Vdub'z Dual Solex Diagnostic Thread

[vdubz]

Hi, I have followed the dual Solex carburetor adjustment procedure in the Fuel Delivery Forum, but I have come to a problem, i have got to the part of fine tuning the mixture with the cutoff's. I removed the right side cutoff wire and the idle dropped about 300rpm, i then put the wire back on and then removed the left side cutoff wire and the engine just stalled, so i richened up the right carb and tried again and again but the engine just kept stalling as soon as i removed the wire, what could be causing this problem?? any help would be much appreciated

[RSorak 71Westy]

The left side carb is the only one the engine is idling off of. Your problem is on the right side. I'd quess the right side carb idle circuit is clogged. When was the last time it was rebuilt?

[vdubz]

Hi, I have just recently rebuilt them, i cleaned them in an unltrasonic cleaner and then after that i blow them through with compressed air, so i very much doubt its clogged. Also i must add that there seems to be another problem with one of the spark plugs, it looks like it has not been firing much? as its very clean, i have checked the spark and its all ok, so maybe lack of fuel?

[RSorak 71Westy]

Yes that far left plug has not been firing, if you say it has spark, the problem is a lack of fuel or a vacuum leak to that cylinder. Since the other plug that operates off that same carb is firing....I vote for a vacuum leak .

[Amskeptic]

seems to be another problem with one of the spark plugs, it looks like it has not been firing much? as its very clean, i have checked the spark and its all ok, so maybe lack of fuel?

Did that left spark plug come out wet and washed?
Or was it dry and clean?

If it was wet - definitely not contributing!
If it was dry, definitely contributing too much!

The other plugs look filthy rich.

Are you able to discern an engine whose idle is dropping due to too much fuel versus not enough? Those black plugs are pretty nasty.
When you noted that the right side would not idle by itself, you might have helped us along by telling us from which cylinder the albino spark plug came from
Is your vacuum retard hose off during this synchronization test?
Commonly, you can't get the engine to run on two cylinders when it is not feeling well. We need to get this spark plug anomaly squared away.
Colin

[vdubz]

Hi guys thanks for your help, i will explain a bit more(should have done that) When i first got my bus it was running rough, so i decided to start replacing/rebuilding stuff, the parts i have renewed are the coil, spark plugs, leads and a svda distributor with electronic ignition(i have plugged the retard hose coming from the air cleaner) i removed the carbs and cleaned them in an ultrasonic cleaner and rebuilt with new gaskets, set fuel level to between 13-14mm and refitted them to the vehicle, i then fitted a new electric fuel pump and a pressure regulator set to 2.5psi. I started the engine it sounded very good but there was lots of black smoke coming out the exhaust(looked like a diesel) so i tried adjusting the mixture screws but even when i set them all the way in it didnt make any difference, so i removed the spark plugs and this is how they looked(above picture^) So i then removed the carbs again and set the fuel level a bit lower to 17mm reffited them and BINGO she runs great with no smoke, so i started going through your adjustment procedure and thats when i come to the problem with the cutoff. The plug that looks like it hasnt been firing much is the right side front(think its cylinder 2) which is side that dies when i pull the wire from the left carb, when i remove the plug i cannot smell any fuel on it but it looks like it has a very fine coating of oil(makes the plug look gold). I have set the valves to 1 1/2 turns in from contact. Also i set the throttle plate gap correctly and also tried winding the throttle stop screws right out(incase the gap was to big some how) but that did not help.

[grandfatherjim]

What year/engine is this? Originally, dual carb engines did not have hydraulic lifters, so the valves should be set with a gap, which I think is 0.006" but may sometimes be 0.008" depending on year.

[vdubz]

What year/engine is this? Originally, dual carb engines did not have hydraulic lifters, so the valves should be set with a gap, which I think is 0.006" but may sometimes be 0.008" depending on year.

Hi, Its a 1972 fitted with a type 4 2L engine, the original engine was a 1700cc but was changed by the PO to a 2000cc CU engine. The gap of 0.006" i think is for solid lifters not hydraulic(i think)

[Amskeptic]

What year/engine is this? Originally, dual carb engines did not have hydraulic lifters, so the valves should be set with a gap, which I think is 0.006" but may sometimes be 0.008" depending on year.

Hi, Its a 1972 fitted with a type 4 2L engine, the original engine was a 1700cc but was changed by the PO to a 2000cc CU engine. The gap of 0.006" i think is for solid lifters not hydraulic(i think)

Well grandfatherjim, we'll beat the information we need out of him one step at a time if we have to.
SO YOU HAVE HYDRAULIC LIFTERS, I HEAR.

Vdubz, no go until we get a cold compression test from you.

8 pulses per cylinder only. Do not worry about propping throttles open. Do disable ignition system by pulling black #15 wire from coil, keep safe from grounding. Where is your fuel pump wired up. It better not be ignition coil sourced!
ColinWeGotWayz

[vdubz]

Well grandfatherjim, we'll beat the information we need out of him one step at a time if we have to.
SO YOU HAVE HYDRAULIC LIFTERS, I HEAR.

Vdubz, no go until we get a cold compression test from you.

8 pulses per cylinder only. Do not worry about propping throttles open. Do disable ignition system by pulling black #15 wire from coil, keep safe from grounding. Where is your fuel pump wired up. It better not be ignition coil sourced!
ColinWeGotWayz

I thought most of the 2L engines had hydraulic lifters anyway, yes fuel pump is wired off the coil, i'm guessing thats bad? where should i wire it? I will do a compression test, what numbers should i be hoping for? so i will remove all spark plugs, pull lead from coil, and you are saying that i don't need to open the throttle or the choke? just turn the engine over 8 turns?

[Amskeptic]

I thought most of the 2L engines had hydraulic lifters

fuel pump is wired off the coil

compression test, what numbers should i be hoping for?

you are saying that i don't need to open the throttle or the choke? just turn the engine over 8 turns?

Whether "most engines" have anything or another is not our concern. Our concern is exactly what your engine has.

Bad. After you wipe out against the guardrail and vault down the embankment upside down, that little fuel pump is going to be working as hard as it can to empty up to 14 gallons of gasoline over your broken body. I will put up a diagram for aftermarket electric fuel pumps for carbureted VWs.

There are no numbers that we are looking for. We are looking for discrepancies, so get us the numbers and we will see if some cylinder over there on the right side of your engine is not happy.

[vdubz]

Ok, some strange results from the compression test , cylinder 1= 0psi, cylinder 2= 30psi, cylinder 3= 0psi, cylinder 4= 20psi. Now i am very confused, the cylinder which looks like it has not been firing has the most compression! I also tried unscrewing the right carburettor solenoid slightly which cured the tickover problem, but the engine still stalls(not as quickly as it used to) when i remove the left carb wire.

[Amskeptic]

Ok, some strange results from the compression test , cylinder 1= 0psi, cylinder 2= 30psi, cylinder 3= 0psi, cylinder 4= 20psi. Now i am very confused, the cylinder which looks like it has not been firing has the most compression! I also tried unscrewing the right carburettor solenoid slightly which cured the tickover problem, but the engine still stalls(not as quickly as it used to) when i remove the left carb wire.

Not strange results . . . we were expecting them. That is why we are here in diagnostics instead of wandering around the dual carb adjustment sticky.

As mentioned in the write-up, you must have all other factors nailed down before doing the dual carb procedure. Others mentioned valve adjustments and gave solid lifter gap specifications, then we find out you have hydraulics, but your compression is completely botched, so do you really really have hydraulic lifters? Do you know how to check that you are actually pushing in the push rod and not opening the valve as you adjust to 1 1/2 turns in? Do you know how to take care of hydraulic lifters that refuse to bleed down, which they have to do in order to set the 1 1/2 turn pre-load?

I cannot see your answer for my question about the clean plug being wet or dry. We cannot move forward without accurate information. We can speculate all day about what constitites a spark plug that is working versus a spark plug that is not working. A black spark plug is not necessarily working and a white insulator spark plug is not necessarily not working.

Step One: let's get your compression readings up. Recheck your valve adjustments, and if they are really hydraulic, you will see the pushrod move down towards the lifter as you preload. If the valve/valve spring keep getting pushed open, then you have either a lifter that refuses to bleed down, or solid lifters.
Colin

[vdubz]

Thanks colin, I will recheck the valve adjustments and see if they push the valve or the pushrod. The way that i set the clearances was by running the engine for 10-15 mins and then immediately setting them(as i was advised to do) and the reason that i think they are hydraulic is because a couple of times when i have started the engine(on cold days) i have heared a tapping noise which goes away within about 5-10 mins, anyway i will check the adjustments as you say to find out if i have pumped or solid lifters. The clean spark plug when taken out after running the engine is dry and does not smell of fuel, the only thing thats on it is a very light coating of oil.

[Amskeptic]

Thanks colin, I will recheck the valve adjustments and see if they push the valve or the pushrod. The way that i set the clearances was by running the engine for 10-15 mins and then immediately setting them(as i was advised to do) and the reason that i think they are hydraulic is because a couple of times when i have started the engine(on cold days) i have heared a tapping noise which goes away within about 5-10 mins, anyway i will check the adjustments as you say to find out if i have pumped or solid lifters. The clean spark plug when taken out after running the engine is dry and does not smell of fuel, the only thing thats on it is a very light coating of oil.

Do NOT listen to the people who say to pump them up! That is a good way to get them rock hard right when you want them to be soft. That means Boston Engine NO! Ratwell NO! I'm serious.
You can adjust soggy lifters far more easily than pumped up lifters. We NEED the plunger to go down the bore of the lifter. You want a delicate clickity-clickity with the screw backed out, then gently find "0" point, the point where click goes away, then in 1 1/2 turns.

They always pump up after a few to several minutes after the engine is running.
Colin