Engine only starts when I spray gas into the carbs

[saabfast]

I haven't had a car with Stroms for about 40 years and cant remember the detail, but it would seem odd that both fail together. I would drop off the float chambers and jet units and check that something is not in upside down. Do yours have the adjustment from the bottom or the top? Pity Mildred got her knockers in a twist, she had some articles on adjusting Stroms in the Workshop bit.

[FI Spyder]

Er...that would be knickers in a twist. While spending all day talking with Monica a few years ago, one topic led to another and she mentioned she (and possibly others) thought Mildred was actually Ghostbuster (I may have the name wrong) and was using the Ozarks (I called it Lil' Abner) persona as actually a cover for him as he had left the forum and pulled his posts. I voiced that I had my doubts as to that but now I'm not so sure. Very similar, you old time forum members will know who I'm talking about.

As to why the carbs aren't drawing in gas with fuel in the floats if the slides are going up (are needles going up with them, something loose?) something drastic is going down like blocked jets or somehow assembled wrong with taking apart possibly making it reveal itself. I'm no expert on Zenith (yet) but will be when I go through the ones on Yellow TCT but I do know the basic physics of their operation.

[saabfast]

I swear I wrote knickers!!! Possibly interesting auto-correct somewhere, but then 'i' and 'o' are next to each other and my eyes are failing....

[Cobber]

Knickers,knockers or knackers all could apply in this case I suspect.

[sgstepp]

With your help I have made some progress. With a bottle of gas sitting on the roof of the car and a hose hooked directly to the carb fuel rail I was able to get the engine started after the old fuel worked its way thru the carb fuel bowl. Fresh gas made a big difference. But it doesn't run consistent. I must continually keep pumping the throttle to keep putting gas into the intake manifold. The Pistons in the carb goes up and down with each stroke of the throttle and the engine rpm varies with the amount of gas it gets. Shouldn't the Pistons stay up in relations to the throttle position and keep feeding gas into the intake manifold. Right now the Pistons fall and the engine rpm goes down when I hold the throttle down. Another stroke of the throttle starts the process all over again. I must keep stroking the throttle to keep it running. The engine does become more responsive to the throttle when it warms up. If anyone has any ideas, please let me know. Thanks for your assistance. Would checking the valves adjustment be in order? What keeps the Pistons up to keep feeding fuel to the engine?

[saabfast]

The Strom is a constant depression carb. The airflow creates low pressure above the diaphragm (venture effect) which lifts the piston and needle (if memory serves!). The airflow draws the fuel into the airstream into the manifold. Adjustment depends on the type of carb, some are from the bottom nut and some need a tool inserted in the damper hole. Have you tried a google, there are a number of articles on the net on adjusting the carbs.

[Hasbeen]

Pumping the throttle should have no effect on your carbs. These carbs do not have an accelerator pump to inject fuel when the throttle is opened.

If it runs with gravity feed fuel from the roof it indicates you have a pump problem of some sort.

If a float bowl needle & seat problem, remember, if you are having trouble finding them, the Zenith & SU carbs use the same needle & seat.

From your description it also sounds as if you have a balance problem. Have you tried to equalise the suction of each carb, or is it running too badly to do that. You will need the suction equal to start to get any tuning achieved.

You could have a vacuum leak, making tuning impossible. Your symptoms sound a bit like it. You could also have one carb just not operating at all at idle. The throttle could be completely shut. If so, you must first get the suction on each carb nearly equal, as a starting point. Trying to go from only one carb feeding the engine to both working in steps is almost impossible. as the inactive carbs starts to do just a little, the thing runs much worse, making you think you are going the wrong way.

Hope this is some help. What might easy beside the car, is damn near impossible at some thousands of miles.

Hasbeen

[FI Spyder]

Let me have a stab. The throttle opens the butterfly valve (like on an American carb). This varies the vacuum in the carb as they see more of the vacuum from the intake manifold (which it gets from the engine pistons exhaling (pushing) air out of the combustion chambers and drawing more air from the intake manifold, like an American carb). Here things start to diverge. This vacuum draws in air and the rushing air past an orifice of a channel (that goes to top of carb) creates a vacuum (Bernoulli Effect) that is transferred to the top of the (carb) piston which lifts it up allowing more air in. As the piston raises, the attached needle gets drawn up (and gets thinner) allowing more gasoline to be sucked in to match the increased volume of air. Although Saabfast called it a constant depression carb over here it is more commonly known as a constant velocity carb (CV) which is basically the same thing. In an American carb opening the throttle (butterfly valve) would produce a lean mixture so they need a pump to pump raw fuel (albeit a fine spray) into the carb air flow. Because of the slides (pistons) this doesn't happen so CV carbs don't need a pump. The oil at the top of the slides (pistons) act as kind of shock absorbers delaying (cushioning) the rise and fall, the thicker the oil the more of an effect (more isn't always better, there is a Goldilocks zone).

So in conclusion the throttle isn't directly connected to the pistons but only to the butterfly valve. The piston position(needle height)/air velocity/air volume are all related to give you the right mixture regardless of rpm, elevation changes, etc. more or less. There are adjustments to set idle, richness, air flow (balance carbs). It was enough for many N/A mechanics to throw up their hands and say "I can't work on this". There are lots of youtube things you can watch to get a handle on it as motorcycles used them as well. Just go to youtube and/or google cv carbs.

[sgstepp]

Thanks to you all for your responses. I will get into doing more testing and settings of the carbs to get a better response from the throttle. I will watch the Google videos to understand the process better. I did talk to one foreign car mechanic and when found out they were zenith carbs he did just as you said, he threw his hands up and said no way! You hit it exactly right. I will keep you posted. Oh one more thing, I have been all over these carbs and I can only find one adjustment screw for setting the idle speed???? The workshop manual shows three different screws. I will watch the videos. Thanks again.

[sonscar]

Never having experience of these carbs I could be way off base,but is the idle screws open enough to let air in to start it?,Steve..