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andymcp

Herald 13/60 twin SU carbs

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When fitting twin SU carbs to a Herald, what do folks use for the throttle pedal?  Modify the Herald setup or install a Spitfire type?

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Why do you need to modify the Herald pedal? You just make up a cable of the right length with the relevant ends.

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Actually, that's what I meant by modifying the Herald setup.  Years ago I did see a car with a Spitfire pedal, that the guy said bolted straight in.  Just canvassing opinion.

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I believe the Spitfire pedal will bolt in, but not tried. I quite like the Herald pedal, one of the easiest cars to heel and toe because the pedal is so large. Having said that, never tried a Spitfire might be just as good.

But the normal problem is throttle cable length as the Herald one is too short. I made a custom cable from a bicycle brake inner and outer, I've had no problems with it. The only awkward bit is the bulkhead ferrule, which I had to remove from the old cable and araldite (other brands of Epoxy are available) to the new one.

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Herald pedal it is!  I'll start with a Spitfire cable and see where I end up...

Cheers Guys.

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I have a feeling the Spitfire cable is no good either, because the bit through the bulkhead is shorter due to the pedal design. If memory serves me correctly a Vitesse cable is a bit longer, not sure if RHD or LHD though.

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These days I just make cables up.

I use PTFE/teflon lined outer, and similarly coated inner cables. Buy some small solder less nipples and off you go.

The adjusters are also available. All off fleabag....

Premade cables for cars don't seem to last well or be very smooth.

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Or available at your local bicycle shop, AKA 'brake cable'.    They will have screw on end nipples and anything else you need for a neat installation,

J.

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Ok, carbs installed and control cables sorted as suggested.

Next little issue.  I can't set the idle speed to less than 1200 rpm without seriously compromising the tune.  This would suggest an air leak, but I've carefully re-seated the manifold and carbs twice and sprayed wd40 around to test without any noticeable effect.  I had renewed the spindles and discs.  Shining a torch through the carb shows the merest hint of light around the butterfly valve.  Linkages are loose, so there is no interaction between carbs.  Initial set up as per SU guidelines.  If anyone has any ideas what to look for they would be much appreciated.

 

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Really doesn't need much air to get a 1200 rpm idle.......  When you renewed the spindles and discs, did you shuffle the disc around to get a snug fit in the carb bore and hold the spindle tight shut while tightening the screws?  Can be tricky to get the throttle discs properly centered.  If you have a balancer, does this show more flow through one than the other even with both fully backed off? (or  more hiss from one that the other if going by ear....)

Got to be extra air getting in somewhere........ I did once have a slightly similar issue (900 - 950 min rpm) that turned out to be a crack in the manifold casting by one of the bosses underneath where it bolts to the factory exhaust manifold.  Only ever found that because I was mean with the choke one day so it spat-back on a cold start and blew the boss right out of the manifold.  Wouldn't start at all after that and it wasn't immediately obvious why!  It was only when I saw the boss on the floor the penny dropped.....

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Ok, carbs installed and control cables sorted as suggested.

Next little issue.  I can't set the idle speed to less than 1200 rpm without seriously compromising the tune.  This would suggest an air leak, but I've carefully re-seated the manifold and carbs twice and sprayed wd40 around to test without any noticeable effect.  I had renewed the spindles and discs.  Shining a torch through the carb shows the merest hint of light around the butterfly valve.  Linkages are loose, so there is no interaction between carbs.  Initial set up as per SU guidelines.  If anyone has any ideas what to look for they would be much appreciated.

 

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Do your butterflies have popoff valves in them?     One could be jammed open.

Try a spray of brake cleaner?  More inflammable that WD40, might reveal where the leak is.

"A merest hint of light"   It's gotta be enough, make it smaller!

I had a problem with the spindle wearing a throtttle body, and leak there, may apply to carbs?

John

Edited by JohnD

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Andy,

This may sound stupid, but you are aware that the throttle discs are supposed to fit in one direction? If you look carefully at the edges you'll see a chamfer, so if you get it right the full edge of the disc seals, get it wrong and only a corner seals.

Apologies if you already knew that, just that I happen wear that particular T-Shirt :biggrin:

Cheers

Phil

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Hi John,

The original butterflies had popoff valves. One didn't look too clever so I replaced them with plain discs. I was going to solder them up but managed to destroy one removing it (those tiny screws can be bl00dy tight)!

Not sure what happened with the repeat post. It was supposed to be a response to Nick. I will investigate the discs and spindles again.I

P.s. Rear carb was drawing more air than front. Leaning out the mixture ( a lot)  reduced the idle speed but had the engine 'bogging' when lifting the piston. 

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1 minute ago, thebrookster said:

Andy,

This may sound stupid, but you are aware that the throttle discs are supposed to fit in one direction? If you look carefully at the edges you'll see a chamfer, so if you get it right the full edge of the disc seals, get it wrong and only a corner seals.

Apologies if you already knew that, just that I happen wear that particular T-Shirt :biggrin:

Cheers

Phil

Phil,

All suggestions gratefully received, but I was aware and had spent a fair bit of time already trying to get the best fit.

One thing I have noticed today is that when the butterfly is fully open there is a few thou of lateral movement on the spindles which isn't present when closed. I'm wondering if the butterfly is binding on the carb body and not closing fully.

All good fun!

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56 minutes ago, andymcp said:

All good fun!

They can be a royal PITA...….. 

Mind you, PI throttle bodies are worse.  Some of those will only seal once they've sooted up - which is a long process and with 6 x 46mm discs...…. well, let's just say 1200rpm would be a distant dream!

 

1 hour ago, andymcp said:

I'm wondering if the butterfly is binding on the carb body and not closing fully.

It will be something like this I think.  Good luck sorting it

Nick

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Some success tonight!

A couple of hours spent fiddling - removing, fitting, filing - the butterfly discs has resulted in a rough idle down to 850 rpm (without yet setting the mixture correctly). I have concluded that the new discs are not particularly well made, being roughly stamped out with inaccurately positioned mounting holes. I found the biggest improvement if I fitted the disc loose with only one screw, then manipulated the spindle so the disc found it's natural position. Having done this the second hole did not align precisely with the spindle. Easing the hole with a fine file allowed the second screw to fit whilst producing the best seal of the butterfly in carb body.

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2 minutes ago, andymcp said:

I have concluded that the new discs are not particularly well made, being roughly stamped out with inaccurately positioned mounting holes.

Usual dodgy parts story...... :down:  Sounds like you are on the right track though.

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