350 sbc bogs and sputters at moderate acceleration

The plugs will give as good an indication as anything for the jetting. It wouldn't hurt to experiment and try a few things.

If you use the #2 cam hole be sure to readjust the pump linkage to remove any slack there might be and to be sure there IS some slack (0.015" is enough) at WOT so the pump diaphragm isn't damaged.

Check the vacuum w/the engine idling and in Drive if you have an automatic trans. Usually a 65 is about right. The 85 will richen the air/fuel every time the carb is below 8.5 in/Hg vacuum so it may be a little rich, depending on the vacuum in gear.


Register now (free) or login to remove ads

hello sir.
by now i have adjusted the accelerator pump, it was set way to loose. i adjusted the rear float also... and i ended up puting in #40 squirter. it had #31 in it and i tried #32 also. but it seems to be happiest with #40 but i need to get me some more squirters and try them out. right now it has good responce while driving but sometimes after it has been ideling for a minute or so and i give it WOT it hessitates a bit, but very litle compared to how it was. so we ar making some progress here. it does not bog if i give it some gas, let it idle for few seconds and then do wot ! does that indicate i need to give it some higher idle speed ?

You can try a higher idle speed, sure. Just keep it to where you don't have to stand on the brake to keep it from rolling away from a stop light. You want to avoid raising the idle so much that the mechanical advance begins to come in. If you find this is happening, using one stiffer spring will control the mechanical advance. This will also raise the "all in" timing RPM but shouldn't be a problem if you only change one spring to the next stiffer spring.

Another thing that will possibly help is to add some initial advance to it. I should have mentioned the timing before the carb tuning. This also increases the idle speed but more importantly it helps the off-idle response even if you adjust the idle speed back down to where it belongs. You will need to remove some mechanical advance to compensate for adding initial timing or the total timing will be too high- and this can cause detonation so must be done!

If you have the vacuum advance hooked up to a ported source, try it hooked to manifold vacuum. You will have to lower the idle speed, but that can help the off-idle response w/o messing up the total timing.

forgot to mention that i have rised the initial timing to 18' now 38' total and am running the vacuum advance through full manifold vacuum, i belive the idle speed is now around 650-700 rpm

Is the 650-700 RPM idle before or after you raised it? Either way, that's a fairly low idle speed, even for a stock cam (is it a stock cam? I don't recall seeing a cam mentioned in any of your posts).

That Streetmaster intake is an open plenum design and does nothing to help the vacuum at idle. Or anything else, for that matter (IMO). I don't care for it and would MUCH rather see you using an Edelbrock EPS intake if you have a stock or mild cam.

Be very careful using 38º total timing w/the 58cc aluminum heads you have. You have to avoid any detonation, so stay on top of listening for detonation ping and keep an eye on the plugs for any signs, and use premium fuel.

i use 93 oct fuel, the camshaf is crane powermax 272/284 216/228 @50" and 454/480 lift LSA 112'
should i back the ign time to 36' ?
it does not show signs of ping yet, but i haven't put max load on it yet. i adjusted the idle speed to thi setting after setting the carburetor and ignition timing.

last weekend l did put Chevrolet aluminum dual plane intake that had been heavily ported and it had very good topend power along with goodthrottle response, it also showed no signs of hessitation when wot from idle, but the idle speed was near 1000 rpm's at that time. i was experiencing some other problems wit it though... i suspected vacuim leak somewhere because i was only getting 12" vacuum at the time so i changed back to the streetmaster intake and i ran like crap. much worser han before i changed to the Dual plane intake...

I cannot say whether you need to lower the timing but it wouldn't surprise me if you experience some ping under load w/the engine hot. So keep a close eye on things even at 36 degrees, just to be safe.

Hard to say exactly what was going on with the dual plane but a vacuum leak makes sense. All you really need is a stock Performer or EPS intake, so if one comes your way, grab it. The Performer intakes are relatively cheap, used. You don't see the EPS for sale used that often- at least I don't- but it would be the best of the two by a small margin. Small enough margin that if it cost much more than a Performer I'd probably pass on it, we're only talking about a 5 HP/9 ft/lb difference according to Edelbrock.

just my two cents here but go to napa our autozone and invest a couple bucks in a vacuum gauge hook it up to manifold vacuum, usually the line for the power brakes works best. then conduct you're tests. the gauge is simple to use and easy to learn and will fill you in on sooooo much more than hit or miss tuning, you could have a sticky valve or a collapsed lifter that is causing the laziness. its a tried and true method, once i learned it and saw the effects ill never tune another car without one

I'we hooked up a vacuum gauge to the engine and the highest vacuum reading i get is 16/17" Hg and it's steady so that indicates that everything is in good condition right ?
But shouldn't i be able to get it higher thought ? is it the manifold design that's altering that (low rise open plenum) or is it the camshaft that's a bit milder than stock ?

I'we put the total timing to 36° now and am going to try that out now. I will listen for detonation very well.

I'we been keeping an eye out for Performer intake, But here in my country they don't get up for sale that often. As is I don't even remember to have seen EPS intake in my life...

Best regards.

Generally speaking, the milder the cam (less overlap, wider LSA), the more idle vacuum you will see, all else being equal. It's not unusual to see upwards of 20 in/Hg vacuum on a well tuned engine in good condition internally w/a stock-type cam.

The vacuum reading can differ between different gauges. If possible, see what a couple bone-stock engines in good condition read on your vacuum gauge. That will give you a reference for comparison.

HERE is a vacuum gauge reading guide.

THIS is another one.

nice guides cobalt i gotta print them out haha