Hey all, just wanted to give a quick update for those that are considering installing a big bore kit and wondering what to expect. I have had my bike for a few months now (2007, bank repo, roughly 3200 miles) but just not fully happy with the torque for my wt (215). Preface all of this in that I havent really done any real engine work at all prior to this for those questioning their abilities. Did the free mods previously, rejetted with the 300 DJ kit, 13T front. Wanted more so i opted to go with the 351 kit. was considering paying someone but have been real unhappy with dealership capabilities here in Richmond VA. Decided to have a go at it myself.

Whole process took me probably 7-8 hours or so (one late night/ one real early AM). Would have gone better had it not been for a tired evening, followed by a whopping 4 hours of sleep and a worse morning (and a wife and children who were determined that my attention be with them :P) Really not a bad project. Read through the manuals a few times and studied the parts diagrams to make sure i understood the whole process as much as i could before i dove in. Only a few problems in the process. For those of you doing this, watch out for the spring and washer on the fix mounted cam chain guide which is located in cylinder. For some reason this doesnt show up on the manuals i have but the whole assembly sprung loose during the last phase of disassembly. Not being sure what happened other than stuff went flying everywhere , I stuck my stick magnet into the cam chain chamber to do some fishing and found a cylinder dowel pin (DOH how did this get here...). pulled out a flashlight and looked down to find the missing washer under the cam chain and fished it out with a magnetized screw driver. getting the cams right during reassembly was the only real challenging part and took me more attempts and some swearing than care to admit before i had it right. got it back together fired it up and watched oil spraying from the gasket on the cam cover. Once again, DOH! stupid tired mistake, somehow had two bushings on one bolt (i really need to do this with sleep), tried to lift tank enough to tighten it and tore a fuel line (oh god, why am i spraying 93 octane all over the garage....hope the pilot on the water heater doesnt make a bad combination.....once again....DOH!!!). Ran out to napa, spent 2$ on some fuel tubing, fixed it and it actually ran!

After doing a heat run and sure i had everything right, took it for a little spin. Seems someone put helium in my tires while i was working because the bike lofted the front end for the first time ever. I wanted to have a little party as i shed a tear of joy.....now if i can have the patience to break it in a bit....

I think the carb needs some additional tweaking which i need to do. I upped the main jet from the DJ 128 to the DJ132. still at 2.5 out and didnt try any changes on that. I dont have any pilot jets (stock), but am ordering the 38 and 40 today. Throttle response lost some of its low end snappyness that i had right after the DJ kit original install when the big bore was done. Low end and idle are not the same, but i was expecting it to be not be the same. Seems to run better cold (which my first guess is pilot jet from what i am reading). Any suggestions from those that have done this before would be great. Still on the stock exhaust right now (with a few breathing holes in the back plate), but am guessing I will throw a q4 onto it soon. Also thinking about going back up to the stock 14T front sprocket.

All in all, if you have some patience have a crack at it. Read any manuals you can get your hands on several times first. Take digital photos at everystep so you remember what things looked like before you dug in, use labeled baggies for fasteners at each step to avoid confusion. It was fairly simple to do. My only other mechanical work was auto shop in high school roughly 25 years ago, tearing apart a 5 HP B&S go cart engine and putting it back together. Make sure you have a couple good torque wrenches (i bought a 1/4 inch for low range torque) and the 3/8 i had. an antenna magnet is also a good idea . This far and away was the most significant change to the bike that I have made and am REALLY happy with results so far. Hopefully everything will hold for the long run, if not i wont be so nervous to dig in again. For those of you considering it, go for it, i think you will be really happy with it!!!

 

My 351 is running perfect with a 132 main, stock pilot, 1.5-2.5 turns out, and the DJ needle on the 4th clip I believe..

Bike starts in a half second every time, and runs like a dream.

Good job doing it yourself! No reason to bring it to a dealer. If you ever had to do it again you could probably do it in half the time. I changed my head gasket to the new design, took me a tad over an hour start to finish.. I'm a pro at this motor now

Good luck

 

Congratulations on tackling this job yourself. I may try increasing the displacement this winter, but am worried about the exhuast. The exhuast will have to be changed to increase air flow, but I do not want to increase the noise factor.
I like a quiet bike, and all of the aftermarket exhuast systems seem to add a significant noise factor.

 

Im running the stock exhaust with the BB and it works fine. I drilled a few small holes around the main tube, but i dont think they do much (and may be patching them up as i dont want to kill the SA for riding in the woods. I had the same concerns but spoke to a few ppl who did it with the stock exhaust and they both really liked it.

I took it out for some offroad for a little bit today and the low end grunt on the bike is really amazing now compared to what it was. Much more enjoyable onroad too. i almost tossed myself off by being a little too aggresive in starting out on the road and lofted the front end in second with a cranked exhaust..... Dont think its a necessity, its not and by far hands down the best mod on the bike, stock exhaust and all!

 

Hey Mattyw
Thanks for the good info, but now I am really confused.
It is my understanding that an after market exhuast is required to allow more air movement that is required to generate more power. Now, it seems that the original exhuast will allow more air movement to generate this power.

What are we talking about here for a 330 or 351 kit, about $600? If so, I may have a project this winter.

 

Even though the bike is still choked off it still produces significantly more power with the big bore and stock exhaust. See Bills Website here and look at the 351 dynos with and without stock equipment. Much better with a new exhaust but compared to the stock numbers the big bore is also a huge improvement. http://bandbcyclerestorations.com/page_2.html

I dont know how much my drilling around the outside of the pencil exhaust really affected it or if the restrictions are really deeper in the exhaust. It sounds nice and runs like a champ now though. Bill charges $527 for the 351. It really is like riding a different bike...was just out for a bit and i can easily loft the bike in two gears now, which i could not do at all before the switch!

 

Larry, you're at Sea level right? I'm probably going to order the kit very shortly and I'm looking at using the stock carb. Thanks

 

Yeah, I ride at the most like 2k feet.. But 98% is SL to 1k - runs great with stock carb.