First drive running rough, 2.0 weber 40's Options

[skota23]

Hi Folks,

I was able to take my new to me 914 for a short drive yesterday. The car is a 74 with what I think is the original 2.0. It has Dual weber 40's and what I think is the stock distributor. The cap and rotor look practically new and the plug wire in good condition. It wouldn't start a few weeks ago and I pulled the plugs (NGK 7) and cleaned them, fired right up after that (Never had webers before and I think I flooded the cycling a little pumping the gas pedal thinking it would help start.

Other observations.
The few times I have started it (usually after sitting over a week) I crank the engine, and give a dab of the gas pedal to get it to fire, usually takes several tries to get. running. After warming up a bit engine goes through revs well.

On the drive the engine runs very rough usually between 2-3k its barely pulling. Lots of hesitation and at odd times it pops to live a pulls great.

My first thought is to pull the carbs, do a thorough cleaning and check to see what jets are fitted and the condition of the floats.

Also planned are a timing check, valve adjust, oil and filter, fuel filter.

Is there any other details I can provide for suggestions on how to get things running well? (IMG:style_emoticons/default/poke.gif)

Thank you!
Steve

[GregAmy]

Welcome to carbs. You'll learn a lot.

You really need an AFR system to properly see what the engine is doing and tune accordingly. Could be lean mid-range, could be fat; could be the accel pump during transition. You just won't know w/o AFRs. - GA

EDIT: oh, and buy one of these: https://www.cbperformance.com/product-p/6537.htm

[rhodyguy]

FWIW, usually the engine will catch after 3 slow regular pumps on the gas peddle when cold. Feather the gas for a minute until it idles on it’s own. As made 44s are pretty big for a 2.0. If that is what is installed. ESP if the webers have 36mm Venturi.

[skota23]

FWIW, usually the engine will catch after 3 slow regular pumps on the gas peddle when cold. Feather the gas for a minute until it idles on it’s own. As made 44s are pretty big for a 2.0. If that is what is installed. ESP if the webers have 36mm Venturi.

Those little tips on things like the start up help so much, It has 40's not 44's so I should be good there. Thank you!

[skota23]

Welcome to carbs. You'll learn a lot.

You really need an AFR system to properly see what the engine is doing and tune accordingly. Could be lean mid-range, could be fat; could be the accel pump during transition. You just won't know w/o AFRs. - GA

EDIT: oh, and buy one of these: https://www.cbperformance.com/product-p/6537.htm

Thank Greg,

Ideally I'd like to get it running well without adding much to the system, but I'll look at a AFR system.

I have a flow meter already that I've used for tuning Solex's on my 912 so I should be all set there.

I've seen folk recomend a book for tuning Webers (cant think of the exact book right now) but I'm not sure how helpful it would be compared to looking things up online and youtube videos. More research needed, and help from you guys! (IMG:style_emoticons/default/beerchug.gif)

[NARP74]

You will find lots of carb info and jetting guidance here if you can spend some time doing searches, or people will pop them in eventually. Altitude matters...

SOT, where did you get the air hoses for the blower in that first pic?

[930cabman]

I am also in the carb camp. What condition are the guts of the engine? compression, leak down, ... The carbs are probably tunable, but if the engine is not up to snuff, it is all moot.

[skota23]

You will find lots of carb info and jetting guidance here if you can spend some time doing searches, or people will pop them in eventually. Altitude matters...

SOT, where did you get the air hoses for the blower in that first pic?

They came with the car so not sure, they look perfect though, haven't seen anything exactly like them before.

[jhynesrockmtn]

If the car has been sitting for a while prior to your purchase I would definitely pull the carbs and go through them. Also make sure your fuel tank is clean and doesn't have junk plugging the outlet restricting fuel flow. I have refreshed a few cars after long period of sitting and fuel just gunks stuff up. They have ranged from a 356 that ran poorly to a 6 conversion that wouldn't even start it was so bad. Attending to the whole fuel system made them run great!

[skota23]

If the car has been sitting for a while prior to your purchase I would definitely pull the carbs and go through them. Also make sure your fuel tank is clean and doesn't have junk plugging the outlet restricting fuel flow. I have refreshed a few cars after long period of sitting and fuel just gunks stuff up. They have ranged from a 356 that ran poorly to a 6 conversion that wouldn't even start it was so bad. Attending to the whole fuel system made them run great!

I dont think it sat without running for years, my understanding is that it was started and driven once in a while, Probably with some decent size gaps in there.

I looked in the tank and it looks very clean. I'll put in a new fuel filter in soon and before trying to run it again.

[NARP74]

You will find lots of carb info and jetting guidance here if you can spend some time doing searches, or people will pop them in eventually. Altitude matters...

SOT, where did you get the air hoses for the blower in that first pic?

They came with the car so not sure, they look perfect though, haven't seen anything exactly like them before.

Agreed, maybe someone else will chime in.

Try some seafoam for a cleaner. I have some fogging oil for storage but I have not tried that for cleaning, not sure if that works, but you can spray in right in the carbs.

[rhodyguy]

Skota23 I sent you a PM. Post a picture of your flow measuring tool. Fuel pump and location too.

[Superhawk996]

My first thought is to pull the carbs, do a thorough cleaning and check to see what jets are fitted and the condition of the floats.

(IMG:style_emoticons/default/agree.gif)

While AFR gage is nice - carbs were successfully tuned without them for decades, and decades, and decades.

Webber 40s as purchased have venturi’s too large for good driveability. Putting a set of 40s right out of the box on the car results in over carburation for most 914s.

[rhodyguy]

As produced 40s work pretty good on a 1971. It’s the 44s with the big Venturi that are dogs on smaller displacements. Back snapping and popping. Terrible transition. No telling what sort of cam is in the poster’s engine. A lot of unknowns. Starting with the fuel pump.

[CCE]

As produced 40s work pretty good on a 1971. It’s the 44s with the big Venturi that are dogs on smaller displacements. Back snapping and popping. Terrible transition. No telling what sort of cam is in the poster’s engine. A lot of unknowns. Starting with the fuel pump.

I have the 44s and yes on the back snapping, yes on the popping, but transition? Sorry can’t understand, (second lenguage issue here). My motor is 1974, 2.2L with ported and polished heads and manifolds. I use the car in high altitude Mexico City.
https://youtu.be/LIo7AnmsMPo

[flyer86d]

Try to determine which cylinder is missing at idle. Pull out the idle jet for that cylinder and blow it out. This is a very common issue with Webers as they run up thru mid throttle and RPM range on their idle jets. I carry a stubby screwdriver in my car the remove the idle jets at the side of the road.

Charlie

[Superhawk996]

I have the 44s

Basically 44s are too big. Especially so at high altitude where air has less density and requires less fuel.

You need to find Venturi’s that are about 28mm diameter to get a good vacuum signal. Rejet after you replace those. You’ll still have issues with off idle performance due to the larger 44mm throttle butterfly but it will drive better.

Ideally you should sell the 44s and use a set of 40s. In my experience running 40s on a 1911 cc engine with a performance cam, it needed smaller venturis 28s for good driveability. 30 mm Venturi’s were better on the top end at high RPM but that is not how a car gets driven in normal traffic.

@bbrock is at similar altitude - he posted his carb and jetting setup (for 40s) a while back.

[Superhawk996]

Transition is how the motor performs as it comes off the idle jets (up to about 2500 RPm) and begins fueling off the main jets.

Most of the time at light throttle, the idle jets are providing the fuel.

[GregAmy]

Basically 44s are too big.

(IMG:style_emoticons/default/agree.gif)

Somewhere in this forum there's a chart from, I think, the Dellorto bible, but I can't find it now. Attached is bascially the same thing.

CB has 44 IDF venturis available down to 32mm:

https://www.cbperformance.com/product-p/6356.htm

[rfinegan]

A plugged or partly pugged idle jet will pop and low power and run poorly like a dead cylinder. When it hits the main circuit it will come alive again and pull good .

Try to determine which cylinder is missing at idle. Pull out the idle jet for that cylinder and blow it out. This is a very common issue with Webers as they run up thru mid throttle and RPM range on their idle jets. I carry a stubby screwdriver in my car the remove the idle jets at the side of the road.

Charlie