Suzuki DRZ400 With Flat Slide Carb

Published on 15 April 2023 at 09:48

It's a funny old game buying and selling bikes. You can't possibly know every single bike inside out so if you are buying something outside of your usual fare it's always a bit of a gamble. That was definitely true with my Ducati Multistrada that took me 5 times as long as I had budgeted for, it also looks to be true for my latest acquisition but in a much more positive way.

A guy I know and have bought many bikes from told me he had bought a few bikes from the widow of a friend of his, he wanted to pass them on fairly quickly as he had sunk a fair bit of cash in to them, which he needed to recover. It turned out that one of the bikes was one of my all time favourites - a Honda CBR400RR, the other was a Suzuki DRZ400 that I was much less familiar with. In fact I have never had one before and had to do a google search to find out what it was. I thought it was a bit expensive but it came with two sets of wheels - one with road tyres and one with off road nobblys, a couple of spare tyres, two spare exhausts and a few other bits. He told me it had not been run for a couple of years at least and that when he tried to start it the carb dumped fuel all over the floor. I weighed it up, figured that there should be a profit if it didn't cost too much to do up and the deal was done. 


He delivered both bikes to me, that was the first time I got to see them in person, I trust Simon from previous deals so it was all good - he hadn't let me down. The DRZ was just how he got it - filthy but solid, no signs of anything untoward apart from a sticky front brake caliper, we couldn't get it to start, but the engine turned over fine and seemed to have good compression.

Once Simon had left I got out the jet wash and gave it a good going over so I could see more clearly what I had - it really did look good and despite some cheap after market stickers succumbing to the superiority of Karcher's finest it looked much better already. 

Being a blokey sort of bloke I had to hear the engine - it's something to do with my hormones I think, the sound of an engine stimulates something in my brain and I'm only ever truly happy when life involves petrol. It didn't want to go at first so a brief shot of carb cleaner was introduced to the air filter and she popped in to life. Only briefly but long enough to tell me there was a spark there and that she was going to be a runner. I tried again and it ran for a wee bit longer, eventually I got it so it would run ok on tickover with some choke but would die if I opened the throttle - classic symptoms of fuel starvation / an excessively weak mixture.

Simon had given me a carb service kit with he bike as he knew it was over filling  - although strangely it showed no sign of that thus far. I decided it was time to take off the carb and see what was what. It was an absolute pig to get off and I started to get the feeling that it didn't leave the Suzuki factory like that - the mixture adjustment screw was touching the starter motor - Suzuki wouldn't put something like that out. HMMMM.

Once I got it on the bench and had taken off the float bowl it was obvious that the carb service kit was not for this carb. It said it was on the packet but it was clearly not right - some investigation was  clearly needed. It turns out there is a popular upgrade available for this bike - a flat slide carb that is said to release another 5 BHP over the standard item and give much cleaner pick up.  It's expensive - about 350 quid at the time of writing - but many people feel it is worth the cost, as had one of this bike's previous owners.

Mine was very dirty, just cleaning the outside took a good while and a whole tin of carb cleaner. I soon found what I believe to be the main problem though - an o-ring on the mixture screw had completely disintegrated and would have been letting a huge amount of unmetered air in. To make matters worse one of the jets was blocked, all of them were coated in varnish from dried up petrol so all need replacing. I have ordered the full kit which gives me a new set of jets, new o rings and everything else needed to make the carb as good as new again. Once that is done it's on to the front caliper rebuild but I don't think it's going to need much more than that.

UPDATE - I have since found out that there are various different models of this bike - mine is the highly desirable e model, which has been upgraded for road use. It has different cam profiles to the s models and produces an extra 9bhp, which is a fair chunk on a bike of this size, you will definitely feel that. I look forward to trying it out when I have finished the various jobs it needs.


Suzuki DRZ400 Right Side View
Suzuki DRZ400 Left Side View
Suzuki DRZ400 Instruments
Suzuki DEZ400 Flat Slide Carb Service Kit

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