and two tight bends in the intake manifold restricting flow. Poor low rpm throttle response is again the big 39mm chokes. I'd buy a nice manifold frome Pierce Manifold in Gilroy, CA.

Could also be running rich. I'd have to drive it. Contrary to what RB says, 4.5 psi is too high. I run 2.25 measured with autometer ultra lite 2 1/8" gauge mounted in cockpit and plumbed into a holley fuel pressure regulator about 1' away from carb. I have the 4.0-9.0 psi regulator spring and I dialed it down to 2.25psi.

Do you have both return springs? Large one on the right, and tiny one on the back of the linkage, sorta in the center widthwise of the carb. Exhaust wouldn't make the throttle not return to rest. It's the carb. Make sure the throttle cable isn't binding or contacting everything and that it's little barrel on the end is seated in the linkage pull arms properly (those pull arms do need to rotate freely. don't overtighten).

Make sure the choke is shutting off completely. That would cause high idle and richness.

BradP

 

I have been running a Dell for the last month or so... I'm very very happy with it. Of course I also cleaned, rebuilt and adjusted my carb before installing it. I'm gonna try and give you some of the insight I've learned from my experience and others I've talked to.

First off, have a look at this webpage for a ton of info:

www.gruntled.com

Next, can you give some more information on what you have done with your carb?

Have you examined which jet sizes are installed? Make sure they are the ones spec'ed by RB; people put all kinds of weird ones in there. If you have some strange jets in there, it will certainly be a frustrating tuning experience.

From my experience and advice I've received from others, there are 3 tricky things when tuning these carbs. These 3 things must be done perfectly if you want to 'go' when you hit the gas.

1) Accelerator pump travel - must be within RB spec. You may have to bend the rod to achieve the right length. There is info on that webpage about this.

2) Float adjustment - again, must be within spec.

3) Pump jet installation - there are some tiny holes that must be lined up; the determining factor is the thickness of the washer/gasket used. Pretty annoying and tricky to get perfect. I had to make my own washers out of the right thickness gasket paper to get it right.

There are, of course, more things than this that must be right. However, those are the ones that I thought were the most crucial and easy to mess up.

Brad's right about the high idle, I had that problem too at first. You need to mess with different spring configurations to get it right. I ended up using the throttle spring off my Nikki carb, cut down a little bit. It's not perfect, but it's close. I still idle around 1400 or so if I've been coasting with my foot light on the gas, but a quick blip will bring it down to 900 again.

As for the stumbling, a misadjustment in any of the above 'crucial areas' could cause this. Beyond that, it sounds to me like you need to work on getting your idle mixture adjust screws set properly. I think I ended up around 4-4.5 turns out or something like that. It's a fine adjustment, and it determines to a large extent whether you'll stumble or not when you hit the gas.

Here's my 2 cents on your fuel pressure strategy - I run the exact same fuel setup as you. However, all the automotive guages I've tried are very innacurate. They have all registered much lower than actual pressure. Your "4.5" psi could very well be much more than that! AND - I was able to flood my Dell out easily with my Holley 4.5-9psi regulator screw turned in just a little too much. It took experimentation and road testing to find the right setting. Don't rely on that guage too much - it may be fooling you into running too much fuel pressure. Set your fuel pressure by turning the regulator bolt almost all the way out, then back in a bit - so theoretically around 4.5 psi. Drive it and see how it works - then turn it in a little more (higher fuel pressure) and go for another test drive. Keep doing this until you start to run too much pressure - your car will start idleing shitty and it won't feel as good overall. Now lower the pressure a bit until it feels good again. With some experimenting you'll find the best setting.

Don't get discouraged yet. You can't expect to bolt up a carb and have it run perfectly for your car right off the bat!!!! Perfect tuning takes time, hard work and attention to detail.


Brad,

How do you know that "2.25" psi is correct?? I've tried 2 different guages on my car (with both Nikki and Dell setups) and read two different pressures - both much lower than actual. Others have had the same experience. I don't think a Dell would run properly at 2 pounds, I think it would make more sense that you're actually around the 4-5 mark.

Just my 2 cents.

Also, I know you prefer the lake cities manifold for your street port, but I don't think the problem he is describing has to do with a weakness in his setup. I have the same RB manifold and 39mm chokes and I certainly don't have the problems he describes!! Neither does a friend of mine with the same setup. The RB setup might not be ideal for everything, but it isn't gonna be the cause of stumbling or hesitation like we're talking about here.

 

well, guys i thank you for the input. i hope you can be patient with me. i'm a lot better with tuning a Nikki, because i limit my mods to the activation and size of the secondaries ... but this progressive stuff is new territiory for me.
anyway, i will take what all of you said into consideration and try to work it out. i would agree that a lot of it lies in the accuracy of the gauge. because even at the indicated 4.5 psi, the thing pisses gas out of the overflow hole and even out the rear rotor air horn if i try to turn the idle screws in (i have them almost wide open)
unfortunately, Drivefast 7, i'm nowhere near SoCal, so that might b a problem, but thanks for the offer. i won't forget it, and if you ever need anything, just ask. i don't forget kindness!
but like i said, I'll take what you and SilverRocket said and try to do my best with this thing. i'll have to check which jets i have in there now (i changed them back in '94 because i was having problems with a built engine and i thought the carb might have been the culprit - i was wrong) however, i scrapped that car, and my mom misplaced all the other jets when she moved - so what i have is all i have to work with. i checked out that gruntled.com site a few months back, but i will check it again in case i missed something. i also checked out CB performance website ... i haven't bought anything, but i'm going to see if i can get some jets from them.
i'll keep you guys posted.
thanks, again!

 

Sounds like you really do have way too much fuel pressure - turn that thing down already Could be your whole problem.

 

Ok, ok... There's simple fixes to everything you describe.

The low rpm "hanging" idle is caused by an improperly adjusted throttle pump. If you look at how the pump linkage is designed, adjusting the pump past a certain point will cause the carb to bind near idle. In this case, your idle adjustement screw becomes useless. If you take a look at your throttle pump rod, you should notice that it is slightly bend. This bend was done by RB to try to acheive the maximum pump arm travel. To fix your idle hangup problem, you can either reduce the pump arm travel (by turning the nut and lock nut) on the arm counter clockwise, or you can bend the rod out more. I'd recomend a bit of both.

Do exactly what Silver said when it comes to fuel pressure. Set your 4-9 psi gauge to the minimum psi it'll go. Dellorto's will operate from ~3 psi to ~5.5 psi. From the problems you are describing, you are running too much pressure.

Adjust your idle mixture when the car is HOT. This is by far the trickiest part of tunning a Dellorto carb. The main problem is that idle quality will vary greatly depending on the weather. What works awesome in the cold might be less than smooth when it's warm and vice versa. Your best bet is to adjust your mixture right after driving hard. Once you find a spot that works, back the mixture screws out another full turn to be on the safe side. Also, keep your idle around 1100rpm when setting the screws and leave it at that rpm afterwards. That way, if your idle speed happens to drop, it wont go much lower than 800rpm and you wont stumble or run the risk of stalling.

I have most of this info in my write on Gruntled.com ( http://www.gruntled.com/Dellorto/Will-Jetting.html ). I suggest you read through it . Good luck and let us know how it goes!

 

Silver Rocket, I read the 'how to powertune weber & dellorto dcoe and dhla carbs' cover to cover before messing with my carb and in the fuel pressure section page 53 it says to run 1.5-2.5psi plain and simple. High fuel VOLUME is needed with these carbs, not PRESSURE. My local carb shop who has been rebuilding and tuning them for a long said the exact same thing.

My friend with a Mikuni 44pph was running 4.5psi like everyone says to on his car and with his air filter off I saw fuel steadily dripping out the velocity stacks. He didn't care, because he was running the infamous 4.5psi. DOH.

Having two different fuel pressure gauges reading two different pressures is to be expected due to different designs and tolerances of these low dollar auto gauges. That's why I mentioned EXACTLY what my fuel pressure regulator and gauge and plumbing were so he could replicate it if he wishes. 2.25 works great for me with that setup. I have (had) the carb jetted perfectly with my setup and I was watching my air/fuel meter and dual EGT's A LOT during tuning. Did I mention when I had it at 4.5psi fuel was dripping out the velocity stacks, soaking the air filter and creating gas fumes. When the roll cage was being welded in the car caught fire for a quick minute. At least I got new braided fuel line and air filter for free!

Remember, a fuel delivery system is just that: a system. Consists of many components, not just a pressure regulator. Needle and seat size and quality, float size and quality, float settings, etc. I'm saying 2.25psi works great for me with my system. Other people sure could try and use 4.5psi, and adjust the floats and jetting accordingly and try to get it right. But keep an eye on their velocity stacks for dripping and peek into the venturis and see if theres gas pooling up in there.

Idle adjustment screws on these carbs are traditionally turned out 2-3 turns. If you need to turn them out more, your idle fuel jets are too small. Less means they're too big! Small idle fuel jets means the transition stage of the carb is too lean. Transitioning from the idle circuit to the cruising circuit. Also known as the 'just off idle circuit'. Hmmmm..... How many turns out are your idle mixture screws??

As for the Lake Cities manifold, it fixed the just off throttle dead spot that the RB manifold was creating. My dead spot might not have been as noticable as diabo's, but it had one. Going up to 90 accelerator pump jets and 82 idle fuel jets helped somewhat too. My accllerator pump was squirting just fine. And I know u had probs aligning the pump jets, but frankly I couldn't put them in the carb without them being pointed towards the throttle plates.

Backing the idle mixture screws out a full turn after finding a good smooth idle is too much. Rotary Reliability and Racing told me years ago to turn it out a quarter turn for good luck! Good info about the weather.

Hope this helps. Keep on rotating!

BradP

 

We obvioulsy have varying opinions on the subject... but we've both acheived good results, so who am I to argue. My carbs (personal and customers) and Silvers are all adjusted for 4-4.5 psi. This is what works with RB's recomended float height (which is generally what we use) and this is what works for us.

What led Silver to question your results is because we tried various pressure tests on our setups with different gauges and found similar results to yours. Silver, running a 7psi pump through a 4-9psi regulator could only register a maximum of 3psi on the gauge (even with the reg wide open). My setup with a 6psi pump and a 3-9psi reg could only see about 2.5 psi. Ignoring the gauges and by going by what "should" be the actual pressure being put out by our setups, we where flooding out the Dellortos at around 5.5psi. To this day, I have yet to find an ACCURATE low pressure gauge. The search continues though.

Again, with the idle mixture, jetting and manifold, you have your own ideas of what works and I have mine. I know for a fact that the carbs I rebuild work perfectly and mimic the behavior advertised by RB when they sold these things.

 

wow ...
i see there's been a pretty heated discussion in my absence (i was away for a while and didn't have a computer) - anyway, i'm back home now and i will start to take all you guys' advice to heart and see if i can get this thing to work properly. i think i'll get a regulator that goes below 4 psi just to get it to stop pissing the gas out the velocity stacks (it's already adjusted all the way down).

bottomline is that i need to get some jets because i'm almost sure at this point that they are helping to aggravate the problems i'm having.

thanks ... sooooo much!

 

Question, besides the pump jet, is there any other jets that need to be seated specificly?

 

Pardon my question, but I am having some similar (not quite as severe) problems with my brand new Weber 48DCOE-SP...How closely related are the Weber and Dellorto carbs..I know the Dellorto has the fuel inlet on the other side but overall they look almost identical....

Any Weber sites you guys know of??

Thanks!!

 

actually, that's a question i've had for a while, too. because i find getting parts for Webers to be a lot easier than getting parts for Dells. i mean, it's like ... you go into a store and ask about them, and if someone even knows what you're talking about, then it's like they try to change the subject and act like Dell'Orto's are figment of your imagination ... what's up with that???

but, yeah ... come on, all you pros at this carb-stuff ... let's hear about the similarities between Weber sidedrafts and Dell'Orto sidedrafts ....

 

No, that's the only one that's tricky. To the best of my recollection, all the others just screw in without any picky things to line up. You'll need some new o-rings and washers for a few things, but nothing too hard.

The important thing when rebuilding the carb is to make good use of a diagram like the one on the above website. That way you know how all the little pieces are supposed to fit together and in which order. If you have the right jets, you get everything cleaned and installed right, and you set the float height and accel pump travel right, you'll be just fine.

 

I don't know too much about Weber/Dell differences; what I've heard is that the Dell is an updated and improved Weber design with more adjustibility and some inherent problems eliminated. What the specifics are I couldn't tell you.

If you want parts, just hit up www.cbperformance.com. It's the best place that I know of.

 

Just a quick note about fuel pressure gauges. Paul Yaw has done a good deal of research on this and has found one that really seems to be accurate. When you buy one of his carbs he requires the use of this specific gauge. Here is a link if you are interested in more info. - http://personal.riverusers.com/~yawpower/access.html

 

okay ... i'm excited now, so you guys might want to get a beer or milkshake next to your computer because there's no telling when i'm gonna shut up on this post.

anyway, since i'm jobless (and therefore BROKE) i decided not to touch this thread until i had some money to facilitate the tuning the carb ... right now i'm covered in gas, and mosquito bites, but i just changed the regulator from the 4.5-9.0 psi unit to the 1.0-4.0 psi unit. Man - what a difference!!!!! i still think i hate the Dell, but at least i got it to stop pissing! i decided to keep the gauge i have for financial reasons right now, so any reference to pressure that i make will be with respect to my original readings (in ther words, it may or may not be accurate, but who cares - at least i know i'm moving in the right direction.

i'm pretty sure i feel an increase in power already! i know! i know! i may just be too freakin' excited and i may be imagining it - but let me have my moment. anyway, it's a bit damp out on the road, so that may have a little to do with it, but for the first time since i put this motor in last year, i'm actually burning tires without slipping the clutch. i feel young again! anyway, the power comes on strong all the way to 6000+ RPM (i didn't try to pass that too much because of two reasons, i was running out of road and also i had to start thinking about turning around to go back home since gas started spurting out the empty side of the regulator) i fixed it with a pressure cap and some gasket paper ... right now, i'm running an indicated 3.5 psi, and there is no trace of gas at idle.

with some jets and a little time, i'll be able to start the fine tuning now!

okay ... now for the sour notes!

i haven't driven the car in about 3 weeks, because 3 weeks ago i was out and noticed the temperature creeping past half and i figured my radiator is going bye-bye now (it's the only part of the cooling system that i didn't change when i put the motor in - besides, it's just old!) anyway, before i get sidetracked ... i haven't driven the car in three weeks because of that, but that same day it started getting hot, i noticed the fuel was boiling. so i figured that that's going to be an issue now. any ideas on how to deal with that? does anyone here run a fuel cooler? how well do they work?

the other sour note is that the idling problem is still there, but i noticed something that i hadn't noticed before. when the engine is hot, even when i move the throttle back to the stopper by hand, it starts to move off it by itself (without me touching the cable). anyone know what that is? i'm guessing that that is what rxcetera was talking about in this post below:

now, rxcetera, hopefully you're reading this ... don't get to mad, but i'm not sure if i know "exactly" what you mean for me to do with the throttle pump thing ... i had tried taking off the throttle linkage and i guess i must have done the wrong thing, because the thing that i took off can't be moved (there's a groove on it, so it only goes on one way) and i didn't feel comfortable bending the arm since i was unsure if was doing the right thing.

i also didn't realize that you were the one that wrote www.gruntled.com - good job, bro! i got a lot of info from that, it's just i'm not used to mucking with these Dellorto's (i used to play more with 12A's and the Nikki) and even though i've had this carb since '94, i only just now started to use it - so please bear with my retardedness (not sure if that's a word)

anyway ... if it's possible, i have a copy of the Dellorto diagram with all it's parts, could you try to explain what you meant in that post that i quoted from you ... just one more time ... i promise, i'm paying attention, it's just i'm not used to this thing yet.

i think that's all for now ... you can all breathe a sigh of relief.

thanks for listening! damn, i feel so good now that i'm getting closer to having this thing work right ...

 

Haha, you're one excited **** lol. Ok, I'll try my best to explain what I'm talking about by refering to that exploded diagram on the Gruntled site. And... the site is down lol.

Let's do this without the diagram then. Stand on the right side of you car and look at the manifold. See the part that is stamped "racing beat"? Right next to that, there is a "hole" in your manifold where the left and right passages are seperate. Inside that gap you'll notice a little black rod and 2 nuts threaded onto it. What you want to do is turn those nuts (one is a lock nut) counter clockwise until your carb returns to the idle position. half a turn to a full turn should do it. Hopefully, you havent reduced the pump arm travel too much by doing this. If you find that your carb studders while applying the throttle after doing this, check back here and we'll get a little more drastic lol.

 

two forward steps in two days!!!

rxcetera~
first of all, there is absolutely NO WAY that i can thank you enough! i guess i found the right thing, because i just came back from driving around for a while and i swear i was driving a brand new car! it idles at about 900 RPM (and the only reason that it's not silky smooth is because i have to adjust the idle mixture on the rear rotor - it's missing the spring for the adjustment screw) -but i'm dead serious ... THANKS! YOU ARE THE MAN!!!!!

i just checked it up to about 6000 RPM, frankly, i probably won't be trying to go above that too much because without a job, i can't afford to carry on with some of my usual high RPM antics - but i guess the travel is fine.

the rest of things, i'm pretty sure i can work them out with time and money as it comes.

one thing i must ask is this: can you explain exactly what the problem was, because i still don't fully understand it. mainly, it's the thing where it would return to the stopper when it's cold, but would actually move itself off the stopper when hot ...

again, i can't thank you enough for helping me! i'm sure my saga will continue with other episodes, but hopefully this is it for the Dell'Orto issues though. (crossing fingers now )

 

one thing i noticed with dellortos and 12a's(or at least mine) is that lots of folks have stuttering and lack of power down low. then by coming out 4-5 turns on the idle screws, it gets a little better. when i had the 13b jets in there, i had no probs down low(bigger idle jets), but rich as hell everywhere else. i went up from the stock 75's to 80 idle jets (thanks brad!) and now have the idle screws about 2.5 turns out. she's running like a champ now! and to think, i just ordered a crap load of jets from cbperformance, and i've got it dialed in with what i already had. oh well, at least i got some stuff to play with for when the streetport comes along.

 

well, i'm not glad that you were having problems, but i'm glad that i wasn't the only one ...

anyway, mine's running fine now. idles great (solid 900 RPM), no problems from a dead stop (no stumbling, choking, etc.) it pulls pretty strong ... i'm almost afraid to mess with the jets, but alas, i will do it as soon as my budget allows me to start messing with the car again, because i still haven't gotten my exhaust system yet.

 

oh yeah, and jets are super cheap. check out www.cbperformance.com

 

okay ... i'm gonna start messing with jetting now. i've been going through the old threads on Dell DHLA's and Weber DCOE's because i just checked out www.cbperformance.com for one last time before i posted this, and i have failed in finding DHLA-specific jets.

just an aside - i e-mailed them and they never responded, so anyone planning that mode of communication - think again!

anyway, my question is this ... does anyone know if the DCOE jets that they have listed will work on my DHLA? from the info i gathered, it would seem so, but i want to know for sure.

also, i just wanted to link this other thread to this one so it will save time for anyone else looking for Dell'Orto information (I figured that there aren't that many of us out there) - MORE DELL'ORTO INFO

 

Ok,

Well, I just got done reading all the interesting posts on this topic.

Now, the question that will help me understand it all.

Are you installing a Weber or Dell carb for a power modification? Or, do you just like the other carbs better for personal preference?

And, if it is any power mod......what sort of hp are we talking about compared to this stock Nikki I have....?

 

Just call them on the phone - I haven't dealt with them myself, but Will (Rxcetera) has several times and as far as I've heard their service is excellent.