engine and drivetrain Weber Woes

[Zorac]

I have two weber down drafts and I would be happy if i could get just one running right.

 

32/36, hard starting when cold, the colder it is, the worse it is.  any  longer than roughly an hour after turning the car off it becomes an issue.  if there is still some heat in the block, i have to put just enough pressure to open the throttle a crack, and that seems to resolve most of it.  if its overnight, i have to pump the pedal lots, and even then its usually 2 or 3 tries where it catch, than dies.  check the bowl, and there is always fuel in it, check the float and tried a few mm high and a few mm low to no effect.  running a spacer gasket between carb and manifold for heat transfer.  seems to be a fuel starvation issue.

 

38/38, starts perfectly every single time, which means the starting issue with the 32/36 is a carb issue, not timing/valves/plugs/etc, but the 38/38 leans out on transition.  catches almost as soon as the starter engages, although usually needs a bit of a stab on the throttle right after it catches.  no fancy pedal work like the 32/36 though, just one press to engage the choke if its old, or nothing if its warm.  when it leans out at transition, it happens to be at roughly highway speed in 4th.  ive jetted a little rich to compensate (afr roughly 12-13) to keep it from stumbling at highway speeds (roughly 14-16).  i don't like seeing over 15, but it doesn't stumble, so maybe its ok?

 

ive googled this to death, for the 32/36 suggestions are usually the spacer or float, and for the 38/38, that just seem to be an issue related to a carb being slightly to big for the engine its on.  Timing and valves have been checked, plugs regapped, and spark plug wires have less than 5000km on them.

 

anyone have any suggestions beyond the usual?

Edited July 28, 2014 by Zorac

[TobyB]

32/36- choke is working properly? 

Sounds like you're describing a car with a non- functioning choke.

2 or 3 pumps cold isn't unusual if it's jetted right.

 

38/38- Sounds like the problem I had, and never really resolved.

The carb is designed for a 2.8 v6, with one barrel feeding each 1.4 liter bank.

Since both are feeding all 4, it's waaay more carb than a 2l engine really

wants, and so the transition circuits poop out too early, and the mains come

in too late. 

In theory, you could drill a small bypass hole in each throttle plate to keep

the transition circuits alive longer.  You'd probably want a very accurate, repeatable

throttle position sensor on it (in the name of science) just to see how much

it'd take, since you'd have to experiment to see how big was big enough.

I meant to do this, but then the power valve diaphragm gave up

and I went back to a 32/36 in a fit of practicality.

One of these years, I want to modify a 2bbl manifold to feed 1 bbl to 2 cylinders

and see what THAT does.  Might be fun...

 

t

[Zorac]

Thanks Toby, you have actually tried to help me with the 38/38 before.  You got me closer but I never nailed it for the reasons you mentioned.  It so close, and the window where its an issue is so small, but its right where one spends most of the time when driving.

 

32/36, the choke is working fine, I was always concerned both the choke and idle set screws are further in than they should be, but when i pull the carb off, i'm not exposing the wrong holes too early (eg, only idle holes, no transition holes showing, for idle).  the 32/36 in general looks to be a Friday assembled carb.  although nearly new, the 32/36 has some serious fitment and play issues.  The 38/38, although it has 20 years of wear on it, is much better.  problem its its a lot of pumps, 5 or 6, then turn it over, then it catches and dies, and you have to repeat the process 3 or 4 times trying to give it just the right amount of gas after it catch.  seems to be starving for gas.

 

that said, fast idle and butterflys work as they should on both carbs.  water choke setup, and i just swap the part with the spring back and forth.

 

ive actually looked for a tps, found one diy solution, but that's it.  a vacuum gauge plugged into the distributor advance port above the butterfly might tell you something close to  the same.  on the 32/36 i was thinking of doing a simple pressure switch so i knew when the secondary started opening, that would be jetting alot easier.  or even a second spring on the secondary, so you could feel it in the pedal, which should be less complicated than a switch.

 

i also though the 38/38 would probably work alot better on my car if it had progressive linkage like the 32/36.  i though about swapping it over from my 32/36, but i'm not sure if they would bolt on.

Edited July 28, 2014 by Zorac

[jireland2002]

If it accelerates smoothly and has good power at full throttle 15 to 1 should be ok at light throttle cruise.  Especially if you do not have a vaccum advance distriubtor.  If that is your only issue with the 38 it should be ok.  If you need more help let us know the af ratios at full throttle etc.  Also include the jets in the carb and ingintion timing at full advance.

[Zorac]

thanks jeff.  jeremy helped me with the timing and this carb once before.  the advice on the timing helped, sill messing around with the carb though!

 

im timed to +8 degrees on the ball at 3000rpm (for a total of 33 degrees).  its an old mech advance bosh distributor with a vacuum retard (not hooked up).  car also has what i believe to be is a bmw sport 300 cam, and the idle has ways been a little lumpy.

 

jets on the 38/38 - 215air, 145main, 45/50idle (primary/secondary)

 

jets on the 32/36 (primary/secondary) - 145/185air, 140/130main, 50/40idle

[71bmr02]

the 32/36 on my engine started giving me the same problem. long story short, it turned out to be a clogged accelerator pump jet. pulled one out of an extra carb and problem solved. No idea what clogged the jet, fuel bowl was clean, maybe something worked lose in that part of the system and made its way to the jet.

G

[jireland2002]

Note:  We always replace the 200 needle and seat with a 250 on our race cars.  At sustained high RPM the 200 can not supply enough fuel.  We normally do not find this necessary on street cars as full power can not be used for long periods without running into traffic or the law. 

 

The 215 air jet seems a bit large.  Perhaps you arrived at it by trial and error but we would normally be at 185 or 190.  The air jet has more effect at higher rpm's so if high rpm mixture is lean try a smaller air jet.

 

Also at light throttle cruise the idle jets are a big contributor.  We normally use 50 idle jets and even 55's on some engines

 

[Zorac]

double checked the accelerator pump jet, it was originally an issue (on the 32/36), but it was the diaphragm, but not the jet, replaced that and get a nice squirt now.  i do get a spike on the afr if i go hard brakes to roughly 50% throttle fast (full throttle doesn't do it). put the float to 38mm which seems to of helped that but not eliminated that issue.

 

needle will be the default, i bought the rebuild kit from jeremy, so its likely the 200.  the 215 air is a bit of a cheat, i want to run 140 mains, but that makes the transitions issue worse. i end up running 1 size too big on the mains and trying to compensate with the air jets. similar issue with the idle jet, i want to run 45s, but i put a 50 on the secondary to help the transition.  if i have 50s on both sides, i end up way to rich when just barely touching the throttle (running on transmission holes, with the mains not yet exposed, i think)

 

toby once said in on my other threads, that once i have spent enough money on my carbs that i could of gone fuel injection, i will give up carbs and go fuel injection (so end up spending double).  i think im getting close....   carbs should be so simple though!  they should be more reliable too once you get them going. 

[jireland2002]

Maybe you are worrying too much about the AF read out.  A bit rich is ok if it runs well.  I would set it up for best performance and driveability.  For a stock (or nearly stock) compression with a slightly more agressive cam I would normally start with 140 mains, 185 airs and 50 idles.