Jump to content
Sign in to follow this  

XL 75 Modifications

Recommended Posts

I picked up a 1979 XL 75 and I was wondering what were some good options for motorswaps or performance mods. Also, what are the differences between it and a XR?

Share this post


Link to post
Share on other sites

Not sure about the upgrades, but the XL is the street legal version of the XR the XR was only and off road bike accept the XR250L which was street legal...

Share this post


Link to post
Share on other sites

I believe the '86 XR100 engine will fit into the engine mounts

of the '79 XL75. The bolt diameters are the same and I believe

the case holes are in the same location.

The '79 XL75 coil does not include an external condensor (its

condensor is with the points under the left case engine cover),

so get the XR100R's coil, too.

The rubber tube and air box for the '86 ProLink XR100 is different

than for the twin shock era ('81 - '84) bikes. Either use an

aftermarket cleaner or consider sourcing an XR100 tube and

air box from the twin shock bikes. There is some air box part

sharing between the '84 XR100 and XR80, but the '79 XL75

uses different tube and box components.

TUBE, AIR CLEANER CONNECTING

'84 XR100 17253-KA9-000

'84 XR80 17253-176-000

'79 XR80 17253-176-000

'79 XL75 17253-152-010

COVER, AIR CLEANER

'84 XR100 17228-153-000

'84 XR80 17228-153-000

'79 XR80 17228-153-000

'79 XL75 17228-152-770

HOUSING, AIR CLEANER

'84 XR100 17230-KA9-770

'84 XR80 17230-176-750

'79 XR80 17230-176-750

'79 XL75 17230-152-770

While the XL75's exhaust manifold might mate to the XR100's

head, it is small and would restrict output. An OEM XR100 from

a twin shock era ('81 - '84) ought to bolt right up - the attachment

hardware and gasket for the pipe is available from Honda, but

try to get all the fasteners included when buying a used OEM pipe.

The XR100R uses a 428 pitch chain while the XL75 has a 420.

I don not know whether the XL75 drive sprocket will fit the XR100

output shaft - this would allow retention of the XL75/XL80 driven

sprocket with its integral tabs that engage the cush drive rubbers

in the hub.

Some differences between a 1979 XL75 and the 1979 XR80.

(Note that several if not all of the '79 XR80 parameters below

were the same for the '78 XR75.)

** === 1979 XL75 ================================= **

Carb: PC08 (15mm)

TUBE, AIR CLEANER CONNECTING - smaller outlet than XR to suit PC08 carb inlet

Exhaust: Smaller head pipe dia than XR

Stator: Primary winding for ign and secondary winding for lighting/charging

Ign Condensor: Under left cover

Trans: 4 Speed (1 down/3 up)

Final: 14T Drive/36T Driven

Chain: 420 (94 links) Roller dia: 0.3125

Engine Mount Bolts

Front: 8X60

Rear: 8X95

** === 1979 XR80 ================================= **

Carb: PC10

TUBE, AIR CLEANER CONNECTING - larger outlet than XL to suit PC10 carb inlet

Exhaust: Larger head pipe dia than XL

Trans: 5 Speed (1 down/4 up)

Stator: Primary winding for ign only. No secondary winding for lighting/charging

Ign Condensor: With coil under tank

Chain: 420 (100 links) Roller dia: 0.3125

Final: 14T Drive/46T Driven

Engine Mount Bolts

Front: 8X60

Rear: 8X95

** === 1986 XR100R ================================ **

Carb: PD80B

Trans: 5 Speed (1 down/4 up)

Final: 14T Drive/

Chain: 428 Roller dia: 0.335"

Engine Mount Bolts

Front: 8X62

Rear: 8X102

Edited by EddyCurr

Share this post


Link to post
Share on other sites

incidently, while the '86 XR100R rear mount bolts are 8x102,
the '84 XR100 twin shock uses 8x95, like the XL/XR 75/80.

 

The XR100 cases are the same for '84 & '86

 

CRANKCASE
'84 XR100 11100-KA9-681 - Right
'86 XR100 11100-KA9-681

'84 XR100 11200-KA9-681 - Left
'86 XR100 11200-KA9-681

Share this post


Link to post
Share on other sites

Would a 1986 xr 100 motor bolt in?

 

Yes it does :thumbsup:

 

As Eddy said, different exhaust, carb, manifold and rubber boot needed , sprocket fits shaft.

 

But you will lose your lights, cause the XR series don't provide a light coil. Maybe, i'm not sure, your existing light coil can be transplanted into the XR stator plate.

 

If so, you still got no light yet. :naughty:

 

That's because the XR flywheel offers only two magnets for ignition, and two dummies for weight ballance.

But you can use your 75cc flywheel with the XR100 engine too.

Just laydown the two flywheels side by side, and you will see the different timing marks (be sure the woodruff keys are parallel)

Take over the 100s timing marks on the 75 wheel and enjoy.

 

I think, the woodruff keys are slightly different - 4mm at the 100 and 3mm at the 75.

Grind down the 100s key on both sides to 3mm (where it takes part in the flywheel) and everything will be OK.

Don't forget to lose the flywheels with the right tools. Otherwise you will damage the scarce wheels forever.

Tighten up the wheels very, very strong.

 

Alex

 

@EddyCurr - The PC08 venturi diameter is just 15mm. No XL75/80 ever had a 5speed tranny, just the lustless 4.

Edited by Alexxxx

Share this post


Link to post
Share on other sites

@EddyCurr - The PC08 venturi diameter is just 15mm.

No XL75/80 ever had a 5speed tranny, just the lustless 4.

Alexxx, thank you for pointing out the PC08 venturi dia error.

Ditto on the '5 speed XL'. However this one is a typo. My intent

was to list differences between the '79 XL79 the OP owns and

the '79 XR80, as he requested. But the list for the latter was

captioned as '79 XL80, instead of XR80.

Fixed now.

About the Woodruff Key. Both the '79 XL75 and the '86 XR100

call for a 3mm - p/n 90741-035-000.

Edited by EddyCurr

Share this post


Link to post
Share on other sites

you can always get an aftermaket lighting coil (stator) for the XR100 motor to keep the lights.

in fact, listings I see call for the XR80 and XR100 being the same stator, so maybe the XL75 will swap over.

I own a 1985 XL80S and a 2000 XR80R, but have not had the left side off either.

Share this post


Link to post
Share on other sites

Great info Eddycurr!!

Hey guys. I'm hoping to hear an update on this project. I have a perfect condition 78' XL75 .... But she has 4300 miles on it. It's falling out of gear and is hopelessly slow with me on it. I have found a xr100 bike to strip the motor out of.

Any updates on this project?

Thanks

Edited by Skipstr71

Share this post


Link to post
Share on other sites

Can anyone confirm that I can take the stator and charging system out of my 79' XL75 and instal it into a 91' XR100?

Share this post


Link to post
Share on other sites

You can get a Ricky Stator or Baja Designs stator with a CDI set-up and have enough power to run a complete street legal bike.  Plus, you get the stability of a CDI system. Baja Designs make everything you need. You just need to center the key in the late model flywheel or find a stepped key. Engines Only used to sell them.

Share this post


Link to post
Share on other sites

Socalxr... Thanks for the info. I've realized that I would need to change the appearance of my perfect little bike to get the 100 engine in..(remember be the carb boot,header,ect).

So now I am looking to get a XR 80 motor in there. I would get the 5 speed and retain all the stock look. I realize I will still have to do something with the stator though...but all that is not seen.

Share this post


Link to post
Share on other sites

Rubber boot of the 100 would fit the 75 air cleaner housing, carb and manifold fits too.

Biggest problem would be the muffler, a 100 muffler wouldn't fit the XL75 frame at the shocks and the 75 muffler is too restrictive for the bigger engine.

You can switch the stator coils onto the 100 stator plate to get lights.

 

But much more easy would be the 80 engine. You may also switch the coils and you can keep your muffler.

Share this post


Link to post
Share on other sites

Yeah the 80 motor is the best thing for my situation… Like I said I want to keep it completely looking original. It is the five-speed I am truly after....making it at least somewhat safe on the streets in the city I live in.

Do you have any idea the difference in carburetors. The reason I'm asking is because the 80 motor that I'm looking at buying has carburetor issues, where my carburetor off my 75 seems perfect.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×