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Old 20-06-2014
Arctra's Avatar
Arctra Arctra is offline
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Kawasaki KLX-351-BB build

Back in 2010 I bought myself my first brand new bike ever, a humble KLX250S. When I got it I intended it to be my daily commuter for work and then on weekends it was my fun bike. I learned a ton on the bike, gradually going through a process of modifying it. The guys over at the Kawasaki Forums were a great help and kept encouraging me as I went through the processes.

Out of the box the bikes jetting was horribly lean so one of the first things I did was swap the stock #35 pilot jet for #38 and I put a Kouba fuel screw so I could make adjustments to the air fuel fixture easily. After running it in I put on an FMF PowerCore4 slipon, a Dynojet kit, cut the backfire screen out of the airbox (which in hindsight was probably a waste of time), put on a Twinair air filter on and the bike woke up nicely.

Next came the suspension. Being tight I only upgraded the springs after bottoming out the suspension a bunch of times on my first trail ride. The heavier springs made a huge difference but the valving still sucked. I stuck with it though.

In time I replace bent handlebars, put radiator guards and bash plate on, replaced bent pedals and levers, put a braided steel front brake line on to improve brake feel, changed the gearing by first putting a smaller front sprocket and then a larger rear sprocket on, replaced my broken speedo with a Trailtech Vapor, IMS large tank, and a few other things. I?ll be honest, I put the bike through hell and it just kept going. But eventually the abuse started taking its toll and I had to get the valve clearances sorted. That lasted a while and then even that wasn?t enough. As it stands now the bike will not run and it is just sitting at home gathering dust.

I have been getting more adventurous mechanically of late so I have decided to turn the bike into a full blown project bike. Because the engine won?t run the first thing I am going to do is a top end rebuild in the hopes that it will run again. I ordered a 351 big-bore kit from Bill Blue which comes with a re-sleeved barrel, gaskets, piston and rings. I like the sound of a KLX 351 BB to complement my Beta 498RR! To handle the extra power I will put a set of Barnett Heavy Duty clutch springs in the hopes that it will make the clutch last a bit longer.

Once I get it running again with the stock CV carb I think I will try getting the FCR 35mm pumper carb working (I have had it sitting here in a box for a while after I failed to get it working properly on the 250. I am hoping it will work better on the 351.

Next I will indulge my interest in suspension and buy a Racetech Gold Valve kit from Terry and see if I can revalve it myself. I have bought a copy of the Racetech Suspension Bible which I will read beforehand to try and increase my knowledge. The stock KYB 43mm fork valving has a horrible compression spike as the valving has pretty poor flow. The stock KYB 36mm shock only has low speed compression adjusters, no high speed compression adjusters. I have found the rear end kicks quite badly so reckon some valving work should help that.

I think I would like to have a go at changing the seat profile to make it a little flatter like modern bikes. In time I will figure out other things to do too. Any suggestions from you guys would be interesting.
Old 20-06-2014
ktm wrench ktm wrench is online now
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G'day Dean'o, I would like to have a read of the suspension bible one day. I tried to buy a copy at the Goulburn Amcross from the Shock treatment stand but Grant didn't know how much they were, even though there was about 5 copies sitting on the table with all the other Race Tech stuff .
The Gold valve kit is easy to install but you will have to have a few goes to get the valving stack right for your weight and riding style.
You certainly are getting more adventureos with your mechanical work. Good stuff mate the only way to learn is to play with things and see what happens.
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Old 06-07-2014
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Arctra Arctra is offline
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351 kit install

Well, finally, I kicked off my project today thanks to ktm wrench (a.k.a. Chris) being kind enough to help me out. I tell you what, I'm only too glad he did help me because after today I realise that I would not have been able to do it myself. Not only did 2 sets of hands help, but Chris' knowledge and tricks were invaluable!

I had done as much preparation work as I was comfortable with doing before he came. Coolant was drained, tank, seat, header pipe and cam chain tensioner were all removed first. Then I whipped off the cylinder head cover and cams and wired the cam chain up so it didn't fall down into the case. I also laid out all the tools I thought we would need, and had cleared surfaces so we had space to work on. And I think all of that prep-work was WELL worth it!

Cylinder Head
I had a strong suspicion that my valves were done and needed re-doing, so I had phoned up a couple of places to see how much it was going to cost me to have them re-done.

The cheapest I could find was $300-odd but fortunately there was a guy on the Kawasaki Forums that was selling his near-new head and I got it for $275 delivered. Admittedly it was a gamble buying it as it could have been totally stuffed but I got photo's beforehand and it seemed OK, so I took a leap of faith. As it turns out the assembly was in good condition with the valves still in spec on the stock shims.

The head is off a US bike though I believe, so unlike the Australian head which has the emissions system all closed off (actually, it looks like the Aus one just hasn't had the holes drilled out of the cast and a reed valve put in it).

Fortunately I had some Exhaust Cement at home so I have filled the hole in and will look into getting a blacking plate to cover it nicely. There is also a difference in that the Aussie head seems to have a coolant circuit coming off the radiator whereas the replacement head had a temp sensor in that hole instead.

Strangely, the sizes of the holes is different so I couldn't just remove the temp sensor and plug the pipe connector from my old head in. So instead I have just left the temp sensor in and I have blocked off the coolant circuit with a bolt in the end of the pipe and a clip to keep it in place.

Original 250 Barrel and Piston
After removing the old cylinder head we removed the old 250 barrel and piston. Now, I must confess to not knowing a hellava lot about being able to identify a "good" or a "bad" piston and barrel, but I do know you want your bore to have nice cross-hatching and my old barrel was like a mirror!

On inspecting the piston we discovered that the first compression ring (the top most ring) was actually stuck with its gap closed, so it was nearly flush with the piston. It took a bit of fiddling to loosen it so it opened properly. Surely that could not have been helping matters with the compression? Chris then told me that the "technical term" for the pistons condition was F#CKED!! So the top end rebuild was clearly justified!

Big Bore kit
After I had finished scraping away the old base gasket we were ready to start the installation of the new top-end. Putting the 250 barrel side by side with the 351 big bore barrel it is VERY clear that there is a BIG difference in the bore size!

Chris did the installation of the new piston so as to save himself the pain and frustration of watching me fumble around with it. Whilst he was doing that I oiled up the big bore, wiped it clean to get ride of any manufacturing rubbish left behind. Then it came time to try slip the barrel on over the new piston. Although I have a piston ring compressor it was too big to use on this job I had to rely on Chris' skill. The old zip-tie trick didn't really seem to work that well due to the spacing of the rings and the fact that the biggest zip-ties I have weren't wide enough. Anyway, between Chris and I (mainly Chris) pushing on the rings to get them into the barrel we managed to line everything up and get the barrel on. How people do this job on their own is beyond me! It HAS to be a 2 person job as far as I saw.

With the barrel installed we slapped on the new cylinder head and install the cams. Fortunately for me Chris insisted on re-checking the cam timing and we discovered that I had put the cams onto the chain 1 tooth off where they should have been. We went through the process of adjusting it and then bolting everything back together for the second time, and this time we were happy that the timing was right. If it had been me doing the job on my own I would have thought the first setup was OK and no doubt would have trashed the top-end.

Chris helped me get things back together to a point where I can go through the process of getting it into a running state now. I need to put coolant in, new spark plug, re-jet the carb and fit it up again, and then temporarily fit the tank again to see if I can get the bike running. I just need to motivate myself to do it now as I am feeling pretty stiff after yesterdays ride. Here's the final 351 Big Bore Kit and new cylinder head installed:
Old 06-07-2014
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Wellsy Wellsy is offline
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please use something better than a bolt and that style of clamp to block that pipe. I would hate to see so much hard work wasted if that thing pops out under pressure. If you were sweep on a ride no-one would be able to see you dropping coolant. I just noticed you have a temp gauge. I would still keep a eye on it though.
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Old 06-07-2014
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Arctra Arctra is offline
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Originally Posted by Wellsy View Post
please use something better than a bolt and that style of clamp to block that pipe. I would hate to see so much hard work wasted if that thing pops out under pressure. If you were sweep on a ride no-one would be able to see you dropping coolant. I just noticed you have a temp gauge. I would still keep a eye on it though.
Fair point - thanks. I have just put a small screw clamp on the end and made it nice and tight to it is squeezing the rubber tube against the threads of the bolt nice and tight. I'd be very surprised if it was to pop off, but I will probably look to getting a new radiator hose to replace the stock one and not put in the T-piece that the little pipe comes off.
Old 06-07-2014
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kawasaki glenn kawasaki glenn is offline
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Enjoy reading your bike builds Arctra, I went through the same with my KLX450,valves were toast and pale rider helped me take the head off ready to be sent away,I always shied away from mechanical work but after seeing how it all comes apart and how little there is to 4T's im much more confidant of tackling stuff myself.cost me $550 for new delwest KX intake valves,4 new guides and seals and re cutting the seats,a lot better price than I was expecting and will be more reliable.

I look forward to seeing how your bigbore kit goes on the 2 fiddy.
Old 06-07-2014
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Battered Sav Battered Sav is offline
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Great thread mate, well written and enjoyable reading, thanks.
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Old 06-07-2014
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Arctra Arctra is offline
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Carb holder headache

It took some motivation, but my impatience eventually overcame my lethargy so I headed to the garage again and re-jetted the carb. I have a Dynojet kit for a KLX300 which worked very nicely with my 250 bore running a 128 main DJ jet, 38 OEM pilot, and needle on the 4th clip. According to guys on the Kawasaki forums the best starting point for the 351 kit is to open the fuel screw another turn using the 38 pilot, bump the main jet up to a DJ 132 and leave the needle where it is. So that's what I did and then went to put the carb in.

I suspected the carb slid into the carb holder on the cylinder head rather easily but in the poor light I just put it down to a bit of good luck... until I inspected it closer. There was a ton of free play - something clearly wasn't right. So I whipped it off and compared it to the carb holder on my original cylinder head. BIG difference!

On the left is the original holder and on the right is the holder that came with my bought head:

Putting the original holder on top of the replacement one it became obvious that I wouldn't just be able to move my original holder across to the new head as the new head holder has mounting holes quite a bit further apart.

My first thought was that the port sizes of the cylinder heads were different too, but when I measured them with the veriers I was relieved to see they are the same at about 32mm. The inside diameter of the original carb holder where the carb goes in is just under 40mm if I read the verniers correctly, but the replacement holder has an inside diameter of 46mm. That's quite a difference, right?

So now I need to figure out what to do. I'll contact the guy I bought the head off to see what carb he was using. The way I see it I have a few choices. The cheapest solutions would be to figure out a way of "filling out" the OEM carb neck so that it fits in the larger diameter of the holder I currently have that fits (the one that came with the head). But that's quite a significant amount of spacer I'll need to add and I question how reliable it'll be. Next option is to try and get a new holder that'll fit the wider apart holes of the head that I have with an inner diameter of my OEM carb neck. The other option is to get an FCR carb that'll fit the carb holder neck and airbox I currently have.

Given I already have an FCR 35mm carb which I had intended putting on the bike once I have run it in, ideally I think I'd like to go the way of getting a holder that fits my head and has the right inner diameter. But the FCR 35mm carb is a fairly basic pumper carb that is nowhere near as tuneable as more modern FCR-MX carbs. If I go that route I will really be in the dark with tuning the carb though as I have not seen anyone on the Kawasaki forums or elsewhere that is running the larger FCR-MX style carbs.

Decisions decisions!
Old 07-07-2014
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Pygmygod Pygmygod is offline
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When you put the cam chain back on how did he check that it was 1 tooth out?

Do he just line up the TDC marks again?

I've done my valve clearances once but was only following the manual without a skilled person to assist...
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Old 07-07-2014
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that extra coolant hose im fairly sure just leads to the fuel bowl, its because the Aussie spec KLX's were also supplied to Japan I think where they need to have antifreeze around the carby bowl during winter.
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