Sure fire way to benxh test SU throttle shafts?

[goonfan]

***Post 15 details how I "sealed" worn throttle shafts.

 

So my shaft is worn out... In my carbs...pervs!

 

I'm looking at a few different used sets and don't need another bad unit. I know how to test them in the car but not on the bench. I was thinking I could spray a thin oil on directly on the bushings and look inside for leaks. Not sure if that will work.

 

Any ideas or known methods?

[ggzilla]

Yes, sure. Just use the feel test. If you can move the shafts up/down or right/left, they are bad.

[goonfan]

Is that really it? I tried that on mine with them still mounted and I didn't notice any play. After a few seconds of starter fluid it will rev up though. There is some play in and out when I turn throttle, that must be it.

 

Actually it looks like they may have been replaced, I'm not sure the bushing is proud of the carb body, that's why I was thinking it may have been rebushed at some point.

 

Just got home and will start with the testing in a minute or 60, lol. Looooong day could use a break

[ggzilla]

Rotate the shaft a little. Then wiggle it. Yes, that's really it.

[I'm BLUE]

Su throttle shafts are generally worn out unless a bigger company has refurbished them.

Some people make their own bushings

ztherapy in salem/oregon completely repairs/rebuilds them.

 

***if you have to tune your carbs 2 times a month or hard to tune ***

 

^^^ chances are they are bad along with worn mixture needles.

[goonfan]

thanks!

 

 

I'll give it a shot soon. I know one is worn for sure and something is a miss with the rear "carb area". I say area because I tested out the shaft with some of starter fluid and it was fine but while I was washing it yesterday I had it idling, I was very careful, and when I was spraying the cowl off it stumbled a bit. So I made a few quick passes with the hose on "mist" and it would stumble some more.

 

I've been pricing rebuilds and they seem overpriced too me. ZT bearings alone are $325, that's not something I can justify paying for knowing what a bearing costs and how long the set up time would take for reaming and pressing in new bearings. Not that they don't do good work. If I can't source good carbs I'll try to install my own bushings, probably on a spare carb body.

 

Did find a guy who does rebushings for $80 per carb, that may be a route I take if I don't go DIY.

[goonfan]

Okay. They're worn.

 

Can't get the front to wiggle axially but it slips in and out a good mm or so of he carb body. The rear wiggles axially just a bit and moves in and out of the body 1/2mm or so... but fuel started seeping out of the shaft, so that's some conformation right there, lol.

 

My theory is that a we bit of in and out is not as bad as axial play. I have too much in and out on the front and too much wiggle coupled with axial play in the rear.

 

I'll may try to tune them still, can't hurt. but I'll probably focus on some wiring problems today.

[Boaty]

The shafts on my 38mm's are worn badly. They desperately need to be rebuilt before I run them again on the L20b.

 

I could tune them - sort of. With the shafts worn as bad as they were, it is a nightmare to get them synced properly and I had better luck just winging it by ear.

The issue I had, was that I could not get a stable idle less than 1200rpm or so, and it ran off depending on ambient temperature. During summer, they would run completely different during the day, than at night. Even with an exhaust probe and several other people assisting, I could never get them tuned 'right'. But after 2000rpm or so, it wouldn't make a horrendous difference and I still managed really good highway MPG (27 average over 5 years).

 

Z-therapy is a proven option, albeit expensive - but it's probably your best bet on getting them fixed. They do amazing work and I've never heard of a single complaint regarding their methods. When the time comes, I'll be sending mine off to be rebuilt by them. If you do the whole kit and kaboodle, you end up with fully polished carbs (medium polished, not buffed) and re-plated linkage, everything will be brand new, etc. They don't reman YOUR cores, but they exchange them for ones already rebuilt and go from there.

[goonfan]

Yeah, they look great and I'm sure will function fantastically. However I can buy a whole "new" engine with a cam, header and DGV's for $400...

[Sealik]

Here's a DIY...... :D

 

 

 

http://www.classiczc...hread43184.html

 

...... "When the butterfly is completely closed, the side-to-side movement of the throttle shaft is restricted because the butterfly is a tight fit in the carb bore. But when the butterfly is opened, the throttle shaft can move back and forth a bunch before either the butterfly or the linkage bits hit the carb body"....

 

Also...with 'new' SUs you will notice that the throttle shaft changes position 'axially" as the throttle is cycled....thus the tiny bit of axial movement at 'idle'

 

Got my 46s re-bushed from Norm at at Zeddsaver

[goonfan]

Hmmm that looks like its worth a try. I tried something like that on Friday but didn't use o rings.

 

I actually talked to norm earlier today. Right now in leaning that way. I think don't want to go with an all out rebuild at this point but new bushings and replated linkage would be $200.

 

That leaves me with no Z and puts me back into my 8-10mpg truck. So I may swap in my other motor for the time being or swap on my triples from said motor.

 

I looked at 6 SU carbs on Saturday and every single one was worn. have one more set to check out over in Seattle but when I had him check for play I was not confident in his results. I don't really want to waste an evening and $20 to find another bad set.

[MikeRL411]

I posted this before but it was part of the mysterious dissappearances occuring last week. Quick check, put a ring of Silicon Grease [DC4 for the older generation] around the shaft to body junctions of both SU carb shafts and see if performance improves. If it does, then you need new bushings. If not then you still have $200 in your pocket.

[goonfan]

So I just put together the parts needed for a little DIY shaft sealing. I'll be using an ultra high temp silicon gasket material to make my own flat washers out of. The dimensions look like they will end up being 0.40 ID x 0.65 OD x 0.125 H. The material has more give than viton and will have much more contact area. On the opposite ends I'll try out some epoxy and caps.

 

This is just temporary until I make up my mind. If it holds up well than I'll look into doing my own rebushing job on some loaner bodies.

 

 

[goonfan]

Just finished putting the silicone washers on. I ended up having to under size the ID and make it fit around the shaft, I also used a viton o-ring as a washer. After some tinkering with different setups that seemed to give the right balance of tension between closed and WOT. One side is set up different than the other, I had to use an extra washer in the rear carb. I also pulled the lock washer that holds the throttle connecting nuts to the shaft. I'll drop a dap of thread sealer on there if this works, I don't want to actually lock them down of course.

 

Used some plastic caps and 2 ton epoxy over the other ends, we use this epoxy at work on stainless steel so I'm hoping it works. Letting everything set up before I start her up and take her for a test drive.

 

I took pics and will post them when my cell is done charging.

[goonfan]

Now for what you've all been waiting for!

 

First I disassembled ONE linkage, you can see the gasket I cut out here too. I cut the ID bit smaller than my planned 0.400" probably 0.375", I'm not sure as I was using a hole punching set and just grabbed the next size down.

 

 

 

As I was saying earlier I used a Viton o-ring as a "washer", this was done because the compression wasn't even, closed vs WOT. It's still not even compression of course but it's much better than with a washer. Notice there is no lock washer, it was not giving me even compression so I pulled it out. I'll deal with any potential "backing off" later.

 

 

 

Front carb.

 

 

 

I epoxied caps onto the ends of the throttle shafts. It's a little sloppy on the rear because I was using 5 min epoxy and it set up real quick.... that end I had a little hick up, got it in my hair, doh.

 

 

Front carb

 

 

 

It worked out very well. I used a whole can of starter fluid, spraying directly on the gaskets and caps. Not even a hick up. There are still some issues that I'lll need to address though. I had to get a stronger throttle spring for the rear carb. The gasket and o-ring were binding a bit, I plan to put a dab of grease between them. Also one of the gaskets was cut a hair too large on the OD and has got hung up on the boss for the throttle shaft. Still holds vacuum but I don't see it lasting too long if I leave it as is.

 

 

 

Front Carb

 

 

 

As for driving experience it has made a big difference, hasn't cured everything but it's much better. I went from 1500 to 700-800 at idle, it's steadier as well. It is starting to pull like an actual Z and doesn't completely fall on it's face past 4000. Sadly she is still gutless, I'm hoping to make the corrections to the setup and get the carbs tuned tomorrow night.

 

Fingers crossed this brings her back to life!

[goonfan]

Looking at my handy work.... I may just need to flip the gasket on the rear carb over. I noticed they have an almost cone shape to them and the front carb gasket, the one w/o issues, has the smaller side towards the carb body. I'll try it out tomorrow.

[ggzilla]

It is sounding like those carbs are worth fixing! Only $80 for rebushing sounds very reasonable.

 

A stronger spring will make the shafts wear even faster. Better to get them tight again so a stronger spring is not needed.

[goonfan]

It is sounding like those carbs are worth fixing! Only $80 for rebushing sounds very reasonable.

 

A stronger spring will make the shafts wear even faster. Better to get them tight again so a stronger spring is not needed.

 

Well, I talked to that guy today and it turns out it doesn't do work on Hitachi's, so that's out. I'll end up doing it myself or going with Norm at Zedd Saver.

 

The stronger spring is gonna come off tomorrow when I grease up the o-ring, well that's the plan anyway.

 

I'm only going to run with this setup until I have my 72' on the road again. I need something that gets better mpg than my truck in the mean time.

[goonfan]

POS SU carbs! Argh!

 

Had a bitch of a time setting the float levels... The floats are not anchored well at all, just taking out the screws moves the floats a ton.

 

I did the clear hose trick and even though I got 23mm the bowls would not fill at all, so I made more adjustments. I'm going to have to go with the look at nozzle and adjust from there method. I got it to idle but it back fires off idle. Centering the jets was a bitch too.

 

I'll have to tackle it some more tomorrow. If I don't have it done by tomorrow then I'm just going to stick it out in the truck for a bit longer, if it looks like it will be a while I'll just swap motors until the 72' is welded back together.