| T O P I C R E V I E W |
| Jimmys old Saab | Posted - 04 Sep 2020 : 19:22:25
My 96 is running OK with the large Nikki twin choke; however it is reluctant to start, especially when hot; I'm pretty sure it's overfuelling.
Now, the Spark plugs are near as old as the car so I was going to change them anyway. I was wondering if going to a hotter plug might help reduce any fouling owing to running an oversized carb at low engine speeds. Importantly is a hotter NGK (they are what I tend to use) going to foul the pistons?
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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| 15 L A T E S T R E P L I E S (Newest First) |
| melle | Posted - 26 Apr 2021 : 13:24:27
That's a clever solution Joe.
www.saabv4.com |
| EdinburghJoe | Posted - 26 Apr 2021 : 12:56:22
Someone on this forum a few years ago suggested inserting a spring into a normal length of silicon hose to prevent it folding flat on the tight bends for this pipe. It locks very firmly into position on the bend so it won't move up and down the pipe. I used the spring from a door stop - pretty much the right size and it has been doing the job for me over the last few years.
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| melle | Posted - 25 Apr 2021 : 16:46:43
You can vent to a pot, but then you won't have the advantages (for both your engine and the environment) of a fully enclosed PCV system. I have a catch can between the rocker cover and the PCV valve, it catches rather a lot of oil, so worth fitting in my opinion. john-saab on here stocks the original shape hoses I think, they're a weird shape and pretty much nothing else will fit as most hoses will easily kink due to the compound narrow bends. Samco may also do them in silicone iirc?
www.saabv4.com |
| Jimmys old Saab | Posted - 25 Apr 2021 : 16:27:20
I just dont have a suitable piece of hose, it needs a piece with a 90 degree kink in it. The PCV I still have from the old set up and will re-use. No reason why you couldn't vent to an oil catch pot though is there?
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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| melle | Posted - 24 Apr 2021 : 18:41:44
I sort of assumed you plugged the rocker cover too, but either way you no longer have a functioning PCV system. The oily fumes that normally go back into the intake are recirculated within the engine, so they're part of the metered (by the carb throttle plates) air intake volume. If the port is left open unmetered air messes up the mixture (i.e., leans it out). Was there any particular reason for removing the PCV valve?
www.saabv4.com |
| Jimmys old Saab | Posted - 24 Apr 2021 : 18:19:54
quote:
Originally posted by melle
quote:
Originally posted by Jimmys old Saab
Firstly, the rocker cover to carb intermediate plate hose is not in position so the port to the plane was open, hence a source of air to the inlet manifold. I plugged the hole. That may make some difference but there are oily fumes going in there anyway so maybe not...I would imagine that would alter the fuel/air mix anyway?
Not a good idea not to have a functioning PCV system in my opinion, the pressure will build up and eventually escape somewhere (through a seal, rocker cover gasket, dipstick tube etc.). See https://en.wikipedia.org/wiki/Crankcase_ventilation_system and/ or the workshop manual.
quote:
Originally posted by Jimmys old Saab
Choking the venturi with am airbox is sufficient to increase the speed of the charge.
If the air filter is indeed that restrictive it's either horribly dirty or way too small too small I suppose?
www.saabv4.com
You've mixed up what I was saying there; I have plugged the carb plate, not the hose on the rocker cover, that is just venting to atmosphere.
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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| Derek | Posted - 24 Apr 2021 : 14:32:05
The hose from the cover to the carb should probably have a very small metering valve or a one way pcv valve or both. An open hose will have really bad effects on the mixture being effectively a massive air leak. The hose from the cover can go to a spigot on the engine side of the air filter as per original. There is a thread on doing this with an aftermarket filter for the Weber ICH on here somewhere. |
| melle | Posted - 24 Apr 2021 : 09:18:22
quote:
Originally posted by Jimmys old Saab
Firstly, the rocker cover to carb intermediate plate hose is not in position so the port to the plane was open, hence a source of air to the inlet manifold. I plugged the hole. That may make some difference but there are oily fumes going in there anyway so maybe not...I would imagine that would alter the fuel/air mix anyway?
Not a good idea not to have a functioning PCV system in my opinion, the pressure will build up and eventually escape somewhere (through a seal, rocker cover gasket, dipstick tube etc.). See https://en.wikipedia.org/wiki/Crankcase_ventilation_system and/ or the workshop manual.
quote:
Originally posted by Jimmys old Saab
Choking the venturi with am airbox is sufficient to increase the speed of the charge.
If the air filter is indeed that restrictive it's either horribly dirty or way too small too small I suppose?
www.saabv4.com |
| Jimmys old Saab | Posted - 23 Apr 2021 : 22:51:22
The problem with starting appears solved. Firstly, the rocker cover to carb intermediate plate hose is not in position so the port to the plane was open, hence a source of air to the inlet manifold. I plugged the hole. That may make some difference but there are oily fumes going in there anyway so maybe not...I would imagine that would alter the fuel/air mix anyway?
Secondly I am convinced that air velocity into the engine is much reduced from normal because of the size of the venturi of the twin choke carb. At start up the engine struggles to pull enough air into the engine. A bit like trying to suck lemonade through a hosepipe as averse to a straw. What made a difference was adding an air filter to the carb and pumping the throttle at least three times. The carb is so much bigger than the original FOMOCO that I'm convinced that the engine's volume is insufficient to gain enough velocity on start up to draw fuel from the jets into the mix. Choking the venturi with am airbox is sufficient to increase the speed of the charge.
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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| melle | Posted - 26 Sep 2020 : 19:35:14
saabv4[at]saabv4[dot]com I think I have a Nikki manual PDF, if you email me, I'll send it with my reply if I can find it.
www.saabv4.com |
| Jimmys old Saab | Posted - 26 Sep 2020 : 18:33:30
Melle- what is your email? I will send you some pics of the carb in situ.
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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| Jimmys old Saab | Posted - 26 Sep 2020 : 18:31:01
Hello again; the fuel level is exactly on the line- apparently it is critical for fueling that it is on these Nikki carbs.
However I have taken another look at the 96 this afternoon. I had already found out that winding the idle screw out several turns seemed to help starting. This time around I blipped the throttle a couple of times- sure enough, I could see the accelerator pump squirting fuel into the secondary venturi. Then I pulled the choke and she started.
As I said earlier I suspect that now starting is relatively easy the car will idle too rich. So the carb and engine do not match as well as I'd have liked but that's no surprise, it will do for now until the car has gotten some miles under it's tyres.
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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| Derek | Posted - 24 Sep 2020 : 11:39:46
The dribble could well be due to too high a float level. Yes it is showing as on the line but you could try it a fraction lower. I noticed a similar dribble when I had a leaky and heavy float in the FoMoCo. The dribble floods the manifold. Obviously an electric pump will do this easily with the ignition on but with the mechanical it will also flood the manifold if it doesn't start immediately and you keep on churning.
Would the Nikki needle valve allow you to add a washer to lower the level? Some floats don't have an easy to adjust tab to set the level. |
| melle | Posted - 24 Sep 2020 : 09:43:33
The fact that it starts on carb cleaner doesn't necessarily mean it's not getting enough fuel. Carb cleaner ignites much easier than the mixture your carb produces, so it's great to hide vacuum leaks or ignition issues. Fuel dribbling out of an orifice doesn't sound good to me; you say it's in the centre of the venturi, which I assume means the orifice is some kind of booster jet? I'll dig out my Nikki (which has been used on a V4) this weekend if I have time, be interesting to learn more about them.
www.saabv4.com |
| Jimmys old Saab | Posted - 23 Sep 2020 : 19:38:38
I started her up again this evening, needed a good puff of carb cleaner; now, in the past with stock Weber or similar carbs I've set up the idle by turning the idle valve screw in until the engine begins to stumble and then backed off half a turn. I turned the idle screw out another two full turns and she started fine. I think now that the carb may be a little large and so the speed of air may be too low going into the venturi so not getting enough fuel to start easily but fine at idle. Now I can visibly see more fuel going into the carb at idle. Now that she starts OK, I'll run for a while and see what state the plugs get into, It may be that at higher rpms and greater velocity she will lean out. I'll get the colourtune out and have a look through that too.
I would be interested to know what amount of air the standard FOMOCO moves versus the twin choke Weber and my Nikki, the Nikki looks to have a similar or slightly smaller area to the venturi but that will not give a very accurate indication of the air it will consume.
Saab 96 1971
Datsun 120y coupe 1975
Saab 9000 CSE turbo 1993
VW T5 LWB 2012
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