Technical SBC 350 with 2 barrel rochester rough on acceleration/idle

Thanks! I love this truck because its low stress (when I drive it places) and it's been great for my rowboat, paddleboards and the occasional home depot run... it has a lot of body rust that I don't want to deal with and a high mileage engine so at the same time I'm wondering what good spending extra on a better carb/intake will do... maybe a little extra fun climbing hills on my way home? Occasionally my neighbor across loves to rev up his Harley and I feel I'm missing out so I put 18" glasspacks in this truck... when I pull this out of my garage I'll rev it a bit and this carb generally seems just fine for dishing a little love back at him

The $20 for the rebuild is plenty reasonable I'll get a rebuild kit... at least I can learn something along the way in doing that so it's money worth spending. Although I was hoping to give more time to my 50 shoebox ford

 

Sounds like you don't drive it very often, you very likely could have sour gas, try fixing that before getting the tools out

 

I thought about that! The fuel gauge is at a quarter or less. I had put 2 gallons of premium in this thing recently, one a couple weeks ago and another yesterday. I usually take my 1 gallon container with me when I fill up my daily driver and put premium in it and fill the truck little by little. I don't think it has sour gas (although I could be wrong).

 

Try filling it half way with just regular, not premium, my friends and I have had some interesting experiences filling our cobra's with premium...it doesn't get sold as fast as regular, and depending on where you buy it, it could be months old and in bad shape. I use only regular now, runs fine. Good luck

 

Oh that's interesting! I get my gas from Shell here in San Diego in a busy part of the area too.

 

For any matters of engine tuning, always connect your vacuum gauge to a source of full manifold vacuum.

You seem to be obsessing over setting the valve lash. If you had solid lifters this might be acceptable since you're setting lash within a few thousandths of an inch. But that kind of precision is not necessary with hydraulic lifters. You just need zero lash and maybe a 1/4 or 1/2 a turn of additional preload. And you're done.

If it were mine, on a used engine, I would adjust the lifters with the engine idling at operating temperature. This method seems to meet with some disapproval around here, especially from folks with "show quality" engines. But that's not your situation here. If a bit of oil splatter bothers you, lay some shop towels or rags over the rocker arms and move them aside from the adjuster nuts as needed for the valves you're adjusting. Or buy or borrow a set of rocker arm clips that snap in place over the pushrod end of the arms to deflect oil spray from the pushrod holes.

Connect your vacuum gauge and place it within your view while making your adjustments. This is not mandatory. But it's interesting to watch the gauge readings while doing the adjustments. You're not looking for the highest vacuum reading necessarily, but rather how steadily the gauge reads, or how much it fluctuates. The steadier, the better.

Now at idle, slowly back off the adjustment on one valve at a time until you can hear it ticking. Stop, wait a couple seconds, then slowly turn down the adjuster nut till the ticking just stops. You are now at zero lash. Wait a few seconds and then slowly tighten an additional 1/2 or so turn for pre-load and check your vacuum gauge. The pointer may be a little jumpy and the idle might be a bit rough momentarily, but it should all smooth out as the lifter bleeds down to its final setting. This can take several seconds, especially on an older used engine with some weaker valve springs and/or a bit of varnish in the lifters. Then repeat the procedure 15 more times and you're done!

For additional fun (and education) get an extra length of hose and route the vacuum gauge inside the vehicle so you can see it while driving. Watch the changes in manifold vacuum at idle in park, at idle in gear, under light and heavy acceleration, when climbing a grade, when driving into a headwind, when hauling a load, when de-accelerating, etc. After a while you'll begin to better understand when and how things like the transmission vacuum modulator, distributor vacuum advance and the power valve in your carburetor work.

Looking for better fuel mileage? Try keeping the manifold vacuum as high and as steady as possible when driving. You've probably heard the expression about driving like you have an egg under your foot on the gas pedal . . . ?

 

Thanks, yea I'll give your suggestion a go as well. It won't take me long to get the valve covers off to adjust while running.

 

San Diego? Hell run it by @lumpy 63 he'll help you out

 

I put a like but I’m not saying Lumpy has been nominated. Op is doing his best but with so much input I’m afraid he’s a bit lost and some one on one is in order. Typed help only goes so far.

 

Haha... yea lots of input from several.. right now I'm going to start with the basics to make sure I didn't mess something up... I'm about to get going on this and recheck timing (correctly), set valve lash while running, then look at resetting the idle mixture screws. I'll report back after that. It could be an accelerator pump, carb in general, new fuel pump putting out too much fuel pressure, etc. and maybe could get help from a fellow HAMBer locally at that point.

 

Ah if ol lumpy could lay his hands on it, miracles would happen! The man is a genius

 

Just realizing I need a piston stop to accurately check my timing mark on the balancer! Can't find a single auto parts store that sells any locally in San Diego.. how bizarre. I don't have a welder (I need to add that to the list) so may have to take an old spark plug and gut it and use epoxy for a nut and use a bolt for the inside to run through that epoxied nut.

 

NO
Started out good , but went quickly downhill from there LOL

 

Yes, that's the easy way..No epoxy needed . Use a 1/4 -20 threaded rod and nuts on both ends .Might need to grind the inner nut just a tad. Go slow near the top of piston travel.

 

I went in to work where I have access to lathe, press, vice, mills, taps, etc…. I’m gutting the spark plug and tapping for 3/8-16

crazy you can’t buy a tool like this without ordering online!

 

Below is a photo of what I made. I’m thinking grinding out all the thread and smoothing would be kind of a pain… I read some people complain the bolt threads may knick the piston. I rounded the very tip with a file so it’s not as sharp there…

 

Made another version.. I don’t think the length has to adjust. I cut off the end of a shoulder bolt and smoothed out the end… no threads to knick the piston.

 

The ported vacuum port is only open to the manifold when the throttle is slightly open [cruising at part throttle]
It will show some vacuum .
The ported port on the carb is above the butterflies [throttle blades] whereas the manifold vacuum port of the carb is below them . [I showed both on the photo "post #29"]
Both these ports have the same size hosetail end so it is easy to hook a gauge to either of them.

once you get the timing and the mixture set, the engine will idle a lot higher [so you need to adjust down the idle stop screw and recheck the idle mixture]
With the idle stop adjusted down , there will be a significant drop in ported vacuum , but manifold vacuum should still be high.


An Edelbrock carb and 4 barrel manifold would be an end goal, BUT it will still need some tinkering.
They are notorious for "Heat Soak" so you'll need to play with phenolic spacers or alloy manifolds [block off heat risers etc]
But before you go down this "rabbit hole" keep dicking around with what you've got. [Keep Learning, and don't be afraid of making the occasional mistake]
You should be able to get it running pretty good [for an old engine] A Rochester 2G can be a responsive carb down low.
Don't overthink it [especially main jets] because nearly ALL carbs spend 95% of their life on the idle circuits.
I have never needed to change main jets on one yet on a rebuild [I've just cleaned them]
If this was a 2 barrel race engine, then yes.

Just pull the plugs out and DO NOT turn the engine over by the starter [do it by hand /or ratchet on the crank pulley bolt]
Mark the TDC on the timing cover so it is easy to see, and then mark the "correct' position on the balancer. [below]
This mark on the balancer is where the "0" on the timing tape goes.


On my friend's 350 Chevy we moved the TDC position to the edge of the timing tab [below]
This made it easier to read [especially with accessories in place]

 

Good job on the stops. Second one is probably too long. The first might need adjustment too ..Better to get it as short as you can.Then you can split your marks easier.

 

thanks I can shorten the second one so I’m working with a smooth surface for the piston. I wonder what a good length is from the base of the drilled out spark plug.

 

I'd say either the new fuel pump made some junk break loose inside the carb or a wire got crossed when you changed the plugs. Isn't it 5&7 that you can reverse and it'll run fine till you put a load on it? Your timing and mixture screws are close enough that it shouldn't 'barely make it home'. Pop the top off the carb and see if it's got rusty junk in the bowl. I've run gallons and gallons of fresh fuel through carbs that have sat, and somehow they will still have brown fuel in the bowls until you take them apart and blow them out.
I would just try playing with the timing by ear, advance it a bit and run it down the road. If the stumble doesn't change then open up the carb. Need to go back to step one and narrow down whether it's a carb problem or an ignition problem IMO.

 

Just start out high and then adjust till it hits then give it a bit more.

 

I got it dialed in and cut it shorter and smoothed it. I will keep this tool handy for the future!

 

Ok so one problem (sure there are plenty more) just found. Indeed the damn timing mark on the balancer is off! Using the piston stop tool I made I marked tdc in both directions. It appears the mark on the balancer is about 8 to 10 degrees too far right or clockwise. The true tdc would be 10 degrees counter clockwise. I will mark this actual TDC and use MSD timing tape I had leftover from a different project and time to 12 deg advanced based off that.

So if I had it set to 12 degrees initial with my dialback if my logic is right that means I actually had 20 to 22 initial? Maybe with the valve adjustment and carb adjustment it made it worse to where the way off timing is now noticeable?

some history… this thing had a distributor with some electronic module and other stuff completely disconnected. It had no vacuum advance. On my 53 Chevy (sold it) with sbc 350 I installed a new street fire hei distributor and kept the ac delco distributor it was working fine I just wanted a newer looking one at the time…. I installed it in this engine, put new wires and new plugs and timed it according to the mark on the balancer. I ran that for the last 5 years. No backfire and just some stumble on the top end if I hit the pedal hard otherwise I didn’t really notice any issue other than cruddy #3 and #7 plugs.. then in April when it was stuttering more and I checked the #3 and #7 plugs and they were cruddy again so I decided to change valve stem seals and add positive deals and umbrellas in addition to changing out the o-rings. New plugs put in.

 

Is it still Drivable?

 

no but it might be soon now that I found the timing was wrong because the balancer mark was clockwise too much by 8 to 10 degrees.

I’m in the bay Ho part of San Diego by the way

 

Ok , Let me know if that works. I will be at the shop tomorrow from about 7:30 to 3:00 , I will Pm you the address . As most of you guys know I stay away from online diagnostics, I need to see it , hear it, touch it and smell it

 

As I’m ready to put some timing tape I look and I’m missing the 6.75 one that I need! I must have used it in the 53 Chevy when I installed the MSD street fire. Bummer you can’t buy this stuff in stores! I guess for now I’ll mark the new zero and use the sears craftsman dial back light I have. I could always go back and add tape and verify the dial back set it right.

 

Here’s a photo showing the two marks I made using piston tool. This is from underneath the car where I has more room to look clearly. I’m going to make a new zero mark and use my dial back light to set 12 deg advanced.

 

Was indeed off about 10 degrees. Looking from top of engine red is new mark blue is previous factory mark on balancer.

If I set 12 deg initial on the incorrect mark before must have been 22 deg initial.

maybe with the distributor connected to manifold it was driveable before since timing dropped when giving it throttle but it stuttered as the engine adjusted to the changes. Now with it connected properly to port it gets way too much advance timing when giving it gas since it’s off by 10 degrees!