Weber 40 IDS problem

John Rogers · 01-21-2004, 07:48 AM

I have Weber 40 IDS carbs on my 2.2l race engine and they were just rebuilt. Now the hi speed enrichment circuit is not working since at full throttle the mixture goes very lean on the a/f meter. I have chacked with Weber USA and others and they say the rebuild kits for the IDA and IDS are the same. Fuel pressure is 4#, flow is 1 pt in 15 secs and filters are clean. Any ideas?

jpnovak · 01-21-2004, 07:58 AM

I assume they were not running lean before the rebuild. DIY rebuild or shop?

Is the lean condition gradual or sudden. What rpm does it onset. How lean does it go? Could be too small main jets.

My guess would be a plugged passage. I would take off the air cleaners, carb top and unscrew the high speed tubes. Use an air compressor to blow through them. It could be that the cleaning procedure moved dirt/crud from one area to another. Reassemble. See if that helps out.

RPMClassic · 01-21-2004, 08:14 AM

You might have a an air leak at the manifold spacers....

john walker's workshop · 09:32 AM

Put in smaller air correctors and see if that helps. The smaller you go, (within reason), the more fuel from the main jet at higher RPMs. they're like a hole in the side of a drinking straw. the bigger the hole, the vacuum pulls less fuel and more air.

John Rogers · 01-21-2004, 10:51 AM

The mixture was dead on before the rebuild. Done by a shop and they have not seen many IDS model carbs. They (and I) have checked with other shops, Weber USA, etc and they have said there is something different about the circuits compared to the IDA but can't remember what? The lean comes when going to full throttle, say from 4000 RPM and comes on fast after a slight delay from the gas pumped in from the accel pump. The candy canes are all in place and are open. I did check the spacers and gaskets with spraying cleaner and nothing changed. Also checked the tall secondary venturis and they are in correctly.

RPMClassic · 01-21-2004, 11:04 AM

How many miles on the rebuild. Did you retorque the head bolts after the break in period ( 700-800 miles?). Can you see any carbon streak or leak underneath the engine where the cylinder and cam housing meet? Sounds like the carbs are reacting to something else that is going on. How do the plugs read? All the same, or is one cylinder different then the others. Check #4, as for some reason that can be a source of problems on some motors.

RoninLB · 01-21-2004, 11:07 AM

Quote:

Originally posted by john rogers
there is something different about the circuits compared to the IDA but can't remember what?

yep.. it's never mentioned anywhere that I know of. The machined part is actually expensive to replace.

John Rogers · 01-21-2004, 11:14 AM

The engine has three vintage race weekends on it. No leaks or signs of weaping anywhere on the engine. The carbs were loading up badly on the race I did in Tijuana since there was a 1st gear U-turn at each end of the course. So we figured a rebuild was a good idea? The plugs all look the same, good color and no signs of lean running as we don't rev it more than a couple of seconds since the a/f meter responds quickly. We also checked the MSD box and MSD coil and they are working okay with a SUN test machine. What is machined different on the IDS carbs, if anyone knows?

J P Stein · 01-21-2004, 11:37 AM

As I read this, the variable seems to be the rebuild. I would recheck the float levels. I can't bring myself to have the motor running while that sight glass gauge is attached, but you may have no option.

I seem to recall....yes.

There is a pic of the IDS enrichment circuit in BA's book, pg 82.
The feed is into the top of the secondary venturi. Tall secondaries
would seem to be a problem....the feed would not reach the top of them or, if extended, there may not be enough vacuum to draw the fuel that high. ....one could drill holes in the side of them
and feed the "pipe thru....maybe. Were the tall secondaries there before the rebuild?

John Rogers · 01-21-2004, 11:48 AM

Thanks for the help so far. The float levels are at the bottom line of the PMO gauge. The tall secondaries were on before the rebuild. I have found out there is possibly a check valve under each "candy cane" and I am wondering if it can go in wrong? I do happen to have that book at home so I can check later.

Frostie · 01-21-2004, 02:48 PM

Just curious John…what type of Air/Fuel meter are you using? I was always under the assumption that those Auto Meter A/F gauges are just not accurate enough for good feedback?

John Rogers · 01-22-2004, 05:52 AM

The meter is from CB Performance and I use a generic 3 wire O2 sensor. Response is pretty fast as we have tested it against a 5 gas smog machine and it responds just about as quick as the big tester. I put the meter in since I worry a little about going too lean a full throttle, which is what is happening now??!!

911pcars · 01-22-2004, 09:36 AM

May be a rebuild issue. The IDA/ITP versions don't have a high speed enrichment circuit and they don't necessarily lean out at high speed. Your carbs are probably jetted for this enrichment circuit and for some reason this circuit is not "turning on" after the rebuild, thus the high speed leanness. Some suggest this enrichment circuit is not needed and are thus blocked off; and instead use the appropriately sized mains and air correction jets.

I would suggest inspecting the enrichment circuit again; also set the float level to the top of the two lines. What jetting are you using BTW?

Sherwood

john walker's workshop · 01-22-2004, 09:46 AM

did you try my suggestion about going down one size on the air correctors yet? it does work.

RoninLB · 01-22-2004, 01:41 PM

Quote:

Originally posted by john rogers
What is machined different on the IDS carbs, if anyone knows?

OK. I brought up the issue only for general IDS info. because,
I sold my IDS and,
I was hanging out with this ME who cast and machined a complete running engine for his disertation in the 50s. Now he does custom machine work on webers, etc. Anyway we were at the Parts Obsolete Camp Out for a few days together. A wonderful guy to hang with. and he starts explaining the IDS specific machining that costs big bucks to replicate.. and he said this piece puts a prem on the IDS. I don't remember.

He'll answer any questions.. and you could report back here, huh

911pcars · 01-22-2004, 04:00 PM

Ron,
Harry Bieker had his machine shop in Burbank, CA until he "retired" some years ago. I guess he's still at it. He did a lot of the machine work on my engine. He knows his stuff.

Sherwood

RoninLB · 01-22-2004, 04:15 PM

Quote:

Originally posted by 911pcars
Ron,
Harry Bieker had his machine shop in Burbank, CA until he "retired" some years ago. I guess he's still at it. He did a lot of the machine work on my engine. He knows his stuff.

he sure does.. he's a regular every year at the Camp Out. He has a gigantic following in the 356 world.

69 Soft Targa · 69 Soft Targa's Garage

From follow up thread... posted to finish the thread for the archives.

per "john rogers"

Weber 40IDS Problem Solved

If you remember the earlier post about the hi speed lean problem with my Weber carbs, well it has been solved. The small tab on three of the floats had depressions from the old needle valves wearing on them and when new needle valves were put in, this caused the floats to stick low so fuel level was way too far down. The shop rounded up 4 level gauges and watched the fuel level and it would drop some and then stay down. Putting in 3 new floats cured the problem and now the hi speed enrichment circuit gets enough gas! The wear marks can be seen if you look very carefully at the float tabs.