Vapor lock Stromberg vs Holley

Bums F-1

Bums F-1

Member
I have never had a vapor lock with a Holley 94 but after changing to a Stromberg 48 I am experiencing what appears to be a vapor lock. Runs out of fuel and will not restart, but after a cool down starts and runs fine. The Stromberg preforms much better on my truck other than this problem, are Strombergs prone to vapor lock ? Electric fuel pump set a 2 psi,MSD ignition 6A box,100 degree ambient temperature,coolant 185,electric fan. I changed the Holley do to a blown power valve. I had the Stromberg in my stash rebuilt by a pro here on the Barn, I love the way the Stromberg preforms other than this problem.
 
Ross F-1

I am running a MSD distributor with mechanical advance only.and a
6A capacitive discharge box. Timing set at 2 initial 18 at 1700 total 20.
I have run this set up with a Holley 94 for 10 years with no problems.
 
Have the tank and lines been cleaned out? Junk collects in the lines (low point of system) and can starve fuel randomly.
 
Bums,
Strombergs are much less tempermental than 94's in my opinion. I used a
48 for years on my '41 1/2 ton with no VL issues at all. Just for the hell of it try 2 new
unused carb to intake gaskets to assist in insulating the carb from heat transfer.
You'd be real surprised the insulating effect of the extra gasket. 34 has an interesting
thought however regarding VL with an elect pump.
If you happen to be using the small reg that has OFFENHAUSER on it
be aware these are problematic....I have much better results with the low pressure
HOLLEY regs Speedway # 427-12804.
Charlie ny
 
Seems like the issue could be related to that particular Stromberg 48. How long has that rebuild been in your stash? Maybe long enough that some of the components are not alcohol resistant? Not all proffesional rebuilds are flawless either. Maybe you could get your hands on (or borrow?) another Stromberg carb from a known good running application and try that on your vehicle. If the problem goes away, it was the carb. If not, you need to keep looking for the real problem. Did you happen to make any other changes, however insignificant they may seem, when you removed the Holley and installed the 48?
 
I agree with above on trying a known good Stromberg, easiest way to prove or eliminate the problem.
Where is the pump mounted? If it's at the back you really shouldn't be getting vapour lock. If carb is really the only change, it's more than likely the carb that's playing up.
Also good call on doubling up on the gaskets, seen that work before.
I'm interested in your statement that you prefer the way it performs other than this issue, what is it you prefer about the Stromberg? How is it better?
Only asking as I never ran a Stromberg, always 94's and would be interested in real world back to back seat of the pants feedback.
Martin.
 
The carbs don't get vapor lock while running, their problem is after shut down when the heat builds up at the base of the carb and boils the gas out making it hard to start. Bob Shewman (gadgiteer@aol.com) makes a 1/2" vented insulator that solves this problem. Vapor lock occurs in the mechanical pump at low fuel pressures. I don't know what a LOW 2 lb pressure will do with and electric pump because I don't use them. On mechanical pumps the pump pressure drops as the pump get hot, the hotter the pump gets the lower the pressure. At 1 1/2 lbs the vapor lock starts and a fuel gauge between the pump and carb shows the pressure starting to jump up and down. As the pump gets a little hotter the pump stops working pumping air. With only 2 lbs pressure cold I'm not sure what effect the heat in the mechanical pump would have if your pumping through it with an electric pump. I run 3 1/2 to 4 lbs to minimize the vapor lock as the pressure gets low from the heat. To find the problem you need a 0 to 10 lb pressure gauge in the carb fuel line, a laser pointed thermometer to check the temperature at the top of the mechanical pump and the base of the carb. You can feel the carb base above the intake manifold to see how hot it feels. The carb base is usually cool and even cooler when running and even sweats in high humidity. G.M.
 
GM
Sounds like you have made a thorough study of the vapor lock problem,I am running a electric pump at the tank to a Holley regulator into a 3 carb. fuel block. The secondarys are block off for show only.Looks like I could have a low pressure vapor lock problem,I can't tell yet I have a liquid filled gauge its not accurate when its warm.

Scooder
I do not have any specific numbers on the performance only seat of the pants info. the acceleration is a lot stronger than the Holley 94. The Stromberg 48 have larger venturies and flow 175 cfm the Holley 94 flows 150 cfm.
Does any one have any experience with the phenolic spacers ?

Thanks to all for your input.
Bum.
 
Bum, thanks for reply, I may have a play with Strombergs at some point. Don't worry about numbers, seat of the pants is as important as numbers.
I'm not sure it's a vapour lock problem you got yourself. When it quits, try popping the gas line off the carb see if it's pumping gas. If it is, I feel you should be looking at the gas inlet to the carb needle valve. It could be sticking. Maybe try running higher pressure. I have had better luck with the original metal needle rather than the rubber tipped one's, not sure the the rubber ones are ethonal resistant.
And yes you need a better pressure gauge, the liquid filled ones get hot and the needle drops to zero, seen this many times.
Good luck and keep us posted.
Martin.
 
scooder said:
Bum, thanks for reply, I may have a play with Strombergs at some point. Don't worry about numbers, seat of the pants is as important as numbers.
I'm not sure it's a vapour lock problem you got yourself. When it quits, try popping the gas line off the carb see if it's pumping gas. If it is, I feel you should be looking at the gas inlet to the carb needle valve. It could be sticking. Maybe try running higher pressure. I have had better luck with the original metal needle rather than the rubber tipped one's, not sure the the rubber ones are ethonal resistant.
And yes you need a better pressure gauge, the liquid filled ones get hot and the needle drops to zero, seen this many times.
Good luck and keep us posted.
Martin.
Click to expand...

All good info Martin.

Since the OP didn't respond to any questions in my previous post, I am thinking they were probably too insignificant to him to bother answering :confused:
 
I was blinded by the fact that all my problems started after I installed the Stromberg, It turns out it was a fuel delivery problem,pump going bad. I drained the fluid from the liquid filled gauge it works fine now when its hot. On the road again. Love the sound of the old Flathead, I don't need a radio.
 
Thanks for the follow up. It is always nice to hear what the final fix turns out to be.

And Yes, it is hard to beat the flathead sound....
 
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