"...that hole in the end of the main nozzle is not supposed to be oval - it should be round."
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by: Martin "Tiny" Squire - ISRA#53 Long and the Short Version If you don’t want to read the whole sage and just want the juicy bits skip to the ‘Executive Summary’ at the bottom of the page. Background For those of you who don’t know the story a bit of background to set the scene for this long saga is worthwhile. I am the proud owner of the custom VStar (originally called the Dragstar downunder until Yamaha marketing realised that calling a macho bike a name usually associated with men dressing up in women’s clothes probably wasn’t a good idea!)
I’ve owned this bike for over three years having purchased it second hand with around 1400km on the clock back in Easter ’98. At around the 12,000km I purchased and had installed a BAK along with a set of Jardine dragpipes with HP Plus baffles. Bike ran really strong with this combination of pipes and jetting and averaged around 250km per tank before switching to reserve. The Problem At around 32,000km mark I started to experience a very small but annoying problem. First symptoms I noticed was a slight increase in fuel consumption ie dropped from around 250km a tank down to 235-240km. I mainly use my bike for commuting with the occasional longer trip. The other main symptom was a very slight stumble off idle - I could describe it as a cough or misfire but essentially what would happen was that the bike would stumble and then work through the stumble and be ok. Top speed cruising etc was fine with no problems. The problem would only occur when using very light throttle to accelerate. Try to imagine taking off in 1st gear and holding the throttle at a fixed position. The stumble would occur between 20-30 km/hr. At around the 34,000km I thought I would take my bike in early for its service to see if the problem could be identified. Unfortunately at that stage I hadn’t worked out how to replicate the problem so my mechanic was unable to identify the problem or offer a possible solution. After the service my fuel consumption dropped even further - now down to around 225km per tank. At this stage I was starting to get quite frustrated as I rely on my bike for full year round transportation. Following on from the success of Steve ’Sandy’ Manthorpes’ dyno success I decided to get my bike dyno’d. While I was happy that the mechanic to identify the problem he wasn’t able to solve it by changing the jetting. After the dyno fuel consumption dropped even further, now down around 190km per tank. At this stage it was time to get serious - extra fuel was costing me money as well as a bit of heartache. My intentions with this bike is to hang on to it until around the 70,000km mark so I needed at least another 2 years reliable service. I’ve got half an eye on the new Roadstar Warrior as a replacement but I don’t think its coming to Australia. Possible Solutions Fellow Australian V-Star rider Steve Manthorpe started to sit down with me and work through what the possible problems could be. Now I’m not a car or bike mechanic (much more happier installing a hard drive than disassembling a carburettor) and usually leave that sort of stuff to those who know what they are doing. Steve convinced me that the jetting part etc wasn’t really that hard or difficult - he was right. Our first Saturday morning was spent disassembling the carbs and checking for obvious signs of wear. The only thing we could find was a slightly worn main jet. This came as a bit of a surprise to me not realising that petrol was an abrasive and would cause brass components to wear. Main jet was replaced and we also replaced the pilot jets (Barons, maybe #27.5) with stock pilot needles (#20). The following day we went on a ride around 600km down the beautiful Australian coast. Problem had only occurred one or twice during the warmup, fuel consumption was back over the 200km mark and we thought we had the problem fixed. That was until around 7pm that night on the run back into Canberra when I started to slow down and the bike just about died after coughing and spluttering. Time to have another look at the carbs. As a good way of testing to see whether the problem was to be found in the carbs or electrical Steve very kindly offered me his carbs. A day of riding around with Steves carbs attempting to induce the problem convinced me that the problem was to be found in my carbs. Time to strip the carbs down again.
This time I removed all the components I could inspecting each for wear, this included main jets, needle jets, floats and the main nozzle. Eureka ! Both of the main nozzles were worn - you may be able to see the wear in the photo below but that hole in the end of the main nozzle is not supposed to be oval - it should be round.
The problem had arisen as a result of the needle moving back and forth in the main nozzle - titanium rubbing against brass or even just touching the brass when it moves results in the wear. Now on the bench it looks like the needle should never touch the sides of the main nozzle - however with vibration, flow of fuel etc etc, rough roads, you name it that needle will touch the side of the main nozzle. Cost to solve this problem - around A$100 for two main nozzles - and the wonderful advice from a bike mechanic - "We always change that part when we swap needles..." Duh! Follow this link to take you to a exploded diagram and order the part if required. It is Part Number 11. In hindsight the solution to this problem should have been obvious, something was wearing out causing the bike to run rich and the problem would be with the carbs. Despite talking to two different bike mechanics, posting on the ISRA board and hours of searching the net I haven’t found any one else who has had this problem. My bike now has just over 40,000km and back running strong - I’m looking forward to the next 30,000km and any other challenges along the way. My last tank of fuel got me 253km before hitting reserve - a lot better than 195km ! Executive Summary ( aka the Final solution )
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