Carb Puzzle

Henry/Kokomo

Henry/Kokomo

Well-known member
I have a stock '46 Tudor w/dual exhaust. When I got the car, the engine ran rough at all speeds. In the course of getting it to run better, I had the carb rebuilt by a professional. He did a great job. The engine stated fine, idled well but ran rough at higher revs with no load. The roughness wasn't noticable under load (driving).

It was suggested the carb might be jetted too rich and/or the PV was too high a number. Rejetted the carb from .051" to .049" and installed a 4.5 PV. Much better throttle response, no gas smell but still had the high rpm no load roughness.

Fast forward. I wanted to test a Rochester 2GC carb with .055" jets which I built from a pile of pieces. I bought an adapter an bolted it on the 59ab with absolutely no other changes. Surprisingly, it worked and worked very well on the first try. The engine was a bit "over carbed" at lower RPM's but ran like a banshee at high speed. No stumble, no rough running just smooth power. Seems to me the engine wasn't getting enough fuel at higher RPMs with the stock "94".

Q: What's wrong with the "94" that's on the engine? Jets? Other? Will changing jets make the engine run smoother?

Sorry to be so long winded but curious minds want to know. Thanks in advance.
 
I was wondering why there seems to be so many problems with the 94's as well. Is there a better Carb or setup to avoid all the stinking power valve problems?
 
Take a look at the picture of the the two power valve bodies. The one on the left is a plug that is modified to correctly seat in a 94. The one on the right is what comes in the rebuild kits. These are made for a later Holley(wide base 4 bolt 2 bbl and 4 bbls). The black fiber gasket they come with is junk also. They will leak when installed in a 94. I know first hand. I chased this problem a year ago. Either get a modified body PV or machine the one in the kit and use a nylon gasket. Another place to look is the needle and seat. I have had the seat loosen. It causes a similar symptom.
 

Attachments

  • PV bodies.JPG
    PV bodies.JPG
    83.6 KB · Views: 31
Henry,

Your 2CG over carb'd condition in the low ranges might be caused by too much accelerator pump travel.
 
The question regarding what is wrong with that 94 carb might be difficult to answer------It could be anything from a power valve to a metering orifice burr to float level to air bleed. Or, it could be something in the ignition circuit. If you knew what the fuel pressure, and the A/F ratio were at the time of the behavior problem it might give a clue. When you installed the bigger carb the vacuum in the intake would have changed, which, if using a stock distributor, could alter the timing curve. It would sure be fun to install a different 94 carb, in a back-to-back test, and see what happens.
 
JWL - I know the fuel pressure on both carbs (2GC & 94) is/was 2.5psi. Vacuum was 17-18" Hg. w/94 and 18-19" Hg. w/2GC. I'll see if I have another 94 to try. No way to measure A/F ratio at this point.
 
Paul - Relative to a better carb, the reason I built the 2GC was to put on a 276" flathead I'm building. The engine is "updated" with PCV, full flow oil filter, different ignition, EAB heads, etc. It appeared to me it was going to need a bigger carb or two carbs, based on displacement increase and different cam. I was advised that a 2GC was almost as good as two 94's and a single carb is a lot easier to tune than a pair. The fact that the carb fits on a Merc. intake manifold and very little work is required to "blend" the manifold passages is a big plus, in my mind. Also, 2GC's are a couple of decades newer than many 94's.

Based on VERY limited experience, I'd recommend using a 2GC, maybe with smaller jets, on any flathead 239 cu. in. or larger.
 
Well, the symptoms ceased when the carb, and only the carb, was changed. The distributor was professionally rebuilt and set up and subsequently the coil was rebuilt as well. I had no problems, before or since the "test", that SEEM to be ignition related. As with anything else, I certainly could be wrong.
 
Henry/Kokomo said:
I have a stock '46 Tudor w/dual exhaust. When I got the car, the engine ran rough at all speeds. In the course of getting it to run better, I had the carb rebuilt by a professional. He did a great job. The engine stated fine, idled well but ran rough at higher revs with no load. The roughness wasn't noticable under load (driving).

It was suggested the carb might be jetted too rich and/or the PV was too high a number. Rejetted the carb from .051" to .049" and installed a 4.5 PV. Much better throttle response, no gas smell but still had the high rpm no load roughness.

Fast forward. I wanted to test a Rochester 2GC carb with .055" jets which I built from a pile of pieces. I bought an adapter an bolted it on the 59ab with absolutely no other changes. Surprisingly, it worked and worked very well on the first try. The engine was a bit "over carbed" at lower RPM's but ran like a banshee at high speed. No stumble, no rough running just smooth power. Seems to me the engine wasn't getting enough fuel at higher RPMs with the stock "94".

Q: What's wrong with the "94" that's on the engine? Jets? Other? Will changing jets make the engine run smoother?

Sorry to be so long winded but curious minds want to know. Thanks in advance.
Click to expand...
It will be most interesting to hear what others have experienced.I have an identical problem right now!
 
When using the 4 to 3 carb adapter you don't take advantage of the larger flow of the biger carb due to the smaller port size if the adapter and intake. Alsoas JWL says, the 2GC is not designed to operate the stock distributor.
Here's a suggestion: try a differant distributor with the 94..
To take advantaje of the 2GC the intake shuld be bored out to the same throttle bore size and a distributor with a Cintrifical and vac advance should be used.
 
Ron - The 2GC is for a 276" flatmotor which is under construction. I have a 4 bolt Merc. manifold which has the passages bored to match the 2GC throttle bores. The ignition is a modified SBC with centrifugal advance. The advance curve was set up by Jim Linder (Bubba) in Indianapolis. Still trying to fin out what's wrong with the 94 on the stock 239" engine in my '46.
 
Henry,some of the professonals out there are not to professanal Lawson yea where is the spell check?? Send it to me and if i dont fix it it'll be NO CHARGE except shipping back to you. ken ct. If it cures your problem then you can pay me. Hows that sound!!!!
 
Henry/Kokomo said:
I have a stock '46 Tudor w/dual exhaust. When I got the car, the engine ran rough at all speeds. In the course of getting it to run better, I had the carb rebuilt by a professional. He did a great job. The engine stated fine, idled well but ran rough at higher revs with no load. The roughness wasn't noticable under load (driving).

It was suggested the carb might be jetted too rich and/or the PV was too high a number. Rejetted the carb from .051" to .049" and installed a 4.5 PV. Much better throttle response, no gas smell but still had the high rpm no load roughness.

Fast forward. I wanted to test a Rochester 2GC carb with .055" jets which I built from a pile of pieces. I bought an adapter an bolted it on the 59ab with absolutely no other changes. Surprisingly, it worked and worked very well on the first try. The engine was a bit "over carbed" at lower RPM's but ran like a banshee at high speed. No stumble, no rough running just smooth power. Seems to me the engine wasn't getting enough fuel at higher RPMs with the stock "94".

Q: What's wrong with the "94" that's on the engine? Jets? Other? Will changing jets make the engine run smoother?

Sorry to be so long winded but curious minds want to know. Thanks in advance.
Click to expand...
The 4.5 PV sounds a little low i would go with a 5.5 one on a single carb mtr. ken ct.
 
You must log in or register to reply here.
Back
Top