Project Husqvarna TE610 Part 6: Horsepower and Handlebars

,

Valve adjustment
On the remaining list of work to initialize the bike was checking valve adjustment. Some people do gymnastics to check the valves without draining the coolant, but there’s so little and it’s so easy to do that I found it faster and easier to just dump the water and get the radiators out of the way. The bike’s age, if not mileage, meant it needed a flush anyway.

Valve lash is adjusted through covers on the top of the cylinder head. The job is a challenge with a conventional feeler gauge set, but this Motion Pro tappet feeler gauge makes it easy. The spec for intake and exhaust valves on the TE610 is 0.002 in. The Motion Pro tappet feeler gauge has leaves at 0.002 in. and 0.003 in., so you have a “go” and a “no go”. The leaves are just big enough, and at the perfect angle, with the handle providing the stiffness to slide them in and out without twisting or bending the leaves excessively. The gauges are available in several sizes to suit different bikes. The Motion Pro feeler gauge ends up being a lot cheaper and more convenient than buying a complete set of normal feeler gauges just to get the one or two that you need to “customize” to get this job done. The Motion Pro feeler gauge doesn’t come with any sort of case; I found the telescoping plastic case a 1/2-in end mill comes in works perfectly for protected storage.

Husky TE610 valve covers leak, covering the cylinder head in oily dirt. The gaskets are OK, but the holes for the bolts holding the covers go all the way through the cam carrier casting, so oil wicks up the threads and out under the bolt heads, regardless of the gasket’s condition. To stop that, I installed reusable Parker Stat-O-Seals, purchased at McMaster-Carr. You could also use RTV silicone or Loctite #518 anaerobic sealant, but I didn’t want to have to scrape those off and re-apply to the bolts every time they’re removed.

Analog mechanical fuel delivery
Cleaning the carburetor is certainly a good idea on a bike that sat parked so much more than it was ridden, even though my first rides near home on pavement revealed no issues. Cleaning the carb was also the perfect time to rejet (how cavemen tuned fuel maps). There are many “how to” guides for jetting a Keihin FCR carb online, and you should find a few and read them if you want to really understand. It’s not complex, just different than milliseconds of pulsewidth, duty cycle, cc/min or lb/hr and psi.

Many TE610 riders have good results with a set of jetting specs attributed to “someone at Malcolm Smith Racing”. These specs are the same as an old post on ThumperTalk titled “Jetting your 2006 TE 510”, which has the same basic carb as the TE610. Given the number of positive reports, I figured that would be a better starting point than stock. There are a few differences between the TE510 and TE610, which allow you to skips some steps from the instructions mentioned above. I just installed the jets – it was most like “Option 2”.

Remember when I said the Keihin FCR series of carbs is shared with most modern four-stroke dirt bikes, and how that’s a good thing? It means you can buy Husky parts at the Yamaha dealer instead of the BMW dealer. Other part numbers provided are for Sudco, the default aftermarket distributor of jets for Keihin and other carbs, even to most OE bike dealers.

After everything is clean, but before installing any jets, check float height, which was perfect on this bike. Float height in a carb is the equivalent of fuel pressure in an EFI system. If it’s wrong, everything else will be, and you’ll just chase your tail trying to get it right. It’s also worth checking the throttle position sensor readings, which are used by the ignition system to determine timing. If there is a problem with your TPS report, the bike may respond sluggishly or ping. This one was right in the middle of the ranges specified in the manual, both when closed and wide open.

The Keihin FCR uses the combination of pilot jet and fuel screw to set the mixture at idle and small throttle openings, tapering its influence above 1/4 throttle but with some minor effect at all positions. This is the most basic adjustment, and the only one that can be changed externally, as the carb designers recognized the need for it to be tweaked regularly for optimum performance when weather conditions change. On the other hand, you can just run the recommended initial setting and will probably be happy.

Many people like their results with an iridium spark plug, so I threw in one of those, too. It’s supposed to really help with an on-off-on throttle stumble that I had noticed several times with the Husky. With a better understanding of jetting, my thinking is that excess fuel delivery caused by the plugged leak jet on the accelerator pump causes a rich bog if the throttle is opened quickly, and the iridium plug helps fire through that and make it less apparent. So call this a “belt and suspenders” approach.

I also changed the fuel hoses to new, 1/4-in diameter hose stretched over the Husky's weird 7mm barb fittings, and added an inline fuel filter between the petcock and the carb. These filters with clear plastic housings and sintered metal filter elements cost about $3 at any dealer and are worth far more than that in peace of mind. 

Overall, I’m happy with these settings. The bike definitely has crisper throttle response and pulls stronger than it did with stock jetting. With the #60 leak jet to dial back the accelerator pump volume and the iridium plug, the roll-on stumble has not recurred. These results are totally worth the $80 or so they took to accomplish (jets, needle, Flex Jet and Iridium plug).