[caribbean camaro]

Yesterday, I went for a grudge day at track -
I normally use AC -R43TS plugs - and as subject says - by 2nd pass plugs were breaking up - checked my tool pan for new set of NGK v-power plugs

turns out I bought wrong set of NGK plugs - stock no 4091 - R5671A-7
thread too big for my WPII's (my fault - I have heard about v-power 7's working well in chevy drag motors and ASSumed that they were chevy std. fit )

Either way, I find that even on a new set of AC plugs - after 2-3 passes - I have to floor throttle - to even hope to start - otherwise it just turns over

I am currently running 74/82 on the 650 - the back power valve is plugged - it was used and came with 66/71 - but would flat spot terribly as soon as you come off idle on my engine - initially only way I could get it to rev cleanly was to install 84 at the back

I played with it until I got to 74/82 - it idles smoothly - no problems, but I believe the plugs are being flooded - and it probably is being masked by the open header extensions - I use 37 squirters too - but she revs cleanly once plugs are new

should I baseline again and try to see what works - and if so what jets would you start with and follow up

any other ideas on flooding - no real evidence of flooding in carb

[travis]

Pull a plug and see if they are solid black and sooty after a few runs. Thats a definate indication that it is jetted too fat.

[Nantooch]

figure out what your elevation is. for every 2k above sea level drop one jet size from stock. You can go to mortecs site and see what your carb came with as far as stock jetting if you dont remember.

replace the power valve in the rear and get it rejetted accordingly.

[kristofer]

my two cents says, attack the off idle stumble in the pump cam and discharge nozzles.... here is my combo and what i run

396(402) with a 292 Magnum cam...244 I/E at .050", 550 lift, on a 110LSA, in a 5 speed tremec with 3:42's, holley 750 DP- 67/77 jets, 28/31 squirters,idles at 950 rpms, two holes 1/8 in diameter drilled in primary throttle blades. jet hot long tube headers, stock air filter and assembly, i run 91 octane gas, i use a R44 or R45XLS i think....

no hesitation and power is there...but i will be dyno tuning very soon...

what is your combo? your hard restart could be from vapor lock, or float bowl setting,...have you looked down the carb after you shut the car off....continue to look for several minutes..to see if carb is loading up after shutdown.

more input

[oger]

If you have to floor it the carb is leaking down. Either from heat or the float is too high.

[Eric68]

Too much jet IMO -- 10 over box-stock is just too much IMO and if that is what the engine wants/needs you are probably masking something else.

I went through this with my Demon and as it turned out I needed a hotter plug and some good wires. A rich mixture is easier to fire than lean so as I went richer the car ran better.

I'm not sure what kind of plugs those SP II heads use but if they take a 3/4" reach 14mm gasket style plug try and extended tip plug like the Autolight 2393's or an NGK FR4. The extended tip plug is easier to fire and stays cleaner -- especially if you drive it on the street. I had issues with the NGK racing #8 plug causing my engine to break up . . .

[caribbean camaro]

Thanks for the responses - Eric & Kristofer - you are probably right - the off idle problem was actually a popping backfire - and so I tried to jet the problem away - and I did - but wasn't really running the car at the track at that time competitively

we checked the float level - and they were ok - the back had a slightly faster dribble than usual - buy it wasn't pouring

This is a quote from world castings web site

"Spark Plugs: Sportsman II heads use a 5/8 reach plug such as an Accel 276 or equivalent. Sportsman II heads with angle plugs, an Accel 276S may be used to gain additional header to spark plug clearance.

I do think I need a hotter plug than AC R43TS - they are 45TS and 46TS options

Does anyone have any cross references (or a site that does cross references) to the extended tip autolites or AC delcos that Eric mentioned

By the way the plugs were all dusty white when I pulled them - I used VP 12 racing fuel during those runs - does race fuel kill plugs at a faster rate??

[Eric68]

I personally belive that race fuel does in fact "kill" plugs faster -- the lead deposits don't help matters any.

I'll post if I can find a cross-reference, but it will be little harder because the cross-reference charts won't tell you what std plug is equivalent to what extended tip . . .

[caribbean camaro]

Eric, I picked up cross references at advanceautoparts.com website - looked up plugs for my car as World Wportsman II use same plug style as std. chevy heads

Thanks to all for the tips so far -

I have not started her up yet but I have baselined the carb as close as possible to stock (well just one jet size up both ways) to 68/77 and the squirters to 31/28 (stock is 28/28)

I thought I would try to play with front squirter at 31 and upwards to see if the off idle stumble stays away

will keep you posted

[Fast Jack]

Put a new power valve back in it,(take an idle vacuum reading cut that number in half add 2 this should be close for the power valve) or it will never be good going down the strip and running around slow to get back to you're pit. The jets are also to big put whatever holley had in it to start with, reset the flotes and work from there. The plugs don't matter much at this point so save you're money for now and use AC or Autolite what ever are on sale until you sort out the carb
Make sure that gas is not over flowing and running down the bores when you shut it off.

Jack

[Fast Jack]

Power valves are a big subject. First there is almost no manifold vacuum at full throttle. The power valve is an enrichment circuit, low RPM vacuum holds it closed, when the carb goes full throttle the lack of vacuum lets it move to the open position allowing more fuel into the air full mix. If you take out the power valve, you need to enlarge the main jets so the carb doesn't lean out on a full throttle pass. However when you're not at full throttle the vacuum pulls to much fuel through the large jets making the mix very rich (ie: raw gasoline in the plenum) the raw gas gets everywhere in the runners on the valves, in the cylinders and on the spark plug, This creates a very rich condition that does not help the spark plugs start the engine. The best solution hear is to lean the area out (more air less fuel) so open to full throttle and you get more air into the engine and at full throttle there is less manifold vacuum so less fuel moves through the jets helping to lean out the chamber as the air fuel mixture leans out the plugs become able to light off the mix and it fires with a pig puff of smoke and sooted plugs.

If you don't tow you're car around the pits you need a power valve. Don't get me wrong I do believe it can be tuned to work OK but not good. I think the only reason anyone would want to remove the power valve is because of other problems in the tune up that would cause a back fire, but this is the problem that should be addressed, not by just removing the power valve. A back fire can blow out the power valve, when this happens the power valve can no longer hold the enrichment circuit closed, and the air fuel mix goes rich.
The only other reason to remove the power valve would be just to tell there buddies how bad there motor is because they use bigger jets.

Jack

[caribbean camaro]

Fast Jack - the metering block on the secondary side of my carb came from factory without a provision for power valves

I did not plug the rear power valve myself - according to holley numerical listing info - the 650's have "n/a" for a power valve part number for the secondary metering block

Thats why the factory jetting is listed as 67/76 on my DP 650 carb list number - which has a " -4 " suffix

I do have a power valve in the primary metering block

As it happens I started the car last night with the 68/77 jets - 31/28 squirters and some good used R45TS AC plugs I had at home, and it is free revving cleanly without any off idle stumble or popping

So I am back on the road - I will see how the car performs with this baseline and go from there

Thanks for all the help

I will start from there to see how that

[Fast Jack]

Great to hear that you're back on the road! Oh and by the way I didn't mean that you took the power valve out I read in you're post that you are working with a used carb, and was guessing that the previous owner may have removed it, It happens a lot then people think the carbs are junk, and sell them off.
So anyway it sounds like you're getting a handle on it , and bringing it around. If the problem persist check the power valve for a hole. They are a diaphragm so a very small hole will cause it to malfunction. Any backfire could cause a leak, or even just old age, and the alcohol additives in gas that dry things like these out and they sometimes crack. Also if the dead spot off idle comes back check the accelerator pump for a good smooth squirt.
Anyway have fun cruising

Jack

[SLEEPER 86]

try the 70's in the primaries!tune the holley's accelerator pump to perfection,make sure the floats are close,check for vaccum leaks!
oh and don't forget to clean the needles and seats,or replace them!my bet is the needle n seat that control the float level got some crap in it that you can't even see.or the air bleeds are clogged.
Eric B