8ba stumbles at freeway speeds

52cruiser

52cruiser

Junior Member
Well I had the 8ba in my 52 customline rebuilt this past winter. Pretty much just a stock rebuild, I ended up having it bored .060 over and put a Canadian single barrel aluminum intake on it with the stock carb and an aluminum timing cover. I had the machine shop check and reuse my stock cam and lifters to save some dough but they had to grind the end of the new stainless valves to achieve the right lash. I'm really happy with the way everything turned out, its running great and sounds great. I'm just having some problems some where in the carb. As the title goes the engine is stumbling only at 65+ mph at a constant throttle (I don't have a tach in my car but i'd guess the rpms are at around 2,000) and at high rpms in first gear. I can free rev it in the garage with no problems as well as wind it up through second gear with no issues at all. It just pops out the exhaust and stumbles when I have the problems. The only remedy I've found is to pull the choke half way out at 65+ mph and it runs great. So some how its running lean. Here's the list of stuff I already checked:
- timing is dead on (I did disconnect the vac. advance to check this)
-vacuum advance is working and holding vacuum
-I have pertronix instead of points and it seems to be doing its job
-I rebuilt the carb prior to installation, new power valve tested good and I have 51 jets. (does that mean .051"?????)
-float level is dead on
-20" of vacuum at idle
-adjusted air/fuel mixture screws to achieve highest vacuum at idle
-Idle is not irradic and vehicle runs GREAT except when stated above
So my thoughts are bigger main jets, if anyone could let me know what the next bigger size recommended is? Also it seems kinda weird to me that the jets were never an issue before the rebuild, could it have something to do with the ethanol fuel and the fresh engine with good compression?
I know there's someone on this board that will think of something I haven't checked! Thanks guys, the info is greatly appreciated!
 

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See that you have Pertronix installed. Do you also have spiro-wound plug wires?
Solid or carbon core wires can cause problems with electronic ignition due to radio emissions.
 
I had dual carbs on my 53 took one off and it stumbled like yours is doing, the power valve was not large for single carb. Take off carb and check power valve there is number on the bottom, I am unable to read my eyes arnt good enough. Call Bob Baxter at Baxter Ford and he will help you, as he did me. Call Bob 785 842 9256. John Didde
 
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sounds as though you are starving for fuel since it runs better with the choke out do you have a strong fuel pump no plugged filter also those ventura in the carbs plug so easy ive had had to take mine out and spray carb cleaner in them and blow out with compressed air also the float bowl what about the rubber hose from the line to the fuel pump had trouble with the hose collapsing from the heat
 
Looks like you are running the stock 6 volt and still have a generator. The Pertronix ignition requires lots of constant voltage to work correctly. Make sure that you have battery voltage going to distributor. The symptoms you are describing sound like the issues I had with my '47 and I also thought it was a fuel issue. It ended up being a voltage issue.
 
Did you have the petronics in it before the rebuild?
Looks very very nice under your hood, well done, I like it a lot.
Seem to recall as above. Petronics need the stability of voltage you get from an alternator and special plug leads. Points don't give a rat's arse what leads or what charging system.
That's my experience from running and working on lots and lots of old stuff.
Could be worth bunging the points back in and see what happens. At the least it should tell you it's not or is the triggering system.
Good luck,
Keep us posted,
Martin.
 
Sorry it took a while to get back to all of you. Yeah i had the pertronix in before rebuild, I did have a 6 volt alternator on it though...
Johnydidd, I was thinking maybe I have the wrong size power valve in, I'm assuming it's a 65 that came in my rebuild kit from speedway
 
The number on the power valve indicates the vacuum that it opens. Has nothing to do with the amount of fuel it lets in. That is controlled by something called the power valve restriction, which is built in to the carb. It's possible that there is a clog in the carb that is restricting flow. Also might try a different power valve as a test. By the way, 51 jets should be right on.
 
Flatjack, when you say "try a different power valve as a test" do you mean a different power valve of the same number?
 
Alright guys, I tried swapping power valves and nothing changed! Back to the main jets....any recommended size to swap in?
 
Your problem is not the main jets. Not sure what it is, but I am reasonably sure it is not the main jets. Do you have another carb you can try?
 
Raise the float level ABOVE spect or (dead on ) for a test run, you may be surprised .... today's corn gas is nuts .... OLD....BILL
 
did you try anything I suggested remember you don't need a lot of fuel for around town but lots of fuel for highway travel
 
Joe 1950-I blew air through the jets and all the passages in the carb when I rebuilt it, I checked the fuel filter screen and it was clean. I have new black rubber line from my pump to my carb and I don't know if it's collapsing.
 
what about the hose that comes off the tank sender the best time to check this is after a run when everything is good and hot these hoses can fool you they should feel somewhat hard but not like soft and thin some of these old cars had what they call a sock on the end of the pick up tube in the tank pull the sender and check this hope this helps keep us old guys informed
 
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