fuel dumping into secondary

[Scutch]

Hi,

I have 35/40 Zeniths. I rebuilt them two months ago and they have been running pretty good except for small choke issues.

A new problem has arisen, problem #345 so far, since buying this car. Problem #300 for the carbs.

The rear carb is running so rich that fuel is being pulled into the barrels at idle so much it is all wet in there, especially the secondary.

I thought it was a stuck float needle, but that is only two months old. Today I switched out the float needles and the car seemed to run okay until it reached temperature. Then the idle slowly started dropping and the rear carb sucking noise got louder. When I looked in the barrels I can see raw fuel being dumped. It will eventually stall. This happened last night too.

When I had taken off the part of the carb that the float is attached to there was fuel all over the place. The level was 19mm. I replaced the valve and put a new gasket on and put it back together.

Also, on a 40 degree day, how long should I expect the choke plates to take to open? They seem awefully fast, i'd say a couple minutes. The car isn't really warm by then.

The front carb seems fine. I checked the fuel pressure and I think it was around 5psi.

I suppose I will have to blow all the jets out, but can anyone give me a clue as to what passage I should target.

Thanks for the hand.

Eddie

[MunichTaxi]

1. Do you have a fuel filter installed, before the mechanical pump?

2. If so, could your fuel lines after the pump be so deterioated that small pieces of rubber are being deposited at the needle & seat (float)?

[ctaylor738]

My suggestions/ideas -

Be sure that the idle air passage is not plugged. You can see the little hole on the top of the carb. If you plug it with a pencil eraser and the idle doesn't change, then it's plugged.

If your carbs are badly out of balance, one may demand more fuel than the idle circuit can supply and it will drip out as you describe.

If you have a warped top plate, you can also get the symptoms you describe.

[todds]

I had the *exact same* problem this past summer, on the same car on the front carb only. My solution at the time was to replace with webers, however, I wish I had just kept and diagnosed the zeniths. My webers started having a problem about two weeks after I installed them, this problem was due to sediment buildup in my fuel tank clogging up the brand new carbs. I checked the zeniths later after installing the webers and besides bad gaskets with leaks all over, they also had about a half inch of sediment at the bottom of the float bowls (and most likely clogging up many of the jets/passages) Were your bowls clean?

As far as the chokes, they might have been calibrated to work in conjunction with the dreaded heat riser flaps, which might be disabled on your car. The only other thing I could think is that the 40 year old heated spring in them might have weakened with age or be getting excessively high voltage. I'm not aware of any adjustment for RATE of the chokes opening other than the typical spring tension adjustment by rotating the housing. Did you go through the chokes pages in Jaimie's zenith manual? I'm not sure the chokes could be adjusted properly in light of your other problem. You should probably fix that beforehand.

[Scutch]

Thanks for the replies guys. I appreciate more help.

I do have a filter that is before the mechanical pump. It is as new as last summer. I have replaced two of them in one year, but only to rule that out. I have never found anything in the old filters like I used to in my other 230s with the rusty tank. I think the fuel lines are metal, right?

I checked the bowl and it was clean. I did seem to have a problem with some sediment on the front carb months ago. When I would blow out the accelerator circuit, it would fix it. I may still be having that problem. The rebuild seemed to fix it, but maybe it was only temporary. The symptoms were ticks in the idling. I was having that before this excessive fuel thing started happening this week. I'll keep an eye out for sediment, but I haven't seen any yet.

Since the car has been running without this problem now for two months I don't think the plate got warped. There has been no major heat issue.

The idle air passages are definitely not plugged because when I start my car in the cold when the choke flaps have opened (I think too soon), the backfire when I step on the throttle seems to shoot gas out of those little holes. When idling and I plug them with my finger I get a brief drop in rpms then a misbalanced idle. It immediately clears up when I take my finger away. Each carb seems to have almost exactly the same response when I plug those holes. I will take that to be a good thing.

I did disable the heat risers last summer. I am pretty sure the balance is fine. I have not tweaked it since I got them balanced a month ago. The throttle response has been great since.

So something is plugged by debris is most likely the answer since it seems to just start happening. Yes? This is what I figured. But debris from where? I will crush the old filter and look.

So for the float bowl to be overflowing there would have to be something keeping the float from rising. Seems an unlikely coincidence that witha clean bowl and a new sprayed out needle valve that the carb floods like that after just a few minutes. Can anything else cause the fuel to leave the float bowl in a disorderly fashion like that? Both of the gaskets I have used here have been new. I just rebuilt the carbs two months ago. Otherwise they seem fine.

Some day I would love to see a schematic that clearly illustrates what goes on inside my carburetor. The lack of this makes diagnosis a little silly. Even better I would love one of those fancy computer graphics things like on the Discovery Channel that would put us inside the carb and show us exactly what happens in a number of varying situations.


When the weather warms up. I'll change the fuel filter again and blow out all the jets. then I suspect it will work fine for a week or two, until the next thing.

I think about those Weber carbs sometimes when I am alone and no one is around. I think of the grass being greener. I think of the simple things like my car going a week without something new kicking me between the legs. I think of owning carburetors that I know have all new parts and fittings, where all that is unknown is whether I have adjusted them right.

Thanks. From viewing this message board, In know I am just another poor guy who took a chance and figured he might get by on a rebuild and some good luck with the 35/40s like he has for 15 years on his VWs. I hear people say that once I get them right, they are great carbs. Sure, one day, these carbs may make it to the promise land. I have seen the promise land on this forum! I may not get there with them. . . But I have read about the promise land!

Happy Thanksgiving

Eddie

[MunichTaxi]

What I remeber when I rebuilt mine was a critical seal (or 0-ring) at the top of carb, on the side of the venturi.

That would be Part # 101 in this picture

[Scutch]

I took both carbs apart and did find some very slight debris in the bowls. I switched the fuel filter. It did have some sediment in it.

I cleaned everything up and put it back together and it seems okay for now. We'll see after a few days.

I am getting a fair amount of backfire out of that idle air passage at the top of the carb when warming up. (the little pinhole.) When the car is not totally warmed up and I increase the throttle the carbs will spit gas out of those holes in a loud popping sound.

Can anyone tell me what that indicates?

Munich Taxi, my carb doesn't look quite like your picture, but I know the part you are talking about and those rings are new.

Thanks Eddie

[ggenovez]

Timing is off or a vaccum leak.

The way I set my timing is disconnect the vaccum lines, increase RPM to 3K and set it to the upper range of what the manual states.

Vacuum leaks can be found by spraying carb cleaner on the vacuum lines, around the carb, and intake manifold.

Hope that helps.

[ggenovez]

Oh, forgot to mention,

When you had the carb off, did you check to see if the secondairy was all the way closed? there is an adjustment screw and if it's open it will suck more gas.

A quick way to tell is to get a hose and stick in the secondairy and listen for a sucking sound. compair to the front secondairy.

[Scutch]

The timing is correct. There are no vacuum leaks other than the sloppy way the engine breather connects to the intake manifold. Maybe I will just run a tube direct. Right now the breather outlet on the air cleaner just fits into a fitting on the manifold. It is not airtight, but looks stock.

When I plug that hole while it is idling the rpm change is very slight if at all.

I did set the secondaries to be as closed as they can. That is not completely all the way, maybe because of wear, but I have the adjustment screws so they don't touch.

Once I fixed those, I was able to get the carbs to sync and few weeks ago.

I bought a fuel pressure regulator yesterday. I am not expecting that to help, but I have to try. My fuel psi is 5psi. I'll set it to 2.5psi.

Thank you

Eddie

[ggenovez]

Eddie,

The reason I mention it is because I had a ton of problems with those 2 items. The left most nut on the intake manifold was too tight and it had a huge vacuum leak. Also on the left side of the manifold there might be a accessories line. Try plugging that in.

Also, my 72 had emmission that failed and needed to be bypased. Originaly it called for setting 4' ATDC @ 800 RPM. So I would move the vaccum to the retard dial it in to the above, then enable the advance and adjust the carbs to 800 RPM.

It ran like crap. I could not go up my driveway 30' incline until I set it the way I described.

Also a problem I had was the coil was on backwards. I reversed it and the RPMs jumped up by 2-300.

Between the 3 above I went from something that couldn't go uphill to something that chases.

And I was like you. Timing is right, no vac leaks... can't find the problem. You need to look at every hose, gasket, seal, and every direction. Have you sprayed the base of the carbs all the way around?

[Scutch]

Well,

I THINK I made progress. You were right about the vacuum leak. It was the engine breather to the intake connection. When I put a tight direct hose between those two it kept the car more stable. I test this in the driveway by having the car in drive with the break on. With the old leaking connection I would be lucky to get smooth acceleration. With the tight fit, I barely have a stutter. I will make further checks for leaks.

Also, I put on a fuel pressure regulator. Before doing so my pressure was 5psi. I put on the device and set it to 2.5. The car kept stalling. I cranked it up to 5psi and the car ran fine. SO FAR, it seemed to stop my idling ticks. I rechecked the psi and eventhough it was set to 5psi. The meter said 4psi. So a 1psi drop made a difference. That is hard to believe. Maybe the fuel return is still not working exactly right.

I'll tell you how it runs after a few days -- the real test.

The coughing of fuel out the idle air passage still seems to be there. I will try it again in the morning and see if that got better as well when it is cold. I made the mixture a bit richer as well.

I will consider the timing issue as well. I have had two certified mercedes mechanics tell me it was just right, but I am completely willing to believe that by the book isn't always best. The best way to set the timing would be to put a sniffer on it and adjust until there is a minimum of hydrocarbons, right?

You got your car to chase, huh? I have resigned myself to the idea that the automatic tranny starting in 2nd gear will keep me forever a tortoise at the start. I would love to someday be proven wrong.

Thanks

Eddie

[ggenovez]

Ed,

Don't forget that all the guys that where dealer machanics for these cars have died, are on respirators, or suffer from alzhymers.

How did they test it? by putting a timing light at idle? that might have worked when the car was new but that's no way to take into account wear of the weights in the distributor housing.

If it's right the way it's set it will be right the way I say it.

As for the hydrocarbon, that's way to test for the idle mixture. Another way is to hook up a vaccum gauge and adjust for maximum vacuum (for the idle mixture again)

Good luck.

[Scutch]

I don't have the repair receipt, but I believe they gave me a number at 3000rpms or something close.

These mechanics were both of the very anal type. I'm sure they did it by the book.

But I will double check it sometime.

But still I thought when timing is set right you are burning the most possible gas on each spark and that shows up on the sniffer, in some form. Is it the CO2?

Eddie

[ggenovez]

Setting timing will bring it to the default the factory has as a generic number. meaning it will work with every engine that comes out, no tinkering or timing light needed.

As you advance the timing, the spark will occur sooner and causes a better burn and lower CO, until you reach the point where the engine begins to ping.

As for my comment about settign the mixture with vaccum, this would be your idle mixture. Setting this too lean will cause damage to the cylinders, too rich and you're burning too much fuel.

Also the color of the spark plugs will also indicate what your mixture looks like.