When adjusting a holley carb, what does "stumbling" mean?

Yea that pink cam is for your basic duty street applications, and out of the box Holley carbs are de-tuned to be able to run on almost any compatible engine, so they carbs and rebuild kits don't come with the performance parts. You have to order the performance parts separate most of the time. I've been lucky so far as I've only been tuning for economy not performance, so I haven't ever had to search for the other stuff.

I bet Groberts knows where to get it though. And I swear in one of the videos the specifically use the 6.5 jet and the pink cam as the example for when you need to get a new cam

 

If that is for basic street duty, the no wonder I stumble when I gun it.

When I ride basic street duty, it runs fine. Only stumbles when the pedal hits the floor.

I have a store between home and work that sells all the hi-performance stuff. They probably have the holley parts, and if not, they can get them.

Could always go to summit or jegs, as well.

 

ok... as you now seem to now be indicating that this may not be a lean condition caused from delayed power valve opening or running too lean a jet.. you likely need more pump shot on the secondary side to fill in the hole during heavy throttle transitions. Probably quite a bit more pump cam too.. and you can start there to narrow the troubleshooting process down a bit faster.

Not sure what major parts store chains you have there?.. but many bigger chains also have small performance section that will likely have a cam kit in stock. I'd start with a red cam and then move to the blue to see what the trends are. If it gets better then go to the brown cam. After the trend becomes obvious.. you need to get a bigger shooter. Maybe start with a 35 and back the cam off slightly to end up with a balanced setup.

Typically.. you want to end up at the point where you just start to see some black smoke from the rich condition caused by too much pump shot but I doubt you'll run into that issue with such a small squirter. From that point we lean it out a bit with a smaller shooter and/or slightly less aggressive cam.

How far open are the primary blades?.. and also the secondaries? Particularly the amount of transition slot that is exposed.

 

Also. Are you running a stock stall speed in that C4?

If so?.. you'll likely need much more initial pump shot to come off the line so that gear can help you come up on the cam quicker. Shorter gears won't help much on heavy initial tip-in's when the main jet/s hasn't really started flowing well yet. My guess is you'll end up with a 32 shooter in front with a red or blue cam.. and 35 in back with a red or blue cam. Black smoke is your tuning tool.

I also think that you're secondary jet is slightly too large for such a small induction package too. That manifold is really small(I have one on my shelf and have used them more than a few times to better judge firsthand) and doesn't have the port sizing or plenum volume to make full use of that big a secondary jet. It'll soften up the upper rev's.. but that's nothing to be concerned about right now anyways. Far better to be a bit too rich than not rich enough @WOT. Just another thought to consider.

 

All of that was the tipping point for why I stayed 2 barrel. So much simpler to tune a 2-barrel for minimum fuel than a 4-barrel for freaking anything.

Don't forget that every time you change the cam or the jets you have likely have to re-adjust everything. The first time I changed the cam hole my 302 started pinging.

Totally gonna be worth it though, because once you get it set it should stay set.

 

I understand the philosophy involved with that thinking and there is some truth to the relation of the number of parts involved.. but a VS 4 barrel is actually easier to tune for an extended rpm range than a 2bbl is when you consider that the tuning requirement is spread across twice as many barrels. So, in that respect.. 2 barrels are being tasked to do more than they are designed for when performance comes into the picture.

Plus.. a 4 barrel can have smaller primaries and makes low range power production potentially more precise.. and crisp.. than having to compromise a 2bbl's setup because it's tasked to do more than just idle and run up to 3,000 rpm. Kinda' like a front wheel drive powertrain asking the front tires to do more than they were designed to do. Something's gotta be sacrificed.

As for changing a pump cam causing pinging?.. all the accell pump does is to "fill the hole" before the jets are flowing enough fuel to keep up with the air demand of sudden throttle openings. IMO, such an occurrence only points towards the tune being marginal and "on the edge of detonation" to begin with. The most an incorrect pump shot ever really does is to create a stumble.. or lean pop.. until the main jets catch up.. or push black smoke out the tailpipe.

 

So, should I get a cam AND squirter kit? I could probably come home with both tomorrow, if I need to.

Worst case, order from summit/jegs and have next week.

 

I would buy both locally if you can. Start with the more aggressive pump cams and when the trend becomes more obvious.. pull back to more moderate levels on the pump cam and add the larger shooter. Rinse and repeat until it's dialed in.

That way you can at least take the nozzles back if the pump cams don't do what we thought they would. I really don't think that will be the case though. You'll probably need both.

In fact.. if you don't want to screw around with all the trial and error stuff?.. just throw the blue cam on the primaries and brown cam on the secondary side and hold on to yer britches when the car comes off the line and the secondaries open up. It will be quite obvious as to what the motor likes. You'll smell rubber burning when you get it right.

 

FWIW...this is a street car. It is more important that I can idle in my driveway, and pull away from a red light without it hesitating, than it is to pull "off the line".

I want this to be a reliable daily street driver, to use on the highways and surface streets, with only the VERY occasional use at the track. In fact, I haven't been to the track in probably close to 10 years.

So if it is capable of 390 hp, I am fine with a nice streetable 350 hp. I have no desire to push it to its limit, which is why I sold off the nitrous kit.

I will swing by the store tomorrow and see if they have the squirters and cams, otherwise, I will order from online, and mess with it when the parts come in.

 

Hmmm...Almost sounds like this thread went from "that is too big a carb for your engine" to "you need to beef that carb up to work well with your engine"...

 

Not really. The carb has been changed from its original calibration, is all. Likely changed by the dyno guy to make those hundreds of dollars seem worth it.. but it's still too big.

To give perspective here.. I've had my 750 HP race version to 7,400 rpm on my 385 Chevy and it still has 0 engine vacuum. Just about perfect form my setup that moves much more air.

 

Dyno guy didn't touch the carb. Made suggestions, I did all the work. That is how I got two hours dyno time for $100.

 

OK, I get it. It seems to me that it should be more about getting it closer to optimal.. and stumbling is not even close in my book.. so it performs as it was intended to and I wasn't necessarily trying to push you towards low ET at the track. If max power(around 340'ish) was the intended purpose.. I would have dug into my old tune sheets to find a similar combo to help you establish much closer baselines from which to start. At this point I was just going off learned memory.

Your cash.. your time.. and I was only trying to help you out by sparing some of my time. Either way.. I didn't expect a award and it's fine by me if you're done fiddling with it. :Handshake

 

When purchasing squirters, what is difference between straight and tube types?

 

And no, I am not done with it. I don't want it trying to die when I get into it.