Stuck Carb Slide

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rocc99
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Stuck Carb Slide

Post by rocc99 »

I currently have my mechanic working on my 72 T350 which seems to have a new problem every time I talk to him. First let me say that this guy is very good, he's been working on vintage motorcycles for the last 25 years and really knows his stuff. With that being said, he's got me a bit concerned since even he doesn't have much of an answer for our most recent problem. I'll do my best to relay the issue, hopefully you guys have some advice that can pull me out of the depths of despair:

So apparently the one carb slide has a tendency to stick wide open. It appears the issue may have been due to the intake bolt being too tight which caused the slide to bind. So, we backed that bolt off and the slide moves freely, but then it seems like we are getting some sort of air leak. At one point, the bike just shot up revs and continued rising. It didn't even stop once we killed the key...had to put our hand over the carb to stall it out. So it seems like too tight and the slide sticks, too loose and the bike won't run right. He also said that he's been having a hell of a time to get the bike to idle right and a little bit of throttle is almost always needed. He tried a light block sand on the body to try and get a better mount, but it didn't help. Neither of us are not sure what other options we have - he seems to think the carb body has been overly warped and new carbs would be the next logical step.

So, any other suggestions? If not, any recommendations on what to do as far as replacing carbs? I'm thinking I'd go new since you never know what kind of issues come along with used carbs. If new, any particular models you'd recommend as well as best places to purchase?

Thanks for all the help - I'm really hoping I get to ride this motorcycle at least a few more times this summer, Ha!
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tz375
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Re: Stuck Carb Slide

Post by tz375 »

He needs to grind/file/lap the flange face flat and then fit a new O ring.
rocc99
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Re: Stuck Carb Slide

Post by rocc99 »

He already block sanded it to a straight edge. We also replaced new o-rings.

Do you think additional sanding would be helpful?
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tz375
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Re: Stuck Carb Slide

Post by tz375 »

Not if it's flat. Check it on flat plate - not a dinner plate - something really flat. Windows are pretty flexible but if you have an old mirror around the house that would be perfect. Lightly coat the flange face with something sticky. Grease will do or assembly lube or vaseline. Bearing Blue is my favorite. Then press it against the flat surface and lift it back off.

You should be able to see high and low spots.
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Re: Stuck Carb Slide

Post by GT750Battleship »

:up: Hi,a very common problem on the T20,the carb body's do warp through heat exchange with the motor...over the years,consequently the slide is no longer a perfect fit inside the carb body ! Not much can be done..once warped,always warped !! I have friends who have used carbs of other bikes to overcome the problem :wink:
Cheers,
Roger
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joethebike
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Re: Stuck Carb Slide

Post by joethebike »

Afraid to say a warped carb body on a 350 is common and the only possible cure if a warped slide chamber is not the fault is to check the brass pin in the side of the body that keeps the slide properly oriented by engaging with the slide groove.

If the pin has moved inwards it could cause the slide to jam.
1972 Suzuki T350 160,000km +2 Castrol 6 Hour races
1982 Honda CX500 EC 272,700km
2005 Suzuki DL650 145,000km
rocc99
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Re: Stuck Carb Slide

Post by rocc99 »

Thanks for all the info. I'm going to have him try sanding down once more to get it perfectly flat. I'll also have him check the slide pin to make sure there isn't any interference. But, let's assume that the carb is warped and I'm stuck (forgive the pun):

Would you look for a used stock replacement for the failing carb and keep the working one?

Or would you purchase a new pair of modern carbs? If this route, any suggestions on where to look.

Based on the manual, I show a Mikuni VM32SH as the stock carb. I quick Amazon search resulted in the following:

http://www.amazon.com/Mikuni-Round-Seri ... =mikuni+32" onclick="window.open(this.href);return false;

Would this be something that could bolt on with the addition of rubber boots and correct jetting?

Thanks again.
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Re: Stuck Carb Slide

Post by Vintageman »

joethebike wrote:Afraid to say a warped carb body on a 350 is common and the only possible cure if a warped slide chamber is not the fault is to check the brass pin in the side of the body that keeps the slide properly oriented by engaging with the slide groove.

If the pin has moved inwards it could cause the slide to jam.
+1 on pin. Also if out the slide can rotate and cause high idle. check this pin.

Make sure cable routing is not binding

Make sure Idle Adjust rod in straight and has no kink causing slide to catch

For sticking slide, us some Aluminum polish like Mother's in body cylinder area for slide. It will take some material away and make it less sensitive to warping when tightened.

Won't idle well. Does this have the second pilot jet still? If so that hole is tiny and any corrosion will restrict flow. I used a number drill and cleaned mine up. Be careful start a little smaller and work your way up to size. Those drills are small and snap easy.

I think the flange was originally a little concave (I have seen other flange carbs like this) so when torqued to flat counter acted inevitable bowing. Be careful removing material. try the above first and lightly torque on nuts.

I had all these issue on my bikes and no problems now with OEM and they work wonderful.

Sure new carb is an option too Dyrberg... is running VM28 Flat slides for example PM him
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rocc99
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Re: Stuck Carb Slide

Post by rocc99 »

Vintageman - thanks very much for all the useful info. Definitely going to go through all of those things at least a few more times before we go down the path of new carbs. Fingers crossed.
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Re: Stuck Carb Slide

Post by rocc99 »

Update: messed with the carbs for a bit and still having issues. Probably going to have to go with new carbs. I PM'd dyrberg123, but haven't heard back - has anyone else had any experience with a carb swap?

In other news, we decided to crack the engine again to make sure some of our air leaks weren't from internal seals. Well, unfortunately, they are! They looked good when we replaced the outer seals, but after running it, they've turned hard and are useless. So, looks like I'll be sending the crank to Bill Bune for a inner seal replacement. Seems like most everyone from this forum has had good experiences with him, so fingers crossed. A bit concerned about the bearings though, they seem to be good enough, but I'm hoping Bill can tell me for sure. I know the outer bearings are still available but the inner is NLA...
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Re: Stuck Carb Slide

Post by Vintageman »

Usually the center bearing OK since it is lubed by gear oil not injection.
The only issue is sometimes they spin on shaft. I don't think he has to press that off the shaft if OK.

You'll be impressed how fresh big end needle bearing alone will reduce side to side rod shake

Your carbs. They still stick at WOT? Did you try sanding a little with fine gritt paper (may have to remove the pin and press back in after) Then use aluminum polish or fine steel wool to smooth. You should not need to remove much?

How much torgue do you apply to nut?

I mean torque it easy and then see how much before it sticks. If you use a fresh lock washer you should not need much torque to seal it up and nut will hold


Maybe your not so lucky as me. Both my bikes had this problem. What is odd is now they don't. I used to have to torque very very lightly on nut. but now I can go more (still easy for don't want to ruin a good thing, but I bet to factory spec if I could measure) as if over time OK it has formed to this position better

good luck
Current Bikes
74 GT250 (T350 upgrade),
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77 Yamaha RD400 (Daytona Cyls),
rocc99
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Re: Stuck Carb Slide

Post by rocc99 »

Thanks again for the info Vintageman. We did some light sanding with emery cloth originally, but haven't really touched the slide since - we were a bit worried about taking too much off. Now that we have some time waiting on the crank were going to work on the slide with some fine grit steel wool a bit more as you suggested.

The torque on the bolt was very light (though I don't know how hard the previous owner had it torqued down, I expect quite a lot). Hopefully we can persuade the slide just enough to allow for a torque that produces a good seal, but we haven't had much luck so far.

Regarding the crank, I was actually able to locate a center bearing from a shop in NC who had one NOS. They were also able to order the outer bearings from Suzuki since they are still available. I'm having all three sent directly to Bill Bune, figured it was worth having all three replaced while the crank is out.

I'll let you know how it all turns out once the crank is back in and the carbs back on...hopefully end of next week.
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Re: Stuck Carb Slide

Post by Vintageman »

rocc99,

I have a twin crank I want to do too. Let me know how it works for you. Did you condider possibly new rods?


On carbs. If you see no obvious damage with carb or insulator (I did not see anything obvious ). pay attention to the point where slide sticks.

I assume they do not stick until torque applied... correct?

I put mine on and torque nuts a little at a time. There was a definite point it would stick and near WOT only. I did not need to take much off at all for the sticking to stop. A few ft/lbs holds well with fresh lock washer and O ring seal. Use a drop of loctite blue or something. And as I said both got better. The carbs are made out of are junk metal IMO, but malleable. These carbs work real nice a little large for bike, but when engine is ready they give great performance.

Did Dyrberg reply PM... he's here... maybe reply to one of his own post... I am bad at checking my PMs
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rocc99
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Re: Stuck Carb Slide

Post by rocc99 »

Vintageman,

To be honest, I hadn't given much thought to replacing the rods. At this point the costs just keep piling up so I figured I'd stick with the basics and do new seals/bearings. But, I will definitely let you know how it turns out - really hoping everything goes according to plan.

As for the carb, you are correct - the slide only sticks at WOT and only when mounted/torqued to manifold. We replaced the o-rings with fresh ones (I tried ordering OEM, but got sent something entirely wrong...we were able to locate the same size rings at a hardware store, so hopefully they are sealing up properly). We also have new nylon lockers on there.

We are definitely going to focus on sanding down the sticking spots to see if that clears everything up. I think the main concern is that we had the slide not sticking at one point and then after the bike warmed up you could feel it start to want to stick again...wondering if the warp gets a little worse with the heat exchange from the motor.

I wish there was a way to just switch to rubber boots since that should technically alleviate the sticking...but that's obviously impossible due to the hard flange. I did read somewhere about someone doing a "carb squeeze" to slightly unwarp the body, but that sounds like something that could easily end up making the problem worse...

Anyways, hopefully find time to work on some light sanding this weekend...I'll let you know how it turns out. Thanks again.

Oh, and yes, Dyrberg did get back to me. He said the VM28 was not an exact fit and required some modifications. Let's just say I'm really hoping we can get the stock carbs to work!
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Re: Stuck Carb Slide

Post by Vintageman »

OK if you want to try and use stock carbs. Make sure your are not actually over tightening nut. Try to bolt them on with light torque, test for stick apply a very little more test for stick and repeat until it sticks. I found that at a few pounds (guess) no issue. Now there is no way I can get a torque wrench in there but enough practice to know what a few pounds feels like.

Nylon lock nut. that may melt with heat I think. I would go with fresh lock washer and nut. I noticed when the lock washer just flattened fully a add more is enough torque to keep things tight.

That mother's aluminum polish take a little metal off each time. I really don't think you need to take off too much. It took me a couple iterations and my guess is I am using 5-6 ft/pounds torque. Many thousands of miles trouble free. Yup the T350 vibrates too. never stuck never loosened up


I'll stop driving this method. I hope you are as lucky as I was. Just funny I had two carbs do this (both left side more so). I have heard others with this problem too on this post,
Current Bikes
74 GT250 (T350 upgrade),
76 GT250 (T350 upgrade),
71 T350,
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74 GT380,
75 T500,
73 GT550,
75 GT750,
72 Yamaha DS7 (R5 upgrade),
77 Yamaha RD400 (Daytona Cyls),
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