Zenith carb issues

[DaveSeries1]

Hi guys, this will be one of many questions I'll have now that my car is up and running. It seems I can't get the correct amount of fuel to the rear carb. It runs pretty well, but with the air screens off and I rev it up, there is no fuel coming from the accelerator jet, and very little from the main jet. Front carb is fine. Both carbs were fully rebuilt, and I dismantled the rear carb again and found nothing wrong. Float level was good, all passages clear. Idles fine and seems ok on the road. With the carb top off, I pushed the accelerator piston multiple times and no fuel discharge. Any thoughts? Dave

 

[husky drvr]

Dave,

The most likely problem with the accelerator pump would be one, or both, of the check valves are inoperative or missing.

I think the one in the float chamber is a "reed" type valve. The one under the delivery port is a ball bearing.

The fuel pump should have the capability to pump excess fuel volume to the carbs. Since it is a common delivery system, fuel should be pumped

to both carbs until the floats close both needle valves. If you are experiencing a fuel deficit to the rear carb, you should check for an obstruction

between the line junction to the first carb and the rear carb's needle and seat. You might possibly check the fuel pump output.

Hope this helps,

 

[junkman]

I understand you'd like to keep the original set up ,BUT, you will be doing yourself a great service if you ditch the zeniths and put a single Weber on. The purists may say keep them, and they're entitled to their opinion. I'm not the only one that will tell you go Weber, speaking from experience, you'll thank me. There is a reason I have at least 6 complete Zenith set ups laying around in boxes that nobody wants. Just my opinion.

 

[alpine_64]

I understand you'd like to keep the original set up ,BUT, you will be doing yourself a great service if you ditch the zeniths and put a single Webber on. The purists may say keep them, and they're entitled to their opinion. I'm not the only one that will tell you go Webber, speaking from experience, you'll thank me. There is a reason I have at least 6 complete Zenith set ups laying around in boxes that nobody wants. Just my opinion.

You mean "Weber"

As for the single down draft, agreed it's the easiest set and forget setup... DCOE are also set and forget....but the "set" can take some time.

If the Zeniths are freshly rebuilt and the throttle spindles and bodies are ok...I'd run them till they show signs of wear... Then consider alternative carbs.

But also... Just my .02 as well.

 

[beamdream]

Dave,

The most likely problem with the accelerator pump would be one, or both, of the check valves are inoperative or missing.

I think the one in the float chamber is a "reed" type valve. The one under the delivery port is a ball bearing.

The fuel pump should have the capability to pump excess fuel volume to the carbs. Since it is a common delivery system, fuel should be pumped

to both carbs until the floats close both needle valves. If you are experiencing a fuel deficit to the rear carb, you should check for an obstruction

between the line junction to the first carb and the rear carb's needle and seat. You might possibly check the fuel pump output.

Hope this helps,

Hi guys, this will be one of many questions I'll have now that my car is up and running. It seems I can't get the correct amount of fuel to the rear carb. It runs pretty well, but with the air screens off and I rev it up, there is no fuel coming from the accelerator jet, and very little from the main jet. Front carb is fine. Both carbs were fully rebuilt, and I dismantled the rear carb again and found nothing wrong. Float level was good, all passages clear. Idles fine and seems ok on the road. With the carb top off, I pushed the accelerator piston multiple times and no fuel discharge. Any thoughts? Dave

Are we talking WIA or WIP Zeniths ?

 

[bernd_st]

There is a reason I have at least 6 complete Zenith set ups laying around in boxes that nobody wants.

If you don't need them, just sent them to me. I'll rebuild and make good use of them within the community ;-)

 

[DaveSeries1]

They've just been completely rebuilt after cleaning in an ultrasonic parts cleaner. Two rebuild kits and careful reassembly, check valves are there and clean. Front carb is fine. With top cover off, I push the brass plunger down repeatedly, and no fuel sprays out. I wonder if the piston is worn and there is too much clearance between the piston and walls to draw a vacuum in.

 

[bernd_st]

Hi guys, this will be one of many questions I'll have now that my car is up and running. It seems I can't get the correct amount of fuel to the rear carb. It runs pretty well, but with the air screens off and I rev it up, there is no fuel coming from the accelerator jet, and very little from the main jet. Front carb is fine. Both carbs were fully rebuilt, and I dismantled the rear carb again and found nothing wrong. Float level was good, all passages clear. Idles fine and seems ok on the road. With the carb top off, I pushed the accelerator piston multiple times and no fuel discharge. Any thoughts? Dave

Check the accelarator non return valve on the bottom of the float chamber and whether the small steel ball on the upper non return valve Is properly there and in place. Have seen many Zeniths without the ball .

P.S. I'm not neccessarily a purist, but just keen to repair the original Zeniths. They are great carbs and still the best set coming from the factory. Just my 2ct. ;-))

 

[DaveSeries1]

The ball is there and not stuck. I do wonder if the non-return valve in the bottom of the chamber is stuck open as a tiny amount of fuel will get into the piston area, but not enough to fill the chamber. I know the ball is good and not stuck. I do like the Zeniths very much and had them on my original S1 many years ago. Once set up, they never gave me a bit of trouble.

 

[bernd_st]

They've just been completely rebuilt after cleaning in an ultrasonic parts cleaner. Two rebuild kits and careful reassembly, check valves are there and clean. Front carb is fine. With top cover off, I push the brass plunger down repeatedly, and no fuel sprays out. I wonder if the piston is worn and there is too much clearance between the piston and walls to draw a vacuum in.

There MUST be fuel spraying out the nozzle if you push the brass plunger down, already on the first stroke. The plunger has to be a snug fit in the bore.They are good if they just move in the bore without sticking...

 

[DaveSeries1]

If I prime the chamber and push it down, it'll spray, but will not refill the chamber after that.

 

[bernd_st]

Non return valve wrong or piston having too much play...

 

[junkman]

You pay shipping Bernd I will send them to you!

 

[alpine_64]

Check the accelarator non return valve on the bottom of the float chamber and whether the small steel ball on the upper non return valve Is properly there and in place. Have seen many Zeniths without the ball .

P.S. I'm not neccessarily a purist, but just keen to repair the original Zeniths. They are great carbs and still the best set coming from the factory. Just my 2ct. ;-))

They were the most powerful setup the factory used for sure.... But they certainly have their own "character" ... I dod like the induction roar on them and how it used to harden about 3000rpm.

 

[bernd_st]

I like their excellent and stable idle plus superb power output uphill on full throttle. They must be in good nick however to work up to their capabilities...

 

[DaveSeries1]

Guys, Success! It was the check valve in the bowl. Changed it out with a spare, worked fine. Thanks very much for the input and suggestions. This group has been a big help during my 4 1/2-year restoration.

 

[beamdream]

If you're prepared (able) to work on them, it's well worth the effort.

I get that most people are easily frustrated with them and take the Weber option, but, IMHO it doesn't get much better than listening to a pair of well tuned Zeniths in full cry.

 

[alpine_64]

If you're prepared (able) to work on them, it's well worth the effort.

I get that most people are easily frustrated with them and take the Weber option, but, IMHO it doesn't get much better than listening to a pair of well tuned Zeniths in full cry.

Try a pair of well tuned DCOE......

 

[bernd_st]

Guys, Success! It was the check valve in the bowl. Changed it out with a spare, worked fine. Thanks very much for the input and suggestions. This group has been a big help during my 4 1/2-year restoration.

Bingo ! Another pair of Zeniths rescued from the bin ;-)