356C Losing Power

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James Cronin
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356C Losing Power

#1 Post by James Cronin » Wed Aug 14, 2019 2:02 pm

Greeting all... I drove my 356C to Lake Geneva WI. a few weeks ago. It ran great for 75 miles, then started to lose power. I slowed down and eventually the power came back. When it loses power there is no backfiring. Car may run fine for 25 mile before this starts or show up in a few miles. Here's what I have done.

Replace points and condenser - did not fix
Replace coil - No fix
Ran with loose gas cap - No difference

Pulled fuel pump and verified fuel flow. - Fuel flows fine
I used a vac gauge and verified that suction holds on fuel pump... it does
Pressure side on pump does move the needle, it holds while rod is depressed and immediately drops when released.

Seems pump is fine.


Any suggestions?

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David Jones
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Re: 356C Losing Power

#2 Post by David Jones » Wed Aug 14, 2019 3:30 pm

Float valve sticking closed?
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: 356C Losing Power

#3 Post by James Cronin » Wed Aug 14, 2019 3:46 pm

Hi David - I did disassemble the pump... it looked brand new inside... but I know that's not necessary an indicator all is well. I'll look again. I'm also checking all hoses for tightness. I did notice that the one on the pump suction was not "sealed" to the tubing the way the pressure side was. ( sealed meaning it twisted right off without a "snap") guess it's possible it could have been sucking air. I'm going to look at all of the other connections too - but otherwise no gas smell while parked in garage.

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Re: 356C Losing Power

#4 Post by David Jones » Wed Aug 14, 2019 3:54 pm

Bill, I mean the float valve in the carb. I had an instance where the float valve in a Solex PII40 expanded in the float chamber and jammed against the wall of the float chamber and held the float up in the closed position so the engine was effectively running on the other carb. You have a Zenith carb and brass floats so I doubt it is the float but a piece of debris could make its way into the float valve and restrict flow. It may be worth checking if all else seems good. I would think if it was ignition you would get a huge backfire as it came back on song and ignited the raw fuel that would have been sucked through while the cylinders were dead.
If I had known I would live this long I would have pushed the envelope a little harder.
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Re: 356C Losing Power

#5 Post by Geoff Fleming » Wed Aug 14, 2019 4:50 pm

Please give a bit more specifics on what happened. Did the engine die, or was it able to only maintain a low speed?
If it happens again, pull off the road and remove the linkage of one carb, now see if one side is running and the other not, or not so well. In this way, you can isolate a carb/fuel problem. A bad condenser would most likely not allow the engine to fire at all. Sounds fuel related, follow David's advice and inspect all aspects of the carbs, especially the floats and jets. One clogged idle jet can make it feel as if you have lost half the engine. A clogged main jet will affect the engine's cruising speed, ( 3,000rpm and above.).

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Re: 356C Losing Power

#6 Post by James Cronin » Wed Aug 14, 2019 6:51 pm

More info on failure:

At 65 MPH, I began losing power (after having traveled 75 miles with no issue at all) I was losing speed so I pulled over to the shoulder while pumping the pedal. I limped on the shoulder for about two miles, then all power came back. I got off the highway and topped off with fuel and went to my destination. The next day a drove all day without issue. This was highway and off highway driving. Teo day after - I was driving highway miles to a local lake... all was good. On the way home it lost power but recovered a few times. No backfires in these examples. On another day it lost power at low speed and backfired once or twice... and recovered. The car did die one of the other times I was experiencing this issue, but started right back up.

I have an inline electric fuel pump too (been installed for 12 -13 years). I have it wired so it only works with the key off. I'll rewire to include run mode and activate it while in the failure mode next time.

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Re: 356C Losing Power

#7 Post by Brad Ripley » Wed Aug 14, 2019 8:08 pm

Fuel filter upper part of petcock?

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Re: 356C Losing Power

#8 Post by Ron LaDow » Thu Aug 15, 2019 12:48 am

Jim,
I think you have a Pre Mat float gauge; if so put it in one carb and do your test drive until it chokes. If it's low, move it to the other carb and do the same drive.
If one is low, the problem is the cross-over fuel line. Both, it's north of that.
BTW, if you don't have one, just take the aircleaners off before the drive(s) and take the carb tops(s) off when it chokes; you're looking for a low fuel level and trying to locate the cause.
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Re: 356C Losing Power

#9 Post by Bill Oldham » Thu Aug 15, 2019 7:37 am

Your symptoms are what I had when condenser went bad. The contact inside the can gets flaky. Of course another possibility is chunks of something clogging fuel filter then dropping off on slowdown/ stop. But do swap distributors with someone to check for condenser problem.
Bill

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Re: 356C Losing Power

#10 Post by Vic Skirmants » Thu Aug 15, 2019 8:42 am

One correction: Zeniths also have plastic floats, not brass.

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Re: 356C Losing Power

#11 Post by jay darlington » Thu Aug 15, 2019 3:59 pm

have you checked the fuel filter sounds like you may have gotten some bad gas ( water ) it just takes a thimble full to get sucked up into the float bowel to cause a momentary problem.
Jay D.
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Re: 356C Losing Power

#12 Post by James Cronin » Thu Aug 15, 2019 8:00 pm

Thanks all - I'll replace the filter this weekend and re-install the fuel pump. I'll check all hose clamp connections and then move to the carbs if all if this fails. One issue is the car is still in Lake Geneva where I don't have my tools of lifts... gonna be fun. Thanks and please keep the suggestions coming.

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