The Cal-look Lounge

   I have a problem with my engine which is a 2276 and running IDAs.  I have an idle mixture screw (#1) that is unresponsive when trying to adjust the idle mixture.  I've done a bunch of trouble shooting and am at a loss for what could cause this.  I've changed the manifold base gasket and checked for vacuum leaks with an unlit propane torch.  No change of engine speed with the propane torch trick. With my SK synch tool (snail synchrometer) I noticed that the vacuum signal is a little higher in that barrel as well. I was thinking I have a twisted throttle shaft, but it checks out to be ok.  I'm stumped.... Any ideas without doing an engine teardown?  Thanks DS

Step one- swap the carbs from side to side and see if the problem follows.

Step one see if the cylinder picks up on the mains.

   OK I'll try that...  Thanks.

    benlawrence, how do you mean "see if it picks up on the mains"?

Rev it or drive it, if you can stutter around on 3 cylinders, mash the throttle , if it picks up onto 4 cylinders and runs hard it means you have an issue with fuel supply ( blocked idle jet ) on the idle circuit on one cylinder. If it doesnt pick up you either have an ignition issue, a combo of fuel and spark or worst case a mechanical issue.

Start with the basics, if the engine runs up on 4 clys when you mash it , you have a jet or mixture problem idle side, if it doesnt check the spark to the plug, if you have spark swap out or check the plug. A

   I got the offending carburetor reinstalled and synched up.  I checked each throat with my SK synchrometer and found that 2,3 and 4 are idling nicely at 6 on the scale.  #1 is idling at 7 on the scale.  The idle mixture screw is now functioning and I'm able to detect a difference in the idle speed when I screw it in or out.  I'm still a bit concerned about the #1 barrel being higher than the other three.  Right now the engine idles at about 1250 rpm. What are your thoughts regarding my idle speed?  Thanks

i think 1200 is a bit high on idle.

henk!!!

If I were you, I would adjust the valves. A tight exhaust valve can cause carb tuning issues.

    Adjusting the valves was one of the very first things I did in my troubleshooting quest.  I will go pop the valve cover and check again.  Thanks for the input.  I'm aching to drive this car.  It's been throwing be a curve ball since April.

every blue moon or so one of my idle jet holders will loosen up in carb and back out.

   Thanks Jim, I verified the idle jet holders are snug.  I swapped the carbs from side to side and the problem didn't seem to follow, but the carbs seem to be in balance on all four barrels now.  Could my engine just prefer a particular carb on a particular side of the engine??? 

maybe a rogue spark plug too. I've had it bite me.

   Thanks Jim, I have new plugs in it too.  I've been trouble shooting it for a few weeks now.  I'm close and think it may be a twisted throttle shaft or maybe the engine prefers a particular carb on one side rather than the other. I swapped the carbs from side to side and the imbalance seems to be less. Any other ideas are greatly welcomed.

That's odd for sure... I would expect the problem to either follow or stay, not be fixed...

  Tell me...  I'm gonna swap the carbs back to their original positions and see if I have anything different again.  While I have them off I'll see if there is a difference in clearances between the gaps of the throttle plates and carb body.  That will show if the throttle shaft is twisted or not.  Thanks

I'd say some sort of vaccuum leak, these engines are very sensitive to leaks.  Also, if your idle is too high, the distributor advance can start to come in, which further muddies the waters/confuses.

    I agree on the idle speed/ignition curve theory.    Let me ask if you use any kind of sealant on the manifold base gasket?  And what that sealant might be.....?

No sealant for me.  Just make sure everything is flat and seating correctly.  Also the manifold nuts have a tendency to back off from engine vibration, especially if you don't use lock nuts.  I use nylocs on all studs except #3 which is too tight to get a 13mm nyloc on.

   Ok, at one time I think I used hylomar.  I usually put a thin coat of bosch grease on the intake gaskets and tighten the manifolds down as tight as I can get them.   I use an 8mm wharpy washer under the nut. 

Grease isn't a bad idea to prevent the gasket from sticking and tearing.  Yes, use 8mm wave washer and nyloc nuts where you can. 

Thing is, when you swapped carbs side to side, did you lift them as manifolds/carb assemblies from engine or just unbolt the carbs and switch them? Reason I ask is that if you unbolted the manifolds and then swapped carbs, then bolted them back down, the chance of you having the same vacuum leak as before the manifolds were removed, is slim.

it's easy to see if that one throttle butterfly isn't closing. Remove carb and insert like a 0.008 feeler blade between butterfly and throat on one butterfly and adjust idle stop screw so the feeler just drags... then try it on the suspect barrel. Does it just fall through?

How much differently does the mixture screw in question react /not react? By more than 1/4 turn?

About 15 years ago I built a nice 90.5 x 84 for a for a friend's convertible, all new parts, almost all new. Carbs were his exisiting IDF Webers and we used his existing 009/Pertronix. Everything else was brand new, inspected etc. After the engine ran through its cam break in I went to set mixture and idle speed, but the engine was exhibiting a classic IDF "plugged idle jet" issue... limpy idle and non responsive mixture screw on #1. Everybody knows plugged jets are a part of life and a bitch with IDF's so I said a few choice curse words and removed car to clean it and move on. Installed carb and same issue, same screw. Checked for vacuum leaks. No luck. My friend Tony (I was working for him at the time) asked if I used a new cap and rotor. I hadn't. We threw a new Bosch 04033 rotor and magically the down cylinder came to life. Would have never guessed. Just FYI

  Thanks for the info Wignition.   I removed just the carbs.  I will now install another new intake gasket and go from there.  I was using a complete Mallory unilite, cdi and coil. I removed all that and installed a freshly rebuilt Bosch 010 that I got from Glen Ring for a different project.  I'm confident that the ignition system is now functioning correctly. I'm going to also try the feeler gauge trick.  I'm missing something and I'm sure it's a small detail.  With your suggestions It'll surface and this thing will be back on the road.  Thanks Doug S.

Hmmmm, on a stock bug engine, an unresponsive idle mixture screw means only one thing: the idle jet is too lean and you need a bigger jet. You have to drill out the jet.

    I put some compressed air to #1 cylinder and did not get any indication of air coming past the intake or exhaust valves.  I'll install a new intake gasket and go from there.  Still stumped....

   I swapped the carbs back to their original positions and I have the unresponsive idle mixture screw again...  Let me pose this question....  If I have a cylinder that has a bad ring seal that would mean less vacuum.  Therefore the fuel wouldn't be drawn from the idle passage....Correct?

   I did some redneck engineering and did a simple flow check on the offending carb.  I used some duct tape, shop vac and my SK flow tool.  I found that the barrel over #1 flowed 5.5 and the barrel over #2 flowed 3.5. Twisted throttle shaft...  Here's what I'm thinking is going on... There's not enough vacuum on the bottom side of the throttle plate of barrel #1 therefore more flow but not enough to pull fuel from the idle outlet orifice. This will cause a lean miss.  What fuel is getting into the cylinder is not being ignited bot going into the exhaust where it is then lighting off which is popping out the exhaust.   Sound like a logical theory???

My VW brother, I feel your pain... The best way for you to check your complete system is to do a Leak Down test with a leak down tester. This will be able to determine the percentage of ring and or valve wear. A very useful device and will perhaps save you a lot of further headaches.  Hope this helps in some way for you..?    Good Luck, Dyno Don

  Thanks Don... Point taken.

Dirt in the idle jet will do that.

I have to say it. Change that spark plug. So many times I chased my tail swapping jets and fixing what I thought were vacuum leaks and cleaning carbs and setting floats, only to have the same symptom persist.
Now yes, sometimes a driveability issue was carburetor related.
But just as many times it was an bad plug or some other ignition related fault.

You are creating more work for yourself by NOT swapping a plug.

I once fought my 48's for an entire day off from work (because I had to drive the car to work the next day). I had the problem carb off the car 3 times, thinking eventually I would find the issue. Nope. I finally realized I had swapped plug type for something I thought would work better, but they clouded over easily (no MSD in my car back in those days). I had a spare set of Denso resistor plugs in the cabinet for some Vanagon motor and since my heads then were 14mm long-reach... I decided I might as well try them.
Viola- I had 4 hard hitting cylinders.

Also, when I first got my Super Flow head/2276cc motor going in 1992, I had been playing with 48IDA for only about 18mo, so I was real green at making them work (at all). My boss offered to help me after work one night. We spent 90 minutes swapping jets and driving around, to no avail. Either it was too lean or it was pig rich and falling on its face. He suggested we remove the Bosch blue and 009 and drop in a locked Vertex. Instantly the motor woke up. The carbs were 1,000,000 easier to adjust mixture on. I, still to this day, have eyt to see anything done to my engines/tunes that had such a profound effect as his magneto had.

So don't overlook plugs/ignition. You may think they're OK.... but...

99% of carb problems are ignition. Say this to yourself over & over. ;D

   Thanks to both of you....   I know this is truly a carb issue.  I found a twisted throttle shaft.  YAY!!!  I'm finally a 1%er. I had a complete Mallory ignition system on the engine and there are some issues with it.  Therefore It was suggested that I remove the whole system and go with a basic blue coil and points distributor.  I installed a known good functioning Blue coil and a fresh 010.  It fires and runs great on this ignition set-up...  I could try every trick in the book to try to sync the carbs but the barrel over #1 was consistently showing more flow on my SK sync tool and I couldn't get the idle mixture screw to change the speed of the engine at idle.  My hypothesis is this:  The throttle plate over #1 was open just enough to lessen the vacuum under the throttle plate. Therefore less vacuum means the fuel cannot be drawn from the idle discharge orifice, hence no result from adjusting the idle mixture screw.  I will hopefully make more headway tomorrow after I do a compression check and see if I have any weak cylinders. Thanks again and keep your ideas coming while I dial this thing in.  Doug.

I actually do something similar as well. I have manifold to mount a single IDF or DRLA that has been modified so the runners are no longer individual, they are common plenum. On one side of the manifold I put a shop vacuum and block off the other side. With a flow meter I measure if the throttle shafts are bent and with some careful finesse I bend them back when needed. Works great! I have it on good authority that this is actually somewhat common practice but fancy shops don't use a shop vac, they use a flow bench.

    I did a compression check and found that I have a low cylinder.  #1 is at 95psi and the other three are consistent at 115psi.   Now what to do... I really don't want to pull the engine to have the cylinders honed and install new rings.  But I'll do what I have to in order to get this thing running tip top again.....   

You may want to do a leakdown test as well.

To test for leakdown, rotate the engine by hand until each cylinder approaches TDC. With the plugs installed you can hear the leakage past the rings into the case, or past the valves, or past the head to cylinder seal or a combo. Bug engines have plenty of leakdown normally, but if you have a leak you have a leak.

     After finding the compression to be low on one cylinder, I have chosen to remove and tear down the engine.  I will have the cylinders honed and install new rings. Hopefully this will also mend some of the high crankcase pressure problems I've also been experiencing.  I look to have it back on the road within a month and we'll go from there.  Thanks for all the advise   Doug S.

Check your heads for warping too. A leak-down test before tear down will help you find exactly where the compression is leaking from. Could be valves as well. A couple of my (high mileage) engines developed loose head stud nuts and warped heads were the problem.