please help guys i have a 79 350 bored 40+ and im running a speed pro cam part # cs-1095r This cam is 224 at .050 and 450/460 lift 114 C/L right now i have a holley 750 vac sec elec choke but seems to run rich and not want to idil, any ideas??????? im retarded when it come to carbs no experience what so ever.....

 

Your 750 vac sec carb should work with your engine & cam. Whatever it is, your problem is not with the carb size.

First : Tell us about your timing. You have to be sure all ignition parts are in good shape and timing is accurately set before trying to adjust carb.

Second : How much idle vacuum do you get with your cam ?
If vacuum is too low, the power valve can open too soon, causing a rich condition.
Or maybe your vacuum secondary spring is too weak and the secondary butterflies open when they should still be closed.
Check that you don't have a vacuum leak, even a small one. A vacuum leak can cause weird effects at idle...
Check that your electric choke works like it's supposed to... If it doesn't, this can cause excessive richness too.

Third : How old is your carb ? Perhaps it only needs to be correctly set or rebuilt.


See Lars papers for timing and carbs. You'll learn a lot

 

a bigger carb does not always mean a better carb... if your going to use the 750 you need to reduce the main jet sizes by a lot. I have a bbc and a wideband o2 sensor, and I have dropped 10 jet sizes from the stock 750 and it is still running rich. A smaller carb will increase low end performance but will suffer when the rpm's get really high. Most of us do not run 7000 rpms much, so I can never understand why so many people with street driven cars recommend oversized carbs. Here is a carb calculator:

http://www.usaimports.co.uk/Carb_Calculator.htm

A 350 which revs to 6500 and 100% VE requires 658 CFM...

 

The size of the carb has nothing to do with idle quality - you can make an 1150 Dominator idle just fine on a 350. A bigger carb will not run richer - in fact, a bigger carb will usually run lean when operated on a small engine due to decreased fuel metering signal.

Your 750VS, however, is a fine size for the 350 it should run with no problem. You have issues with either timing, timing curve, or carb setup that you need to address. Changing the carb size will not resolve those issues. Suggest you first verify your timing at 36 total and make sure vacuum advance is correctly hooked up and operational so you're getting about 30 degrees of timing at idle. Then, make darned sure your carb's transition slot exposure is correctly set up using the secondary idle speed to balance out primary and secondary sides - if you're exposing more than .020" in the primary side, you will run rich with no mixture control due to fuel being pulled from the transition circuit. Verify float levels, and correctly balance the idle mixture screws. Run the stock jet sizes for your list number - Holleys seldom need more than a 2-jet change for good performance, and jet size has little or no effect on idle quality since the main metering circuit flows no fuel at idle.

Lars

 

lars i have checked the float levels they are now fine when i remove the sight plugs and rock the car slightly fuel dribbles out. a friend of mine rebuilt the carb so its all new, as per adjustments im clueless, i know we took out size 72jets that where in it and put in size 66. timeing is correct. a local shop reccomended pulling the power valve out and putting a delete in. any help would be appreciated

 

this im sure is a dumb question but hey im a noob when it comes to vettes and the repair book has a crappy image. any way when it comes to running the wires from the cap. i know the firing order but what wire is directly to the right of the part that sticks out to plug the capactitor into and battery feed. is it # 1 cylinder wire or is # 2 cylinder wire. i hope i didnt confuse anyone. i think its # 1 but i have found an image that tells me im wrong so i just want to confirm.

 

What brand was the carb kit?

That is a horrible suggestion. If you remove your power valve you will have jet up so that you arent running lean under a load. Then when your not under a load the car runs pig rich.

 

That would be the #2 post.....#1 is the next one clockwise

 

wow well that would make a difference hmm

 

ok new issue........ when looking at the timing mark with the engine running with a timing light the mark should not move around right?????? because mine does i have a feeling my distributor might be shot but hell if i know...

 

All the "help" you're getting is terrible. You dropped the jet sizes by 6 sizes?? Put the stock jets in the carb and set the carb up right as I described and as outlined in my papers. You're running so lean that you're running on the main discharge circuit at idle, causing an artificial rich condition - you're not running on the idle circuit (I'll bet you have more than .020" of the transition slot exposed). Deleting the power valve is the worst idea I've heard yet. You'd have to bump the primary jet sizes up to 80 if you did that, and you'd be fouling plugs all day. Timing is "correct?" So you have total timing set to 36 and your vacuum advance is pulling in 16 degrees at idle? If the same people who are giving you advice on the carb are also setting your timing, your timing is not right. You really need to start over and do a complete, correct setup on the engine starting with the timing and timing advance.

Lars

 

Probably not. The timing can be set with the #1 post in any location in the cap. It's all a matter of how the last guy dropped the distributor in. Distributor orientation and location of #1 tower is irrelevant to timing as long as the distributor is not limited in its rotation when setting the timing.

Lars

 

Here is a pic of how the wires are usually laid out.
Not sure who's pic it is.

 

any ideas on this one?????

 

First check that your harmonic damper hasn't slipped ( external ring ) and that the 0° timing mark is still the #1 piston TDC.
You can use a piston stop like this one, it only takes a few minutes :

http://www.summitracing.com/parts/SUM-900189/

You can't set your timing until you're sure about that.

If it's OK, check that your centrifugal and vacuum advance mechanisms in the distributor are still working.
You could also have too much clearance in the distributor shaft ( or gear ) or a bad ( stretched ) timing chain,
or even a camshaft timing gear with broken / worn out nylon teeth...
All of these are possible causes of ignition timing abnormal fluctuations.

You're a lucky guy. With Lars' help you're on the right way !

 

ok well seeing how the harmonic balancer is new and it dosn't seem to have any issues with it im going to say its good. now the distributor didnt look the greatest underneath the cap and rotor it was used, i should have never installed it with having everything else new i should have forked out the money and got a new one before but hey i cant rewind time.... i dont believe its a problem with a camsaft timing gear but to be honest hell is i know..... im hoping its the distributor i ordered one and it should be here wednesday so we will see..... thak you all for your continued help with this.....

 

My timing mark bounces around a little, mine always seem to. Had the Digital ECurve distributor in there once and the line was rock steady don't know why, would have kept that dist. if it didn't almost blow up my brand new 427ci small block with backfires at full throttle. Pictures of the cap where taken etc and MSD gave me my money back and no harm to the motor luckily.

I'll go one further than Lars, the guy who told you to run no power valve is an idiot plain and simple no other way to describe him.

You need to start right from the beginning and the first thing I would do is make sure the carb works properly. I have heard so many "Holleys are junk, my engine ran like crap and I put a brand new Demon on it and it runs like clock" I think it's the other way around now though

The point I am trying to make is someone has 30 year old Holley on their warmed over 350ci and it runs like crap because it's a 30 year old Holley and who knows what has been done to it. You put a brand new Holley on it and it will run just as good as a brand new demon.

Take the carb off and put it on a buddies car that runs good and see if it runs OK. Then you go from there setting up the carb properly, setting timing etc. It ain't rocket science but if you haven't done too much wrenching find someone who has

 

The cure for any holley is to know how to unscrew the power valve for sure or the main jets Lars sure gave you good information and i will try to third person not taking your car to the shop you described anymore.

 

I just bought a new Pertronix FlameThrower distributor a few weeks ago, with Ignitor II Hall Effect module, and now the timing mark is rock steady at 37° / 2800 RPM.
I only use the hall effect module to trigger my MSD-6AL ignition box. The coil is a Mallory ProMaster.
I also checked cylinder #6 and found exactly the same result.
But my double-roller timing chain and gears are brand new too.
More infos here ( today's post ) :

http://forums.corvetteforum.com/c3-t...lled-pics.html