engine and drivetrain Carb Basics

[doug73cs]

Some questions and confirmations on what I think are basics for setting up a 38/38 weber. I have a stock motor and cam, Petronix, hotter coil and correct timing with less than 30,000miles since an unknown rebuild. The car drives between 2000' and 6000'. Personally, I think the carb is more than the engine needs given spec and altitude which makes getting it running well without be over rich at some point is difficult.

What does a "hotter" range with respect to spark plugs have on ignition?

The idle circuit controls mixture to 2000 rpm, the mains through the whole range and the air corrector can fine tune mixture above 4500rpm - correct?

Does the air corrector jet have any effect at the lower rpm range? Say 2500 to 4000?

Any comments on the questions appreciated.

[TobyB]

1- hotter plug will be slightly more detonation prone, fouling- resistant.

 

2- I wish it was that simple.  If the engine's under load, with a lot of throttle, the idle circuit can have negligible effect

at 1200rpm.  If the car's on overrun going down a hill, it can be the only one active at 4500 rpm.

It's throttle- position dependent, mostly- once you're a certain amount off the stop

and have enough airflow the other circuits start to kick in, and then begin to take over.  It's a very

'soft' transition... which is where the science of tuning starts to blur into an art

 

2.5 as above, the air correctors start to increase fuel emulsification ('lean it out') above a certain flow rate.

So yeah, at 2k, the motor just doesn't really flow enough air to pull on them- but if you're at WOT at 3500, it may.

And if you're at small throttle opening at 4500, there won't be enough airflow to pull them, either...

 

3- Yes, it's possible at high air flow rates, but I'd guess that 3500 might be the lower limits.

 

Think more in terms of airflow, and it'll help your mental tuning model.

 

Get a wideband meter.  It'll help connect your model to what's going on inside your engine.

 

hth

 

t

Edited October 14, 2014 by TobyB

[doug73cs]

Airflow.  Thanks Toby - this helps - I was unsure whether there were three variables at work at idle/low/mid throttle or just idle and mains.

 

I have a wideband meter in the car and that does help see what is going on.  I'll focus on the idle and mains for start, low throttle and cruise and then main and air jets at WOT.  Was 50/145/185 now currently 45/150/185.

[Napes]

My engine was just re-built by Ken Blasko (in Long Beach, CA), and, although a little different than your engine (I have new 9.5:1 pistons from IE, [stock cam, because I have an automatic and they do better with the stock cam], and on my brand new Weber 38/38 I have the following jets:  Idles I went from 45s back up to 50s, mains are 132, and air corrections 195.  Except for the idle jet size which I changed the others were as Ken had set the carb up.  He's at sea level though and I live at 4,000' elevation in Nogales, AZ, and once, or twice, a month drive to Tucson which is at 2,100' 

 

My idle is a little higher when I get to Tucson, but not too bad. I am currently running NGK plugs (BP6ES) and a new IE Shorty Header in place of a tii manifold.  Car is a '75 automatic.

 

With this set-up my car runs great and accelerates like crazy.

 

Hope this gives you a little more info.

 

Bob Napier

[doug73cs]

I had marked this as ANSWERED but have to take that back.

 

 

Taking Toby's info and some searching the forum for comparable jetting given my engine (thanks for the info Bob), going one range hotter to NGK BPR5ES and adjusting my float level to spec I hoped I had resolved my set up.  

 

No luck.

 

Assuming I can attach a photo you can see that plug 1 is sooty to the point of fouled, #2 is lean to the point of knocking #3 looks just about right and #4 is showing rich - and this is a new set of hotter plugs.  Using Best Lean Idle setup procedure with 45 150 185 jets, it drives but not well and within minutes it's missing and jerking at any rpm but slightly above idle and #1 is fouled.  Same thing happened when jetted 50 145 185.  

 

So everything is new with less than 500 miles on it and the timing set with ignition at idle (900rpm) 12 BTDC. Starts like a champ and the electric choke functions just fine. 

 

So what combination of air fuel and spark produces over rich on #1 and 4 and lean on #2 and 3 ??  One carb feeds all 4 sparks from a common source - fuel pressure regulator in place.  Coil is newish Flamethrower and points replaced with Petronix.  

 

The same air/fuel mix is being supplied to each cylinder but with very different results so is the problem is electrical?  Replaced the plugs had no effect. Replaced the dist cap with OEM had no effect.  Checked for spark and all four showed strong spark.

 

Distributor?

 

Grrrrrr

Edited October 17, 2014 by doug73cs

[Hans]

plug wires?

valve adjustment?

[doug73cs]

Plug wires?  They produce spark when pulled and grounded to the block and the likelihood that they would cause such discrepancies in pairs?

 

Valves were freshly set (by me so....) but I will check.

 

But thanks

[Napes]

Just to add to my above specs I run a Bosch Blue coil, new plug wires, an old '72-'73 tii dizzy with stock points.  My OE fuel pump is about a year old and I have no need for a pressure regulator.  Don't know if this helps, but I just wanted to clarify my setup.

 

Bob Napier

[TobyB]

What cap and rotor?  I ran into trouble with Jenn's car with resistance in the secondary side of the coil-

resistor plugs, Bosch 5k rotor, carbon wires, the impedance of the secondary went up too high, and the longer

wires weren't firing well under heavy load.

 

Switched rotors and wires, and everything cleared up just fine.

 

Not sure that's your problem, tho, Doug...

 

Air leak (like, #2's missing the gasket) at the intake?

 

t

[jireland2002]

For your setup I would normally suggest a 50 idle and 135 or 140 main.  At the higher altitude a 45 idle may be ok but we never go that low around here (below 3500ft).  #2 must have a big air leak or else it's not getting fuel.  Make sure the runner is not pluged.  I assume you have checked for spark on #2.

 

Timing >> you need to check the timing at full advance.  Full advance would be at something over about 3200rpm.  I'd suggest 32 to 34 degrees at full advance.

[psalt]

I'd say #2 is not firing or your have no compression in that cylinder.  My experience is that the outer two plugs always show a slightly different mixture because of the manifold design.  I just took a 38/38 off one of my 2002's (mild cam and headers) after 29 years and +100K miles.  It has 155 mains and 165 air jets and the MM modified power valve. The plugs, NGK  6's or 7's, always look perfect. I do not run 5's on anything but a worn out oil burner, they always come out bright white on all of my 2002's.  You need to drive the car 5-10 miles under load to get a decent plug reading.

 

Does anyone know if the 32/36 throttle shaft bearing kit fits a 38/38 ?

Edited October 18, 2014 by psalt

['76mintgrün'02]

Does anyone know if the 32/36 throttle shaft bearing kit fits a 38/38 ?

 

 

I found this Opel link which claims they do fit the 38/38:

http://www.opelgt.com/forums/aftermarket-down-draft-carbs/15873-new-items-weber-dgv-dgav-series.html

 

I found this listing for the bearings on eBay, much cheaper than what I paid... ($20 for two).

I wish I had done both shafts, while I was at it (in my 32/36).

 

http://www.ebay.com/itm/Throttle-shaft-bearing-Weber-DGV-DGAV-DGAS-DGES-DGEV-rebuild-kit/221187481490?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D25879%26meid%3Dec58908209ba41edafb27b0884cfb9ed%26pid%3D100005%26prg%3D10819%26rk%3D3%26rkt%3D6%26sd%3D221187481483&rt=nc

[psalt]

I saw that ebay listing too, it is from Austria and shipping takes a month !  He must have found the source for the $2 bearing and is undercutting the US suppliers. 

[willie002]

Don't give up on the plug wire idea too easily. I had a brand new set of plug wires that made my car do some odd things like messing with the ignition I was getting. Took them off and throw them down a rat hole, put some standard wires back on the mystery problems went away. 

['76mintgrün'02]

Don't give up on the plug wire idea too easily. I had a brand new set of plug wires that made my car do some odd things like messing with the ignition I was getting. Took them off and throw them down a rat hole, put some standard wires back on the mystery problems went away. 

 

 

I had the same thing happen to me.  Bremi wires FWIW.  Two bad ones in that set, as a matter of fact.  

 

it drives but not well and within minutes it's missing and jerking

 

 

(same symptom)

 

I have never had a bad cap, so I typically hold on the old one when I replace it.  Do you have any old 'working' parts to put back for a bit?

 

Maybe a long shot, but you could try rotating the doughnut on the distributor shaft, to see if you got a funny one.  If that was the cause, it seems like the problem would switch to another cylinder.  I have never heard of such a thing, but it could be possible, no?

 

Did you stuff rags in the intake when you ported the manifold to match the 38/38 and leave one in the number two runner?  Sorry.  Just trying to think outside the box.  I am eager to hear what it turns out to be.