ASIM

Hey Guys,

Have a 71 Camaro.

327, 202 heads. Cam is a 490 lift, 235 duration. Gear is a 3.08 with a 4speed Super T-10 in between.

Car ran real good with a Holley 750 on it after 2000rpm, but had to keep a lot of clutch in it down low avoid bogging.

Decided a 650 was the right fit, but now can't get it to run right. Just missing and hesitating a lot all the way through the rev band.

Would you agree a 650 is the right size to start with. Jets in the front of the 750 were 70's, this 650 has 67's up front. Both are mechanical 2nd's and the car makes about 14lbs of vacum.

Any advise is appreciated.

Thanks,
Asim

Stephen 87 IROC

Buy a "new" carb

angel71rs

Not going to have much low end torque with the 235 cam, especially in a 327. Recommend more gear, at least 3.73s. If you want to keep the 3.08s, consider a smaller cam, especially if you run a taller tire like a 275-60.

It can also help to give it more initial timing to improve low end torque/response with a bigger cam, but restrict the total timing to ~ 36*. What is the compression ratio?

Sounds like the 650 has unrelated issues, though it might be a better size for your engine. Even new ones can come with problems, Holley's quality control isn't what it used to be. Yours could simply have trash in a passage/jet, misadjusted floats, etc.

Did you drill the butterflies on the carbs? Helps to reduce the rich idle problem and off idle stumble that typically results from having to crank up the idle stop screw with a bigger cam. You want ~ .040" of the slots exposed under the butterflies.

There is a kick azz book on Holleys. I've had my copy for > 20 years, has saved me $$$ buying used Holleys that were "no good" for cheap; the 3310 on my 71 was a freebie that the original owner gave up on. It had an undrilled brass bushing in an idle well, came that way from the factory.

Get your copy at local speed shop, B&N, or online off ebay or amazon:

http://cgi.ebay.com/ebaymotors/HP-Bo...spagenameZWD1V

ASIM

11.1 compression. I've gone through each plug which I changed 1000 milles ago and they look good. Cylinder 1 was a little sooty so I changed that plug+wire, but no difference.
Drove it 5 times this weekend - Twice it ran like a top. The other 3 times is was anywhere from close to noticably stuttering. Timing has always been a mystery for me though.
Could a timing issue cause such an on/off effect?

Thanks,

Rice Killer87

^ YES !

At idle you should start at about 12 degrees advanced. Full advance should be in between 3,000-3,500 and should be around 33-34 degrees.

With the engine idling and warm,use a timing light on teh #1 plug wire and point it at the balancer reading what number the timing pointer is pointing at when the light flashes. After you get that set (base timing) then have someone bring the RPMs up to about 3,000 and see where its at. Should be around 34 like I said earlier,if its not you maybe need to change the springs/weights...depending on what dist. you have.

EDIT: Where did the carb come from? Ebay? New from summit/jegs?

ASIM

I will try that. Got the carb from a local place that's been in the business for 20+ years doing nothing but rebuilding carbs. They rebuilt the 750 I had on there previously.

Thanks very much!

tomcowle

Look at the secondary accelerator pump cam

Slick_Sammy

set your timing right, first. then play with the carb setup. check plugs afterwards. too much or too little jet can do strange things. i'm not exactly sure what you're saying it is doing though. is it just when you go WOT or is it when you transition to WOT .... does backfire any, miss real bad? might have some fouled plugs.

Privateer454

Concer with the above, we need to know if this is at WOT part throttle or both. Your first post said all the way through the rev band but was that with enough throttle to open the secondaries? If it drives fine at part throttle when your are only on the primaries that would tell us (and you a lot).

If it was just the accel pump cam I would expect it to stumble early with fast throttle application but not so much if you got on it slowly.

Are you seeing any smoke? Black smoke would indicate a very rich condition.

ASIM

Thanks for the advice thus far.

When its off it runs bad all through the rev band. Not just WOT. Matter of fact, I don't think I'm past quarter throttle more than once a week.

I also noticed this week, that it ran bad on the cooler, wetter days. When its hot and humid its fine, but just before or after rain it runs real bad. Stumbling all the way from 800 to 4000 (don't go past their). I tried stepping on it last night and it just backfired hard.

I did take a timming light to it and it is at 36 total and 9 initial. I questioned the guy who put the cam in about the 9 and he said that was to give torque low end with the 3.08 gear I have.

He's suggesting its almost certainly an iginition issue.

Wires, Cap/Rotor, could it be the coil?

Rice Killer87

Could be.

Easiest would be to look at the cap/rotor and make sure theres not some nasty crap growing in there of any holes burned in the rotor.

Doubt its the coil.

What are the jets in the front/rear? Sounds like it could be running pretty rich b/c it gets worse in the rain.

ASIM

Guys,

Problem solved. It was the carb after all. Got my hands on an Edelbrock 750 sitting in a box for 3 years. Bolted it on and the thing ran like a champ. No turning, no nothing. Just a box off idle, but I think that's cuz the timing is set at 9 degrees initial.

I also noticed the vacum advance doesn't do anything, but after 1400 the car runs fantastic and now over several days.

Thanks very much for your help.

ASIM

Gentlemen,

I mentioned above that the car runs great after 1400 but there is an off idle stumble.....its a big one. I bumped the timing to 12 degrees initial. No real difference. I am not running a vaccum advance (its plugged in but doesn't do anything). Its been suggested to me not to fix the vaccum but get the right mechanical advance. What are your thoughts? Its a 327 with a 490 lift 230 duration cam with a Edelbrock 750. I've played with all the idle mixture/accelerator pump setting as best I can but its still got a big dead space under load off idle.

Thanks,

Slick_Sammy

bring your float levels up a little higher than normal. see if that helps. should be just trickling out a little at idle from the holes. bring it up a little more than that particularly the rears. make sure idle mixture is set for highest vacuum / rpm at idle. i don't know much about vacuum secondaries but i'd keep it if its mostly a street driver. mpg sucks with double pumpers. double pumpers are the only thing you want for drag strip use though.