Author Topic: Achievement Unlocked! V-twin carbs  (Read 862 times)

Offline mr72

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Achievement Unlocked! V-twin carbs
« on: March 09, 2019, 06:36:23 AM »
Couple of weeks ago my dad and I went for a ride and had to cut it short because there was a lot of fuel leaking/dripping from the carbs on his Honda Shadow VT750DC (dual carb). I volunteered to help him fix it. I ordered a pair of rebuild kits for the Keihin carbs and we fixed it over the past two days.

Man those carbs are hard to get on and off of the bike. Getting them off was no picnic, which is not aided really by the coolant hoses being in the way. But the V arrangement makes life quite difficult. Parallel-twins FTW!

Once the carbs were on the bench it was a straightforward job to clean them and replace all of the o-rings. We didn't make any jetting changes because the bone-stock bike was running perfectly fine before whatever leaking thing went south. Getting the carbs back in the bike was a serious chore. OMG that's a pain to get both carbs to seat on the intake boots.

We got it all together and attempted to start the bike in high hopes that everything would be perfect only to discover it would crank slowly and backfire a couple of times then the battery went dead before it ever started. We figured the battery was just nearly flat when we gave it a try and put it on the battery tender to try again the next day. While we were cleaning up the tools I made a shocking discovery: the big spring that goes between the diaphragm cover and the diaphragm from one of the carbs was still on the bench. Oops. So I figured we'd get to practice taking the carbs off and on again the next day.

So yesterday I went back over to help him put that spring back and see if it'd work with a fresh battery. Fortunately we could get the diaphragm cover off without removing the carbs so it really wasn't a hard job to get the missing spring back where it belongs. Once we got the whole bike back together it started instantly but had a mis and occasional weird puffing backfire at idle that had me scratching my head. It also had a hesitation when opening the throttle and I said out loud, "it almost acts like it has a big vacuum leak", just as I noticed that while we were jostling the carbs getting the top on and off we managed to pull the vacuum hose that runs between the carbs (weird?) off of one of the carbs so indeed it had a vacuum leak the size of Rhode Island. I stuck the hose back on while it was still running and it instantly smoothed out and the idle came up a couple hundred rpm. I set the idle speed, we let it warm up a little on the side stand and then went for a ride. My dad said it ran as good as ever.

This bike is about a 2004 model I think, it has just 8K on it, my dad bought it with about 3K a few years ago, a year before I got my GS. The pilot needle ("screw") o-rings were completely flat and hard and misshapen and in fact one of the places where it was leaking was the pilot needle on one carb. There was rust in the carb bowls that was kind of alarming, and the float needles and seats were corroded. Well we replaced those parts. Really alarming was how badly ruined the float bowl gasket was. We had to pick it out of the groove with a pocket knife on both carbs and clean the groove. I'm sure this was also leaking. Funny thing is I have never had to replace this part on my GS carbs. I would have expected the condition of all of this to have been much better on a modern Keihin carb bike with so few miles. I think it's the E85 fuel we have around here that's done a number on all of the rubber parts. My dad strictly runs ethanol-free fuel now so it should be good to go for a long time.

As we were working on this my dad shared his frustration that everything on this bike is "fake". Most of the chrome parts are actually plastic and stick on like body panels even though they are made to look like they are functional stuff. In fact some of them even have fake molded-in allen bolt heads, but they are snap-on panels. The chrome "valve cover" are actually just plastic trim pieces that come right off. Even the cylinder fins are not functional; they are just bolted on and are completely removable, which is handy if you want to clean them or paint them. But yeah I kind of get how this really comes off as a bunch of bling. You could remove 50 lb from the engine by taking off non-functional stuff and leave a lump in there that would be more fitting in a lawn tractor. But the thing does run like a top, is far less finicky than my GS, gets 50% better fuel mileage than my Triumph and is just as smooth as butter.


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