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Re: ZS Problems

To: "Childs, David" <dchilds@lawson.epri.com>
Subject: Re: ZS Problems
From: Charlie Brown <cb1500@erols.com>
Date: Mon, 28 Jul 1997 20:42:18 -0700
Cc: triumphs@Autox.Team.Net
References: <c=US%a=_%p=EPRI%l=USNCEX01-970728203043Z-7949@usncex01.epri.com>
David,

When I was running a single ZS, I vented the charcoal cannister 
through a hole in the backing plate of the air filter. The object of the 
charcoal cannister is to store the fumes from the fuel tank then gently 
draw them off while the car is running. The vacuum created within the 
filter housing is generally enough for that purpose. I think the Longflow 
comes with holes drilled and plastic 1/2" fittings. Mine did 2 years ago. 

What else, if anything, have you got attached to the carb's vacuum port? 
Are you creating a large air leak through that port. How have you routed 
the crankcase ventilation? 

When you say if you remove the filter, the car will run. Does that mean 
just the foam, or the backing plate also. Is the backing plate covering 
the air compensation port for the carb piston chamber? 

I've got one of those red Purolator fuel pumps. They are supposed to 
produce 4-7 psi. If you're only getting 2.5 psi, something's clogged or 
not working properly. That will definately cause the highway driving 
problem you're having. The pump can be disassembled for inspection by 
unscrewing the shorter of the two 7/8" end fittings. Do not, repeat, do 
not try to remove the housing cover. I destroyed a perfectly good pump 
finding that out. As the fitting comes off, watch how the parts come out 
for proper reassembly. There may be a small piece of gas tank crude in 
there, keeping the pump from producing proper pressure. If there's no 
dirt inside, perhaps it's time for replacement. Stick with the red pump 
and a pressure regulator dialed to about 3 psi. 

Unfortunately, later ZS carbs are best tuned with a CO meter. I've got a 
unit that's similar to the Gunston (sp?) that's carried by Moss, JC 
Whitney, etc. Some folks have good luck with a Color Tune. 

Your best be at this point is to compare the backing plates of the OEM 
and the Longflow, looking for any differences that may be causing air 
blockage. If necessary use the OEM filter to get the car working 
properly, then change over once you know the car is running right. I 
think I'd be inclined to cap off the vacuum port during the initial 
mixture setting to make sure the car is running only on the air/fuel 
coming through the venturi. That should also make any adjustments 
more noticable. Then, hook it up to the crankcase ventilation, using the 
proper restriction fitting between the 1/2" hose and carb tube.

Good luck,
Charlie B.
Spitfire Pilot
> 
> Has anyone used the Longflow air filter on a Spit with a ZS carb?
> Has anyone successfully removed the charcoal canisters?
> 
> Here is what I have found.
> If I remove the charcoal canister and plug the hole on the carb the car
> will
> not start.  If the car is running and the hole is plugged the car will
> stall.
> Note when the car runs all other holes on the canister are plugged.
> 
> If I remove the air filter (big black can) the car will not run smoothly
> over
> 4000 RPMs.
> 
> I have tried tuning the car with the air filter off.  Runs fine up to
> 5000.
> It seems the problem is when I get it on the road and put the car under
> a load
> that I lose power and does not run correctly.  However, as soon as I put
> the old air filter
> on it it works.  It should also be noted that when I tested it with no
> air filter I used
> the air filter screws.
> 
> I have a fuel pressure gauge in line along with a regulator.  I have
> installed a electronic
> fuel pump.  The electric fuel pump is a red labeled Prolator (SP?).  As
> I recall this pump
> could deliver more fuel than the blue label pump.  My fuel pressure
> gauge will not exceed
> 2.5     PSI.  To get 2.5 PSI I need to set the regulator to 3.5 or better.
> Why?  Note my old
> mechanical fuel pump would deliver 2 to 2.5 PSI.
> 
> Here is my tuning procedure.  I adjust the A/F ratio with the special ZS
> tool until
> I get my idle to a maximum.  Is there some other way?  I make changes in
> ¼ turns or less.
> I do not see much of a change between ¼ turn too rich and ¼ turn too
> lean.  Is this
> normal?
> 
> I have new clear glass fuel filters that do not seem to be collecting
> any crud.  Could
> I have a partly blocked line?
> 
> I hope that someone out there can help me with this one!  I don't know
> what else
> to try.
> 
> Thanks
> Dave C
> 
> 79 Spit (stupid ZS carb)
> 75 Spit (parts)


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