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High idle 5k plus


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#1 Stunt

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Posted 13 May 2012 - 05:48 PM

I have a 71 240z w/ L28 n42 head all stock. Triple solex c40, cannon manifold,square port headers. Electronic dizzy. Adjusted the valves to spec(cold). Then try to sync the carbs. 5 and 6 cylinders not enough vacuum like 1-4. So I decided to run fuel line direct from fuel pump to first set of carbs and then daisy chained to the other 2 carbs. No fuel return line.
I have to hold the choke cable and adjust to idle speed. If I open the choke all the way. The idle will jump up to like 5k rpms and the header will turn bright cherry red. I would then have to shut off the engine. Mind you the dizzy is @ full retard. What would cause that sudden surge from 1.2k rpms to skyrocket? Please any advice would be appreciated.

#2 Stunt

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Posted 13 May 2012 - 06:02 PM

If I also give it gas while @ low rpms. The car would stall out.

#3 beermanpete

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Posted 13 May 2012 - 09:45 PM

Low vacuum on 5 and 6 could be a vacuum leak. Is the header red on all cylinders or only one or two?

#4 rejracer

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Posted 13 May 2012 - 10:54 PM

Having the ignition retarded will cause the exhaust to glow. Ensure both the mechanical and vacuum advance are in tip top shape, set the timing to the correct setting, then play with the carbs.

#5 johnc

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Posted 14 May 2012 - 07:12 AM

What he said ^

If you didn't have enough air flow through the third carb, why did you think re-routing the fuel line would help? Max fuel pressure for those carbs is 4 psi so make sure your fuel pump isn't blowing fuel past the needle and seat.
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#6 Stunt

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Posted 14 May 2012 - 08:41 AM

How do I add pics?

#7 Stunt

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Posted 14 May 2012 - 08:58 AM

I set the timing to normal. I start the car with the choke full open and it still revs to lil pass 5k.

#8 NewZed

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Posted 14 May 2012 - 09:55 AM

I'm not familiar with the Solex carburetor at all but most carbs have a throttle plate to control air flow. Your description shows that you are basically using the choke plate to control air flow. It sounds like your throttle plate(s) is(are) stuck or adjusted too far open.

Timing at "full retard" doesn't mean much either. Meaning no vacuum advance or distributor twisted as far back as possible? To control idle speed? That's not the right way to do it. An actual static timing number is what you need.

Just an observation of carb and engine basics from an EFI guy...

#9 z240

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Posted 14 May 2012 - 09:58 AM

Back to basics!! After fuel pressure confirmation as above, disconnect linkage on all three carbs and make SURE all idle adjusts are just off, (ALL the butterflies closed, no contact from mechanical idle adjust). Your idle mix screws all at 1.5 turns out? Then hook up linkage to each carb making sure each is the same length all arms are at the same angle off of the main shaft (assuming here you have the standard shaft with three arms and three variable length links to the each carb) and applied NO additional throttle application once connected. THEN see what happens when you try to start it. You will have to hold the linkage open a bit since your linkage has no idle in it, but that should do away with the crazy idle speed. Then dial in a tiny bit of mech idle on each in turn so it can hold its own idle. Verify same idle flow on all 6 barrels with unisyn or similar. Go from there.

Edited by z240, 14 May 2012 - 09:59 AM.


#10 Stunt

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Posted 14 May 2012 - 01:46 PM

Ok. I'll try that. Keep you guys posted. Thanks

#11 Stunt

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Posted 18 May 2012 - 10:38 PM

Found out one of the solex carburetors butterfly was stuck open. Im putting on some round top SUs for the time being until I rebuild the Solex triple carbs. Thanks for the help guys.

#12 BluDestiny

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Posted 19 May 2012 - 06:22 AM

Mmmm tweaked butterfly's. To everyone else reading this, mechanically inspect your carbs before install. It'll save you guys tons of time.
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#13 Stunt

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Posted 19 May 2012 - 06:28 AM

The solex carbs was installed before I bought the Z. I was too influenced to buy the car just cuz of the way it looked. I never really took the time to really check it out. Learn from my mistake fellas or females that's looking to purchase a vintage Z. Make sure you really inspect the car.




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