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Hi everyone! I have a 2004 Intermeccanica with a 1776 and weber carbs. I just moved it (and me and the fam) from Vancouver, BC to Calgary, AB. I got in the driver's seat super excited to take her out on a sunny day and was little worried once I left the driveway! She idled fine, but once I got out of first and into second it felt like she was gonna die. She had been sitting for a 3 months but had been started regularly, and I have now let her warm up for 25 mins only to have the experience again. Eventually it got a bit better, but still doesn't feel right.

I spoke to my friend Ben who I bought it from and he said due to the altitude change from sea level to 3500ft I would likely have to change out the jets. I've done a search on here and there's a lot of conversations about it but I lack the technical knowledge, and some people say it should be fine, but she was running like a boss before the move. AND, I'm keen to learn.

I've attached photos of what's in there. Any direction would be fantastic. Thanks for your help!! I just want to get out and drive, and be able to drive home! haha.




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Last edited by MarkusG
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Those jets you show are the mains. You might want to go down on the mains from 115 to a 110 or a 105.

The ones that make the most difference are the idles: i.e. under 3000 rpm, where you drive a LOT. Those jets are in picture #4 under the fuel hose under the slotted brass screw.(I'm going to guess you have .50 or .55 idle jets) They may or may not be the size that's on them.

You may also have to reduce the amount of accel squirt as well.

All due to the thinner air, but 3500 feet isn't that high. I didn't re-jet for my trip to North Carolina and we got up as high as 6000 feet. Nobody else did either.

It is possible your car is jetted too rich as is for the lower altitude, and the 3500 feet just pushed it into pig-rich and undrivable.

Or most probably, a plugged idle jet...I'd clean them FIRST and see how it goes. If it still runs like crap, look into smaller jets.

Last edited by DannyP

Thank you everyone for your answers! Please excuse any ignorant questions I have... I promise they come with gratitude for your advice and patience!

When I parked it I did use a fuel stabilizer! I posted about it on here before I did it and got some great advice!

I was looking up how to change the idle jets and/or clean them... does anyone know what carbs I have? Also, what do you use to clean them? In order to order different ones, what size would you suggest?

@Carlos G I undid that screw for the idle jet holder to clean them... and now I find myself in a bit of a conundrum as it appears as though the jet is still in the hole. It's pretty impossible to get it out. How would one do that? gahhhhh. This is how we learn, right?!

here's what it looks like in there...


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They certainly look like Weber 40IDF carbs to me.

I really don't think you need to change anything. Clean yes.

Get a pick and hook tool set or make one from a piece of wire and pull the green O-ring out. Put it back onto the jet holder that you took out. Using a pair of really skinny needle nose pliers, fish the jet out. You might have to get some special right angle needle-nose pliers in a Speedster engine bay, or possibly remove the carb. After you get it out, VERY VERY gently spread the ears with a thing screwdriver. This will tighten the fit into the jet holder. Worst case: if the jet breaks they aren't expensive and are readily available.

Alright... so I finally got that jet out. It's a 50. Can I just mention how friggin hard it is to access these?! haha. It felt like I was a surgeon, and there's another one on the back carb too?? and then both sides?! good lord. I do have a love/hate relationship with these sorts of challenges.

Okay, so I need to get a bit of advice on next steps:

I put a carb cleaner in the fuel and that did not make a difference. It still runs rough and when I accelerate it struggles to the point where I put the clutch in and save it from dying... then it goes back to idling normally. It's weird... it's like as I give it more gas when it's in gear it starts to feel like it's not getting enough. (or maybe too much?!)

It definitely has a fuel smell when I park it (more than normal) -- would you recommend adjusting the fuel mixture? Should I change out the idle jets? and/or the main jets? If so, to what size do you guys recommend?

I can understand the love affair with these as it makes driving it worth it so much more appreciated!

Everything was running perfectly before and parked it and it had just been serviced... so I'm at a loss here. When I parked it I had a friend start it every few weeks and I did put fuel stabilizer in the tank.

I just want to drive her as the weather is getting better and better!!

Any help would be appreciated. I'm in Calgary, Canada if there anyone else here!



Well, let's get this discussion going so you can reliably get out on the road.  Let's start with the idle circuit:

1.  Find your fuel filter(s) by following the fuel line away from the carbs.  There might be more than one filter and they may be on each end of the car (front/back).  Make sure there aren't any kinks in the fuel line causing loss of fuel.  Replace any fuel filters that you find - they may be full of crud and causing a loss of fuel such that it idles OK but can't operate at much above idle 'cuz there ain't enough fuel getting to the engine.

2.  Changing the idle jets won't affect any change in the raw gas smell when stopped.  That is usually caused by a gummed-up pilot valve in the float bowl leaking fuel into the bowls and overflowing when it's parked after running.  (also, sometimes it can cause black smoke under acceleration because of running rich - Do you see any smoke?)  Sometimes you can detect a stronger smell on one side of the engine than the other when recently shut off, and THAT pinpoints which side needs attention.  Look around the outside of both carbs after it's been running and now shut off and see if any of the carb seams are leaking by looking for a slightly darker, wet color on the outside.  

To service the pilot valves you'll need a service manual for the carbs:  There are a couple on the CB Performance web site by Bob Thomlinson, one for Webers and one for Dellortos.  Pick whichever one fits and find out how to clean and set up the pilot valves (you end up setting the float height and that's critical for good operation so maybe something for an experienced mechanic).  This might be something for someone with carburetor rebuild experience to do the first time.  Maybe ask if you can watch so you can learn how to do it.  Maybe buy him/her lunch for showing you.  * See #4 and maybe add that to his/her list to do for you, too.

3.  Jets:  the 50's you have should be in the ballpark.  If anything, you could drop down to 45's but if it was running OK before on the 50's then it should be OK now with them.  Instead and assuming that it had been running OK and just has a clogged jet, then go ahead and remove each jet (all four of them) and blast some carb cleaner through them (use the needle tube on an aerosol can).  Once the jet is blasted and before you put it back, go to the carb and blast straight into the hole where the jet resides - several seconds should do it, then replace the jet just as it was.

4.  * Carb cleaner in the gas tank takes at least a tankful run through the engine to make a difference, maybe two tanks, and that's at a high concentration.  I prefer Seafoam, but CRC or Gummout should both work OK but remember, it takes TIME for it to work.  It's always faster to remove the jets and blast them with carb cleaner (aerosol can with needle tube) and replace them.  Don't forget to gently turn the mixture screws all the way in til they hit bottom while counting 1/4 turns til they stop so you'll know where they were to replace them at the same point, then remove them and blast.

5.  Anything beyond these four steps would, I believe, be getting into the advanced range and you might strongly consider taking the car to someone experienced on carburetors to help out as you might also be looking at a potential vacuum leak or something hard to diagnose like that.  While it might be easy for him/her to diagnose and fix, the potential for inadvertently screwing something up if you attempt repairs is high and the whole point of all this is to get you back on the road, NOT get you through "Carb Tuning 201".

Last edited by Gordon Nichols

Honestly, cleaning them out is not that big a deal. You don't need any advanced degrees. If you follow my instructions, you can clean the carbs without taking them off the car. But you have to follow my instructions, and you can't skip any steps.

You have Spanish Webers, which is a GOOD thing.

Before you do anything, check your fuel pressure. This is OFTEN overlooked, but important. No more than 3.5 psi with Webers. Period. If it's over, it will NEVER run right.

1: Disconnect the battery, OR massively tape/insulate the hot wire on the alternator.

2: Remove air filter tops and air filters.

3: Remove the 4 nuts on ONE carburetor that hold the velocity stacks and air filter base/linkage in place. Use a magnet on the nuts and washers so you don't drop them. Remove the two velocity stacks. Gently lift the air filter base up, keeping tension TOWARD the center of the car. There should be a spring inside the hexbar on both sides. You don't want them to fly off! Gently release the tension and grab the springs.

4. My advice, do one carb at a time. With the air filter base removed, you can lay the hexbar down, making sure it DOES NOT TOUCH the hot post on the alternator. Remove fuel hose, usually just a hose clamp.

5. At this point, you can follow these instructions:

If it's easier for you, the carb can be removed and cleaned on the bench.

FWIW, I use 10mm(plus 1mm for the gasket, so 11mm total) for the float height and 30mm for the drop. The drop isn't as important as the cutoff valve, but both should be identical.

And just removing the idle jets and cleaning them is NOT the whole job. The entire idle CIRCUIT must be cleaned. This involves the idle mix screw AND the idle jet. Both must be removed so the circuit can be flushed out. Carb cleaner squirted through the circuit both way works. Some carb cleaner will squirt into the main fuel well, that is where the idle fuel comes from.

My money is on goo in the float wells and idle circuits. You will most probably see white goo, black dirt, and possibly some varnish in the float wells. I cleaned the wells with the carbs on the car a few times. Lint-free rags are a must here. Paper towels or cheap rags will not do.

6. Do the other side.

7. Reinstall one carb top, tighten all the hardware, then lightly grease the hexbar springs and balls. Re-assemble, carefully.

8. After all this work is done, you'll need to synchronize the carbs. Do it engine HOT, not cold, not idling for ten minutes. You MUST drive the car and get it HOT, the synch.

Any questions, read Mark Harney's articles referenced above, or ask here. If I don't respond(doubtful) PM me.


Mark, you are getting good advice from Danny and Gordon, both here and in the links they provide. The Mark Harney articles Danny links to are the generally accepted Old Testament on Weber setup and tuning.

But there is a quick-and-dirty test you might try before pulling everything apart, especially since you say the car was running well before you moved.

I live close to sea level, at the foot of the Sierra Nevada mountains, and my carbs are tuned for that, but most of the good Speedster roads around here are up in the foothills, so I drive at higher elevations a lot. Up to about 4000', there's no noticeable performance hit. By 5000', there Is, and up at Lake Tahoe - 6000' - the engine is definitely down on power, and the idle has dropped noticeably.

If I'm staying up at Tahoe for more than a day or so, I'll do a quick tweak on the 'idle mixture' screws to raise the idle back up and help low end response. As a test, you could do the same to see if that makes any difference. It's possible your jets and idle circuits are clean, and you just need a slight retune. If so, the engine should respond to this little test.

Try backing off (unscrewing) the 'mixture' screws about a half-turn. Do each one the same amount and note how much you turn them so you can set them back to where they were if this makes things worse. The screws are marked 'idle jet adjustment' in the photo Carlos posted above. They're knurled, spring-loaded thumbscrews, made to be adjusted by hand.

It's probably a good idea to do a complete teardown, cleaning, tune, and possibly a rejetting, as Danny suggests, but this might make the car more drivable for now.


For reference, I live at 711 ft (+/-) above sea level, and am jetted with a wideband Lambda meter.

I've driven my car from here to Kalifornia on I80, across Nevada on US50, and up from San Luis Obispo to Las Vegas on CA58 and I15. I've taken the car all over the golden state, from sea level on CA1 to over 9000 ft in the Sierra Nevadas.

The car ran great pretty much everywhere at sea level and across the high plains, a bit rich over the Donner Pass, and would barely idle at the Yosemite east gate at Lee Vining. I never touched a thing, and the car ran well up to about 7000 ft.

The problem really, really has nothing to do with jetting for 3500 ft of elevation.


Um, yeah, leaner, richer, in, out, less dense, more dense, ipso facto, QED.

Except the last time I did this, I could swear I had to back them out to get more idle revs at altitude. Maybe that's only in 'R' months?

I do know that someone comes on here alla time lecturing us about how the idle 'mixture' screws don't affect idle mixture at all, but rather the volume of stuff that gets spritzed down the hole when the butterflies are shut, or nearly shut.

Don't know much stoichiometry.


@Sacto Mitch posted:


Um, yeah, leaner, richer, in, out, less dense, more dense, ipso facto, QED.

Except the last time I did this, I could swear I had to back them out to get more idle revs at altitude. Maybe that's only in 'R' months?

I do know that someone comes on here alla time lecturing us about how the idle 'mixture' screws don't affect idle mixture at all, but rather the volume of stuff that gets spritzed down the hole when the butterflies are shut, or nearly shut.

Don't know much stoichiometry.


Yeah, And?

Mitch sings "don't know much about stoichiometry, don't know much about Italian carbs"

He he he!

Last edited by DannyP

As someone mentioned further up this thread, if the carbs were tuned on the very rich side at sea level, they could start bogging at 3500 ft. Only way to know is to adjust them or put a wideband O2 meter on it. Right?

You or I would know a lot by pulling a plug or two as well, but I think we're sticking Mark's head under the business end of a firehose here, and expecting him to come up refreshed and ready to roll.

The thing we're asking him to do has frustrated every single one of us, to the point that some of us have of wished the earth would open up and swallow the stupid car and put us out of our misery. Guys sell their cars with <500 mi. on them with some "no garage room" excuse or another when we all know it was the dreaded idle jet

... or maybe the ignition pickup module loosened up. Or maybe the manifolds are falling off and the whole thing is sucking large gobs of air downstream of the carbs themselves. Or maybe the entire main-jet stack backed out and is laying beside a velocity stack. Or maybe a plug wire is burnt and making poor contact.

The possibilities are endless. Every single one of them has happened to me.

Regardless, we're asking that he do this right out of the chute and without the background, tools, or spares which would ensure that he was able to get those carbs apart and back together again without a brass thingie moment. We're offering support as we sit in our offices or dens or kitchens 1000 miles away, throwing out best guesses (which almost never get to the root of the actual issue). I'm waiting for somebody to suggest the stupid Tomlinson manual. If Mark had wasted his time and money on all of this back in high-school, he would have ensured that he was inadequately compensated for the rest of his life - but he also would be equipped and outfitted to do what we are asking.

Even if one has the knowledge, tools, and background - something as uncontrollable as one's physiology often plays into this. I've been told I've got "Chevy hands". I struggle to find gloves that will fit over my paws, and I tend to break things trying to get them just tight enough. Pulling jets on Weber carbs in a pan-based replica engine bay requires hands the size of a small child's, but with the strength of a pipefitter's - and the delicate touch of a mother with her newborn. It requires almost contortionist levels of dexterity and being deeply, madly, and passionately in rut with your car just to get at the front jet. The back ones require some sort of deal with the devil or taking a sawzall to the inner fenders of your car. These are skills useful in almost no other endeavor in life  - not even with other cars.

It's madness.

Calgary is a big city with a lot of loose money floating around. Surely there's somebody with the tools and the shop to diagnose and repair the car without treating it like some freak-show oddity. Even better would be an aircooled club that populated by at least a few guys who work on their own stuff. I'll bet Mark could have his car running well in an hour if there was somebody to help walk him through it.

As it stands with our interweb troubleshootin', I'm not so sure we're even aiming at the right thing here. He says it idles fine - it struggles under load. Perhaps we're chasing the red herring because it was suggested to him that maybe he would need to rejet. If it's load related, I'd look hard at ignition before I dove into the black heart of darkness. 95% of all carburation issues are ignition.

Either way, I'm tapping out. I'll be anxiously monitoring this thread for a resolution. Good luck, Mark.

Last edited by Stan Galat

Stan, define "idles fine". An engine can idle almost fine on three cylinders, but boy does it suck at part throttle. It will absolutely suck until over 3000. It will sit there at 800 rpm or 900, not really caring about that one jet. If all 4 were clear it would idle at 1000 or 1050.

Taking the carb tops off accomplishes two things. One, you'll know they're clean after you're done. Two, it is SUPER EASY to remove Weber idle jets in any car with the tops off.

You're right, I am asking a lot from this guy. Maybe he can do it, maybe not. Maybe it's ignition, maybe it's not. If he tries he may fail. If I was him and even a little confident, I'd try it. But I'd also have a backup plan of somebody who could bail me out.

And absolutely I know I'm correct about cleaning the WHOLE idle circuit, not just the jet. Been there, done that, LOTS.

After our 2021 WCC run this past weekend I now fully believe that the whole idle circuit needs to be cleaned before you can call it clean. Before the cruise I had removed the idle jets and used carb cleaner and a wire to clean them off and I put them back in. The car was running okay but it seemed like it was still a little rough. I had asked for and received advice on cleaning the whole circuit but I've been so dang busy I hadn't a chance to do the whole process.

During the WCC I was getting a soft backfire on deceleration. I called it "chuffing" because the backfiring seemed to be very soft and not like the backfire that set my air filter on fire several years ago. Anyway, to help stop the "chuffing" I just put the car in neutral during the long downhill sections and drove like normal during the level parts. I was quite disappointed in myself for not handling it before the event.

I have no transport jobs this week so I have plenty of time to get things done. I have concrete to remove, a fence/gate to demo, a load of rocks to rake up from my house and take to my daughter's apartment, replace the kitchen faucet, change out the pool lights, a few repairs I need some trades people over here to get done, and lastly some things need to be done with the Speedster. I need to clean the whole idle circuit, set the valves, change the oil, order some Cocomats, and get the car detailed as I've let it sit for too long with the cover off of it.

The first thing I did today was clean the whole idle circuit. I removed the air cleaners and filters. I took off the velocity stacks and the bottom plate. I took out the mains, the idle jets, and the idle mixture screws. I cleaned all of the parts with some carburetor cleaner. I used thin/stiff wire to make sure there was nothing sticking inside the mains and the idle jets. I used carb cleaner on the idle circuit using the included flexible house to spray cleaner into all of the openings. I let it sit for a minute and then I blew air into all of the openings as well, including the thin brass rods coming out of the top of the carbs. Once I was satisfied the whole circuit was clean I put it all back together. What a difference that made. I will no longer consider the "circuit" clean until and unless I do what I just did today.

Even with the JayCee idle jet holders (IJH) on my Webers it is a little difficult to get the idle jets out so I modified some tools to make it easier. I took the correct size allen wrench for the IJH and cut it short enough to fit in them and not hit the side of the engine bay. The allen wrench needed further modification so I took a Dremel and put most of the shaft on a diet by grinding out the portion of the key that doesn't go in the end of the IJH. If you need a little more leverage to tighten it up you can slip an extended socket over the end of the key to get some grip on it. Just don't crank on them too much, it isn't necessary. I also took a stubby flat blade screwdriver and cut off a significant portion of the handle and epoxied the blade back in the handle.  The cut down stubby screwdriver made it easier to count the turns while backing out the idle mixture screws after seating them upon install. I couldn't see the IMSs at the back of the carbs so I just felt for the correct position of the blade while backing each one out.



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Last edited by Robert M

Pineapple Mike wrote:  “Mark, listen to these guys. They know more about keeping carbs running smoothly than just about anyone.”

We have to.  Who the heck else are we going to go to in our areas?  “Carb Whisperers” are getting fewer and much farther between, no matter where you live.  The combined knowledge on here is priceless.

True story: the "go-to" German car shop in Peoria is owned by a guy who owned a Vintage Speedster for about 15 minutes about 10 (+/-) years back. I met him and @Panhandle Bob about the same time, and for a brief, sihining instant I didn't feel like the lone weirdo out here in the corn and snow. They both ran with a considerably nicer crowd, but I got to know them both.

The other fellow sold his car after determining it was pretty slow, and Bob moved away a few years later, but it was fun while it lasted.

Anyway, I've had this shop do some work on my car over the years - they've got an alignment rack and we adjusted the ride height and did a corner-balance and alignment. I also had them do the rear suspension bushings one summer when I just ran out of time. They also diagnosed (over the phone) a problem with my mom's SLK, and did the work for me. They're sharp and do excellent work.

However.... a couple of years ago, I got a call from the owner. A guy was in to get his 911 carbs worked on and of the 8 or 10 mechanics he had at his disposal, none of them felt confident working on the carbs. He called and connected me with the guy doing the work to pick my brain a bit. I didn't actually go in do anything to them, but it was hinted that kind of thing might be in the cards if they took more "antique" Porsche work, assuming I wanted it.

I don't.

There's not a lot of guys left in major markets, and none left in minor ones. Calgary is a major market -  there will be somebody, but I hope for Mark's sake that he's a fast learner. We're all going to need to be going forward.

Last edited by Stan Galat

First off I have to say THANK YOU for all of the generous information shared here. I appreciate you all taking the time to help me out. There is so much knowledge on this site and this thread is filled with little tricks and tips. I followed the instructions to adjust the mixture and that helped a lot. It still feels like it's missing a few horses when I'm flooring it through 3-5k rpm. I don't have space in the garage to take apart the carbs myself as we just moved but will create a work bench for future needs.

I drove it about 50 miles today and when I went to start it again it takes a bit to start. When it's a cold start it whips right up... but I've noticed a few times after I park it for a moment and it's still hot the start feels I little scary. I don't have a lot of trust with it yet as I don't know her fully since I just got her in January.

Anyways, you guys have been awesome. I'll order those JC jet holders.. is there anything else you guys think I need that makes things easier?

Also, @Bob: IM S6 sent me the info for a shop in Calgary that specializes in air cooled VWs so I gave them a call and they have a cancellation for tomorrow AM! So off to Tony's Auto Service I go!

Happy Father's Day to all of you to whom it applies. Much appreciation over here!




Good to hear you're making progress, Mark.

The suggestion to tweak the 'mixture' screws wasn't meant as a final fix - just a test to see if you had a clogged idle jet or not and a way to possibly get the car driving better until a thorough tune can be done.

One of the peculiarities of most carbs on our cars is that they will be a little harder to start after they've been driven, parked briefly, and restarted. There are a few reasons for this, but normally, this will clear up in the first mile or so. And again, a proper tune should do a lot to help that, too.

Let us know how things go.



For a hot start I've found MOST cars with Webers like it if you hold a SMALL crack open of the throttle while cranking, and they fire right up.

Cold start: 2 pumps(maybe 3 depending) and turn it over until it fires, then keep feeding SHORT stabs of gas for the first ten seconds. Then hold it steady until it starts to smooth out. You don't want to rev it over 1500-2000 rpm in your startup process. After 30 seconds or so it should stay running on its own.

Last edited by DannyP

Dells are a whole 'nuther animal. I have a set on my bench right now I'm rebuilding. They should get completed this morning and shipped out today. They have a LOT of parts to remove, clean and put back. They have a LOT of passages to clean. The idle circuits have plugs to remove so you can clean the whole thing. I swear they're equipped with THREE times the amount of brass plugs and screws, brass weights and check balls etc. They have a LOT more O-rings(I count them later when I re-assemble).

Webers are simpler to rebuild for a regular guy. I wouldn't attempt to rebuild Dells unless I had more experience than most. It's been a while since I've done a set, I forgot just how many pieces they have. Webers have two O-rings for each circuit, one for the idle jet holder and one to seal the mixture volume screw. That's it. Carb top gasket and float valve, and some aluminum crush washers on the fuel inlet and float valve. No check balls(other than the one inside the accel pump valve).

My point is that to clean Dells you really need to remove them to the bench. Blackline/whoever totally deserves the money they get for a rebuild. Webers can be cleaned really well ON the car, only removing the carb top and idle circuit stuff.

Dells are great carbs, but complicated to do them RIGHT. Webers are certainly easier to maintain IMHO.

Last edited by DannyP
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