different carb

Upgrades, downgrades, modernizations, alterations or just being creative.

Postby RiverPatrol » Mon Jul 09, 2018 12:49 pm

L60Boerne wrote:Thank you RiverPatrol. I can't wait to discover the difference!


Me too!
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Postby richw » Tue Oct 15, 2019 9:12 pm

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A while ago I decided, having read this thread, to go for a Motorcraft carb from Michael at Gronk Performance.
My original Hitatchi carb was showing its age and I had an intermittent big flat spot under acceleration that could only be overcome by flooring the throttle when normal service would be resumed. Not great driving like that! All the basics checked out, clean main jet, accelerator pump squirting a good stream of fuel and it idles perfectly.
This is on a low mileage engine with valve clearances adjusted, good compression and new points set correctly with the timing bang on and the vacuum advance working normally.
The intermittent nature of the problem stumped me, carbs are not normally like that!
About the same time as the carb arrived so did a workshop manual that covered my Hitatchi carb.
I read about the 'power valve'. There's something I had not come across before, if this was working one moment and not the next that would cause my problem...see description from the manual here.

With the carb off of course I had to try the new one.
The package had arrived damaged but a broken vent stalk and throttle arm didn't seem a big deal.
The carb comes with an adapter collar for the P series motor with the standard single bore intake manifold.
Initially I had the carb fitted 'back to front' so the throttle butterflies fouled this adapter.
An easy mistake as it looked the correct way around.
Once full throttle action was acheived I connected the fuel line and started up.
It sounded great and idled nicely...but there's not much to learn about performance revving up in neutral!
The next issue was throttle linkage.
Not so easy!
The 2.5" action from the standard set up gives you upwards travel.
This carb needs outward travel from a point in space towards the master cylinder!
I rigged up some spectra line and various 'fairleads' and achieved a 'working' throttle.
Off for a drive I go.
To be fair it wasn't a proper trial. The throttle action kind of pumped this carb from mid throttle to 3/4 in a rush.
The engine ran smooth with fixed throttle but when that 'gush' of throttle came on it did not like it and actually stalled out.
At that point I decided that discretion was the better part of valour and headed home.
I could have ploughed on and made a more permanent throttle set up, most likely using a cable driven by the original arm(?) BUT instead a good friend of mine helped me look into this power valve thing. His history is porsches, he has mini syringes on wire clips to measure output from accelerator pumps!
We remove the power valve diaphragm and the 46yr old rubber looks OK. We find that the valve stem is very slightly rough and it feels 'sticky'.
Some '00' grade steel wool and a bit of a polish and it feels much smoother.
In short order it's fitted with all the vacuum lines checked.
Problem solved, normal acceleration and she runs like a dream.

So, sorry not to have a firm opinion on the Motorcraft.
The carb is well priced but some 'home assembly' is required.
Michael threw in an air cleaner but at 2" it was too tall and the bonnet would not close.
For now I'm happy with the original set up and I'm fortunate that my carb does not have high mileage problems like worn shafts and perished diaphragms.

Has anyone out there worked out a throttle linkage for this carb?
I'd like to see that.
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Postby richw » Tue Oct 15, 2019 9:17 pm

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Here's the low down on that troublesome 'power valve'.
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Postby RiverPatrol » Wed Oct 16, 2019 10:04 am

Nice that you were able to get the original one performing well for you.
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