Tuning 40 DCOE Weber 151 on an L24

[LeonV]

BTW,

I played with the Z a bit last weekend. Switched the hypojets from H223 to H221, meaning the smallest air bleed hole. H22 denotes a .022" orifice, the third number is air bleed size with 1 being smallest and 4 largest. A smaller air bleed enriches idle while leaning transition. You can look at the hypojet as a "teeter-totter", which balances out idle and transition mixtures. It's an awesome tuning feature of the hypojet, essentially making 1 idle jet into 4 (e.g. 50F8, 50F9, etc).

Therefore, moving to the smallest air bleed enriched my idle while simultaneously leaning out transition/cruise. The Z ran even better! Idle was rock solid at ~14.5:1 at about 1 1/4 turns of the mixture screw and cruise mixtures were leaner, in the 13:1 range. Testing was done on a relatively cool day so I'd like to lean out cruise mixtures further. Keith recommended blocking off a hole in the e-tube to see if cruise mixtures get leaner (part-throttle AFR is controlled by a combination of the idle jet and e-tube), although it may have an adverse effect on transition. If this experiment doesn't give good results, going to a smaller hypojet should do the trick.

The only real issues I still have are my carbs not always going back to idle (mechanical issue), hesitation when suddenly jumping on the pedal at low rpm, and going too rich at WOT. New internal throttle return springs and 110 mains are on order from Pierce Manifolds which should help the throttle return and going rich issues. I'm working with Keith to solve the sudden WOT hesitation and will be putting in stiffer accel pump springs as soon as he gets them in. That should strengthen the pump shot. I checked and have size 40 pump jets, but did not check bleed back. Keith believes that the springs will have a bigger effect than changing either the pump jet or bleed back jet.

One other benefit I noticed last weekend, the car starts much easier when it's warm. I no longer have to crack the pedal to start it. Cold starts require pumping since I don't have my cold-start units connected, which I never needed before since I was running so rich.

[steve91tt]

He did. 'Adequate' to paraphrase. You don't have a problem if you aren't starving.

Agreed, when I was running the RX7 pump in my Mikuni powered L30 track car I did not see any adverse effects of the undersized pump other than very low fuel pressure until I changed to 37mm chokes. When I moved up to the bigger chokes I started going lean at WOT near red line in 4th so I switched to a bigger pump and solved the problem. I can see no downside to the occasional 0psi reading on the fuel pressure gauge as long as AFR's don't go lean. If fuel supply is an issue the lean spot will generally occur after long periods of sustained WOT operation I don't see this being an issue with a street car unless the fuel system is badly undersized. Just my $0.02.

[LeonV]

BTW,

I played with the Z a bit last weekend. Switched the hypojets from H223 to H221, meaning the smallest air bleed hole. H22 denotes a .022" orifice, the third number is air bleed size with 1 being smallest and 4 largest. A smaller air bleed enriches idle while leaning transition. You can look at the hypojet as a "teeter-totter", which balances out idle and transition mixtures. It's an awesome tuning feature of the hypojet, essentially making 1 idle jet into 4 (e.g. 50F8, 50F9, etc).

Therefore, moving to the smallest air bleed enriched my idle while simultaneously leaning out transition/cruise. The Z ran even better! Idle was rock solid at ~14.5:1 at about 1 1/4 turns of the mixture screw and cruise mixtures were leaner, in the 13:1 range. Testing was done on a relatively cool day so I'd like to lean out cruise mixtures further. Keith recommended blocking off a hole in the e-tube to see if cruise mixtures get leaner (part-throttle AFR is controlled by a combination of the idle jet and e-tube), although it may have an adverse effect on transition. If this experiment doesn't give good results, going to a smaller hypojet should do the trick.

The only real issues I still have are my carbs not always going back to idle (mechanical issue), hesitation when suddenly jumping on the pedal at low rpm, and going too rich at WOT. New internal throttle return springs and 110 mains are on order from Pierce Manifolds which should help the throttle return and going rich issues. I'm working with Keith to solve the sudden WOT hesitation and will be putting in stiffer accel pump springs as soon as he gets them in. That should strengthen the pump shot. I checked and have size 40 pump jets, but did not check bleed back. Keith believes that the springs will have a bigger effect than changing either the pump jet or bleed back jet.

One other benefit I noticed last weekend, the car starts much easier when it's warm. I no longer have to crack the pedal to start it. Cold starts require pumping since I don't have my cold-start units connected, which I never needed before since I was running so rich.

Tried 110 mains today and they're way too lean. Car doesn't want to accelerate at WOT and AFR reads 15-17. Ordering 120 mains today, those should be close to what I need. Haven't put in the new return springs or pump springs since Keith accidentally sent 2 springs instead of 3. Silly Lotus guys!

[240260280z]

I just ordered some 115's for an L24 that had 125's and ran rich. The owner now has 120's that Stephen loaned me and just reported it ran better and less exhaust smell so The 120's will prbably be great for your L24 Leon.

The car is ~400km from me and my O2 sensor so I'll measure the 120 A/F in the spring and also run the 115's and plot.

Please measure A/F with the 120s between 3k and 6k

[Zedyone_kenobi]

Just a note no fuel pressure, I have found the holy grail of fuel pumps for high volume good preset pressure and dead quiet.

THe RX7 pump was great, but I was only getting 2 psi out of it at anytime. I was having issues in 3rd and 4th gear as my air fuel ratios were raising under sustained load. Not sure if it was the pump or not, but I upgraded to this little jewel.

It is a Mallory 4070LP electric fuel pump. It is preset to put out between 3 and 4 psi without the need for regulation. I fired mine up and sure enough, I could not even barely hear it. I leaned over to the engine and it was dead on 3 psi. This pump has a bypass screen that allows you to up the pressure further if you need to. But I think I will be just dandy at 3 psia. It was the last thing I wanted to do before my rally. I am bringing the RX7 pump as a back up.

I think I am currently running 130 mains in my L28. I still need to do some data logging. Or get a reliable copilot to pay attention while I drive. The roads around here are not conducive to high rpm 3rd and 4th gear runs.

[conedodger]

Tried 110 mains today and they're way too lean. Car doesn't want to accelerate at WOT and AFR reads 15-17. Ordering 120 mains today, those should be close to what I need. Haven't put in the new return springs or pump springs since Keith accidentally sent 2 springs instead of 3. Silly Lotus guys!

Leon,

It just so happens that I have two pump springs and two carbs worth of O5 tubes. Maybe you could send me one set of yours? 8O Lotus guy, Senna did pretty well today (last night) in India though...

[LeonV]

I just ordered some 115's for an L24 that had 125's and ran rich. The owner now has 120's that Stephen loaned me and just reported it ran better and less exhaust smell so The 120's will prbably be great for your L24 Leon.

The car is ~400km from me and my O2 sensor so I'll measure the 120 A/F in the spring and also run the 115's and plot.

Please measure A/F with the 120s between 3k and 6k

Good to hear, Blue. Will do!

Just a note no fuel pressure, I have found the holy grail of fuel pumps for high volume good preset pressure and dead quiet.

THe RX7 pump was great, but I was only getting 2 psi out of it at anytime. I was having issues in 3rd and 4th gear as my air fuel ratios were raising under sustained load. Not sure if it was the pump or not, but I upgraded to this little jewel.

It is a Mallory 4070LP electric fuel pump. It is preset to put out between 3 and 4 psi without the need for regulation. I fired mine up and sure enough, I could not even barely hear it. I leaned over to the engine and it was dead on 3 psi. This pump has a bypass screen that allows you to up the pressure further if you need to. But I think I will be just dandy at 3 psia. It was the last thing I wanted to do before my rally. I am bringing the RX7 pump as a back up.

I think I am currently running 130 mains in my L28. I still need to do some data logging. Or get a reliable copilot to pay attention while I drive. The roads around here are not conducive to high rpm 3rd and 4th gear runs.

I hope you mean psig!

Good find, although it may be out of the budget for some. Looks like a good (better?) alternative for the RX7 pump. I've got an RX7 pump sitting around as well, I'll put it to use eventually and see what happens.

Leon,

It just so happens that I have two pump springs and two carbs worth of O5 tubes. Maybe you could send me one set of yours? 8O Lotus guy, Senna did pretty well today (last night) in India though...

Yeah, I suppose Lotus guys are OK.

Hopefully Keith sent out the missing links today. I'm expecting the mains and Keith's final spring to come in at some point in the week and then I can do some more tests, as long as it isn't wet out.

[conedodger]

Dry as a bone here. Literally I think. I hooked up my fuel pump differently. I ran a 12 gauge wire directly to the coil with a 20amp fuse just before it connects to the coil. Increased my fuel pressure to 3psi. I took it for a spin and it acts differently. I would imagine partly because I eliminated the MSD box. It probably was covering for some problem. I have to do that EDIS! By the way, Leon, why did you do two different mounts for your EDIS stuff? You have the box on one aluminum plate and the coil pack on another. Are you avoiding interference? It seems everything would fit on that one mount...

Waiting on the package from Keith to start tearing in to things. I suppose I could do two carbs but...

[LeonV]

Dry as a bone here. Literally I think. I hooked up my fuel pump differently. I ran a 12 gauge wire directly to the coil with a 20amp fuse just before it connects to the coil. Increased my fuel pressure to 3psi. I took it for a spin and it acts differently. I would imagine partly because I eliminated the MSD box. It probably was covering for some problem. I have to do that EDIS! By the way, Leon, why did you do two different mounts for your EDIS stuff? You have the box on one aluminum plate and the coil pack on another. Are you avoiding interference? It seems everything would fit on that one mount...

I wanted a cleaner look and I like that the EDIS module is somewhat hidden underneath the fender. Interference issues are a good point to consider as well.

Frankly, the placement was really dictated by available holes already in the body (didn't want to drill new holes). The right fender had perfect holes in it already for a coil bracket and as a bonus, it places the coil pack such that the plug wires stay short. The battery tray area had plenty of space (and holes) after removing the 260Z's emergency start button for a relay/module bracket.

Waiting on the package from Keith to start tearing in to things. I suppose I could do two carbs but...

Same here.

120 mains shipped from Pierce today, they should arrive tomorrow.

[conedodger]

Well, it wouldn't run with the O5 tubes. It would start and run badly but no coaxing of the throttle would get me moving at all. But when I put the original tuning-day configuration back in with the new accelerator pump springs things went back to running like it did at the tuning day and on the way home, with one strong exception. When I jump into the throttle from anywhere, the A:F ratio goes to 12.5:1 and stays put. It loves the springs! In fact, if I do go with my plan, to sell these rare beasts to some Maserati, Ferrari, Morgan restoration guy, I will buy 45DCOE 152's and replace the springs!

[LeonV]

Well, it wouldn't run with the O5 tubes. It would start and run badly but no coaxing of the throttle would get me moving at all. But when I put the original tuning-day configuration back in with the new accelerator pump springs things went back to running like it did at the tuning day and on the way home, with one strong exception. When I jump into the throttle from anywhere, the A:F ratio goes to 12.5:1 and stays put. It loves the springs! In fact, if I do go with my plan, to sell these rare beasts to some Maserati, Ferrari, Morgan restoration guy, I will buy 45DCOE 152's and replace the springs!

Rob, that is great to hear, now I really want to get home and try them out! The stumbling at sudden throttle input (e.g. quick, rev-matched downshifts) has been my biggest gripe.

[conedodger]

Leon,

What is this? It looks like a pump jet but shorter. Keith put them in my package and I would imagine yours but all he mentioned was the O5 tube.