Very Successful Lifan 125cc swap into 1981 Honda C70 Passport

I pondered whether to post this in the Lifan engine thread or to add it onto one of the many Honda Passport threads but in the end decided to start my own thread. I hope to provide enough information that a person could duplicate my effort without having to go thru the missteps I took and prevent them from buying the same thing twice because something didn't work out right the first time.





My goals were to:

*Still be able to use the stock leg guard with minimal alterations
*Still be able to use the stock airbox (although modified slightly)
*Find a carb that would have a built in petcock to prevent having to have a "T" inline or hang a stand alone petcock on the frame somehwere
*Have good driveability
*Still get good fuel mileage
*Be able to lazily cruise at 45 mph with me (think lumberjack) on it
*Have a reliable electrical system

The engine I purchased was the common Lifan 1P54 54mmX54mm bore and stroke, semi-auto motor. I bought mine from PCC Motor because they are local but they are available all over the internet and Ebay. You can buy this engine in kit form and receive a carb and coil, but the carb you'll receive will likely be a Chinese Mikuni 22mm -- a workable carb but quite a bit longer than stock. When the manifold that comes with the engine and this carb are used, the carb must be mounted to the side or to the rear at an angle. I considered mounting the carb sideways thru the leg shield, but didn't want to listen to the intake air honk and it would make riding in the rain or washing the bike a hassle. Going to the rear was an option but would require cutting a big hole in the leg shield to make it fit.

The ATC125M and TRX125 both used a similar Honda horizontal engine -- bigger bore, shorter stroke, but 125cc nonetheless. It made do with a 20mm Keihin PB carb. Bigger Honda engines were sold with 20mm carbs. So, the option is to look for an EBay ATC125m carb -- nice because it's a genuine Keihin and has a built in petcock. Or, as I did, spend almost nothing on a chinese Keihin clone. The Keikhinkt 20mm clone carb I bought is a good quality carb, equipped with a built-in petcock. Though it is advertised as a direct replacement for an ATC125m, the jetting as delivered is completely wrong for the Lifan or the ATC125m. It can be made to work well with a jetting change. The stock ATC125m uses a 38 pilot jet and a 92 main. I got my Lifan running very well on the clone carb with a 38 pilot and a 110 main. The needle is currently clipped in the middle groove. I did open up my airbox slightly.



The carb matches perfectly to the intake mainfold designed for Honda-derived pit bikes with perimeter frame. It's inlet side is the same size as the outlet of the carb. It is smaller than the intake port on the Lifan motor -- 24mm versus 26mm. I thought about enlarging the outlet to match the port, but as it is running very well as is, probably won't. The manifold will allow straight forward mounting when a ring-style pit-bike intake adapter is used. The adapter is necessary to lift the carb above the intake valve adjuster opening. The stock throttle cable will work with the clone carb. With the Mikuni clone, a custom throttle cable is necessary. It is necessary to adjust the float to mate with the angle that this manifold sets the carb at. It does angle upward slightly.



The carb mates to the frame intake tube with a 41mm 4-inch 90 degree silicone hose section I purchased on Ebay. With this manifold and carb it requires a slight amount of trimming but clears the front fender by about 5mm. The pictures make it appear closer than it really is.



The stock exhaust can be made to work with a modification to the mounting plate but the engine really needs to the breathe better than the stock exhaust allows. I found an all stainless-steel exhaust for C90 and derivative Hondas for $139 shipped on Ebay. The seller is from Cyprus but receipt occurred in about ten days. The quality of the exhaust is very good. It is louder than stock, quite a bit louder, but just within the range of my tolerance for noise. I've heard much louder pit bike exhausts. This one's not bad but is louder than stock. I had two stock exhaust mounting brackets so I shortened one and then drilled a new hole to mount the Ebay exhaust. I'm not completely satisfied with my bracket in it's current state and will likely add a second mounting hole and bolt in the future.

I was able to reuse the Passport kick starter and shifter. I like to use the heel - toe shifter on this bike -- heel for upshifts. I will have to make the contact area of the heel shifter larger. With the additional width of the Lifan motor, the heel shifter sits closer to the engine leaving less area for the foot to contact. My plan is to enlarge it by welding a larger contact area that I will cut from a right side foot brake pedal from a Passport or CT. I had a wider footpeg bracket available. To use the stock footpeg bracket would necessitate widening it by 30mm or so.

I decided to keep the bike 6 volts -- at least for now. I installed an electronic regulator/rectifier on the bike that steps voltage down from the Lifan 12 volts to the 6 required by my 1981 Passport. It is easy to install, keeps the battery charged and all lights are bright. One advantage is that even at idle the Lifan puts out 11 volts or more. My lights do not dim at idle and are much more effective at night than the same lights powered by the original Honda engine. I adapted the engine to the bike using a harness section from DrATV but did not permanently alter the bike's wiring harness. I can unplug the engine and adapters from the stock harness and go back to the stock engine very quickly.





To duplicate this project, one could purchase:

**1P54 Lifan 125 semi-auto motor -- Ebay, PCC Motor, etc.
**Keikhinkt 20mm or other clone carb for ATC125m applications -- Ebay, Amazon
**38 and 40 pilot jets (Keihin 3J style) from www.jetsrus.com
**105, 108, 110 main jets (Keihin N424-35 style), 3.9mm threads from www.jetsrus.com
**Perimeter-frame style intake -- PCC Motor part# IN03
**26mm Intake Adapter -- PCC Motor part# IN10
**4 feet 3/16" fuel line and clamps (6) and one 3/16" fuel filter (for reserve side)
**41mm by 4 inch 90 degree silicone hose (Ebay or other) and two 41mm clamps
**Coil -- pitbike coil for CDI. I bought one from PCC Motor, part# CO02, but used my stock cable and plug because I felt they were of better quality
**CDI -- PCC Motor part# CD02. Don't waste your time or money buying one of the racing CDIs. I could find no one who said they produced more power or were of higher quality. I bought two so I can carry one as a spare.
**6 volt regulator/rectifier, tboltusa, DrATV or others -- tbolt part# TRC0503, and harness, part# TRC-0797
**Chinese engine adapting wiring harness -- DrATV, part# SUB-W-1.5
**Exhaust gasket -- DrATV, part# 89M or tboltusa, part# TRC-1189
**Exhaust system -- Ebay search terms: (cut and paste) Exhaust muffler Honda Chally C50 C50Z C90 GLX50 / Astrea 100 /Supra 100 DY50 C70
**Mounting bracket -- either shorten and cut your existing bracket or buy a spare and shorten and drill a hole lining up with the front hole on the exhaust you use.

The bike runs well. I can easily keep up with traffic while pulling away from stop lights and quickly get up to 50 mph. Once there, I can back off the throttle and maintain 45mph without issue. Power is very strong for a 125 and carburetion is clean throughout the throttle range.

I am currently running a 16 countershaft sprocket but am unable to pull to redline in fourth gear. I may try a 15 sprocket. The 1P54 Lifan uses a special 20mm countershaft sprocket. DrATV has the correct one available from 14 to 17 teeth. The chain is a newer 420 non-oring and the rear sprocket is a near new, stock, 36 tooth steel sprocket.

I will run for a month or so without the leg guard in place in case I have to make any adjustments. I will have to fashion some kind of mount for the lower leg guard holes. The 70cc motor had flanges to attach the leg guard to the engine. The Lifan does not.

Very nice work, and write up. Thank You. Dave

I read your thread with great interest as I also have a 1981 Passport. I like bikes stock when possible, so I liked your comment, "I can unplug the engine and adapters from the stock harness and go back to the stock engine very quickly." That is cool to know that you can have a powerful engine, yet can still go back to stock.

Very nice indeed!

AMAC

Great pictures and write up. A very nice, clean installation!

Cooler than the other side of the pillow.

Excellent job and great informative write up. I have a Lifan engine waiting to install in my CT90. They seem like a great motor to keep these little cycle on the road.

nicely done

Thanks for the kind words, everybody.

An update -- after saying all the nice things about how well the Keihin clone carb works, I've had two cold starts (in the 40s) where the choke physically closes but the bike stumbles and idle is low and driveability poor until it reaches operating temperature.

I have an ATC125m carb that I've ordered a kit for and will see if the genuine Keihin works better. I'd prefer to use the stock cable choke versus the lever on the carb anyway, so we'll see how this'll work out.

Seeing the ease of this swap into an '81 has convinced me to take the plunge with mine. This is enormously useful, and if all goes well, I may even consider making the jump with my CT90s!

I also happen to have this laying around:

http://www.amazon.com/gp/product/B00H4H7P3C?psc=1&redirect=true&ref_=oh_aui_detailpage_o06_s00

So I'll report back if it's a viable option or not for this swap.

That appears to be the correct intake manifold for the forward facing 20mm carb.

Update:

The ATC125M carb I have had a poor looking casting after coming out of the Pine Sol. Several areas have corroded away and I question whether or not the jet bore threads will hold up over time....so, it was back to work on the Keikhinkt carb. I have found that the engine and carb combo like to start on full choke but almost immediately requires a change to half choke to idle properly when cold.

I've corrected a float adjustment I set too low and settled on jetting it seems to like very much -- 38 pilot, 108 main, needle clip in middle groove.

My daughter and I went for a ride together -- her on the Passport and me on my Goldwing and she was able to cruise at 50 mph and topped out over 55 mph.

I want to adjust the valves one more time and put the body work back together.

It's running really well. I took it for a ride tonight and had a driver flash me for having what he perceived to be my high beam on. I didn't. Imagine, a 6 volt headlamp too bright for oncoming drivers.

Good info, thanks!

Nice job on the conversion and write up.

Got up Sunday morning and did the valve adjustment and my daughter and I went for a 40 mile ride. With her on the Passport (all 130 lbs of her), I couldn't keep up with her. I was riding a brand new Royal Enfield I just purchased and am in the early stages of the break-in period and they break-in very slowly and at really light throttle openings. She would speed away from me at signal lights and if I was lucky I could filter up to the front to catch her before the light turned green.

At one point, she was cruising at 55 mph and I just watched her getting smaller and smaller as I struggled not to exceed 50 mph in fifth gear.

I finally caught her at a light, she flipped up her visor and said, "This thing's fast!"

Nice job! Good timing since I have a 1965 Ct200 that's giving me reliability fits. I'm seriously considering shelving the vintage motor and doing a Lifan 125 swap. I like how you kept the 6 volt system, and I plan to do the same. Did you have to do anything special with the ignition switch? I've read how the powered ignition will fry the CDI, and John Pardue makes a relay to address this.

The CT200 has a more complicated five (I think) position ignition switch with various modes of lights on and off and power to the coil, etc. If it was me, I'd use the simpler on-off ignition switch from a Passport, use the electronic 6 volt R/R, get the pitbike sub-harness and adapt it to your CT200 -- easy, simple, reliable.

I also have a 1964 C200 with a very tired example of the pushrod 90 in your CT. You will not believe the difference in power and driveability that the Lifan will have in comparison. I'm a big fan of the pushrod motor but it doesn't compare to a modern Lifan in any performance category.

Yes, the CT200 has a 3 position key switch for off-on-on with headlights. I'll take your advice and do the passport switch. So that has no power that fries the CDI I assume? I rebuilt the pushrod motor last year, and it looks great, but runs like crap... I think it will be saved for garage art and the lifan will be a hell of lot more fun!

I'm only about 15 minutes away from PCC Motors in Ontario, so I'm hoping they sell "will call". I can see a Lifan 125cc swap coming soon. I need to figure out a way to cobble the sweet chrome ct200 exhaust to work with the new motor and I should be all set. Thanks again for your help!

Correct. It is a simple on-off, four wire switch. DR. ATV has a 1981 C70 wiring diagram on their site. You can view it there, or, if you need, I can e-mail you one. PM me if you'd like.

I've purchased will-call from PCC Motors when they were in Pomona. I'd think they'd still have will-call available at their new place in Ontario.

I've found with my stock Passport the brakes are merely adequate at best. Did you change, or consider modifying them to handle the increased Lifan powered speeds?