Solex PDSIT twin carbs on 78 Bay - RH carb cannot adjust mixture

Hi All,

When I cut power to the central idling circuit on my 78 T2 with 2.0 Type 4 engine, the van runs on the LH carb only - the RH mixture screw does nothing at all. I have confirmed with a Gunson Colourtune on one of the RH cylinders that there's a nice blue spark but nothing else. If I apply some throttle or reconnect the power to the central idle, then the RH bank will start firing.

If the van is left to idle for a few minutes with the central idle disconnected then it just runs on the left two cylinders - exhausts on LH are hot at manifold, RH side is stone cold.

Bit of background:
Carbs rebuilt a couple of years ago (using a mix of Ratwell and Itinerant Air Cooled procedure) following a roadside recovery for engine cutouts (think I got the rebuild kit from JK) and van has never run properly since. Will drive OK and seems to have good power; but popping out of RH exhaust when coming off throttle probably due to RH cylinders not idling properly.

Air/fuel passages blown through with compressed air on numerous occasions. Even got desperate and used some cleaning wires as well even though that's generally not advised. Carbs were originally set to Bentley specs for throttle stops although I've now backed them off fully although it's made no difference (LH still runs like a dream and mixture screw does have an effect).

Have checked valves (twice), replaced distributor cap, HT leads, spark plugs, checked for Vacuum leaks etc. Also swapped idle jets for the non-electric type (55s) to rule out any electrical problems. Cannot find anything obvious.

Does anyone have any idea of what this could be? I'm hoping it's something that someone's seen before and it's an easy fix but that's probably just wishful thinking.

One other thing. The van used to idle quite high (around 1200 at a guess). It looks like a previous owner had jacked up the idle RPM using the throttle stops and the central idle didn't seem to be doing anything before. I thought this was because maybe they didn't know how to set these carbs up but now I'm wondering if they had the same problem as me and just gave up and jacked up the idle speed.

Thanks in advance for any advice.

Cheers

 

Each carb also has a mixture screw, have you tried adjusting that?
And the idle jets are in the cut-off valve. Is it working?

 

Have you tried setting them up using the ‘Itinerant Aircooled’ process? Easier to understand than using Bentley.
http://itinerant-air-cooled.com/viewtopic.php?t=7767
It recommends ignoring the Bentley process for setting the throttle stops…

 

Thanks for the replies. My initial post did ramble on a bit but essentially the problem is that the right mixture screw does nothing at all, while the left one adjusts the mixture as you'd expect. I am talking about the main mixture screws at the side of each carb, with the central idle circuit disabled and out of the equation.

Have followed the itinerant air cooled guide as much as is possible until it gets to setting the mixtures when I get stuck. The electromagnetic idle jets have both been replaced for the non-electric type i.e. just plain brass screw-in '55' pilot jets - I did this to remove the possibility of problems with the cut-offs. Again, LH mixture screw works fine, RH (both electrical and non-electrical type) do nothing. People have suggested the RH must be blocked - I've tried compressed air, cleaning wire etc but nothing makes any difference and I get a good soaking with petrol spray when I blast the jet or the carb with compressed air so all seems OK.

 

If I have read this correctly, you are saying that it idles on the left cylinders only? In which case, no amount of adjusting the right mixture will make any difference. Have you put a snail meter on both carbs? It sounds like the right hand carb needs the throttle plate adjusting. (Assuming you have compression, and no air leaks that side) what happens if you screw the throttle stop in? Does the revs rise?

 

All I can think off is to get another RH carb body to try.

 

Or maybe you have undetected air leak somewhere on non-firing side.

 

I can get the RH side to idle if I screw the RH throttle stop in a lot - i.e. equivalent to opening the throttle and way past the 'contact plus one turn' recommended for idling on pilot jets.

Currently both throttle plates are closed (throttle stops not touching) - I have seen this recommendation on a YT video from someone else with aftermarket exhausts (Empi GT) and if idles fine on LH carb only. I did have the same issue though with both throttle stops set to 0.1mm gap as per Bentley base settings.

Compression was checked a while ago and from memory was around 110-120 on both RH cylinders. The van has barely been driven since that check.

I have been thinking possible air leak on RH side also - I'm fairly certain there's nothing from the carbs or vacuum pipes on the RH side have checked numerous times. What's the likelihood of a cracked cylinder head affecting both RH cylinders? If it was a single cylinder I'd be thinking that but both RH cylinders leaking at same time?

 

This seems like a good suggestion. My engine ran rough when I got it many years ago. Twiddling the threaded adjustment rod on the RH carb (the one attached to the cross bar, not the choke) brought the two sides into balance. You release the nuts each end and twist, rather like aligning the steering. It needs a snail meter to do this reasonably accurately, but you can hear whether this is making a difference without one.

As to the mixture screws I'd set them up initially equally at 2 1/2 turns, and sort them out more accurately later. I've got a Gunson's Gastester and it showed that 2 1/2 turns is pretty close.

 

Re: the snail meter - no I don't have one I have the cheap carbtune with the 'bouncing ball' - TBH I don't think it's accurate at all but I can feel strong vacuum on the RH carb which I would have thought should indicate no leak - at least good enough to get the cylinder to fire. Both screws have been tested at 2.5 and 3 turns.

 

I had the "bouncing ball" carb balancer and eventually got a snail. Neither are terribly accurate. The thing that helped me a lot is the Sarran 1955 video. . In that he's using a carb balancer, but he's set up the carbs so well that no further adjustment is needed.

 

That Sarran 55 video is excellent I saw it a while back. I wish I could get to the point of balancing the carbs and setting the mixtures.

I think I'm going to have to go back to basics on this. I'll whip the RH carb off, strip it down again, clean it again but this time with an ultrasonic cleaner I've just ordered (well I've been looking for an excuse to buy one), check all the mating surfaces are smooth, make some new gaskets if necessary and try again.

If that doesn't work I think next option would be Zed's suggestion of trying another RH carb body. I'll post an update here if I manage to get it sorted.

 

I would also check the standard "does the idle shutoff solenoid click" on the right hand carb. It could be as simple as that has failed - swap the solenoids over ... see if the fault moves.

 

Thanks Mike. That appeared to be working but i swapped both pilot jets to the non-solenoid plain brass type just to rule that out and still no joy. If I move RH jet to LH carb the LH carb continues to work fine. It's a real head-scratcher this one I'm hoping when I dismantle it all there'll be an obvious tear in a gasket or something, or when I clean the carb again i find a lump of crud in the bottom of the ultrasonic tank. Failing that, the RH carb will be heading out of the nearest window.

 

I spent last night in bed trying to reason this out. I suspect if you are getting no power on the RH carb at idle, then the main butterfly is not set right. Check you have a 0.1 mm gap when it's sat on the throttle stop. Sarran uses a depth gauge measuring the distance from the mouth of the carb to the high side of the flap when closed then adds 0.1 to push the flap open and then sets the stop screw, though it's hard to see that part. Although the geometry isn't quite the same you can use a 0.1 mm feeler gauge in the gap providing both carbs are done like this. This is what he does with the 0.6 mm welding wire to set the choke.

Mind you if your spindle bushes are worn this will upset stuff somewhat.

 

Andy - good to know I'm not the only person who thinks about carb tuning when I'm trying to get to sleep. I have tried the 0.1mm wire on both carbs to set the throttle stops and unfortunately it made no difference.

You might be onto something with the spindle bushes though - I will be checking for play on the throttle plate when I take the carb off for another clean. From memory there was none when I last checked but this is now a case of going over absolutely everything again.

Thanks for all the suggestions everyone. Hopefully I can get this sorted soon and post the fix here.

 

Hi, all the driver's side carbs I've took apart have more spindle wear. Linkage pressure?
All the guides say, with wear - impossible to set up. Well I think still should run...
The bushes are plastic coated, but the spindles wear too (pitting).

 

Have you checked float height? If Fuel level too low might affect idle more than higher revs?

 

So do I.

 

Took the carb off today. No noticeable play on the throttle plate, but the brass 'spring' that holds the float spindle down was missing which could cause a fuel level problem as per Tom's suggestion. I'm not getting too excited about that one though as I'm sure I heard a 'ping' the other day when I took the lid off that carb and think that spring might have only dropped out in the last couple of days.

I cleaned the carb with the ultrasonic cleaner that arrived today and despite me having 'cleaned' it two years ago in a bucket of vinegar/baking soda, I was surprised at how much gunk was at the bottom of the tank.

Plan for tomorrow, weather permitting will be to put it all back together and locate the missing spring (or make one from aluminium if I can't find it as I believe replacements are unobtainable).

Hopefully a combination of a spotlessly clean carb, float retaining spring in place and new gaskets will sort this once and for all.