2.2e pistons and cams on a 2.7 case with webers. need weber help

[marlinaness]

not sure which forum to post to, but his one has 10 times the numbers of the rebuild forum

I have a 2.7 case with 2.2E pistons and cams, giving me about 9.5 compression 2.4 E engine. It has headers, M&K muffler, and O2 bungs on each header so I can take AFR readings with an LM2.

I started with the info below based on a similar build I did in the 90s with Webers and the following:

F.S. 911 weber 40 IDA's
Pelican Parts Technical BBS - Powered by vBulletin

The engine was rebuilt with new piston rings etc, so I did this during the 20 min breakin meaning I ran at higher RPMs and did not check the idle, didn't really check the balance except side to side, used the LM2 to see how they were doing.

32 venturies
135 main jet
55 idle jet
180 air correction
F26 emulsion tubes

The AFR was lean around 16-18 at 3k-4k. There was a lot of backfiring out the carbs, popping, etc. This did not make sense based on all the previous documentation I had read. Nevertheless, I changed to

32 145 55 180 F26 and was still around 15 or so on the AFR from 3k-4k

I had spare 30s, I didn't have bigger main jets, so to reduce the lean condition, I naivelly changed to

30 145 55 180 F26. AFR was 13-15, most popping and snapping gone but then briefly took the engine down to idle and it was 16-18 AFR, way too lean and would not run at idle. This only lasted a few seconds.

I then tried
30 145 60 180 F26.

this was improved, but still too lean at idle and the engine died.

I know I have to get the idle fixed and have to get rid of the lean condition to get the air flow, balancing and idling correct. What do you recommend to fix the idle lean condition: increasing idle jet and by how much or reducing the air correction and by how much or both? I also have read F3s are better than F26. Should I go back to 32s and try 70s or 80s and reduce to 170s, and try F3s? I do have 170s and F3s I could use, but nothing larger on the idle jets. I will have to order.

I need to get this thing idling first before I can do much else.

Recommendations?

[1QuickS]

Jetting with 32mm main venturis sounds good; the F26s are typically replaced by F3s but these affect main circuit.

Did the Webers come from a running engine before the rebuild? If not then there may be fuel delivery issues in the galleries.

Have you tried disconnecting the drop links from the throttle lever arms during idling? I recommend this to eliminate side-to-side linkage adjustment errors during idle setting. You might like to review the idle setting using this procedure as a guide: Weber Carbs Technical

Within the Procedure is a method to "blueprint" your throttle linkage and crossbar which may be a source of idle setting ills.

[marlinaness]

Paul
these webers were on a 2.7 and it ran ok. I made several changes including going from 34 to 32. Idle readings are baffling. I am going to change to F3s and try smaller air correction jets when I return from traveling. May also try larger idle jet just to keep it running. All of the changes I made had a material change to the AFR, just could spend too much time at idle because it was so lean and died.

I couldn't do too much playing around this weekend because I was trying to break in the engine and was keeping the revs around 3k for the 20 mins. Next weekend will try again with new oil. Won't have the new distributor for a few weeks, but should be ok around idle.

I have used you website in the past. Brilliant material and it has never failed me. Will review again for next weekend.

thanks
regards
Marlin

[marlinaness]

Paul,
one source of problem might be the idle jet holders. I am using the thicker headed ones, but did not use o-rings. How would I know which body type uses the thick holder vs the thin one. I have Italian IDA3Cs. Should I use o-rings with the thick one, or should I use the thin headed one without o-rings. I have both.

I assumed the thick one did not need an o-ring because it went deeper into the hole.

recommendations?
thanks
marlin

[1QuickS]

Hi Marlin,

The earliest Webers did not use o-rings on the idle jet holders. The later ones (starting in 1968) used them and the heads of the holders became longer. This means the throttle bodies designed for use with the o-ring'd jet holders allowed the head of the holder to fit into the throttle body a little bit. If you use late style holders (thick heads for o-rings) on an early body then the idle jets will not seat and you will have VERY RICH idle issues. You can use early style holders on all Weber throttle bodies without issues.

I post a picture of the two types of idle jet holders on my web page: Weber Carbs Technical. Look at the image just past that of the air horns to see the two different types of idle jet holders.

Check to see that the 1.0mm diameter hole for the mixture screw isn't blocked. The tip of the mixture screw can get stuck and twist off in the hole.

I recommend getting a Colortune tool for diagnosing idle issues; tedious but very direct and you can isolate the issue in each cylinder to spark vs. mixture fault. I offer "Tips" on using the Colortune on my Technical web page which I linked in Post #2 above.

Do you have a STE Synchrometer? Readings above 5.0 indicate a rich idle. Larger STE readings suggest the larger throttle opening required to supply sufficient air to burn the rich fuel mixture. If throttle cross bar is connected to both carbs and one carb may be opened up then the other closed down from a balanced running condition. Remember that AFR readings are averaged for all exhaust gas the sensor "sees". So, it is possible you have an averaged AFR reading that masks a side-to-side imbalance issue.

Obviously, double check that each idle jet is clear from crud blocking the tip. Also, be sure your gaskets are in good shape and that there are no open air taps on the flanges of the carbs.

If your carbs have the "folded spring" shaft coupling between throats 2 & 3 and throats 5 & 6 as opposed to the later, cylindrical coupling then there is the real possibility of the short throttle shaft becoming bumped out of it's correct rotational relationship with the long shaft. Your STE will ferret this issue out as an air flow imbalance that cannot be adjusted with the idle air screws.

Another thought: During cleaning of the carbs a lead plug may have fallen out of the fuel delivery gallery that feeds the idle jet. If this plug fell out then there would not be sufficient vacuum at idle to draw fuel up from the fuel bowl to feed the idle jet. This lead plug is located just inboard of the idle air bleed jet (little brass plug with a small hole in it) which is on the top of the main throttle body just inboard of where the idle jet holder is located.

[marlinaness]

great info.

so, no late idle holders for the old throttle bodies (even with o-ring) and add the o-ring for the late idle holder on the late throttle body. This is clearly something that needs fixing.

I do have 2 STEs, I also have O2 bungs on all six exhaust headers so I can check AFR on each cylinder. both left and right (3 and 6) were consistent 3k to 5k, too lean at idle.

Carbs have cylindrical coupling, also the lead plugs are still in place, but will check again.

I will check everything you suggested and will post results.

thanks
Marlin