Bushyboy's build thread


I have been chasing my tail trying to figure out this intermittent almost random backfire at idle in what seems to be the carbs. I have recently installed 78 mm pistons and rebuilt top end. Everything I am about to describe I have checked multiple times. I have checked cam tension, TDC, valve adjustment, verified timing, float level, carb sync, and for leaks around carbs/exhaust. I swapped out for new and correctly gapped spark plugs (0.030 inch NGK BP7ES). I have checked my ignition coil and spark plug wires. I have checked carbs and plug color to verified it isn’t a problem with tuning being to lean or rich. When I have used the color tune; I‘ll hold for laughter, it would indicate rich only when it popped at idle. When it isn’t making this random once in a while pop everything is normal. My battery is good and no issues with charging. I have also checked brushes on alternator, rotor ohms, magnetism, and seating was correct. I have found no issues with wiring and have checked pretty much any that is in the system. I have checked the slide diagrams for damage and function. I should also say I didn’t have any issues with carbs before I took this bad boy apart. I have done heat cycles and break in procedures to ensure rings were sealed and have rode around 40 miles afterward. I have completed a compression test on both cylinders. The engine has been re-torqued to specs. Also even though I am not 100% sure the whole tank has premium I put that in my last two fill ups so its at least 2/3rd 93 octane. CHECK OUT THE VIDEO AND THE POP HAPPENS AROUND 0:16 WHEN IM FOCUSING ON THE TACHOMETER.

My next thought is to maybe open the gap in the spark plugs?
 
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Well I believe I found my issue. I checked the first set of spark plugs that were on the bike and one was definitely bad. The second set I thought were practically new had one that could have been bad. I went to store and bought a new pair of NGK BP7ES and for shits and giggles checked the electrode resistance. One read normal and the other was a around 15k ohms. I installed the known brand new good one and one of the practically new plugs reading normal around 0.04 ohms on electrode. I gapped both plugs to the upper range of 0.032 inch. I fired her up and no issues. I hope I chased the gremlin away.
 
Got the bike out for a little fresh air today. It was such a beautiful day for a ride. Trying a few pics with the side cover installed; still unsure. Maybe a good old fashion hand painted race number on the side.
 

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@Jim since I have put quite a few miles on the bike with the license plate bracket I can now give a little more feedback on the structure and durability. The only issues I can report is I have lost one bolt and my cheap aluminum inspection bracket broke. Today after a long ride my bolts in the only section (see pic) that has loosened must be tightened and this time I’m adding thread lock. The inspection sticker bracket; which is no concern really, is thin sheet aluminum that has felt the effects of parallel twin vibrations. Other than that I think I got an actual good Chinese product; even though I hate to admit. My bar end mirrors came from China too and surprisingly are good quality.
 

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I've been using my aluminum backing plate/rubber sheet "sandwich" mount for a good 20 years now on all different bikes. Never lost a bolt or cracked a license plate or backing plate .....

on4m0BX.jpg


ASiTMma.jpg


A bit less messy than troweling silicone all over the part too, lol.
 
Just made the bike even faster with some race numbers; +10 hp.
 

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Sunny Sunday ride up the coast.
 

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Added a windscreen today to the bike. I was a little hesitant and thought it would look tacky, but actually looks pretty good IMO. I had ordered a headlight grill also, but found out I wouldn’t be able to use it with the current setup. Oh well it could have looked tacky, but I guess I may never know.
 

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Tried to make it up to Turtle Bay today, but as usual traffic was backed up and we all no sitting in traffic makes the XS mad. So whipped it around and hit up the Ka’ena point. Always a good ride up that way. The new wind screen helped out a little bit so it isn’t just for looks.
 

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Well just a little update on what's going on with me as far as my build goes. I haven't been active on here in a while because I was in the process of getting my friends 1978 Yamaha XS750 up and running. It was a little bit of a pain, because there isn't much information out there for the motorcycle. Pretty much did a full tune up, rebuilt/tuned his carbs, and adjusted timing. Sounds simple enough, but you can trust it took over 15 hours to figure it all out. As for my build I have a right side Brembo caliper and parts coming in the mail. I decided I would stay with the stock forks instead of going inverted. So first will be the caliper upgrade followed by progressive springs and then an 2.15 18" WM front rim and 100/90-18 rubber. Once I am done with the front section then I will move on to the swing arm. Still deciding if I'll swap the swing arm out or not.
 
Installed the progressive suspension front fork springs. I set my pre-load to mid setting on the fork adjustment, but I guess I’ll put a few miles on it and see if that’s good or needs to go one way or the other.
 

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