Technical Upgrade from Rochester 2G to Edelbrock 1406 worth it?

I think my first carb rebuild went well and I figured out the issue! Headaches galore, not even my fault (I don't think).

I took the top apart and looked at the float assembly and it was slightly crooked but not much but it was hitting the pin for the power piston assembly, though ever so slight. The pin was a little crooked so I bent it straighter so the float didn't touch it but that wasn't the issue (at least I don't think!).

It was running kinda choppy and I remember that exact behavior/tone earlier this year in the summer. I checked the fuel pressure and bingo maxed my gauge out past 10 psi! I installed the Holley 12-803 (range is 4.5 to 9 psi and I set it to the lowest it goes) and it idled fine. Took it for a drive around the neighborhood and drove smoothly. I still see the gasket looks wet but I'll let it dry overnight and fire up and recheck in the morning I think this suggests my carb rebuild went well!!!

Now for some history on the headaches and not sure what I should do:
1. I was working on the cylinder valve seals since I was blowing so much smoke all the time. Coincidently when I put that back together the mechanical fuel pump just happened to go out and was leaking out.. for some reason (I don't remember) well before that I had measured fuel pump pressure at about 3 to 3.5 psi.

2. I changed out the fuel pump with one from AutoZone, the Delphi AMF0001. That thing put out about 8 psi or so and the carb seemed ok for a while but to be safe I decided to install a Holley 12-803 regulator and put it down a bit lower in pressure near the lower limit. I ended up finding it was acting a little weird at times and it behaved differently off transition from idle and was sensitive to how I adjusted the idle mixture screws and the exact pressure in the regulator.

3. I decided I must have the wrong type of pump so I was able to return it and instead got one from Napa that claimed to be lower psi application part number FUP BO1086P. I installed it without the regulator and great! It was putting out 4.5 psi so I decided to leave the Holley regulator out (one less thing to worry about and less hoses).

4. Eventually I found something fidgety with bogging when accelerating and some suggested I rebuild the carb.. When it bogged, I could get by with turning the engine off, then adjusting the idle mixture screws... typically turning them out 1 1/2 turns after tightened all the way in and it seemed to not bog at that point... I wonder if the fuel pump from Napa little by little was putting out more pressure and that was the issue! I'm not sure why I see 10 psi now, I would think the pressure wouldn't change over time since its regulated by a spring unless maybe the rubber diaphragm changes characteristics after wearing in and the spring behaves differently? I read in another thread of someone else complaining of the mechanical fuel pumps creeping up its output pressure over time.

I'm not sure if I should take that fuel pump out and go back to Napa and get another one or just give up and leave it and use my 12-803 regulator along with it? The 12-804 goes from 1-4 psi which would work better but won't accept anything north of 7psi input so not likely to help my situation if 4.5 psi is too much for a Rochester 2GV.

Either way I'm relieved I put the carb back together and didn't mangle it... to be honest this ended up being very easy.. I dreaded this for a while not knowing exactly what was involved. I've done so much more intricate stuff with underwater robotic systems ive designed and built.... although I better double check in the morning the carb is working fine again before I jinx it!!!

 

Sounds like you found the problem.

Great!

Jon

 

thanks still puzzled why a mechanical fuel pump would put out higher pressure a few months later compared to when first bought.

also on the idle mixture screws is that something you sell? I couldn’t anything for sale online with the part number you gave.

 

Possible you had some restriction in the pickup that slowly cleared itself

 

I wonder too! The only spec I can find on the pump I got from Napa is 23 gal/hr which isn’t enough to determine what psi it would put out.

I’m thinking just to leave whatever pump is in it and not try to get a replacement of the same part number.

 

I keep an excel spreadsheet with logs of all work done and I just went back again to look at my notes. It turns out on 10/1/23 I decided to return the AutoZone Delphi AMF0001 fuel pump and got the Napa FUP B0186P and installed it. I had the Holley 12-803 installed and made a note it was stuttering so I ended up removing it and measured 4.25 psi from the pump without the regulator.

Strange to be getting maxed on my gauge which only goes to 10 psi now and needing to reinstall the holley 12-803... im not sure where a restriction would have existed and cleared, nothing obvious when I looked it all over.

 

That style tank is notorious for obstructions in the actual sending unit. In fact when I was in Arkansas a year and a half ago pulling my engine from a truck at my old job I worked on my old boss's 64 C10 while I was there. It was bad enough that if you drove it without warming it up you could actually drive it on short trips. Once warmed up you'd maybe make it a mile before it stalled out. A new sending unit and a quick flush of the tank and it was back in business

 

Interesting! I found some huge pieces of gunk/silicone in the rochester filter (some time in June) and had cleaned it out and replaced the filter and I was having some issues after that as well and imagine the fuel pressure maybe changed. Then again maybe that was part of the old fuel pump as it was falling apart and eventually leaked.

 

Anything the kinda looked like mud?

 

no just soft rubbery pieces

 

I fixed my throttle linkage so I get the full range and I get to WOT before my pedal hits the floor.. in doing so I backed the fast idle screw out all the way and forgot to put it in some... when I fired up the truck the fuel pressure was at 10 psi even after the 12-803 regulator, and it was not happy and I could hear what sounded like valve train knocking but was the mechanical fuel pump (I remember also hearing this a while ago earlier in the fall when it was idling rough and I had to turn the engine off and reset the idle mixture screws).. I tightened the fast idle screw in and raised the idle and the fuel pressure dropped down to 4 psi or so and it seemed happy.... does this suggest a problem with the carb? I remember this thing being finicky with the idle mixture screw setting and now am understanding it was also likely a function of the fast idle screw....

During the rebuild I cleaned the passages all with a wire really well, everywhere I could in the carb, most especially the idle passes below the throttle blades.

As a test I took the 12-803 holley regulator out and tried again and right back north of 10 psi even with the idle at 800 rpm.

I took the fuel pump out and went to Napa and got a replacement with the same part number. I installed it with 4 gaskets (yes 4 gaskets, I read somewhere a trick to reduce pressure is to install multiple gaskets which makes sense since spring force is proportional to the amount compressed) and it idled nicely.. i set it to 800 rpm and without the holley regulator it was at 4.5 psi and then dropped below 3 psi (maybe when the needle opened?), then rose back to about 6 or so psi... when I rev it it and leave it, it drops a little back down to 4.5 psi... I decided to leave the regulator out for now. I drove it around the block and it felt good.

I wonder if I damaged the first Napa fuel pump running the holley pressure regulator when I had first installed it and then when I removed it, maybe it was already damaged and got gradually got worse.. I read somewhere else some of the dead-head regulators can cause damage to a mechanical fuel pump but I don't know how true that is.

The only thing left to do carb-wise is buy idle mixture screws which I can't seem to find a source for the number 7013116.

Other than that I guess next thing is for me to check compression.. and maybe that will help determine if I just need to do the timing set, or change the cam at the same time?

 

Idle mix screws-

https://www.carburetion.com/products/ProductDetails.aspx?Part=16-122

 

Anyone know if a little leak of fuel from the throttle body gasket between the throttle body and the fuel bowl portion is a flooding issue or perhaps I need to pull the carb out and recheck how tight the screws holding the throttle body in are? I didn't see any fuel leaking above that point when I rechecked this morning.. it was only a little.

Also when first firing up I need to hold my foot on the throttle just a little and then it wants to fire up and idle and I can let off the pedal... hmmm.

This is with the new fuel pump.. perhaps I need the regulator still. I'm going to take the carb out and recheck the tightness of the four screws connecting the fuel bowl to throttle body.

 

Hi all, quick and final update to close out this thread.

I took the 2G carb out again and took it apart and really cleaned up the power piston as I thought maybe that was causing an issue... carefully seated the two check balls again, and carefully torqued everything down and filled the bowl with fuel before installing.. also checked the needle and seat were working properly including with fuel in the bowl and everything checked out.

With the swapping of fuel pump (from Napa with same part as the old) and running the Holley 12-803 I have 3 psi fuel pressure. The carb isn't leaking fuel like it was before and I've got 19 in hg vacuum at idle with 800 rpm. I set the idle mixture screws for highest vacuum and took it for a drive around the neighborhood. It drove nice and no stuttering upon acceleration.

Next up is the timing chain set which I'll be doing this upcoming Friday through Sunday and will use the other open thread I have going related to cam/timing questions.

Thanks everyone that provided insight/advice. I'm going to buy new idle mixture screws and run with this 2GV carb/intake combination and stock cam since it should work for my needs.

 

Here is what you are looking for:

The extended head is useful for idle adjustment in some cases. There is another valve that does not have the extended head, but the same thread and the long taper.

And before you ask, I only sell them in rebuilding kits, not ala carte.

Jon

 

Thanks I assumed you don’t sell them individually. I ended up buying an electric choke conversion kit for my divorced choke setup and the less tapered idle mixture screws from Mikes
Carburetor

do you think I’ll be fine with these?
Mike said to just get the similar taper I already had.

 

If the thread and length are correct, the short taper will work. The long taper just works a bit better, as the adjustment is more precise.

Jon

 

Darn!! I'll have to use the short taper. By more precise meaning less sensitive while turning and watching the vacuum gauge? I imagine I can get it close enough with the short taper screws just a little more effort/repeating..

my vision is starting to fall apart on me quickly and that's probably the real bottleneck when reading the gauge

 

Not gonna save if the carb you buy has an unforseen issue .....,Your carb is available on exchange basis...Dont open a can of worms ,,,,,jusr rebuild or exchange for a rebuilt one...

 

On evil Bay .....https://www.ebay.com/itm/1261673053...OP5W/QvOnezaJNLAxFMkv2VHE=|tkp:Bk9SR9LBh4KgYw

 

I’ll summarize 8 pages of this thread…. To rebuild or upgrade to 4 barrel… discussed to death and I said fuck it after most people’s advice and rebuilt it on my kitchen counter over Xmas break… it came out ok but took two tries. Thanks! Currently starting the timing set change project on this thing (separate thread open on that)

 

Also, one last very ironic thing to close out this thread with... as I'm working my way to getting the timing chain set changed I found a stamp code that says V0916TXA. The TXA suffix indicates its a 1975 motor with 4bbl and 165 Hp. I guess whoever put the motor in the truck decided to change to 2 barrel intake and 2G Rochester carb. Why , I dont know, maybe snagged the 4 bbl intake/carb for another project?

 

Makes sense...Years ago more shade tree mechanics working on their cars and trucks......cool when you start to do forensics on a car or truck .someone before you got their hands in there.....have a great weekend..thanks for sharing...

 

Thanks, the only thing really bothering me now is how much power I would gain going from 2 barrel to 4 barrel given the motor itself was originally set up for 4 barrel from factory (assuming stock heads/cam)... the 4 bbl was rated at 165 hp.. I wonder with the stock heads/cam for this particular motor what hp drop I would see with 2 barrel carb.. I rebuilt the rochester 2G because most suggested I should do this but we didn't know this motor was originally set up for 4 bbl according to the engine code hmmmm

 

The thing is CFM ,,,,An engine is essentially an air pump....The bigger the carburetor CFM , the more air passes through the carb air horn and being a variable venturi design at part throttle fuel is discharged accordingly...more air flow more fuel up to the limits of design...I would think you would only see a 10-20 HP gain with a 4bbl carb switch...

 

Makes sense, the factory 1975 350 with 4bbl had 165 hp, and with 2 bbl 145 hp. I imagine 20 hp isn't going to be a gigantic difference although since I'm already running low hp I wonder....... although it seems a pain to hunt down a Qjet/4 bbl intake etc.

I believe the engine may have a little more hp than stock because the smog parts were removed.. It has ram head exhaust manifolds (heard they flow better than smog era exhaust manifolds), it has dual glass pack exhaust. I put an HEI distributor in it. I imagine the cam and heads are stock (though haven't verified that). Maybe I'm back to 165 hp with those changes.

 

If its not your daily driver and desire more power..., budget allowing of course.....a hotter cam , with the intake and carb swap will get you the kick in the pants you seem to be wanting....I learned by doing , consulting older car guys when i was in my twenties....Keep us posted and you will get the best advice and guidance here .....maybe drive it till spring and then go for it....

 

I'm currently doing the timing set change which is why my mind is spinning right now because I'm sort of half way there... money isn't an issue for finding another cam, intake, carb but at the same time I don't want to have to buy new heads/springs, etc... someone suggested for this smog era motor changing the cam wouldn't do much if I kept the same heads. I found a photo from when I had the valve covers off and I have 462624 heads which are 76 cc and not considered good at all.

If it weren't for finding that engine code and realizing the motor was 4bbl from factory I would not care as much about having a Rochester 2G and would just finish the timing set and stop there for now.. At the same time my compression numbers were 120 psi (pretty close to even on all 8) which indicates maybe this motor doesn't deserve any real money into it.

I'm changing the timing set because I bought the parts from RockAuto and it would cost me $50 to return so I'm just going for it. Chevy Pope suggested I change the timing set in case it still has the original nylon gear set.

 

You're getting bogged down by overthinking your situation! The carb is rebuilt and appears to be working as it should, so move on.
By the way, since you seem to like to super-analyze this engine, take a look at what rpm the horsepower ratings are given.... probably 4,500 or so. Unless you are constantly revving that high, the noticeable horsepower difference will be negligible.
Put this thread to bed and see how long of a thread you can create with your timing chain swap!

 

I stand corrected, I thought you could've done a complete ring and bearing job in the time you've spent on these threads. I see now that you could've done the bodywork and paint as well.