[110rider]

Does anyone know how fast an XR75 is compared to a stock KLX110? I have a non running 78 project XR75 and I was just curious.

 

[dustinmoto425]

why is that even a factor? are you drag racing or something?

 

[110rider]

why is that even a factor? are you drag racing or something?

I have a big bore 110 and the guys I ride with have all gone back to stock 110s. I don't really want to remove the big bore from my 110. I was hoping that once I finish the XR75 its speed will be close enough to a 110.

 

[GSjimmy]

If your worried about speed, you are giving up 35cc's of displacement and 1 gear. This will cause you greater RPM drops between gears. Also, there is limited gear sets available for the XR75/80. In '79 Honda bumped the displacement up to 80CC (79 cc) and added a 5 speed trans for improved reliability.

Gear set is either 13/46 or 14/44, with the first set being "opimal" for trail riding (steeper, with better pickup). The 110 has you at a disadvantage from the git-go. It should have a better torque output due to a larger displacement, so with simular gearing, it will win (on paper anyway) the drag race. Weight will also play a factor in this question. The Kawi will be lighter due to improved suspension and aluminum componets. The XR is just cool looking. The nickname for the XR is the "Trail Tractor", she ain't fast, but will get the job done. I believe that our '79 XR80 topped out around 50 mph. Kept up with the CR125's fairly well on trail rides, but was never first.

So if I have not scared you off yet there is a couple theings you can do to the bike to wake it up. Install a hot rod cam into the engine, and bore it as far as possible. Bigger valves and more compression helps too. Add in an after market pipe, or build your own. Look at VintageMX's post for ideas there (he built one from scratch).

As for weight, an aftermarket aluminum swingarm and slightly longer (13 inch) piggyback shocks. Get the frontend off a KX80 to get better travel and weight reduction (aluminum rim & disc brake), also convert to taper steering bearings instead of "damn it" loose ball bearings. There is also a frame cradle you can add to stiffen the chassis and protect the engine.

Poor man's way - Get a XR100 or CRF100 complete engine/electronics and bolt it in. Now you only gave up 10 cc's and the rider can overcome that difference. Bonus here is CDI instead of points. Then try to shave as much weight as you can. If you add an XR100 swing arm you can run a larger CR80 rear wheel (bonus - aluminum construction).

If you end up with more than 600-700 bucks into the bike, don't expect to get it all back at sale. Which everway you go it will have the cool factor going for it. Plus your going to know what you have with the satisfaction of building it yourself.

Jim

PS. I have an engineless '79 XR80 chassis.

 

[Maktastik]

But still stock 110 are way faster out of the corners then a xr100

 

[110rider]

Thanks for the feedback. The XR has the cool factor and will be fun to rehab regardless of the resulting speed. The forks and front rim are bent. Now the decision that I have to make, replace it with stock or go with a longer fork and swing arm.

 

[GSjimmy]

If you go longer on the forks, either CR80 or MR175 will work. VintageMX cut a set down on his & it worked out slick. The rear is stock at 11.8" (shock length). The piggy back China shocks on ebay are 13.1". I have the 12.0's on my '79 XR80 and they work nice and hold a 180 lb rider w/o issues. The "vintage" XR dual shocks are way cool and no one sees much of them. Had ours over to Aztalan this September and it drew a crowd.

For rims, go with the CR aluminum rims. You will need an XR100 swingarm though.

 

[storminnorman07]

Does anyone know how fast an XR75 is compared to a stock KLX110? I have a non running 78 project XR75 and I was just curious.

Stock vs stock max hp outputs are pretty similar. As already stated the lighter klx chassis will accelerate and feel faster than the xr 75. This is a apples verse advark comparison. Both can be made to go faster....the klx will do so with less effort put forth and less money due to all the aftermarket support. Where as the xr 75/80/100's don't have many aftermarket performance mods. That doesn't mean cool shit can't happen with them just means it will have to be custom ;-) here are some setups that I have done and posted 1973-76' xr 75 now supporting 150cc and potentially may jump to 160 some odd cc's here this winter.http://planetminis.com/forums/vinta...da-xr75-jdm-vertical-motors/173142-if-only-takegawa-made-head-73-76-xr-75s.html

Here's a huge valves xr 80
http://planetminis.com/forums/bigger-minis-forum/164064-start-big-huge-valve-xr-80-head.html

Here's a +r big titanium valves xr 100
http://planetminis.com/forums/bigger-minis-forum/174885-takegawa-xr-100-r-make-over.html

And if you want a true one off piece check out my mutant.
http://planetminis.com/forums/bigger-minis-forum/162221-mutant-motor-xr-klx.html

 

[110rider]

Will the CR80 or MR175 triple trees bolt in without mods? Stormannorman07, wow, nice work. Wish I could do that, I am just a bolt on wrench.

 

[GSjimmy]

Shoot Bill (VintageMX) a PM and ask what all he did to make it work. I believe the triples are a bolt on. Fork length was custom. Rims are 1980/81 CR80. Depending on your budget, XRminiracer.com is a good source for parts. They do have swingarms, frame cradles and such. They also carry "Mini Mudder" front fenders in the correct Tahitian Red.

One cool mod I did on the KX/XR conversion was to cut the sprocket cover to reveal the front sprocket & chain. Should keep it running "cleaner" with this extra access. Easy to do with a sawzall & grinder. Cut it close and grind off any excess. If you mess up, there are brand new covers on ebay for cheap.

 

[110rider]

Shoot Bill (VintageMX) a PM and ask what all he did to make it work. I believe the triples are a bolt on. Fork length was custom. Rims are 1980/81 CR80. Depending on your budget, XRminiracer.com is a good source for parts. They do have swingarms, frame cradles and such. They also carry "Mini Mudder" front fenders in the correct Tahitian Red.

One cool mod I did on the KX/XR conversion was to cut the sprocket cover to reveal the front sprocket & chain. Should keep it running "cleaner" with this extra access. Easy to do with a sawzall & grinder. Cut it close and grind off any excess. If you mess up, there are brand new covers on ebay for cheap.

Thanks. Work to begin as soon as the weather turns too cold to ride.

 

[GSjimmy]

Come up by me. The weather is already here.

 

[110rider]

Found a nice set of MR175 forks on eBay today. Now I am committed to long fork and swing arm.

 

[hobbeekid]

Ummm the 77/78 xr 75's came with a five speed gear box also, to make it competitive, with the 110 add a 82cc big bore kit, cam, some porting ,& a pipe will wake your xr right up! Or find a xr 80 and put a 98cc big bore kit with the same mods and it will really wake your bike up! I had a 98cc one once upon a time & I loved the performance!!!

 

[110rider]

Ummm the 77/78 xr 75's came with a five speed gear box also, to make it competitive, with the 110 add a 82cc big bore kit, cam, some porting ,& a pipe will wake your xr right up! Or find a xr 80 and put a 98cc big bore kit with the same mods and it will really wake your bike up! I had a 98cc one once upon a time & I loved the performance!!!

i am finding it difficult to spend $170 on a big bore piston and rings and then another $50 or so to get it bored. My thought is to put a stock piston in it and ride it until I find a good deal on an xr100 motor. The 100 seems to be a better way to go in the long term.

I am making the assumption that a stock 100 engine performs better than a 75 motor with a 50mm piston. Is this assumption correct?

 

[hobbeekid]

Sorry for the long time reply, the 100 will make gobs more torque over the 75 based on displacement alone.however ,it's been brought to my attention that the 100 cylinder head has ports that are huge compared to the xr75/80 head and that the smaller xr80 port will make better power down low with better veloctiy. Plus now you can get a xr80 poked out to 119cc! the xr80& 100 share the same stroke..

 

[110rider]

Thanks. I decided to do a top end on the XR75 engine. I will still keep a look out for a low price XR100 engine.