Zenith carb baseline settings source?

[dang]

I'm using a set of Zenith carbs I took off my '69 coupe for my '69 E3. They sat on the shelf for maybe five years so I took them apart, made sure everything was clean and open and put them back together. I didn't change any settings and the worked well on my coupe. After getting the engine running I'm having a hell of a time getting them to run anywhere close to smoothly. Popping and spitting and won't rev without cutting out and popping more.

I'd like to start with the basics and put the carbs at a known starting point if there is such a thing. Any good sources for basic tuning? I didn't have any luck here.

Also, the carbs do not have chokes. I took them off years ago because they started acting up and I hardly need a choke where I live. I used them that way for years on my coupe with no issues.

 

[HB Chris]

Check the accel pumps, they should squirt a good stream with engine off. They aren’t in the rebuild kits. Carl has them.

 

[dang]

Squirting but maybe more like they have enlarged prostates.

 

[dang]

I have a message into Carl. Other online prices show $150 for both. Yikes!

 

[Honolulu]

Are you (how are you) certain the problem is in the carbs? Too often we (certainly includes me) incorrectly assume that poor running is the fault of the carburetors.

 

[dang]

Are you (how are you) certain the problem is in the carbs? Too often we (certainly includes me) incorrectly assume that poor running is the fault of the carburetors.

Good question, and one I thought about last night. I know the long block is good, compression is all very good and consistent per Mike Goble (I got the long block from him). I don't have any reason to think otherwise, but I do plan on checking the valve clearance today. I have a smoke machine so I'll also check for vacuum leaks to eliminate that also. I have the timing at TDC with the advance line connected but have tried every combo in the universe. It runs best at TDC. Right now the rear carb seems to be the only one popping and back firing.

 

[Stevehose]

Disconnect and plug the advance line and check for leaks. Have you adjusted mixture settings?

 

[dang]

Disconnect and plug the advance line and check for leaks. Have you adjusted mixture settings?

I've tried everything carb related. Since there's no chokes I covered most of both inlets with tape to test it and it ran better but still popped on the rear carb. Adjustments didn't help so I'm going to check for vacuum leaks and valve adjustment next.

 

[Stevehose]

yes sounds lean so leaks are very possible - base gaskets, gaskets between head and manifold, vac ports.

 

[bavbob]

Assume you went through the Tech Literature on the Zeniths on this site. Besides timing and adjusting the choke settings, I have run a vacuum line from one carb to the other as per DeQ and it smoothed things out nicely. Also I believe the floats are very picky and have to be adjusted perfectly. Also those little square boxes on the sides are like cold start valves so you need to ensure the work, I cannot recall what I did to test, hot water, hair dryer. They work like thermostats and if they are stuck, you may have too much gas when warm or too little when cold.

 

[deQuincey]

I'm using a set of Zenith carbs I took off my '69 coupe for my '69 E3. They sat on the shelf for maybe five years so I took them apart, made sure everything was clean and open and put them back together. I didn't change any settings and the worked well on my coupe. After getting the engine running I'm having a hell of a time getting them to run anywhere close to smoothly. Popping and spitting and won't rev without cutting out and popping more.

I'd like to start with the basics and put the carbs at a known starting point if there is such a thing. Any good sources for basic tuning? I didn't have any luck here.

Also, the carbs do not have chokes. I took them off years ago because they started acting up and I hardly need a choke where I live. I used them that way for years on my coupe with no issues.

@dang

a humble comment, there are many ways of rebuilding these zenith carbs wrongly, if you made a mistake during the process then you have to go back and correct, you will never get good performance out of bad rebuilt carbs (not saying it is your case, only saying it happened to me)

i.e. if you rebuild them and you are asking for table settings now, i would be suspicious about it, table settings are essential

table settings are extremely delicate, if you handle them wrong, you would probably never be able to fine tune them in the car later

i can make a summary of table settings for you, but it will take some time to do it properly

removing the chokes surprises me, i would like to understand what did you removed exactly, i.e. you can probably remove the electric solenoid, but the chokes are essential to a good cold start, you can not remove chokes no matter if you live in bahamas,



p.s. your problem may have very little to do with the accel pumps

 

[deQuincey]

Assume you went through the Tech Literature on the Zeniths on this site. Besides timing and adjusting the choke settings, I have run a vacuum line from one carb to the other as per DeQ and it smoothed things out nicely. Also I believe the floats are very picky and have to be adjusted perfectly. Also those little square boxes on the sides are like cold start valves so you need to ensure the work, I cannot recall what I did to test, hot water, hair dryer. They work like thermostats and if they are stuck, you may have too much gas when warm or too little when cold.

agree bob, but in my opinion Dang should go back to the table first, if he does not know where he is it will be very difficult to continue this erratic journey
as to the additional air valves, their presence depends on the version of the carbs, first euro versions do not have them for example

 

[deQuincey]

there are al least 4 different table settings,

close point of primary buterfly
close point of secondary buterfly
limiting closing of top buterfly for cold start at 3mm by means of the triangular membrane (the most difficult one)
setting the iddle screw at basic position

if you need it i will prepare some info backing it with pics of one of my several rebulids, preferably per email

 

[dang]

@dang

a humble comment, there are many ways of rebuilding these zenith carbs wrongly, if you made a mistake during the process then you have to go back and correct, you will never get good performance out of bad rebuilt carbs (not saying it is your case, only saying it happened to me)

i.e. if you rebuild them and you are asking for table settings now, i would be suspicious about it, table settings are essential

table settings are extremely delicate, if you handle them wrong, you would probably never be able to fine tune them in the car later

i can make a summary of table settings for you, but it will take some time to do it properly

removing the chokes surprises me, i would like to understand what did you removed exactly, i.e. you can probably remove the electric solenoid, but the chokes are essential to a good cold start, you can not remove chokes no matter if you live in bahamas,



p.s. your problem may have very little to do with the accel pumps

My logic is that since the carbs worked well on my coupe I didn't want to change anything unless I rebuilt them completely, which I'm trying to avoid. I took them apart, cleaned what I could within reason and put them back together. I didn't change any settings and they were basically very clean to begin with. The accelerator pumps seem to be working now that I spent more time making sure they're cleaned up and the motor accelerates okay with the exception of popping and hesitating. I didn't remember the nozzles being to tiny before but they're working now.

When I first got my coupe the choke assemblies on the carbs were not working right. I gave a half-hearted attempt to fix them but decided just to remove them all together (butterfly valves, controls, everything). The motor always started right up but idled low (expected) so I would keep the rpm's up for a minute and it was good to go. Was it the right thing to do? Probably not for most but I'm fine with it.

The takeaway from all of this is with a healthy long block, good ignition and no vacuum leaks the motor should run way better than it is, regardless of cold start. I have to eliminate igntion (all new components), vacuum leaks and valve adjustment as the problem, then I'll go back to the carbs.

If I were to walk up to my motor right now and not have any history of what's been done I'd start with vacuum leaks and valve adjustment. That's where I'm at.

 

[bavbob]

When you pull a plug, it should have a story to tell. It sounds like a rich story to me.

 

[stphers]

Are you sure that this jet is in there ? # 3 in the diagram, one per carb I have seen a few " rebuilt " carbs with this jet missing easy to do or the bottom bakelite gasket, the o rings are damaged or missing

Some reason, I cannot attach picture in realoem look at picture 13/11a

Thanks, Rick

 

[dang]

Are you sure that this jet is in there ? # 3 in the diagram, one per carb I have seen a few " rebuilt " carbs with this jet missing easy to do or the bottom bakelite gasket, the o rings are damaged or missing

Some reason, I cannot attach picture in realoem look at picture 13/11a

Thanks, Rick

There is no #3 in that image. I didn't take anything off that I didn't clean and put back one at a time.

 

[dang]

When you pull a plug, it should have a story to tell. It sounds like a rich story to me.

Here's the plugs. They all look the same. Looks more rich than lean but why would it run better when I cover most of the air inlets?

Also, valve clearance is good.

 

[stphers]

On mine it shows up In the right hand picture, it is the far right hand jet, it can fall out very easily it just drops into the housing if that is missing, your described symptoms will show up

 

[dang]

On mine it shows up In the right hand picture, it is the far right hand jet, it can fall out very easily it just drops into the housing if that is missing, your described symptoms will show up

I looked up a '69 E3 if that makes a difference in images. I'll check for the jet if I need to pull them apart again but I didn't have any left over parts so that's a good sign.