Topic: CB 836cc f1 turbo - spoked kickstart street turbo

[70CB750]

I may be wrong, but isn't the original swingarm width at the frame bolt something like 242mm?

I'm quite sure its 225.. same as Kz650 and kz1000..

I would expect you to know

Thanks!

[Ilja]

I may be wrong, but isn't the original swingarm width at the frame bolt something like 242mm?

I'm quite sure its 225.. same as Kz650 and kz1000..

I would expect you to know

Thanks!

The swingarm I had in the CB750 previously came from my kz650 and later fitted it to my kz1000.. So all the same.

[Ilja]

For anyone looking for an offset sprocket... CycleX also has them for 69 dollars... 

http://www.cyclexchange.net/Honda%20Cafe-Front%20End%20and%20Suspension.htm

[70CB750]

I am taking apart my K0 these days, the transmission needs to be rebuilt plus other things.   I pulled the swingarm yesterday and with all the caps and washers, what was mounted in the frame comes to 9.25" - ie 235mm.

Anyway, I am toying with the idea of modern swingarm and fork, but all the newer bikes use 17" wheels, not sure if that's what I want.  It may sit too low - well maybe that's the purpose

Sorry for the hijack, just thinking aloud.

[Ilja]

Yes true, with modern 17" wheels the bike will be a lot lower... Especially if you also fit a newer fork.
My z1000 with TL1000S wheels, swingarm and fork is really al lot lower now.
For the CB750 I used a CBR900 fireblade fork and rear swing and 17" wheels... but I put some additional spacers in the front fork to make it a bit more stiff and high.

The bikes ride excellent with the newer 17" wheels though... no comparision. 

[Ilja]

So I had the bike out for first time today!!
All in all the bike runs pretty good.

Down low it pulls fine and the turbo kicks in at 4k rpm and has full boost already at 4.5k RPM and pulls like hell once it boosts. The clutch slips like hell also if I apply more then half throttle with boost kicking in, so it needs an APE clutch or at least stiffer springs. I don't want to go to lockup clutch because I think I need to loose the kickstart if I would.. And you can't shift with the clutch no more.

Unfortunately the fuel filter gets clogged with rust from the fuel tank all the time, you can see the A/F going up on the A/F gauge..
As soon as it starts doing it it gets dangerous for the engine as I think I can hear a little detonation then. So I definitely need to de-rust the tank.

The rear sprocket needs to be a 42/43 to get the ratio equal to stock because of the 17" wheels. (so 17/42)
Right now I have 46th at the rear which makes it go something like 92kmh at 4000rpm at fifth which is a bit revvy for highway use.

The gpz600 CV carbs with dynojet kit in combination with the completely modified head seem to work fine also!!! 

All in all mission accomplished, just need some finetuning!
 

[Jerilee]

Congrats on the success!

[marting100]

awesome built! nice work and great looking bike!!
M

[Ilja]

Thanks!

The last couple of days I've been trying to clean the tank via Electrolysis and it's been working great!
Also easy to do...
Just put the -clamp on the tank (clean metal contact) and put the +clamp on a sacraficial piece of steel hanging free in the liquid inside the tank. (not touching the tank itself)

Put inside water mixed with cleaning soda.... 1 spoon per liter or something.
After 30mins you will already see a lot of rust sticking to the piece of steel.. 

I also installed HD clutch springs and rebuild the oil pump with the plunger rebuild kit available on this forum from Elan!
Great that we have this again!

I will install a smaller rear sprocket in weekend and take it out for some rides, hopefully with a clean fuel filter!
Can't wait!!!

[70CB750]

What sprocket(s) do you run now? 

[Ilja]

Right now I have 17-46 with 17 inch wheels. This means 92km/hr at 4000rpm.
It would need to be around 17-42 to be like stock... which gives 102km/hr at 4000rpm.

I have a 43tht sprocket but its a used one.. so I'll just mount it to see how it runs and to check if the chain is still high enough above the swingarm.

[70CB750]

There are gearing calculators available,  like the one attached.

[GV1390]

Solid, looks like tons of fun!

[Ilja]

So, I did quite some work on the bike again this weekend!
Installed 43th rear sprocket and HD clutch springs.. solved the slipping clutch for now..

I still had major rust clogging issues so I modified the fuel tank with another fuel tap with an in-tank filter.
The inline filter was staying a lot cleaner now but still clogging a few times (I need a bigger filter).

Driving around the bike runs great with boosting turbo when opening throttle up to 30-40%, pulls throughout the whole rev-range. The A/F ratio stays somewhere around 11-12:1..so also good.
Absolutely NO comparison with the stock bike... pulls like hell! Too bad my gopro doesnt seem to be working nomore..

If I twist the throttle more then this, the A/F leans out up to 14:1-ish and I hear an on-set of detonation... light crackling sounds like some small metal parts are loose... not good!
I think it's a combination of mixture and too much ignition advance.
I have a dynojet kit in the carburettors which *might* also consist of weaker springs for the vacuum slides, which perhaps causes them too open too fast.
Also, I'm using 1 pitot tube for both atmospheric ports.. I think I'll change that to two pitot tubes, one for each port just to be safe.

I might have an issue with the ignition...
When I use the timing light I can see that the advance marking, the "-mark, is lining up with the case marking when I rev the engine, but the case marking does not line up with the F marking when idling.
I now aligned the ignition with the F marking, but this means not getting full advance anymore. So something's wrong there..

So got some stuff to sort out! Well, at least it's working ok-ish! 

[Oette]

Hi Ilja,

You might want to check out ignitech in czech republic for their electronic ignition. Since you're running a heavily modified turbo engine the installation of a throttle position sensor would make sense which would work with their ignition. You will be able to develop a proper ignition mapping customized for the needs of your turbo engine with their software. Another big plus is, that you can get rid of the mechanical advancer and get absolutely precise ignition timing.

I'm using it on a heavily modified but still naturally aspirated engine and there is much more potential in using this kind of electronic ignition.
In addition there is the option to use their system called "Ignijet", which combines their ignition system with a programmable fuel injection. Running a turbo with carbs is tricky and since you seem to be into mechanics and have access to the necessary machines, a fuel injection is another option.

Those guys at ignitech are very helpful and assist you with every issue. They are selling nearly every necessary sensors and accessoires to run their ignition/injection systems.

http://ignitech.cz/en/

Just my thoughts on your issues... To get the motor running well under every state of load some additional electronic work might be the solving route to go.

Greets from Germany,

Mathias

[Ilja]

Hi Ilja,

You might want to check out ignitech in czech republic for their electronic ignition. Since you're running a heavily modified turbo engine the installation of a throttle position sensor would make sense which would work with their ignition. You will be able to develop a proper ignition mapping customized for the needs of your turbo engine with their software. Another big plus is, that you can get rid of the mechanical advancer and get absolutely precise ignition timing.

I'm using it on a heavily modified but still naturally aspirated engine and there is much more potential in using this kind of electronic ignition.
In addition there is the option to use their system called "Ignijet", which combines their ignition system with a programmable fuel injection. Running a turbo with carbs is tricky and since you seem to be into mechanics and have access to the necessary machines, a fuel injection is another option.

Those guys at ignitech are very helpful and assist you with every issue. They are selling nearly every necessary sensors and accessoires to run their ignition/injection systems.

http://ignitech.cz/en/

Just my thoughts on your issues... To get the motor running well under every state of load some additional electronic work might be the solving route to go.

Greets from Germany,

Mathias

Hi Matthias,

Thanks for the tip!

A programmable ignition would be nice, one that can be linked to a boost sensor, so it reduces timing when measuring boost. :-)
The Dyna 2000 can do this, but they are something like 450 euro's...
So I'll look into the options and also try to retard the stock ignition! (and enrichen mid-range by installing heavier throttle slide springs)

I also have another turbo bike, a kawasaki 750 turbo with DFI and a PC3 which is linked to the boost sensor. This bike currently has a kz550 ignition with 35degrees (stock 32 degrees) and runs up to 20psi of boost with no detonation.

The Honda should also have 35degrees if I'm correct... or did they change it for the F1 Supersport models?

Now with the Honda it's the first time i've heard detonation, never heard it on the Kawi while i've pushed it much more (20 PSI and wacked out throttle on autobahn)
... it's really hard to notice, just a slight crackling sound like pump-cavitation. (think of your garden pump)

[ivanhoew]

hi ilja ,

 in case it helps , on my 400/4 turbo  runnig 8.5:1 cr , i took the springs off the advance weights ,so effectively running fixed timing .then set the timing to 24 degrees . i have run up to 15 psi like this ,and done over 10k miles with no probs . it made 85 bhp at 8400 ,,,thats when the clutch gave up completely .

so that's a cheaper option for you that you could try . the timing figure will depend on your cr etc .


re the carbs leaning out , it sounds a lot like you need a more dynamic pitot tube ,and maybe some bigger main jets?

regards
robert.

[Ilja]

Hi!
I have the same CR... somewhere between 8.2:1 and 8.5:1.. :-)

You could probably get away with a bit more as you have a smaller bore engine which is better against detonation. 

Currently I have 1 pitot tube connected to both athmospheric ports.
Perhaps I should install a second one and have 1 pitot per atm. port.. it's an easy change.

About taking of the weights.. I can try that, or modify it so it doesn't advance fully.
How did you check the exact degrees? With a timing disc or timing light?

[ivanhoew]

worth trying the pitot tubes pointing into the flow with a flare on the end .

i checked with a digital  timing light adjusted to be on the tdc mark ,then just read off the degrees . if you dont have a dig light its easy to just mark the degrees you want by doing the circumference/360d thing.

mine definately detonated when it was run too lean  and on full throttle for a while .i needed a bigger flow tank tap ,,but i was on a suck through system .my blow through system on the 500 twin uses a gm fi pump and malpassi fpr .

regards
robert

[Ilja]

Yesssss, solved the ticking issue which was (beginning)detonation after all.
Raised the main jets from 124 to 140, pilots from 38 to 42 and needle clip position to the 3th of below.

Now I can give full throttle without ticking and noises and I get a consistent 10.5:1 A/F all acros the rev range.. only at 1/3th thottle opening I get a stumble and the A/F drops to 9.5:1..
So, overal the fuelling is a tad too richt over the whole range..but at least detonation is gone!
Other turbo bikers were scaring me that the pistons were probably already f*cked now with breaking ring lands from detonation, but I did a compression test and all four are still fine with exactly the same compression. Yay!

Goal is to end up with an A/F at around 11.5:1. I now want to try 135 mains and then it should be okay-ish..

Bike pulls absolutely fantastic through every gear.. clutch still slips a bit with HD springs so I will probably order the APE kit later.

Other jobs that need to be done now is, new tires, paint the rims, rebuild and paint the rear shocks, connect the lights and try to make a small buffer catch can below the turbo so it drains better... I get a big cloud of smoke 1min after starting untill the bike has heatened up caused by cold thick oil not flowing to the sump fast enough.. 

[Ilja]

Jetting all sorted out! ... threw out the dynojet needles.

Kawasaki zephyr 750 OEM needles with 2 small rings underneath (came with the cvk carbs), 135 mains and 42pj. Runs beautiful! 13-14 A/F at tickover.. 12 when pulling away and going to 11 A/F full throttle with 0.7 BAR of boost.
Made a little front fender because my face and the front of the bike were one big mudguard... gotta love those autumn roads..
 
Bike runs absolutely fantastic now! Pulls very strong with full boost from 4.5k to top.
And also before 4.5K the bike pulls like stock!
But not ridiculous power like my kawasaki, so the bike is VERY usable to just have fun with and drive around! Exactly as I wanted it to be!

I can always up the boost to 1 BAR later by removing 1 spring holding the wastegate actuator back... but then I will need a better clutch / lockup and perhaps a bit more ignition retard...or an intercooler but I'd rather avoid that on this bike.
So for now I'll leave it at 0.7BAR.

Only have a smoking-during-startup issue and clutch slipping at peak torque issue left..

Smoking is caused by a high oil level after the engine has been sitting for a while (wet sumping) and also the thick oil when cold not running back fast enough through the return line when the oil level is high.
Once hot, no smoke at all!

I want to attach a pipe to the exhaust at 45 degrees with a checkvalve, which will create some vacuum and connect this to the crankcase. Combined with a vent-line just after the turbo oil return port, this should pull the oil a bit out of the oil return line.... which will solve the smoking issue. Parts are ordered!

I hope I can install & test this system before December, because you cant ride classic bikes here in Dec, Jan and Feb since last year.... more rules. 

Cant wait to ride again this weekend! Need to get a new Gopro so I can make a movie!

[Ilja]

The angled venturi pipe on the exhaust didnt work..
But! I stopped the smoking by adding a vent line just after the turbo oil return port and reducing the restrictor to 1mm.
At least, when I don't rev it during warm-up it doesnt smoke anymore. 

Also fitted a gpz600 electrical ignition! So no semi-electrical stuff like dyna s... fitted quite right!
Revs a lot better! Did not drive it yet, but curious! The weather is #$%* now so I need to wait untill it clears a bit.

Not too hard of a mod but i never see anyone do it? You can quite easily retrofit these 80s/90s ignitions, you need a lathe and a wiring diagram and the original wire colors on the IC igniter so you know what is what. 

[Ilja]

 

[SOHC4 Cafe Racer Fan]

What figures is this bike making at the wheel?

[Ilja]

What figures is this bike making at the wheel?

I have no idea! Based on the other guy on this forum that got 101hp with a completely stock cb750 engine, a bit bigger turbo+IC and 0,5BAR...I would estimate mine with 836cc, bigger carbs, bigger ports and 0,7BAR somewhere between 110 and 130hp.
My smaller turbo is less efficient at higher boost pressures...normally a bigger turbo feeds more are with the same boost pressure and a smaller one starts creating pressure by heat at a certain point. But we aren't running high pressures so not sure.

I had it running at 1 BAR (15PSI) because my boost gauge was faulty and this was the stock wastegate pressure.
The clutch kept slipping, and to be safe during the first miles and tuning I turned it down to 0.7 BAR.

Maybe it sounds strange, but I don't want it to make too much HP because I think the two main chains, the clutch and the output shaft isn't up for the job (especially with my offset sprocket held by the honda-clip ) Also I believe the trans is not undercut from factory.
In principle if you put on a T25 turbo, an Intercooler and raise the boost to 1-1.2 BAR you could probably get 150 HP out of it... but its tricky with carb fueling and you will probably need to lower the compression ratio to 7.8 to 8:1. (mines at 8.5:1).

I have two more weeks before a 3 month winter stop kicks in due to changed classic-regulations from the goverment. (tax related...people were using old mercedes cars for daily transport)

If everything is okay, I can put it on the trailer and do a Dyno run with the bike. :-)