weber conversion results-long post

[bluebenz]

Sorry for the long post!!! This great forum has helped me a lot in the past, and hopefully some of you can give me pointers so I can enjoy my car again! I spent a lot of money on a weber conversion and so far the results are not as good as expected, although it is an improvement!

I fell in love with the MB 114 when I was a kid, and I bought one off ebay last fall. A 1973 280C with 90000 miles. Great looking car and I enjoy it a lot although the past months have been frustrating at times!

When I got the car last year, I had a tune-up done: new NGK spark plugs, new plug wires, distributor cap, rotor and points (no condenser, couldn't find one), new air and fuel filters, oil and filter change, transmission oil and filter changed. I also replaced the battery, new battery cables. The previous owner had recently changed most belts and hoses, fuel pump and rebuilt the solex carb.

The car ran extremely well for 8 months, then some problems started: Very hard to start when cold, rough idle, stalling, sometimes hard to start when warm. First step was to remove a leaky fuel return valve (could not find a new one so just removed it) and that seemed to help a lot, at least temporarily. I then installed a crane XR-700 pointless ignition system with a new crane coil, and thought the problems were solved for good.

Unfortunately in september the cold start problem got worse and the stalling at intersections made me nervous. The solex carb was leaking, float was stuck, and after reading a lot on this forum I decided to get a new redline weber 38 dges conversion kit. Got the new carb installed by my trusted mechanic. Removed the egr and some other emission stuff at the same time. Timing was set after carb installation.

Now the car starts well when cold or warm, the idle is smooth, and it doesn't stall anymore. Car is powerful and smooth. The only problem is an annoying flat spot or hesitation on take off (the car does not move for 1-2 seconds when you press on the gas and then it goes) and a shorter hesitation when accelerating hard from a cruising speed. The only way to avoid this initial hesitation is to accelerate very slowly from 0 to 10 mph and then you're OK.

The weber web site says the fuel pressure should be 1.5 to 3.5, mine is 4.5 but I dont think it is causing my problem. I suppose I could install a pressure regulator but dont want to spend more money if it isn't necessary.

Hopefully we will be able to fine tune the carb (accelerator pump adjustment maybe?-could not find out how to adjust it on the weber web site) and enjoy this car again! I was wondering if anyone who had done this conversion had similar problems?

Thanks for your input!!!

[cth350]

Did you keep the original fuel return setup with a vacuum controlled return valve?

Also you should have the fuel pressure match the specs. Aside from preserving the carb gaskets long term (not that only 1psi would cause a problem there), the various metered bores that the fuel flow through are calibrated based on assumptions madea bout operating conditions, including fuel pressure. -CTH

[nhdoc]

Has it always had the flat spot since the weber was installed? Typically flat spots like that are a sign that the accelerator pump is not functioning. You should be able to hear liquid gas squirt with the engine off and the throttle opened if you remove the air cleaner. It is possible you got a defective carb or the pump is clogged. It should not be too hard to determine if the accelerator pump is working and if not to replace it.

I suppose it could also be a vacuum leak if the pump turns out to be working. Could also be timing or the timing advance not working right but assuming all was well before the weber was installed I'd start with that being the culpret.

It's a very nice looking car...love the color too!

[bluebenz]

First of all thank you both for your replies!

To cth 350: I didn't keep the original fuel return setup, figured that since the main function of the return valve was to prevent vapor lock on hot days and were I live in Canada we unfortunately don't have many hot days, I would be OK, so just plugged that line. And I will get a weber or holley pressure regulator, only 20-30$, and at least everything will be as specified.

To nhdoc: Yes, ever since the weber was installed I have had the hesitation, a problem I didn't have before! The weber did solve the hard starts, rough idle and stalling issues though, but the hesitation on take off makes driving it in traffic very dangerous!!! The hesitation when you accelerate hard from a cruising speed is very subtle though.

I suspected a vaccum leak too, but everything looks good under the hood, although didn't measure the vaccum. Timing was just reset after weber installation. Mixture has been adjusted too, was a bit too lean, which got rid of the rare backfires. Idle speed has also been adjusted and seems fine. Other than that it seems to run fine, no smoke, oil pressure very good, running temperature very good, no strange noises, good power, etc..

I will check if I can hear fuel squirting when I press the throtlle (engine off but warm I imagine?)

I did email weber redline again, maybe there is a way to adjust the accelerator pump! Will keep you posted!

Again I am very grateful to have found this forum!

Patrick

[nhdoc]

Yes, listen for the fuel squirt with the engine off...doesn't matter if it is hot or cold but you probably should remove the air cleaner to listen in the throat. I don't think the pump is adjustable...most consist of a diaphragm that squirts fuel and if they are stuck or torn they just don't work...you simply replace the diaphragm as a unit. My bet would be that it is the problem.

You might also confirm the vacuum advance is plumbed correctly and there's vacuum from it and that the advance itself is working. On my '64 there were two vacuum ports on the carbs...the one which produced vacuum with the throttle open was the one the vacuum advance was supposed to attach to not the one which has vacuum on it at idle so you might want to check that too because at some point they changed the design. I believe they call it "ported" vs "manifold" vacuum and mine used the ported source but later ones used the manifold source. Your tech may have plugged it into the ported when it should be manifold vacuum.

[MunichTaxi]

You might also confirm the vacuum advance is plumbed correctly

How does the timing advance look with a timing light?

[nhdoc]

Originally Posted by MunichTaxi

You might also confirm the vacuum advance is plumbed correctly

How does the timing advance look with a timing light?

There are two types; vacuum and centrifical. I check the vacuum advance by using a mityvac and drawing a vacuum on the line while watching the timing mark at idle with the timing light. If the timing mark advances under vacuum and returns when the vacuum is released it is working. You'll also be able to hear the engine's speed change when it advances. It should also hold vacuum pretty well...doesn't have to be perfect but should not leak down fast or require constant pumping on the mityvac to hold it. If it leaks too fast it usually means the diaphragm has a small hole and should be replaced.

Then, with the vacuum advance disconnected I rev the engine and watch the timing mark. If it advances then the centrifical advance is working...if not then you know you have to look at it and see why it is not working. The shop manual will tell you at what engine speeds the advance should be in degrees and there is usually a curve they follow which you can use as a reference. It does not have to be perfect but should be working.

[Housecrew]

the crane and pertronix setup is good for distributors that are not worn out.
if the car still feels sluggish with them, watch out for a 123 ignition.
maybe there are dealers in canada too: http://www.123ignition.nl/id/25.html

[JMURiz]

Originally Posted by Housecrew

the crane and pertronix setup is good for distributors that are not worn out.
if the car still feels sluggish with them, watch out for a 123 ignition.
maybe there are dealers in canada too: http://www.123ignition.nl/id/25.html

Is this just like a Mallory distributor? The info on the web-page is rather vague about what the triggering system is. I'll read the whole page when I get time.
If it's like a Mallory this may be the ticket for a more modern style ignition w/o the need to go crank-fire style.

Anyone used one of the 123 systems before?

[agav]

This is a very old thread and also my first time one this forum (Hi everyone!) - but I thought I might still get in touch with someone who knows this.

I am about to go through the same Weber (K248 kit) conversion on my W116 280S after I finally caved in (my Solex is badly bent from previous owner bolting it on with too much torque and a complete rebuild didn't help either).

My question is:
There is a thick insulator with glued-on gaskets on the intake manifold onto which the carburetor mounts (this one here). Is that still required with the weber kit? Or does the kit's adapter plate bolt directly onto the intake manifold?

Thanks!
Agav

[mb aussie]

Originally Posted by bluebenz

Sorry for the long post!!! This great forum has helped me a lot in the past, and hopefully some of you can give me pointers so I can enjoy my car again! I spent a lot of money on a weber conversion and so far the results are not as good as expected, although it is an improvement!

I fell in love with the MB 114 when I was a kid, and I bought one off ebay last fall. A 1973 280C with 90000 miles. Great looking car and I enjoy it a lot although the past months have been frustrating at times!

When I got the car last year, I had a tune-up done: new NGK spark plugs, new plug wires, distributor cap, rotor and points (no condenser, couldn't find one), new air and fuel filters, oil and filter change, transmission oil and filter changed. I also replaced the battery, new battery cables. The previous owner had recently changed most belts and hoses, fuel pump and rebuilt the solex carb.

The car ran extremely well for 8 months, then some problems started: Very hard to start when cold, rough idle, stalling, sometimes hard to start when warm. First step was to remove a leaky fuel return valve (could not find a new one so just removed it) and that seemed to help a lot, at least temporarily. I then installed a crane XR-700 pointless ignition system with a new crane coil, and thought the problems were solved for good.

Unfortunately in september the cold start problem got worse and the stalling at intersections made me nervous. The solex carb was leaking, float was stuck, and after reading a lot on this forum I decided to get a new redline weber 38 dges conversion kit. Got the new carb installed by my trusted mechanic. Removed the egr and some other emission stuff at the same time. Timing was set after carb installation.

Now the car starts well when cold or warm, the idle is smooth, and it doesn't stall anymore. Car is powerful and smooth. The only problem is an annoying flat spot or hesitation on take off (the car does not move for 1-2 seconds when you press on the gas and then it goes) and a shorter hesitation when accelerating hard from a cruising speed. The only way to avoid this initial hesitation is to accelerate very slowly from 0 to 10 mph and then you're OK.

The weber web site says the fuel pressure should be 1.5 to 3.5, mine is 4.5 but I dont think it is causing my problem. I suppose I could install a pressure regulator but dont want to spend more money if it isn't necessary.

Hopefully we will be able to fine tune the carb (accelerator pump adjustment maybe?-could not find out how to adjust it on the weber web site) and enjoy this car again! I was wondering if anyone who had done this conversion had similar problems?

Thanks for your input!!!

hi , sounds very fimiliar, what ignition timing are you running, initial timing With out vacuum, I had a lot of problems in the start too, I went With the holley from jam and its a good set up With fuel squirters .I found out in the end that I had to increase my initial timing to about 15 degs, made a huge amount of difference.I also disconnected the vacuum advance(dont use it any more)i HAVE ALSO READ SOME PLACE THAT THE WEBERS DONT HAVE SQUIRTERS , which in turn causes a flat spot on initial start. Try advancing Your timing to about 12-17 deg and give that a og first..in there is a sweet spot. good luck