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1978, Honda CX500
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Discussion Starter · #1 ·
Hi guys,

I am in the process of bringing back to life a CX500 I purchased a few months back, stored in a shed for a decade.

I have the the engine and other stuff sorted out and it was time to fix the exhaust leak on the right hand side. I digged up some old threads and bought a set of Harley cans, specifically 65613-97 & 65605-97.

The flange from the H-box is in bad shape and I haven't tried to use shims and mount the exhaust yet to see if it fixes the leak. I also find that I need a bracket to mount the exhaust.
The old exhaust used a bracket that also held the rear footpeg. Any direction on what you guys used to fix this?

Also, if I go ahead and remove the H-box, what should I be using to bridge the gap? Any fuel economy hit to be expected, can the fuel economy be recovered?

Thanks
 

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1978 CX500 "The Grub", '83 GL650, '82 GL500 Project "AdventureWing", '79 CX500C, '78 CX500 Scrambler
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If you intend to keep the pillion, use the original mounts and fabricate an adapter using thin flat stock or heavy sheet metal.
Murray's Carbs offers mid pipes to replace the h-box. They're shaped to accommodate the gear shift and brake pedal.
 

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To connect to the existing pillion peg mounts, I just used some stock metal, cut to length, and drill some holes. On the RH side I needed a spacer as well, shown in pic.

I sacrificed the passenger pegs as the wife won't get on this one anyway.
208919
 

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1978, Honda CX500
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Discussion Starter · #4 ·
Does the OEM and H-Pipe provide back pressure that affects the fuel economy of this bike?
 

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Does the OEM and H-Pipe provide back pressure that affects the fuel economy of this bike?
For a data point, at a recent fill up I got 142 miles on 2.55 gallons, so 55+ mpg with h-box and HD cans. It's not a precise measurement since filling the tank can vary each time.

I have no info on mileage without the h-box.
 

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1978, Honda CX500
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Discussion Starter · #6 ·
For a data point, at a recent fill up I got 142 miles on 2.55 gallons, so 55+ mpg with h-box and HD cans. It's not a precise measurement since filling the tank can vary each time.

I have no info on mileage without the h-box.
Thanks for those numbers.

The H-box, which i removed to remove the rust and get it painted doesn't look to be a complicated design at all. It seems there are some perforated plates welded on the camshell and the outlet ports are visible from the inlet side.

Thanks,
 

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... the outlet ports are visible from the inlet side.
That does not sound like it is a stock Honda H-box. The inside of a stock H-box looks like this;

208934
 

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1978, Honda CX500
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Discussion Starter · #9 ·
Mine doesn't look that bad :D

I will flash some light later today, and verify if there are any pipes like the picture posted by Mike.

Thanks
 

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1978, Honda CX500
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Discussion Starter · #10 ·
It seems the bent tubes are perforated and I was seeing the light through the holes. I managed to clean the H-box, pressure washed and painted with high temp paint and installed it.

I used coke can as gasket and have installed it without any leaks. Fabricating stainless steel brackets now to hook it up to the footpeg bolts soon.

I am planning to file the metal bracket to line up with the footpeg tab to act as stopper. Let me see if that works.

Thanks
 

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Show pics of your final fabrication please.
 

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Turned out great and looks fairly simple to do with basic hand tools, thanks!
 

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good fab job for hiding them. mine are more conspicuous, but my CX isn't a beauty queen anyway.
 

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Discussion Starter · #15 ·
I didn't intend to hide them, but was trying to round off the corners, just kept going :D
 
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