Calling Weber 38/38 owners....

[shanon]

Can I pick your brains a bit??

I just installed a couple of Weber 38/38s onto my new sport motor, 3.3L w/ a 300 cam & 9.3 compression. (Hurray! Finally my new motor got swapped in the Coupe!) Carbs are jetted at stock/baseline (145 mains, 185 Air correctors, F50 emulsion tubes & 45 Idle jets). Motor runs like watch but experiencing some air/fuel mixture issues, currently adjusted rich to be safe.

Currently, car has no oomph up to 2k RPMs, cruises fine from 2k to 4k, then flattens out at 4k......I assume this a air/fuel mixture or jetting issue.
I realize the cam/power band should come on later around 3500-4K and sore to 6k. The head was rebuilt/mod'd by Terry Tienney (Livermore,CA) and am confident in his work/reputation.

I realized that this issue would be best solved on a Dyno but considering the Coupes new 'home' (steep drive way & very hilly terrain), I'm not sure I can get her up & out of her new 'home'. She bogged down heavily up a steep hill in first gear and barely made it up....couldn't get the RPMs past 1800.....my ol' 2.8L had more balls than my hot 3.3L currently... :cry:

Coupe cruised just fine from Monterey to the East Bay but bogged heavily in the steep hills after the relatively flat freeway cruise home. Could the plugs have fouled that much in a two hour drive?

Any wisdom for a home tune appreciated (so I can 'get' to the Dyno/experts later), I don't want to see another 'flatbed' for long time.

TIA
-shanon
'70 2800cs (very manipulated)

BTW: Operation: Arctic Wind a success! What a battle! Re-cored (3) high-flow radiator, new water pump, 2500 cfm Aux fan, mod'd thermostat...(and a new sport motor. :twisted she's running ice cold now, maybe a bit too cold, but she's desert proof now.

Lesson: If your having cooling issues, get the radiator pressure tested first! Could save you a lot of time and $$.

 

[decoupe]

Shannon – I can only summarize what I’ve learned by changing on piece at a time (which is a PITA on the 38/38).

I’m at 4500’ alt. with a 3.5l. 282 cam, twin 38/38, assumed less than 9: 1 compression – mild performance upgrades relative to yours.

I’m 12.5 – 13.0 A/F ratio at wide open throttle with Main 140 and Air 200 so it’s tuned for best power output. Idle is 50 and the A/F at “normal” around town throttle is 13.5 – 14.0 with the mixture screws turned out 7/8ths to 1 turn and idle speed 600 -700rpm. Very good transitions all the way through. My timing is 30 - 32degrees total advance which my guru race buddies suggested in order to get more top end with the altitude. I get zero knock under any conditions on premium and no dieseling shutting off the engine without cut-off solenoids.

Your jets are the stock factory Weber 38/38 sizes and are what mine had when I picked up the car from TJ at or near sea level. Given your engine build, I assume it’s running lean but the bogging down almost sounds rich. The Idle jets sounds fine. Ooppps, reread this and your idles don't sound fine - they are probably at least one size too small if mine are 50's at 4500'. Did you use the Weber best lean idle proceedure to set them up? The idle jets are what you run on at low to 2500 rpm so that might solve part of the problem.

Before spending money on dyno time consider installing a wide band O2 meter. I’ve been very happy with one from Western Motorsport (no blah blah blah) www.wmswideband.com/ . There are, no doubt, others to chose from but being able see in real time the A/F ratio under different throttles is very helpful in setting the jets.

Lowering the Air Jets richens the mid to upper rpm fuel mix without altering the idle and low to mid. Changes in the Main jets alters everything but the idle. Changing the idle only effects the idle but can mask the accelerator pump jets (according to Pierce Manifolds) but ignore that.

Recommendations? Check your plug color. Check your timing. Check your spark is strong to all cylinders. Check your linkage is synch’d. Check that the carbs are drawing equally.

If your plugs are very light tan to grey, try one size larger main jet – 150. If it improves try another increase. By not changing the Air you will be further increasing the richness at higher rpm’s.

If it gets worse (bogging down) go opposite direction with the Air jets first (down to 180) to see if there is any improvement.

 

[shanon]

many thanks decoupe

Any chance that it could be 'over cam'd' regardless of jetting, etc??
Or, gulp, under carb'd (do I have to have triples w/ this cam/set-up)

:?
-shanon

 

[AndyM]

I second the suggestion on the WBO2. It will be money well spent and will save you countless hours of frustration -- not to mention peace of mind knowing that you're not going to melt down a piston running 20:1 at WOT. :shock:

Your distributor is probably going to need some attention to run right with that much cam. If you haven't already addressed it, keep it in mind or you'll end up chasing your tail indefinitely.

 

[decoupe]

I don't know if it's possible to be over cam'd or not. Call the tech guy at Pierce Manifold or Steve at Top End Performance - both have been a great help to me.

I think the key here is to get the Idle circuit dialed in using the Best Lean Idle procedure from Weber - http://www.racetep.com/webtechframe.html - the 38 DGAS link. The less turn out on the mixture, with the biggest jet produces the best results (for me anyway). Your idle setting will be a bit higher 800 - 1000 because of your cam.

From what I have been told the downdrafts produce better results in the low to mid range and sidedrafts in the upper to peak rpm's.