Topic: carb insulator condition

[crashmaster]

1972 CB750 K2. I am wondering about the re use of the carb insulators that go from the carbs to the cylinder. Mine look fine other than the rubber is hard from age. Does that matter? Do we typically re use or replace these 4 items? I see used insulators on Ebay for the same price as new ones? Thanks - see pic

[kyle750]

I also am looking to replace my old and hard as a rock carb boots on my CB750.   I've read that many of the new reproduction boots are not a good fit and are made of inferior rubber and they won't last very long.  I've also read about treating the old boots with the Peppermint treatment by soaking the boots in a mixture Wintergreen Oil (methyl salicylate) and xylene. I don't know if this actually works.   IMO too much risk to buy old, used rubber boots as they might be worse than what you already have. 

I am thinking about buying this set from Yamiya

https://yamiya750.com/en/products/e153

[crashmaster]

I wouldn't buy non Honda boots. But be careful - there are knock offs that are shown in Honda bags. But if you look close, the white Honda logo is missing from the top left of the red part of the bag. There are LOTS of these on Ebay. Still would like to know what the consensus is on keep or replace. Here are links to a phony set, and an expensive used set.

https://www.ebay.com/itm/406742203684?_trkparms=itmf%3D1%26aid%3D1110006%26rkt%3D4%26mech%3D1%26algv%3DSimVIDwebV4WithCtxRankerV1UnifiedFeatures%26pmt%3D1%26amclksrc%3DITM%26sd%3D406455200733%26sid%3DAQALAAAAEP8gq8nGWh1BMGsKNcZW25I%3D%26itm%3D406742203684%26noa%3D0%26plcampt%3D0%3A159938122010%26algo%3DHOMESPLICE.SIM%26brand%3DUnbranded%26asc%3D20231107084023%26ao%3D1%26rk%3D1%26pid%3D101875%26b%3D1%26mehot%3Dnone%26lsid%3D100%26meid%3Dba80f7a669254d84a3aebd1f31b5e8be%26pg%3D2332490&_trksid=p2332490.c101875.m1851&itmprp=cksum%3A406742203684ba80f7a669254d84a3aebd1f31b5e8be%7Cenc%3AAQALAAABIKLoGo41gKHtqPfIa5lF%252FWjQjdzIQ73rtGosP%252BBGmcPis1364XGSU%252Fh7VHaFLoC%252BlkaPaNCbgY4QUTnxR74G5%252B6%252Be9mNmVFjzPbGkN7S6tk8OM6iRaa2STgyN1QEIwXbdnX96FnXWD7LcV48k9f2Tws6zYbfBfBclbvZ0N3oJzVNzlt0xYIR7twM7oiZd%252Fa60cHagjmi%252BjC21w1gmExHdVzv6hU6khVoLe7NJgBCQz6V%252F1KdoNqlRNubq5kiGjSXs4DwzN1P5EYCG9xJg8GsVCVU%252Fusps469VmHWXALM5I2Cys8GaD2lQNyD6uQXtexHiX7F5vdNZS0rfc8uBDhG%252FKg%252BTodLmabmb3EpJNY%252BE4q2Z%252Bo%252B7OD%252FrZFUz4n%252FebpXCw%253D%253D%7Campid%3APL_CLK%7Cclp%3A2332490&itmmeta=01KMY7C37SSN1MC23RX41M7141

https://www.ebay.com/itm/375266052142?var=0&mkevt=1&mkcid=1&mkrid=711-53200-19255-0&campid=5338590836&toolid=10044&loc_physical_ms=107808&customid=f99f53ca154f151c737f3a03cdf6fe7e&gclid=f99f53ca154f151c737f3a03cdf6fe7e

[kyle750]

Original and genuine Honda boots are available but expensive.  But how long ago were they actually made?  Even if OEM Honda old rubber deteriorates.  New rubber is new!

Thank You for showing the Fake boots.  Terrible.   Fake parts are a minefield nowdays!

[HondaMan]

I get them from South Sound Honda. Look under:
Shop with Us/ViewOEM parts/Honda Powersports/Motorcycle/Model with no Year section, scroll down to the CB750 stuff.

The boots get very hard and will not seal well (or at all) on the head's nipples, and then the sparkplug for the leaking (or leaky-EST) cylinder(s) get black, quick, because the airspeed in the carb with the leaky boot is moving slower than the other carb(s). Since these carbs mix much richer as the airspeed thru them slows, that plug will get dark, quick.

Lots of online misinformation revolves around this simple fact about having 4 carbs with one crankshaft: I see lots of exspurts out there talk about how the leaking vacuum causes white sparkplugs among the set: total nonsense. Heck, at 1/4 throttle (about 50 MPH in top gear) in about 10 miles at steady hiway speed with fresh sparkplugs you can see which one is leaking vacuum: it will be darkest of the set. At idle speed these carb mix at approximately 8:1 Air/Fuel ratio: at 1/4 throttle it is about 13:1. So, if there is a 20% vacuum leak at 4000 RPM in, say, the #3 boot, the #3 cylinder will receive mixture mostly from the overly rich idle circuit because the airflow over the mainjet's hole isn't high enough to create enough vacuum to suck up the fuel, and the resulting turbulence makes the idle circuit, which is quite rich, keep burping up unaerated fuel in 'chunks'. This can be felt around 1500-1800 RPM when the spark advancer's springs are also too soft, which makes this whole thing worse by advancing too soon to full advance by then: the engine starts gagging on the extra fuel in that cylinder and spitting back toward the carb, slowing down its airflow even more. Then the plug that follows in the firing order will also start getting darker because the engine stumbles slightly from that one's too-rich mix.

Get enough leaks, and all 4 plugs can get black in 100 miles. I've fixed that MANY times with new boots.

[crashmaster]

Yes - South Sound seems to have the best price. I'll swap em out. Thank you

[kyle750]

South Sound Honda - price for 4 is $120 plus shipping.   Everett Powersports also has genuine Honda -  price for 4 at $140 with shipping included.    I've ordered lots of parts from Everett on Ebay - super quick and easy to purchase, buyer protection, and parts are shipped the same day and are delivered very quickly. 

[crashmaster]

South sound wanted $30 shipping which was their flat rate and it's ridiculous how much they have raised that. I also went with Everett

[kyle750]

My clamps are horribly rusted and I bought this set of 8 used on ebay for only $20 for all 8. Trying to work within a budget

[crashmaster]

It does get pricey 

[newday777]

If your carb rubbers and the airbox rubbers are stiff and not pliable yes replace them, with new, from a reputable Honda dealer. Yes Everett Honda on Ebay is reputable as is JT Marks on Ebay.
I usually buy from South Sound Honda but figure in the shipping price and make the order big enough to make shipping work out reasonable.
As Mark said, the rubbers play a big part in proper air flow in the carburators if you want it to run good.

Buying used rubbers are going to give you poor results, at best.

Ebay is always buyer beware. You have to do your due diligence to know the real from the fake. If you are trying to get through it cheap, you will get bit.

The clamps are important too so that you get a good seal. I've bought new from South Sound but recently they have gone to cheaper black bands that don't have the edges that turn up so they could cut into the rubber easier.
I have straightened out the used clamps at the screw tabs to get the out of shape screw tabs squared up so they do the correct job. I use some square bar stock, cut to fit in the tabs and use a vise to hold the 2 pieces of the bar stock and the clamp along with a couple of hammers to straighten it out so the screws set square and flat again to the tabs. I also polish the clamps up on a buffing wheel to make them look better.
New screws too.

[newday777]

It does get pricey 

Everything about bringing these bikes up to snuff is. If you think you can only go cheap that is when you will get bit....

[Don R]

  New airbox rubbers are essential, old ones that have been fuel soaked are often hard as rock on one side. They don't soften evenly with the oil of wintergreen trick. I had a set that I left soaking too long come out looking like modern art.
  I've had some luck using the oil of wintergreen/water on intake rubbers and in my ultrasonic cleaner. I test softened a couple sets and sealed them in a jar. The next time I'm out there I'll check to see if they stayed soft. When they were freshly treated and warm from the ultrasonic bath they went on as smooth as new.

[kyle750]

Hard-to-beat price for OEM Honda airbox boots??  JT Marks is another seller offering quality genuine Honda parts and I have purchased many times from this seller.

https://www.ebay.com/itm/221403789823

As a quick Fake check.  These look like counterfeit and terrible quality:

https://www.ebay.com/itm/388830009769

[grcamna2]

subscribed

[kyle750]

Quick question to the SOHC community.  Are the engine side carb boot clamps the same size as the clamps used on the airbox side intake boots? Airbox clamps looks a little smaller??

[newday777]

Quick question to the SOHC community.  Are the engine side carb boot clamps the same size as the clamps used on the airbox side intake boots? Airbox clamps looks a little smaller??

The airbox uses smaller clamps

[kyle750]

Quick question to the SOHC community.  Are the engine side carb boot clamps the same size as the clamps used on the airbox side intake boots? Airbox clamps looks a little smaller??

The airbox uses smaller clamps

Thanks Mate! 

[seanbarney41]

Personally, I have had some success using old, hard carb boots but if it is a bike you intend to ride often and/or keep for a long time, just buy oem boots.  Don't get confused by these guys ebay listings.  The airbox boots are very affordable.  The carb boots are quite a bit more!

If you have no choice but to use old, hard carb boots, there are some things that can be done.  Heat em up with a hair dryer, heat gun or very hot water and they get soft.  But you gotta work fast before things cool off.  Also some old boots are harder than others, so at some point, they are just gonna be unworkable.  Also, I use marvel mystery oil to clean and soften them.  The results are not drastic, but at least they get a bit slippery as well.  Having good clamps is also very important.

[kyle750]

I just received an email from Everett that the OEM Honda carb boots have shipped and a tracking number was provided.  Many thanks for steering me in the right direction

[kyle750]

Apologies for the slight detour but still boot related    I just inspected my airbox to carbs intake boots and I was surprised to see that some of the clamps are not clamping at all. They rotate freely yet are tightened down to the maximum in the collars with no additional threads in the bolt. Luckily the boots are still attached and not loose.  I'm not sure how this happened?  Did the rubber compress and shrink so much over time that the clamps are too big and can no longer do their job?? Are the clamps not the correct clamps and not the right size???

Late Edit:  The clamps also appear to be put on backwards as the adjustment screw should be accessed on the outside bottom 

[bryanj]

Not unusual the rubbers seem to shrink with age

[kyle750]

Not unusual the rubbers seem to shrink with age

Thanks Mate.  New rubbers ordered and on the way 

[bryanj]

I find there are 3 main things that shrink with age

1 your belt, it must do it wont go round anymore

2 your bladder, you need more pees per hour

3 your tolerance for idiots!