TheSamba.com :: View topic - Need help with Dellorto 40 set up on new 1776

Thu Apr 26, 2012 8:58 pm

Hello All, been doing a lot of reading but could use some advice. Engine specs. 1776 with stock heads with HD springs , 110 engle cam 8:1 CR Everything ballanced. Picked up a used set of 40 dells. Cleaned and put in a rebuild kit.
The dells are set up as follows; 34 vents 180 stack with 140 mains 55 idles and 35 acell pump jets. ( I am at sea level)
I have someone with lots of experience with duel weber helping me sync it. The problem we are having is poping at idle. I have the performance book but nothing I do seems to make it better. For the time being I am using a empi pressure regulator to adjust the fuel pressure. I do seem to get gas dripping from the venturies. At higher RPMs the Carb sounds great. At the moment we are running the engine outside the car, I think that we are running lean.I tried replacing the idles to 60 but seemed to make it worse. Can someone tell me if we are in the ball park in the way the carb is set up.

Thu Apr 26, 2012 9:03 pm

34 vents? Your mains are also big, for the back firing go over your exhaust, any leaks will cause it.

Thu Apr 26, 2012 9:05 pm

I'd rejet to 52/135/180s. Recheck your float levels and set your pressure lower. Readjust idle/mixture and see if it runs better.

Thu Apr 26, 2012 11:00 pm

Make sure all the idle jets are the same size

Don't forget the idle mix screws are fine thread, normal can be three or four turns out.

Empi pressure regulator? does it work? Did you pay for that?
I'd use gravity feed if you are bench testing it. Mount your 1-gallon fuel tank a foot above the carbs

Fri Apr 27, 2012 7:13 am

No exhaust leaks. Idle jets were checked with a gauge and they are all 55. I have checked the The float levels a couple of times. They are set at 6 mm and 13 mm. The Gas can has been on the ground. I will relocate it. The Empi gauge is only temporary. It was new out of the package. I am running a mechanical fuel pump . I will be changing it out for a electric fuel pump before it goes in the car.

When I turn in the air mixture screws all the way I dont seem to get a big change in the way the engine sounds. Does that seem right? I am going to try and find out today exactly how much pressure the pump is producing. The popping that I am getting is through all 4 cylinders.

Fri Apr 27, 2012 9:29 am

What sort of linkage are you using? Do the carbs open at the same rate?

Fri Apr 27, 2012 10:43 am

I am running the same carbs with the same jetting and vents except smaller mains on a stock 1600 356 engine. Surprisingly it ran alright considering the vents are too big. I'm swapping in 30mm vents currently which should improve things I hope. It had the occasional pop just off of idle but that is it. Based on my recent research, I would say that your idle jets are on the small side for an engine of that displacement but the problem is likely elsewhere.

I'm no carb guru but turning the mixture screws in all the way should stall the engine. There is something wrong.

Fri Apr 27, 2012 11:25 am

I bet the fuel pressure is too high. I would get rid of that empi fuel pressure regulator and then tee in a vacuum/pressure gauge and then stack gaskets on the fuel pump to get to the pressure level you need.

Fri Apr 27, 2012 3:26 pm

The linkage is the hex style and the carbs open at the same rate. I have put a guage to the fuel pressure and I am getting a constant 3 psi. I can turn it up if needed. I gather that my vents are to big do to the size of my valves. I should go to 30 or 32s ?
On one carburator I can get the the same sync from front to back. On the other the back is off from the front and turning the air bypass screw dosen't seem to affect it at all. I still seem to get fuel dripping from the venturie which causes popping. I gather that my idle jets are on the small size. Should Ialso change my mains?

Fri Apr 27, 2012 4:51 pm

You don't need a fuel pump nor regulator, gravity makes stuff go downhill

Fri Apr 27, 2012 9:11 pm

I was tuning my Dells tonight after having them apart. The engine ran well but the idle wandered,one set of mixture screws had no effect on engine speed and the engine puffed black smoke when starting and revving (sometimes). I couldn't get a consistent idle speed either. I noticed gas dripping down in the vents on that side after I stopped the engine. I suspected float level on the one side and checked it. It was around 4mm when it should have been 5 to 6mm (I checked it before???). I'll run it tomorrow and hope this is the problem. The symptoms are typical of high float level. I would check the float levels as suggested in an earlier post. Assuming the 48s are the same as the 36/40s, you have to check the floats with the lid turned on the side. The measurement should be taken just as the needle touches the seat without compression. If this procedure isn't used the float level will be too high. If both carbs leak into the venturi then high fuel pressure would be a possibility too as the symptoms would be similar.

Sat Apr 28, 2012 12:25 am

Idle jets are plugged.

IF on ANY dual IDF or dellorto... you hold the linkage/throttle at like... 5% throttle and it starts popping through the muffler.... the idle jets have debris in them. I mean, like linkage coming off the idle stop screws like 10-50 thou per side. Engine wont go over 1500 rpm and just hold it there and you will hear it start huffin and popping through the muffler. (often when plugged bad enough they will cough back through the carb on the plugged barrel...ie too lean)

This is THE most overlooked issue with these carbs and i see and hear it at EVERY show. With people driving through the show grounds poppin and backfiring and they have NO idea what the problem is or that the problem even exists.

You may have to clean the jets 10-20 times in the first 100 miles as you begin driving it.

Best to use brand new air filters and clean every part of the carb up top where air flows. Cause if not, any tiny debris will find its way to the air passage for the idle jet and go through and end up stuck in the idle jet.

What distributor are you running?

You will likely need a 57 idle jet, 135 main and 180 air. What emulsion tubes do you have in there?
Should be 9164.2

I have dell 36s on my bus now. 1679 with engle 100 and 8.6 to 1 CR.

i have 55 idles and its WAY lean. As in, 56 or 57s would be best.
I have 128 main, 9164.2 and 180 air. On the freeway its 15 and 16 to 1 AFR. which it seems to like despite having an 009 dist in place.
Ordering one of johns SVDA's soon.

Sat Apr 28, 2012 6:20 am

mightymouse wrote: Idle jets are plugged.

If he replaced the idle jets and the problem got worse wouldn't that rule out plugging? These things are hard to troubleshoot first hand let alone second hand :) (Last week I tried to troubleshoot my daughters boyfriends starting problems over the phone. She and her BF put a new battery into his car. I would have never guessed they didn't tighten either of the terminals. She brought the car over after boosting it and I pulled them off by hand. :roll: )

Sat Apr 28, 2012 7:42 am

I really appriciate all of the help. I am going to reset my float level from 6 to 5 and see if that makes a drifference. I am also going to try playing with the different mains and idle jets. I have checked the emulsion tubes and they are correct. How important is the syncing from front to back? As stated before when I mess with the air bypass screw it dosent seem to make any difference. I will be at work the next couple of day so stay tuned. (pun not intended)

Sat Apr 28, 2012 8:36 am

If you are getting a noticeably different reading on the "snail" from front to back on the same carb, the "low" cylinder has a misfire.

I'm with mighty mouse on this one. You have a plugged idle jet(s). Sometimes they will get stuff in them that does NOT want to come out. You can't just clean the jet itself either and expect it to be clear. Take the jets out and blow air or carb cleaner down inside the well. I also blow through the passage that runs diagonally from the top of the idle well down towards the carb throat. A quick test to check for a plugged idle jet is to squirt a small amount of carb cleaner into the stack with the motor running. Just a real quick spurt, or you'll flood it. If that cylinder isn't getting enough fuel you will hear it pick up and run when the carb cleaner hits it. You can also use propane, I just use carb cleaner cause I always have some nearby.

On a side note, I don't know why they are even called idle jets. The only time they affect your idle is if they are plugged. They really should be called progression jets. You are in the ballpark with 55 idles. 60's are too big. Also, you said they checked out at 55. Is that .55mm or is that 55 dell? Dell jets are smaller than webers. A 55 dell is actually around .52mm

Sat Apr 28, 2012 11:22 am

pat griffith wrote: No exhaust leaks. Idle jets were checked with a gauge and they are all 55. I have checked the The float levels a couple of times. They are set at 6 mm and 13 mm. The Gas can has been on the ground. I will relocate it. The Empi gauge is only temporary. It was new out of the package. I am running a mechanical fuel pump . I will be changing it out for a electric fuel pump before it goes in the car.

What pump are you using since you reduce the pressure ? if the stock one, no need.
Did you replace the inlet valves ?
The float height is too "low". Dells need to be about 4 mm. from gasket closed. Adjust that and reset. Then your popping will dissapear and your mix at WOT will realign.
34 mm venturies on a 1776 like that is on the large side, but should work OK.
Even though the carbs are alike except from size, you cant always directly transfer jetting from a 36 to a 40. It is close, but not 100% the same. But yes, Idle is normally 55 to 58 on similar engines.
T

Sat Apr 28, 2012 4:48 pm

Warning mini threadjack ahead

Alstrup, your the first guy ive seen suggest 4mm on floats for dells.
I am having an issue now that ive never seen before so id like to ask why, and or where that info comes from.

The problem i have is with this set of 36 dells. The right side carb only wants half turn out on the mixture screws and its dead on. The left carb needs 1.5-2.5 turns out on the mixture screws and its dead on. (cyl 3 1.5 turns out cyl 4 2-3 turns out WTF)

It was exactly this way on my roomates 1699, and now they are on my 1679 and do the same. He needed 58 idles and 130 mains, i have 55 idles and 128 mains.
So i checked the floats (i rebuilt them 3 years ago) and they were dead on. i have like mid 5s on the floats and 13mm dropped.

I decided to drop the right float and see if that affected the mixture screws and was maybe my problem.

I put the 1/2 carb at 6.6 mm and 13 drop. I now can back the mixture screws out 3/4 to 1 full turn and they are in the happy spot. But that still doesnt match up with the driver side carb at all.

SO weird. Makes no sense.

Id imagine at 4mm the mixture screws would JUST need to be cracked off the seat and itd be good. Which again, makes no sense.

Any thoughts? from anyone who reads this, not just al.

Thanks guys.

Sat Apr 28, 2012 4:50 pm

MM, are the idle air bleeds the same sizes?

Sat Apr 28, 2012 4:52 pm

whoa.. didnt know dells had idle air bleeds. where are they located? ive rebuilt a few sets and only ever seen idle jet holders.

Sat Apr 28, 2012 4:55 pm

some POs try to fix everything with a drill bit....

just saying don't assume anything!

This is also a problem on the Weber IDA. The reason idle jets are only available in increments of "5" on the IDA, while you can get increments of "2.5" on the ICT, DCNF, and IDF, is because the IDA uses a changeable Idle Air Jet. Stock is 120. To make a small change in the progression tune, change the idle air to a 110 or 130, keeping the idle fuel the same.

This is also why some of the early 36 IDFs use 60 idle jets. This doesn't make sense until you see the idle air bleeds are huge compared to the later IDFs. Ratio wise it makes sense.