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-   -   lean mixture? (http://www.hotrodders.com/forum/lean-mixture-228567.html)

jeepers creepers 01-19-2013 07:36 AM

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:
http://s1.postimage.org/pc8ogk0fz/IMG_0960.jpg
picture hosting

http://s14.postimage.org/p0guhyo5t/IMG_0958.jpg
images

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.

jeepers creepers 01-19-2013 07:42 AM

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.

vinniekq2 01-19-2013 07:54 AM

try a tighter gap to start.Do you have access to an A/F meter?

jeepers creepers 01-19-2013 08:07 AM

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.

vinniekq2 01-19-2013 08:36 AM

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.

jeepers creepers 01-19-2013 08:44 AM

Quote:

Originally Posted by vinniekq2 (Post 1636491)
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...

vinniekq2 01-19-2013 09:06 AM

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.

jeepers creepers 01-19-2013 09:18 AM

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...

meldrum 01-19-2013 11:11 AM

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

jeepers creepers 01-19-2013 11:18 AM

Quote:

Originally Posted by meldrum (Post 1636552)
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...

cdminter59 01-19-2013 11:56 AM

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.

64nailhead 01-19-2013 01:54 PM

Quote:

Originally Posted by jeepers creepers (Post 1636482)
.

Unfortunately i've no A/F meter here.

:confused:

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 - :D:D

Can you datalog with the Howell system?

ssmonty 01-19-2013 04:34 PM

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

jeepers creepers 01-19-2013 04:57 PM

Quote:

Originally Posted by 64nailhead (Post 1636608)
:confused:

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 - :D:D

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.

vinniekq2 01-19-2013 06:55 PM

what ssmonty said,check your timing


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