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Old 01-19-2013, 07:36 AM
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lean mixture?

Hi guys, i just finished the build up of my 355 GM first gen, it has an Howell TBI using stock GM components, engine is mildly modified with the pathetic common components like Edelbrock performer intake and cam, headers ,nothing fancy, it runs ok except for something that i will call misfiring and loss of power at WOT under acceleration, weird thing is that when doing burn out or just revving the engine in neutral it has great throttle response and runs great, apparently the issue happens just under load and from 3000 to approx 5000 rpm on the tach...

Set timing with the timing light, put foam in the fuel tank (trying to keep pick up wet at all times) because i thought was a fuel related problem, than i took off spark plugs this morning and i've seen this:

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Plugs look all like that, they have a white spot on electrode and ceramic surrounded by a dark layer down below.
What do you think about them? Mixture is ok but too hot plugs?
Any help will be greatly appreciated.

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Old 01-19-2013, 07:42 AM
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i forgot to mention about gapping, those in the picture i posted before are Accel 576S and they're gapped 0.81 mm, the stock ones used by GM are AC R45 TS and gapped 1mm, the only reason i went for Accels is because they are very short and great for my stupid headers clearance.

thank you.
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Old 01-19-2013, 07:54 AM
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try a tighter gap to start.Do you have access to an A/F meter?
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Old 01-19-2013, 08:07 AM
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Tighter? i Thought .081 it was already too tight...
Distributor is a HEI with the stock coil wich is brand new but a cheap one...

Unfortunately i've no A/F meter here.
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Old 01-19-2013, 08:36 AM
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gap

The HEI and others like MSD have more than enough voltage to jump .080. Problem is;as the plug wears,and other resistances go up,the wires develop leaks. The spark can jump to the V/Cs,headers or inside the cap.When the leak is really bad its easy to find. Stock HEI cap runs out of voltage after 5k,if your engine revs then you will need an external coil.
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Old 01-19-2013, 08:44 AM
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Quote:
Originally Posted by vinniekq2 View Post
The HEI and others like MSD have more than enough voltage to jump .080. Problem is;as the plug wears,and other resistances go up,the wires develop leaks. The spark can jump to the V/Cs,headers or inside the cap.When the leak is really bad its easy to find. Stock HEI cap runs out of voltage after 5k,if your engine revs then you will need an external coil.
Got it, i'll try to see if there's any leak, any suggestion about wires to use?
My problem are those stupid headers, they're so close to the plugs that i had to wrap them and the wires too to avoid to burn them up.

I prefer to buy universal wires and cut them to match the right lenght...
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Old 01-19-2013, 09:06 AM
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put heat socks on the ends of the wires.I use aurora wires,but many brands are very good.Make sure you crimp the ends when you shorten the wires. Don t run 5 and 7 parallel.
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Old 01-19-2013, 09:18 AM
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i do have heat socks on them but apparently they're not enaugh, if i rev up the engine for a few seconds, you can literally see headers glowing underneath...
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Old 01-19-2013, 11:11 AM
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I have read the responses in this thread concerning plug gap and am unsure whether you are both using the same units of measurement. My understanding is that .8mm is approximately .031 inches. Can the original poster confirm that the measurement is indeed .8mm?

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Meldrum
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Old 01-19-2013, 11:18 AM
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Quote:
Originally Posted by meldrum View Post
I have read the responses in this thread concerning plug gap and am unsure whether you are both using the same units of measurement. My understanding is that .8mm is approximately .031 inches. Can the original poster confirm that the measurement is indeed .8mm?

Regards,
Meldrum
Thank you for this, i was thinking about the same thing, i just converted dimension from inches to mm, i usually use mm because i'm more familiar with...
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Old 01-19-2013, 11:56 AM
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lean mixture?

On the spark plug gap if using mm gap them 0.8890-1.0160. MSD plug wires are one of the best wires for HEI.
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Old 01-19-2013, 01:54 PM
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Quote:
Originally Posted by jeepers creepers View Post
.

Unfortunately i've no A/F meter here.


I'm not familiar with a 'Howell EFI' system, but I would find it hard to believe that it wasn't designed to be used with either a narrow or wide band 02 sensor (A/F meter same as AirFuelRatio gauge.) I recommend an Innovate LC1, but there are others are out there that work also.

EFI without AFR gauge is like marriage without sex - what's the point -

Can you datalog with the Howell system?
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Old 01-19-2013, 04:34 PM
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Headers glowing red is a symtom of late ignition timing or a rich mixture. Whats your initial and total timing? Whats your fuel pressure?
ssmonty
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Old 01-19-2013, 04:57 PM
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Quote:
Originally Posted by 64nailhead View Post


I'm not familiar with a 'Howell EFI' system, but I would find it hard to believe that it wasn't designed to be used with either a narrow or wide band 02 sensor (A/F meter same as AirFuelRatio gauge.) I recommend an Innovate LC1, but there are others are out there that work also.

EFI without AFR gauge is like marriage without sex - what's the point -

Can you datalog with the Howell system?
The TBI kit comes with the oxygen sensor so it should manage the air/fuel mixture a little.
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Old 01-19-2013, 06:55 PM
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what ssmonty said,check your timing
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