Topic: My first complete build 72 CB750 - completed for now...

[algophobe]

got the bike running again, I did some preliminary mods to the Keihin CR31's. Previously she idles well only if the air screw was 1/4 turn from completely down, I increased the Pilot (slow) jet to 62's which allowed me to have more room with the air screw.  now she idles well at 3/4 turn from bottom. I knew the bike was running too rich at 1/2 throttle and up so I did some prelimiary adjustments with wider needles yy9 and increasing the main air jet to 250. i'm certain that i'll need to go down on the main jet too but i'll just work with the clip position on the needle first. the carbs were originally put together by Dime City which was slight variation from stock settings for CR31 according to the manual. some light turn of the throttle to 1/2 turn produced some dark exhaust smoke, so either the clip position need to change or go smaller on the main jet.  After a couple of twist of the throttle to full, loud clanging was noted on the top end. Lo and behold this happened. hopefully tightening the tapet bolts will correct it and correct the noise. the damage seems superficial on the tappet covers, hopefully thats it. also i took out the spark plug to inspect and number 1 and 2 cylinder (left two spark plugs) were significantly darker than 4, #3 is ok but cold be better. not sure what the difference would be due to but, looks like there are a few issues i need to sort out before dealing with the difference in combustion from 1/2 to 4. more to come.

[algophobe]

I readjusted the rocker tapers again and tightened them down snug, she seems to run fine now. Had a chance to check the timing again, advanced her to 10+, recheck the carbs for balance. I lowered the size of the main jet and drop a clip level on the needle. She seems to be running leaner as I want her to. I’d like to take her on the road again and do the series of spark plug chop to really see how the plugs do with the smaller jet. Problem is I don’t have a final drive chain.

I do, but need a master link. I bought some 530 JT x ring chains from Bike Bandit years ago, but seems like their stock is on back order for a few weeks now. Anyone have any thoughts on using O or X ring chain versus the original chains? I’ve plugged up the oiling mechanisms so have to keep with the O ring types. I see that 4into1 has the Fire Power brand.. but it doesn’t say if they are O ringed or not.

[PeWe]

X-ring has replaced o-ring chains. Improved design.
Use a modern good quality x-ring chain on a street bike.

Lubricate frequently so the x-rings do not wear and let the grease out.

I killed a strong chain with chain wax. It was not new, but no signs of giving up the nearest rear tire life.
Used Maxima Chain Wax and the wear accelerated really quick. A strange red brown dust around front sprocket cover that I later understood was rust.
X-rings worn out and the links degraded within 3000 km.
One of the markets strongest 530 chains. Chain looked like the stretch was sideways.

I do not like lubricants that are sticky. Chain will look lubricated but is not when lube can not flow where needed when scuffed off which happen when driving.

My favourite lube is Motorex Road, strong.
I have a bottle of Motul that is the sticky variant too. Maybe possible to mix with a cheap not sticky.
Best lube is not the one that does not make rear wheel dirty.

[algophobe]

X-ring has replaced o-ring chains. Improved design.
Use a modern good quality x-ring chain on a street bike.

Lubricate frequently so the x-rings do not wear and let the grease out.

I killed a strong chain with chain wax. It was not new, but no signs of giving up the nearest rear tire life.
Used Maxima Chain Wax and the wear accelerated really quick. A strange red brown dust around front sprocket cover that I later understood was rust.
X-rings worn out and the links degraded within 3000 km.
One of the markets strongest 530 chains. Chain looked like the stretch was sideways.

I do not like lubricants that are sticky. Chain will look lubricated but is not when lube can not flow where needed when scuffed off which happen when driving.

My favourite lube is Motorex Road, strong.
I have a bottle of Motul that is the sticky variant too. Maybe possible to mix with a cheap not sticky.
Best lube is not the one that does not make rear wheel dirty.

funny thing, i was at a track day event and was criticize by a suspension expert for using chain wax on an xring chain. he insisted that all you need is WD for for cleaning only. i guess its only partly true

[PeWe]

I think MTB guys and other bicycle racing guys use WD40.

Racing guys use most likely what gives less power losses.
Thinner chains and probably thinner lubricants.

I met one guy that lubed the chain everytime he filled the tank. Bike on centerstand, spray thin lithium grease spray.

I always hear from the dyno guys to lube chain and higher rear wheel pressure to get max power on dyno. I use what I ride with.

Dirt bikes have no x/o-rings at all if I have got it right.

[seanbarney41]

Plenty of oring and xring chains on dirt bikes nowadays, PeWe. 

I have had best durability with just cleaning sealed chains with wd40, no lube until chain is near finished, just to squeeze a few more miles out.  I have been getting 15 to 20000 miles out of street bike chains this way.

[algophobe]

i guess i'll continue doing the wd40 thing from here on.

the replacement master links for JT chains are finally in and finally buttoned up the bike. with all the parts on, the new location regulator/rectifier doesn't look like too much of an eyesore as i thought. almost forgot what the bike looks like all together since she's been in pieces for a few years. hopefully i'll have a chance to test run her this weekend and maybe even do the first series of spark plug chop.

what i think may have happened with the first iteration of the build, there was quite a bit of oil leak into the combustion chamber, the spark plugs were quite wet and black with the addition of running her too rich as well. the leaks likely came from the valve guides. after running the bike with the new rebuilt top end, the spark plugs are much drier and dark. more like a rich fuel mix than oil leak. now with the smaller main jet and raised clip position of the needles, hopefully i'll get better results... crossing my fingers.

side note: i met Vincent and his CR750 at Newcombs Ranch up in Angeles Crest Highways about a month ago. boy its a thing of beauty even with a dent in the tank. we swapped stories about our builds and how he just simply dropped in his Keihin carbs and never had to fuss with them. even with the rebored cylinder he was using CRS29 carbs. makes me think i was headed for this trouble with a rich mixture since i started out with CRS31's on essentially a stock top end.

[SOHC4 Cafe Racer Fan]

Just my $0.02 but CR31s are better suited for a high performance motor and can be finicky for street use.  Probably good for displacements over 900cc or you will run rich.  The CR29s are easier to tune for street use on a stock motor up through a higher performance/compression 836 with a cam/port job.

[algophobe]

Just my $0.02 but CR31s are better suited for a high performance motor and can be finicky for street use.  Probably good for displacements over 900cc or you will run rich.  The CR29s are easier to tune for street use on a stock motor up through a higher performance/compression 836 with a cam/port job.

with hind sight. i completely agree, it was under the advice of Dime City who built it for me... maybe a little bit of upselling?

[algophobe]

so i ran her around the block for the first time in 2 years since the bike broke down coming home from the OG moto show in Los Angeles. The brakes are squeeky as hell even with the shims purchased from our fellow SOHC4 member... i'm hoping it takes some more break in than just 100 miles.

she runs fine at idle to 1/8 turn of the throttle, hesitates like crazy at 1/4 turn up to 1/2 turn, and has a burst of power at 1/2 turn all the way to full throttle. I had lowered the clip on the needle from 5th to 4th position hoping to lean it out and may have been too much, which have been in addition to using a leaner (thicker diameter needle) needle yy8 to yy9.

but the spark plugs are looking great, the char from the same spark plug are turning more brown and drier.

next step would be to set the clip position back to 5th position and if the hesitation disappears then i'll proceed with a spark plug chop.

oh and a gratuitous pic of the kids on with the bike.

[algophobe]

lowering the clip to 5th position sure helped with the 1/4 turn throttle to 1/2 throttle. however now i'm noticing a flat spot just before 1/4 throttle, a faint hesitation but doesn't occur all the time. of course this hesitation only occurs around the neighborhood. I took her up a little higher in the canyons near my house and she sure likes the thinner air (which is where I intend her to perform best in). i'll play with the air screw a little bit before swapping the needle to YY8's (Skinnier).

what i did learn is that the reserve setting on the petcock is crap! i decided to test it by running it half the test on reserve. the bike dies and gasp for fuel to fill the float bowl. certainly better with the petcock on "on" position. but i still feel it may not be enough.

anyone have advice on the Pingel adapter/petcock? or is there a known issues with air lock on the OEM petcock?

[algophobe]

who knew a 1/4 turn inward to richen the air screw made such a difference. the throttle is smooth throughout the range. she runs well at normal commute type altitude around town, im sure it would be perfect in the canyons. no fueling issues with the petcock on "on" position. performed the spark plug chop down a straight 1/2 mile road near the house at 1/2 and full throttle without having the neighbors calling the cops on me. not sure if 1/2 mile is sufficient enough to cause the discoloration marks as desired. but i can't imagine sustaining full throttle for that long. definitely learned that the bike can get quite squirrely and gives a massive head shake if you put too much weight over the front wheel in a full tuck, i forget i have more seat to buck up into to distribute more weight over the rear wheel.

the only resemblance of results with the light discoloration ring on the 1/2 throttle #2 plug. i'm not sure how much i'm learning from today's chop exercise, but she's running great so I can't complain. at some point i may just put her on a dyno and see what i get, and maybe a steering damper may be a good idea.

[algophobe]

A little photo shoot at the end of the test... for now she's done.

[Jimcg]

A little photo shoot at the end of the test... for now she's done.

What a great looking bike! Such a beauty!!!

/Jim

[algophobe]

thank you jim, i'm liking your color scheme as well. similar taste.

[greenjeans]

Just found this thread.  Somehow I feel a bit of kinship with you as I fought my 836 build with The CR29 carbs.  Took a bit of tuning, but definitely worth it afterward. 
Great build, I really dig those colors on there.  Well done sir.