CB750 Chopper Revival - Boiling The Intake Manifolds To Soften Rubber!
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- Опубліковано 7 січ 2024
- Like all of you I have fought removing and installing carburetors due to hard intake manifolds and wish there was an easy trick to help. Well here is an easy and cheap trick that works very well and it's simply boiling them in water! Now, this is not the BEST way but it does help a lot.
From what I have seen, wintergreen oil is possibly the best method and I plan to soften these intakes and you can see that in this great video from Doc Jones Garage where he demonstrates the process:
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I prefer my intake manifolds Al Dente, personally
Maybe when you do this with the Benelli you can try throwing in some olive oil and Oregano and a pinch of salt
Well maybe I should have done these in my rice cooker for better flavor. The Benelli will be a special recipe for sure though!
@@BrickHouseBuilds 😂Never too late to give them all a shot of Teriyaki and stuff some broccoli in them
It's too early to be hungry for lunch my dude
@@BrickHouseBuilds hahaha
Don't forget the garlic! 😊
You’re doing the lord’s work. Frankly I would not be working on projects rn if it wasn’t for your work
🙏🙏
I have used ethanol and winter green oil. It does work. But 2 minor points. Don't get distracted by a cold and leave them soaking for a week - they were lovely and soft, but rather bigger than they were meant to be! Secondly, I would say to do it in an area that can be easily ventilated as they smell of the winter green oil is strong.
Good tips!
BJ, love your mad scientist way to approaching what you are doing. Figuring it out and thinking through issues is such a valuable quality in life. Love the effort you put in to keeping as much original as possible and showing your personal techniques and willingness to show your errors. Like many others these videos are invaluable to me! I learn so much I am looking forward to applying myself.
Well thank you! Im just like anyone else working to bring these bikes back to life so it's my goal to show the tricks as well as where I go wrong
I've used the wintergreen method and I have found it works. If they are exceptionally hard, you may need to soak them for 2-3 days. Love your videos.
A lesson in patience. Thank you, it's nice to see that it happens to you Pro's aswell.
Old machines require patience for sure
That is why , we put a small mark, with relative place on engine , or whatever, before dissasembly.
I have encountered exactly the same problems on my 4 cylinder Kavasakis, years ago. I set the manifold out in the direct sunlight, for a couple of hours, and that warmed/softened them enough to install the carbs, and then the airbox. I have used a small rubber mallet to fully seat the carbs before airbox install. Good, concise, video!
Glad you enjoyed!
Took off the airbox from my YZF750R last night to swap out the plugs and couldn't for the life of me put it back on because the rubber boots were hard as a rock. I think spraying some silicone spray after taking them out of the boiling water might soften them up even more. I will definitely try this method! Thanks!
Cool idea, boil the rubber manifolds, forget the boiled eggs☕🍽
I saw guys using wintergreen oil years ago but never took it seriously. I look forward to your results. She's looking good. I saw someone use a ratchet strap to draw the carbs into the manifold. Worked, lol.
I've done that many times. By simply boiling them there is no need for straps any longer.
Needed to be repositioned just a couple of degrees to be back where they had been for the last 50 years. Nice work, easy to follow and some good tips.
Usually I can see and feel where they were but think with having them switched around I missed it by a degree which is all it took. Simply fix that made for a great demonstration though so win win!
Hey BJ great video as usual! Thanks for the shout out!, like you saw in my wintergreen update video, after a year plus the boots were still pretty soft, maybe stiffened up a tiny bit but no where near as bad they were at the start.
I paid around 50 bucks US for that amount and you can use it over and over. 🍻
Oh definitely liked the results with your follow-up video. You had fantastic results
I did this same job 43 years ago. It was just as painful as I recall. I bought mine, a 1976 K6, in bits so no point of reference as such. Great bike all the same!
A great vid BJ, love you being so honest, no retakes to cover up any oops moments, top respect to, not only your skill, but also the perfection you require, before you are happy, I am just the same in my line of work. 😁
sometimes the simplest things work best - nicely made and presented too 👍
Thank ya
I've experimented with the wintergreen method and learned that it can be a good short-term fix, but they do harden up again. After treatment, they can get as soft as new, which is great for assembly, but after a few weeks (depending on temperature, etc), they do harden up again.
If it's an application where the hardness doesn't cause a problem after they're installed, then it's a simple and very cheap solution, and makes installation SOO much easier than trying to dunk in got water or use a heat gun. But, if you need them to stay soft for proper function, then it's not going to make much difference in the long term.
I've done it with 3:1 alcohol and wintergreen oil, and soak them for a day to a week, depending on the part. They do swell up, but I've found they shrink back down to proper size in another day or two.
I also use silicone oil for assembly and rubber protection. Unfortunately, it does not seem to help prolong the softness of wintergreen treatment much.
When I commented previously, I was watching the first stages of your dispute with the airbox. I should have watched all the way thru, because you showed the solution to a problem I have fought for years!
Thanks for showing an old dog a new trick!
It happens! Glad you found it useful
I had a heck of a time getting my CB750 carbs back on the first time I took them off. Every time I've had them off since then has been a breeze. Maybe my technique has gotten better. I use 2 heavy duty zip ties to hang the carb rack from the motorcycle frame just above it and get it so it's sitting right against the manifolds, then I grab them and work them in. Sometimes starting with one side then doing the other...which is why the zip ties help hold it in place...and if it falls it won't take tumble.. Tilting from bottom to top rather than just a straight shove inward seems to work well.
Ive used straps in the past but since taking more time with the manifolds like shown I havent needed to use straps.
When you boil them, leave them in the water to cool slowly. They will stay softer for longer - it's similar to not quenching metal when it's red hot to harden it. The slower the molecular structure cools from its heat agitated state the softer it's likely to be.
That would make for a good experiment
@@BrickHouseBuildsif you want a further experiment soak them in a solution of three parts isopropyl alcohol and one part methyl salicylate for 24 hrs. These are the basic ingredients that make up Wintergreen but in a more refined mixture specific to softening rubber
Great vid! Yeah, numbers on the intakes don’t face 100% north or you’ll end up with skewed carbs. Learned that on my last 750 😂 was fighting the airbox too
Its like 99% true north lol
@@BrickHouseBuilds correct!
Never tried this trick but I definetaly will. Thanks for the helpful tips man. Im happy I found your channel.
Glad you found it helpful! It's not a forever fix but definitely works for a while
Great Job young man, Hope you had a Great New Years. Don, California. 1-8-2024.
Great catch on the angles for air box!
Hopefully it helps others
Try Rubbing Alcohol - lightly spraying from a repurposed spray bottle -on those rubber boots when sliding them into place/on the cylinder head stubs. Evaporates quickly....no need to drench, but you do have to work fast
Nice video BJ. If there's a will there's a way. RIDE SAFE OUT THERE!
I have also used Methyl salicylate (oil of wintergeen). It works well. I have put them in ziploc bag with the oil and floated it in my ultrasonic with just the heat to speed up the softening. They can swell if left too long but a rinse with hot water and let them dry for a couple of days will shrink back to size.
Good tips!
Great video
After boiling, and in general, Permatex green silicone grease is awesome for rubber parts!!!! And for my leather boots 😂😂😂😂😂
Wow! Great to know about the orientation and numbers on the boots! Thanks!
Glad it had some helpful info!
I had the same exact issue when I put new intake rubbers on. Make sure to check that the carb float bowls are level with the earth.
Awesome video BJ! They are so helpful! BTW I'm going (this morning) to look at a 1973 CB750 that has been sitting in a garage for the past 10 years. She knows what it is worth so no 100 dollar deals here. But it "looks" complete and nice in the pics. I'll let you know... Your videos (which I have watched over and over) will be key in helping me get this thing back on the road (if I buy it). Thanks again!!
Good luck with it! That sounds promising though!
Nice job BJ we can’t be perfect if we don’t make mistakes 😉 can’t wait to hear it should be nice man 👍👌❤️
100%
Thanks for letting us see the thinking through the issues 👍
Thats how I like to do it! Makes it easy to follow. I have a great one on diagnosing an electric fault on my cb750 that demonstrates this perfect
Great video BJ informative and helpful tips
Thank ya
Great advice
🤘🤘
I was working on a friend's Suzuki lt250r that had a rock hard intake manifold and I got the idea of soaking it in lacquer thinner overnight and it worked for me. Sprayed some Armor All on it afterwards to protect it. Saved me from having to buy a new one
Nice!
Another Master Class! Thanks for sharing all that you do!
🙏🙏
Another excellent instructional video, man! 🍻🤘💜
Thank ya!
Those carbs look fantastic! Wow, they went in easy!
Pretty easy considering you need a prybar to remove them
Hey BJ; I sprung for some wintergreen oil, and wintergreen infused isopropyl. The latter costs the same as regular alcohol. Guys use 1 part wintergreen to 3 or 4 parts straight alcohol. I figure I can stretch that a bit as the oil's $45 a pint!
Yeah I definitely plan to try that
You'll always see, it's a small thing, that can drive you nuts and you have to fidle at least 15 min. until you wise up and start thinking, shit i really do need to screw this and that loose!
Nice, funny thing is that i use that CB750 (80-81) rubber intake manifold to connect a PWK carb on my chinise enduro because of the curvature and internal measurements.
We are all learning till the brain loses control, - you fixed it naye problem
🤘🤘
I use either my heat gun (carefully) or an old hairdryer when fitting old intake rubbers, it’s just a matter of getting them hot ,and hot air is more convenient than winter green or water I recon, the hairdryer is probably best as you can leave it running blowing hot air in the direction of the intakes whilst you push the carbs into place (using light oil as well of course).
I have always used heat but feel they rapidly cool and need to keep going back. Boiling these was noticeably easier for installation as compared to my normal heat gun.
On my 72, I replaced the airbox boots with OEM Honda, but the very next time I r&r'd the airbox, they had hardened and shriveled up, such that it makes it almost impossible to get them fully seated onto the carbs, much more difficult than the intake manifolds. I hope you have better luck than me.
Or at least don't have to take the airbox off again.
Stellar!
🤘🤘
Hello BJ, that was an interesting little struggle! To be honest, with the benefit of watching your video on a TV screen, it became apparent that when looking at the carburettor, when correctly seated, the line of the upper frame with the air box mounting bracket was parallel to the upper carburettor throttle cable mount and the float bowl upper line.
So you could use a T square from the upper frame to set the carburettor mounting rubbers at 90 degrees which should help align all the mounting rubbers ready to accept the air box.
Great video BJ thanks for the update. Looking forward to seeing this one progress.
Best wishes Kevin.
It would be close but it doesn't need to be that technical. Normally I can line up the indentations on the manifolds but these were just harder to see.
Lunch is served!😂 Very interesting trick! 🤔
Lol boot soup especial
In 50 years of this....I nominate the 87 to 90 Ninja/GPX 750 as the WORST rack to wrestle into place!
I bet those are very tricky indeed
Like others mentioned, Wintergreen works very well. Three to one ratio with rubbing or isopropyl alcohol and they soften up nicely. Check after a day and then adjust as needed.
Noted! I definitely plan to try it
The wintergreen oil works very well, but, use caution and make sure to check it at least daily during soaking as they can tend to get too soft and elongate. Takes far longer to shrink back than getting them more pliable. Just a note from someone that left in a bath for 7 days and had to get NEW ONES cause they were way out of size.
Noted
the bigger and older the piece, the more benefit from wintergreen. outside air will be valued highly. also takes longer than 5 min what I really want though is a can of Goof Off
Wintergreen is expensive. Methyl salicylate is the same thing really and it really works.
Ill have to look that up
Excellent video on how to(or how not to)reinstall the carbs on the CB750, only one way they go on! Try a CBX carb rack sometime...................do get new rubber manifolds if at all possible for bikes like that.
Great job, bet that bike is gonna run like a watch. Thanks BJ!
Yeah I'll replace the cbx intakes for sure. That's a pain I don't wish to experience
When I am fitting this type of rubber boot, I smear some petroleum jelly on the interfacing surface. It greatly reduces the amount of force needed to get them seated.
When I use that I get a lot of comments saying its a terrible thing to do. Thats why I use silicone lubricant.
What are the negative comments referring to?
@@BrickHouseBuilds after some research, it appears that petroleum jelly will attack natural rubber. While the boots in question are not natural rubber, I'm sure you'd rather avoid the grief from commenters ;-)
In the past any time I've ever use petroleum jelly I get many comments saying the world will end
Methyl Salicylate (Wintergreen Oil) is the business.
I mention wintergreen oil in the video yes
Hi. Brilliant video top man. Be very grateful it’s a Honda 750 not a kawasaki kz650. same job Bloody nightmare, Jeff.
These are definitely the easier airboxes to fight with
wd-40 deteriorates rubber , i use straight silicone , a light coat place in freezer bag let it sit it takes awhile but they come out like new .
Looks like those manifolds got real heavy all of a sudden! Lol, even worse if there's a tiny unnoticed hole in the finger of a glove!😂😂❤❤
😂😂
Hey BJ… have you ever tried Motul Shine & Go on your plastics ? I use it for painted and unpainted surfaces, works great, spray on, let sit… wipe off. Find it better than the Back to Black..
I have not but will keep that in mind
Looking very nice, BJ! I normally hate the stuff but I have experimented with Armor All a few times. I have soaked sidecover grommets and ECU mounts over night and the rubber acts like new. I would try it on one of the old airbox boots to see if it could work on those.
Do they sell a volume of liquid or anything?
Well, beyond what's in a spray bottle
@@BrickHouseBuilds
Not that I am aware of. My bottle was from the 80s, spray type.
@@BrickHouseBuilds I have a half gallon or so jug of it so I know they sell it besides spray bottles
Good soup
Not much flavor though
They can be a fight.
Definitely
Vaseline is your friend 😊
If I would have used that I would get many comments saying I was ruining the rubber for some reason. I've used that in the past and many people threw a fit lol
I have tried wintergreen oil as well. Too long in the juice and the rubber tears like wet paper!
Wow I wish I had thought of this before tackling this project. Always seems to be during winter right? I may have missed a video but what spring did you use for throttle return on the carbs. Mine is a beast to turn even with new cables. The carbs move smooth without the spring.
Winter doesn't really have an effect here. Just heat cycles and age. Making sure the carbs can actuate freely is important as well as a lubricated throttle, lubricated cables, and proper cable routing which makes a huge difference. In my electrical video after this you see me hook up the cables but still have to lift up a pcv hose for smooth operation.
I have an experiment for you if you have an extra old hard boot lying around, and I have no idea if this will work. If I had one I would try it myself. What would happen if you coat an old boot with vaseline to see if it will soften it? Or some other lube? Just wondering.
🤔IM hungry my friend 😅
My VN750 has intake boot alignment marks on the rubber and intake itself. Did you happen to check for such marks on this set? I do understand the numbering system for the boots, but maybe there's actual alignment marks.
These do not on the cylinder side. Usually there are marks on the velocity stacks that help but not all the time
I noticed that the airbox said,750F could they be a difference with K models
No they all say that actually
Made in Japan millimeters 😊 kvalitet 👍 But today not desam Thailand Kina Italy india 😢
I dont understand what you mean
I have a ZL1000A1 and I would rather disassemble the whole engine and lick it clean before dealing with the rubber boots going to the air box. I have never found an easy way to deal with them.
Thats pretty extreme lol
I know you have your own bikes you work on and enjoy, but do you help viewers by any chance?
I get multiple emails, calls, and messages daily from the moto community and do my best to help everyone with their questions. I don't have time to take on physical work though
Maybe try this method if you’re the type of guy that likes ripping your carbs off every now and then. I’m not the type. I just buy new OEM carb holders, they cost between $25 to $35 each and last for decades.
I don't see your logic here
If money isn't an issue then yeah, replacement them. But if they aren't cracked then I don't see why you wouldn't just try to reuse them and save $100-$140. might not seem like a lot, but you can nickle and dime yourself to death with these old machines.
The Wintergreen oil method is a good short term fix, but the rubber returns to a granite like state after a few months unfortunately..
Hmm, that would be unfortunate
That's been my experience as well. After treatment, they can get as soft as new, which is great for assembly, but after a few weeks (depending on temperature, etc), they do harden up again.
If it's an application where the hardness doesn't cause a problem after they're installed, then it's a simple and very cheap solution, and makes installation SOO much easier than trying to dunk in got water or use a heat gun. But, if you need them to stay soft for proper function, then it's not going to make much difference in the long term.