Weber rebuild, junk found and reference to good thread
 

There is a great old thread from the engine building forum which really belongs here. I'm re-posting it here as it has been invaluable and relevant to more than just the EB forum:http://forums.pelicanparts.com/911-engine-rebuilding-forum/239742-71-t-still-backfires.html

This thread has some great information in it so I'm appending in hopes it helps others...


Check out the gunk I found in the bottom of the 4-6 bank carb. The forward bowl on the 1-3 bank was even worse, must have been 1/2 inch (10cm) of napalm in the bottom.



I also found water in the bottom of the 1-3 bank bowl. I think I needs to drain the tank...

I found all the bowls were set differently, with the forward 4-6 almost empty, and all the mixture screws were significantly different.



Idle air correction jets were all backed way out too.

Found I have the following installed;
2.7
Weber IDA40 3C
34 venturis
145 mains
185 air correction
Emusion tubes were stamped "F2?" The ? looks lightly-stamped and could be a 5, 6 or8.
60 idle jets

Cams are still unknown.

Muffler unknown but appears to be 2-in 1-out factory.
Heat exchangers are factory. I have a spare set of SSIs I am considering installing.

I had serious popping out the intakes before I decided to rebuild the carbs this morning. Lets see how the tuning adjustments go tomorrow.http://forums.pelicanparts.com/uploa...1189245180.jpg

Very helpful, thanks!

Well, I had a mostly successful morning.

It fired right up without complaint. I followed the instructions on that link above precisely and it all seemed to go well with a single exception and some puzzling outcomes...

Adjusted the air correction screws so all the cylinders are pulling 6.5 on the flowmeter.
Linkages are all equal.
No vacuum links.

I've got some funny symptoms though.

I couldnt get the mixture screws in #1 bank to get the idle to drop per step 7 of the instructions, when I notices the fuel pressure was up way too high, like 6#. So I adjusted the fuel pressure down to 3.5#. I was then able to get the idle to drop and come back up by adjusting each of cylinders #2-6 but #1 mixture adjustment screw adjustments still seems to have no effect. I cleaned it out very well so don't think there are any blockages.

Symptom #1 - It likes to idle up around 1200. backing off the throttle screws and it eventually idles down, very slowly, until it dies after about 1 minute. As it is dying #5 cylinder "coughs" and sometimes flames and then it dies. I backed out the #5 mixture screw 1/8th and that cured the #5 cylinder cough but it still dies.

Symptom #2 - I can rev it up freely and it sounds great. However it I throttle it up to 3000 and then let idle back down it dies quickly.

Symptom #3 - On a test drive it pops a lot and I need to keep the hand throttle on a tiny bit to keep it from dying when idling. It popps under anything less than gently acceleration.

Any hints much appreciated.

Any help please?

It sounds like you may need to clean them more thoroughly. Are your float levels spot-on?

Your internal parts sizes sound close to what is on my recommended Settings for Weber carb sheet, but the specs change depending on what 2.7 you have.

Examples

2.7 E,S
main venturi: 34
Main: 145 Air: 180
Idle: 60
Emulsion Tube: F-3

2.7 CIS
main V: 32
Main: 135
Air: 180
Idle: 55
Emulsion Tube: F26
Hope this helps.

just my 40 settings


34 vents

55 idles at 2 1/2 turns [a little rich]

135 mains [140's are noticeably rich]

10 deg initial & 35 total ignition

NGK BPR5ES


combustion power measured finely w/ digital EGT numerical and bar graph

i kept the richness till i cruised 5k, +- 200 rpm, in 5th for 30 miles in N Nevada at 85deg ambient for a real check out last May. Plenty of room to lean without burning valves or pistons.

Thanks guys. Here's another link to the best 40IDA3C diagram I've seen. Some of the scans posted are a bit blurry... http://www.racetep.com/weber/40IDA_46IDA.pdf

Here's a good page with lots of Weber tuning info... http://www.racetep.com/webtechpage.html

John, yes, my floats are exactly on...the meniscus is between the two upper lines on the float tool.

I was sure I had cleaned them immaculately. Wouldnt a blockage in the idle circuit make it even more lean? That #1 cylinder is definately firing, I just can't get it to lean off enough to make it stumble.

Your first example is almost exactly what I have. I assembled an Excel spreadsheet of your, Ronin and other's settings before tearing into mine. I am about to place a Pelican order and would liek to include alternative jets/tubes in that order since getting parts over here takes so long, if you can even find them.

Hi Ronin,
Your idle jets a 5 smaller than mine, perhaps that is the difference? Same plugs, venturis and ignition settings (mine is MSD/Blaster 2 coil)



Any ideas why it would idle fine, then when revved to 3000 and let off it dies?

note that my 8.5 compression wil develop less hp than a 10:1 and demand less fuel. 8.5 can also run more ignition advance.



also sometimes another crazy issue is dirty or clogged air jets and the passages. But you were able to adjust them so i guess they're clean?


"Your idle jets a 5 smaller than mine,"
--------- my 55s at 2 1/2 turns will load new plugs during city driving only in a few hundred miles.


and if it was mine I might warm it up with a 10 mile drive, return to home and simulate the 3,000 rev and die situation.. Then increase idle ignition timing to 5, then 10deg and only rev to 3,000 again and see if it still dies.
I guess you're only running mechanical advance w/ vacuum pot disconnected?


keep cleaning plugs, especially way down inside plug where porcelain meets the plug housing.


all the best on this dying problem

THanks, yes I am running mechanical advance, 8 initial to 34 deg at 3500.
I'll check the plugs and compression too.
Those passages should all be clean, I really got in there with the fluids and air. Everything was coming out clean.

i'm not a pro so another wild guess is closed throttle plate position. It's a fine position related to progression holes etc. I just read about it in the Pat Braden "Weber Tech Manual"


I guess if you look into the throats at 3,000 you don't see any gas drops falling on the plates? Use a mirror or use safety glasses. Lucky I wear glasses when I was eye balling a rochester carb years ago and it popped.. A few toasted eye brow hairs and a slammed head when i jerked back and hit my head on the boat engine cover.

you replaced the fuel filter, right?

I have some popping on my 2.2T w/ webbers. I did the monthly clean the idle jet routine yesterday, and I noticed that the little rubber o-rings get shaved a bit when installing the idle jets. In my case, I bet I have a bit of rubber from the o-rings in the idle circuit somewhere.

I had popping on the 4k rpm transition. Now, I have a bit of stuttering below 3k rpm. ARGH!!!!

YMMV

I havent cleaned the filter, which is a Canton Mecca 1-micron unit. I know dirt is usually the first culprit but in this case there was no debris in the bowls or circuits, just the jellied gas which was thoroughly cleaned.

I've got some 57 idle jets on the way to try and lean it out a tiny bit. I was needing to screw in the other 5 cylinders' mixture screws to almost .5-.75 turns out from the stops to get the idle to drop.

Although those may not work either since I interpreted the popping I get at anything above idle would be a lean condition.

I checked for vacuum leaks at all the throttle shafts and manifolds, no change when carb cleaner shot at them.

Pitargue, I also noticed when I changed out the orings the old ones "crumbled" so I'm not surprised if slivers or chunks fall off those buggers.

Glad to see that someone still appreciates my instructions on how to set up Webers.

Yes, thanks John.

Another helpful item from the Tomlinson book is the "if this is your symptom, do this procedure" section. More of those symptom-procedures would be helpful...

John's write up is great.