Weber DFEV 3236 Stumbles

[psg]

Recently I swapped out original carb but retained the original intake manifold (1978 1800) for a new Weber 3236, also installed new tube header from Bayless and performance exhaust system from Vick. The car starts well, idles well, cold or hot. Moderate acceleration the car does well and can pull through any of the gears without a down shift.

The problem occurs, a severe loss of power/stumble, when I put my foot in it, especially when a down shift occurs or merging in traffic. If I "kinda" accelerate by backing off the gas pedal I can manage the stumble and do okay. So everything works except the real fun part of the car.

I am pretty confident the points and timing are okay so I want to focus on the carb. I am presuming the carb (since it is new) has the stock jets and I am wondering where to start and the best place to order/get jets to begin trying different combos. To me the car acts like it is being flooded... Any questions or especially any thoughts? Paul

[131]

To me the car acts like it is being flooded...

Sounds more lean to me. Check your accelerator pump is working correctly, and size of pump jet, before jumping in to change jets.

[majicwrench]

Ditto. When cars stumble on accel is almost always lean.
And I would not mess with changing jets. That carb was built with jets that would supply plenty of fuel for the size of the venturis. As said above, accel pump has to work well.
Keith

[psg]

Hmm I can check that but it doesn't feel starved or hesitate. What is interesting is if I start from a dead stop raise the rpm's and slam through the gears it doesn't miss a beat. It is the roll on acceleration where the problem shows. I will look at it when bk in town.

[georgeramos]

I have the same issue. The carb is new, could the accelerator pump be failing/faulty or should it be a simpler adjustment?

[Dombrockt]

Pull your spark plugs and see what they say. Should be pretty easy to see a lean or rich condition. I know from having one on my car, that the stock idle jet is too large for a stock 2L engine. Accelerator pumps don't typically need anything on these cars. Look up tuning for a Weber carb on the internet. A good read; http://www.classicinlines.com/WeberTune.asp

[psg]

I tend to agree with your thinking. Since the car runs well except under heavy roll on acceleration will the plugs still reveal a lean or rich condition? psg

[lm48]

I have the same carb install on a 2l with 1800 head. I had the same issue after the conversion. It was very reach at idle, will accelerate good under a very smooth and easy pedal push but under heavy acceleration will starve. I play with timing, spark plugs with no results. I end up modifying the link between the first and second barrel forcing the second barrel to open early. Huge improvements. I change the idle jet to the next size down but the engine was running to reach.( to heavy smell and smoke under heavy acceleration). After numerous jets replacement I end up with to lean configuration. (No smell and no smoke under heavy acceleration). The car will start hot or cold at first crank but do not have the original kick. I just order a kit to convert the carb from progressive to synchronize operation which will give me a good mid range throttle response. After conversion I will go a lithe reacher step at the time. Mpg is not an issue when you drive 20 miles/ week

[Dombrockt]

It doesn't take long to get some color on the plugs. Be sure not to let it idle long on the new plugs. Recreate the conditions you are having trouble with, and pull the plugs for a read as soon as you can afterwards, as not to disturb them with other conditions such as rich or lean idling.

[lm48]

Just a feed back after the conversation fron progresive to synchronized
The kit advertised on line will not work with our carb. Completely diferent application but the feed back from Opel owners convince me to try to make something working. After a lot of work welding and grigind I manage to use few pieces from the kit. What I difference, completely different car. On 4th gear at 2000 rpm floor the gas and no hesitation. It wort the 3 h in the garage. I am not afraid any longer to accelerate quick and hard. I will run the engine for few weekends and check the spark plugs. I may go one steep reacher.

[Dombrockt]

Another Weber tuning aspect to keep in mind while you are trying to get it to run well is the idle adjustment. If you are between 3/4 to 1 1/2 turns from contact, you are in good shape. If you are further in than that to achieve your correct idle speed (850 rpm), you are starting to run on the progression circuit (aka transition circuit). The engine will run rich, and not respond to the mixture screw. It took me a good bit of time to figure out this was happening on my car. I am running a 2L, with 1800 manifold and 32/36 DFEV. Everything else is stock. I found the best idle for me was achieved using a 55 idle jet, as opposed to the stock 60. I tried the 50, but it would backfire out the intake, a sign of running too lean. With the 55 in place, I was able to tune for just under 18 inches of vacuum. With the 60, or the 50 in place vacuum would only pull around 16-17 inches. Using the 55 also eliminated the backfire.