Have New Set-Up, Have an issue, Please Help

[BigBlockMonte]

Hey all I have an issue with the new set-up in the chevelle. Sometimes it's there and sometimes not. First heres the new set-up

 

468 BB

SRP/Je Pistons (26cc Dome)

Eagle H Beam Rods

Forged Crank

Compression comes in at 10.23

Aluminum Heads (320cc runners) 119cc Combustion Chamber(rect Port)

Scorpion 1.7 roller rockers

Edelbrock Air Gap Intake

Holley Avenger 870 Carb

Comp Cams XE284h camshaft. 574/578 lift. 240/246 duration @.50 110 lobe seperation

Proform HEI distributor with Scott wires( pretty thick) maybe 10mm.

NGK plugs gapped at .35

110gph fuel pump

hooker comp headers (2" tubes) 3 1/2 collector.

Exhuast gets reduced from collector to 2 1/2 to what appears to be advance auto muffler(not sure). Then after muffler goes to 2 1/4.

torque converter is trans specialties low stall conveter 2800-3200 stall.

28" tall tire in the rear with a 3.31 gear (single spinner)

trans is a TH350 with mild shift kit.

 

Need other info just ask.

 

Heres what is does.

 

You step on it one time and it's flat up the RPM range until about 5k then it clears up and then she screams. It's like i'm pulling something, then someone cuts me loose at 5k.

 

Then other times, you step on it and she'll come in alot sooner and scream the whole rpm range.

 

I thought it was to cold at first. I had a 160 thermostat in it, and it wouldn't go about 155-160. It appeared to run a little better when warmer. So I replaced the 160 with a 180. Now it runs at 180-185. Same deal. Step on it once, (flat) next time, (hold on)

 

the fuel line from the tank to pump is still 5/16. It will be changed over to 3/8 this weekend.

 

my nieghbor thought the squirter was a bad design, and took one of his double pumper. The one is took out I believe said 42, the one he put in said 35. It seemed at first to wake up ealier than 5k. i felt it approx 4500rpm. But then the next run. (flat again).

 

I'm not sure if any on you have gone through this, but I don't know what to try. I don't have another carb to put on it to try, but i'm working on borrowing a holley 750. ( i know its too small, but if its not flat, maybe thats my problem)

 

Please any thoughts on this are very much appreciated.

 

Thanks everyone.

[monte70car]

You have three choices to check one is the squirt which your neighbor changed to the 35, the second item to check is the pump arm make sure you have either .10 or .15 clearance with a feeler gauge at the pump arm you use want to be able to push the feller gauge between the arm and the pump arm, the last item is the pump cam which the pump arm rides against. I've found the pink color one to work the best with my 750's

[Winston Wolf]

If it's an intermitant problem, you may want to try a different distributor if you have one laying around.

[Heckeng]

Have you played with the vacuum secondary pod and or spring by chance? It sounds like you could have an intermittent vacuum leak on the carb and the secondaries are playing games on you.

 

You can get a bog if the secondaries open up too quickly and then once airflow picks up again, the engine will come back to life. What spring is in it now?

 

There is a cork gasket that seals the vacuum pod to the main body that can dry up or crack sometimes. Also, the seal around the secondary diaphragm could be leaking, and if you have a quick change kit, the rubber seal under the quick change cap could also leak.

 

Could also be distributor like mentioned already. Maybe your mechanical advance weights are sticking sometimes?

[wallaby]

5000 rpm? that's pretty far up there to be waiting for power to come in.

You need to figure out why the engine doesn't want to run slower. Most problems iron themselves out by 3500 rpm or so, but yours is holding you back until the engine speed can overcome it, and that's not happening until 5000 rpm!

 

It might not happen all the time, but when it does, it sounds pretty major. I'm with Scott on this one; I think it sounds like your carb is opening the secondaries too wide too early...or they may not even be delivering fuel. I'm not a Holley guy, but is it possible the secondary float level is low, or there's a fuel restriction to the secondary bowl?

 

Does the engine run smooth through this process, or is it misfiring or coughing?

[BigBlockMonte]

the engine runs smooth through the whole rpm range. the carb is new out of the box from summit. been on the car for a couple days now. I haven't changed anything on it minus the squirter yesterday. I did ajust the fuel mixture screws on the side. I adjusted them to where I would get the most vaccum. adjusted the idle to run at 1000 in park, and around 800 in gear.

 

One more thing, my neighbor also thought the choke wasn't opening all the way starving it of fuel, so he wired the choke all the way open.

 

That issue may be deleted once I changed the thermostat to a 180 instead of the 160 I started out with.

 

I'm goin to remove the wiring of the choke and let it be as it was.

 

 

[Mike 57]

What is your "all in" timing

 

[wallaby]

I'm still stuck on the "sometimes it does it, sometimes it doesn't" thing.

My gut says it's fuel related.

[BigBlockMonte]

well i did a few things today, changed out carb gaskets just to be sure and resealed the carb, ran the car without the brake booster on to see if the problem could be an air leak at the booster, no luck. also ran the car without the trans vacuum line( still no luck). Maybe its me but it just seems like I hear alot of air moving. Maybe the air gap intake, aluminum heads etc. don;t know. I sprayed some carb cleaner around all the vaccum lines to see if the engine revs up a bit from sucking it in. no luck.

 

still flat, then hold on. I did nail it once tonight and it broke the tires loose from a roll and screamed up the highway. so I don't know. I'm really thinking theres something goofy with the carb. I talked my buddy in getting his holley 750 over tomm and swapping it out to see if it does the same thing. if not, then i have to figure out how summit will get me a new carb, since its only a few days in use. never had to do that before.

 

but if it does the same thing with the 750. i don't know. guess i could go down to the parts store and buy a msd street fire dist, slap it on and see what that does, if it fixes it, cool. if not, just return it.

 

tonight it felt the power was coming on then going out then coming on again at 4500 to 5000 then cleared up. it did this consistenly, minus the one time i was at a 25mph roll and nailed it.

 

my neighbor seems to think my secondaries are not coming on fast enough. told me to put a screw in the slot for the secondaries to make them come on quicker. sound right?

 

wish i wasnt so dumb on the v8's. but this is how you learn right.

[Andy's Auto]

Time to get back to the basics. And I don't mean Lukenbach Texas. I honestly think you do not have enough cam to support those monster heads. Remember, an 049 out the box only flows arund 280 CFM. I have built a few 400RWHP engines with bone stock GM irons. And aluminum tends to draw a lot of heat from the combustion chamber. 320 CFM? Yeah, thats pretty big.

 

But to make the best of what you have you need to go to work on the tune. I do like the Proform HEIs but .035 gap? How much nitrous are you running? I would replace them with another set of hot Delco R45TSX gapped at .055 to start and see if she likes your touch. If so, advance the snot out of the timing until it hard starts hot then back it down a couple. Or start at 10 degrees initial and total it 34 and work you way up to 40 if the starying system can handle it. Alloy heads love timing, but they eat starters if you go too far.

 

Pin the secondaries? Never. Muck with the springs but never pin a vac sec. Just begging for a huge bog until the fuel starts to flow.

 

You have a 475 horse Mans Engine but building it is only half the equation. The other half is tuning. What you will find is something Bigiie reallyt likes and a bunch of stuff that won't hurt you.

 

Andy

[BigBlockMonte]

Time to get back to the basics. And I don't mean Lukenbach Texas. I honestly think you do not have enough cam to support those monster heads. Remember, an 049 out the box only flows arund 280 CFM. I have built a few 400RWHP engines with bone stock GM irons. And aluminum tends to draw a lot of heat from the combustion chamber. 320 CFM? Yeah, thats pretty big.

 

I still have this camshaft laying the garage, i didn't use it because i feared it wouldn't be a streetable cam.

 

http://www.lunatipower.com/Product.aspx?id=2044&gid=248

 

 

 

 

Andy

[BigBlockMonte]

also would it be easier to put a wideband on it to see if it goin lean or rich causing it to go flat then come back to life?

 

instead of buying new plugs, could I just regap the ngk's i have?

[wallaby]

Really I think it has to be something that changes from time to time. Spark plug gap is a constant. Sometimes it runs great, other times it falls on its face. I'm wondering if maybe it's fuel flow...you start out great until the float bowls go dry, then it just so happens that it takes the bowls the same ammount of time to refill as it takes for the engine to stagger up to 5000 rpm.

You need to find a pattern to its behavior. Does it run great the first time you go through the gears and then fall flat on the second attempt? Does it make a difference when it's cold or warmed up? How well does it perform if you use less than full throttle? ...stuff like that. When you can predict when it's going to act up, you've got it more than half way solved.

[Andy's Auto]

The Wallaby might have a point, or he might not. I wish it was in my bay right now. I would go ahead and regap the plugs and give it a beat. Crank the timing a bit, give it a beat. Lose the Street Avenger and thow a 750 double pumper. Either a Holley, an AED, or a Prosystems. I hate vacuum carbs even though I sell a bunch. Kids can't keep a chokeless carb running cold to save their lives. Give it a beat. Double check the valve lash.

 

just for gigg;es, throw a volt meter on your ignition hot and make sure you have batt voltage.

 

Don't feel bad about anything. I have built a ton of "11" second cars only to have them fall on their face, break up, and run mid 13's until I found out where my brain went.

 

Andy

 

Andy

[TommyP]

I would check the the rear float adjustment first as it's easy and free. Then maybe check the timing with a light to make sure that it's advancing when the RPMs are going up and also what your total timing is. I guess after that I'd look at the secondaries on the carb to see if maybe they are sticking sometimes and not opening up till you have a bunch of air flow.Stock I think that a Holly comes with a fairly stiff spring in the secondary so I'm not sure that they would be opening too soon or result in that long of a bog if it did.

[BigBlockMonte]

well some progress was made tonight. My buddy came over with the 750 holley, we put it on, and instantly things seemed better. it idled better and smoother. it also drives alot nicer now, i actually don;t mind the stall now. took it on the highway and she screams all the way up. I did lose a little top end, simply because its a smaller carb.

 

so I'm guessing I have either a bad carb, or I went to big for my application.

 

Called up summit and told them, and of course they say those carbs are perfect out of the box, and flow tested to 100%, blah blah blah.

 

he said he would give me another carb if i wanted to return that one.

 

i'm questioning should I stick with the 870 avenger series.

 

or maybe go with a smaller carb, say a 850, or 830, or maybe an 800 even. I like the way the 750 drives, idles and behave minus the loss of top end. so I'm figuring going a tad bigger will give the same response the 750 is but give the top end as well.

 

what size would be optimum for my set-up?

 

I changed nothing else from the 870 to the 750. no timing, no messing with idle screws, nothing. I would like to keep this one, but my buddies not giving it up.

[Sam (Bones)]

I wouldn't go smaller than a 850

[BigBlockMonte]

okay, then the 870 avenger must of been just junk. If i can get the car to drive like it doing now with the 750 and have the top end it did with the 870. I feel she'll be perfect for me. Maybe a tad more gear a posi rear end and leave here alone.

 

i'm just excited the car actually ran good, i thought i messed something up, and the whole time the carb was the culprit.

[Mike 57]

I have a 870 avenger ran 11.6s on my 505 also ran good on my 60 over 427. Had to tinker with it to get it just right.

[BigBlockMonte]

maybe the avenger series is okay to use. I have issues with two of them now. the 770 that was on the monte and now this 870 on the chevelle.

 

I'm wondering why a old holley 750 makes the driveability so good, even though it lost some up top. The stoplight to stoplight driving is damn near perfect.

 

what is the big difference between the 750 & the 850? will an 850 have less street manners but perform up top?

 

i need a lesson on carburetors choices and the way they will act with certain set-ups.

[Mike 57]

Smaller carb has better low speed manners, more velocity because of the smaller venturies.

[Andy's Auto]

Duder, I would pull that Avenger apart and see what got caught up in it. I used to get pissed when I would buy a new carb only to have it run like crap out the box. I try to return it only to get denied. That is how I learned how a carb works and what it does.

 

i would guess that something got caught in the float bowl either clogging up a jet, pinning the power valve or covering an air bleed. Carbs just do not have that many moving parts so what goes wrong with them is usually from an outside source. Dirt, water, and sweat wreak havoc on carbs.

 

Glad you are on the right track with getting that transmission smoked.LOl.

 

Andy

[Heckeng]

Like Andy said, there is nothing wrong with that carb generally speaking, you just need to tune it, or in this case, maybe figure out what the problem is with the one you have. I would guess crap in the bowl clogging jets, or potentially shavings in the air bleed lines or something.

 

OR. . . you could just send it back like Summit said they would do. I have run a 750 vac sec holley and a 750 Speed Demon on my car and they have both been excellent. I would stick with the 750 as opposed to the 850/870 because I believe they use larger main body venturi diameters which will lose velocity. If you didn't want to do the 750, I would get a 950 Holley which uses smaller venturi diameter than the 850 but a larger base plate.

 

Just my $0.02

[BigBlockMonte]

so the 950 will act like the 750 does now, but keep pulling hard up top?

[BigBlockMonte]

so using the 850, i'll lose my quick snapping throttle response. the 750 gets up a goes. had it out tonight. smokes the tires through first into second. getting on the highway from a roll, just smolders the tires (well tire since its a single spinner).

 

or could it be a perfect union between the snappy low speed driving and keep you in the seat in the upper range, if i was to maybe jet the primaries down a little. or am i thinking about this all wrong?