New to me XS750...need some ideas

[Fleksta]

Recently picked up a '78 XS750E project and have been slowly plugging away at it. Decided to tackle the carbs last weekend and encountered a serious problem when dismantling. Someone managed to twist off all three idle mixture screw tips . So I need some ideas as to how I can tackle this without making things worse. I ordered a pin vice and a set of tiny jewelers drill bits, but would like to leave that as a last resort.

Pics of the bike for those who are interested:

Has a set of cool 3 into 3 pipes that run tucked up tight under the frame:

 

[MaxPete]

I've always had a thing about those bikes - looks nice - although you don't see too many cafe racers with plush king & queen seats.

 

[5twins]

...... but you're asking in the wrong spot, the wrong forum. I'm sure those bikes have their own forum. That's where you need to go ask.

If your mix screws have been modded like you seem to think, the only solution I see is replacing them.

 

[azman857]

I've wanted one of those tanks for a while. Nice one to work with for a project. Keep us informed of your progress please. Thanks for the pics. Will those ends press out since there is no threads holding them in?

 

[TwoManyXS1Bs]

Yes, I can see the broken mix screw tips in all 3 carb throats.

Those carb bodies are likely Zamak, which has a higher coefficient of thermal expansion, versus the brass mix screw tips. So, you may have a fair chance of popping them out, tapping down on the exposed tip, from the carb throat. We're talking serious heat here, at least 400°F. Carbs MUST be completely stripped down first, before heating...

 

[xjwmx]

That's too radical and very iffy solution. Can't you delicately grab them with tiny flat-jawed needle nose and push them back out the screw hole? If not, maybe a 90 degree bend in the tube from can of compressed air would blow them back out the screw hole.

 

[jonesey]

Hi Fleksta, well i had the same problem with an XS11 some good few years ago, a common problem on those too. they may be the same carbs. You will not believe how solid those broken off tips have become, its as if they have swagged or friction welded themselves in.
I also don't remember mine protruding so far but anyway i got mine out by cutting them off flush, then with the Butterfly and shaft removed made a very hard drift from an old compas or divider tip, grinding it to length until it was about 4mm short of the top of the carb throat. I then flattend off the sharpend end of the drift to 1mm diameter. Holding the drift vertical against the broken off tip and with the carb body in a vice I inserted a medium sized flat screwdriver between the top of the drift and the top of the carb throat and levered down and forced the tip loose, don't go too far, just loosen it or it will damage the drilling.
What I found then was that the passageway was tapered from the force that had been exerted on it by the old Air screw.
I then had to use a Colourtune to get mixture right on the 2 that i had rescued with the new screws as number of turns out didn't work the same with the slightly larger passages.
Now thats what i did but check out the triple and the XS11 forums as well, they may have a better method. The other alternative is to get a new set of carbs. I don't have pictures as it was years ago.
Regards and good luck, those things are stuck mighty fast.

 

[Signal]

If it all goes bad and the carbs are no longer useable late model triumph trident 900 carbs will fit.
Some are Mikuni some are Keihin CVK. If you can go for the CVK's.
A fair bit of info on this swap on the Yamaha triple website.

 

[Fleksta]

If it all goes bad and the carbs are no longer useable late model triumph trident 900 carbs will fit.
Some are Mikuni some are Keihin CVK. If you can go for the CVK's.
A fair bit of info on this swap on the Yamaha triple website.

This would be a great option, but I can only find two complete sets on Ebay and both are $499...more than I paid for the bike.

There is only one set of Mikuni MKIIs from a '79, but they look pretty haggard themselves. If they go cheap enough I might put a bid in, but they're already up to about $60 with shipping. More than I'd like to spend given the chance they have the same problem.

I'll have to try the compressed air trick, already tried using needle nose pliers (wouldn't budge). The triple forums pretty much have two solutions, file the tips flat and use a push-pin or cut down sewing needle in vice grips to press them out...or as a last resort try a pin vice with the smallest bit you can find and drill them out. I'm thinking that might work best as they were screwed in so far that the hole is probably enlarged anyway.

 

[fredintoon]

- - - I'll have to try the compressed air trick, already tried using needle nose pliers (wouldn't budge). The triple forums pretty much have two solutions, file the tips flat and use a push-pin or cut down sewing needle in vice grips to press them out...or as a last resort try a pin vice with the smallest bit you can find and drill them out. I'm thinking that might work best as they were screwed in so far that the hole is probably enlarged anyway.

Hi Fleksta,
my son's XS750 had a busted-off needle in it's middle carb.
Like you we tried all those allegedly guaranteed extraction methods to no avail.
Then we drilled the bastard out.
A 1mm (0.039") drill-bit is the smallest that can be gripped in my drill-press chuck so that's what we used.
The needle's turns for running nice will need to be determined but at least it'll work, eh?
The hard part is getting the drill-bit centered.
Place the carb body on the drill-press work table.
Find a drill bit that fits in the needle's threaded hole.
Chuck that drill-bit and use it to center the carb body.
Clamp the carb body down.
Swap in the 1mm drill-bit and drill the pin end out.

 

[Fleksta]

After much head scratching and cursing I threw in the towel and drilled them out carefully with the pin vice (my drill press wouldn't grip the tiny bits). The holes appear to be straight & round, but I won't get too excited before getting them reassembled and trying to start the bike. My fear is that the holes have been enlarged given how far the tips were protruding...hopefully it will just be a matter of proper tuning.

 

[gggGary]

https://chicago.craigslist.org/nch/mcy/d/yamaha-xs-no-title/6222596160.html

different ad
1980 YAMAHA XS 850 SPECIAL (CHICAGO)
FOR SALE PARTS FOR 1980 YAMAHA XS850 SPECIAL
PARTING OUT
CALL FOR PARTS 773-814-5181 TOM

There is a guy Johnny in oconomowoc WI was kind of an XS750-850 specialist trying to find his number

 

[fredintoon]

After much head scratching and cursing I threw in the towel and drilled them out carefully with the pin vice (my drill press wouldn't grip the tiny bits). The holes appear to be straight & round, but I won't get too excited before getting them reassembled and trying to start the bike. My fear is that the holes have been enlarged given how far the tips were protruding...hopefully it will just be a matter of proper tuning.

Hi Fleksta,
good that you got the stubs out.
Don't sweat too much about the enlarged needle holes.
We found that our own enlarged needle hole was still OK for tuning.
FWIW I've seen sets of small diameter drill bits with 3mm hexagonal ends on them so they'll fit in a drill-press chuck.
Too late for this fix but there will be others.

 

[weaselbeak]

...... but you're asking in the wrong spot, the wrong forum. I'm sure those bikes have their own forum. That's where you need to go ask.

If your mix screws have been modded like you seem to think, the only solution I see is replacing them.

Why? They have the same carbs as the 650 don't they? BS38?

 

[fredintoon]

...... but you're asking in the wrong spot, the wrong forum. I'm sure those bikes have their own forum. That's where you need to go ask.
If your mix screws have been modded like you seem to think, the only solution I see is replacing them.

Hi 5T,
yeah, but we're smarter and more helpful and like weaselbeak sez, they're the same carbs except there's one more of them.
Or if you have an XS11, there's one less.

 

[jetmechmarty]

...... but you're asking in the wrong spot, the wrong forum. I'm sure those bikes have their own forum. That's where you need to go ask.

That forum is useless. That's why he's here. The triples forum appears to be inactive. XS650.com and XS11.com are active. I don't see many triples, either. Even though they're great bikes.

 

[gggGary]

This ad is from "johnny" he's knee deep in triple parts.
https://milwaukee.craigslist.org/mpo/d/yamaha-parts-titles/6202306886.html
Check and see if he has a good set of carbs?
PM ducatiman on here he's an XS750 guy.

 

[Fleksta]

So I finally got around to reinstalling the carbs on the bike. I cleaned them as best I could, installed new pilot, main, needle, float valve, checked levels, and replaced one diaphragm that had an old rubber cement fix. Mixtures were all set 2.5 turns out from light seat. Reassembled and put them on the bike.

So it idles fine, steady at service manual spec with choke/enricher off(~1k rpm). However it dies when given the slightest amount of throttle.

 

[Fleksta]

Might have found the issue when testing the coils. All pass the primary @ 3 ohm, but two were reading nothing on the secondary test until I removed the plug caps. So I have some new caps & wire coming. It must just have been idling on one cylinder.

 

[Fleksta]

Been a while, I had sent the carbs off to OldSkoolCarbs for a complete once-over & rule out a dirty pilot circuit (they are now a thing of beauty!).

Put them on the bike with new plugs and caps...and still have the same issue. Starts fine, idles fine, won't rev past 2k. Get loud pops out of the exhaust when attempting as if it were extremely lean.

Could this actually be a faulty CDI unit? Is there a way to test these?