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View Full Version : Vapor Lock? Possible after fuel filter change?



congerz83
12-04-2012, 09:58 PM
So I had some time to tackle the cars "running like sh*t" issues yesterday...

Drove up to Advance and bought a new fuel filter. I figured what the hell for $4... Well what do you know, the car instantly ran better... But yesterday only after a short drive I attempted to restart the car and it seemed very difficult for a vehicle that was running just an hour ago... The same "longer start" happened after parking the car and leaving it for an hour to eat dinner...

Cut to today... On my way to work, I stopped for for lunch, about a 5 min trip. 5 Minutes later got back in the car and it did nothing but crank... It took about 5 more minutes until I got it to sputter to life.

Just an hour ago I made two short stops and everything was fine. It started as normal.

Is vapor lock a possibility?

I made adjustments to the carb to attempt to correct the "running like sh*t" issue... Could changing the filter cause the adjustments I made to be "over-kill" and running too rich? I played with the floats in the past and the acc pump... I know the acc pump shoudn't have anything to do with it. Perhaps I adjusted the floats "to much"...

Could mis-adjusted floats cause an engine to run rich?

Grateful for ANY help...

Bitsyncmaster
12-05-2012, 04:36 AM
Sounds like your leaking fuel into the intake after you shut the engine off. A bad float valve or setting could do that. It's not that hot these days to be vapor lock.

Ron
12-06-2012, 01:13 AM
+1

Sounds like it's flooding whatever the reason... I would also suspect that the choke is set to heavy, especially if it always starts well when it has sat a LONG time -- not enough info on how it acts other times.

If it was getting enough fuel to run down the road before you changed the filter, it's very doubtful that the filter had anything to do with the problems you mentioned here at all. (Basically, if it starts and handles a power run, the filter is ok.)
Yes, mis-adjusted floats WILL cause the engine to run either rich or lean -- That is their job...

From what you have said here alone, the carb needs to be set up from scratch IMO.

Bill Robertson's Sock Puppet #1
12-06-2012, 10:26 PM
If your fuel pump is located in the gas tank then no, it is impossible to vapor lock ever. If your fuel pump is located between the gas tank and the engine then yes, it is possible to vapor lock under certain conditions (low flow pump and hot ambient temperature around the pump).

Is your carburetor the same one Sam Hill uses (Motorcraft 2100)? If so I would be surprised if your problem is fuel seepage into the intake after shutdown. The only way that could happen would be through the air bleeds directly under the venturi assembly, and I don't think the float could rise that high before hitting the top of the carburetor housing. I suppose you could bend the tab that presses against the needle valve so high that even with the float trapped against the top of the carb the needle valve is still left open. Quick way to tell if your intake may be flooded is to hold the throttle plates all the way open while cranking the engine (choke plate fully open -- stick a screwdriver down the throat of the carb to hold it open if necessary). If the engine coughs momentarily, then roars to life, the intake could well indeed have had liquid fuel sitting in it.

Note that insufficient choke plate opening while cranking will have the same effect -- liquid fuel puddling in the manifold (and air starvation). You only want the choke plate fully closed for a fraction of a second. As soon as the engine is spinning ~300 RPM the choke plate needs to crack open. Sam's carburetor has a vacuum operated diaphragm hanging off the back, connected to the choke mechanism with a rod, that accomplishes that very task. If that rod were to come loose his choke plate wouldn't crack open, and his engine would be very difficult or nearly impossible to start. Sam's diaphragm also has an adjustment screw in the back that controls how far his choke plate cracks open. If he were to turn that screw too far in the effect would be the same -- insufficient choke plate cracking open.

I would look closely at what your choke plate is doing.

Note that Sam's carb has an electrically operated heater wired to the main relay that gradually opens his choke plate. If he were to energize his car and wait a few minutes, even without starting the engine, his choke plate would fully open anyway. By that time a misadjusted or inooperable choke pulloff wouldn't matter. I suppose yours could be similar.

congerz83
12-06-2012, 10:30 PM
+1

Sounds like it's flooding whatever the reason... I would also suspect that the choke is set to heavy, especially if it always starts well when it has sat a LONG time -- not enough info on how it acts other times.

If it was getting enough fuel to run down the road before you changed the filter, it's very doubtful that the filter had anything to do with the problems you mentioned here at all. (Basically, if it starts and handles a power run, the filter is ok.)
Yes, mis-adjusted floats WILL cause the engine to run either rich or lean -- That is their job...

From what you have said here alone, the carb needs to be set up from scratch IMO.


Well... The car ran like crap at start-up... But it DID start with a couple of pumps...

I disconnected the choke last year because it would randomly engaged/dis-engage...

Yeah I'll have to set it up... No Maybe youtube to the rescue...

Bill Robertson's Sock Puppet #1
12-06-2012, 10:46 PM
If you removed your choke plate then yes indeed, your engine will be difficult to start. It's there for a reason.

If you simply removed the choke plate's connecting rod so now it's flopping around loose then all bets are off.

Ron
12-07-2012, 12:08 AM
Well... The car ran like crap at start-up... But it DID start with a couple of pumps...

I disconnected the choke last year because it would randomly engaged/dis-engage...

Yeah I'll have to set it up... No Maybe youtube to the rescue...
You will never get it to behave without the choke plate!
(It's bad enough that you realli can't use a manual and the electric ones leave a lot to be desired.)

I posted a link or the actual document of a ridiculously detailed procedure for rebuilding the specific carb everyone seems to be using (Bills favorite(s) for sure) in this section somewhere. Search for it, get the better TRW kit (not a Jiffy kit etc) and go through it. If it doesn't act right then, bite the bullet and get a quality reman (...probably worn out or has internal blockages you are not going to get clean). It's not worth all the trouble you have been having even at the cost these days IMO....especially since you had one on there that worked OK (Bill's? or ??), iirc.

Bill Robertson's Sock Puppet #1
12-07-2012, 10:56 AM
Actually once his engine is fully warmed up he will be OK without a choke plate, but it will be terribly difficult to start and drive cold. A lot of circle track racers remove their choke plates.

If the choke plate is still in place but flopping back & forth loose, it would be quite a shock to have it accidentally flip closed while driving.

congerz83
12-07-2012, 08:13 PM
The plate remains... I just disconnected the rod...

Ron
12-07-2012, 09:35 PM
Actually once his engine is fully warmed up he will be OK without a choke plate, but it will be terribly difficult to start and drive cold. A lot of circle track racers remove their choke plates.

If the choke plate is still in place but flopping back & forth loose, it would be quite a shock to have it accidentally flip closed while driving.

Yeah, but to warm it up, he has to get it started, which seems to be the problem ;-)
I'm with you on the circle trackers. But they and most other racer carbs are far from stock, not to mention they usually don't move around much until it's warmed up, and after that, they don't know what idling at 750 RPM is ;-)

If the rod is off, I'd assume it's is wired open??

Maybe he shouldn't have messed with it after you set it up...:devil:

congerz83
12-07-2012, 10:25 PM
Yeah, but to warm it up, he has to get it started, which seems to be the problem ;-)
I'm with you on the circle trackers. But they and most other racer carbs are far from stock, not to mention they usually don't move around much until it's warmed up, and after that, they don't know what idling at 750 RPM is ;-)

If the rod is off, I'd assume it's is wired open??

Maybe he shouldn't have messed with it after you set it up...:devil:

Wow... Did Ron just pull back a curtain?

opethmike
12-07-2012, 11:16 PM
Wow... Did Ron just pull back a curtain?

Not really, it is screamingly obvious it is Mr. Bill 'Ban me' Robertson

Bill Robertson's Sock Puppet #1
12-08-2012, 01:08 AM
If the rod is off, I'd assume it's is wired open??

Congerz83 didn't say that the choke plate was wired open -- only that it had been disconnected from the operating mechanism. For all we currently know it could be flopping back & forth in the breeze. Either way, without a properly functioning choke, his engine is definitely going to be difficult to start and drive until warmed up, any other potential misadjustments notwithstanding.

His best option at this point is to find someone familiar with whichever carburetor he is using to reset it from scratch.