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Zenith 32 IF7

malcolm

malcolm

& Clementine the Cat
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Mr Reno sent a few carbs over including a couple of zeniths. One of the zeniths has cleaned up really well. I've had it apart and blown out all the jets and cleaned all the filters.

What a transformation after running around with that solex 32DIS for a fortnight. Runs really nicely, idles smoothly, and power is up a touch on the Solex especially mid range.

There is one snag though - jab the throttle sharply at low revs and the engine dies a bit before accelerating. Happens reving the engine at idle too. I'm wondering if it might be the accelerator pump which needed a bit of effort to get working and still feels doubtful. I've checked the vacuum advance, that the restrictor is in the vacuum pipe from the manifold, and that there aren't any obvious vacuum leaks. Oh, and I've blocked the vacuum thing that opens the choke (if it's shut) under high vacuum.

Anyone had this symptom before? And anyone know of any botches to get a good seal in the accelerator pump on these things?
 
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Malcolm, this is the same carb as on my car and forms part of the infamous 'Hennessey hot up kit'.!!! I never had any problems so I reckon it's the accelerator pump plunger that's worn. This carb was originally fitted to the later R5 Mk 1's. No botches I'm afraid but I bought an overhaul kit which included the plunger from the carb people in Leighton Buzzard.
Rudi bought one of these carbs from me and as far as I know, it's working fine.
 
I'll give that a shot. For some reason I'd got into my head it would be difficult to get a rebuild kit, though the carbs must be very common.

I wasn't sure an accelerator pump would make so much difference, but I guess they put it there for a reason. Either goiung to be that or an enormous vacuum leak, but the carb is perfect for everything else.
 
I think the rebuild kit cost me £20 or so - from the 'Carburettor Exchange'. Silly question, but has this carb got the water heated flange? If so, have you fitted the R5 water pump and correct hoses etc. The other thing that comes to mind is the state of the gasket between the water heated flange and the carb body. If there is a split in that then you'll get a weak mixture.
 
Adding the water heating is a job for today. :D The gaskets and insulating block look OK, but not new. One thought - are they supposed to have the insulating block? I had to search around for longer mounting studs to fit it in.

I've found the Carburettor Exchange website. Will give tham a call on Monday for a kit (useful to have anyway).
 
Just had a look at my car and there is a 1/4" insulating block between the carb and the manifold. Is the bore in the manifold the same size as the carb? Should be 32mm.
 
Sounds like mine is right then. I've got a 32mm manifold with extra long studs for the insulating block. Didn't get around to fitting the waterpump this afternoon so ducted the air hose to the exhaust manifold which helps the throttle response, though it does it from cold too so I'll get that rebuild kit.

One thing that seems odd on first use is there is more oomph than I'd expected on light throttle, but less than expected on full throttle or high revs. Power delivery doesn't seem as balanced through the throttle range or rev range as I remember the R5s. Might try another exhaust.

Still, running great and starting instantly from cold too (a first for this car).
 
Best to get the carb overhauled first before playing around. It's unlikely to be the exhaust, more likely to be the main jet. When you strip it down check the value of the jet - it may be a 117 (which equates to 1.17mm). I drilled mine out to 118 and it improved things. However, before going to such drastic action, overhaul the carb, set it up as per Page 255 of the Haynes manual. Use the R5 air filter assembly with a new filter. Ensure distributor is working ok, play around with the timing and if all else fails, enlarge the jet as described but only by small increments. If you're clever you can remove the jet without taking the carb top off each time. Then keep on experimenting - it will be worth it as you've already had a taste of more oomph!
 
You might be right there - Occasionally I get the feeling the car goes slightly faster with the throttle released slightly.

But how on earth do you drill a jet out by 0.01mm? Have you got a set of 1000 drill bits? I might have a fiddle once I've done the repair kit thing. Nothing to lose as I've got a spare with a seized mixture screw so could use the jet from that if all goes wrong. And what's the technique for removing in situ? Thought I had it before I realised they aren't magnetic.

I'm going to have to admit to having a Femsa distributor. Though I'm down to my last vacuum advance so may move to something else later. Was the ignition curve for the 4 the same as the 5?
 
femsa distibutors should have all stayed in spain!!
ducellier = much better
malcolm i have got ducellier distributor see other thread as babyblue has not got back to me
found that best results on performance is to mark timing on dist clamp with marker pen then keep advancing slightly until it pinks in top at 20 mph under acceleration then retard just enough to stop pinking
alternativly they do have rolling roads for this sort of thing may be you could do a bulk booking?
 
malcolm said:
But how on earth do you drill a jet out by 0.01mm? Have you got a set of 1000 drill bits? I might have a fiddle once I've done the repair kit thing. Nothing to lose as I've got a spare with a seized mixture screw so could use the jet from that if all goes wrong.
Click to expand...

I bought a cheap set of micro drills from my local hardware store. You'll need to use a small drill held very carefully as well!!
 
Rolling road Paul? Where's your sense of adventure? :D

Had a brainwave on the way home tonight. Unplugged the vacuum advance and everything is much nicer. Good progression on the throttle and the stuttering on sudden throttle opening is gone. No more performance of course as the vacuum advance only advances on light throttle, but without it there is probably a lot of scope for advancing the ignition as a whole.

Makes sense to mess with timing - I've got a much more sensible mixture now so the distributor doesn't need to compensate for a weak mixture any more. Will fiddle this week.
 
of course i know where all this is leading to , obviously you want to win at santa pod next time (when is it ?)
seriously the R5 conversion makes a big difference just a shame i didnt find this forum earlier as threw in scrap 3x complete 5sp 1108 engines/boxes 18 months ago - sorry

good luck paul
 
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