Didn't know where to post this, Datsun troubles (Fuel)

DannyBoy · Post by **DannyBoy** » Sun Sep 16, 2007 10:45 pm

Well, my Datsun 510 has been acting weird the past few months. It starts and idles fine, and runs great for about 20 minutes. Than once it's fully warmed up and you come up to a stop. It doesn't wanna hold idle. It will idle really really low or just die. This started happening when the car sat for about 3 months. Plus if I turn the car off after about 30 minutes of driving, than let it sit for awhile, than go to restart it, it wont hold idle. It'll start perfect than I'll rev it up than when it comes back down, it just dies.

My 510 has a 302 in it with a Demon 525 CFM carb. Does anyone have any ideas on why it wont idle after it's fully warmed up?

CA180 · Post by **CA180** » Sun Sep 16, 2007 10:49 pm

Probably time for a carb rebuild.

Did you check your plugs 60% of the time it works every time.

03blackrt · Post by **03blackrt** » Sun Sep 16, 2007 11:02 pm

This may sound like a long shot, but... intake gasket. I'd guess a vaccum leak (intake gasket). The idle speed could be tuned to compensate for the vaccum leak when cold. Then whe it gets hot, everything expands and the leak goes away, starving the motor of air, causing it to die, also causing fuel to pool, since the mixture would likely be rich once the vaccum leak goes away, makeing it hard to restart.

lambostealth · Post by **lambostealth** » Sun Sep 16, 2007 11:20 pm

Sounds like a pump, or filter (fuel) problem, sounds like the bowls are full, then empty out. Check lines, filter, pump, and the carbs accelerator pump for tears. Also make sure there isn't fuel dripping from the secondary jets at idle.

Could it be an ignition problem??

What are you running for a distributor?? Electronic ign? or points?

DannyBoy · Post by **DannyBoy** » Sun Sep 16, 2007 11:23 pm

lambostealth wrote:Sounds like a pump, or filter (fuel) problem, sounds like the bowls are full, then empty out. Check lines, filter, pump, and the carbs accelerator pump for tears. Also make sure there isn't fuel dripping from the secondary jets at idle.

Could it be an ignition problem??

What are you running for a distributor?? Electronic ign? or points?

It's got full MSD ignition, MSD 6A, distributor, and wires.

DannyBoy · Post by **DannyBoy** » Sun Sep 16, 2007 11:24 pm

03blackrt wrote:This may sound like a long shot, but... intake gasket. I'd guess a vaccum leak (intake gasket). The idle speed could be tuned to compensate for the vaccum leak when cold. Then whe it gets hot, everything expands and the leak goes away, starving the motor of air, causing it to die, also causing fuel to pool, since the mixture would likely be rich once the vaccum leak goes away, makeing it hard to restart.

It's not hard to restart at all, it starts up fast and strong. Just doesn't hold idle well.

CA180 · Post by **CA180** » Sun Sep 16, 2007 11:45 pm

I'm tellin ya, there's crud in your carb.

Sounds like air jets are getting blocked.

DannyBoy · Post by **DannyBoy** » Sun Sep 16, 2007 11:48 pm

CA180 wrote:I'm tellin ya, there's crud in your carb.

Sounds like air jets are getting blocked.

But why only when it's fully warmed up?

CA180 · Post by **CA180** » Sun Sep 16, 2007 11:50 pm

Shit probably settles on the bottom of the carb till you get to moving. I dunno... Hmm..

Now you got me thinking.

My ford seams to do that too. Its got a 302. Stock 2 barrel. Just replaced the intake gaskets.

Only difference is mine doesnt like to start when warm. But idles like a champ.

I still think theres crud in your carb. That can happen when you let it sit too long. Thats the red flag in my mind.

I mean, what else could change? Timing wont move when it sits. Gaskets dont really go bad sitting. So that leaves me with carb, or bad gas.

03blackrt · Post by **03blackrt** » Sun Sep 16, 2007 11:52 pm

That's why I say Intake gasket or a crack in the intake somewhere... something that closes/opens when it gets warm. It can't be an ignition problem, or fuel delivery. They just don't have them symptoms.

EDIT:

CA180 wrote: I mean, what else could change? Timing wont move when it sits. Gaskets dont really go bad sitting. So that leaves me with carb, or bad gas.

Gaskets do go bad, It could have just went bad while sitting; or was masked by something else prior to this. Carb or bad gas don't normally have symptoms that occure only while hot, usually they will cause trouble all the time, at specifice engine speeds or throttle settings, not corresponding to engine temp. IMO

Or maybe Fords are just weird. Maybe it doesn't like being in a Datsun

Arro · Post by **Arro** » Mon Sep 17, 2007 3:45 am

03blackrt wrote:Or maybe Fords are just weird. Maybe it doesn't like being in a Datsun

Sorry DannyBoy, being a current Datsun 280ZX owner, I had to quote this

LowNSlow · Post by **LowNSlow** » Mon Sep 17, 2007 2:39 pm

http://forums.hybridz.org/

CA180 · Post by **CA180** » Mon Sep 17, 2007 7:21 pm

I'm still positive that your carb is gunked up.

And I verified this with some other tech around my shop today.

Your idles circuits are probably dirty, but the reason it only runs when cold and has trouble when warm is because your motor is really running off the choke circuit when its cold. That forces the gas in there. So probably what you might try doing is measure how far out the air jet needles are out (i.e. 2 turns, 1.5 turns...) then take them out. Clean them up, and spray some carb cleaner through the openings. That should help. Also try running some carb cleaner additive through your tank. But run it strong. Gas may have varnished up the inside of your carb a little.

Let me know what you think and how it goes.

DannyBoy · Post by **DannyBoy** » Tue Sep 18, 2007 7:28 pm

Thanks for the research CA180!

I asked my coworker too and it was kind of what I thought, he said it mainly needs a carb adjustment and a good cleaning. So I'll try it out probably on thrusday and report back how it goes.