new cam for 305

[flipster30]

i recently replaced the cam in my 83 caprice 305 it only had 74,000 miles on it,but 3 lobes on the cam were completely round. anyway i replaced it with just a slightly better than stock cam a lunati rv cam i got it back toghether and now it doesnt want to hold an idle at all it sounds good when u rev it but spits at idle and im not sure what to do with it now. my uncle is helping but we r stumped at the moment. cap and rotor button plugs and wires water pump starter fuel filter valve seals timing gears and chain all new so any advice would be helpful i would love to find a vacuum hose diagram

[97cavalier]

you need to have your prom changed, you need to have it up graded. There is a guy that does it at www.tbichips.com he is good at it. What it is doing is it is not getting enuf gas at an idel, or the cam is to big and really big cams don't have a good idel.

[silicon212]

Originally Posted by 97cavalier

you need to have your prom changed, you need to have it up graded. There is a guy that does it at www.tbichips.com he is good at it. What it is doing is it is not getting enuf gas at an idel, or the cam is to big and really big cams don't have a good idel.

Bah. You don't need to change the PROM. I do have a couple of questions for the original poster though - #1, did you properly follow flat tappet cam break-in procedures (i.e. NEW LIFTERS, and idle set to 1800RPM, and let run at 1800RPM for 20-30 minutes upon startup)? #2, did you check to make sure that all vacuum lines are properly hooked up and new gaskets used on the carb and intake?

What's the specs on the cam?

Lobe separation (affects overlap) angle?
Advertised duration?
Duration @ .050" lift?
Lift?
Degrees timing?

If the separation is 110 degrees or less, expect the engine to idle rough. Expect it to idle rougher if the .050" duration is greater than about 220 degrees on the intake. Exhaust can be slightly longer. Lift greater than .460 could cause idle issues, as well as broken valvetrain components if you didn't plan for it (rocker arms, valvesprings etc).

Also keep in mind that what might idle decent on a 350, as for cams, can make a 305 lope.

[97cavalier]

if this motor has a prom, it needs to be changed, because when i do my lt1 cam in my 305 the engine will not even start with out a new prom or mine reprogramed. And if it does it will run like total crap. You will probly also need new valve springs, depends on how high of a lift.

[flipster30]

im not sure about the specs on the cam but all we asked for was just the next step up from stock its nothing radical. i didnt remove the carb from the intake and yes we replaced all gaskets. no i didnt run it for 20 -30 min at the rpm u said i havent driven it yet or anything i think i might have a vacuum problem. should i have to tune my carb like i said it isnt a wild cam or anything it purred at an idle before and would spit when u accelerated now it revs great but idles like crap

[silicon212]

97C - his engine is carbureted, not injected. The computer in his car "learns" the new cam after a couple of days driving it. There's no need to replace the PROM in it. I know, I've done it. Carb'ed cars do not respond negatively the way that EFI cars do.

FWIW, my '88 has an ECM and PROM for a 145 H.P., 255 lb. ft. TQ 305 in it now (LG4). I'm running a seriously modified 350 in it (275 H.P., 350 lb. ft. TQ) and it runs just fine.

Flipster - you might as well do that 20 minute run now - if you don't, your cam will not survive ten thousand miles. This break-in is absolutely CRITICAL for the life of the cam - if it doesn't get lots of oil on it during its break-in period (hence the 1800 rpm engine - the cam only gets oiled by the oil slinging off of the crank), the lobes will burn off rapidly. Don't start your engine up until you've traced all vacuum lines. In fact, remove them all and plug the vacuum ports on the engine.

[TommySS]

You don't need a new chip for an RV cam. If it spits and stumbles at idle, yet runs good when you romp down on it, the chances are real good that you have a vacuum leak. If your hoses are good, I'd be lookin at the intake.

Get some carb cleaner, start the engine and spray the edges of the intake, If it smooths out, you found the leak.

The cams in the 305 for a period of that model year were not hardened properly and wore the lobes as you described



You should've done the break-in.

[flipster30]

i will do the break in we did run it for 10 min or so at high idle. im thinking its a vacuum leak somwhere i didnt mark hoses or take notes so somethin is either not hooked right or somethin. thanks for all the info

[flipster30]

where on the web can i find a diagram for the vacuum hoses that would be helpful

[97cavalier]

i did not know it was carbed, i thought he had the tbi.

[TommySS]

Originally Posted by flipster30

where on the web can i find a diagram for the vacuum hoses that would be helpful

If it's out there, I'll be doggone if I know where it is.

However, I have a scanned original/unused underhood sticker.

PM me w/your e-mail address and I'll send it to you

[TommySS]

Also, the carb bolts tend to loosen up after several engine heat/cool cycles. Make sure you torque 'em to spec. I had to do mine 3 times before it finally "took".

[silicon212]

Keep in mind that you may never get it to idle silky smooth, due to the cam profile. My engine has an RV cam in it too (Crane PowerMax) and even though it's not a radical cam by any stretch, it will make the engine a little lopey on a slow idle if the engine isn't fully warmed up.

[TommySS]

Absolutely. Make sure that what you're experiencing is a vacuum leak and not cam lope. There's a difference between the two, but w/o a sound clip of what you have we need to check for leaks first. The difference is that the cam lope sounds "healthy" and the leaks sound "sick" (sick as in "ill", not sick as in "really awesome"). If it was supposed to have a lopey idle, you probably DO need a new chip (which the cam mfg can provide/source for you)

Not having much experience with an RV cam (but tons with vacuum leaks), I'd say do the leak check and let's go from there.

[flipster30]

thanks for all the advice i havent been able to mess with it for the last several days because its in my uncles garage he lives about 40 min away and has been not feeling well so as soon as i can get over there and work with it i wont know what the problem is. i appreciate the help and will let u know how it turns out. i love this car an old lady owned it and i bought it for 900$ last year it has 74,000 original miles and the interior is cherry. no rust anywhere which is impressive for an 83 i think. its even clean underneath ill post a pic once i get it up and runnin