Topic: 74' cb750 - my rat bike

[TheHun]

Before you got clip ons..what kind of handlebar did you have. BTW great build

[Really?]

How many fingers can you stick between the bottom-most part of the header and the ground?  I can only stuff 3 1/2 of my gumby fingers in there.  I may end up getting another pipe that is flatter on the bottom like cyclex's 4-2-1

[dp2275]

Before you got clip ons..what kind of handlebar did you have. BTW great build

i had chrome drag bars.  they sat about 3" higher and 3-4" further back towards the rider.  they didnt look bad, but they just werent quite what i was after as far as looks/riding position is concerned.

[cdoggy81]

AWESOME!!! Really like it
Do you have a pic of the other side?

[dp2275]

How many fingers can you stick between the bottom-most part of the header and the ground?  I can only stuff 3 1/2 of my gumby fingers in there.  I may end up getting another pipe that is flatter on the bottom like cyclex's 4-2-1

ill measure exactly sometime today, but its alot more than it looks.  i can drag pegs before the exhaust touches.  i think its around 4" clearance from the innner pipes to the ground.  the outter pipes run right beside the frame rails so they have plenty of clearance.

[dp2275]

AWESOME!!! Really like it
Do you have a pic of the other side?

thanks!  unfortunately, i dont have any pics besides what ive already posted in this thread.  i can safely assure you that the opposite side looks exactly the same with just a taillight/license plate mounted on the shock 

[cdoggy81]

No worries

BTW, I wanted to let you know that I liked your bike so much that I am changing the direction of my build b/c of it! I'm going to build one now similar to it! I'll find another cb750 to cafe out but...
http://forums.sohc4.net/index.php?topic=47753.0

[dp2275]

No worries

BTW, I wanted to let you know that I liked your bike so much that I am changing the direction of my build b/c of it! I'm going to build one now similar to it! I'll find another cb750 to cafe out but...
http://forums.sohc4.net/index.php?topic=47753.0

wow, thanks, i feel special!  i tried to build what i thought id like instead of what other people told me to build and im just really happy that it turned out as well as it did.  i put 40 miles on the bike this past weekend and ive already had 2 people stop me in the middle of the street to ask what it was! 

just some warnings if you plan on building something similar..the rear tire hits the fender over hard bumps so im going to dissassemble the shocks and throw a spacer in there to stiffen the springs up and also id recomend cutting the front springs and using a spacer there also to stiffen it up.  use some thicker fork oil for better damping and it should prevent any bottoming out. the ride isnt really that bad...even for these #$%*ty dirt trails that PA calls roads 

[dp2275]

guys, i need some help...

the bike has been running awsome..ive logged around 200miles in the past 2 weeks.  BUT, one of the cylinders isnt running like it should.  there is plenty of power and the bike holds a steady idle but one cylinder is fouling plugs no matter what rpm.  the plug thats fouling seems to be carbon fouled and not oil fouled so A) its getting too much fuel due to a carb issue or B) ive got a misfire/coil issue which isnt completing the burn.

the fouled plug isnt wet..its covered in dry carbon so i dont think its a misfire as thatd leave wet gas on the plug.  i also just redid the caps/plug wires so all of that should be in good shape.  has anyone seen issues with a single carb like this before?  i rebuilt the carbs a few weeks ago with ALL new components.  i set float heights and synched them.  im not really sure what would cause such an issue unless i bumped a float or something before reassembly..

i drained the carbs today..ill pull them apart next weekend and double check everything as well as try a compression test and recheck all of the valve adjustments.  id like to hear any opinions/tips if anyone has any..






on a good note, heres the metal bandsaw i just finished refurbing...bought it for $35 at a local auction.  should aid in future fabrication experiences!





and here is a pic of the tailight/plate setup i concocted as well as my seats.

[dp2275]

so i rebuilt the carbs a third time to try and fix the cylinder that was running rich....i richened up the midrange by shimming the needle with a very thin washer as it was a bit lean there.

i also replaced the center needle seat thats pressed into the carb body with new ones.

the bike ran great before but sooted one plug up.  now the bike doesnt run for #$%*...wtf?  i really didnt change anything that should affect idle but its not getting hardly any fuel at idle and runs hot.  once moving, the mid/top end are great.  ive got the idle air screws at the richest setting and its still lean at idle.  getting on the throttle causes the bike to fall flat on its face when below 2-3,000rpm.  could changing the needle seat cause idle to lean enough that id need larger pilots?!? 

[mlinder]

What do you have the idle air screws at? How many turns out?

[dp2275]

What do you have the idle air screws at? How many turns out?

ive tried every setting imaginable for the air screws to see if anything made a difference.  currently, i have them @ the richest setting but the plugs are so lean that they wont color.  just for reference, im running:
-velocity stacks
-open drag pipes
-125 mains
-needle set on bottom clip(max rich) w/ 1 thin shim
-#40 pilots
-float height set to 26mm

every replaceable part in the carbs is new..it sputters from about 1500 and doesnt smooth out till around 3000 @ which point it runs great.  im going to try setting float height to 24mm tomorrow to see if there is any difference.  according to the carb tuning manual that i have, float height controls mixture from 1500-2500 under full throttle which is exactly where im having the most problems.  maybe i should just go fuel injection..i have no problem tuning that 

[dp2275]

update:

ive shimmed the needles a bit more and changed float height from 26mm to 24mm.  the bike runs great once you're moving.

im still having problems with the idle.  im thinking the pilot jet is too lean so im going to pick up some 45's and try those out.  its very weird..the bike is exhibiting both lean and rich signs?!?  when you close the choke and the bike is cold, it sputters and dies (shows too rich).  the plugs look like they are reading lean but the bike also takes forever to warm up (usually, lean causes running hot and getting to temp fast).  messing with the air screws doesnt really do much at all.  carbs are synched, tightened the cam chain, did valve clearances, set timing, ect so all of those issues are factored out.

[PxTx]

Can you try and swap the coils and verify that you've got good spark?

[dp2275]

ive swapped plug wires around and visually checked spark externally with a spare plug but unfortunately, i dont have any other coils to swap in or anything.  id like to swap in some hotter coils and go with hondamans transisterized ignition to get some better firing at idle eventually but i dont have the funds currently.

[PxTx]

Okay, well only one plug looks sooty, so when you swapped the wires, did another plug soot up?

[dp2275]

Okay, well only one plug looks sooty, so when you swapped the wires, did another plug soot up?

i guess i shouldve mentioned the sooty plug isnt the problem anymore.  after i replaced the needle jets and reset the float heights, it seems to have cleared up for the most part.  beforehand,  swapping plug wires didnt help with soot (aka, it wasnt a coil issue).

the bike runs great but it just doesnt idle for crap without screwin with the idle stop. for instance, when its cold the choke wont make it idle but if i screw in the idle stop, itll idle fine.  when it warms up, idle increases to over 2,000rpm so i have to adjust it back down.  once its warm and i set the idle, itll hold 1100 pretty steady until its cold again.  ill throw larger pilots in and retune everything and see if that helps any.  its burblin and poppin on deceleration which is supposed to be a classic lean pilot symptom.

[coyotecowboy]

Its too late for me to re-read everything, but have you synched your carbs?  My 750 had the same #$%*ty idle problems until I synched the carbs, now it idles dead smooth @ 1000.  It will idle lower and stay smooth, but its too much of a PITA when taking off.

[dp2275]

spent the last 6 days on the road.  racked up over 900miles..

rolled down through fredericksburg, virginia the first night.  second night we stayed in newport news, virginia.  third and fourth nights we stayed at first point state park in virginia beach, virginia.  nights 5 and 6 we stayed in chicoteauqe, virginia.

[SUELZER]

so no breakdowns? no nothin? that's f'n fantastic
best has got to be using the hand-dryer on the pant leg photo...ingenious 
guess you kinda make do with whatcha got after 900 miles!
thanks for sharing all the photos, looks like a blast

[dp2275]

so no breakdowns? no nothin? that's f'n fantastic
best has got to be using the hand-dryer on the pant leg photo...ingenious 
guess you kinda make do with whatcha got after 900 miles!
thanks for sharing all the photos, looks like a blast

no breakdowns on my part..my clutch started slipping but thats to be expected on a 40,000 mile motor with 18/40 gearing    ..the other bike had a leaking gas cap and allowed alot of water in the tank (we got 2 inches of rain on day 4).  we pulled the lines and purged them and no problems after that.

that little hand dryer did wonders for drying out our boots!  we actually hung out in the bathroom for a few hours because it was the only warm place we could find!  the trip was awsome.  we met alot of nice people everywhere we went..seems anyone is nicer than most the folks here in PA!!

[PxTx]

I can relate to trips like that, although it' been a while.  Thanks for sharing some pics of it.  To your credit, the ride on the CB is much less comfortable than your buddies bike.  Definitely a young mans trek with nearly a hard tail.

Since the gearing is so steep, what did you see for MPG?  For point of reference my 73 gets about 55.

[dp2275]

I can relate to trips like that, although it' been a while.  Thanks for sharing some pics of it.  To your credit, the ride on the CB is much less comfortable than your buddies bike.  Definitely a young mans trek with nearly a hard tail.

Since the gearing is so steep, what did you see for MPG?  For point of reference my 73 gets about 55.

yea, i dont think the ride can get much more uncomfortable than my bike.  unfortunately, the foam in the seat has seemed to go flat so now all you feel is two frame rails in your ass cheeks.  need to fix that soon   

only saw average of 43mpg.  i think the gearing is so long that its actually hard for the motor to pull highway speeds in 5th.  for example, 4000rpm in 5th gear is around 80mph.  the clutch was also slipping pretty bad and my midrange is a bit rich.  i think much better mpg is to be had after a few tweaks.

[dp2275]

some updates for anyone thats been watching this build:

Replaced the clutch using EBC heavy duty plates and cir-cicle 'purple' heavy duty springs.  The clutch grabs like yall dont even know     its even got a bit of chatter if i try to slip it too much (reminds me of the 6-puck clutch in my turbo bmw).  I also used an 1/8" drill bit to drill additional oil holes (around 2 times the stock amount) and enlarge the stock oil holes in the center clutch basket.  Now it shifts and goes into nuetral smooth as butter.  I paid $60 for the friction plates, $20 for the springs, and $10 for the gasket.  Def worth the $90 into it!

I replaced the front 18t sprocket with a 16t sprocket.  Better than before.  This sprocket coupled with the new clutch has created a few hairy situations (the tire will break loose rounding corners in 1st/2nd gear if im not careful).  I think ill add a few more teeth on the rear sprocket and i should be happy with it.

I purchased a transistorized ignition module from hondaman and installed that...works beautifully!  also did some more carb work/tuning and now the bike runs like a champ.  idles solid at 900rpm all day and pulls strong till 9k.  currently running open pipes and no filters..and people said it couldnt be tuned  

The stock triple tree was bothering me a bit so i replaced the top clamp with a billet unit from cyclextreme!  

Ive got almost 2,000 miles on this thing so far this summer and im having a blast!  Ill try to get some pics of all the new parts this weekend.

EDIT:  Forgot to mention, im picking up a frame this weekend and building a 2nd hardtailed bike.  That should be fun 

[dp2275]

mustve had the camera on the wrong setting in those first few pics...but you get the idea