Engine not running right

[johng]

It feels like the idle circuit is working (it ticks over normally and runs okay on very light throttle) and the secondaries are fine (it pulls okay if you floor the throttle), but in between one of the passageways or jets is blocked (it accelerates very slowly and sounds like one or more cylinders aren't running). I don't know if water can actually block a jet, but can't see where dirt would keep coming from. Why would a vacuum leak only affect mid throttle opening?

 

[Oneball]

Maybe it is crud. I guess cleaning the carb Wil confirm but I’d expect to see something come out the carb.

Could be bad fuel line after the filter.

 

[johng]

The filter on a Quadrajet is actually at the inlet of the carb, so there is no fuel line beyond it. Trouble is when blowing out the passageways and jets it is easy not to notice if tiny bits of crud come out. I certainly didn't have any noticeable amount of dirt in the carb

 

[Roscobbc]

Perhaps the inclusion of a temporary clear filter 'in line' between the fuel pump and carb would allow you to observe the state of fuel flowing to the engine - perhaps even regular replacement if crud is visible. As water/petrol don't mix no sure if you'd see water.

 

[teamzr1]

I would think if the fuel filter is at fault than higher engine loads would run worse and does not sound like it is
Looking at the color of spark plugs should show if all are showing too lean or rich or a spark issue to one or more cylinders

Could be a metering issue when carb is running on primary float / jets and gets better when secondary kicks in

How old is the gas, how much Ethanol is the tank ?
Test gas to see how much of it and also water it might have

 

[johng]

So the good news is that I've stripped the carb down, blown through all the jets and orifices with carb cleaner, rebuilt and replaced it and it is now running properly again
The not quite so good news is I couldn't see any obvious dirt in the system, or which jet/orifice was blocked. I wonder how long before I'll be doing this again.

In answer to JR's question about the fuel, the last time I filled up was 2 weeks ago. That time I used super unleaded with 5% ethanol, prior to that I had been using Esso super unleaded with no ethanol, which is sadly no longer available.

 

[teamzr1]

Was the same tank of gas used after the rebuild as when it would not run well ?

Did you replace any of the carb parts for the rebuild ?

Due to using gas with that crap Ethanol which attracts water, add a fuel cleaner product with each tank of gas
esp type that helps reduce problems due to water
Ethanol is a harsh cleaner so if any crap buildup in gas tank gets washed into the gas and into the carb

Also, the water Ethanol attracts builds up at the bottom of gas tank so do not allow gas level to be low as than
pump is pushing more water percentage through fuel system

 

[johng]

Yes same tank of fuel and no I didn't replace anything (I didn't remove anything other than what's needed to separate the 3 sections). It will be interesting to see how long it lasts! Plan is to get a rebuild kit and do a more thorough strip down, clean and rebuild over the winter.

 

[Mad4slalom]

Further update, connected my timing light to each cylinder in turn and they are all firing. Measured the exhaust temps again and realised that the drivers side is running much hotter than the passenger side. I'm beginning to think I have got a carb problem after all, maybe just a jet or passage way blocked in the passenger side of the carb. I've stripped it down and blown through all the passage ways I can see and rebuilt it, but ran out of time to refit to the car. Hopefully tomorrow.

I had a similar issue where it would bog and stumble until the secondaries opend when it was fine, turned out to be a little bit of blue gasket blocking this jet.

 

[johng]

Yes I've been wondering if a bit of gasket or seal is breaking up inside the carb. Brilliant idea of yours to fit blue gaskets, makes it much easier to spot than black

 

[Mad4slalom]

Yes I've been wondering if a bit of gasket or seal is breaking up inside the carb. Brilliant idea of yours to fit blue gaskets, makes it much easier to spot than black

Ye

Yes I've been wondering if a bit of gasket or seal is breaking up inside the carb. Brilliant idea of yours to fit blue gaskets, makes it much easier to spot than black

yes I fitted them as part of the Blue motion fuel economy package to my holley carb ! Vast improvement as I get 5mpg now instead of 3 !!

 

[Roscobbc]

Yes I've been wondering if a bit of gasket or seal is breaking up inside the carb. Brilliant idea of yours to fit blue gaskets, makes it much easier to spot than black

Holley 'blue' gaskets are supposed to be re-usable.......however just like is shown in the picture small fragments would come-off the material and as shown block jets.....and worse still cause float valve to jam open with resultant major carb flooding!

 

[Mad4slalom]

Holley 'blue' gaskets are supposed to be re-usable.......however just like is shown in the picture small fragments would come-off the material and as shown block jets.....and worse still cause float valve to jam open with resultant major carb flooding!

That sounds scary