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Search for running carbs...
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   Maintenance and Repair -> CarburetorsMessage format
Posted 2017-04-17 10:50 PM (#153056)
Subject: Search for running carbs...


Posts: 5

Location: Huntington Beach, California
Okay, first of all, I'd like to say thank you to all of you on this forum. The information I've been able to find here has been life saving in getting my motorcycle running.

I bought a XS750D in silver, the same model, color, and year as the first bike I ever bought back in the 80s.

A couple of years ago, as part of following "So you just bought a tripple", I rebuilt the stock carbs and replaced the petcocks with some manual ones from MikesXS. I found a post on here about Viton tipped needles and that seemed to be the magic bullet for preventing gas oil. I had my fair share of bumps in the road, racing throttle when I had the carbs too far out of synch comes to mind. I couldn't find a replacement air filter for the stock box, so I bought K&N filter pods. I knew to avoid cheap knockoffs due to possible blocking of the air jets.... Thanks Triples Forum!

Around town the bike was running pretty well. The first time I tried to take the bike to work I lost power in one of the cylinders after running a few minutes at 65-70 mph. I was on the 405 in the car pool lane in SoCal traffic. Not fun to try to get to the right low on power. Boy I was frustrated!

It seemed like it was a fuel issue, maybe the tank wasn't venting properly. I ran with the cap off to rule that out, same issue. Then I thought maybe the screens on the petcocks were clogged. I checked those and witnessed fuel flow out of them, everything seemed fine. I rebuilt the carbs again, pulling out all the tricks I knew of from 30 plus years of riding. Same issue.

My next thought was a vacuum leak. So I found a place (thanks Tripples Forum) that sold the manifold rubbers. Still same issue. I replaced the vacuum tube plugs, same issue.

I started thinking that maybe it wasn't the fuel system after all. I began suspecting the ignition system, so I searched here and found C5 ignitions. The thing about C5 is that you get new coils with the kit, killing two possible problems with one stone. I wasn't fond of adjusting points and individually timing each cylinder, anyway. A few months later the C5 ignition was fitted to the bike. I had the bike running well with the new ignition system for a few weeks and tried to take it to work again. Same issue, though this time I stayed to the right in case the bike took a dump again. I was disappointed, to say the least. The bike went in the garage for 6 months before I got around to working on it again.

So about a month ago I decided to start working on the bike again, even if it was just to sell it. I spoke to Paul at C5 (he's a helpful guy), traced my steps installing the ignition system, and redid a couple of things. No change in symptoms.

At this point I was ready to put the stock ignition system in again, but I didn't save all the parts

Before blaming Paul's system, I considered the possibility that it might be fuel related again, retracing and verifying everything I thought I knew about the bike. I still suspected something in the carbs I ran the bike steady state at 65-70 mph and a cylinder would cut out after 4 or 5 minutes. Okay, time for a fleabay intervention. 300 bucks later I had a set of Mikuni BST carbs off of a 1994 Triumph Trident, and that's where I sit today...
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