Jetting for Dual Carbs

Cold(er) air/fuel mix comes in the intake valve.  Hot(er) exhaust mix goes out the exhaust valve.  What you saw sounds normal to me.

My guess on jetting (but the only way to really be sure is with an air/fuel gauge):

36 mm Venturi

.50-55 idle jet

1.50 main 

1.60 - 1.80 air correction

Getting the jetting right is a real trial and error thing, especially without a wideband, but it can be done. Pay attention to how it runs cold vs how it runs at operating temps- not running really smoothly until it's quite warm can mean it's a little on the lean side, while running great when relatively cold and then the crispness of the tune seeming to "go away" as it warms up usually means too rich. Be prepared to spend a small fortune on jets (consider it the cost of doing business), unless you can find someone who's already gone this route. Start with the idle and go smaller (1 step at a time) until it starts to run rough, and then go back up 1 size. If the engine has a centrifigal/vacuum distributor you may be surprised how small the idle fuel jet ends up.You should notice a mileage increase. Never change more than 1 thing at a time.

Aircooled.net has a good article or 2 on tuning, and 1 of the things I've heard him mention is to actually take the main jet stacks out of the carbs and drive around like this when tuning the idle circuit. It forces you to concentrate on the low throttle. Fwiw, I haven't tried it myself...Al

Gordon Nichols posted:

My guess on jetting (but the only way to really be sure is with an air/fuel gauge):

I agree 100%

... but when I told Krusty this on the "colortune" thread-- no love for the Stanster from my buddy elGordo. Unless you are an old hand at this (I'm not), an A/F gauge is really irreplaceable to see what's going on.

Bobby has proven he's a better wrench than 99% of us here. He rebuilt his own engine (twice). I'd recommend getting a wideband meter (LM-1, or similar) and reading all you can.

Anything else is just guessing.

Absolutely.

Guys that don't have a wideband like to make themselves feel better about being cheap and try to justify that stance by touting the "you can jet by trial and error" method. 

Buy once, cry once, and don't look back!

By the way, the carbon on the intake stem is caused by intake reversion.

Less than $200, the price of admission is lower. Weld a bung in your exhaust. 

http://www.ft86speedfactory.co...d8LcOfg#.WWI3M3MpDqA

Mic dropped.

Stan, I love ya - and It's not the use of an A/F meter I have difficulty with, it's the cost.  $350 and up is kind of steep for me, but if I could find someone locally who has one (and knows how to use it) for, say, under $100 bucks to set up a pair of Webers or Dells for me, THAT would be cool.  An A/F meter is one of those things you buy and use once, maybe twice - ever.  Once your jetting is nailed down it doesn't change.  It's kind of like the TIG welder I bought and haven't yet found the time (or inclination) to plug in, only to find out I don't know how to weld.  Of course, my son might use it.......

Come to think of it.....Maybe I can talk my son into buying an LM-2 - the specs look awesome!  

Not 350.

$189. Innovate MTX

That their new one?  Price is getting down to where I can't complain about it anymore!

While you guys are right in that it's much easier (and probably faster) to nail the jetting with a wideband, and considering the cost of an engine runs anywhere from 3- 8 or even $10,000 it's probably a good investment to purchase such a device (especially now as they have come down in price significantly and you could turn around and sell it when you're done) as the final stage after installing the engine, with patience it can be done without such said electronic wizardry. It takes longer and you'll have to pay more attention to what the engine is doing, but it's the way it was done before such technology existed. The very idea that it can't be done without such equipment- I don't think so...

I am the first to admit a wideband makes it much easier, though.

I'm secretly waiting for Stan to adopt me so I can use all his stuff (and he has really good stuff, too!)  Haven't made it public before this as I'm waiting for his shop/garage to be finished so I can move in.

It's getting close, so it won't be long now....Almost time to start packing.

Haven't used a wideband turboencabulator, so mine is a somewhat uninformed opinion.

But my engine idles, transitions, and runs full bore smoothly. Power, torque, and fuel consumption are all pretty good.

We got the jets right on the second go around.

It helped a lot that the guy who spec'd the engine and the builder had built the same mill half a jillion times and pretty much knew what to expect. Venturis, emulsion tubes, mains, and air jets were right on outta the box. Idles got bumped up one size.

Using the turboencabulator, in THIS case, wouldn't have saved any time or gotten us any closer.

If I were a little more, um, retentive, I might feel better knowing exactly what my numbers are. But probably not, as the numbers are never spot on perfect and retentive types lose sleep over stuff like that.

The car sounds and feels pretty much happy. And I'm happy too.

If I were attempting an exotic build, with a combination of parts I had no previous experience assembling, the turboencabulator would probably be a quicker path to happiness.

But, like with a lot of this crap, it depends.

Gordon Nichols posted:

I'm secretly waiting for Stan to adopt me so I can use all his stuff (and he has really good stuff, too!)  Haven't made it public before this as I'm waiting for his shop/garage to be finished so I can move in.

It's getting close, so it won't be long now....Almost time to start packing.

I still like the idea of all of us retiring to the same community and in the middle being a communal garage...

Hey guys,

Thanks for all the input.  I think what I have in the car now is too rich.  I am guessing by how the pistons and cylinder head look.  Does any one have a picture of combustion camber and piston tops of a properly tuned carb?  

I have a handful of jets.  Can step my idle jets down to 55 or 45 from the 60 they are at now.  I also have 160 mains, 155, and 145.  Air correction jets I have 2.00, 1.80, and 1.75.  So I have a lot of shells I can move around and play the game.

I am not sure the wife boss will let me spend any more money to purchase a/f meter.

First step- find someone with a set of jet drills and verify the different sizes are what are marked. Once you definitively know what you've got, put the 55 idles in (if that's what they are), re-adjust and see how it runs. If it runs great with the 55's, get some 50's and try again. If it runs great, go down again; if not, go back up to the 55's and drill out the 50's to 52 1/2's and try them.

John at Aircooled.net would trade jet sizes if you originally bought from him, so if he still does it is worth looking into. 

thanks Al.  What about the main jets?  Are the 1.55's too big.  I have a set of 1.45's.

"I still like the idea of all of us retiring to the same community and in the middle being a communal garage..."

That's what I had in Beaufort, SC - HUGE old warehouse building repurposed to a car club "Man Cave" with a machine shop, lifts, lots of tools and lots of car storage.  Trouble was, it was way down there and the rest of the family was up here, 1,000 miles away.

My guess on Mains would be 1.50 but try the 1.45's and see how they feel.  If they're weak or give hesitation, ream them to 1.50's and drive on.

Or just stick with the 1.55's

But I don't have a turboencabulator 5000 either, so whaddo I know?

Someone asked about color inside of the combustion chamber.  Pull a plug and look at the color of the porcelain at the tip inside the chamber;

White is too lean

Beige is just right (color of a light/regular coffee) 

Black is too rich.

And THAT is without the benefit of a Turboencabulator 5,000.

Bobby D posted:

thanks Al.  What about the main jets?  Are the 1.55's too big.  I have a set of 1.45's.

Don't know, and you shouldn't fiddle with the mains until you get the idle circuit sorted out. That's why I haven't mentioned the mains at all. Sort out the idles first.

Gordon Nichols posted:

 

... And THAT is without the benefit of a Turboencabulator 5,000.

I have advocated and will continue to advocate for the Turboencabulator 5,000. In the interest in economizing for my skinflint Yankee homeboy, I would perhaps allow a Turboencabulator 4,500 (for those times when $200 is OK, but $375 is just too darned much), but not the Turboencabulator 4,000. That's just a bridge too far.

I'm Bill the Cat, and I approved this message.

Bobby- after driving my new (2013) VS stock 1600 CC (with dual 40mm Empis- I know, but Kirk was using them and I did not know any better) for about 6 months I did a general tune up and found the plugs with large amount of black soot. I posted on this forum what I finding and the group just responded with; like you have seen in this thread a boat load of great information, especially carb tuning . One person, can not remember who mentioned it but buy the Weber Tech Manual by Bob Tomlinson. And I did, spend a week reading through the manual since I had no idea what was what and where on the carbs. Understanding the different phases of the carburetor, lots of patients and trial and error I went from idle jets of 60 to 45 and settled on 50 after opening the main air. Al has a good thought I should try some jet drills and test a 47 1/2 to see if the plugs can get just a bit more coca color and they should look after 1000 miles.    

Suggestion: A "Community Wide Band & Jets Kit."

10 dudes x $20 + $5/year "subscription fee." The tool and parts are left to one centrally-located dude (such as Stan?) And that guy ships them out to whoever happens to be crying at any given time. The borrower returns when their carbs are right or in six weeks, which ever is first. Kit keeper keeps count of the jets and sizes & stocks as necessary. 

Membership in the club is $20 +$5 a year subscription & you have to be an SOC Supporting Member.

Discuss.

Ed

I like that idea.  I would sign up.   I also have other specialty tools I purchased for my build:  crank shaft gear puller, piston ring compressor for 94's., deck height measuring tool and distributor drive gear puller.

Mike B.

I do have a copy of the Bob Tomlinson book.  It is a great book.  I used it to get the setup I have now.   I am too rich so I have to start working backwards to lean it out.  I just dropped the Idle jets down to 55 last night.  I won't have the engine on the run stands for another day or so.  I need to get the idle jets sorted out before the motor goes back in the car.  I is not easy to change them once motor is back in its bay.

Michael B (aka bluespeedster SoCal) posted:

...One person, can not remember who mentioned it but buy the Weber Tech Manual by Bob Tomlinson. And I did, spend a week reading through the manual since I had no idea what was what and where on the carbs. Understanding the different phases of the carburetor, lots of patients and trial and error I went from idle jets of 60 to 45 and settled on 50 after opening the main air. Al has a good thought I should try some jet drills and test a 47 1/2 to see if the plugs can get just a bit more coca color and they should look after 1000 miles.    

If you still have the 45 idle jets, Michael, you've got nothing to lose in trying 47 1/2's. If they're too small, throw the 50's back in while knowing they're the right size, and if they work mileage will be that little bit better (not that that's a big issue with these cars) and light throttle response/power will be that little bit crisper. What I like about Bob Tomlinson's Weber Tech Manual (and his Dellorto version) is the troubleshooting section.

Bobby D posted:

Ed

I like that idea.  I would sign up.   I also have other specialty tools I purchased for my build:  crank shaft gear puller, piston ring compressor for 94's., deck height measuring tool and distributor drive gear puller.

Mike B.

I do have a copy of the Bob Tomlinson book.  It is a great book.  I used it to get the setup I have now.   I am too rich so I have to start working backwards to lean it out.  I just dropped the Idle jets down to 55 last night.  I won't have the engine on the run stands for another day or so.  I need to get the idle jets sorted out before the motor goes back in the car.  I is not easy to change them once motor is back in its bay.

Most people recommend jetting on the rich side to start; that way you start the engine up and you don't have to worry about melting it down because it's too lean. Way easier/safer to drive around sneaking up on a better tune that way. Most people who bolt dual Webers/HPMX's/Dellortos and drive around without working on the jetting are running their engines pig rich, with the resultant drop in power (and mileage) that goes with it.

One note, guys- If when going down in idle fuel jet size you get a point where it still runs well but get a noticeable rise in engine/oil temps, it may be wise to stay with the 1 size larger jet. This is more expected with centrifigal only advance distributors, and idle circuit jetting may have to be compromised slightly.  You can run leaner mixtures at light throttle settings successfully (the engine using only the carbs idle circuits) with an svda (mechanical and vacuum advance) distributor. Mechanical advance distributors were designed for stationary powerplants and full throttle settings (racing conditions) and are a bit of a compromise on the street (even the 010's and 019's everyone so raves about), while the street is what the svda was built for. Given the same distributor as mechanical only or mechanical/vacuum combo (svda) for a street engine, the svda is the smart pick every time. It's not uncommon for a car with a well tuned dual carbed, 2 liter + engine with an svda to get mileage figures approaching 30mpg or more, even at higher highway speeds, because the engine is running on the carbs idle circuits and only dips into the main circuits occasionally. Al _{(and boy, am I done for now. Time to go get some work done!)}

PS- I have a couple specialty engine tools that my VW friends don't have, and the cost of borrowing is usually a 6 pack and they usually get 1 or 2 (or even 3 if they stick around long enough) so it's not really a big deal. 

`

Several years ago I suggested setting up a tool registry where we could all list the special tools we have. Then, anyone would know who they might to to to borrow what they needed.

I will let you guys know where I end up on idle and main jets.   I have to do most of my testing on my engine stand/transjack.  Once the engine is in the car, it would be impossible to get the spark plugs out to take a look at their color.  I have those CB manifolds for the Panchito heads.  They have a thick flange that makes the studs and the nut interfere with a spark plug socket.   Has anyone ground down the top of flange on these fat manifolds?

Bobby D posted:

... They have a thick flange that makes the studs and the nut interfere with a spark plug socket.   Has anyone ground down the top of flange on these fat manifolds?

Can you just clearance the edge of the manifold so it clears the spark plug socket? Or is it the bolt down stud/nut that interferes? Can you take a pic?

PS- I have a spark plug socket that I'd shortened the overall length of (1/2"? came off the bottom) and rounded the top edge of to clear manifold to make changing plugs easier in my (long gone) Cal Look bug with IDF's. If you get a spark plug socket with the rubber insert to hold the plug, pull out said insert and shorten it the same amount as what came off the bottom. If needed you could even shorten the top a little. You should be able to change plugs in the car with whatever manifolds you have. It may not be easy... 

Hey Fellas

I got the motor all setup for a test run tomorrow on the stand.  Primed the oil pump.  I fired it up to see where I am at.  It pipped and pop for about 20 seconds then settled down.  I will start to tune it tomorrow and let you guys know how it goes.  Keeping my fingers crossed.

Bobby, I know you're trying to get the jets right with the engine still out because of limited space, but you'll probably still have to swap the idle jets some after you're actually driving it. And you'll still need to get the jets out every so often to clean them, anyway.

So, why not make life easier with these hex head (and allen key) idle jet holders? Much easier than trying to line up a stubby screw driver blade with a slot you can't see.

These motors almost always run differently once on the road because they never heat up as much on the stand as they do under load in the confined space of a closed engine bay. And too, you'll probably want to start out a little rich and lean it out a bit once the rings seat and it's broken in.

Learning to remove the jets, squirt some cleaner in the carb passages, and replace the jets all by feel without dropping anything into the black abyss is one of the rights of passage with these engines.

In yoga, it's called the crouching mechanic praying position.

Al, I remember in my saga of jetting you or Gordon or Wolfgang mentioning not to go too lean for engine temp. I noticed, with that advise road testing using the 45 temp was higher than using 60's. With the 55's plug looked better but just not right. Someone else on this site suggested driving the car down a straight more than one mile in length with rpm over 3500 and shut the engine off immediately, then pull off the street to pull out several plugs. Look at them and what do they show. Going from the 60's looking wet, to the 45's being drier was a big difference. After many runs with different jets installed the 50's were the best. Engine temp runs in the middle or slightly less (depending on outside are temp) with better mpg and what seems good engine performance for the stock 1600cc dual carb. 

Thanx again to all who piped in to help me keep the valves running cleaner.

Mitch

I have never seeneed hexadecimal head jet holders. Where did you purchase them?

Darn auto correct

Bobby D posted:

Mitch

I have never seeneed hexadecimal head jet holders. Where did you purchase them?

Insider's tip, Bobby-- if you see blue text it's generally a link. Click on it, and go to whatever is being referenced.

Mitch's link:

http://www.jayceevw.com/store/...Idle_Jet_Holder.html

Sacto Mitch posted:

In yoga, it's called the crouching mechanic praying position.

Question for you pan-based guys with Webers:

How come nobody cuts access panels in the wheel-wells? It seems to me like this would be a "cry once" solution for the ridiculous access issues you have with idle jets and spark-plugs.

And I agree with Mitch-- you're never going to get the jetting 100% right on the stand. On a dyno perhaps, but not on a stand.

Hey how long does the engine need to run for the lean/rich colors to show up on the spark plugs?  I want to get the idle jets squared away today.

Stan Galat, '05 IM, 2276, Nowhere, USA posted:

 

Question for you pan-based guys with Webers:

 

How come nobody cuts access panels in the wheel-wells? It seems to me like this would be a "cry once" solution for the ridiculous access issues you have with idle jets and spark-plugs.

Bobby D posted:

 

Mitch I have never seeneed hexadecimal head jet holders. Where did you purchase them?

 

 What Stan said, just click the link.

JayCee makes the holders, but I see that you can also get them at CB Performance at this link.

They sure are easier than a short screwdriver.

Bobby D posted:

Hey how long does the engine need to run for the lean/rich colors to show up on the spark plugs?  I want to get the idle jets squared away today.

For my engine set up it was around 200 miles. I'm sure if the engine runs richer, it will take less miles. 

Ok,

Got the motor running and trying to get the tune right.  i am running about 9.5 degrees advance on idle.  I balanced the carb with snail meter.  I went around adjusted each mixture screw to highest idle RPM.  It is idling ok at between 750 and 810.  However, if I give it some throttle the carbs start to pop upwards.  So does that mean I am too rich or too lean?  Running 60 idle jets.

So if I am running the magnaspark II distributor with the stock red bushings and stock light sliver springs the centrifugal advance should be 20 degrees.  If I set the initial advance at idle (750 RPM) 9.5 degrees, then my total advance should be around 29.5 degrees.   Could that possibly to much advance the motor I built?  I am just suck right now.  I can't seem to dial in the idle mixture to stop the popping in the carbs.  Any advise on what to do next?

I run a standard Magna Spark II with the Magna Spark coil and have the disty set at about 8 degrees at 900 RPM idle. When I raise the Idle to 3000 RPM she holds steady at about 28 degrees which seems to work well for my 1915cc with Dual Dells.  

Just a thought.

Make sure that all the little rubber o rings are in the proper place on both the idle and the main jets. It is easy to have one out of place or missing.

The popping could be an air leak problem. Happened to me before.