New member - need advice on tuning TB42s

Please read this first if you are new to the forum
Dust&
Newbie
Newbie
Posts: 5
Joined: 11 Jul 2018 19:26
Full Name: Alex Watson
Nickname: Alex
Home Town: Sedgefield
Current 4x4: Y60 Patrol TB42 carb
Home Language: English

New member - need advice on tuning TB42s

Post by Dust& » 13 Jul 2018 15:57

Hi All,

I recently picked up a Y60 TB42 carb model and have picked up a few gremlins that I would welcome some advice on.

I started by doing a basic service (spark plugs, air filter, oil & filter, cleaned out and tested pcv valve and hoses).

I have been trying to tune the engine and have found the following:

1. the timing was set to 20 BTDC by one of the POs. I tried retarding it back to 10 BTDC but it completely lost power and struggled to start. The distributor has been upgraded to electronic but I am not sure if this mod requires the timing to be advanced as far as 20 degrees? I then advanced the timing progressively higher from 10 BTDC and anything under 17 degrees results in hesitation when accelerating .

I have tested the vacuum advance unit with a vacuum pump and guage and it works perfectly (advances and holds). However, if I disconnect the vacuum advance hose, I can not feel any loss of power when driving. There is also no noticeable change in advance when checking the timing with the hose on or off the advance unit.

2. The air mixture screw seems to be damaged (tip crushed) as I have to turn out 4 turns to get the max revs. Also if I continue to turn the screw out the revs remain the same. From my experience with bike carbs the idle should become rough if you screw out beyond the sweet spot. I have been looking for a carb kit, including air mixture screw, online but can't find anything locally. Anyone know who would carry a TB42 carb kit in RSA?

Any advice would be welcome!

User avatar
Peter Connan
Moderator
Posts: 5421
Joined: 10 Sep 2010 07:21
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.5SGL
Home Language: Afrikaans
Location: Kempton Park
Has thanked: 285 times
Been thanked: 366 times

Re: New member - need advice on tuning TB42s

Post by Peter Connan » 13 Jul 2018 18:44

Hello and welcome Dustin

First question: is the vacuum advance connected to the correct port on the carb? The electronic ignition module should not change the timing requirement at all.

As for carb kits, I have managed to source them from SP Carbs here in Kempton Park. But there is a glitch: they told me their importer has stopped importing them, and had only three kits left, which I promptly bought up, and unfortunately distributed to forum members.

They have now told me that they will persuade the importer to get more, but I have no idea how long this will take.

You can also ask Marinus (Marino 4x4 here on the forum). He imports Terrain Tamer parts. Upon finding out that my local source was probably not going to stock them anymore, I asked him if he could supply, and it seemed like he could get a reasonably complete kit.

I do have left-overs from a couple of old kits, if there is something spesefic you need?
Mag ons ons kenniskry met lekkerkry aanhoukry.

User avatar
Kagiso II
Patrolman 1000+
Patrolman 1000+
Posts: 3666
Joined: 10 Jun 2009 16:58
Full Name: Mac Mc Menamin
Nickname: Oom Mac [Uncle Mac] [Uncle] [Oompie] Kagiso
Home Town: BrentwoodPark, Benoni
Current 4x4: 1982 Datsun Safari 2,8 aka LOBO; [1,300,000 Km verby !]
'99 PATROL 4,2 diesel.
2012 Jimny [SWAMBO se Kantoor-toe]
Home Language: AFRIKAANS
Location: Benoni and wherever the Outreach takes me.
Has thanked: 291 times
Been thanked: 109 times
Contact:

Re: New member - need advice on tuning TB42s

Post by Kagiso II » 13 Jul 2018 22:51

There is a Carb place in Church Street Pretoria, Arcadia [just on "Lion Bridge" I got the NIKKI Carb service kit there [2013 .. .. maybe they still there ?
Don't bring God down to your level of faith ... bring your faith up to His level!

Dust&
Newbie
Newbie
Posts: 5
Joined: 11 Jul 2018 19:26
Full Name: Alex Watson
Nickname: Alex
Home Town: Sedgefield
Current 4x4: Y60 Patrol TB42 carb
Home Language: English

Re: New member - need advice on tuning TB42s

Post by Dust& » 14 Jul 2018 23:24

Hi Peter

thank you for the info and your kind offer. I will try and source a full carb rebuild kit if I can but if not would very much appreciate any spare gaskets and an air mixture screw.

As for your question, the vacuum hose leading from the vacuum advance on the distributor is connected to the carb just above the air mixture screw. Is this correct? I have found a few basic vacuum diagrams online but they don't show exactly where the hoses connect.

I also have a few other vacuum gremlins to work out:

1. the hose from the idle compensator that connects under the airbox was disconnected on the other end. The only port I could find to connect it to was one on the tree connecting to the intake manifold under the air mixture screw. Is this correct? The other two ports on the tree were plugged and I need to work out where they were connected to.

2. I found some other cut and plugged vacuum hoses, one from the altitude compensator.

If you have a detailed vacuum diagram, other than the one in the Nissan service manual, that would be very very helpful.

User avatar
Peter Connan
Moderator
Posts: 5421
Joined: 10 Sep 2010 07:21
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.5SGL
Home Language: Afrikaans
Location: Kempton Park
Has thanked: 285 times
Been thanked: 366 times

Re: New member - need advice on tuning TB42s

Post by Peter Connan » 15 Jul 2018 08:04

Dustin, that is the correct port for the vacuum advance, whichs brings up another question:

These engines are very sensitive to ignition timing. Mine will ping audibly at higher revs and loads at anything over 7 degrees idle advance. Thus I must wonder whether your crank pully hasn't perhaps shifted? Have you pulled no.1 plug and checked that it is at TDC when the mark is at the TDC?

vacuum system: the big (bottom) pipe on the compensator goes to the bottom of the air filter box.

The three top pipes go to the three ports on the "upper story" of rhe carb, keeping the same sequence. In other words, working from the rear of the car, the rear port on the comp goes to the pipe furthest back on the carb, the front pipe on the comp goes to the pipe on fhe front of the carb, above the "viwing window".

The branch on the intake manifold's big pipe goes to the bottom of the air filter box. The tiny one goes to the vacuum solenoid on the firewall which switches when the air con is switched on. The other side of the solenoid should go to the diaphragm mounted at the back of the carb. This system increases the idle speed when the air con is switched on.

The third one is plugged. Looks like a factory part.
IMG-20180715-WA0011.jpg
IMG-20180715-WA0010.jpg
IMG-20180715-WA0009.jpg
IMG-20180715-WA0008.jpg
Note that mine has a non-standard air filter setup, but I did tjat myself with careful consideration to keeping the vacuum system the same.
Mag ons ons kenniskry met lekkerkry aanhoukry.

Dust&
Newbie
Newbie
Posts: 5
Joined: 11 Jul 2018 19:26
Full Name: Alex Watson
Nickname: Alex
Home Town: Sedgefield
Current 4x4: Y60 Patrol TB42 carb
Home Language: English

Re: New member - need advice on tuning TB42s

Post by Dust& » 15 Jul 2018 21:35

Thanks Peter, that is very helpful.

The big vacuum hose from the branch was plugged with a screw and the small vacuum hose from the branch to the vacuum solenoid was missing! Got that sorted out now, just need to replace the left side hose from the altitude compensator as it has been cut and plugged with screws on both sides. I will test the compensator first.

I think you might be right about the crank pulley having shifted, will check TDC tomorrow.

There is one other thing regarding the vacuum system that you could perhaps advise me on: there is no evap canister in my engine bay!? There is also no EGR system. My Patrol is a 1995 SGL, did these not come stock with this model? I found today whilst traveling home that there was significant pressure build-up in the fuel tank. Could this mean that the breather pipe was blocked and the evap canister was ditched?

Thanks again for all the guidance.

User avatar
Peter Connan
Moderator
Posts: 5421
Joined: 10 Sep 2010 07:21
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.5SGL
Home Language: Afrikaans
Location: Kempton Park
Has thanked: 285 times
Been thanked: 366 times

Re: New member - need advice on tuning TB42s

Post by Peter Connan » 16 Jul 2018 05:13

Dustin, there should not be an evap cannister or EGR on these.

Check the tank's breather system, it is located under a plastic cover in the driver's side rear wheel-well, under the filler cap. I am not sure but I think the filler cap itself should also be able to breathe.
Mag ons ons kenniskry met lekkerkry aanhoukry.

Dust&
Newbie
Newbie
Posts: 5
Joined: 11 Jul 2018 19:26
Full Name: Alex Watson
Nickname: Alex
Home Town: Sedgefield
Current 4x4: Y60 Patrol TB42 carb
Home Language: English

Re: New member - need advice on tuning TB42s

Post by Dust& » 17 Jul 2018 16:40

Hi Peter

I checked the TDC and it is spot on, mark is at 0 when no.1 piston is at top of compression stroke. Not really sure why it needs so much advance then? If the chain stretches over time you need to advance a little to compensate but not 10 degrees! Anyway, any other ideas?

As for the carb, I pulled out the idle/air mixture screw and the tip seems fine. However, I could not find an O ring in there, does this screw not have an O ring?

Thanks

User avatar
Peter Connan
Moderator
Posts: 5421
Joined: 10 Sep 2010 07:21
Full Name: Peter Connan
Nickname: Piet
Home Town: Kempton Park
Current 4x4: 1996 Patrol 4.5SGL
Home Language: Afrikaans
Location: Kempton Park
Has thanked: 285 times
Been thanked: 366 times

Re: New member - need advice on tuning TB42s

Post by Peter Connan » 17 Jul 2018 18:52

Interesting...

Perhaps there is something wrong with (or somebody has modified) the mechanical advance mechanism? Perhaps check the advance at higher revs? According to the graph in the workshop manual, mechanical advance should top out at about 1400 rpm and between 10 and 12 degrees advance. This is with 0 degrees of advance at 525-600 rpm.

These values are all at the distributor, and this is where my maths fall a part a little bit, but I think everything should be doubled, which would mean that you should have about 20-25 degrees more advance at 2800rpm than you have at idle, and from there on it should remain basically steady.

I seem to recall that the maximum advance should be around 35 degrees.

According to the drawing in the manual, and my excellent forgettery, there should be (working from the shoulder of the screw toward the carb) a spring, a washer and then an o ring.
Mag ons ons kenniskry met lekkerkry aanhoukry.

Dust&
Newbie
Newbie
Posts: 5
Joined: 11 Jul 2018 19:26
Full Name: Alex Watson
Nickname: Alex
Home Town: Sedgefield
Current 4x4: Y60 Patrol TB42 carb
Home Language: English

Re: New member - need advice on tuning TB42s

Post by Dust& » 17 Jul 2018 19:09

I will do some more research and play around with the timing a bit more.

The missing O ring could be significant! Could explain why I need 4-5 turns out to get max rpm. Should have one that fits amongst my bike parts. Does it fit up against the washer or where the needle meets the thread?

Thanks for taking the time to lessen the angle of my learning curve :thumbup:

Post Reply

Return to “01. Start Here”

Who is online

Users browsing this forum: No registered users and 2 guests