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datberger

SU carb tuner in Perth?

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Just wondering whether there are any SU carb specialists in Perth? 

 

I drove my 240Z for the first time this week (to licensing) and noticed a bit of a rough idle and an unwillingness to rev much past 3000rpm.  I pulled the plugs today and noticed plugs 1-3 are all black and sooty but plugs 4-6 look good.  Methinks the front carb is running very rich.  I checked the choke and that wasn't stuck on or anything.  I also felt a little bit of fuel on the bottom of the carb.  Maybe time to re-kit the carbs?

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Yeah sounds like a good time to rebuild them and replace all gaskets etc.. then reset them. Not willing to rev past 3000rpm though could be an ignition issue.

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Not willing to rev past 3000rpm though could be an ignition issue.

Thanks, yes that was my first thought - at least until I pulled the plugs anyway.  But it could be ignition as well.  So where do people buy SU rebuild kits?  Nissan, ebay?, ZTherapy?

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I've seen a few kits on eBay etc.. never bought 1 online though. Ztherapy does the roller bearing throttle shafts which can help with a common issue which is the throttle shaft needs rebushing, if the throttle shaft is worn it causes a vacuum leak which can make tuning the carbs almost impossible to sync etc..

 

I've not tried the roller bearing modification but it's apparently the ducks nuts., from what I've heard.

http://www.ztherapy.com/products/SUReman.htm

 

Throttle Shafts are sized to receive double sealed stainless steel roller bearings.  Carb bodies are precision machined for shaft alignment and installation of both bearings. This alignment process in conjunction with the bearings virtually eliminates shaft binding, vacuum leaks and idle problems for years to come.

 

Just a shame nobody local offers this level of detailed service for these carbs. I'm not sure if you can get the roller bearings sent to you with the rebuild kit, it's worth sending an email though.

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Could it just be the float level in the front carb?

Mick

Maybe.  I don't know much about SUs (yet).  Not sure if an incorrect float level can cause rich running.

 

Sounds like time to start reading up about how they work.

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Order the Ztherapy SU video it is 1 of the best videos there is and I can highly recommend it as I have a copy. The float could cause issues, but so could the needle and seat if they are worn. It could cause excess fuel to go into the engine.

 

S.U's are incredibly simple once you see how they work, but they are also such a great piece of engineering.

 

You can adjust the front carb mixture using the bottom screw below the carb itself. Winding it downward causes it to become more rich and winding it up makes it more lean. You could try backing it off (so it goes up) a turn and a half, clean your plugs up and go for a drive (5 - 10 mins) and re-examine the plugs after.

 

How long ago does it look like they might have been attended to? Are they relatively clean on the outside or do they look like they have done a few years of service?

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A really rough check for faulty needle / seat is to blow (fairly gently) through the fuel inlet line, while pushing the float arm up (use a clean bit of fuel hose to avoid the dreaded petrol taste in the mouth afterwards). Once the arm closes the needle / seat, you shouldn't be able to blow through it anymore.

 

The old brass floats wear out over time and allow fuel to get inside. Easy to check - take the fuel lines off the top of the float chamber, undo the 3 or 4 screws on top of the float chamber, lift it up carefully making sure the needle / seat / float pivot arm doesn't fall to pieces, you'll see a brass (or possibly black plastic) round float just floating there in the chamber.

 

Lift it out and see if it has fuel inside it (give it a shake and you'll hear it sloshing around in there). If so, chuck it away and get a new one.

 

And yep, float level being out or a holed / leaking  / sunken float will cause the symptoms you describe.

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You can adjust the front carb mixture using the bottom screw below the carb itself. Winding it downward causes it to become more rich and winding it up makes it more lean. You could try backing it off (so it goes up) a turn and a half, clean your plugs up and go for a drive (5 - 10 mins) and re-examine the plugs after.

Thanks, I was reading about adjustment via that screw.  I will give it a go today to see if I can make a difference.

 

A really rough check for faulty needle / seat is to blow (fairly gently) through the fuel inlet line, while pushing the float arm up (use a clean bit of fuel hose to avoid the dreaded petrol taste in the mouth afterwards). Once the arm closes the needle / seat, you shouldn't be able to blow through it anymore.

 

The old brass floats wear out over time and allow fuel to get inside. Easy to check - take the fuel lines off the top of the float chamber, undo the 3 or 4 screws on top of the float chamber, lift it up carefully making sure the needle / seat / float pivot arm doesn't fall to pieces, you'll see a brass (or possibly black plastic) round float just floating there in the chamber.

 

Lift it out and see if it has fuel inside it (give it a shake and you'll hear it sloshing around in there). If so, chuck it away and get a new one.

 

And yep, float level being out or a holed / leaking  / sunken float will cause the symptoms you describe.

I'll also have a go trying out your suggestions.  Thanks for the tips.

 

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It is probably the needle valve not closing correctly - may have worn down too much. This means the fuel level gets higher, and fuel dribbles out the carb. Adjusting the underside nut - which moves the needle up/down, isn't going to stop the fuel from dribbling out, and hence not fix the problem. You can buy new valve off ebay for a few dollars from memory. Rebuild kits would also come with one. If you want to rebuild the carb(s), there are bushings etc that need replacing to properly rebuild them, which you may not be able to replace? In which case, perhaps buy rebuilt carbs from a reputable company (probably an oversees company).

 

The SU are quite simple, I learnt a fair bit by reading the service manual, watching a few youtube vids, and fiddling with the carb. Then rinse and repeat a few times until it all sinks in :D

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It is probably the needle valve not closing correctly - may have worn down too much. This means the fuel level gets higher, and fuel dribbles out the carb. Adjusting the underside nut - which moves the needle up/down, isn't going to stop the fuel from dribbling out, and hence not fix the problem. You can buy new valve off ebay for a few dollars from memory. Rebuild kits would also come with one. If you want to rebuild the carb(s), there are bushings etc that need replacing to properly rebuild them, which you may not be able to replace? In which case, perhaps buy rebuilt carbs from a reputable company (probably an oversees company).

 

The SU are quite, I learnt a fair bit by reading the service manual, watching a few youtube vids, and fiddling with the carb. Then rinse and repeat a few times until it all sinks in :D

I think you are right.  I attempted to adjust the mixture yesterday and couldn't fix the issue.  If anything, the car is now running worse.  I think I'll start looking into options - checking ebay for kits, contacting  ZTherapy for rebuilding etc.

 

Thanks for your input. 

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