Need Carb Jet Guidance, Weber 40 IDFs Options

[bbrock]

Plans to Megasquirt my car got delayed over the winter so my Webers will stay on for another summer. So, I finally hooked up my wideband to see if any adjustments are needed to keep the engine happy and safe until I can do the conversion.

The only real "problem" area is idle and low speed driving on the progression circuit where it is running too rich. It idles smooth and steady at 700 rpm with AFR of 12.3. That with idle mix screws ~ 2 turns off their seats. That's the leanest I can adjust and keep the engine happy. Just off idle at 20-40 mph @3000 rpm it goes even more rich to around 11.0 +/- 0.5. I don't think that's alarmingly rich but wasteful and I do get a bit of annoying surging/bucking driving below 30 mph.

Current jetting is as follows:

Venturi - 28
Emulsion tubes - F11
Main jet - 115
Correction Jet - 200
Idle jet - 50

I'm thinking I should reduce the idle jet but not sure by how much. I can get .047, .045, or .040. Any suggestions?

I could also use some advice on mains and/or air correction jets. If I didn't plan to swap the carbs to FI, I'd try for a little leaner highway cruising mix for better economy and maybe flexibility. In limited testing running in good ranges for performance at the expense of economy - WOT ~12.5, Highway cruise ~13.5 but rarely goes above 14.0 even on downhill and decel. Weather is crappy here this weekend so I've only done a short drive in hilly conditions. I need to get it down in the valley for some long level runs to see where it settles. I think I can live with the numbers I'm seeing now, but do wonder what it will do when I attempt to cross a 10,000 ft. pass. I'd rather it not die of oxygen starvation if I attempt it. Any thoughts?

BTW, I live at 6,000 ft. elevation so I'm not surprised it is running on the rich side with out of the box jetting.

[bbrock]

Well I think I can finally declare victory. There has been a lot of fiddling since the last post and what's more fun that endless fiddling farting with carbs? [sarcasm dial set to 11].

First thing was to take Jake's advice and try the 50 idle jets with more advance. Adjusting to about 34 degrees total advance did wake up the engine and lean the AFR numbers a little. It was still running rich but I decided to call it good enough and run with it for the summer.

I had a 600 mile work trip to the Blackfeet Nation a couple weeks ago so decided to take the 914 on its first long trip since the restoration. It ran like a dream on the way up and was a blast to drive. I calculated the mileage and I got 28 mpg on a tank that included 50 miles of start/stop town driving and short stretches of highway that were more foot down acceleration than cruising. I thought that was pretty good. However, about 150 miles from home on the return trip, I started to notice a stutter and the tach would jump. It got worse the closer I got to home and I was pretty sure the plugs were fouling again.

I pulled the #1 and #2 plugs and sure enough. There was a carbon track forming on one side of #1 and deposits forming on #2. I decided to order a set of 47 idle jets rather than risk having to replace plugs every thousand miles. This morning I dialed in the new idle jets with new plugs. I noticed the #1 idle screw wasn't as responsive as the rest but I was still able to find best lean idle. The AFR at idle was about 11.3 which still seemed rich but I took it for a drive. I was very happy to see low speed (20-30 mph) numbers in the mid 12s to low 13s on the way out. I was really happy until I got it up to speed on the main circuit and it went way rich (10s and 11s) at 70 mph. Then on the way back home, it stayed rich even on the idle circuit. Something was definitely amiss.

Thinking of the unresponsive mixture screw, I decided to pull that carb to recheck floats, make sure it was free of blockages, etc. I found the o-ring was pinched on the #1 idle jet. Mystery apparently solved but I went through the whole carb anyway after replacing the O-ring. I also decided to switch the AC jets back to the original 2.0s to see if that leaned the main circuit. It didn't make much sense to me but I've given up on understanding all the possible combinations of how these carb changes affect AFR.

After re-dialing the carbs the AFR was still around 11.3 at idle, but as soon as it was under light load, it leaned out to mid 12s to low 13s. Drove around on the idle circuit for quite awhile and it stayed consistent. Taking it up to speed was very satisfying. Cruising at 60 mph is low to mid 12s and cruising at 70-80 mph is mid 12s to mid 13s. I like those numbers! There was some stumble on transition between circuits, but a bit of fiddling with the accelerator pump adjustment smoothed those out. I really appreciated how being able to read AFR during acceleration helped to dial those in. I think I could get it even better, but I'm pretty happy with where it is.

So glad to have this finally done. Monday I have to head back to Blackfeet Nation so will be repeating the trip for a good shake down. Here is my final setup:

Altitude: 6,000 ft.

Venturi - 28
Emulsion tubes - F11
Main jet - 115
Correction Jet - 200
Idle jet - 47

[930cabman]

Well I think I can finally declare victory. There has been a lot of fiddling since the last post and what's more fun that endless fiddling farting with carbs? [sarcasm dial set to 11].

First thing was to take Jake's advice and try the 50 idle jets with more advance. Adjusting to about 34 degrees total advance did wake up the engine and lean the AFR numbers a little. It was still running rich but I decided to call it good enough and run with it for the summer.

I had a 600 mile work trip to the Blackfeet Nation a couple weeks ago so decided to take the 914 on its first long trip since the restoration. It ran like a dream on the way up and was a blast to drive. I calculated the mileage and I got 28 mpg on a tank that included 50 miles of start/stop town driving and short stretches of highway that were more foot down acceleration than cruising. I thought that was pretty good. However, about 150 miles from home on the return trip, I started to notice a stutter and the tach would jump. It got worse the closer I got to home and I was pretty sure the plugs were fouling again.

I pulled the #1 and #2 plugs and sure enough. There was a carbon track forming on one side of #1 and deposits forming on #2. I decided to order a set of 47 idle jets rather than risk having to replace plugs every thousand miles. This morning I dialed in the new idle jets with new plugs. I noticed the #1 idle screw wasn't as responsive as the rest but I was still able to find best lean idle. The AFR at idle was about 11.3 which still seemed rich but I took it for a drive. I was very happy to see low speed (20-30 mph) numbers in the mid 12s to low 13s on the way out. I was really happy until I got it up to speed on the main circuit and it went way rich (10s and 11s) at 70 mph. Then on the way back home, it stayed rich even on the idle circuit. Something was definitely amiss.

Thinking of the unresponsive mixture screw, I decided to pull that carb to recheck floats, make sure it was free of blockages, etc. I found the o-ring was pinched on the #1 idle jet. Mystery apparently solved but I went through the whole carb anyway after replacing the O-ring. I also decided to switch the AC jets back to the original 2.0s to see if that leaned the main circuit. It didn't make much sense to me but I've given up on understanding all the possible combinations of how these carb changes affect AFR.

After re-dialing the carbs the AFR was still around 11.3 at idle, but as soon as it was under light load, it leaned out to mid 12s to low 13s. Drove around on the idle circuit for quite awhile and it stayed consistent. Taking it up to speed was very satisfying. Cruising at 60 mph is low to mid 12s and cruising at 70-80 mph is mid 12s to mid 13s. I like those numbers! There was some stumble on transition between circuits, but a bit of fiddling with the accelerator pump adjustment smoothed those out. I really appreciated how being able to read AFR during acceleration helped to dial those in. I think I could get it even better, but I'm pretty happy with where it is.

So glad to have this finally done. Monday I have to head back to Blackfeet Nation so will be repeating the trip for a good shake down. Here is my final setup:

Altitude: 6,000 ft.

Venturi - 28
Emulsion tubes - F11
Main jet - 115
Correction Jet - 200
Idle jet - 47

I was unaware of an idle jet 47? (correction, Pierce has them in 1/2 sizes) either way victories are always good. Would it be safe to say the Webers will stay and the $$ you save will go into another project?

[bbrock]

I was unaware of an idle jet 47? (correction, Pierce has them in 1/2 sizes) either way victories are always good. Would it be safe to say the Webers will stay and the $$ you save will go into another project?

Nope. Drove the 914 almost 500 miles today over several high mountain passes (it choked). Carbs are running better and I got great mileage, but are still nothing like a good FI. The carbs and the 1950s era ignition have to go. There is no way I could trust this car on a long trip, and no, 500 miles is not a long trip.