Dual Solex Vapor Lock

Does anyone have any suggestions on curing carburetor vapor lock? I installed an electronic fuel pump under the tank, and I T'd off the fuel lines behind the engine wall, then ran the lines through the wall to each carb hopefully minimizing any vapor lock within the line itself. So at this time I believe it's vapor locking within the carb itself. Is this a common problem with Solex carbs? If so, would a carb overhaul or changing to Weber carbs solve this problem? Any suggestions?

Where are you located that you would still be getting vapor lock? In the 60-70's here in Northern VA. I can see vapor look on a 98 degree day or a long trip perhaps. You say electronic duel pump under the tank. You didn't use one of the cheap $25 Facet pumps did you? They aren't designed to push fuel that distance. A better choice would be a rotary pump ($75-120) with internal (3#)pressure regulator or an add on adjustable pressure regulator. My guess is you aren't getting enough fuel/pressure to the carbs.

As Wolf said, it's probably your fuel pump. Another issue, not commonly known is that the tank must be vented. If your vent line is kinked or plugged, that can cause a condition that seems like it's a vapor lock...

Just to be sure, get under your car, locate the fuel line and make absolutelly sure it's not close to a heat source. If it is, relocate the line or insulate it to prevent the fuel from bubbling.

A rotary pump is a great investment and Kragen/Schucks/Checker sells such a pump. The part number is E8016S. Greg at Vintage Spyders has been using them successfully for many years. They work great as I've installed them on Spyders and Speedsters. CB Performance also sells a great little self regulated pump.

All, Thank you for your suggestions! I did install a Facut, and was wondering the same thing...if was able to do the job. Are these pumps that you suggested quiet?

Both of the pumps I mentioned are very quiet. Your Facett is a plunger/pulse type pump and is usually noisy, the other 2 pumps are rotary and make noise that's only audible when the engine is turned off and it's very minimal.

The motor starts to stall about 15 minutes into the drive. The Faucet that I purchased is the barrel solid state type, rated at 30 gallons per hour. Shouldn't this be able to push enough gas into the reservior....? And why would a small pump cause the carb to vapor lock?

First thing, have you confirmed that your fuel bowls are empty???
Second, have you checked your gas tank vent???
Third, have you checked your fuel line location (away from heat)?


It's not that a small pump will cause vapor lock, it just may not have enough power to overcome bubbling fuel.

But,,,, check the 3 things above then report back.

Vapor lock results in lack of fuel in float bowl or lean/low volume-pressure of fuel delivered. These are same conditions caused by a low volume/low pressure fuel pump (or as others said a cloughed fuel filter/tank strainer or cloughed/no air vent). If it is indeed caused by heat then moving lines from heat source and wrapping them in aluminum covered insulation will cure the problem. Loosening/removing the gas cap would eliminate the vent problem (carry a good fire extinguisher thoug!) If you still have the mechanical OEM pump add that into the circuit and see if added volume/pressure cures it (If so then fix is a quality rotary fuel pump like an Airtex or Carter). Here's article I found that might help -

http://www.racetep.com/webfuelspark.html#webfuel

You should probably check your fuel pressure coming into the carbs. Buy a simple pressure gauge at the auto parts store and tee it in the line and then check while the engine is running. I know that a lot of carbs like 3 or 4 pounds of pressure, but I am running the Solex/Kadrons on a 1835cc with a stock mechanical pump and my carbs run best at 2 psi. My stock pressure setting was 3.5 to 4 psi. I adjusted pressures from 3.5 down to 1.5 psi by using additional shim spacers and gaskets under the pump, thereby reducing the pump plunger arm travel and thus, pressure. I have read that the needle/seats on these carbs are not of the best design or quality and can't tolerate additional pressure. Check the Kadron site at lowbugget.com (sic?). You might also want to check the screen wire strainer in the bottom line fitting of your fuel tank. These sometimes become clogged. The vent on top of the tank and cap is a good place to check also as mentioned. I seriously doubt you have vapor lock due to heat.

My gas tank vent checked ok and I placed the lines as far as I could away from the heater boxes. I changed the stock 1/4 inch lines with a Good Year 1/4 which was a little bigger. What a big difference, but there was still a little hesitation when it warmed up. The Facet pump that I installed is rated at 35 GPH at 2.5 to 4.0 PSI. Do you think that this pump with the 1/4 inch lines are adequate for my 1835 cc dual Solex motor? What are you guys running?

Ok, if the hesitation is still present, have you tried adjusting the accelerator pump?? This device squirts raw fuel into the venturi when you open the butterfly valve (step on the accelerator)

It is possible that it's starving the carb or flooding the carb. (both conditions can appear the same)

Start by moving the adjusters "in," in equal 1/8 turns and test the car. If that makes it worse, then return to the original setting and adjust them "out" Report back with your findings

Since changing the lines made a big difference, it seems that my problem may still be in the lack of fuel getting into the reservior (hoping that there isn't a problem hiding behind this one). Do you think that the Facuet pump I installed needs to be upgraded to a larger volume pump that can push more fuel through the 1/4 inch lines? If so, what GPH and PSI pump should I look for? If you think that the Facuet that I installed is okay, where is the accelerator pump adjustment screw located on the carb?

For now, work on 1 thing. Try adjusting the carb's and see if that makes a difference. Here's a great web site on how to adjust your carb's. http://www.lowbugget.com/help_section.html

Hey Larry, thanks for sending the link! I did notice that the adjustment nut for both carbs are all the way in. I'll add a couple of washers get more throw on the arm and we'll see what happens.

I was troubled with similar heart burn for what seemed like years. Thought it was vapor lock at one point. Went through 2 mech. fuel pumps, 2 elec. pumps, sloshed the tank and added a vent. It turned out to be the original ('59 conv.) fuel line that was rusting on the inside. After adding a new steel line front to rear, my problems were solved.

Ernie, thanks for the insight. If the adjustment doesn't do the trick, I'll install a new line, bypassing the original hard fuel line from the tank to the motor. It sounds like a good thing to do anyway.

The fact that it runs OK for about 15 mins says something I think. Does it run OK for a shorter period of time with a full tank and longer with than nearly empty? If so I

Bill, The tank vent is clear, and the motor starts to studder after about 15 minutes of driving, especially when taking off from a dead start. I experimented and took off the motor hood to give it more air, and it helped a little. So as far as I can tell, it seems like vapor lock because it's hard to start after I shut it down. The weather here in California has been in the 60's, so it's got me in a loop. Something to note, the car now idles better after I replaced the old original skinny braded nylon fuel line. The problems aren't as severe now, but it's still not performing when warm which leads me to the carbs.

Where in CA are you located??? It's got to be northern CA as it's about 85+ here in Ontario, (Pomona Valley, close to Chino, Pomona, Montclair)

Hey Larry, I'm located in the SF Bay Area and it's been around 70-80 degrees. I didn't have much time to work on the car this weekend, but I'm going to tune the carbs today to see if it helps the problem. It seems that there were a couple of issues because the car seems run better as I go on, but it still studders after about 15 minutes of warm up. I ordered an Pertronix electronic ignitor and a blue coil....should have it in a couple of days.

Don't forget to re-time your engine after installing the points eliminator. Since all we have is crap 91 octane in Calif., set your ignition timing at 28 degrees before top dead center with the engine at 2,500 RPM's. Don't bother setting the timing at idle, your only concern is maximum advance. If you don't have a degree pulley, buy one.

The accelerator pump adjustment screws on both carbs were all the way in, so I adjusted it out a little at a time. I also adjusted the mixture. The car seemed to accelerate a little better, but it didn't eliminate the problem. Once warmed up, the motor runs okay when crusing, but it has problems under acceleration The motor seems as though it's getting fuel because when taking off of the line it wants to go and I can hear it rev up, but it studders. When I'm softer on the accerator and try to slowly pick up speed it does better. Do you think under hard acceration the ignition may be having an issue? It also idles now, where before it didn't once warm. Did we solve the vapor lock problem, with an ignition problem hiding behind it?

It's been my experience that 95+% of reported ignition problems are actually carburetor problems. Continue adjusting the carb's.

Hello Larry, what carb adjustment should I make next? I already adjusted the mixture and the accelerator pump.....?

Keep adjusting with the accelerator pumps until the engine doesn't stumble. If they are an off the shelf set of Kadrons, the accelerator pumps need a lot of massaging.

Do you think the rubber membrane inside of the pump may be stretched and worn out and requires replacement? There are two membranes, one sandwiched on the other. They're seperated, but there aren't any holes or tears.

It's very difficult to diagnose the problem over the Internet but, if you're in doubt, buy accelerator pump replacements, (both carbs) and give it a whirl. (the advantage is that you've eliminated that as a problem)

Remove the carb's and leave fuel in the bowl. Activate the throttle plates. If a steady stream of fuel is delivered via the accelerator pump nozzle, I doubt the diaphragms are bad. If the fuel is delivered in a sporadic fashion then replacement is needed.

I adjusted the nuts out on both pumps and slowly brought them in (giving the pump arm a longer throw) at similar rates, then test drove the car each time. I found that after making each adjustment the motor had better acceleration. There was a marked inprovement, but the engine still studders when accelerating, although not nearly as much. How do you find the sweet spot for each carb on a dual carb setup? Also, the exhaust started to pop on de-acceleration and at idle. I re-timed it, but it didn't go away.

Another condition that may be present is a vacuum leak. Go to your auto supply store and buy a can of Ether (starting fluid) It's in an aerosol can and is used to help an engine start.

Start the engine and spray a small amount of the fluid around the base of the carb. and where the manifold attaches to the cylinder head. If the engine reacts to the spray, you have an air leak.

Don't breath too much of the spray or you'll go to sleep.


Finding the "sweet" spot for the accelerator pumps requires patience. Only turn the nut 1/4 turn during your tests.

You were right. I tightened the left carb down and which solved the popping problem. I'm close on the accelerator pump adjustment, but not quite there because it still studders. I adjusted the right carb first, then ran the car up and down the parking lot until I thought it was close. Then I did the left side. I previously installed a couple of washers on top of the springs to give it a stiffer throw, but I'm going take them out because I think that it may have some affect on why I couldn't get it right. Trying again this afternoon.

I guess you're getting the picture why mechanics get so much money to sort out carburetor issues???

Once you've got the accelerator pumps "close" it's time to move on to the carb adjustments.
I'd suggest you go back to the link I provided http://www.lowbugget.com/help_section.html

And read about idle mixture adjustment.

Turn the idle mixture screw clockwise until the engine stumbles, then ever so slowly, turn the screw counter clockwise until maximum RPM's are achieved. (RE-READ that section in the link provided)

Next,
Use a balancing tool and make sure that both carbs are drawing the same amount of air. This is done at idle with the linkage removed from one carb. If a Carb is drawing more air than the other and the idle RPM's seem high, rotate the idle adjustment screw counter clock wise on the carb that's drawing more air. If the idle RPM's seem low, adjust the idle adjustment screw on the carb that draws less air, clockwise.

The idea is to get both carbs drawing the same amount of air at around 900 to 1100 RPM's.

Next. Adjust the linkage so it's free and not prematurely opening one carb before the other. With the engine off move the linkage open and closed until both carbs come off of the idle stop at the same Check, double check and triple check this procedure.

Larry, I'll make the other carb adjustments as advised this weekend. Yesterday I received and installed the Pertronix Ignitor electronic ingition and after re-timing the motor I took it out. What a difference it made! It must have added 15% plus more horses with a smoother and higher rev limit! But the exhaust popping came back, although not as much. Do you think that there's still a vacume leak somewhere or is it the EI?

Check the manifolds and carb's with the starting fuel as I suggested in an earilier post. If the engine changes RPM's (even for a split second) during your test, you have a vacuum leak.

Also check your exhaust gaskets, if there is a leak at a gasket or slip joint, it can suck in cold air and casuse popping noises.

Larry, I adjusted the accelerator pumps on both carbs and along with the electronic ignition the car runs great! Thank you for all your help, I couldn't have done it without your patience and advice! While I have you here, do you have any recommedations on upgrading the stock front disk brakes and perhaps replacing my rear drums with disks? What I have is adequet for slowing down, but not quickly stopping.

If your brake components are in good shape, their performance can be improved by replacing the rubber hoses with quality stainless steel hoses and by using a larger diameter brake master cylinder. Sounds like you need to start a new thread as its getting off topic.

Actually the replacement hoses are stainles mesh wrapped to keep them from bulging.

I'm in Las Vegas (SEMA Show) using a slow dial up connection but, Brakes should be a new thread and when I get home on Friday, send me an e-mail with your phone # and I'll call you. LJOWDY at AOL.COM

I'm in Las Vegas (SEMA Show) using a slow dial up connection but, Brakes should be a new thread and when I get home on Friday, send me an e-mail with your phone # and I'll call you. LJOWDY at AOL.COM

Just got back from the SEMA show in Las vegas - an experience that can't be described by mere words! Very Cool!

Peace - Out!