engine and drivetrain Jetting Question - Main & Corrector

[Cru Jones]

Well, if bigger correctors helped, maybe you're running RICH at WOT and lean at idle/light cruise.

 

A bog's as good as a lean, as far as power loss is concerned.  Black smoke out the tailpipe when this happens?

 

I agree, fuel pressure's maybe not the most likely, but it's also easy to rule out with one of those compound vacuum/pressure gauge

that I seem to accumulate...

 

A suggestion- get a main jet leaner and a jet richer than you have.  Try them.  One bore at a time.  If it's lean on the primary

and stupid rich on the secondary, that MIGHT be doing what you're getting.

 

Next random thought- power valve is good, right?

 

hth

 

t

 

No smoke that I've seen at any throttle opening.

 

Lean on primary and rich on secondary was actually my first thought when I found out what the mains were. Seemed too different to me. How do you go about properly tuning that though? Do you get a WBO2 and just notice the AFR before the secondary kicks in and after? If it were just too lean on primary how do you really tell? Oh, power valve seems ok. Wasn't sure how that would factor into what I'm experiencing.

[TobyB]

The power valve is a bit tricky- it opens whenever there's little vacuum downstream of the throttle plate.

 

So it's open when the car's off, it CAN open at low revs only on the primary- but it's mainly designed to open under WOT.

 

And yes, you tune the primary as best you can, locking the secondary closed, and then you let it open, and

see how things change after that.  I've never gone beyond 'ballpark' as I had 40's and a 38/38 on the cars I tracked-

 

the 32/36 on the street car never got the same level of attention.

 

http://www.wide-band.com/bpsx_digital_wideband_wbo_controller_enclosure_display

 

just ordered one of these so I wouldn't have to move the LM-1 around- we'll see how it does.  Price was right...

 

Never got to http://14point7.com/

 

but the guy seems to know what he's doing...

 

t

 

 

t

[Cru Jones]

Well, stumbled upon an interesting discovery tonight while lubing my heater fan. Seems one of the POs in their infinite wisdom decided to remove the accelerator pump linkage. Never thought to give that a second glance because why would you ever mess with that? Pretty sure the diaphragm is still intact, but am truly baffled why someone would remove that.    Luckily, I have a spare 32/36 laying around that I can scavenge parts off and will do that sometime this weekend. At this point I feel I've got to take the carb completely off and make sure it's not totally fubar'd. 

[eurotrash]

Long shot, but how old is your carburetor?  It could be that you are sucking air around the butterfly shafts. 

 

After a year or two of driving, and during a summer rebuild on my 32/36, I installed these on my the main shaft of my fairly new carb (20$ for TWO at Pegasus). I did so because I had noticed evidence of weeping around the ends... the bearings cleared it right up.  Later, after adding sync-link to the thing, I wore out the secondary shaft's bushings and it was leaking gas at the shaft during low RPM, and sucking air at high RPM.  Made very obvious by the staining on the carb and intake manifold. 

 

Point is, these are a good addition to any rebuild.  And put them on both shafts.

 

http://www.ebay.com/itm/Throttle-shaft-bearing-Weber-DGV-DGAV-DGAS-DGES-DGEV-rebuild-kit-/221187481490

 

Edited November 19, 2013 by eurotrash

[Cru Jones]

@eurotrash - At this point nothing is out of the realm of possibilities. I'll make it a point to check that when I take the carb off this week.

[Cru Jones]

Ok, update for those playing along. Firstly, I haven't had time to get my WBO2 sensor hooked up. Life has unfortunately been in the way. With that said, I did get a 38/38 Weber put in, so problems are bit different now.  I guess at this point this thread is just for me to catalog my changes and to hopefully help someone else in the future. Current setup is 38/38 with 45 idle jets 1 1/2 turns out, 150 MJs and 180 correctors. Car runs well and will get to redline, but only if I'm easy on the gas pedal. If I floor it it will stumble until I ease the accelerator off a bit. Checked screen at pump and cleaned it out, screen in carb is clean and pickup sender is clean as well. I'm at the point now where the issue seems to be either with the fuel delivery in some way (still need to hook up the pressure gauge and see what it's doing when it stumbles) or it's to do with the ignition. My MPG last tankful (or thereabouts) was ~20mpg, which led me to think that I'm still running rich, hence the change to 150 MJs from the prior 155 MJs.

[Cru Jones]

Further update...I suspect I have a multitude of issues, but my most pressing that I'd like to sort now is the venting. My '74 still has the stock setup from the expansion tank to the engine bay (charcoal canister removed), but I think that the line isn't flowing that well and may actually be broken somewhere in the cabin. The easy solution I've found is to run some sort of 'euro vent' via the trunk  and bypass the tank for now. I plan to find a universal charcoal canister (I'm open to suggestions as to which one) and run through the expansion tank once I've proved that venting directly via the euro way solves some of my issues. Also, after some research I've decided to move the idle jets up to 60. I'm still on 145 mains and the car seems to be running pretty rich based on it's "bucking" at times, which is oddly worse with more gas than less. Some of the posts I've read about the jetting being somewhere in the 135 range when running idle jets as large as 60. So, plan is to do euro vent tonight and see how that is and then move main jets to 135. With that said, my last 215 miles on the car with 145 main jets got me a good 24mpg (per odometer), which is better than I've ever gotten with the 32/36 prior. So, seems to be going on the right track...

[mike472]

I have two brand new in the package bearing kits which are enough to do both shafts I bought and never used. $35 for both plus shipping including a new accelerator pump.

Also have good used carb that was rebuilt except for these bearings that you can have for an additional $75 with quick link installed.

[Cru Jones]

Further update...did the euro vent and saw no noticeable change, so issue isn't vent related it appears.

 

Also, change MJ to 135 and car pulls strong up to ~4K then I must lift and coax it to get to 6K, but then again sometimes I don't. I can't explain exactly how it behaves since it's very inconsistent. I have to do coax it to get it to rev hard when I stomp on it under lower revs (~2.5K), but other times not. It's to the point now that I can't help, but think that my root issue is not carb related. I suspect I have some other issue which is preventing me from being able to stomp on the gas and expect it to rev up through 'til redline with any consistency.   If this car were just a street car then I'd be just slightly annoyed, but since this car was bought as a quasi-replacement for my track bike it's beyond irritating. The way it is now there's no way I could take this car to the track.