TRAIL ZONE

ASK DR PHIL

SUZUKI DR-Z400E FLAT-SPOT

Hi Dr Phil: I have a 2006 Suzuki DR-Z400E, that I bought second-hand in May 2009 with 3,800km. It's a good clean bike in stock form (I think). My issue is that it has a big flat-spot off idle and I have found this to stall the bike on the odd occasion. I have screwed the idle up to help stop it from happening, but it still really bugs me ... not to mention the fast idle on steep downhills! This bike still has the original muffler (will upgrade to a TK Pipes muffler when funds permit) and I run a premium fuel and always a clean Twin-Air filter. I gave the bike a full service when I bought it and it now has approx 4,800km on it. I still run the stock gearing 14/47. I want to know: 1. Are there any carb adjustments I can make to improve the flat-spot, as I read in mags about clip changes etc? 2. There are a couple of carb kits on the market (JD etc), do these fix the problem or give better performance? Are they worth it? Please note that I do not need extra performance (but wouldn't complain if it was given), as I would much prefer to keep fuel range for longer distance trips. I have a crap load of TRAIL ZONE back issues but I did not see that you touched the carb on your project DR-Z. What's your opinion?

-- Tim Stone, via www.trailzone.com.au

Thanks for your email, Tim. All the DR-Zs that we’ve had as test bikes and long-term Project Bikes have been de-restricted before they reach us. So first of all, check with a dealer what de-restrictions are required and check that these tasks have all been done to your bike. That's why we never even mentioned the jetting on our last DR-Z400E Project Bike -- it ran perfect as it came to us, and never even needed touching after installing the TK Pipes muffler. But, back to your bike: here are a few issues you should get into: Start by unscrewing the carby drain plug and keep the plug upright when you remove it. Look into the plug and see if there’s a droplet of water in there. Then turn the fuel tap on and flush some fuel through the carby with the plug removed, just be sure to have the bike standing straight up for this, not leaning over on the side-stand. Also remove the fuel tank and flush it out into a clean bucket, and again look for any crap laying on the bottom of the bucket. Check for tightness of the clamp that holds the carby onto the rubber manifold, as an air leak in front of the carb can give a flat-spot. When the fuel tank is removed, open up the top of the carby and remove the needle, write its number down and count which clip position the clip is in, as a dealer will ask you what the needle number is and where the clip is positioned. Also buy a brand new spark plug and fit that, so you’ll know that isn’t the problem. I don’t know of any common issues that this bike has with regards to a flat-spot, but it sounds like something has happened during the time someone else has owned the bike. As for the JD jet/needle kit, yes they can offer cleaner running but I feel you need to sort this issue first, otherwise you’ll fell disappointed if you get the JD kit and the problem is still there. Let us know how you go after doing all of the above, Tim. I also assume that you’re not just twisting the throttle on too quickly: remember that DR-Zs and many trail thumpers won’t rev up as sharply as a two stroke will! Good luck! 

-- Dr Phil.