4.2 carbi, idled high then dieseled when shut off

[mike_nofx]

Here's the story, I took it on a camping trip which was a 3.5 hour drive each way, I had no troubles at all.

When I got home it sat in the front yard for 2 days untouched. I got in it to drive to work this morning and it was hard to start stalled twice, I got it running and drove to work. It was pretty cold this morning.

When I arrived in the carpark (15 min drive) it was idling high, when I stuck it in park it sat at 2000rpm. When I shut the engine off it kept running (dieseling?) for a few seconds. Maybe because revs were so high when engine shut off?

I have yet to try it again, but will this arvo when I go home.

Worth mentioning, when the engine is cold I use the idle up (knob on the right hand side of the dash) I pull it out about 10mm to keep revs up till engine is warm. Is this ok to do? It's not actually a choke is it, just an idle up?

It's a 4.2 carbi auto. I've had it about a month.

Any ideas appreciated!

[chimpboy]

Do you know any history on the carby?

I have seen them get unbelievably grotty without maintenance. Dieseling can result from several different things, even dodgy spark plugs (they stay red hot and can ignite fuel without sparking) or from dodgy fuel. I have heard fuel with ethanol content can cause it but I don't know if this is true.

It does sound kind of carby-related overall though and I would bet that if you pull the carby off and put a kit through it you will find it was really in dire need of maintenance.

[purplebus]

the idle up is just a hand throttle so no probs there. just check that it is releasing the mech back to normal eg from memory the pedal moves.?

also check at the carby that the return to idle spring is not to loose or my diesel would idle high if mud and crap build up in the accelerator cable. just disconnect throttle cable from carby and free rev eng a bit to see if when you release it it returns to idle, repeat with cable on. cables are cheap as chips new from nissan from memory.

as chimp has said as i was typing as well. carbys need love.

[BadMav]

Take the air cleaner cover off and check that the choke plate isn't stuck partially closed too. I totally removed mine including the shaft.

[cooki_monsta]

auto choke is a prob aswell

[jezzaGQ]

one of my mates has the same sort of problem with high revving his auto choke dosent switch off. he has to manually do it theres a little white lever just underneath the airbox at the back just push it down that should take it back to normal idle..

[patrol man]

Here's one you wont find easily,

There is a intake air deflector plate that sits in the base of the carby. (between the manifold and carby base). It is there to direct the intake air to improve flow. It can come loose and cause this fault, it can sometimes jam the butterfly open a little bit (on the secondary's I think).

It is a thin tin plate that you wont notice missing when you throw it over your shoulder. If you look down the carby you may see it with a light and the throttle open, possibly need to hold the secondary's open too.

good luck!

[BeNoS]

Here's one you wont find easily,

There is a intake air deflector plate that sits in the base of the carby. (between the manifold and carby base). It is there to direct the intake air to improve flow. It can come loose and cause this fault, it can sometimes jam the butterfly open a little bit (on the secondary's I think).

It is a thin tin plate that you wont notice missing when you throw it over your shoulder. If you look down the carby you may see it with a light and the throttle open, possibly need to hold the secondary's open too.

good luck!

i had this happen cept the revs jumped straight to redline. as it caught the secondaries bigtime.
it also disinegrated into the intake manifold and thru the engine, i got lucky pulled off the manifold and nothing in there. removed all the plugs and stuff. all ok. but ive seen another do the same thing but destroy the inside of the motor. scored all the bores, cracked head. resulted in a rebuild engine.

[cooki_monsta]

Here's one you wont find easily,

There is a intake air deflector plate that sits in the base of the carby. (between the manifold and carby base). It is there to direct the intake air to improve flow. It can come loose and cause this fault, it can sometimes jam the butterfly open a little bit (on the secondary's I think).

It is a thin tin plate that you wont notice missing when you throw it over your shoulder. If you look down the carby you may see it with a light and the throttle open, possibly need to hold the secondary's open too.

good luck!

i had this happen cept the revs jumped straight to redline. as it caught the secondaries bigtime.
it also disinegrated into the intake manifold and thru the engine, i got lucky pulled off the manifold and nothing in there. removed all the plugs and stuff. all ok. but ive seen another do the same thing but destroy the inside of the motor. scored all the bores, cracked head. resulted in a rebuild engine.

yep had that 2, also had the base (butterfly bit) come loose on me

[v8maverick]

Those carbs have a anti desiling soliniod to check that they all ways play up.

[BadMav]

Here's one you wont find easily,

There is a intake air deflector plate that sits in the base of the carby. (between the manifold and carby base). It is there to direct the intake air to improve flow. It can come loose and cause this fault, it can sometimes jam the butterfly open a little bit (on the secondary's I think).

It is a thin tin plate that you wont notice missing when you throw it over your shoulder. If you look down the carby you may see it with a light and the throttle open, possibly need to hold the secondary's open too.

good luck!

i had this happen cept the revs jumped straight to redline. as it caught the secondaries bigtime.
it also disinegrated into the intake manifold and thru the engine, i got lucky pulled off the manifold and nothing in there. removed all the plugs and stuff. all ok. but ive seen another do the same thing but destroy the inside of the motor. scored all the bores, cracked head. resulted in a rebuild engine.

yep had that 2, also had the base (butterfly bit) come loose on me

Those carbs have a anti desiling soliniod to check that they all ways play up.

I thought it was to stop the fuel entering the bowl. There's some weird sh1t on these tb42 carbs. I like holleys they're easy, but not 4wd friendly

[cooki_monsta]

Here's one you wont find easily,

There is a intake air deflector plate that sits in the base of the carby. (between the manifold and carby base). It is there to direct the intake air to improve flow. It can come loose and cause this fault, it can sometimes jam the butterfly open a little bit (on the secondary's I think).

It is a thin tin plate that you wont notice missing when you throw it over your shoulder. If you look down the carby you may see it with a light and the throttle open, possibly need to hold the secondary's open too.

good luck!

i had this happen cept the revs jumped straight to redline. as it caught the secondaries bigtime.
it also disinegrated into the intake manifold and thru the engine, i got lucky pulled off the manifold and nothing in there. removed all the plugs and stuff. all ok. but ive seen another do the same thing but destroy the inside of the motor. scored all the bores, cracked head. resulted in a rebuild engine.

yep had that 2, also had the base (butterfly bit) come loose on me

Those carbs have a anti desiling soliniod to check that they all ways play up.

I thought it was to stop the fuel entering the bowl. There's some weird sh1t on these tb42 carbs. I like holleys they're easy, but not 4wd friendly

eeek, dont mention holley, they are worse, there was alot of 'what a good idea' at the time that went into these carbs, some of the ideas are magnificent, and they are a ripper carby, they just need to be properly maintained!

a holley on the other hand, you can trash it straight away, simple piece of junk, a fuel bottle connected to your intake, that you squirt by hand would be more efficient then a holley

[BadMav]

Haha, you're right, but I wouldn't throw one away as they do have their applications, on road. I adapted a 350 Holley onto an old pajero astron 2600 for a guy, it revved harder and had better fuel economy than the stocko carb, seriously. It was however the guys daily driver and it never went off road...ever.

I think I've got the tune on mine (std modded carb) pretty good now considering the weight the engine is pushin around on 36's and the lift i'm getting around 19L/100 mix highway and town.

[cooki_monsta]

yea i had one on my 302c and i hated it, used a 600 on a 351, and it was over fueling low down, fitted a MONSTER thermoquad (1200cfm) and its awsome, best carb i have used

[lucifer48]

1st thing to check is the auto choke, make sure it has power going to it and the choke unit is getting hot.
If it has power to it the choke unit might be faulty and will need replacing.
Or you can just wire it open, but make sure the fast idle cam isnt sticking as well.

Check the secondary throttle shaft as these tend to stick and when I overhaul these carbys (thats what I do for a living!!) I always pull the shaft out and clean it up.

If you can not find the problem PM me your phone number and i will see if i can help you.

Cheers Louie