1973 XL175 Vitamin C Hell Ride

Re: 1973 XL175 Orange Soda Hell Ride

Texasstar said:

read the complete string! awesome!

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Much thanks.

I'm definitely in the camp of learning as I go. I got a lesson this weekend on carbs and why it goes blank when I open her up. As XB has been saying all along, the bike is pretty lethargic. I can't open it up from a stand still and expect it to pull a wheelie.

All this time, I'm thinking I have an issue with the secondary on the coil, maybe timing or loss of spark. But as cxman pointed out to me, the motor can't handle the loss of vacuum when I go wide open. It causes it to go dead, even backfire from what amounts to a lean mix since the motor isn't sucking fuel. As a master kiln builder, I should know better. I deal with combustion and the venturi effect every day. There is a specific relationship between the size of the opening to your stacks, the burner ports on the kiln, and the amount of available air and fuel. Mess that up, you can't get your kiln to the necessary 2400°. Or it takes twice as long to get to cone 10, which is a function of temp and rate.

Once the bike gets up to 4500 rpm it comes alive and has good pull. It's just the nature of this beast. I have to teach myself to ride a bike like this.

And now I need to to get a 2-stroke or a bigger beast so I can pull wheelies and race Mustangs. ;D

The oh so dreaded BoG Can you step away and maybe come up with an accelerator pump carb to modify fitment to work on it? Maybe change the cam profile for a little more/less duration to compensate for the lack of vac? won't jump off the ground, but could recover sooner?

Supercharge it. If it won't suck than ram it in.

its too cool to jst give up on the carb with a pump is a great idear at the same time ,cam timing should be cosidrd in myhoe
we know the cam timing is likely retarded a bit from the original intent,any bit of chain wear/stretch does this. low end response/torque suffers
advancing a cam a lil bit should help lowerr rpm response go too far top end will greatly suufer i am sure but it is a super easy thing to experiment with
a degree wheel, dial indicator and a lil ole saw chain file is all you need

xb33bsa said:

its too cool to jst give up on the carb with a pump is a great idear at the same time ,cam timing should be cosidrd in myhoe
we know the cam timing is likely retarded a bit from the original intent,any bit of chain wear/stretch does this. low end response/torque suffers
advancing a cam a lil bit should help lowerr rpm response go too far top end will greatly suufer i am sure but it is a super easy thing to experiment with
a degree wheel, dial indicator and a lil ole saw chain file is all you need

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Kind of like a Bong Hit! let er suck a little and wham open that valve and make that lung expand... I never actually done this, but I seen it in the movies 8)

Tune-A-Fish said:

Kind of like a Bong Hit! let er suck a little and wham open that valve and make that lung expand... I never actually done this, but I seen it in the movies 8)

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hah i never inhaild neather !!

Despite chain "stretch", what is the factor that put these to sleep right from the factory? Same thing with the SL125. The 100, which is the original design for this platform, is much more impressive. As far as little four strokes go, I'm always impressed by the OHC cub motor and the vertical 100cc. So what is it? Changing crank geometry? Bad consideration of cam profile when going up?

Eh, get a DT. You won't get tired of it, unless it kicks back in which case it's your fault for going easy

when slotting the holes on a cam sprocket you can actually use a lil simple math and geology to figure EXCACTLY how far advanced the timing can be moved just by measuring the width of the slot and how far the sprocket moves calkutated on the diameter of the bolt circle reductakated to degrees ,don't need no degree wheel or dial indicater neather
"jus remember 1degrees on cam = 2 degree of advance at crankshaft and crankshaft degrees are what is always spoke in camtalk
so if you wanna be able to say i advanced my cam timing 10 degrees you calculate how wide a slot you need on the cam sprocket holes to allow the cam to be moved 5 degrees on its axis
maybe not such simple math for an artist ?

the best small simple trail bike ever made was the first xr's the lil 185 or 200 what i'm talkin about
one word PERFECTION

xb33bsa said:

maybe not such simple math for an artist ?

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haha... Fuck you. And yes on the XR. I'm holding on to a frame, just in case a motor falls from the sky.

And just to be clear, this bike is fun. I am having a blast riding it. I'm just excited for another build too.


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XR's great for trails. A great mix of simplicity and claw hammer reliability. Also based on the vertical 100. You should see what the XR80's go for here.

This is a beautiful build but I'm curious what's the cause for the performance, or lack of, so it can run as well as it looks and sounds.

yep the cb100 spawned a lot of greatness buit the XL175 is not a 100 based unit,not at all there is not a single bit common about them
it is much closer to the 72 XL250(which draws horizontally split case design from the CB twins proving ground)
the only thing is they forgot to use the 250 kicker shaft design as well as the 4 valve pentroof head :'(
the poor lil xl175 is basically half a cb350 twin with a 3.4mm stroked crank

I've got a mono shock XR frame, but something I've considered with that frame, my other XL175 frame, or a proper XL185 is to do a Seeley TL200 trials inspired build. But that's getting off the subject...

xb33bsa said:

the best small simple trail bike ever made was the first xr's the lil 185 or 200 what i'm talkin about
one word PERFECTION

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I have this exact cycle in the shop, been slowly working through it as I work on my main project, I had to bore it and put a piston in, rebuild the advance mech as it was rusted up, the intake valve was stuck down when the PO tried kiking it so a valve job and cam chain was the last of the motor work. now I cant find plastic so its going to be street tracked I guess.

Bike and motor on the bench, the 350 (it runs!!) was my second stop for the day, the bar mount was the seller for me... no a bad day.

Quick! Someone second this bike for bike of the month!

http://www.dotheton.com/forum/index.php?topic=64234

I second it

eric has done a amazing job of "just cleaning it up a bit and fixing the kick starter ) since he got it

it has been a journey and it has come out awesome well done eric!

deviant said:

haha... Fuck you. And yes on the XR. I'm holding on to a frame, just in case a motor falls from the sky.

And just to be clear, this bike is fun. I am having a blast riding it. I'm just excited for another build too.


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This might be of some help: http://www.ebay.com/itm/NEW-HONDA-2003-2004-2005-2006-2007-CRF150F-CRF-150F-CARBURETOR-CARB-/161446088160?pt=Motorcycles_Parts_Accessories&hash=item2596efcde0

I am ordering one to see how or if it will be an improvement, I only hope it really is a Keihin.

hmm i wonder who might have a HONDA xr350 motor kicking around hmmmmmmmmm?

cxman said:

hmm i wonder who might have a HONDA xr350 motor kicking around hmmmmmmmmm?

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Oh yeah!!!!! ;D ;D ;D ;D ;D ;D ;D ;D :-* :-* :-* :-* :-*

a crf 450 motor would be cooler in that frame 50 hp plus out of one of those

that will cure the bog