Carb help....need some guidance.

Eventhough Chicago just got dumped w/ snow.....I have the achin' pains to do some work on my car. Can't wait til it warms up! Although there's still time before it's warm enough to do that wrenchin'....here goes:

What can anyone tell me about the sp235 cam that I have. I'm not 100% sure, but it's something like 238/248 w/ .491 on both sides @ .050, 112 seperation.

I have a holley 750 dp on top of an SP-1 intake. Stock heads w/ some minor work, headers, HEI, etc.

Before I put the tools away for the winter, I had a hard time getting her to idle well.....and the garage smelled of gas, and my eyes watered. I did manage to get about 10" - 11" hg on the vacuum gauge though, which seems normal, according to posts w/ cam specs similar to mine.

Anyone have pointers? Tips? What is the best timing to set? I'm still dumb when it comes to the whole initial and full advance timing stuff.

Should I maybe ditch the carb? I'm not a carb guru, but double pumpers seem to be a pain in my @ss. I'm having a hard time with this setup.

Then again.....don't have any buddies who can drive over and coach me. Most my friends don't even know what a carb is. o No:

Thanks in advance!

~Mark

PS I just got a bonus.....so I have a l'il extra $$$.....therefore I'll consider any suggestions, as I have a little budget to work with.

 

Actually double pumpers really should be easier to tune than a vacuum secondary carb since you don't need to match a spring to your vacuum signal. Plus there is no diaphram to damage in a backfire. Is your car a manual tranny? DPs really work best on a manual tranny carb.

On the cam, did you install it? If so what kind of chain do you have? A multi keyway chain set is kinda easy to misinstall. If you done wrong here the engine will idle quite poorly and stop short on the top end or have no bottom.

 

What Brad said.

What car is this carb on, Mark? Is it a Skylark or is it a bigger car. On a big, heavy car the vacuum secondaries seem to work best as the carb won't dump all that fuel into the intake until the beast gets rolling some. If it all checks out and it turns out to be a carb issue, I had ecellent results with my Holley by sending it to Jet Performance in Huntingdon Beach, CA. I feel that for a warm-weather car a choke isn't necessary, so their Stage2 build mills off the choke horn. I have never had a problem starting it. I just have to hold my foot on it until it warms up. 3 minutes or so before she'll idle.

This is my opinion, but I would never buy a new Holley, nor would I recommend anyone else do. Their quality control is horrible! I ordered a new float bowl and I had to file down the accelerator pump area as their milling missed all 4 corners and left nubs on each corner. Also, one bolt rubbed on the side of the bowl and needed to have some of the bowl ground off.

Besides, the 2 Holleys NEVER ran right, even the one new one right out of the box. However, since Jet did my build I couldn't be happier with the tunability, reliability and performance from my Holley.

 

You say that you aren't very knowledgable with the whole timing thing just yet?
Larry's links ought to help with that.

Do you have a timing light? What is your initial advance set up as at idle (in reverse)? As a rule of thumb, if you increase your initial timing and your idle increases, your making an improvment. Of course this only goes so far. You'll find a spot where increasing your initial timing does nothing more for the idle adn if you keep going it'll actually get worse.
Keep in mind that even though you may get more idle RPMs by going up to 16, 17 or even 18*, that's not a great idea. Once your mechanical adds to that you'll be in trouble. For starters don't go past 10* and see how she is.

I was once very intimidated by my Holley. A little reading and a lot of hands on fiddling and I'm now very confident I can fix any problemit can throw at me. They aren't very difficult. Do some research on this board as well as the Holley web site. You'll get a good idea about what your facing. Holley's tech line has also been a great sourse of hekp for me in the past also.

 

Thanks for all the replies so far.

My basic question was to find out if anyone has a similar cam, and what numbers I should expext to get in terms of initial advance, idle speed, idle characteristic, etc.

Thanks Larry! After reading the article, I feel I should invest in a new distributor now.

But also, just out of curiosity, is this cam a bad idea for a car that'll be 75% street 25% strip? Granted, it's not my primary driver either, rather a nice weather weekend warrior, and I do want to race at the strip as well.

It's 455 in a GS w/ th400, so maybe a Double Pumper isn't wise?


I've timed it with a cheapo Sears light, and the car seems to love idling when the marker touches 18* - 21* on the balancer. That seems high, with the Tach reading 1,000 rpm or so, but if I turn the distributor to make the light read the marker at 14* or 12*, it idles crappy, shakes violently, and cannot seem to be the way the cam should idle.

Just out of curiosity, on a stock 750 double pumper, how many turns do you pull out from closed on the idle screws? I know it's a vague question, but based on my engine specs.

Finally, is a 750 too small? I've read articles that say Buicks like bigger carbs. Stock q-jet was 800 cfm on a GS stage 1, right?

Oh yeah......about the Holley....when I read directions about getting a valve to match your vacuum reading.....is that for vac-advance carbs only? That's the Power Valve, right?

Mark

 

When you said you had a hard time getting her to idle, the garage smelled like gas, and it made your eyes water it sounds exactly what I recently went through. I had vacume leaks between my Q-jet & the intake spacer and also between the spacer and the intake. Spray all the seams with carb cleaner while its running and you may hear and see the leaks if you have them. It can also be between the intake and the motor but not normally. After I took my carb and spacer off I could tell from the carbon where my leaks were. New gaskets problem solved. Hope that helps.

 

Thanks for that advice.....I'll give it a shot. I used a new gasket when i installed the sp-1. But I used that tub style one....the one with a valley pan.
Are those alright, compared to the 2 piece gasket alternative?