Trans_AM_88

I’ve been having this problem for a while now. If I drive my car nice and slow it seems to run decent, but if I try to 'get on it' a little it just starts misfiring and hesitating like crazy and I cannot accelerate at all. All my spark plugs are black as charcoal so I thought I was running rich.

Specs:
I’m running the Bosch platinum 2 prong spark plugs (I know )
Carbed L98
Holley 4776 600cfm carburetor
Edelbrock performer intake manifold
Holley blue electric fuel pump
Running at 6.5 - 7 PSI fuel pressure at the carburetor.
New cap, rotor, pickup and coil on the vacuum advance distributor.

I have the vacuum advance hooked up, but my PCV isn't hooked up on either valve covers (this carburetor only has one 3/8 vacuum port and I’m using it for the brakes)

Also:
I originally had an edelbrock 1405 (600cfm) w/ elec. choke on it before and it was giving me the same problems. I thought it was the carburetor and since this one was old I bought a new one. However the same problems are still present


My auto shop teacher at school said that I may need some hotter burning spark plugs and/or MSD ignition or something similar. what do you guys think?

Trans_AM_88

anyone?

TraviZ

iTrader: (2)

are you sure your sparkplugs are the right ones for your vehicle? do you have an oil leak that is covering your sparkplugs, causing them to not fire?

iroc-si

This sounds similar to the condition my camaro was in. What I did to fix it was to replace the plug wires (they were looking bad and stock) with accell superstock spiral (yes msd/taylor wires may be better but you don't have to spend that level of cash!)

Also changed plugs from NGK BPR6FS to NGK UR4 This made them the correct heat rating for the engine. and got them to the required gap of 45thou

After that it runs very sweetly. You should not need a MSD ignition module. If you've got the cash to spare then sure they should improve the gas mileage.

One question I would have is the black you mention on the plugs, is it on all the plugs and is it oily or more like charcoal? If its oily then you have a gasket problem, perhaps. If its charcoal, then I'd get the ignition working well first then consider mixtures.

Si.

Trans_AM_88

the wires are like brand new...just been sittin on the car for a while when it wasnt running (~3 months?) so they should be fine. those NGK UR4 spark plugs you mentioned...are they "hot" spark plugs?

my current spark plugs are undoubtedly charcoal black (texture and color). i believe i've got the mixture screws as far down as the engine will go..


ya know, i got these spark plugs from autozone and they pobably gave me the wrong ones

Maverick H1L

iTrader: (8)

The Bosch +2's I picked up at AZ are factory set at .045 gap and should/cannot be regapped closer or farther apart. You may try getting ACDelco plugs (hey, just over $1 each, can't hurt!). Also check your O2 sensor as it may need to be replaced and may be giving out a bad signal. Last but not least, check the vapor can. If it is leaking, you are in trouble! If the leak is serious enough, you can be getting gas in your oil and are on the verge of needing all new bearings, rings, possibly a crank, etc... I know.. this happened to me when I replaced the vac lines with good ones .

iroc-si

The NGK UR4 plugs are 100% stock heat rating for a 305 or 350. They are fairly simple plain plugs. Over the AC delco plugs and a NGK BPR4FS the UR4 plugs have this V groove which I cannot dispute as being an improvment (done the time in a high voltage lab playing with electrode shapes, to know first hand!) with little or no side effects in a near stock engine.

Anyway, AC delco or NGK are the way to go to avoid having any issues, and at $1-$2 a shot they ain't exactly expensive.

Si.

robvas

Try a different carb or have yours rebuilt by someone who really knows

Trans_AM_88

i no longer have TPI. i ripped out the computer, o2 isnt plugged in and i threw the smog canister i nthe garbage

i just bought a new carb...


thanks for the reply. i think that is what i'll do, get the correct spark plugs and keep it simple. it's hard to believe that just the spark plugs are giving me sucha big problem, but you never know.

plumminfool

is it in time?

Trans_AM_88

what? timing? i tried as much as it would go...from 4* advanced all the way up until it started pinging - and everything in between. nuthin solved it, a lot of advance helped though, but not that great

Trans_AM_88

i bought the NGK UR4 spark plugs today. do i have to regap them to .45?

Trans_AM_88

ok i put the NGK's in and i still have this problem unless i run with the choke WIDE open. anything else and i get massive stumble. even with the choke open completely THE POWER JUST ISNT THERE. my buddies 86 irocz 305 (bone stock except a edelbrock 600cfm carb) has way more power than my car (mine is a 350). i thought of possibly the rear end gearing of my car (2.77 i believe) not really helping out either since my car came auto stock (now it is manual)

sorry to spit out all this info at you guys but im really stumped.do you guys think that i need a cam better suited for carburation? technically this is still a L98 (except now it's carbureted) so maybe the L98 cam is giving me troubles???

xpndbl3

iTrader: (5)

i'd post a similar question on the carb board for the best answers.

Trans_AM_88

been there, done that

https://www.thirdgen.org/techbb2/sho...hreadid=220518

xpndbl3

iTrader: (5)

sounds like you need a jet kit. put in leaner jets, and it'll give back some power. watch your plugs and they should turn a brownish/tanish tint when you get close. not a big deal....what jets are in it now?

i'd start with the primaries and go from there. i picked up a BUNCH of power SOTP by leaning it out some, since my plugs were BLACK. also check out your idle vacuum to make sure it's normal and not bouncing around at all. PLus you might need a different power valve based on your idle vacuum in gear.

Trans_AM_88

new jets? this a brand new carb though! its only a 600 and the engine is a 350ci...am i really over carbureted? and my idle vaccum in gear...isnt that for autos? i have a 5 speed

my buddy is running a 600cfm edel. carb on his 305 and i dont think he changed the jets

Danger

Never messed around with the jets in a car before, but motorcycles are very sensitive to jetting changes due to different temps, elevation, humidity and fuel quality. Makes sense that tuning a car carb could provide improved performance.

Fairly Strange

600 Eddie shouldn't be too much for a 350 under any circumstance.

Sounds like a possible weak spark condition. Coil, perhaps.

Vader

You have the idle scres all the way IN on a Holley? Aren't those idle rate screws, not mixture screws?

Trans_AM_88

well theres 2 small screws on the sides of my carb...i turned them in until the engine started dying out...then i turned them out until it idled smoothly.

i agree it may be there is a weak ignition problem somewhere...but i couldve sworn i just replaced the coil a month or two ago...perhaps they gave me a weaker coil that just happens to fit??

ive done so much work to this car its hard to remember what i've replaced and/or fixed lol


do you guys think i can switch over to those systems where the coil is seperate from the cap? like if i get one of those MSD blaster coils and the cap that has the plug in the center? right now i have the HEI setup with the coil directly on top of the cap.

Trans_AM_88

walterrao

platnum plugs are bad for cars not meant to run them, because they take more voltage to fire then regular plugs

xpndbl3

iTrader: (5)

sounds like you need to buy a jet kit like i already stated. go buy a book on holley carb tuning from your local border's or barnes and nobles and go from there. all carbs need to be tuned from out of the box.

Trans_AM_88

damn really? so all that 'out of the box performance' is ? ill stop by barnes and nobles and read some of the books for sure...any suggestions for what i should look for (what kid of jets specifically)?

Trans_AM_88

xpndbl3 i found the holley carb turning book at b&n. i read through it but i didnt buy it because it was like $25 .


also, i put on an accel 45,000 volt coil, and it did NOTHING.

Trans_AM_88

Holley Mechanical Secondary Double Pumper Carb (600cfm / Manual Choke)

Primary Main Jet: .070"
Secondary Main Jet: .076"
Single-Stage Power Valve: Opening Vacuum: 6.5'' Hg.
Primary Discharge Nozzle Size: .025"

Trans_AM_88

are those jets too big for a 350 L98?

xpndbl3

iTrader: (5)

i'm running 66/76 on a 305 right now. so it all depends on the motor, my 305 is about 300HP though so take that into account. are your idle screws set right as well?

Trans_AM_88

whats the best way to choose jets?

xpndbl3

iTrader: (5)

seriously....a book would help you out with ALL of these questions. go to holley.com and they have a tuning section as well.

basically you jet down 2 sizes at a time until the plugs start to look tanish-greyish, or clean, not black and sooty like that look now --ie to rich.

Hodge

Haven't seen any mention of checking the float levels or fuel pressure.

high FP or too high float levels can flood the carb and cause it to run rich.

What is your FP at?

and have you checked the level in the float bowls?

Hodge

Trans_AM_88

FP was at 6.5 - 7 PSI. i have it at 5 psi now, still the same problems.

the carb is brand new so the floats should be ok. one thing though, i went to take off the fuel level plugs but the car stalled out...why is that?

Hodge

I gotta lean back towards weak spark then.

not sure about that stalling thing

PLANT PROTECTION

iTrader: (6)

I tighten up on a $25 book too. Go to your local library.

Trans_AM_88

i just put on a 45,000 volt accel coil on and i have accel wires . what should my spark plug be at gap be at? either way, my plugs are still black as hell, i gotta be running rich


lol, yeah and the book wasnt very big either

Trans_AM_88

double post

Trans_AM_88

ok guys i took it to my dads friend who is a mechanic and he said my carb that is on there now is too big . can i just put smaller jets in, or is carb really too big?

Holley Mechanical Secondaries 600cfm double pumper on a stock L98 5.7 liter engine.

bluegrassz

iTrader: (3)

I had the same problem. I put a holley 750vs on my stock L98.

I had the black soot on the plugs and the hesitation. I ended up changing the jets. I also checked the vaccum and ended up changing to a 8.5 powervalve. You also need to check the float levels. Just because it is new and right out of the box, dont mean it will be right for your car. They just give you a starting point.

I also ended up going up in size with the shooter. takes out some of the hesitation.

You also need to check for vaccum leaks around the carb base and the intake.

Between different jets, correct powervalve, float adjustment, air screw adjustment and timing, you should be fine.

Let us know what you find out.

Trans_AM_88

hey guys, i just talked to my mechanic and he said that i have a 750cfm holley on my car...jegs sent me the wrong carb . im going to call them right now...im pissed

xpndbl3

iTrader: (5)

a 750 is still fine on your SBC, i have a 305 and i have a 750 on it. it's not the carb, it's you not tuning it right.

bluegrassz

iTrader: (3)

Just keep the carb. Like I said, I am running a 750 on my stock L98. Just add a good cam, set of headers and a good gear.

You just need to tune the carb. Either buy a book, find a friend with good tuning abilities, or learn for yourself. It is not that hard.

How much vaccum is the carb pulling?

Trans_AM_88

yeah but read bluegrassz's post...he had to change a lot of parts on his. but then again, seeing as me and bluegrassz have stock L98's, cant i just skip the guessing and get the same size jets, powervalve, and shooter that he has?


blue, can you list exact specs of what you changed on your carb?

i dont know how much vacuum im pulling. how do i check this?

bluegrassz

iTrader: (3)

First, get a vaccum reading from a vaccum line on the carb. Mine was like 17" with the trans in gear (700R4). So this told me that I needed a 8.5 powervalve. What ever you vaccum is, devide it in half and that will be close.

I installed a metering block in the back of my 750vs for jet adjustment. You have a mechanical so no worries. I used 74 in front and 76 in back. This is for cool weather keep in mind. You may need 72 front and 74 back, this would be a good start.

You have a 25 squirter in right now, change to either a 28 or 30. This should help with the hesitation.

Check your float levels. With the car level, pull each site plug out and see if fuel flows out. if it does, its to high. The fuel should trickle out when the car is shook. It should be just below the bottom of the site plugs. You can get clear ones to make it easier.

After these changes, you should be able to adjust the timing between 8* and 12* base timing.

this should get you in a ball park.

let us know the results and good luck.

Trans_AM_88

ok, ill get a vacuum reading when i can. with the float levels, i tried checking them put as soon as i pulled the plug off the car stalled...so i just checked it with the car off, and they were fine.

bluegrassz

iTrader: (3)

OK then, Just get the vaccum reading and we will go from there.

87Formula4bbl

Like most everyone else suggested, I also agree its the carb out of tune. I know theres a huge difference between the two, but I'm going to use my carb as an example. CC Qjet. Had it rebuilt (myself) this winter, along with new heads. Had the topend of the motor completely apart, so I had nowhere to start off here. Slapped the carb on, it ran (idled) pretty rough, but got the base timing set in where I wanted it. Took it up the road and it would sputter and cough and not go worth a crap. I started off with the rich/lean stops almost all the way out, so it was PIG rich. Ran like complete poo. I now have it adjusted down to where it should be, no hesitation, great throttle response, and nice performance. It's all in the tune man. I'd say it needs to be leaned out big-time. Go with these guys' opinions, they know more about your carb than I do, I'm just trying to illustrate how my problem was similar to yours until I got it dialed in, and now it runs pretty dang good.

-Ben

Trans_AM_88

well its all fixed guys. i got it back from the mechanic today and WOW. so much power!! he put in new jets, 64 and 72. and he said he cut something in half (dunno what he said it was a term i was unfamiliar with) and he fixed the linkage for the secondaries to kick in later. damn this car is a beast again!!!!

PLANT PROTECTION

iTrader: (6)

Sounds good, unfortuately you needed to pay someone tho.

Trans_AM_88

yeah, but i just couldnt deal with it anymore. i spent about $500 and it did nothing at all. i got really frustrated and just had to bite the bullet.