help! small block masters tune in...

[87 Blue Beast]

just put a cam in a 350 and im having a little bit of a problem. first off, the cam was a comp cams XE268H (268 int dur, 280 exh dur, .477 int lift, .480 exh lift, 110 lobe seperation). the motor ran perfect before we swaped the cam. so heres the problem... i had my dad crank the motor while i played with the distributer. we got it running and it idled and sounded good. after having it running for a couple minutes, i threw a timing light on it to see where it was at. turns out it was somewhere around 20* at idle (but there is no pinging) which seems like way too much since its supposed to be somewhere around 8-10*. so i cranked it back to 10* base timing and it wont idle for crap. it wont even run below 1200 rpms and it stalls as soon as you put it in gear. i hooked up a vacuum gauge up to it and it pulls 16-17" at best at 950 idle (when the timing is jacked way up, since thats the only way it will even idle). its running rich. its the same carb setup that was on the motor with the stock cam, so obviously it needs tuned. but wouldnt a bigger cam cause it to run more on the lean side apposed to rich using the stock jets/settings? is it possible that it needs more timing since its just running so rich? could the carb be causing all this trouble? i just dont know where to start...

heres a link to the cam card if you need more tech stuff http://compcams.com/Cam_Specs/CamDetails.aspx?csid=86&sb=1

 

[k20]

do you have a vacuum advance on your distributor? Do you have it hooked to ported or manifold vacuum? Unhook it and see where it idles best. BTW that being a flat tappet cam you have a cam break-in to do, which as I recall is like a 20min run at ~2000rpm. I like my roller cams so Im unsure of the exact times & rpm's. IIRC my 496 is at 18* with the vac advance hooked to manifold vacuum, and then the mechanical advance is full in by 2500.

 

[87 Blue Beast]

yes, its a vacuum advance hei distributer. what do you mean by ported or manifold? its currently hooked to a little nipple on the bottom front side of the carb, right above the intake mounting surface. i did unhook it once and nothing happended at all. no rpm change or anything. btw, the cam was broke in correctly. 2200 rpms for 25 mins

 

[toomany]

yes, its a vacuum advance hei distributer. what do you mean by ported or manifold? its currently hooked to a little nipple on the bottom front side of the carb, right above the intake mounting surface. i did unhook it once and nothing happended at all. no rpm change or anything. btw, the cam was broke in correctly. 2200 rpms for 25 mins

Ported has no vacuum at idle
Full (or manifold) has vacuum at idle

What kind of carb are you running? Some people/motors like one or the other. I run ported on my stuff. If you unhooked it and nothing happend sounds like you're on a ported nipple.

Did you check the timing before you tore it appart? Maybe the outer ring of the balancer slipped, causing the 20* reading. Have you checked for vacuum leaks?

 

[misterfnygy]

Sounds like a vacuum leak to me, check there first. I just built a motor with a similar cam- just a touch more lift and it runs perfect at 15*. Bigger cams like a little more timing. This is without advance by the way.

 

[HarrisonTX]

To set the timing at idle, you UNHOOK the vaccum advance, and plug the ports on the carb. If the ports are open, obviously you have will have a vaccum leak.
unhook the vaccum line, and set it around 8-10* advance, at idle. Then, hook the vaccum line back up..

Also, with the cam break in, im sure 25 minutues at 2200 will suffice, but...

The cam lobes are oiled only by "splash oiling" this means your motor has to be moving a fair amount to splash oil on the cam. You dont really want to hold it at 2200. Best results will be had by varying the RPMs between 2000, and 2800. for the said 20-25 minutes.

 

[bigblock72]

Sounds like you broke the cam in properly so that isn't a worry. Make sure you use a Zinc additive in your oil to help keep the cam alive.

With the bigger cam you'll need a lot more initial timing for it to be happy. The reason being the longer duration slows the airflow at low RPMs and also lowers the dynamic compression ratio with the later intake valve closing not to mention the longer overlap etc. All of these factors slow the turbulance in the combustion chamber and make it "lazy and sluggish" at low engine speeds. I've ran that same cam in 350s and had to run the initial timing as high as 26 degrees (I'm higher elevation) to get it to run right. There is absolutely nothing wrong with running the initial timing at 20 degrees if that's where it's happy at. Make sure you check your total advance with the vacuum advance unhooked, you don't more than 38-40 at 3,000 RPM.

 

[pauly383]

Small blocks , with a mild cam , will want up to 36 degrees total timing ( mechanical and static ) . When you leave from a stop you want the timing to be "all in" by the middle rpm range . So you may want to try different combinations of weights and springs in the dizzy .

Some guys even have to remove the vacuum advance with certain combos.

 

[87 Blue Beast]

Ported has no vacuum at idle
Full (or manifold) has vacuum at idle

What kind of carb are you running? Some people/motors like one or the other. I run ported on my stuff. If you unhooked it and nothing happend sounds like you're on a ported nipple.

Did you check the timing before you tore it appart? Maybe the outer ring of the balancer slipped, causing the 20* reading. Have you checked for vacuum leaks?

yeah, i visually checked for a vacuum leak but i didnt have time to spray carb clean around yet. when i set the base timing at 10* i did have the advance unhooked. it just wont idle like that. when i set the base to 10*, its like it sits there and loads up until it stalls. it puffs black smoke and smells horrible, but as soon as i crank the timing back up, the smoke goes away and it idles and sounds awesome . maybe it is possible that it needs that much timing like some of you said. if thats the case, ill take it up to 3000 rpm with the light on it and if it doesnt go crazy, ill let it like that. if it goes to like 40* or something, ill just unhook the advance and run it without it. btw, i believe i read somewhere that this cam has 4* advance built into it. does that mean 4* timing advance or the lobes are 4* advanced... like degreeing the cam 4* ahead?

 

[87 Blue Beast]

To set the timing at idle, you UNHOOK the vaccum advance, and plug the ports on the carb. If the ports are open, obviously you have will have a vaccum leak.
unhook the vaccum line, and set it around 8-10* advance, at idle. Then, hook the vaccum line back up..

Also, with the cam break in, im sure 25 minutues at 2200 will suffice, but...

The cam lobes are oiled only by "splash oiling" this means your motor has to be moving a fair amount to splash oil on the cam. You dont really want to hold it at 2200. Best results will be had by varying the RPMs between 2000, and 2800. for the said 20-25 minutes.

it was actually varried from 2-2300 but i just picked a speed cause i didnt feel like typing it out

 

[TerryD]

In my experience, Comp Cams (and most chevys in general) like around 12* base timing. My Camaro has a XE274h-10 .490/.490 274/286tappet cam, set at 4* advance on the timing set and I run 12* base with total timing at 36*.

 

[87 Blue Beast]

so i did some more research about it and all i can come up with now is that its just running way to rich at idle. i did some more work last night... i checked for vacuum leaks and found nothing. so i then unhooked the vacuum advance and set it to where it was fully advanced at 36-37* (again, with out the vacuum advance hooked up) thinking that i would just not use the vacuum advance and let the mechanical part work itself. it idled and runs decent but nothing like it does with more timing. took it down the road and is just ball-less. it was really lacking power. got back and jacked the timing way up again and it runs like a champ. so heres what im thinking... something is making it run way to rich at idle, wether a float is hung up or whatever, its just to rich. that might explain why it runs so good with that much timing, because more timing makes a hotter burn and gives more combustion time in the cylinder. that would also explain why it wont idle worth a crap when the base timing is set at 10*, simply because its not enough time to completely burn all the fuel thats being dumped into the motor and it just loads itself up till it stalls. so im thinkin im going to go buy a rebuild kit for the carb, replace all the gaskets and float valves, check/set the float levels, and bolt it back on to see if it makes it run better at 10* base timing. does that sound like a plan or make sence to anyone else?

 

[Blue85]

Did you check the timing before you tore it appart? Maybe the outer ring of the balancer slipped, causing the 20* reading. Have you checked for vacuum leaks?

Did you check on this yet? It's futile trying to set the timing if your indicator is off.

 

[TerryD]

This is a holley carb I'm gathering? Did it ever backfire through the carb when you were trying to start it. Sounds like a blown powervalve...

 

[87 Blue Beast]

its an edelbrock performer series 600cfm model 1406. no i did not check the balancer but what are the chances of that? and how would you go about checking it other than getting another balancer and seeing if they line up? the thing that makes me think its a carb problem is because there are two little vacuum ports on the front of the carb, one is in the left bank and one is in the right bank of the motor, since its a dual plane manifold. i hooked a vacuum gauge to the left side and it barely read on the gauge. when i hooked it to the right side, it read 15-16" on the gauge. also, there are two screws on the front of the carb which are idle adj. screws, one adjusts the left bank and one adjusts the right. well you can move the screw on the left side all you want and it doesnt make a difference at all. this is the same side that was barely pulling any vacuum. so i think the rich-ness of the motor is comming from the left side. it almost seems like the float is hanging open constantly. i dont know if i mentioned it before, but i was stupid when we took the carb off and i held it upside down. so i think maybe something happended when i flipped the carb over.

 

[4X4HIGH]

If this is your 87 K5 and you removed the TBI and installed a carb instead and you're also saying it has a distributor with a vacuum advance i'm going to assume that there is no longer a timing control through the ECM?

 

[rollin36s]

just curious did you set the timing gear at 3 degrees advanced with a larger then stock cam, did the engine turn at all when you put the cam in,the distributor could also be 1 tooth off, so many possible problems just check them all and good luck

 

[87 Blue Beast]

not im my blazer, its in an 86 z28. no, did not set the timing gear 3* advanced, why? no, the engine didnt turn at all. i also marked the distributer to the intake and the rotor to the distributer, so im pretty sure its in the right spot. but even if it were a tooth off, it wouldnt matter. you can turn the dizzy any position you want, as long as the rotor is hitting #1 plug wire when its at TDC, it will be in time.

 

[4X4HIGH]

Ok, back to my original question, does this dizzy still have computer control on the timing? Those years had an ECM that adjusted timing and just like our trucks you had to disconnect the EST wire near the brake booster before setting base timing. All bets are off though if you've replaced that distributor with a standard HEI without the ECM controlled timing.

 

[87 Blue Beast]

no, its not the original dizzy. its an older vacuum advance distributer. it has two wires plugging into it, not counting the one that comes right out of the distributer itself, so that isnt the problem.