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1500 DGV - timing

tosoutherncars

Jedi Knight
Offline
Hi all,

As commonly reported, I have a significant stumble on acceleration with my DGV. (see one possible explanation, below.)

Could anyone running this setup post their timing settings? My (california version) '78 has a book setting of something like 2ATDC with the Solex and all the air pump garbage, but I'm wondering whether with the DGV it shouldn't be more like 15-20 BTDC. (Haven't advanced it that far yet to try it out.)

-Duncan



NOTE regarding the use of DGV on the MGB by Doug Jackson of British Automotive (www.mgbmga.com):

"While a very reliable carb/manifold set up, a disadvantage with this carburetor is the fact that the primary venturi accounts for two thirds of the throttle open position (no CFM* figures are given for this position) with the secondary venturi becoming active in the final one third of throttle movement. This carburetor requires excessive initial ignition timing advance to avoid stumble on take off (if the ignition timing was retarded, we would have to open the primary throttle plate to obtain the necessary idle; this would expose the progression bleed holes which in turn would require that the idle mixture be leaned to compensate for this richer mixture condition. The end result being very little progressive richening upon further throttle opening, especially at snap throttle and so the stumble)."
 
Update - stopped halfway to work today, leaned out the mixture (1 1/2 turns from bottom) and advanced the timing by ear. Hesitation on accelleration is all but eliminated, car feels stronger and faster. Would still like to hear how everyone else has theirs set up.
 
Duncan, I was running a richer idle jet with a leaner main jet. Dont remember the numbers off hand, but this allowed me to run a 1 3/4 turns out with 10deg BTC and no hesitation. But I also had a cam and flattop pistons so dont know how accurate that will be. Mostly even with performance parts I was finding the stock Main jets to be too rich. Also be particular about how "open" yopur buttery fly is adjusted, this will cause increased vacum. I had Put richer idle jets in so that at idle I could close the butterfly enough to eliminate the vacum advance from engaging prematurely.
 
Good stuff Duncan,, like I said last night while driving it, it was too rich. Now I am sure it will be fatser than my 1275.

cheers
 
Woodie said:
Good stuff Duncan, like I said last night while driving it, it was too rich. Now I am sure it will be fatser than my 1275.

cheers

Oh man, it really likes to get up and go... definitely picked up a second or two in the 0-60. More power left in the top end, too. Looking forward to going for another spin, it was very nice meeting you.
 
My experience with the weber on my 1500 is pretty much the same as Scott's. I never had a stumble problem( well very occasionally) the main jets were too rich. and i did run the timing a bit advanced. You will know when you get it pretty close, you can feel the secondary kick in. i was running the 32/36 with a kent th2k and dished pistons on a newly rebuilt motor, running a draft tube, hot coil and stock electronic ignition.

mark
 
Excellent... Yes, I haven't checked yet but I'm guessing I'm around 12-14 BTDC, and (comparatively speaking, anyway) the car runs like a scalded cat. "Stock" jets for the 1500, 4/2/1 header, Fireball ignition with optical trigger. It's now got almost a 'musclecar' kind of induction growl when the secondary opens. Very satisfying! :smile:
 
That's good to hear about Duncan. One other thing about the downdraft Webers' stumble problem is that it is sometimes related to problems in the accelerator pump section of the carb.
 
Hi guys,

Thanks for that... thankfully I rebuilt the carb before installing it, so no issues with the accellerator pump... you can actually hear it squirt when you fully depress the pedal (engine off.)

With the stumble varying inversely with the amount of timing advance, I really think the quote in my initial post might explain the problem I was having.

I just wish I had a little more of a sample group, as far as timing. I'm surprised, I figured there must be a dozen or more frequent posters who were running the 1500 / DGV combination.
 
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