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253 wont start after running fine

Bigfella237

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There's no way a different octane fuel alone could have "cleaned out" a carb, although I'm not sure about any additives that may have been added? It's more likely that a bad batch of fuel fouled something up, or stirred something up in your tank.

The only thing you can actually "adjust" on a 350 Holley are the IDLE mixture screws on either side of the metering block and the stop screw on the throttle shaft (idle speed adjustment). Everything else requires changing hard parts like jets, power valve, etc. In fact, if you have the idle speed set high enough, you'll find that adjusting the idle mixture screws does next to nothing because fuel is flowing through the main circuit as well as the idle circuit.

I would suggest you go back to basics and reset your base tune before doing anything else, it sounds like you've been adjusting everything randomly and have no idea where you're at with anything?

Check the plug gaps and condition, check the condition and attachment of the plug leads and, this may sound silly but, recheck your firing order.

If you had points you would set the dwell angle next (aka points gap), then set the base timing at idle RPM, then verify that the mechanical advance is working (timing should advance with RPM while the vacuum advance is disconnected), then verify that vacuum advance adds timing when re-connected.

Also check the timing is stable, Holden V8's with stretched timing chains tend to have the timing jump around, especially while cranking on the starter.

Then check your float level (verify it isn't too high with the engine off, otherwise you'll pump fuel everywhere, then re-check while idling). You may have a spec of crap holding the needle & seat open and making the carby flood? Do you have a fuel filter inline? Might be worth checking that too.

{Insert EDIT: If still flooding you may have to remove the float bowl and check that the float still actually floats, I've seen a couple of Holley floats over the years which leak, fill up with fuel and, well, sink}

Then set your idle RPM, then adjust the idle mixtures and idle speed together (changing idle mixtures will change idle speed). I usually adjust idle mixtures by ear using a length of plastic hose (I shouldn't have to say this but don't stick it all the way in your ear or you'll suck your brains out). With the air cleaner removed, listen to each barrel and adjust the idle screw for that barrel, you'll hear it 'spluttering' when it's too rich, then the sound should 'clean up' when the mixture is about right. I usually leave them just on the clean side of the transition.

Once you're back on track with the tune, you need to be able to duplicate the original problem, when it happens again, a timing light while cranking will tell you whether you have spark, so it would be useful to carry one with you.

No matter how complex, any engine only needs three things to run... fuel, compression and ignition... all delivered at the right time of course. It's a simple process of elimination.

Andrew
 
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1985VK

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If it is back firing it could be there is too much fuel ... like Bigfella suggests it could be a a speck of crap holding the needle & seat open. It might be time to give the carb a service ...
 

anf355

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Hi Andrew, thanks for the detailed response.

Well ive checked the rest of the plugs, they are fouled pretty bad, I tried burning the carbon deposits off them then cleaned them with degreaser, car actually didn't do any better after that, think they're still rough.

Ive read holley pdf, as recommended I wound idle mixtures all the way in then 1 & 1/2 back out for each screw, still ran bad. Whenever I get the distributor near 10 degrees it just backfires and dies.

So tomorrow was planning on confirming Number one on TDC with 1 lead, replace plugs and fuel filter to be sure. The leads, plugs,coil and distributor are only 50-70kms old.

Can I adjust my timing with just the car cranking by starter to get it back on 10 degrees? will need an assistant. I am considering syphoning the tank in case of bad fuel, dislodged debris or condensations.

yes, during the incident I made some random adjustments to get the car home. Until a month or so ago it was running really rich but I had made some adjustments to the timing, idle mixture, after that I didnt need choke on cold start, warm start didnt need accelerator, car was emitting less fumes and I had more power and it always started first kick.

I just cant believe it ran so good then after a 10 minutes drive from getting fresh fuel it just refused to start and now these issues, its been so reliable.

hey thanks again everyone, its been helpful.
 

1985VK

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The 2 barrel varajet has a very fine mesh conical filter at the base of the fuel inlet. Does the Holley 350 have one and if it does has it been checked for debris?
 

anf355

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Didn't know about this, ill check it out. thanks. Ill be moving to the carb next.

Cheers!
 

Bigfella237

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Holley carbs do have a strainer of sorts under the big nut where the fuel line goes into the float bowl, but a lot of them get removed when fitting a decent quality in-line fuel filter.

162-500.jpg


However if that was blocked you'd be starving for fuel, not flooding.

Andrew
 

anf355

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If I used an aerosol starter or fuel directly down the throat of the carby and it didn't start the car, would that remove the carby from the equation?

Ive replaced the Dizzy with a brand new cheap ebay model which was given to me with the car and new plugs but still no luck. Im gonna try get my hands on a coil and coil lead just to rule that out.

If someone could clear this up for me, if the timing chain did stretch on start up, would this have retarded the cam cycle and only allow the car to start up with the ignition advanced so high? (mind you, when it does run that high it sounds awful. Is that my clue?

If it is a stretched chain, id need to replace and dial in the cam with the crank again?

Sorry for the noob questions, I never delved this deep into the mechanical side of things with my last motor.

Cheers for all the input.
 

Bigfella237

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Timing chains generally stretch over time, not all of a sudden. With slack in the timing chain the cam tends to 'whip' forward and backward, as the lifters go over a lobe it will tend to advance until the slack in the chain takes up, then it stops momentarily until the crankshaft takes up the slack on the other side of the chain and the whole cycle begins again.

As I said earlier, the slower the engine is turning over the worse this is, so it's most prevalent while cranking on the starter motor. I've seen this on high-mileage engines that ran fine but were getting increasingly difficult to start over the space of months. If I watched the marks on the harmonic balancer with a timing light while cranking, I'd see the ignition timing bouncing around all over the place because, of course, the distributor is driven off the cam so anything that changes cam timing also changes ignition timing.

A timing light is an invaluable diagnostic tool in situations like this, if you pickup from the coil lead you'll get 4 flashes per engine revolution. If you pickup from each plug lead it will only flash once every second engine revolution. On a Holden V8, cylinders 1 & 4 will fire at Top Dead Centre (TDC) or 0° (plus however much advance you've set), cylinders 2 & 5 will fire around 90°, cylinders 6 & 7 will fire around 180°, and cylinders 3 & 8 around 270° (of course you need a harmonic balancer with degree marks all the way around to see this).

And obviously if the timing light doesn't flash at all it's a good sign that you have no spark whatsoever!

Andrew
 

anf355

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Andrew thanks for your detailed responses, very informative, also to everyone else. I haven't had much time to touch the car due to work demands and will be away on holidays soon for some a while. In time I hope to solve the issue, once I have I will update my results to the thread.

Thanks again.
 

1985VK

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Holley carbs do have a strainer of sorts under the big nut where the fuel line goes into the float bowl, but a lot of them get removed when fitting a decent quality in-line fuel filter.

However if that was blocked you'd be starving for fuel, not flooding.

Andrew


Yes, but if the strainer was missing then debris could get into the carb and may have a spec of crap holding the needle & seat open and making the carby flood as per your post above. It is worth checking out.
 
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