I have a 1970 4.2L OTS. When I first start the car it runs great and goes even better for about 1/2 hour. Then if I shut it down for awhile and restart it it sputters and hesitates quite badly. If I stop at a traffic light it will idle O K but when I take off it sputters again until I get up the RPM's. Then it evens out but will continue to run poorly at low speeds. If I put the car away for the night and take it out the next morning it goes great again for a while, and so on. I am about to do a Weber conversion but thought I should run this senario by everyone first. Could it be vapor lock once the car is warmed up and then shut off for awhile then restarted? I don't have a heat shield between the carbs and the engine. Any advise is greatly appreciated.

Thanks
Don

Submitted by DavidBarnes71@… on Tue, 09/27/2011 - 21:36

I agree with Brian. The floats in the strombergs seem to be prone to leak. I have had them get fuel in them twice in the last few years on my car. When it happened on my car it ran poorly all the time though. I did not have too much trouble removing the float bowl from the carbs with them still on the car

David Barnes
'68 FHC

Submitted by bblackwell@jcna.com on Tue, 09/27/2011 - 21:08

another thing to check is to see if any of the carb floats are partially full of liquid. I would first feel the bottom of both carbs when cold, and when it is misehaving, and see if either is wet.

IF wet, getting to it can be done on the car maybe, but you have to be good at working upside down with tools pointing back at your face. Probably just as easy to remove the four bolts on any wet carb(s).

Submitted by bus2@roadrunner.com on Mon, 09/26/2011 - 21:25

Thanks everyone. I new the Webers would require some field mods for the linkage and might need spacers at the manifold but was not aware that they might creat the same problem I am trying to fix. Thanks

Brian, My pistons do have the whole in the side. I will check the allen screw tomorrow. I can't here the fuel pump once my car has started but I may try what you did. It sould be another cheap test.
Thanks

Submitted by DavidBarnes71@… on Mon, 09/26/2011 - 21:07

Is there some sort of Stromberg carb problem that can make a car run badly after a half hour but still run OK after warm up ?

My '68 with strombergs would act similar to what Donald describes after running for awhile on a hot day here in Houston. My car is a FHC so I could hear the fuel pump start "clicking" loudly like it was cavatating or vapor locking. My theory on my car is that the fuel pump was having to work too hard to pull the fuel out of the tank and up to the pump which is mounted above the level of the tank. I bought an after market small solid state pump and spliced it into the clear plastic lines and mounted it down low at tank level next to the spare tire. So far I have had no mroe problems. I can easlity hook up the stock pump again if my theory turns out to be incorrect but my car has been running fine with this set up for several month now.

Donald here is what I have seen concerning needles. The carb needles on my car are held in place with a set screw acecessed thru a hole in the side of the piston but I have seen a different set up on a freinds Series III Strombergs. Therefore I think the later carbs have a needle adjustment that can be made with a special allen wrench that you insert down thru the cavity that holds the damper oil. I am not sure if a 1970 would have carbs like my car or if they are like the ones on my friends 1974

David Barnes
'68 FHC

Submitted by bus2@roadrunner.com on Mon, 09/26/2011 - 19:30

Wow! thats not getting much distance out of a set of plug wires. That is certainly a cheap first move. I will also check the needles in the pistons. I just had the tops off the carbs the other day because I wanted to check the diaphragms. They were like new. I removed the springs and pistons for inspection and all seemed good. reassembled and replenished the oil. I am not that sure how to check the needles. Are they just press fit in ?

You have helped me several times on here and I really appreciate it. But no matter how much you help me I will never cheer for the Spurs!

Don

Submitted by bblackwell@jcna.com on Mon, 09/26/2011 - 18:36

if you have intact diaphragms, springs, oil in the dampers, and the pistons do not bind when pushed up by hand, I can only suggest making sure the needles are tight in the pistons. If the needle is falling out of the piston even intermittently, it will make it sputter.

Before buying Webers, how new are your plug wires and your fuel pump? I would try the former if theyt are old, as they are inexpensive Higher RPM's do not make either of these two potential causes go away though. If you remove the distributor cap and shake the cap back and forth and the wires are flimsy and provide no resistance to side to side motion, they are shot.
Deep in the heart of the South, mine only last about three years with limited driving.