So fellas, I’d like to figure this out on my current motor (355) before I get the new one done, use it as a test mule if you will. I’ve had a pretty bad bog when I stab the throttle (Holley 4150 650 cfm). I’ve played with jets and timing and really have only made it worse. I really believe it’s pig fat at the moment, plugs are black but more of a black soot than wet and have fouled a couple out shortly after a cold start. It also has a blubber at about 35-40 mph. My question is how would I verify that the distributor is actually doing its job correctly? It’s a new (relatively) MSD. It just seems odd that I’ve had this issue right from the get go and really haven’t made any gains with jet, power valve, timing. I’ve just got to missing something that is probably staring me right in the face. Any thoughts?
Timing or fuel?
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What are your timing settings? What MSD are you using, box and distributor, just distributor?
Lock your timing at 38 degrees and drive it to eliminate distributor/timing issue. Blubbering and a bog I would look into the basics. Don’t over expose transfer slots. Correct vac booster in carb. Correct cam on carb. One step at a time, if not improved, move it back to baseline and try a different area of adjustment. I personally like to lean it out, and add fuel slowly to creep into the tube.
C,
The easiest thing to do is advance the timing about 10 degrees and see what happens. Dont run it real hard like that but if your "bog" goes away you will have a pretty good idea that it is timing related. Does the distributor have vacuum advance ?
The easiest thing to do is advance the timing about 10 degrees and see what happens. Dont run it real hard like that but if your "bog" goes away you will have a pretty good idea that it is timing related. Does the distributor have vacuum advance ?
Quite well said, tuning the engine can reveal a big can of worms with the carb. Lmao Quadra Junk gained it's nickname solely due to people's lack of understanding. Tuning a engine is not plug&play, it can be a real pain in the @$$
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If the ignition tests pan out, the most likely place to then look is to increase the pump nozzle(shooter/squirter) size and pump cam size.....changing jets trying to solve a stumble at WOT stab typically just makes if pig fat everywhere else.
The accelerator pump shot's entire job is to prevent that WOT stab stumble from occuring....if the shot is too small or too late you get that big stumble at the hit.
I'm assuming you've checked the pump arm and link, and that it squirts fuel with even the tiniest movement of the throttle shaft with no delay AT ALL....no slack allowed at the pump arm at idle.
What's the Holley List # stamped on the choke horn of the carb??
So we can look up what it is, specifically and for base calibration specs.
The accelerator pump shot's entire job is to prevent that WOT stab stumble from occuring....if the shot is too small or too late you get that big stumble at the hit.
I'm assuming you've checked the pump arm and link, and that it squirts fuel with even the tiniest movement of the throttle shaft with no delay AT ALL....no slack allowed at the pump arm at idle.
What's the Holley List # stamped on the choke horn of the carb??
So we can look up what it is, specifically and for base calibration specs.
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You need to get the ignition timing set properly before you attempt to adjust the carb. I have the same questions as pockets posted.
But... In the event that your timing is set correctly (both initial and total), I agree with Ericnova72 that you most likely need to increase the squirter size of the carb... and may also need to play around with different pump cams.
Is your Holley 650 a double pumper or vacuum secondary carb?
But... In the event that your timing is set correctly (both initial and total), I agree with Ericnova72 that you most likely need to increase the squirter size of the carb... and may also need to play around with different pump cams.
Is your Holley 650 a double pumper or vacuum secondary carb?
Thanks for the ideas fellas. It is an RPM performer cam, I’m running mechanical flat lifters on it. The carb is a new 4150 duel feed mechanical secondary 650. The distributor is an MSD HEI vacuum advance, I’ve tried it ported and full manifold vac with no change. I’d have to find my notes from last year to tell you for sure where the timing currently is along with jets. I’m sure it’s pig fat currently but when I lean it out it gets worse. I just threw in the towel last fall, I was tired of torn gaskets and not gaining anything.
With that cam, a stock hei curve/timing set up will not work. I would get a msd 88363 lockout plate, install it, and lock the timing out at 36-38.
You didn't say what heads you have or what plugs you are running, or what compression.
Carb tuning starts with the proper plugs and timing set up. I am sure you will still need larger squirters, or different accel pump cams, but start with getting the timing right. If you aren't running enough advance, that makes you need to open the primary blades more than they should be, exposing more transfer slot, and then there can be an issue with not enough transition fuel as it's flowing already. As well a weaker vacuum signal to the carb requires more fuel from the accel pump circuit.
"Lock your timing at 38 degrees and drive it to eliminate distributor/timing issue."
Absolutely the most useless, backwards thing one can do to figure it out. NO ignition system curves/timing will ever get resolved doing this extremely incorrect method
Now, please record for us these specs:
INITIAL timing, vacuum advance disconnected, hose plugged, at idle:
Vacuum advance degrees added in the vacuum canister
Total timing (vacuum advance plugged), combo of INITIAL, and mechanical advance degrees, from idle to when the timing stops advancing on the balancer (DO NOT USE A DIAL BACK FEATURE TO TEST THIS
IDLE timing, combo of INITIAL and vacuum advance degrees, at idle, read on the balancer, FULL MANIFOLD VACUUM for the vacuum advance, NOT PORTED
Absolutely the most useless, backwards thing one can do to figure it out. NO ignition system curves/timing will ever get resolved doing this extremely incorrect method
Now, please record for us these specs:
INITIAL timing, vacuum advance disconnected, hose plugged, at idle:
Vacuum advance degrees added in the vacuum canister
Total timing (vacuum advance plugged), combo of INITIAL, and mechanical advance degrees, from idle to when the timing stops advancing on the balancer (DO NOT USE A DIAL BACK FEATURE TO TEST THIS
IDLE timing, combo of INITIAL and vacuum advance degrees, at idle, read on the balancer, FULL MANIFOLD VACUUM for the vacuum advance, NOT PORTED
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Did you ever figure out what your timing is set to? What PN MSD HEI are you using?
I have not gotten back to it yet guys. Been way to busy at work and with the sky still dropping white stuff there has been some fresh salt dropped on the roads. I will get back to is as soon as I can and will certainly share with you what I’ve got going on. I sure appreciate everyone’s input!!
Well, my timing light seems to be having an issue but I did find my notes from where I left off with the carb. If I’m reading my chicken scratch correctly I’ve currently got 65’s in the primaries, 73’s in the secondaries, it’s either a 5.0 or a 6.5 power valve. Not sure if that helps anyone at all with the carb stuff anyway.
Timing is step one.
And Dave ray I beg to differ. Locking timing at 38 will most certainly tell you if it’s a timing issue.
Weather from the vac advance or mechanical advance or simply not set up correctly.
On a stock or close to stock mild engine I couldn’t agree with you more that the vacuum advance and mechanical advance are needed and beneficial. But that it not every situation.
No disrespect because I’m a big believer that vac and mech advance have there place on many setups but I’d like to see vac advance and mechanical advance be used to make an improvement on my locked at 38 489bbc. 272/[email protected] .50 over 62 degrees of overlap on a 109.
And Dave ray I beg to differ. Locking timing at 38 will most certainly tell you if it’s a timing issue.
Weather from the vac advance or mechanical advance or simply not set up correctly.
On a stock or close to stock mild engine I couldn’t agree with you more that the vacuum advance and mechanical advance are needed and beneficial. But that it not every situation.
No disrespect because I’m a big believer that vac and mech advance have there place on many setups but I’d like to see vac advance and mechanical advance be used to make an improvement on my locked at 38 489bbc. 272/[email protected] .50 over 62 degrees of overlap on a 109.
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What is your initial timing set to? The MSD 8362 Distributor has 22*@4k RPM of mechanical timing built into it.
1968 Malibu sport coupe, 489 ci. 590 hp 600 tq, RV T-400 Freakshow 3200 stall, 3.73 12 bolt posi
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I recently put an MSD stop plate in my Pertronix dist. trying to stop vac. adv. as close to 10* as possible, maybe one of those would help the OP? I would have preferred a Crane stop plate but they're not available now
So if I wanted 35 total my base should be 23? My light at home is apparently crap at this point so I’ll need to go to the shop and use a “quality” one. 23 sounds a little high for base. Sorry guys but I’m an idiot when it some to tuning old school stuff.
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