1987 302 roller cam problems!!!!!!

[mopar_66757]

ok... I have a 87 302 roller cam engine, rebuilt it and its all stock except a Pro Comp dual plane intake and a Holley 600 cfm list 1850-3
and Headman headers, HEI conversion distributor at 7-8deg. adv.. Okay here comes the whining

It starts up fine barely bump the starter and it fires right up, it idles fine and smooth with 24lbs of vacuum, once u start driving say in 3rd gear and starting at 1300RPM and slowly accelerate there is a hesitation about 1/4-3/8 throttle and picks up, but say u are at any RPM and go more than 1/2 throttle it just sounds like it misses on 1-2 cylinders....and it will do it all the way to 6500RPM and more u try to use the "power" the more it misses like if it runs too rich if that makes sense... I went from a 750cfm to a 650cfm now to a 600cfm.... and the plugs were little rich with the 750, but I had it jetted with smaller jets. Now with the 600cfm I've ran the truck for right at 200miles with these plugs.

I pulled them and took pics and I think the motor is running fine on fuel mixture? I don't know what to do....I can close off the metering screws and the engine dies showing that the powervalve isn't cracked or leaking...this motor hasn't ever backfired. this thing is making me very angry! I think Im going to try a compression test on every cylinder, then maybe just maybe that junk Pro Comp intake is leaking vacuum in the lifter valley??? but the plugs aren't oil fouled any and it holds good smooth vacuum???

I'm either going with a vacuum leak or a broken valve spring??? any ideas??? its got me baffled...

 

[v-8power]

I would say if you have a vac leak it would not idle very smooth.
Do you have access to a different distributor by chance?

 

[Teddyzee]

I'm not well versed in setting with a carb, but that is not very much timing.
Does your advance work properly, or as you want it to? My (EFI) truck runs over 35degrees of advance just off idle.

 

[dangerranger83]

7-8 degrees isn't enough. 10-12 degrees is where it should be.

I would adjust your timing and go from there.

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[mopar_66757]

I have tried the advance at 10 and all the way up to almost 38... at idle 500-600rpm its at 7-8 deg. and u slowly rev it up, watch the timing advance nice and smooth.... lastnite I disabled the back barrels....well took a little spring and hooked on to a intake bolt, and to the carb's vacuum secondary diaphram linkage. took it for a drive and it didn't have quiet the power but there wasn't any sluggish miss?
The carb is a used one i got from a friend, Im wondering if the back venturi's has been drilled bigger... allowing too much fuel when the back barrels open up? and somewhere I can't remember the color coding on the diaphram spring... I need to just reconfigure the carb totaly i guess... Im not sure what Info I need to adjust the carb correctly...
and I was off on the vacuum reading It holds 22lbs of vacuum at 600rpm...
I guess I get to search for info on holley..

 

[PetesPonies]

slightly off topic . . but did you use a distributor with a steel, not cast, gear ??

 

[mopar_66757]

you know I can't remember... but somehow on my problem the back barrels seam to be flooding it i guess, so lastnite i took and cleaned out the high speed air bleeds on top of venturi's with carb cleaner.. hoping maybe that was the problem... I'll find out here in a bit when i leave for work...

 

[PetesPonies]

If you used a cast gear it will chew up and spit metal into your engine, because of the steel roller cam. Also, your ignition timing will not be accurate as the gear wears.

 

[dangerranger83]

Staying on subject, mine is acting the same way. Hesitates, stutters, etc...when my secondaries go to open or when I shift into 4th, but once they do I'm fine, and when I'm on it for a bit acts like it wants to die, but won't like the carb is getting drained and use to never do this either till recently. I haven't changed the settings on anything, timing is dead on.

I'm running an edelbrock 1403 500cfm that's not even a year old, dual fuel filters that just got replaced and didn't change how it has been acting either. Idles and starts fine.

Got a new car last weekend so I've been driving it till I get time and money to look into why my truck is doing what it's doing and I hate to do that.

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[mopar_66757]

well after work im going to get enough vacuum line and tempary install a vacuum guage inside and drive it.... Im thinking I need to change the power valve to a 6.0 and get a higher tension vacuum secondary spring so the back barrels open in higher rpm. also i put my timming on 12-13 advance.

with the vacuum guage hooked up and i open it up wfo in nuetual, the vacuum drops to 4-5lbs, im sure the 600 holley has a 65 pv in it.. Im just wondering what it does under a load at wfo ... im no carb guy but the front barrels are jetted right and the back barrels are way too rich??? I guess i need to get learning and try to figure out how to lean out the secondarys?

 

[jmcleek]

What is your gap on #6 and 7 plugs? You have some discoloration near the front of the tip which could be where the gas would hit. Also what coil are you using in your vehicle, using the wrong coil could cause the wrong amount of voltage to go to your spark plugs and causes a miss. I would check your gaps in your plugs and then use a spark plug tester to see the spark or a spark wire tester would work too. A blueish white spark is good but the closer you get to the color orange the worse the spark. On mine we have a smaller carberator, about 500, and it works just fine. For a while I had a miss on one side of my engine but after we got new spark plugs and gaped them according to the specifications of the engine we are using, there hasn't been a problem since.-Becca daughter of jmcleek

 

[87fiveoranger]

I had this same problem once with my 302 and its a 92 model roller motor with cam heads headers hei distributor and i had a 650cfm holley carb on it and setting aat an idle it was fine but if i went down the road it would miss like it was out of time. I done some research and my grandpa and dad both couldn't figure it out either and they are both mechanics and so am I!! So i read and read trying to figure this out and i came across an article about the diaphragm in the carbs going bad in the holley i thought to myself no surely not i took my carb off my truck (brand new carb by the way) took it apart and sure the diaphragm was bad in it i ordered a new put it in put it all back together and my truck ran like a brand new one. I would look into that if you haven't got it fixed by now.
-Brandon