ZS Carb - how hot is too hot?

[Nunyas]

Well, I'm back to that annoying fuel supply problem I have with my B. After the drive I had with Stewart this past Saturday, we noticed that the ZS carb on my B gets pretty darn hot, *much* hotter than the Webber that's on Stewarts car, IMO. Darn near burn my hand hot if I leave my hand on there (on the ZS) long enough.

We looked it over, I have the ZS heat shield and the front cover to allow the carb to pull heated air from around the exhaust manifold in place. I also have the wood "heater" bit in place, gasket between the heater and carb, and a gasket between the heater and heat shield mount. But I don't think there's a gasket between the heatshield mount and manifold.

I had some difficulty getting my car to restart after the drive that night. I'm not sure what that was about. I had trouble restarting my car after driving 20 minutes earlier this week too ( was on a particularly hot day ).

I thought maybe it was running too lean the last time it wouldn't restart (idle wouldn't come down under 1K RPM after fully warmed). So, I've richened it about a full turn. The idle now comes down to a "smooth" 600RPM after the car is fully warmed. However, it still has an "uneven splashy pop" to the exhaust note, though that may be an artifact of the emissions components.

I still need to check that "vapor" separator in the boot. Is there anything else I should be checking out while I'm crawling around under the bonnet and car this weekend?

I'm putting her on the emissions tread mill next week.

thanks,

 

[kennypinkerton]

There should be a asbestos (fuzzy wool looking) pad on the heat sheild metal... If it's there - don't play with it, but if it's not there, that may be your problem. There are newer and better heat sheilding materials around to replace it with. Do a search here... seems like several guys have done threads recently (since I've been here anyway) about the materials they used, and where they bought it.

WARNING!!!
Remember, Asbestos fibers are finer than fiberglass insulation fibers... if you knock any loose and accidentally breath them in, they will be in your lungs until you die... and they can and will cause lung cancer too.

 

[PAUL161]

Rob, Gas will start to vaporize around 150 degrees. Not sure of the exact figure. When it does, vapor lock,(air in the fuel), will start and is probably why the car was hard to start after shutting down. It seems to me you have to lower the heat in the engine compartment. What's causing this is something you will have to work out. Is the coolant running at the proper temp? Is the air flow in the engine compartment restricted? Are all heat shields in place? Good luck on finding the problem. When you do, post it for all to read. /ubbthreads/images/graemlins/hammer.gif /ubbthreads/images/graemlins/cheers.gif PJ

 

[Nunyas]

hmmmmm... the engine temps (according to the temp guage) stay middle normal or a little above (on really hot days) as long as I keep moving. In stop and go it'll start working its way up. I'm using a 160 stat. Air flow seems normal for stock, IMO.

ZS carbs have pads on the hot side of the heat shield? *grumble* I didn't know that... I guess that's another reason to look harder at some heat shield pads... I was beginning to think that the heat might be radiating through the bolts to the carb. The shield on the car, ATM, seems to be some sort of pressed fiber board that's about 1/4" thick, and then metal bits up front for the pre-heated intake.

The current behavior of the car seems to have a sweet spot around 50 - 60MPH. At those speeds, the temps seem to be better controlled; the guage sits dead middle of the guage range. At freeway speeds (70 - 80MPH), the heat seems to build up slowly but continuously. In stop and go city driving, how quickly the heat builds is dependant on a few things like how i'm driving, current air temp, etc.

 

[kennypinkerton]

I think the pads should only be on one side... Sounds like you have them. Mine are a little tatty looking.

 

[Nunyas]

nope... there are no pads on my shield. I put it on well after I got the car, because I didn't know what belonged there. /ubbthreads/images/graemlins/nonod.gif

 

[PAUL161]

Rob, From what Kenny just said, you might have found your problem! Missing heat pads on the shield, but I'm not up on a 76 ZS setup so I'm just guessing. /ubbthreads/images/graemlins/crazyeyes.gifPJ

 

[tony barnhill]

Go to your Moss catalog - you're missing the entire heat shield (#113 in illustration)....it keeps the carb from getting too hot & the gas from boilingcausing vapor lock....on a ZS carb, the heat shield is a formed piece of heat resistant material that bolts onto the carb plate (#114 in illustration).

 

[kennypinkerton]

And guess what else the moron designers did? The catalytic converter is directly under the ZS carb... Hottest part of any exhaust system. /ubbthreads/images/graemlins/smirk.gif Then they put a leaky mechanical inertia switch above it on the firewall too. You gotta wonder sometimes, if they actually thought about any of that when they designed it.

 

[tony barnhill]

The heat shield separates the carb from the cat - which by the way turns almost red it gets so hot!

 

[jlaird]

Sounds like a good thing to get rid of, dangerous.

 

[Stewart]

I dont remember if I saw this piece on your car last week but if your missing it your more than welcome to install mine to see if it will solve the problem.

 

[tony barnhill]

No photo?

 

[Nunyas]

Sorry, been house sitting over the weekend and working on the 'B.

I've got bits that Stewart posted pics of. I also have the shroud that allows the intake to draw warm air from around the manifold.

I looked at the vapor separator in an attempt to make sure it wasn't part of the problem. I found the separator had a small amount of fuel in it. So I cleared it out, blew through it and got good air flow, then blew through the line that went into the tank and got good air flow with the fuel cap off, and blew through the line the goes up to the charcoal canister and got good air flow too. I suspected the fuel that was in the separator probably was stuck there because the separator was just laying flat on the trunk floor. So I found the spot where it was supposed to be mounted and set it up there. Hopefully, this'll make refueling the car easier. I think I was having refueling issues because the vapor separator had some fuel in it preventing air from escaping the tank. With the separator properly mounted any fuel that accumulates in it will drain out into the gas tank.

I checked my plugs today, they looked good for the most part. Golden brown, #4 was a little darker than the others though. I opened the gaps to .045, but I think I'm going to set them back to .035. The engine doesn't like to pick up from idle with the plug gaps at .045.

I somehow lost my gas cap while I was fiddling around with the vapor separator. /ubbthreads/images/graemlins/rolleyes.gif I walked up and down the street I drove down after doing that work looking for the cap but it was no where to be found. That kind of sucks cause now I have to wait for a new gas cap before I can go do my emissions test...

Vapor lock hit me on my test drive today. I went back into Angeles Crest HWY. Around 35 or 40 miles the vapor lock set in. Luckily I recognized it coming and found a turn out to pull off into before it forced me off the road. Engine temp was dead center "normal" when it happened.

Bright side of things, for those of you that have been following my fuel supply issues, the fuel filter no longer goes completely empty. Even when the carb vapor locked on me, the fuel filter near the carb still was about half full.

My catalytic converter is mounted under the driver's floor pan directly below my feet. I don't think the heat from it is directly radiating the carb. I could be wrong about this, but I just don't see how it could happen while driving down the road.