Need advice on repairing a torn slide diaphragm

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extremeodd
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Need advice on repairing a torn slide diaphragm

#1

Post by extremeodd »

I've been working on getting my new to me $150 84 gl1200 up and running the last few days. After bypassing the fuel cutoff relay to get the pump running and replacing a blown float bowl gasket, I got the bike to start up and idle quite nicely.

However, whenever I would try to open the throttle more than 10% it would choke out and die. This was screaming "main jet issues" and despite the PO telling me it was running only a few months prior, my mind immediately went to the main being gummed up with varnish (completely forgetting the pilot has a far smaller orifice and would probably plug up first).

So while waiting on my carb cleaning tools to arrive in the mail I figured that I'd try the lazy man's approach: drain all the gas, dump in a can of seafoam, start it up to get the seafoam into everything and let it sit for a day.

After doing that I realized that by pulling the top cap and slides out I'd be able to possibly dislodge anything in the main from the top using compressed air. The first carb I popped the top off of, I found a torn diaphragm and a fairly scuffed up slide that had some resistance on being pulled out.

The tear is U shaped and is about 1/4in wide. The diaphragm has been patched before with something that was brushed or smeared on and that patch is still holding just fine so I'd like to try and emulate that.

Some quick googling showed that quite a few people have had varying amounts of success using either plastidip or liquid electrical tape. Before I get the stuff and go wild I figured I'd ask you guys for your opinion on this.

Hole is at 12 o clock, repair is at 9 o clock
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Better shot of the tear
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EDIT: After doing some more research, I'm going to attempt using the liquid tape technique where you put a piece of tape on the top side to line everything up perfectly then painting a thin coat on the inside (pressure side), letting it dry, 2nd thin coat, then a thin coat on the backside.
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BlueThunder
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Re: Need advice on repairing a torn slide diaphragm

#2

Post by BlueThunder »

Replace it. Any thing else is asking for continuous running issues.
...Brian
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extremeodd
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Re: Need advice on repairing a torn slide diaphragm

#3

Post by extremeodd »

I wouldn't doubt that it won't work near as well as a new one, but with the bike only running me $150 I am highly incentivized to spend as little money as is possible to get this up and running. That and the only replacements I can find are either direct from China (slow shipping), used (prices are higher than I'm willing to pay), or a "hope I can make it work" piece from jbmindustries.com. Not to mention that I fully expect this bike to have near-continuous issues, running or otherwise, that is the nature of a cheap bike. Nothing in this world much more expensive than a cheap bike.

Never been a fan of the whole 'replace instead of repair' mindset. Unless there is absolutely no possible way to repair something on this bike, I'm not replacing anything.

If the patches I made on the 2 torn diaphragms don't hold, then I'll try again with another recommended technique. Even if that fails and I end up having to buy some diaphragms, the attempts cost me less than half the price of one.

I'm waiting on my carb cleaning tools to come in before I install the patched diaphragms so the next time I'm out in the garage I'll snap a few pics. The one looks like it'll hold, the other doesn't look too promising but it's worth a shot.
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Re: Need advice on repairing a torn slide diaphragm

#4

Post by Rat »

People have used rubber cut from a rubber glove and contact cement ....

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extremeodd
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Re: Need advice on repairing a torn slide diaphragm

#5

Post by extremeodd »

I ended up using liquid electrical tape and patch pieces cut from a nitrile glove. It seemed to work on at least one of the two that I fixed as I was able to actually take the bike on a short ride. With that said, I couldn't suddenly open the throttle but was able to nurse it up to about 2,500 rpm under load. Forgot to plug the alternator back in so I ended up pushing the bike about 1/4 mile home but this is progress. Bike went from nonrunning to sort of running and moving under its own power.

Later tonight I'm going to open up the 2 'repaired' carb tops and see which one didn't hold.
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Re: Need advice on repairing a torn slide diaphragm

#6

Post by Shadowjack »

Might not be important but a repaired diaphragm will be a little bit less flexible and lag In throttle response compared to the others.
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Re: Need advice on repairing a torn slide diaphragm

#7

Post by flyin900 »

Its important to also get the outer edges of the rubber diaphragms sealed solidly into the small round groove around the carb body top. I had to use a product called Hylomar around the outer edges of the diaphragms to seal them securely. Mine had all shrunk around the outer edges slightly from age, even though the rubber diaphragm itself was still in great overall condition.

One or more were leaking vacuum and the bike wouldn't pull properly under acceleration, especially in the 4-6K plus range it had no get up and go anymore. It started and idled excellent and pulled initially away alright from a stop, yet these were the symptoms I experienced from the leaky diaphragms.
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extremeodd
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Re: Need advice on repairing a torn slide diaphragm

#8

Post by extremeodd »

Thanks for the tip on getting the edges seated, I noticed that all of the diaphragms seemed to be like 1% too small and it was a tight squeeze to seat the edges and I wouldn't be shocked in the slightest if they shifted while putting on the caps.

Unfortunately while pushing the wing home the other afternoon I gave myself a bruised/fractured rib so I haven't messed with the bike. Leave it to me to fracture a rib pushing a bike...

For the curious, after the 1/4 mile of pushing, I had a driveway to get up and without resting I pushed as hard as I could and felt the pain start midway up. 6 years of computer work has taken its toll on my muscle mass :(

Either way, fracturing my rib on this bike has me upset so I've given up on repairing them and will simply buy new diaphragms.

EDIT: I might have spoken too soon on giving up on the repair. Replaced the plugs since it seemed to not idle on all 4 and now she idles like a dream with no choke. Also, she is far more willing to rev up than the last time I tried. There is definitely still at least one slide not working but it no longer stalls when I suddenly go WOT. The rpms climb a little, then it hesitates for almost a full second then it revs up to 5500 before I let off the throttle. This is giving me hope that one of the 2 repairs held and I might be able to redo the patch on the other.

Of course, down the road, I will replace the diaphragms but I'd like to get past this part so I can figure out what else this thing needs to be a solid bike.

EDIT 2: Just pulled the diaphragms out and it's just like I thought: one repair held and one failed. So I'm patching up the one that failed and will try again.

EDIT 3: Repatched with just the liquid electrical tape instead of using a layer of nitrile glove to see if that would work better or worse. After it dried I installed it and was able to take her around the block a couple of times quite easily but it wasn't happy and only ran on 3 cylinders for the most part. However, it's running a ton better so I'm definitely heading in the right direction. Now I just gotta figure out why I get no temperature display

EDIT 4: The patches worked! Sadly the left rear cylinder isn't firing at all despite having good spark so I'm guessing that the carb is plugged so I'm going to pull the carb box tomorrow and rebuild them to ensure no other weird issues. Was able to ride 1-2 miles at 30-40 mph, it was a bit rough but progress!
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Re: Need advice on repairing a torn slide diaphragm

#9

Post by extremeodd »

UPDATED DIAPHRAGM REPAIR INFO FOR FUTURE PEOPLE USING GOOGLE
The liquid tape method WORKS, BUT you must perform an extra step.

1: Clean the diaphragm using starter fluid (denatured alcohol should work too).
--There must be no oil or dirt anywhere near the repair area.

2: Line up the edges of the tear on the pressure side (engine side) using a small piece of masking tape or used electrical tape on the backside (cap side) to keep everything in place, but the tape must NOT be overly sticky or you risk tearing the diaphragm when removing it.

3:Coat the tear in a thin layer of liquid tape.
--Do NOT use the brush that comes in the can, personally I used the end of a small zip tie but a cheap artists brush would work better.
--You must work fast as the liquid tape drys extremely quickly.
Make sure that some gets into the tear to ensure maximum adhesion. You do not need to worry about it being smooth or looking pretty.

4: Inspect your first coat. Did it fill up the tear completely, or can you see a visible impression?
--If it's not completely filled, use a 2nd thin coat to ensure it's filled in.
Even if you feel that it is filled in, still use a second coat.
--If this seems like too much, do not worry as we are going to address this later.

5: Carefully remove the tape from the backside.
--If you used electrical tape you may find that the liquid tape has adhered to it quite strongly, if you are careful it should come free without causing any damage.

6: Repeat steps 3 and 4 ensuring the tear is completely filled and the surrounding area has a light coat of liquid tape on it.
Do not worry about over application or smoothness.

7: Once the liquid tape has fully cured (10 mins) you will notice that the diaphragm is fairly stiff where you repaired it.
This has rendered it all but completely useless.
Congratulations, you've completely ruined your diaphragm and it's now garbage!

7.5: Oh... Yeah, this is where the new part of the technique comes into play. Pull the diaphragm out of the garbage (or back out of your carb if you jumped the gun) and keep on reading.

8: Grab a can of carb cleaner, I used the cheap Walmart brand.
--If you're unsure if your carb cleaner will work, spray some on any cut you can find on your body.
--If that was less than pleasant, it should do the job.
--If it didn't hurt, you've either built up a tolerance to solvents or you have some "eco-friendly" fake cleaner on your hands.
--Go to the store and get the toxic stuff.
Use this to soak the corner of a rag.

9: Using the wet rag corner, carefully rub the liquid tape repair to remove the excess liquid tape.
Ensure that you are stopping every few seconds to blow off the diaphragm to keep the carb cleaner from completely destroying it.
--You should be able to carefully massage off the excess liquid tape without damaging your diaphragm until you are left with only the sealed tear and 3-4mm around it.
If you are unsure if you have removed enough, stop and let it completely dry for 10-20 mins then check for flexibility. if the repaired spot isn't nearly as supple as the rest, you need to remove more of the liquid tape.

10: Once you're confident that the repaired area is as flexible as you can get it without exposing the tear, reinstall and let her rip!

11: If the repair fails on you, repeat the above but leave a bit more material on the engine side of the repair.
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Re: Need advice on repairing a torn slide diaphragm

#10

Post by Madhurigore »

Great Information was very useful for me..
Thank you for sharing.
6adan
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Re: Need advice on repairing a torn slide diaphragm

#11

Post by 6adan »

I have done the carbs on a couple of 1500s with the diaphragms from JBM and they work very well. Before you put them on the slides with glue dry fit them and mark them with a spot of paint on the slide and diaphragm.
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Re: Need advice on repairing a torn slide diaphragm

#12

Post by neilt »

As a former Honda dealership mechanic in the 70s, my opinion is replace it. If you don't mind possibly having to do it again, you can try repairing it, but by replacing it with new, you'll be confident of no more problems with it.
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Re: Need advice on repairing a torn slide diaphragm

#13

Post by Gowing »

I’ve used liquid rubber stuff from harbor freight on my fj1200 Mikuni s. There were a couple of very small
holes in rubber. Held well I believe. Diaphragms are very expensive.
Dave

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jdvorchak
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Re: Need advice on repairing a torn slide diaphragm

#14

Post by jdvorchak »

I've had good success by cutting a patch, slightly larger than the tear, out of those blue Nitrile gloves from Harbor freight and using High Temp Blue RTV as the glue. Been holding for 5 years now.
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