Honda C70 Passport - 88cc Big Bore Kit - Installation and Jetting
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- เผยแพร่เมื่อ 19 ธ.ค. 2024
- In this video I install an 88cc "big bore" kit on my 1982 Honda C70 Passport in an attempt to squeeze a little bit more power out of this awesome little motorcycle. I also make some fuel mixture and jetting changes to compensate for the larger combustion chamber volume.
#c70
#bigbore
#jetting
You need a ct90 carb. Stock carb is to small. Yes I did the 88cc with a radical cam. Ct90 carb solved all the weird running issues.
I de-restricted the exhaust on a day 1990 Honda elite 49cc 2-stroke. Whatever the power I expected to gain - say it was 10% more - I enlarged the main jet hole diameter by the square root of that, assuming that the flow through it was related to the square of the diameter. So for a 10% increase of fuel, I increased the diameter by like 3%. It worked great. That bike was indestructible, well except I broke the rear suspension twice from jumping the scooter. Easy fix and the bike performed for me then my friend for years of abuse.
Beautiful Video, Beautiful Project. I completely understand wanting to keep that beautiful bike stock. I have a 1983 C70 Passport that was complete trash when I bought it. Replaced the whole top end with a stock 72cc head and got the dumpster bike running. Because I didn't have to worry about destroying a beautiful bike I then dumped the stock airbox for a cone mesh filter, Up jetted the carb, went to a 16t sprocket. Replaced the rear wheel with a 2.75in one. And FLEW. My baby now hits about 40mph on flats and 50 down on hills. Easily floats 35 or so up hills. The stock engine is definitely the way to go. You are 100% correct saying that the exhaust and intake are the true limiters.
Thanks. Part of me wishes it was a bit rougher so I wouldn't feel bad modifying it. I've seen some really cool stuff done with these little bikes, most of them involved significant, and permanent modifications.
I was taught that in general for 4-stroke, big gains are from the intake - 2-stroke are helped from the exhaust side
Hey i doubt youd reply since its been a while but, what size of jet did you up it too?
I have an 82 passport and I'm about the same weight also live on a hilly road. It seems to have enough power just shift into 2nd up the hills.
i installed a 88cc kit on a 2006 crf70 with a racing cam and a bigger carburetor and intake tube and the stock exhaust and the bike ran extremely good , with a lot of more midrange , so my next project installed a another 88cc kit on a 1970 ct70 with a racing cam and the stock carburetor and the bike ran the same or a little worse than the stock 70, i rechecked the cam timming and ok , the only difference in between both engine is the 2006 engine has a bigger carburetor , so i am going to install bigger jets and might raise the needle and if it doesnt make a difference i will try a bigger carburetor
well i rejeted the carb with no luck ,so i installed a 20mm carb with the side intake tube and the bike had maybe a little more tork ,but still has less power than the stock 70 , so i rechecked the timming and ok and i pulled the new header pipe and installed a old header pipe with out the muffler to see if there was any obstruction in the new pipe and bike still ran the same , forgot to mention that when i build this engine i installed new set of points and condensor , and the cyllinder head has a new valve job , so the next step is to pull the head off and check the hi performance cam because it could be ground wrong , unless if someone could come up with a better idea for me to check before i start pulling the head off
well first i removed the 88cc big bore kit and i installed the stock 70cc cylinder back on with the same cylinder head and the same hi performance cam, and the stock carb , the bike ran really good , compared to the stock 70cc engine this engine has a lot more upper midrange and top end power , for whatever reason the bike ran really bad with the big bore kit
Thanks for sharing your insight on this topic Michael- was considering same for my Passport also, but now think I'll just rebuild a CT110 (Trail 90 derivative) and pop it in. Mine was great when I lived at sea level in coastal Monterey, but now in the mountains at 7350 feet elevation, she doesn't quite have the spunk she used to. Yours is an absolutely pristine example- enjoyed the video.
I suspect the stock carb is going to be a key issue with a big bore kit. The small throat is going to be a bottle neck when you are trying to push 50% more air through the engine. I believe you can get a larger carb and 90 degree elbow that will still fit under the leg guard and save all the stock parts to retain originality. Just a thought.
You're probably right. I think it was wishful thinking that I could just throw on the basic kit and get much, if any, noticeable gain in performance.
50%...? 88/70 = 1.26, so just 26% more air. Also for the exact same speed, the air will most likely be the same.
That’s the cleanest ‘82 I’ve ever seen.
Thanks
I really like this model, this saddle is great
I'm getting ready to install a new top end on my c70 and this video was very helpful : )
I'm glad it helped. Be careful not to over tighten the head nuts, they are prone to stripping.
Thanks for this great informative video. From everything I've read it needs the top end with new cam and larger valves. I bought the same bike which the previous owner replaced only what you had. Have the same issue. Will be looking to replace with larger carb but really want to replace top end.
That's what I've been seeing on forums too. I think given the condition of this particular bike the best thing to do is to leave it stock and do my best to avoid steep hills. Thanks for watching.
@@michaelsams450 what forums are the best for the cub?
@@BB-nn9en I'm sure there are plenty of them out there but I don't know of any to recommend.
Messing with the carburetor to make up for something else wrong some where will only mask a little. Valve and spark timing need to be correct before air/fuel adjustments are made. Too small a carb shouldn't matter much at the low end and low throttle opening. Half open on a 70 carb may deliver the same as a 90cc carb at 3/8 open. But what about not big enough intake tube or valves? Check valve sizes on the 90cc and carb bore. I'm hoping a bigger carb & pipe will do it. Will a 90 head fit?
Good points. To really see an improvement I would have needed to go bigger on just about everything, intake, exhaust, head, etc. This was more of an experiment to see what, if any, improvements could be had with minimal changes and without any permanent modifications and the outcome was not unexpected. Minimal changes = minimal improvements (in this case at least).
Hi. As far as I see after you install the bigger cylinder you got to go with a higher flow exhaust and higher flow bigger carburetor, and also you need bigger valve head with the valve.
*A lot of work for so little result*
( *I would 'swap out' to a 110 and save all the old stuff...now I have the 'best of both worlds'* )
Thanks for sharing ! I have the same year and color c70 I just acquired. Just got it to run and idle decently. Seems to lack power and top end. I'm experimenting with various main jets right now. I'm thinking about getting a lifan 125 motor. Any experience with those ?
I think there's only so far you can go with a 70-90cc engine. I looked into performance head kits in addition to the big bore kit but but at that point you're up around the price of a new engine so the Lifan 125 may be the way to go. That upgrade may require some minor modifications to the bike to fit. There's a pretty good thread on advrider.com showing how it can be done. Have you made any air box/exhaust changes to accommodate the jetting changes you're making?
Re: Blue Collar Money & Investing Channel,
Why not just upgrade to a Honda 110 engine? 60% increase in power and it should be a drop-in fit.
They were making that engine when the Passports were in production, so everything should same-same, with exception to bore and stroke.
I'm thinking a rebuilt versions might be a bit less expensive to get into, as well.
Worth looking into, anyway.
@@DeanMk1 do you mean a 110 from a USDM trail 110 or from a japanese version of the c70 of the same year or later ? I'm not very familiar with the japanese models.
@@michaelsams450 I couldn't get it to rev past 5000 rpms with the stock carb regardless of getting. A new carb fixed it ! Just need to rejet it since it's running a bit too rich. I have an aftermarket open cone filter on it.
@@bluecollarmoneyinvestingch396 I mean the engine used on the Trail 110 , back in the 80's....and speaking of larger engines, why didn't they make the current 125, a 130? Would keep with the tradition of enlarging displacement by 20cc's (50, 70, 90, 110).
Try a mild cam upgrade. I put one on mine and it had a ton more torque after. Night and day difference
Thanks for the recommendation. I'll look into that.
Where could I find this upgrade
@@techwithevan1071 got mine off of Amazon froma company 50 cal racing
@@bradleyyounger8499 just that cam needs to be upgraded? Can you send me a link please
I know most of these new components are well made, but I think you will find a difference after a running-in period, preferably using non-detergent mono-grade oil. I had a C50 that needed a smaller cut-out on the slide, to get better transition from low revs. I eventually ground 1/16 inch off the back of the slide which gave the desired result.
Hi, I have a 50 JDM, could you give more information on your mod and did it improve performance, thanks for any reply.
where did you buy those motorcycle wings
pretty bike
I have a question, my bike have a 47mm cilynder, can i put a 52mm cylinder? I must change the cluch, crankshaft on cilynder head? Can i just put a 52mm piston and cilynder ?
To be honest I don't know enough about this engine to give you an answer. The cylinder kit swap was the only mod that I've attempted on this engine.
@@michaelsams450 ok
Michael - Thanks for posting this video. Very informative and it was fun to take the journey with you.
Did you ever reinstall the 13 tooth front sprocket?
I ended up putting everything back to stock after playing around with a couple different setups. Thanks for watching.
@@michaelsams450 Thank you for the update.
I ASK ON SERVICE HERE AND MY BIKE WITH 47MM CILINDER HAVE 72CC AND THEY SAY I CAN PUT 52MM TO BE 88CC BUT HERE IN rOMANIA I CAN NOT FIND THIS PRODUCT :(
C90 12 v carb shouldbe fine also the same neck and the throtle cable.they are a straight fit
Hey my starter solenoid whent out on my 1980 c70 what do u recommend is anything aftermarket from eBay will work?
Many solenoids will work but you may have to make a bracket of some sort to mount it. The OEM solenoid has mounting brackets attached to the switch housing. None of the generic replacements that I've seen have the correct brackets.
@@michaelsams450 is there one in specific to use?
@@michaelsams450 cuz I can jump the starter and it fires up and I tried to text solenoid and doesn’t click 9/10 those solenoids fail right?
@@AlbertoHernandez-ql3po I haven't replaced the solenoid on my C70 so I don't know which one specifically to use. You could try asking on a scooter forum.
@@AlbertoHernandez-ql3po If the starter works when jumped it is likely either the wiring somewhere in the starter switch circuit, the solenoid, or possibly corrosion on the starter button contacts inside the switch housing. You could also have a bad ground somewhere. You can check the solenoid by putting 12V across the wires coming off of the solenoid. If it clicks you may have a wiring issue. If it does click you can verify further with a multimeter.
what sizes are your tires?
Front is 2.25-17 and rear is 2.50-17
put a lifan 125 on it they are cheap enough to not have to worry about it blowing up you can get them on amazon
I thought about doing that but all of the engine swapped C70s I've seen have required at least minor modifications to the frame/body work and my #1 requirements was to avoid any permanent modifications to the bike.
@@michaelsams450 the lifan should bolt right in given a it is a Honda cub clone engine. The only way to know would be to remove engine and check the bolt pattern.
Hi.i have 6 honda c 70 zero red and blue made in Japan 1980 how much price can I buy
Can get honda C50 for C70 conversation
I had the stock 70cc I went to 16 tooth and went from 35 mph to 47mph iam 190lbs
That's a pretty impressive gain for a simple sprocket change. Much cheaper than the big-bore route and much better results. Thanks for sharing.
My stock 1970 C70 can do about 50mph on a long straight away and I'm about 220lbs
I had a 1973 Honda C 70 ( 6 volt electrics ) kickstart,it would do 45 on the straight & 53mph when warmed up on clock in more favourable conditions ,standard spec engine & chain & sprockets . It would do the same two up ,but take a bit longer to build up speed . This was a U.K. spec model in yellow & white leg shields, points ignition gap 13 thou . I also had a bog standard 1971 C50 model ,it would do the same top speeds two up or solo ,just took longer than the C70 to reach top speed ,& was slower going up hill . The C90 would do 55 top speed & climb hills better than c50 or c 70 solo or two up . The USA C 70 had different styling on front mudguard ,different electrics & other differences like electric start & airbox . The U.K. version of C 70 had a nice chunky seat the best seat ever on any cub model .,it also had ignition key slot in side panel with light , & both side & main stands ,but no front carrier or granny’s shopping basket .
Maybe you didn't show it but I did not see you open the flywheel case to find Top dead center when installing and adjusting the cam chains top dead center & timing... valve timing could be off robbing the power. Video shows you installing the cam sprocket but not aligning it to the flywheel timing and points. Need to set Flywheel T Mark to case mark then on the cam sprocket align the circle stamp with the case mark toward front of motor.
On the later models (this one included) there are 2 caps on the side cover that can be removed and allow you to see the timing mark and also rotate the crankshaft.
You should go with a bigger front sprocket like a 16 tooth for more top end speed .
If it weren't for all of the hills in my neighborhood I would definitely give that a try. My problem is the lack of low-end power. I ended up going to a 13-tooth front sprocket which is working pretty well.
Go a tooth or two bigger on the back sprocket it will go up
Hills easier
How good is it to fill the ring right over the bore getting minute filings in the bore?
Do you mean "file the rings" over the bore? I wouldn't recommend it, or getting any debris into the engine for that matter. With that said, I don't think it will be catastrophic, but any metal in your engine that doesn't belong there is a potential source of scoring, premature wear, etc.
Cool how easy it would be to swap a piston…
Bummer! Sorry it didn't help.
Yeah, I was surprised to see virtually no improvement over stock, at least in my use case. Oh well, it's an easy switch back to stock and the project allowed me to get to know this little engine a bit better. Thanks for watching!
Sad to hear you say you don't want to live a longer and healthier life by losing weight.....
It's not that difficult, just eat healthily and walk more!
Your forgetting one small detail.... HE'S AMERICAN 🐖