9.5:1 Mark IV BBC 460
Voodoo 268 cam
049 Heads with large valves and bowl work
Performer RPM intake
1 3/4"- 3" Hedmann Headers
HEI using vacuum advance with the lightest springs

I just rebuilt a used 3310-3 looking improve performance over an Edelbrock 750.The mains said H99 on them? The engine is pulling 12 HG vacuum at idle. It has new 6.5 Power valve. I put the brown(2nd to the heaviest) spring in the secondaries. I have light hesitation at acceleration at all speeds and surging under load at 2000 RPM. I think it is lean during transition. I drilled the accelerator pump squirters with pen drill from .030 to .035. This made a very very slight improvement. Should I drill the squirters more or change the or change the power valve? Am I on the right track ? What Power valve ? Should I change the springs in the HEI mechanical advance. Thanks for the help.

Where's your timing at?

Have you simply tried using a softer spring in the secondaries? With such a large engine it needs the secondaries to begin openning fairly early.

The timing is advanced as I can get it and still be able to start the engine.

I didn't think that the secondaries would affect anything much until WOT.

This is what I learned...

If your primaries are too lean, you will always get that stumble no matter what you do to the accelerator circuit. If you tinker with the nozzles and cams, and it doesn't really do much, it probably isn't that. I pulled my hair out trying to get rid of a stumble (bought a bunch of nozzles, played with cam position) and couldn't get rid of it - turns out I was a little lean on the primaries. You probably need to be around 74-76 on the front.

Maybe jump to primaries 2-4 sizes from where you are and see what happens.

Phil,what is your intial timing set at,i know you say its set as far as it can be for the motor to start hot but that could be too retartded for a 268 perf cam . This would then show that your car also has issues with the starting system,starter,alt,battery,etc that need to be addressed.

Most aftermarket perf cams like approx 16-18 deg btd intial timing so if you cant get it there and still start the motor then you also need to fix that too but that another issue for another post.

So whats your intial timing set at to where the motor will stillstart hot?

Usually its a lean cond that will cause the part & mid throttle cruise surge and not the secondaries as you already statred.

Scott


scott

I just rebuilt a used 3310-3What primary jets are in this carb?

The primary jets said H99 on them. I have not been able to find any reference to H99 jets. I am sure I have plenty initial ignition advance. I was wondering if all the timing was getting in too soon though? This is a new issue that came with the carb.Thanks for the help.

You need to put a timing light on your motor and confirm where your timing is at base and what the total is.
Having the timing coming in too soon is NOT an issue..it actually improves throttle response.
The statement "I'm sure it has plenty of advance" doesn't answer the question ;) :)
I would then remove the carb and remove the H99 jets and install a pair of 72's for starters.
..and get the brown spring outta there.
The heaviest spring I would use would be the purple.
JMHO and experience.

Also, check your float level, could be a little low.

Squirters are definitely a change to be made. I would not drill them, you never know where you are at - Change them up 6 sizes from the number stamped on the one you have now, then go up 3 at a time. Once at 40, you will need a hollow screw but I doubt you'll get that far.

As said, wait until you get your timing straight first, then hit the carb.

I didn't think that the secondaries would affect anything much until WOT.

Ideally, the secondaries should come into play anytime the engine needs more intake volume based on the vacuum signal. This will vary on every engine, but the main criteria are the size of the engine and the size of the carb. They also don't necessarily always open all the way but you do want them to open when there is a demand and that doesn't necessarily mean only at WOT. The brown spring is way too stiff thus causing the secondaries to open very late and the engine is starving for air/fuel long before the secondaries are beginning to open.

You probably have some jetting issues as well as noted above. You'd be better off changing one thing at a time though so you know what it was that created the fix. The easiest fix is to check your float level, then move on to jetting and when that likely cures your hesitation problem, you'll probably notice that you can then "feel" the secondaries opening which means you need to go to a softer spring.

The timing is advanced as I can get it and still be able to start the engine.

As already posted, that doesn't tell us where your timing is at, especially total. Depending upon how your particular distributor is curved, "advanced as I can get it" could very well be your problem. Just because your engine can handle a certain amount of advance at idle doesn't mean that it can handle the amount you're getting as rpm increases. With too much/too soon, you lose a bunch of power and yourengine acts as you described.