Too Much Carb???????

jspagna1

jspagna1

Member
Jan 23, 2007
53
0
6
Connecticut
#1
That's exactly my question. I played around with my car this weekend and I'm wondering if having a double pumper with mechanical secondaries is not the best thing. One problem is my car is missing the timing pointer,so I'm kinda guessing. I need to get one ASAP. I advanced my timing from 25 - 35 degrees. Kept it conservative since I have no pointer. Definitely improved the performance.
My carb is the only issue I have. It does'nt bog at all, but I am still leary. What do you guys think? Look at my mods and feel free to make suggestions or express opinions.
Thanks in advance for all your help.
 

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#3
You got a good combo for a 650DP.
I read your post and don't see that you have a problem with the carb...:shrug:
If it ain't broke, don't fix it!

Get the timing right first, then supertune the carb.
If you have problems then, come back and talk to us! ;)

Personally, looking at your combo, you got a good carb for it.
A vacuum carb would save a little fuel economy, but that's about it.
 
#5
If it's soft on the bottom, it could very well be the carb doing it. Only way to tell is disconnect the secondaries and run it and see it the bottom end feels stronger. If it does, you can swap to a vacuum secondary carb and tune the secondary opening to meet the engine's needs.
 
#6
The only thing I would question is the auto w/3.55's. Normally you would want a vac sec carb or steeper gears. But I wouldn't change it, even if it did bog. You can tune these carbs like crazy. Take a plug reading after normal driving(easy) and after a WOT run(not so easy). And how does your exhaust look at idle vs WOT? Are the exhaust pipes white, black, or brown? If the plugs and pipes are black and sooty, it may be way too rich. The nice thing about the DP is rear metering block vs a metering plate on the vac secs. You can change the jets, adjust and change the pump cams, change the squirter size, just to start. Sounds like you have nice engine combo. Those heads should easily handle that carb. The only thing I would add, if you don't already have, is a MSD 6A box to help digest that high carb:rolleyes: diet. Happy tuning.

Rob
 
#7
Get an EGT guage and tune based on your exhaust temps. You can't go wrong using one and it doesn't react in milliseconds the way an O2 sensor does. Other than that I think a 650-DP is about perfect for a modified 302. Just make sure you have enough fuel flow at higher rpm or they tend to go lean and fall down.
 
#8
IMO your carb is too small if anything. 205 heads, that is huge, so you are flowing a lot of air. Since the cam is on the smaller side, considering the heads, then 650 is probably about right. I dislike vacuum secondaries period and prefer mechanical ones in all situations, but that is just my preference :)
 
#9
That's about perfect after you stroke it to 331 or 347. It's a little big for a 302 - they can only pump so much air, especially with that small cam. Sealed circle track motors (in area of 350ci) making over 400 hp use 650cfm carbs. Most mistakes on street driven cars is too much carb. That said, stroke that sucker and put in more cam!!
 
#11
It all depends on how you drive a car with Mechanical secondaries, please don't take this as condescending. Mechanical secondaries are fine... as long as you don't floor it from a dead stop and sink the pedal rapidly instead. This goes for coming in at low RPMs as well.
I prefer mech secs myself as I like the throttle response and control. The same reason I went with a flatslide carb on my Sporty, The stock carb makes about one more HP but lacks the throttle response. Its wild tweaking the throttle just abit and feeling the response!
 
#12
Edster said:
. Mechanical secondaries are fine... as long as you don't floor it from a dead stop and sink the pedal rapidly instead. !
Click to expand...

In this case, you'll find out instantly if the carb is too big-------it'll die on you. If it's too small, it'll take off like a raped ape but slightly limit the topend. If it's just right, it'll both fry the tires and have all the topend to motor can make. That's why I prefer vacuum secondary Holleys, you get the best of all situations, once you spend some time tuning it to the engine, and get better mileage.
 
#13
I don't know about the whole "don't push the throttle too fast on a DP" theory.

The whole purpose of the pump cam adjustments and the squirter size variations is so that you can tune the secondary pump (primary for that matter) to suit your car's needs!
If you mash the throttle hard and fast, and don't like what you get, tune the darn secondary accel pump cam and squirter until you do!
That is why they are adjustable.
 
#17
CraigMBA said:
My car sucked with a vac. secondary. I couldn't get the secondaries to open quick enough.

I've got a BG Silver Claw 650 DP on it now, and it's just bitchin'.
Click to expand...

But if you were new to carbs and bought into the "bigger is better" thinking some have and went and bolted on an 850 DP, you'd be singing a different tune.:rlaugh: Whats so different about yours that you can't get the secondaries opened gast enough? On mine, I have gotten them to open instantly and as far as having a 1 second delay, and that's on mildly built small blocks.
 
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