Topic: Stuff that can make you CRAZY!

[BenelliSEI]

Today I’m finishing up the carbs for the Sandcast Project. It uses the very early 4-1 pull cables, so mechanical “bench sync” is a little different. First thing is to adjust all four cables equally slack so the slides all bottom out….. #4 carb refused to close up. Small gap under the slide, but definitely “hanging”. Crap. Did I put the slide in backwards?

Took #3 and #4 off the cables and pulled the slides to compare. Both cables had equal runout, so not that. Pulled the needles and both slides ran smoothly and sat down in the bores, no stickiness, no obstructions. Not backwards. Mmm.

Dropped the needles down into the carbs and #4 seemed to be stopping early and somewhat sticky. Pulled it out and it’s not bent, nice and clean. Get the micrometers out and carefully compare it to #3. Same dimensions, tapers appear identical. Pulled the emulsion tubes and they appear identical, both on OD an and ID. All the holes are clear and clean. Screwed #3 back in and smooth sailing. As I turn in #4 I can feel it dragging as I screw it in…. What the heck? Threads look perfect and then all the lights come on!! Check the second photo carefully; the TOP of the tube is slightly tipped over (bent). The needle can’t drop down fully because the internal bore is NOT straight! How the hell did this happen?

I did get these carbs from someone else and I’m sure he didn’t know about this issue and honestly I can’t even imagine how it would happen? BUT IT DID. Fortunately I went through all my junk and found one in a set of carbs I haven’t used yet. Next time you think you have seen everything; think again!

[BenelliSEI]

I wonder it I can straighten I? Probably not.

[Gurp]

This completely sounds like a day in the life of me at work. Day shift will say yeah we've got this big job we didn't have time to get to today we've gathered all your parts for it and started taking it apart and then we find out that they have half of the wrong parts and the other half of the stuff we need is missing or not in stock...

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[scottly]

I recall seeing something like that before on here; IIRC, the damage was attributed to over-tightening the emulsion tube.

[BenelliSEI]

I recall seeing something like that before on here; IIRC, the damage was attributed to over-tightening the emulsion tube.

Good point, that would do it for sure…..

[scottly]

Are the side holes squished down slightly? Compare the length to a good tube to see if it's shorter.

[jlh3rd]

I wonder it I can straighten I? Probably not.

I wonder if the shank of a drill bit, starting with smaller size that fits, and some light tapping could re-shape that. ...no drilling.

[BenelliSEI]

I wonder it I can straighten I? Probably not.

I wonder if the shank of a drill bit, starting with smaller size that fits, and some light tapping could re-shape that. ...no drilling.

I’ll probably try that and then measure. If it’s “short” nothing will save it…..

[rocket johnny]

some days  you need to stay in bed ...

[bryanj]

At my age thats most of them!!!

[BenelliSEI]

Are the side holes squished down slightly? Compare the length to a good tube to see if it's shorter.

It must be shorter on one side for sure. The photograph (on a white background) makes it fairly easy to see. It’s actually not that obvious. As frustrated as I got, I found solving this very satisfying…..

“If this was easy, any arseh*ole could do it”.

[HondaMan]

I've only seen 2 others bent like that. I still haven't figured out how they can get bent: the emulsion tube towers in the carbs aren't that strong that they could bend the brass part (which is harder) without cracking open or off the carb completely (which was how one of the 2 I've seen happened). That one looks like a corkscrew in the picture!

[BenelliSEI]

I've only seen 2 others bent like that. I still haven't figured out how they can get bent: the emulsion tube towers in the carbs aren't that strong that they could bend the brass part (which is harder) without cracking open or off the carb completely (which was how one of the 2 I've seen happened). That one looks like a corkscrew in the picture!

I agree. The carb body isn’t damaged in any way. I’d have to stick it in a vice and clobber it straight down to make that bend and twist! I have a small box full of “mystery fubar’d parts”. This one is going in it for sure!

[MauiK3]

maybe  lightly tap with a plastic hammer on a hard wood surface to gently straighten? Have to worry about the holes staying round

[BenelliSEI]

I think the only way would be to machine a dowel with an OD to match the ID of the tube, and then press it in from the bottom. With the dowel in place, then maybe a bit of tapping on a hard steel bench….. worth it? Probably not.

[PeWe]

Yamiya has new

https://www.yamiya750.com/index.php?main_page=product_info&cPath=246_21_181_143&products_id=659

If fixing the bad one it might be different than the 3 others.

[BenelliSEI]

Yamiya has new

https://www.yamiya750.com/index.php?main_page=product_info&cPath=246_21_181_143&products_id=659

If fixing the bad one it might be different than the 3 others.

Agreed. Will order next time.

[HondaMan]

If you do replace it with another: try to gage the emulsifier holes in your new one to make sure they are the same as the other 3 carbs. Otherwise you'll end up with 1 carb that is richer/leaner than the others.

This has happened to me when the owner 'rebuilt' his carbs using partly Keyster and partly Keihin emulsifiers. Talk about hard-to-find problems with sparkplug colors, wow...

[M 750K6]

I ran rich on all 4, on my 750, until I took the Keyster brass out and put the original back in. The most obvious difference was the needle width and profile. Thinner and more pointed on the Keyster.

[HondaMan]

I ran rich on all 4, on my 750, until I took the Keyster brass out and put the original back in. The most obvious difference was the needle width and profile. Thinner and more pointed on the Keyster.

In action, these needles are supposed to stop all fuel-mix flow from the mainjet's orifice below 1200-1250 RPM, leaving that realm to the idle-mix screw. The problem I've seen with both the older (pre-2012 or so) Keyster parts was that the needles NEVER shut off the fuel: they were too thin and/or the needle jet's hole too large. This caused the idle speed to run real rich, and the idle-mix screw couldn't control it: the engine either would not idle, would quickly foul plugs, or would spit and backfire from being soaking wet with fuel.

The newer (current) versions of the Keyster needles I've seen can actually jam into the tops of the Keihin needle jets because they are considerably larger diameter than those holes. I have several bags of these needles and their Keyster needle jets, taken out of malfunctioning carbs. I have met 2 riders of highly modified 750s who are using the Keyster parts at least somewhat successfully: one is a full chopper and the other a stripped-bare cafe'd version, neither is ridden more than one oil change per season, though. These are the more recent Keyster parts, but with mainjets like #140 (Keyster) in one and #135 (Keihin) in the other, and both have #42 Keyster idle jets. The air screws are set at 1.25 turns on one of them and at 1.5 turns on the other (I've forgotten which is which) and neither need the choke to start them cold, indicating rich running idle circuits at least. Both bikes use up sparkplugs quickly. One has the 'breadbox' air filter (the cafe') and the other has the OEM airbox and filter, but with very large cutouts applied to the 2 vents.

Seems like an expensive way to enjoy an SOHC4 ride?