Flat spot update.

[Mad4slalom]

To all the folk here that took the time to listen and offer help and advice re the flat spot / bogging issue I had recently. Thank you all, having got a new valve and gaskets , I today had s go,. The valve doesnt seem blown as I cant blow through the diaphram , I replaced it anyway but on removal of the metering block (see attached pic) I found a piece of blue gasket sucked into the right side jet, dont know what jet this is but after re assembly I went for a test drive and the big issue seems to have gone . I can feel the transition from primary to secondaries but can drive smoothly through it without the huge flat spot then the sudden accelleration it had before. Fingers crossed this was the issue , I will check timing too now and report back , would be interested in any thoughts on the blocked jet. Many thanks again everyone

 

[Oneball]

That’s the main jet. That was your problem.

 

[Roscobbc]

As Oneball sez - one main jet partly blocked. And this has highlighted possible issues with some of these 'supposed' re-usable blue Holley type gaskets (to be fair gaskets they may be generic items rather than genuine Holley ones) - I have had one of these gaskets start to break-up and a minute piece blocked the primary float valve preventing it closing properly and (more importantly) flooding, overflowing and drenching the top of the inlet manifold and engine with fuel. Just one spark from the ignition or contact with perhaps a header and.........a potential fire.

 

[Oneball]

As Oneball sez - one main jet partly blocked. And this has highlighted possible issues with some of these 'supposed' re-usable blue Holley type gaskets (to be fair gaskets they may be generic items rather than genuine Holley ones) - I have had one of these gaskets start to break-up and a minute piece blocked the primary float valve preventing it closing properly and (more importantly) flooding, overflowing and drenching the top of the inlet manifold and engine with fuel. Just one spark from the ignition or contact with perhaps a header and.........a potential fire.

It’s interesting you saying that as the Holley Trick Kit I got for mine has those blue gaskets and they do seem ‘bitty’ straight out of the box.

 

[Oneball]

 

[Roscobbc]

It’s interesting you saying that as the Holley Trick Kit I got for mine has those blue gaskets and they do seem ‘bitty’ straight out of the box.

It only takes the very finest 'shard' of gasket material to partly jam open a float valve!

 

[Mad4slalom]

That’s the main jet. That was your problem.

I used the new gaskets even tho they say they are re useable , I also noticed it didnt have any nylon washers on the float bowl screws, no leaks but fitted them now . Thanks again chaps.

 

[Oneball]

I used the new gaskets even tho they say they are re useable , I also noticed it didnt have any nylon washers on the float bowl screws, no leaks but fitted them now . Thanks again chaps.

What were you’re new gaskets like?

 

[Mad4slalom]

What were you’re new gaskets like?

Got them from real steel with the power valve and nylon washers. Blue , looked like the ones i removed. they were sandwiched between cardboard not in a holley pack. The power valve was an 8.5. I also found a perished vacuum blanking cap on the secondary side of the carb ( I found this prior to changing the power valve , i sealed it and road tested it but it wasnt the problem. I will get some new caps and replace them anyway.

 

[Mad4slalom]

Been advised by my US friend to try upping the accelerator pump discharge nozzle I size at a time to fine tune the slight flat spot. Need to check what number is in there then will get a couple sent down , any one else played around with these and did you get positive results?

 

[Roscobbc]

There is really an issue with going too large in terms of discharge nozzle size - for example if you go larger than what the engine requires it won't make a measurable difference in fuel usage - and its unlikely to be big enough to flood the engine - in fact it might help answer your question relating to connecting-up the choke (you may not need it) - see my earlier comments
Seen this?

 

[Mad4slalom]

There is really an issue with going too large in terms of discharge nozzle size - for example if you go larger than what the engine requires it won't make a measurable difference in fuel usage - and its unlikely to be big enough to flood the engine - in fact it might help answer your question relating to connecting-up the choke (you may not need it) - see my earlier comments
Seen this?

Thanks rosco , I will look at the size that is in mine , i think i have the nozzle type but not sure as didnt know about this yesterday when it was in bits. Be interesting to see what is fitted, any idea what is about normal?

 

[Oneball]

Size is stamped on the face of the cylindrical section. You should be able to see it with the carb all together

 

[Mad4slalom]

As Oneball sez - one main jet partly blocked. And this has highlighted possible issues with some of these 'supposed' re-usable blue Holley type gaskets (to be fair gaskets they may be generic items rather than genuine Holley ones) - I have had one of these gaskets start to break-up and a minute piece blocked the primary float valve preventing it closing properly and (more importantly) flooding, overflowing and drenching the top of the inlet manifold and engine with fuel. Just one spark from the ignition or contact with perhaps a header and.........a potential fire.

I see in a pic of a holley carb tuning kit of assorted valves, nozzles jets and gaskets that the gaskets were brown psper looking and not blue

 

[Roscobbc]

The brown ones I'm guessing will be cork (like rocker cover gaskets) - a traditional material and probably the best chioce - perhaps not re-usable after a number of months (I suspect that even though Holley say their blue gaskets are re-usable they still detrade much like the cork ones)

 

[Roscobbc]

Thanks rosco , I will look at the size that is in mine , i think i have the nozzle type but not sure as didnt know about this yesterday when it was in bits. Be interesting to see what is fitted, any idea what is about normal?

Not a 100% sure of squirter nozzle size that would have been supplied new with carb - perhaps a no. 31 or 32? - let us know what you have front and rear?

 

[Oneball]

The brown ones I'm guessing will be cork (like rocker cover gaskets) - a traditional material and probably the best chioce - perhaps not re-usable after a number of months (I suspect that even though Holley say their blue gaskets are re-usable they still detrade much like the cork ones)

Mr Gasket (part of the Holley group of companies) does brown ones but their website says they’re rubberised too.

 

[Mad4slalom]

The brown ones I'm guessing will be cork (like rocker cover gaskets) - a traditional material and probably the best chioce - perhaps not re-usable after a number of months (I suspect that even though Holley say their blue gaskets are re-usable they still detrade much like the cork ones)

Yes , I wouldnt have felt at ease re using them although they came off intact.

 

[Mad4slalom]

Not a 100% sure of squirter nozzle size that would have been supplied new with carb - perhaps a no. 31 or 32? - let us know what you have front and rear?

Had a look, the rear seems to be

Not a 100% sure of squirter nozzle size that would have been supplied new with carb - perhaps a no. 31 or 32? - let us know what you have front and rear?

The rear seems to be an anti puull over type with a 37 or 3.7 on it ,
The front one is the tube type but the number is hard to read as the choke butterfly is in the way. If I undo the brass screw i guess it will just lift out? Thanks all.

 

[stealthyflatfish]

When I've been regasketing my carbs with the blue gaskets, I put a smear of oderless and colourless grease on the faces of the meetering and float bowls
This stops the gaskets from sticking to the faces and disintigrating on the next disassembly.