1969 Honda CT90 | Page 3 | GTAMotorcycle.com

1969 Honda CT90

tricky

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Great work!


Though after seeing it all together, the grey screams to be red to me.
Thanks! And yes, in retrospect I probably should have gone with a louder paint scheme. I think for my first "resto", I wanted to stay on the safer side. I do like the red Honda used, I believe they call it "Tahitian red"
 

tricky

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I was road tripping through California, passed right by a huge distributor of Lifan engines (PCC motor). Couldn't say no. US$280 got me a 125cc manual clutch, with intake manifold, carb, cdi and ignition coil. Another $50 or so got me a Lifan clone CT70 exhaust made for this engine. The engine itself, without the trimmings, would have been CAD$600+ according to a local supplier.

So, on the Honda vs Lifan engine front, I have been tortured since day 1 with this bike. I love the idea of keeping the Honda engine. Lifan = Chinesium after all :roll:

Extensive research online convinced me the Lifan build quality was agreeable, and the engine is reported to be on par or better than the original in terms of reliability. I lose my sub-transmission, but I gain more hp. I lose points and gain CDI, and I lose 6v for 12v. I lose the semi-auto and gain full manual clutch. Unfortunately I doubt the original 19mm carb will work, which means I lose my super cool altitude adjustment knob :(So, some good, some bad.

Today I removed the engine, 6v battery, rectifier and ignition coil, and carb.



Out comes the original engine, which I'll put on ice for now. I'll probably rebuild it down the road so I have the option of going back to original.


Here she is, empty and ready for the new heart


Some notes for the record on this swap:

The engine won't bolt right up. You need to drill out the top motor mount on the engine to 7/16 (I think) so you can use the original top mounting bolt. You also need an adapter for the rear mount. You need another adapter if you want to use the original footpegs (and maybe original engine guard??). Alternatively you can use CT70 pegs I think, but I'm not sure how the engine guard would bolt up. I got both these adapters from DrATV.

The original CT90 exhaust won't bolt up, the flange at the head is wrong. DrATV has an explanation about this. You can get a CT110 exhaust and with some adapters from DrATV you can bolt that up. I'm not sure if you can use the heat shield from a 90 exhaust on a 110, but I imagine you can. Alternatively you can use an aftermarket pitbike exhaust, or a CT70 exhaust (original or replica).

I like the look of the original 90 exhaust though, so my plan is to take the header from the CT70 exhaust I bought and get it welded up to my 90 muffler, so we can keep that original look. The header on my original 90 pipe is rotted through in a couple parts anyway, so this would solve several issues at once.
 

tricky

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So I drilled out the top engine mount of the Lifan to accept the 10mm engine mount bolt.

I also installed the engine mount adapter for the lower engine mount. The documentation here is thin, so this took some freestyling. I had to get a longer engine mount bolt to make this work, luckily I have a pile of misc bike pieces lying around.

Just about nothing lined up with anything in the garage today. I'm not sure if that speaks to DrATV's quality or what. The adapter plate I have to use the original CT90 pegs is the worst of all, I don't know if its workable or not. I think the sprockets are in line, though, but we'll see when the chain is on.

For now, the engine is mounted in the frame. I'll try to get the pegs bolted up next time I'm out there. I also found out I need a different manifold, the one with the Lifan from PCC motor won't clear the downtube on the frame.

Luckily the engine is light enough for me to hold it with one hand and install the engine mount bolts with the other :lmao:





 

tricky

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The bike has been sitting for a while. Can't believe my last post was August.

I finished mounting up the engine properly, with the foot pegs and engine guard as well. It's a bit of a **** show with the rear engine mount adapter, the adapter plate for the footpegs, and the pegs and guard themselves. Nothing lined up with anything, even though it was supposed to. Took a fair bit of grinding, drilling and filing to get it together.

I bought a Honda OEM exhaust for a CT110, which bolts up to the Lifan engine if you have a spacer for the flange. Luckily the heat shield from my rotted-out CT90 exhaust bolted up to the 110.





I rejetted the carb to 40/105, from 30/85 stock. Apparently this will put me in the right ballpark for this air/carb/engine/exhaust combo. Or so say the far reaches of the internet. The mouth of the carb on the air side is too large to fit into the stock air filter boot, and its also about half an inch too far back with this intake manifold. I used a small section of silicon radiator hose to mate the two for now.


It's a straight race to the finish now. I have to hook up the fuel lines, the clutch cable (which is too long right now), and then the electrics. First I'll run it without a battery, then when the bike is running as it should, I will set up the peripherals with a new 12v battery and 12v bulbs

The goal is to ride this to the Horizon's Unlimited meet up near the end of May. We'll see if I make it in time. I have an insurance policy lined up through Dalton Timmins, and I will need to get it through a safety too.
 

tricky

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Worked some more on the bike today. Went to install the chain, realized the Lifan came with a 240 pitch front sprocket, and I needed 248 to match my new chain and rear sprocket. Luckily my local parts store carried the sprocket I needed so I wasn't sunk today.

Also had a bunch of trouble with the clutch. It doesn't seem to want to disengage. Even if I move the clutch arm on the outside of the crankcase full end-to-end movement, the clutch doesn't want to give up. I put it in gear and rocked the bike to try to free up the clutch plates, if that is in fact the problem.

I had a friend help me wire it up to try to get it running today, just the ignition circuit. We took out the old harness, all the bike has now is CDI and an ignition coil. No battery or lights at the moment. Installed the chain, put in an inline fuel shut off right before the carb, drained the engine and filled it with proper oil, and filled up the tank.

With the engine ready to go (and in N because of the hinky clutch problem), I felt zero compression on the kick. Pulled the plug, no compression. Uh oh. Ok, luckily it seemed to be related to the clutch. I put it in gear and got all the compression in the world. Cool. Plug back in, and we put it on the center stand (and a block of wood) so the rear wheel was well clear of the ground. Kicked it over, and it started first kick. Super easy. Super quiet too. I would post a video of it idling, but you would just wonder why I bothered. The wind noise on my video is louder than the engine idle.

Within 5-10 minutes I felt the engine bogging a little, and when I revved it, the engine just wanted to die. ****. Well, luckily I am dumb and I soon realized the fuel shut off was OFF (I switched it off to deal with the clutch/no compression problem). So it was just running on the gas in the float bowl and lines. I turned the fuel back on and it fired up, idled, and revved like a champ. We ran it for maybe 20 minutes, just idling with an odd blip of the throttle. No mysterious oil or fuel leaking that we could see, everything seems ok for now.



So next up, is adjusting the clutch. I figure I'll have to take off the left side engine cover to adjust the clutch, but I'll be googling all of that stuff tonight. Once that is done and working, the bike is functional at least, barring any unforseen issues with the engine. Next then is to wire up the peripherals and button everything up for a safety inspection. :cool:
 

tricky

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It was a bit of a mad dash to finish, but the bike passed its safety inspection and got plated today. We took it on the road to get a sense of how it performs, and my friend (who did all the electrics on the bike) had it sitting comfortably at 75 km/h in fourth gear, measured from a follow car. He road it from Aurora to downtown Toronto (~50 km).

The brakes aren't great, the rear is far more effective than the front. I suspect the clutch is (or was) still sticking a little. The battery is being over or undercharged, or both! The lights are incredibly dim and the winker speed is pretty much tied to the engine RPM. Also we went through 4L of fuel in under 100km, so we must have a leak somewhere. So we have a laundry list of things to iron out still.

I'm going on vacation tomorrow, and my friend will continue to work on the bike to try and fix these things in time for the Horizon's Unlimited meetup near the end of May.

 

Robbo

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Lookin’ good. It’s a great feeling when you make progress on a project and can start to see the finish line .


Sent from my iPhone using Tapatalk
 

tricky

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Lookin’ good. It’s a great feeling when you make progress on a project and can start to see the finish line .
Cheers! It is a great feeling!!

Just an update for those still following. The Lifan 125 came with a 420 pitch 14 tooth front sprocket. We replaced it with a 17 tooth 428 pitch sprocket, and kept the standard 45 tooth rear sprocket. The 17t front sprocket is a tight squeeze for sure, but we deemed it acceptable and haven't had an issue yet. We bought a 108 link chain, and removed one link to get it all together. We could probably lose another link to be up near the front of the chain adjustment, so buying a 106 link chain should be fine.

My friend and I rode from Aurora to Roseneath (~140 km one-way) for the Horizons Unlimited traveller's meeting in the end of May. We loaded up the GS500 with every tool imaginable, and spares of every electrical component on the Honda, anticipating trouble. We didn't have any issues though, the bike ran fine both ways.



I am very content with how the Lifan 125 has turned out. I was a total skeptic, but I wouldn't hesitate to recommend the conversion to someone on the fence.

The to-do list is winding down, but we still want to:
- Replace rear shocks. The DrATV heavy duty rear shocks on there are way too stiff, the bike is effectively a hard-tail and I'm worried about the shock mounts taking too much abuse. I just received a set of Yasusu 13.8" shocks which should be a bolt-on replacement, and should give a bit softer ride
- Throttle has a ton of slop, because of how the antiquated twist throttle mechanism works. Gotta fix that
- The forward heat shield on the exhaust downtube came loose again. The original extra-asbestos wrapping used by Honda had worn out, we replaced it with exhaust wrap, but its worked loose again so we have to go back in and make sure we build up more wrap there. We may wrap the header while we are at it
- Replace the tires and tubes. The knobbies on there are effectively brand new, because the bike sat for years after my uncle changed them. Unfortunately the date code puts them at 9 years old, so they gotta go. I have had a new set for a year, but haven't gotten around to changing them yet
 

tricky

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I should also add, with my friend riding (~170 lbs + camping gear) the bike would settle in at WOT in fourth gear mid-range at 85-90 km/h on level ground. On big hills, he would have to drop it to third and push it a bit harder. We had to be mindful of the traffic behind us at times, but all in all I think we can survive 80 km/h roads without pissing off too many people
 

tricky

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Today we swapped out the DrATV heavy duty rear shocks for the pair of Yasusu 13.8". Seems a lot better now, the back of the bike is lifted up a touch higher. The springs have a lot more give so the back has proper sag and all that with a rider on it. It's no longer a hardtail! Also, the shocks are narrower so the exhaust mount is in closer to the bike like it should be.



We wrapped the exhaust header and built up the wrap under the clamps for the forward heat shield. When we tightened down the clamps, the forward heat shield felt like it was finally on there firmly. We ran the bike for about an hour and it hasn't come loose yet, but we'll see!

We fixed some of the slop with the throttle and also readjusted the clutch. We fixed our tail light which was vibrating loose, too.

We finished the day by trying to replace the tires, but I pinched two tubes and decided to pack it in for the day. I'm gonna read more about how to avoid pinched tubes, I think in retrospect I had a bit too much air in them
 

tricky

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Today, we took another stab at mounting the new rubber (Duro HF335 2.75-17 front and rear, same as the old tires). I didn't pinch any tubes today, the gods were with me

The tires seem so easy to put on, I could get one half of the tire on without irons, then put in the tube after a liberal shower in baby powder, and then I could get 80% of the other side of the tire on without irons. The last 20% took a few ginger bites with the tire irons and it was on. It went very smooth for the front and rear, both pumped up and both held air.

We also replaced the aging and broken speedo cable while we were at it, adjusted the brakes and gave it an oil change. I think we are at about 500 km on this engine now. A great thing about this motor is it starts first kick. When the engine is warm, trying to move the piston past TDC with the kicker will start it up, no matter how slow you try to go!

The list is now really winding down, we don't have any pressing issues to attend to I think. We'll just ride it, and see what happens!

 

tricky

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Update -

Swapped out the 19mm keihin clone carb that came with the engine for a real Mikuni VM26 about six months ago. I think we are riding the edge of over-carburation, but we are getting 90+ mpg still and it will pull pretty good. I think we are on something like a 20 or 25 pilot and a 180-ish main. Still needs a bit of tuning.

Our goal was to be able to ride on the 80 km/h roads without being a nuisance, and I think we accomplished that. It will do 100 km/h on flat ground. Wouldn't want to go much faster on this thing

Other than that, just tinkering with little things... the VM26 has a pod filter on it. We are planning on 3d printing another intake boot to hook up with the stock air filter. Also with the LED headlight on (and all other lights being LED) we are losing charge on the battery very slowly. I think maybe the cheap-o rectifier may be too inefficient, or we are only using 1 of the 2 available coils. We may need to "float the ground" and switch to a full-wave rectifier to boost the output. For future reference
 

basmn

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I like your write up and have enjoyed it...nice restoration job...keep up the good work
Ed
 

Trials

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.... I think maybe the cheap-o rectifier may be too inefficient, or we are only using 1 of the 2 available coils...
If it has only 2 coils, I think you will find that one is for the ignition and the other is your lighting/charging coil.

Nice job on the restoration(y)
 

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