My Carb Vacuum Cover Fix - Top Cover Fix

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sunnbobb
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#16

Post by sunnbobb »

Excellent, might have to grab some brass ones and do a polish job for fun...
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Sidecar Bob
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#17

Post by Sidecar Bob »

I have washers & coins epoxied over the buttons on my carbs http://www.ngwclub.com/forum/viewtopic. ... 333#p92333 (scroll down for a pic). They looked good at first, but they have not been reliable http://www.ngwclub.com/forum/viewtopic. ... 66#p431566

This week I started thinking about finding some sort of cap that will fit over the carb tops to hold everything firmly in place. Tonight I am going to take the broken carb cap from my parts engine and decide whether it would be possible to use the freeze plugs with silicone to seal them and some sort of mechanical fastening to keep them from coming off - maybe a couple of screws at the edges or something like that...
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
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Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#18

Post by Toehead »

Bob,


let me know how it turns out. Mine are just JB welded for now.
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#19

Post by Sidecar Bob »

I broke the plastic out of the cap from the parts engine that was already broken and made some measurements. There is definitely enough meat there to drill & tap for a couple of small bolts.

We will be out of town for a funeral tomorrow but I will see if I can get some freeze plugs at Canadian Tire on Sunday.

I'm thinking that, after I have figured it out on the spare, it should be possible to do 4 caps on a Saturday after lunch, paint them and have them back on before supper.
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#20

Post by Sidecar Bob »

Canadian tire had nominal 25mm freeze plugs for $1.25 each. I might have been able to get them for less at a local auto parts place but I was there so I bought the last 4 he had in stock. In fact, there are 3 slightly different kinds but they are all close enough that they should work the same and once they are in & painted nobody will notice.

We are just in from a longish magnifying glass-fried-ant car trip and I need to lay down in the cool for a while so I probably won't look for suitable screws and see about drilling & tapping the spare cap until tomorrow. I also want to re-read Randakk's page about the differences between the slides for different years before I drill too so I don't mess up a potentially useful cap.

I did take time to measure how far the shaft protrudes when it is all the way up and how deep the freeze plugs are. From what I can tell, there is enough room to glue some thin rubber inside the freeze plug for the piston shaft to hit so that the outer edge of the piston doesn't hit the inside of the cap. Since GL1100 and CX/GL500/650 pistons don't have the buttons for the shafts to hit, I want to get my spare CX carbs from the attic and have a look at what hits in them before I decide whether the rubber is necessary.
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#21

Post by Sidecar Bob »

I do not advise using the freeze plugs unless you provide something for the top of the shaft to hit.

1) I had a look at my spare 650 carbs (no buttons) and they have plastic bumpers in the ends of the shafts. The parts book for the GL1100 shows these too. Unfortunately, they are not sold separately. FWIW, the ones in the 650 carbs are the wrong size anyway.

2) Further measurements on the GL1000 carbs indicate that the top end of the shaft hits the button less than a mm before the skirt of the piston would hit the inside of the carb cap.

3) I do not know the cause, but two of the carbs on my parts engine have broken slides - the flange of the piston broke free from the part that moves in the venturi. Their skirts could not have hit the caps because their buttons were intact at the time this happened. I mention this only to indicate that the slides can break and if they do they are not repairable.

I spent some time this evening measuring & calculating and decided that if I line my freeze plugs with 3mm thick material the shafts will hit the plastic before the skirts hit. As luck would have it I happen to have some 3mm HDPE sheet. I will post pics of my construction as soon as I figure out how to do the screws.
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#22

Post by Hal »

This comes at the right moment for me.

On the rig, I seem to have two different types of plastic top plugs. The front carbs have a flatter type plug, the rears are the normal plug with a more noticeably raised 'nipple' in the centre.

I've been wondering why they should be so different....does anyone know? When I took the tops off the vaccum chambers to polish them I tested them and they are all airtight, surprisingly.
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can lure it back to cancel half a line...

so....probably best use Tipp-Ex in future?"

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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#23

Post by Sidecar Bob »

My carb tops are fixed and seem to be working as hoped for.

As I mentioned earlier, I determined that the shafts of the slides MUST have something softer than metal to bump on before the skirts of the slides hit inside the tops. When I held a freeze plug in place temporarily and put a slide into the top I could feel the slide's shaft hit the freeze plug. With the shaft touching the freeze plug, I measured the distance from the edge of the skirt to the edge of the carb top. I repeated this measurement with a top that had its original plastic button. The difference was about 3mm. Since I had the 1/8" (3.18mm) HDPE sheet I decided to use it inside the freeze plugs and then figured out that if I put a suitable sized O-ring in between the plastic and the carb top it would hold it in place against the freeze plug.

I bought 4 pcs 1" freeze plugs for the carbs, 1 pc 1 1/8" freeze plug for the drilling jig and 2 packages of #4-40 x 1/2" oval head stainless steel screws. I had the 1/8" High Density PolyEthylene (HDPE) sheet and the O-rings came from an assortment I already had.

This pic shows the parts & the critical tools I used. Note that because of tolerances in my jig each carb's parts are individually fitted so they are all marked with the number of the carb their top came from. Note that the slides are also marked because the slides & tops are matched sets and should not be mixed up (per Randakk)
Image

- I prepared the tops pretty much as Keddano described except that I used a flap wheel instead of a stone. Either will work equally well.

- I found a socket wrench that was a snug fit inside the 1" freeze plugs and used it to draw 4 circles on the HDPE, then cut out the circles with a scroll saw. You could use a jigsaw clamped in a vise if you were very careful or a hole saw with the drill bit removed. The resulting parts were not very round so I filed them until they fit inside the freeze plugs snugly. The inside corners of the freeze plugs have a small radius so I filed a chamfer on one side of each HDPE disc.

- Because I didn't want to have to deform the HDPE discs, I decided to flatten the tops of the freeze plugs a bit. I put each plug on the anvil end of my vise and tapped it with a hammer until it was close to flat, then turned it over and struck it from the inside with a large brass drift and a big hammer to remove any dents from the tapping.

- I should mention at this point that the correct drill size for 4-40 75% threads in soft material is #43 and 50% threads in hard material is #41. Since I did not have number size bits and 3/32" is in between these sizes that is what I used. The clearance hole for a 4-40 is 1/8", but since the holes in the freeze plugs will be used to locate the holes in the carb tops the freeze plugs should be drilled 3/32" initially.

- I picked one 1" freeze plug and figured out where to drill a hole in it that would be as close as possible to the O-ring, marked it and drilled it with the 3/23" bit, then drew a line across the centre of the plug, crossing the hole.

- With the 1" plug inside the jig (1 1/8" plug)(one wrap of masking tape around the smaller plug made it snug), I drilled through the hole in the 1" plug and made a hole in the jig. Next I rotated the 1" plug inside the jig until the line appeared and drilled through the hole in the jig to make a second hole in the 1" plug. Finally, I drilled through the first hole in the 1" plug to make a second hole in the jig.

- At this point I had 2 holes in the jig (as shown in the pic above) and one 1" plug with 2 holes. I put each of the other plugs into the jig in turn and drilled their holes.

- A HDPE disc was inserted into each 1" plug and 2 holes were drilled through each disc, matching the plugs.

- A 1" freeze plug was inserted into each carb top and holes drilled through the plug and into the top. These holes only need to be about 1/4" deep (the aluminum of the cap is almost 1/2" thick at this point). I located these holes at right angles to the mounting holes for the tops but any orientation will work as long as you don't get too close to the vacuum port. It is very important to use cutting fluid when drilling these holes in aluminum. I also had to clean aluminum out of the flutes of the drill bit after each hole.

NOTE: UP TO THIS POINT ALL HOLES ARE 3/32"
Sdit: Pics hosted on Photobucket replaced
Last edited by Sidecar Bob on Mon Jul 31, 2017 10:27 pm, edited 2 times in total.
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#24

Post by Sidecar Bob »

- The next step was to tap the holes in the carb tops. Again, it is very important to use cutting fluid and to clean the tap between holes. Go gently and for every 3 turns in turn the tap back one turn to clear the swarf from the cutting edges.

- I used a 3/16" bit to start the countersinks in the freeze plugs for the screw heads, then finished up with the countersink bit. I find this works better in steel than trying to cut the whole thing with the countersink bit.

- The final drilling was to drill out the holes in the freeze plugs and the HDPE discs with the 1/8" bit. Don't forget to turn a larger bit against the hole lightly to remove the burr.

- Next, I put the discs into the plugs (make sure the holes line up), followed by the O-rings - the O-rings will help seal everything as well as pressing the disc against the inside of the plug.

- I mixed up some J B Weld and lightly buttered the sides of the recess in a carb top (be careful around the vacuum port) and then put the matching plug + disc + O-ring into it, lined up the holes (note that it may not work if it is rotated 180 degrees) and started the screws. Before tightening the screws I dabbed some epoxy under their heads. When the screws were done up I wiped off the excess epoxy. The other 3 tops were the same.

- I painted my carb tops with Krylon Hammered Black to match my rocker covers & timing belt covers. (Before I wiped the numbers off of the outside of each top I wrote them on the insides.)

Note non-modified top & broken slide on the right. I am not sure why this slide broke (the button was intact at the time) but it is one of the reasons I am sure the skirt must not be allowed to hit anything.

Image

Image

Image
Edit: Pics hosted on Photobucket replaced
Last edited by Sidecar Bob on Mon Jul 31, 2017 10:29 pm, edited 1 time in total.
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#25

Post by jake2012 »

Won't the HDPE disk limit the travel of the slide. :?: they're domed to allow the slide to go up into the cap. The disk appears to make it flat inside thus nullifying the purpose of the dome.
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1976 Suzuki GT 550
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1952 Pan Shovel
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#26

Post by Sidecar Bob »

That is exactly correct. The HDPE discs are supposed to limit the travel of the slide. In fact, I flattened the domes of the freeze plugs in order to make the discs fit/work better.

Honda/Keihin originally used plastic buttons to limit the travel of the slide and prevent the skirt of the slide from impacting the carb top. They later changed to solid carb tops and put plastic inserts in the top end of the slide shaft. I used discs of HDPE for the same purpose.

If the freeze plugs are fastened into the tops without something soft(er) in them the slides will be able to travel farther than they should and the slides could be damaged by impacting the tops.

I will say it again: It is imperative for the shaft of the slide to have something softer than metal to hit in order to limit the travel and prevent damage to the slide.
Mr. Honda ('83 GL1100/Dnepr) summer New Engine Thread
The Famous Eccles ('84 CX650EI/VeloUral) winter Never Ending Build (CX500forum)
Click: Colour schematics for all GL1000 & GL1100 and GL1200 standard models plus instructions on how to download the full size version
"A guy with two sidecars can't be all bad." - Cookie
Another guy with two sidecars..... Hmmmm... must be something to that....
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Re: My Carb Vacuum Cover Fix - Top Cover Fix

#27

Post by jake2012 »

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1973 Suzuki TC 100
1976 Suzuki GT 550
1983 Honda ATC250R
1975 Elsinore 250
1977 custom hawg chopper
1952 Pan Shovel
2x 76 gl1000s
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