Dellorto Carb Help
 

Info: 1984 GSL-SE Dellorto Carb, RB Upper Intake, MSD 6A 26° Advanced, NGK BUR9EQ Plugs.

Issue: Idle stutter and what sounds like one of the rotors just plain isnt working, in-car air fuel gauge will bounce back a tiny bit towards lean. this ONLY happens on idle and if you rev the car up it'll sputter and kick as well, the second you let out on the clutch and get the car underway it works perfectly but anything under 1/4 throttle from 2,500-4,000rpm it kicks and sputters like crazy but give it some juice and its smooth as butter. And the issue is intermittent it doesn't ALWAYS happen as Im just idling it usually happens as Im comming out of gear rolling to a stoplight.

My Thoughts: I haven't changed anything since the problem began only the temperature in San Antonio has gone from 60s to 40s and 30s. Im possibly thinking it could be a clogged idle jet on one of the barrels which would explain why the problem only occurs at idle or under very slight throttle but before I pull it off and clean it up I just wanted a bit of insight from any other Dellorto people or anyone who has experience with them.

I think your carb is icing up. When I used to live where its colder this was
pretty common. Does it go away once its good and warmed up?

Using the choke helps this some until its warmed all the way up. Even here
in NC on a cold day I can and do experience this with my Dell.

I use the choke to get the car warmed up in the morning and it was perfectly fine till about last week but it does this cold and hot, I wasn't sure if perhaps the premix [MMO] was gumming up the idle jets from being so cold and sitting overnight but I'll have to take the jets out to check.

As well I was planning on picking up a bottle of Lucas Fuel Injector cleaner as I reccomended it to my dad and said he had some decent results with it in his Tundra so I might do that to see if it cleans it up at all or if this could be an issue other than the carb.

Hmm..never really used lucas fuel injector...i did for a while use MMO because my omp wasnt working at the time...well..i did have a sputtering problem...when i first got the carb...and that was due to the stock fuel pump not being able to handle the demand...i solved that by installing a gslse fuel pump and a mallory fuel regulator...what kind of regulator do you have going from your tank to your dellorto? TG farrel is right..the carb can ice up...i've had that happen to me before and that was in Washington...but also..i have had to mess with the mixture screws before when it did get cold in Washington...and then again when it got warm in the summer..

As pinoy mentions you can retune for cold weather but to me its not
worth the hassle. I wouldn't tear into it unless your sure somethings
wrong with it. Its more likely icing in the carb. Like I said mine does it.

Hell in 90 degree weather I can touch the intake with my bare hands
after running hard. Think how cool it gets in freezing weather.

Check for clogged jets or icing, but I'd bet adjusting the idle mixture screws solves the problem.

Will do gents, thanks for the info I'll see if richening the idle up helps. and I have the GSL-SE Fuel pump and a mallory regulator set to about 3.5psi but I haven't checked it since probably september when I last adjusted it.

Update: Put the idle speed screw in about half a turn and brought the idle up to about 1,000-1,000 and brought the idle mixture screws out about 3-4 turns each and the car seems to be running smooth now, Never happened before but I went outside and the throttle body was frozen shut I had to give it a nice nudge to move as well my RB intake was covered in frost. the a/f gauge reads [autometer cheap one just the lights] just bellow rich/green.

Dunno if it would have made a difference but the 5+6 sleeves are also removed which might have aided in the problem so my lesson for today is don't let the idle get tooooo low.

Idle jets are easy to clog as they're rather small to begin with. 0.75 millimeter. I'd say clean the idle jet and jet holder while it's out. And it wouldn't suprise me with that cold weather you can go up one size on the idle fuel jet.

Those 9 heat range plugs are cold, it'll run a lot better everywhere with 8 or 7's. BR7EIX in all 4 work like a champ, bitchin' plug.

Well I had just bought a set of BR9EQs, the prong'd ones and put those in then the problem started so I immedietly changed em back to the BUR9EQs just as a precaution so I'll have to put em back in and see if that helps, my FB Buddy here in town told me those were some good plugs to run with the MSD to help cold starts.

But once I run through those plugs I will look into trying the BR7EIX.

tg farrel makes a point...i've driven around some summer nights and had my intake manifold be very cold. This is just a suggestion but i would recommend a aem uego a/f gauge for more accurate readings..

Well the problem continued so today I took off the carb and upper intake to take a look at everything and see if anything was clogged, I pulled out the idle mixture needles and noticed that while they were in great condition there were 2 rubber o-rings, one on each side that were cut in half, I pulled them out best I could and continued checking everything else, the accelerator pump diaphram is prestine as is most everything else, I put everything back together sans air filter and went to start the car. It turned and turned and putzed a few times but that was about it, I tried again and it fired up but then dropped a low idle and died.

Got out of the car to see what might be the issue and fuel was POURING out the front of the carb onto the top of the motor just draining whatever was in the bowls so I grabbed some towels and cleaned it up, took off the carb and intake again and here I am. I plan on ordering a service kit later this week so I can just rebuild it but does anyone know what would cause the fuel to just pour out of the motor even though the throttle is fully closed?

Floats sticking in the down position could do it. Had it happen to me twice.

I suspect your idle is too lean, made even leaner by the colder/denser air this time of year. Mikuni's run near 8 afrs at idle. The Dell probably needs similar afrs at idle. Beg, borrow, buy a decent wideband. Personally, I prefer working AUX ports, it can increase intake velocity and will increase low rpm performance.

As I had stated before I only managed to pull out half of each o-ring when I took out the screws, turns out the other half of the o-ring on the rear barrell is now partialy covering the idle port hole so it either got there from me fiddling around trying to get stuff out or its just been sitting there. So, I am now on a question to find a paper clip to get it out and search in the other one to make sure there are no obstructions, get new o-rings then re-adjust my floats so they dont overflow or stick.

As for the aux ports, I had thought that the 30s temps here wasn't really helping with the missing aux ports and that, that could have been part of the issue but as soon as my friend gets back from his holiday trip to Georgia I'll see if we can use his wideband and try to really get a set tune on the idle.

no dell here but i use an air compressor when doing carb builds for blowing thru all the small holes in the carb.

Well I've inspected everything, didn't realize the springs in the idle ports came out so easily so I got those out, turns out the other half the o-ring was inside the spring on the front barrell and under the spring on the rear barrel, got 4 o-rings from O'Riellys and used 2 to replace, all looks well I'll just have to re-adjust the floats again to see if I can get it just right and then attempt another startup.

Does anyone have a picture of how far the floats are supposed to be out or a more thurough explination? some have told me its hold the cap verticle so the floats are hanging freely and they should be 10mm [seems offly close] from the cap, and a website on Dells says something like 14mm.

Ok, I got everything re-assembled and put on the car, I made extra sure to watch the carb as I turned the key to ignition but not turned over. it turns out the fuel is leaking from the main jets in a consistant drip, I adjust the floats so the bowls are less full to see if it was an overflow issue but for the life of me cannot figure out why the are dripping like that. I took the cap off and the bowls were still about 1/2 full and the drop had all but stopped but as soon as you put the cap back on, hook up the fuel line and turn to ignition they start dripping again.

Fuel pressure is around 4 +/- 1 psi. Anyone have any ideas? Ive been reading what I can about how the carb works but still alot I dont know. I did take out the pump diaphram and clean it and put it back together but the thing was absolutely spotless as well as the spring which seems to all control flow to the main jets....hmmm...

Edit 1:
Got the car started with the bowls full and the fuel pump off and the car seems to run fine, when I let the fuel pump on the main jets start dripping and thats when the the idle starts to get all ported loppy and stuttering. Could it be too high fuel pressure? I've had that pressure set for...probably 2 months now and never had an issue till it started getting REALLY cold.

4psi fuel pressure, I never needed that much. Lower it to 2.25, that's what I've used for Dellorto even though everyone says to use 4.5 which causes the float bowl to overflow like you're seeing.

You could have unclogged something in the fuel line that lowered the pressure while clogged. Do you have a fuel pressure gauge right before the carb? That's a necessity.

And doublecheck the float level.

Don't know if this is your problem, but be very careful when putting the float bowl cover back on. On Webers, at least, it's very easy for the floats to get hung up on the gasket. I now use a flat-head screwdriver to hold the floats in the up position as I'm installing it.

ok, downed the fuel pressure to 3psi and the floats are no longer overflowing, I also re-attached the vaccume lines to the FPR so its lower on idle, I do have A fuel pressure gauge but the issue is that one is 1/4" or something where the inlet for the FPR is like 1/2" or somethin.

I still can't get the car to idle right and it seems to like to smoke a bit, Ive been checking for intake leaks but the dellorto and my exhaust are too damn loud for me to even hear any idle leaks so I'll replace the intake manifold gasket and then put those freeze plugs in everyone talks about.

Update:
I got the intake manifold off today after letting it sit and trying to relax some frustration over still not being able to get it to run correctly.

As expected the gasket was soaked in gasoline from the overflowing bowls and just generally being dirty as hell. same with the emissions port which was covered in gunk so I cleaned that out as well.

I do have one question though, I've been wondering what in the hell this thing has gone too for quite some time but forgot about it until the manifold was pulled off [refer to attachment], Im trying to replace all seals and rings that might possibly be leaking so at this point [injector plug o-rings were replaced today] as well I'm taking off my OMP. [yes I premix].

Tomorrow Im scraping all the old RTV off the emissions and 6-port block offs and re-doing those, ordering a new gasket from Mazda on Monday and possibly a new exhaust gasket as well and then re-assembling hopefully to have the issue resolved.

That was one end of a coolant line that went up by the throttle body when the engine had FI. No need to do anything with it.

Just caught up in the thread. Looks like your making progress.
Sounds like you need a rebuild kit from here www.dellorto.com,
overseas but ships in less than 2 weeks. Includes all the stuff you
need. Save the AP gasket as thats an extra thick one made by RB
which you can't get anymore.

BTW, I just installed a Carter 6psi fuel pump with a Holley 1- 4 psi
regulator. I've determined that anything over 2.5 psi will cause idle
to jump up and my gas mileage to go down. So 3 psi si still too high
to get a reliable tune on your carb, bring it down to 2.5.

i got my rebuild kit from cbperformance. The accelerator pump gasket i think was a little big and same with the gasket that goes between the air filter and the carb. just a little trim no big deal.

http://cbperformance.com/catalog.asp?ProductID=516