I have built a fresh 2.0 and borrowed a set of weber 40s to get her running, broken-in etc....

I bought a new single vacuum distributor with the flame thrower 3 module inside. Also bought the Petronix coil.

I built up oil pressure, then connected the gas lines, fuel pump, and coil. Tach and timing light too.

After a few tries, she started. As expected running very ruff. Back-firing thru the carbs.

I loosened the distributor and tried to make some adjustments. That seemed to help the back-firing a bit, but not totally. I got the idle timing to what looks like 7 btdc, but it is tuff to work everything without a helper.

I know next to nothing about these carbs, and about the same amount to tune them enough to bench run the engine, but I am looking into that. Any help would be appreciated on the carbs.

I got it idling, again, very ruff. So I wanted to do the cam break in, so I rev'd it up to about 3000 and held there. Maybe a minute and the revs dropped and I had to putz with the accelerator to keep her going. Again up to 3000, same thing revs dropped.

I have a note in to my distributor vendor about how this "rev limiter" on this module works.

So three things here. She is still running ruff, back-firing etc...and there is the high rev cut-off. Lastly the carbs, any quick checks or adjustments there? Any thoughts or suggestions?

Do you have a snail sync tool? Sounds like a sync issue.
Bad linkage adjustment as well, the flat fours are super sensitive to sync issues.

What rev limiter? They cut off at high RPM and shouldn't cause an issue, but the bosch rotors have a resistor that can go bad. Just swap out a regular rotor.

First off:


We need pic of your engine on the run in stand!

For the back firing you need to adjust the carbs and make sure they are drawing equal amounts of air. You need a tool to do this. Search for a carb snail. Its a gauge that you stick into the throat and it measures airflow. You want the airflow balanced between all the carbs.

You also want to be able to hold the engine at 2K rpm for 20 minutes to do the cam break in. And then 3K RPM to set ignition timing. For your run in stand - I put a cheap-o tach on mine, and also rigged a way to work the throttle. A tach is just 1 wire from the dizzy. And the throttle is also really easy. I just put some wire on the carb linkage, pull it to open the throttle to the RPM I want and clamped it off with a pair of vise-grips. field expedient and makes a lot of the tuning easier when you are working solo.

Zach

I will see about getting the snail tool today.

The rev limiter is within the electronic module. appears to be adjustable. Wonder what it is adjusted to?

This came from the vendor: "If you are wondering, the Pertronix Flamethrower III module has a couple of advantages over the original Pertronix. First, the Flamethrower III module changes dwell as needed. It also senses when the key is on but the engine is not running, which used to burn out the original Pertronix! The Pertronix III is immune to this annoying problem! The Pertronix III has a digital rev limiter that you can set to the RPM that you feel is best! We believe these features are worth the additional money over the original version of the Pertronix module.

The Pertronix 3 SVDA Distributor, 12 VOLT is designed to run with a low impedance (0.32 ohm) coil for best operation"

I hear music in the back ground. You Tube may shut me down for no license. But for now.... Here is a vid of generating Oil Pressure. Finally something that did not cause me issues.

Oil Pressure build up Video



https://www.youtube.com/watch?v=h2xtp-eEDQ0

The rev limiter shouldn't be an issue if it's set correctly, pertronix either works or it doesn't.

Your video is marked private

Zach

Depending on the idle speed adjustment screws to balance the carbs might only have the carbs balanced when the screws are on the stops. A worn sloppy linkage is not your friend. Increase the idle with ONE ISAS. The linkage will be in a natural state and the pulsing of the synchro tool will calm down. THEN use then synchronizing tool. Adjust the offending droplink. For timing, you can really increase the RPM and not have to try and sustain a stable idle with the pedal or hand operate the linkage. Makes the ordeal a one person task. The air bypass screws factor in as well. I would lightly seat them.

Thanks. I have marked Public.

Is this all there is to it? Just test or measure 1 barrel at a time either holding the RPMs steady or just idling?


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The number values on the tool are sort of irrelevant. You only have to have the reading be the same. The sealing portion on the bottom turns and exposes a hole. This is to help with the pulsing so the needle doesn't jump. Turning the idle up will help with the pulsing and no need to expose the hole.

Here's my carb tuning procedure from a March 03 post:

Assumptions: the carbs have the optimum jet and venturi package (if you have an unknown engine/cam good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good.

Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist.
Start and warm up the engine.
Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin ignition wrench to snap them off.
Turn the mixture screws all the way in and then 5 half turns out.
Turn the air bypass screws all the way in.
Turn the idle speed screws out til it just touches, and then in 3 half turns. (3 barrels I go 5 half turns)
Put on your hearing protection and start the car.
Use your STE and find the barrel that pulls the most. We'll call this one baseline.
Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter)
Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels.
Go to the other carb and do the same thing.
Snug the jamb nuts on the air bypass screws.
All six barrels should pull the same amount of air at this point, if not repeat air adjustment procedure.
Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance.
Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm.
Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest idle, then turn it in 1/4 turn.
Do the same with the five other mixture screws.
If you have to turn the mixture screws more than two turns either way (from baseline), you've got the wrong jets.
Recheck side to side and individual air balance, adjust as needed.
Road test the car.
If you get snapping and poping out the intake, it's generally a lean condition.
If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich.
If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets.

That's a rough, five minute draft of my carb tuning proceedure, hope it helps!

If it goes good it should take about 45 minutes, if not about three years.

PK

If it's running good but a little rich, you can turn each air bypass screw out to lean it out some, go a half turn out at a time and test drive. If you have good air balance, just make sure you turn all screws the same amount, and recheck the air flow at each barrel.

This was written 16 years ago before wide band O2 sensors were economical and easy to install, get one it will make your carb tuning much easier.

I'll add that if your linkage moves at all when you put it back on, then you don't have the linkage correctly set up. Drop links have to be exactly the same length and both on the idle stop screw

Where in Nashville are you? I'm coming through Friday on my way to east TN (Cleveland). If it's not too out of the way and my week doesn't go to hell, I might be able to stop by for a little bit.

That rules out about 1/2 of the 914 engines in existence right there.

I like how Amazon calls this "deluxe" seeing as it's the cheap Chinese copy.

The better one is the STE, made in Germany. About $20 more, mine's almost 30 years old.

@mark henry

Curious if you have used a Uni-Syn. That's what I've always used and had great luck with that.

East of town couple exits past the airport on I-40. Mount Juliet. You will probably head south (east) down 24 towards Chattanooga. But Cleveland can be reached taking 40 east most of the way. keep me posted.

Clark

Pull out each idle jet and make sure one is not clogged. Weber’s require clean fuel and very small particles will clog the idle jets. Also, Weber’s run about halfway thru the RPM range on the idle circuit. If it is rough at idle but smoth at full throttle, I’d look at the idle circuit.

Charlie

Sorry but to encourage this is irresponsible

Theres a reason you should use a porsche mechinic (with the right tool's) for this kinda thing . unless you dont care if you accidentally melt down your engine prematurely.



( which you could very easily the way youre goin)



Then go ahead.


Reminds me of my step dad who pryed the heads and intake off his cobra replica . so he could go for big power.

The old heads and carb made way more power as they were dialed in . then the new stuff. Which he didnt know how to tune and could never get dialed in properly.

Car just sits now. Weeping fuel .


Im no mechanic beyond oil changes.
But i have a sobering sense of my limitations !!!

That Uni-SYn looks totally different. Does it work the same? Looks like it just sits on top of the barrel.

Several on eBay for 1/2 the China one. I have a raised dis-taste for all things Chinese. I am sure you know why.

Your overall point is valid. But, at this point he's comitted and has already spun it over to build oil pressure and it runs rough that much we know. At the beginning we all start somewhere. Hopefully on lawnmower, go carts, 2 stroke dirt bikes . . . whatever . . . that are less costly to fix if need be.

Are there risks? Yes, but they are limited. I rebuilt my 1st teener engine at 22. It's not rocket science. Tom Wilson book clearly lays out what needs to be done. If one can follow a detailed recipe and have a sense of self imposed quality control, it is pretty easily done. Luckily, I started with a fresh new set of Webers and guidance from someone in the know to guide me. It was a 1.7L converted to 1911 and it all turned out great!

Engine won't melt down on a test stand with no load unless it's being run at WOT for extended period and running lean and/or detonating. Seems OP at least realized something is wrong stopped to investigate. That is the correct thing to do.

Previous post by Mark Henry is a sound plan of action and clearly outlines the preconditions that need to be addressed before trying to run it again.

Mine is ancient and pre-dates the el-cheap China imports. Probably made in Taiwan though back in the day - I'll have to look.

The concept is the same. It measures a baseline airflow. I think it may be a bit more adjustable but since I've never used a snail, I can't say that with any certainty.

It works on flat faced carbs without the need to insert into the venturi or velocity stack. I think you may be able to more precisely control the restriction it presents to the carb during measurement but at the expense of losing vacuum signal that moves the indicator up and down in the sight gauge.

Other than that, everything Mark laid out for you applies.

I was just curious why the snail type was his preference. I see absolutely nothing wrong with the snail type either.

I just hate to see this guy end up like the other guy who had too build his second $$$$$ big /4 because a rod bearing was not secure and melted the thing down .the 1st time around.

Dont learn on a type 4 build a few dozen stock 1600s
And then tweak your teener engine.

Its way cheaper to get a experienced person then to screw it up

Dude, Why so negative? You don't hate to see it, you hope it happens! that is why you are here, lurking for bad news.

You know nothing about me, about my background, my situation, or this engine. This is not my first rodeo. I have screwed up before and I will screw up again.

So take the advice of everyone's grandma and " if you don't have something nice to say, STF".

Here you are in the "garage" giving people advice to " pay someone else to do it" Well find that forum and go play big boy with them.

I am here to learn from the experts and the people that are willing to pass on their mistakes.

And I do thank THEM for chiming in, you?? not so much.

Guess this guy should stf up too .

Op. No class man

I've used both uni-sync and the snail (STE), I prefer the snail. That said I only used the uni-sync once back in the mid 90', didn't really like it, It didn't work on weber DCNF carbs, so I sold it in short order and bought a STE snail. For other cars the snail is more adaptable, mostly using simple plastic cups, that's how I do Solex Kadrons.

The cheap china snail is OK for the home shop use, but be careful with it, as it won't take the abuse of even semi-pro garage operation.

Although I do read his posts from time to time there's a reason I have one and only one member on ignore.

Do yourself a favor and get the german STE, especially if you are going to stick with carbs. It is the one tool you will use over and over again.

Perry's mini guide is a pretty good baseline.

Since we don't know the condition of these carbs it is very difficult to help diagnose the issue. If the jets are clogged you could experience some of the symptoms you have expressed. I have even seen the same rev drops on a single 34PICT-3 (Beetle carb)while trying to tune it. Pull the carbs off, take them apart and soak them in some carb cleaner. They sell a 1 gallon can that it can fit into. Buy some carb kits from aircooled.net or another well known site. Don't skimp on the rebuild kits, get a good kit.

Follow the setup guides to get the floats set properly in both carbs. Set the baselines and throw them on. You would be surprised how carbs just a little dirty can really make an engine run rough vs them being a little out of tune. Also, you can run an engine, and technically drive an engine without having the main stacks installed. Give it to much throttle and it will choke the engine as the mains will start to kick in. This is also a great way to test you have the correct idle jets installed.

Step #9 from my post (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter)

Unisyn restricts airflow and isn't worth the space in your toolbox. If you are going to have an engine with carbs, you need a STE. Can you make it work? Yes but everytime you put it one one of the barrels the engine will start to stumble, not so with the STE

Lots of great info from the 914 experts. I love reading about 914 stuff that has zero to do with my build. So much cool info and the level of help on this forum is top notch.

I got the snail version on the way. I just pulled the filter and it looks like the snail one will just fit better. The other type will require taking the filter base off too. and the jets are in the way. I assume those tall brass screws are the jets, right?

Also have some non-metallic plug wires coming. It seems that the flame thrower 3 module requires them.

Removing the carbs tonight and giving them a cleaning. I guess that will be a good time to set up the set screws.

I also found that one bushing on the hex bar is missing.Click to view attachment

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Any ideas on where to find the bushing. I found one for $5 but they want $15 more to ship it. Guess i better call them.

You might be able to combo ship with other things you might need like rebuild kits, jets, etc.

If not doing the soaking route, be sure to pick up a couple cans of brake cleaner. Remove everything that you can, especially the adjusters with rubber gaskets (the brakeclean likes to eat them) Shoot the cleaner into every port. You can even fill up the bowls and activate the squirter pump by hand to get the cleaner to flow through. I usually follow up with an air tool through the ports. Reassemble and set your baselines. Leave the linkage off until you are almost ready to drive. You will not need it for any tuning except ensuring the carbs are in sync off idle. This is where the snail will help as well. When you get to that point you can hold the idle slightly open at like 1500 -2000 rpm and check that both sides are drawing in the same amount of air. If they are even you know your carbs will be in sync while driving. Again this is the last step before taking it out. The only other adjustments will be with the jetting, but if you start with the base of the carbs (assuming Weber 40 IDF) You should be at:

Vents 28
Idle 50
Main 115
Air 180

Excellent clear description with practical application advice. This should be in the easy access library, especially for novices.

So with the linkage off, there is no choice but to use both hands to rev the engine? Or am i only dealing with idling here and no need to rev?

I was given one years ago and never thought it worked very well,as mentioned it didn't fit on some carbs I had.
I got the STE one and its great with my Zenith's,there is no restriction like the Motometer (Uni-syn ) that I had.
My experience with carbs has taught me to clean,inspect and overhaul if needed before fitting,last set of used Dellorto's I fitted were very clean and looked new on the outside however when cleaning I found dry hard gaskets and bad pump diaphrams,lots of crap in the fuel bowls and elsewhere too.
Also its better to do base line setting before running up and make sure you use new manifold and carb base gaskets.
Good luck to the OP.

No need for rev here unless you are setting the timing, which you will want the linkage hooked up. Once you get the smooth idle addressed then you can move into the linkage sync/higher rpms.

Wow. Never realized there were so many Uni-syn haters. I clearly missed the reference in the early post from @IronHillRestorations .

Honestly, I used mine for multiple carb types (down draft & side draft) without issue. The center post is adjustable and can be adjusted to minimize restriction but at the loss of venturi effect that determines where the indicator is in the sight glass. Since all measurements are relative, I tended to use mine with the indicator low in the sight tube to minimze the restriction to the carb.

But in the spirit of learning something from the tribe, I'll get a snail when I get back around to putting a set of Dell's on one of my next engines. Then I can try both back to back. Unfortunately for OP this is a year or so off for me.

Thanks for all the feedback though!

@malcom2

check the ff link to give you more idea

http://www.redlineweber.com/html/Tech/idf_...nt_controls.htm

https://www.carburetion.com/weber/adjust.htm


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Last week I test run my engine on my garage floor and a little rough idle. So I ended up rebuilding/cleaning them and lots of dirt inside (acquired the 36 IDF used along with the engine). I think it is pretty straight forward to clean this carb but I have no much idea with jet combinations. I just assumed the jets on it will be fine since this was a running engine with the current set up.


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What size engine are those on? @ndfrigi

220 Air
145 Main - this is a little rich for a 2.0
50/55 idles will be good, I can't tell which you have

For anyone interested in the tuning of carbs especially for a type 4 engine. I found this guy on youtube and while he is using knock off carbs (Weber IDF clones) his testing and methods on setting the floats, jetting, and setting up the carbs is pretty sound.

youtube channel -
Motor7710

My plans have changed. Would late Sunday afternoon work?

sorry @malcolm to get into your thread.
@nditiz1 thank you for your concern on my set up. I believed my engine is a 2056 based on my good friend who gave me this engine (one of our best member here) that he just acquired from someone. After adjusting the valves. I have 150 +/- 1 compressions now on cold engine.
I have 50 idle jet and145 main jet, maybe that is why the mix idle screw is way back out to add more air? (from set up before I dismantled it). Didn’t test run the engine yet after cleaning my carbs.

Not this week. Gonna head to Dauphin Island. Looking forward to it. Check in next time you come thru. I don't get west too often. Usually in a rush to work or play golf, etc..... But I will do the same.

I am back at it after a Fall Break with the wife.

The German Snail has arrived, but I seem to have a problem. The snout seems to be too long. It is sitting on the (not sure what it is called) cross bar in side the barrel thus it does not seal up. I am thinking of cutting it around the bar, or making it shorter? Or maybe find a large O-ring to set on the plate.

Thoughts?

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Do your carbs not have velocity stacks? You can use a piece of somewhat rigid tubing placed on the filter base to keep the Unisyn out of the carb throats. Illustrated on pages 30&31 of the CB manual. No need for the tubing with V stacks.

I know it is too late but back when I was riding motorcycles I used something like this to balance the carburetors on my Z1. It was nice because when you adjusted one carb it affected the others and you could see everything that was happening. You need a port to attach the gauges to each intake run so maybe that is why they aren't used on 914s.

https://www.motosport.com/product/?acctid=2...001&variant[MOP000W]=MOP000W-X001-Y001

@malcolm2
Look at the fittings on the STE in this ad:
https://www.cbperformance.com/product-p/6537.htm
Take that adapter off and see what is underneath. That adapter works well if you have velocity stacks on your carbs. You don't. Hence the problem. Not insurmountable, but... you may be able to home brew it depending on what's under the adapter you have or even with that adapter.

I have had a German STE for 20 years. Never needed anything else.

I have used Perry's ( @IronHillRestorations ) carb tuning guide many, many times over the years. I read it to refresh my memory every time I have to go in and do it again.

I think the biggest concern here is you don't want to spend too much time dickin around tuning and syncing carbs before you get that cam break in done. And I don't know how perfect it needs to be just to do a cam break in. I'll leave that to the experts. I'm just dangerous and headin for a meltdown.

Linkage bushing - Check your local hardware store's supplies of plastic bushings. You'll probably find something that works. It doesn't need to be perfect or exactly like the other at this point.

@malcolm2

Here you go. I knew there were more fittings available for the STE

https://www.carburetion.com/Products/Produc...spx?part=STE-SK

I love when a plan comes together..... Well almost.

Pulled and soaked and cleaned the carbs. Set the screws, removed the linkage, got new NON-metalic plug wires. BOOM. ran nice even before the carb balancing. Balanced the carbs with the linkage off... attempted to get the linkage right, but did not. Got close enough for the garage floor.

Once that was done, I checked the timing. Also pretty good. Let her run for 20 minutes at about 2000 rpm. Love the throaty carb sound....

I assume I am gonna need to adjust all the nuts, etc.... on the linkage. I got the turn buckles the same length and that was a big mess. Then just got it "good enough" for break in. Man it sounds really good.

Click to view attachmentClick to view attachment

Linkage is still wacky, but I got it DONE. 1.8 liter out of a 914, converted to a 2.0 liter, with Camper Special Heads, swivel foot adjusters, solid rocker spacers, chromoly push rods, 9550 cam, flamer thrower 3 module and coil, Stock exhaust, dished bus pistons, 7.4 CR for my VW BUS, borrowed weber 40s ( IIRC ) for break-in.

Some may remember my 1911 for my 914.... I screwed that up for sure. Miss-indexed the cam and the crank.... never started, had to crack it open and there is was. That one has 50,000 miles on it now.

Thanks to all that got me this far and thru that mess.

here is the finished product.


https://www.youtube.com/watch?v=bpr5DZUQ4pM


https://youtu.be/bpr5DZUQ4pM