Some of you know that I recently purchased a car with a SD4 in it.
The SD is equipped with a pair of Dellorto DHLA 45s.
It seems to run good, but it has a bit of unevenness to the idle (which may be the cam, but it's hard to tell until I get a new header constructed. Right now it sounds like a Harley.)
Using an IR thermometer to read header temps, cylinders 1 & 2 seem to be running significantly cooler at idle, as well.
It has a bit of a stumble, off idle, but when the revs are up it seems to have plenty of power. Not that I have anything to make a meaningful comparison.

It's been years since I messed with a carb, but I have to assume that these were once set up correctly and running properly, so tuning isn't really going to be an issue unless it really needs to be.

The question is where to start.
I thought about rebuilding them, but if it's just a matter of removing all of the mixture screws and blowing air through the jets and the passages, I'm all for it.
I would tend to suspect that the screws haven't been messed with by any recent previous owners, but before that, I don't know.

I have ordered the "glossy cover" book that is available. I plan to read it carefully before I do anything.

Is this something that I can just run a can of Seafoam through, and expect any meaningful results?

(I thought about just replacing the manifold and installing a Holley 2 barrel, but I don't have a lot of love for Holleys, and everywhere I look I seem to find a lot of glowing reviews for the Dellortos. So I guess I'll keep them unless I get convinced to go in another direction.)

Thanks for any tips.

[This message has been edited by Raydar (edited 01-23-2015).]

You could try checking the balance of the carbs by using something like a Uni-Syn. Here is a link:

http://www.amazon.com/Edelb...rument/dp/B00062YC2E

If there is a forum for MG's or Fiat spyders I would post this inquiry there.

I had one of those Uni-Sync's back in the 80's and used it for synching Dellorto carbs we put on our VW engines. It works mostly on air flow and though can be of benefit in adjusting mixture, it has no way of registering that. I may still have mine. I'll look and let you know.

It worked pretty good but required a lot of back and forth between carbs because as you adjusted one, it affected the other. One carb would start at a +10 and the other at a -10. You adjusted until you got them to meet in the middle. If there were a way to attach them to the carbs, you could use one for each, but since they aren't precision made instruments, each one is different. Best to use just one and go back and forth between carbs.

Steve, contact Ron. I have his phone number if you don't. Not only does he repair helicopters, but he has been a motorcyle guy longer than he's been a Fiero guy and he works at motorcycle shops as a second job. He might be able to balance your carbs when he comes out for next month's meeting.

This webpage is pretty good at describing the setup on those

http://www.s262612653.websi...Andrews/dellorto.htm

They are tricky to get right and it may just be a setup problem.

Arn

During the early 80"s I installed a pair of Dellorto's on my Lotus Esprit. I syncronized them using a rubber hose placed at each intake and then listened through the other end of the hose. I didn't have a UniSync so that worked for me. The only problem I had was that the Vac line was hooked up at just one location on the intake manifold and everytime the cylinder fired on that intake runner, it would cause the vac advance on the distributor to make a dramatic change in advance. A friend, much smarter than me, suggested I take vac from two different intake runners and then to tee in the line to a single line to the distributor. That fixed the problem. I never readjusted the carbs from that initial install, and the motor ran great for the nearly 20 years I owned that Lotus. Added about 20 HP to the 2 litre engine, over the old Zenith carbs that were known to cause engine bay fires in the Esprit. The cool factor alone should convince you to keep them!

Thanks, everyone, for the info.
All looks like good information. (I just got home from work. Will have to check the info more carefully.)
I had wondered about using a vacuum gauge to balance things out. That may work, since I don't have a vacuum advance on the distributor.
Charlie, if you still have your Uni-Sync, I would appreciate the use of it for a bit.

So... is there any magic to rebuilding these things, if it's necessary? Is it just a matter of following directions, getting everything clean, and paying attention to detail?

The rebuild kits look fairly simple. Mostly just an assortment of O-rings and gaskets. Maybe a few replacement needle valves, and an accelerator pump.

What is the DS 4 engine, displacement? I think the Lotus Esprit had a 1600 and a 2 litre. Anyway years ago I .Iived with sidedraft Weber 40 DCOE's for over 10 years, and am familiar with the choke and jetting principles (do not claim expert status). Best if you do not assume the setup was optimized by the previous owner, IMO. The DCOE 40 Webers were precision pieces and a joy to own. I believe the Del Ortos were a copy ( could be wrong).

The Webers were tunable at the choke (bore), main jet and air mixture points, I think the Lotus stock 1600 had 38 mm chokes which slid into the body of the carbs, increasable by 1 mm steps up to 40 mm. The little English twincam 1600 was almost overcarburetted at idle and midrange with 38mm. The Formula B 1600's used 40-45 mm for operation above 4000 rpm. Sizing is basic, so I would double check.

The jetting was easy via push- in jets at the end of the screw -in jet tube. We found some numbered drills which would allow slight jet increases with out buying Weber parts. The mid-upper mixture was further tuned by "air emulsion jets" again push-ins. I may have some literature on these carbs. Let me know if you are interested.

Thanks for the comment.
My SD4 is allegedly a 2.5. At least that's what is cast in the side of the block. Unless it has a stroker crank in it, but I really doubt it.
While it seems to have been carefully assembled, I think it used pretty un-exotic SD pieces. Iron head with pretty much stock exhaust port configuration, etc.
Everything that I have stumbled across, online, leads me to believe that the 45s are pretty much the correct size for the engine. Or at least a good starting point.
Thanks for the offer of the documentation. If I need anything beyond the book I have on order, I'll give you a shout.

As for the carbs having been messed with...
I'm quite certain that the guy who sold me the car didn't mess with them. Probably not the guy before him, either.
I can't speak about previous owners (there is at least one other) but I wouldn't be surprised if it's never been played with. As I understand it, it was assembled in the 90 - 91 time frame. The person who assembled much of the car (not sure about the engine) is on this forum.

I checked for the Uni-Sync and couldn't find it. It may be in the cabinet in the corner behind my wood rack. Unfortunately the rack probably won't be mobile until spring. Sorry. I think I picked mine up at NOPI, though.

here is no magic on rebuilding these old Dellortos. Just lay out the parts as you take them out/off so you have a "guide" to putting them back on.

The rough idle and minimal stumble off start really sounds like your individual throttle bodies are out just a touch at idle. The stumble off is usually a result of the butterflies opening at a slightly different amount when barely moving. One will open a bit sooner and give a bit more fuel than the others and it will produce a bit of a stumble. There is an Inglese video out on the net that shows Jim Inglese adjusting one of his quad Webber setups on a V8 with the vacuum gauges. The process he goes through is what you will need to do after you rebuild them if you choose to do that.

They work really well once they are adjusted but the adjustments take some patience.

Good luck
Don

Thanks Charlie. No worries. I'll figure something out. I appreciate you looking.

And thanks Don. I appreciate your input. I'm going to wait until I get my book, and then I'll figure out what I'm going to do.

I really appreciate everyone's comments. At least I know that I'm going in the right direction and that there are no unforeseen "gotchas" built in.

I think I might dump a can of seafoam into the tank and let it mix for a while. I would suspect that the carbs are at least a little bit gummed up, from sitting. If nothing else, at least it shouldn't hurt anything.
I have one of those clear filters, so I'll be able to see if it breaks anything loose in the tank.

My 911 had Webers, and it was impossible for me to get them idling right. One minute, they would idle so low, it died, then the next minute they would idle at 1500 rpm. I never got them right before I sold it. It ran just fine. The returns and linkage were all fine and loose.