I need some diagnostic help.

Car started missing at low rpm's only.

I thought that it could be a clogged idle jet or poor connection on one of my plug wires (it fits kinda loose).

Pulled all the idle jets and cleaned them up. Crimped the plug connection so it fits better.

No luck. Now it's even worse. Not a miss anymore but what feels like a dead cylinder at low rpm's.

It seems to clear up at higher rpm's but the motor just doesn't seem to pull as strong.

Ideas please...

Compression test

Wouldn't it be better to start with pulling plug wires to find out which cylinder isn't firing first?

I'm going to try that tomorrow, then I'll check all the plugs and see if one of the looks like it's fouling.

Well, I would have figured you tried that first

AFTER you find the one not working, test the wire on the dead cylinder with a fluke....they do die ya know. Could also be the BERU connector end....ya know....the rubber cap thingy that fits over the plug.

Could be as simple as a fouled plug....

Not yet.

Just took the daughter out for ice cream in it and now it's too dark.

Heh....I can locate the missing cylinder, pull the offending plug, gap and install the new one in 3-4 minutes.....did so in the staging lanes of the 2006 Parade AX while carrying on a conversation with Steve Wiener on my choice of heat ranges.

As you can tell, this is not an uncommon occurrence.

So????

Looks like it's gonna be tomorrow at lunch.

I ran off and left my high-voltage gloves at the office (i know I'm a wuss)...

Prolly next to yer "Man Card"....

"high-voltage gloves "

i don't care you ya are thats funny!!!!

What's the problem you have one more cylinder running than I have. LOL

No help sorry.

Smitty

On my 4 cylinder engine, I found the non-firing cylinder by running the engine a bit then touching the 4 exhaust pipes to find the cold or not-so-hot one. Takes out all the guess work of finding a dead cylinder.

Even though you've cleaned all of the idle jets you still can't rule it out. I've had times when one would repeatedly clog and another time where one had a very thin flake of something that would turn one way and open the flow and then turn another and allow the car to idle again. After you think that they're all clean and they're all installed you can loosen each jet holder, one by one, about 1/2-3/4 turn. If it stays the same or runs worse, that jet is clean. If it cleans up and idles well, that jet is clogged. It's a really quick way to check your work.

BTDT myself. Little flaky crap that kept reappearing and clogging a jet after it had just been cleaned.

You thought I was kidding?

Anyway, I have narrowed it down to the #2 cylinder.

Pulled that plug wire and the motor didn't change a bit. All the rest of them were firing well.

Before I did that I changed all the plug wires with new Magnecore's

I'm gonna swap the plug now and see if that helps.

Magnacores drove me crazy. They would not secure well to the plug tip. I went back to old style push-on over the threads bosch wiires.

If it smooths out at upper RPM's, it's probably your idle circut. Take that idle jet back out with the car running and tap your finger over the hole. I know it sounds kinda dorky, but your finger will create a little pressure/vac while you tap it. Doesn't always work. But often I have done that, put the jet back in and the car idles perfect again.

Well, that was a big waste of time.

Re-cleaned the idle jet for that cylinder and I even tried Dan's suggestion and it didn't help.

How can I tell if it's the idle circuit and not just the jet?

swap jets, swap plug wires, if you have another dizzy cap swap that too.

and i'm still at those gloves, just grab a rag if yer scaredyou have to provide a better ground than any thing else around, you'r not standing there bare foot or grabing the cold water pipe to you're house are you?

oh and don't touch the car with your other hand while pull'n the wire.

That's like wearing four rubbers during sex......how the Fuch can you get that in the engine bay?????

Nice gloves.

If you pull out an idle jet, your idle should change. That is one way to know it's clear. Most of the time it isn't the jet itself, but the little passages to and from it. Test a barrel, pull one out and your idle should change. Stumble or pick up, either doesnt matter, but change. Drastic, you could take a little carb cleaner with one of those little red straws and hose it down with a little pressure.

My carbs are so crappy right now (Car not driven enough either), I swear every other time I light it off one of the friggen idles is gummed up. Driving it around usually clears them up. Sometimes I'll get anoyed, pull over and do the finger thingy. It works, car smooths right out. I am running Zeniths though, that might be different than webbers?

I hooked up my timing light to verify that I'm geeting spark to that cylinder and it looked good.

When I pulled the idle jet out while it was running, nothing changed. Is that any type of indicator?

Yes, air is not passing through at all. If you pull your jet out, you have basically removed the metering of idle air and that cyl should either pick up the idle a little or make it stumble. Usually when I remove mine, the idle picks up as more air passes through than should. I know a circut is clogged when I remove a jet and nothing changes.

So how do you un-clog an idle circuit?

I don't know where on your carbs it is but on idf's there are air ports on the top of the carb with a sized brass
jet that feeds the idle circuit that usually get clogged also.

Is this something that is accessable if I remove the air filter assembly?

Should be....you'll have to take those gloves off though.....

BTW, they make some pretty neat insulated plug pliers that work well....

Okay, here's the problem carb. The arrow indicated the idle jet for the #2 cylinder.

I didn't see any place to access the circuit. Any ideas?

take the jet out and spray in the hole.
Also the big flat head screw head below is a plug, The transition ports. Spray in there too.

Did you pull the spark plug out and check it ?

Yep, pulled the plug and even replaced it.

Should I go ahead and do this to all three?

If it aint broke dont fix , I think is best here.
try get the one you know is bad working first.

I pulled the idle jet and the plug you mentioned.

I noticed that after a squirt or 2 into the idle jet port, carb cleaner shot out of the hole on top.

Pic.

Just so you feel not alone....from the 356 old phart list....

> I'm in my 22nd year of 356/912 ownership, and its seems to me that the
incidence of clogged idle jets is on the rise, at least based on my own small
sampling.
>
> Here in NH, ethanol fuel blends have been the norm since May 2006. Most of the
US now uses an ethanol fuel blend. Ethanol gives gasoline a different solvent
property, and has been known to mobilize years of accumulated crud in fuel
systems. It seems to me that since the switch, my car has had more frequent
"idle issues", usually related to clogged idle jets. This has occurred even with
regular changes of the fuel filter.
>
> Have others noticed a similar trend, especially the pro's who service many
cars?
>
> As an related aside, some years ago I took the advice of Alan Klingen at The
Stable, and started using an infrared thermometer gun to diagnose idle problems.
A clogged idle jet is easily detected by the relatively cold temperatures of the
exhaust pipe exiting that cylinder. It's way easier than messing with mixture
screws!
>
> ------------------------
> Eric Nichols
> Newfields, NH

I believe it should, I think that is where is sucks air from. Little different than my 40 idf's.

Success!!!

I guess I must of had something blocking the idle circuit. It took awhile, but after 5 or 6 attempts at dislodging whatever it was with a can of carb cleaner, the #2 cylinder is firing again.

Took it out yesterday to Buttonwillow and she seemed to run very nice.

Still got a small issue with an intermittent back fire out of the exhaust but nothing I'm going to worry about right now.

Just time to

Thanks for all the assistance...

good! if the problem becomes persistant i would suspect crap in the float chambers.

are the spring loaded screws on the bottom of the carbs the idle/air mixture screws? like on IDF series webers? if so, if turning one in and out fails to have any effect, suspect that venturi's idle jet/circuit. carry a little can of compressed air. the orange tube slips way into the idle jet housing hole. manually blowing out an idle jet gets old. blow air backwards thru the jet so you don't jam the bit-o-crap in further.

k

Allan,
Have you considered doing a four cylinder conversion on that thing?

This should fix it.....




Click to view attachment

Now that is just plain STUPID..........


He should have faced the carbs to the rear for better performance....



MFI means never having to clean out a clogged idle jet.

What in the hell is that? Are those SU's?

Yep... somewhere some MG driver is looking at a pair of 3 barrel webers and saying to himself "How in the Bloody Hell do I fit these up?"

Only running on 5 cylinders?!?!?!?!

I'd kill for my car to run on 5 cylinders!

There is a 2.4L six sitting on the garage floor........

I was basically running on five this weekend with my carbs the way they are and the 2.4l still felt stronger than my 2.0l 6. I didn't mind too much. I should take care of it soon though. Need to get better vacuum. I can't wait to see how strong this engine is without any problems.

Glad to hear you got it running smooth again.