engine running problem.. 402 bbc

[matt_field]

hi guys, im having trouble getting my 402 bbc to run right.. i had the motor built last summer by a machine shop close to my town. they since closed shop and are no longer open anyways the motor is .030 bored. cant remember the heads. i think 781? they flowed similar to the 049 heads. my pistons i remember were BIG dome. i have a edelbrock rpm intake. 770 holley, headers etc

anyways the problem im getting is the engine seems to load up so bad at idle. you cant stand behind the truck at idle, your eyes burn its running so rich. when you get on the road and step it down it doesnt want to move like it should. the machine shop figured it would make good hp. cant remember the cam i have. its pretty lumpy, id have to look up the specs. we have tried diff. carbs still does the same stuff. i have a 2300 stall i believe. its been a while since i did it so its becoming foggy what parts i have with out looking.

also it doesnt want to start very good. it acts like the carb may leak down after sitting and it is flooded or somthing, you have to get your foot into it to make it start. the choke is not hooked up either. but have never had trouble with my other vehicles with that not hooked up. any help would be great! sorry for rambling on and on

this thing is just making me frustrated, im wanting to get rid of this motor if it keeps this up! thanks guys

Matt

[corn]

sounds more like a carb issue than an engine issue...

[matt_field]

if an intake manifold is leaking, what would the symptoms of that be? there is snow on the ground now so i dont drive the truck but i want to get this figured out before summer

[Pont406]

Did you have a backfire prior to this? Possible blown power valve. Get a vacuum gauge and check vacuum at idle.

[matt_field]

wouldnt the other carb fix this problem though? i also had a brand new 750 holley on it and did the exact same thing as my 770

[1968SWBBigBlock]

I would get a vac gauge and hook it up and see if you do not have a leak someplace.
This maybe as simple as a carb gasket.
You may also be over carbed for your application. A 402 would prefer a 650cfm carb or jet down your 750 2 sizes
I would look at the vac 1st, it can tell a lot of stories

[hvychve]

if its burning your eyes standing behind it , while its IDLING, Your mixture screws could be way wacked out of adjustment, try leaning em out by turning them inwards , until it stumbles and than back em out, do each one until a smooth idle is obtained, above idle, has nothing to do with mixture screws , may be a jetting issue and possibly like someone else suggested , power valve blown, if you have access to a four or five gas machine , have someone stuff a sniffer in tail pipe and see just what you co and hc emissions are , carbon monoxide and hydrocarbons, this would be a good starting point, from what you are explainning , it sounds like carb issues, but without knowing the specs on all your components, its diffecult to really tell, if you got a total miss match cam for your head flow and big domey pistons with a sick carb, combo is everything, would really like to know what cam and heads you got , but really sounds like carb issues. ... whats timing at? whats it idling at? does it blow black smoke when you romp on it? more details needed.

[JHART]

Originally Posted by matt_field

if an intake manifold is leaking, what would the symptoms of that be? there is snow on the ground now so i dont drive the truck but i want to get this figured out before summer

Intake leaking would cause Vacuum issues that would make your truck run exactly the way you are describing. That and your running rich ... no big deal with running rich ... i do.

But if you already know your intake is leaking i would say thats your problem. But keep in mind if you have even a mild cam you could have issues with vacuum there may just need to advance your timing and adjust your idle.

-Hart

[corn]

most times if you have a vacuum leak it will smooth out when you give it a little gas. Does it run bad at all rpms? It could really be a few different things...

[matt_field]

it idles like it has a good sized cam, it feels like it isnt making much hp, it has troubles starting. im wondering if the machine shop got my cam, for my heads wrong

[mnunn454]

When my Elky showed up, it exhibited the exact same symptoms. 'So rich you could only run it in the garage for 45 seconds before you ran out gasping and wiping tears from your face.

Problem was the Holley D/P carb. I solved the problem by swapping carbs. A better solution would have been rebuilding the one I had. Start with #72 jets in the front, the idle screws seated carefully then backed out 1-1/2 turns, and use a power valve that's at least 2 or 3 notches higher than the intake vacuum you have.

Am pretty sure it'll solve your watering eyes problem. I'll bet it'll run better on the road as well.

While you're at it, change plugs and the oil & filter. Raw gas makes for a lubricant, NOT!

If this doesn't solve the problem, it might be that it needs more air to idle properly. There's a solution to that as well, but let's rule out the simple things first.

[Willys47]

I would check your vacume at idle if the power valve in the carbs metering block is labled with a higher vacume number on it it will be opening up at idle and will make you run too rich and could foul your plugs .ie motor ildes at 4.5inches on the vacume gage power valve is rated 6 inches it will be open you will need to change the power valve to a lower number like a 3 or lower. I had this problem and had to change mine to a 0 so the valve would only open at full throttle. I had a very lumpy cam in the motor and the vacume was poor at idle

[matt_field]

found some info on my motor. comp cam extreme energy cam, 274/286 .552/.555 1800-6000 rpm

pistons are speed pro forged compression 10.81, 107 cc head,.319 dome, closed chamber head.

my heads are 241 bbc heads. oval port 113 cc

770 holley street avenger, edelbrock performer rpm intake.

the motor is .030 over