Solid carb to intake boots?

I'm new to the forum, but not so new to building from scratch... Would there be any major drawbacks to fabbing some solid boots to mount up a carb rack? I know vibration could be a factor, but if properly built to withstand temps and vibration, are there any other reasons NOT to do this?

 

Do you mean the Carburetor Joints? The "boots" that go between the carb and engine? If so, I say go for it if you got good machining and fab skjlls. You'll just want to make sure you emulate size and shape since this affects flow, back pressure, etc. Heck, mold the whole thing and have something cast!!!

They are so prone to dry-rot and getting harder/more expensive to replace. If you found a surefire way to reproduce these out of superior materials, you'd be a hero and could make some cash on the side, for sure.

You'll definitely want to try to somehow incorporate a flex point or two in there. But if you can design something that is easy to replace, possibly even something that is a COTS item to use as the vibration absorber, even better.

Good luck!

 

Yep, that's the one. I've found them listed as carburetor boots, so that's just what stuck with me I guess.

The idea I was playing with was making them as a two piece unit, the manifold side being metal, and the carb side being a length of hose. Worm gear clamps can hold it all together (2 per unit) and make future hose replacement a snap (and CHEAP). The other cool thing about this setup is that it would be possible to adapt other carbs to the engine provided the hose has enough give to make it happen. In other words, hitachis and mikunis would be interchangeable with the right jetting. This would have potential to make our carbs more "universal" across all years and models.

What does the consensus say?

 

I just thought of a potential drawback to this... the transition wouldn't be smooth inside the assembly... could this be an issue, or would it matter?

 

I think you would need a perfectly smooth bore, uniform diameter across all four boots. I would also change from vacuum/petcock to straight on/off/res fuel tap. That way you don't have to over-fabricate the vacuum stubs.
FYI, I just emailed Don at JBM industries about possibly fabricating boots for the HSC 32 carbs - straight boot / no vacuum tube - the stubs may Be problematic

Dave

 

Hmm... I'll have to experiment then. Maybe I can find a way to smooth the transitions... of course if one were to want to retain the vacuum petcock, it would be a simple barb fitting tapped into the "manifold" part of the assembly. I need to find some materials and try this out.

Thanks!

 

How does one do a vacuum sync with no stubs?

 

Oops......lost in translation...and brain meld...meant the vacuum tube..would result in 4 blocked off stubs.

 

That's exactly like the way the carbs on my old race bike were set up. I've only got one slightly blurry picture, but if you look you will see the fabbed up steel adapter (RED) bolted to the head and the industrial fuel resistant hose that attaches the carb with gear clamps.
This was how I bought the bike years ago, but it made carb work easy and the hose was only a couple of buck a piece, so changing them once a year was not a wallet breaker.

 

But again raises the issue of a vacuum sync. JBM [Don] told me that this type of boot with the stub is hard to fabricate and that there are cheaper Chinese versions "out there"..........

Dave

 

Shouldn't be hard to fab this up at all. Steel bar stock for the flanges and steel pipe or tubing for the tube parts, welded up at the outer seam. I thought about o-ringing the mounting surface, but as little as they would ever need to be removed, thick rubberized paper gasket material would suffice. There may even be automotive thermostat gaskets available with the proper dimensions. I'll look through the gasket bin at the parts store if I get a set made.

As far as the vacuum ports go, drilling and tapping the pipe to accept a barbed NPT fitting would be the easiest route... especially if I can manage to get some 1/8" wall pipe or tube.

Honestly, the hardest part about this is going to be drilling out the hole in the flanges to accept the pipe. I might spring for a carbide hole saw if this project shows promise.

Maxim-X, how is the transition inside the hose on that setup? Is it smooth or is it literally just a rubber hose connecting the carb to the manifold?

 

WHERE? Considering all of our carb boots are 30ish years old... :cry:

 

Some bikes already use a similar set up. The rubbers have a step at each end so the transition is smooth.

Some others have the rubber molded right to the metal piece that bolts to the head. Honda used it on the carbureted Goldwings, Silverwings etc.

Adding a vacuum port to sync shouldn't be a big deal.

The important consideration is whether this is an improvement over the original design. I don't see where there is any advantage and it'd be a lot of work. A new set of the factory design should be good for 25 years......

 

The hose slipped over the tube and carb just like the drawing you did, like I said this was for a racing set up but I can't see it causing any problems. I also heard that a little air turbulence before entering a carb was a good thing, at least in an automotive application, not sure if there would be much with this type of design though.

 

Awesome. Thanks Maxim. One more question... did it idle and run in low RPMs normally as compared to a non-racing bike? I understand there were probably cams involved, overbore, etc... but even with the performance mods if it idled well and didn't stumble in lower RPMs, the straight hoses weren't hindering anything.

I will most likely try to insert a "step" into the hose to smooth the transition, but if it doesn't work out like that, straight hoses may still be on the table.

Here's my issue folks: I don't have a running XJ engine to test this on. I have a locked up 650 I can get measurements from though. I really need to get a running engine!

 

Once the bike had warmed up sufficiently it would idle just fine, and yes it was a "built" motor. Here is a "copy and paste" from the spec sheet that came with the bike from the original builder:

Engine: Full 360cc with slightly modified GPZ750 pistons
Exhaust Valves: stock
Inlet Valves: from Honda 450
Racing valves springs, Titanium valve spring caps
Stock crank and connecting rods
Mega Cycle racing camshaft
Inlet Ports 32 mm with 32mm Mikuni Carburretors
Barnett clutch and springs
Crankshaft mounted electronic ignition using ’84 nighthawk black box and pick ups. Other components designed and built by PS. Rev limiter max. RPM 10500
Last Dyno check showed 42 BHP

This was how it looked the last year I owned it, I sure do miss racing, but when the economy tanked and the place I worked closed it's doors and moved to Mexico the hobbies had to go.

Here's a link to one of my races, it's about 25 min long but it sure brings back memories for me.
https://vimeo.com/11014195
The racing doesn't start til about the ten minute mark, but take a look at the needle on my tach it's always in the 9-10000 range except for the slow corners.

 

Wow, that's an awesome build! I bet that thing was fun to wind out... Thanks for the info! I'll definitely check out the vid.

I suspect the crankiness at startup was a combination of the carbs and cam. Heat would help atomize the fuel in the manifolds (such is the case with most engines), and it would run better when warmed up. That may or may not be the case with these homebrew manifolds I'm suggesting.

 

Hey there, Metal Bob: Here's the reply I received from Don regarding the making of Intake boots for the HSC 32's:

"Thanks for your call and message Dave,

I think there are places that make the carburetor sockets in China. I usually don't take on any parts that are being made in China as I cannot compete. I have not seen any of those sockets, but sometimes there are rights and lefts, some have curves, etc. Tooling would be very expensive for the small number that I would sell. I know the Chinese ones are poor quality, but they are real cheap."


Don James
JBM Industries
3761 Morley Drive
Kent, OHIO 44240 USA
330-678-9537
www.jbmindustries.com

I personally cannot find anything resembling the carb/manifold boots....If I were going to keep my XJ for 25 years, I'd get oem's.....but that's not gonna happen...

Oh..Maxim...great video!!!! I got old super 8 [circa 1968] of me riding a Greeves moto x........that was then....

Dave

 

A Greeves, wow, those were the days when men were men and the BIKES scared the sheep! 8O
You should get it digitized and post it.

Graham

 

Ok folks, I need a little help with my preparations. I have a locked up 650 engine to get some of the measurements from, but no carbs. I'm lucky enough to even have 3 of the 4 stock boots too. My question is how much material do I have to mount to on the carb outlet (how deep into the hose), and how thick is it (the wall of the part of the carb the hose would mount on to)?

I assume the 32mm is the ID of the carb outlet?

 

looking forward to what you come up with, good luck man.

 

Maxim-X, I finally had time to watch the entire video you posted... freakin' awesome. Hats off to you sir, that was an excellent ride... especially coming out of turn 1, you absolutely owned that one. Also, the guy at 21:15 probably pooped a chicken when he looked back to see the 350 stuck to his tail... lol

Great video, thanks for sharing! I have to ask though, what did the guy say at the inspection station at the end of the run?

 

If I recall it was something about a puff of smoke coming out of the left exhaust. The next meet a few weeks later the engine grenaded, that's racing!

 

I documented a bit about my efforts making manifolds to adapt EFI in the Pumba build thread on here. However I have the ability to make a simple job complicated.



Unless you just want to weld up some basic old bits of pipe, the job can get more involved than you think.

 

lol darkfibre... I know what you mean. I try to keep things simple, but it often ends up not getting done because of complications... lol

You had those machined from solid round stock? My carb versions would be much simpler... flat bar stock (probably rough cut for the test units) with pipe or tubing welded into it. I need the ID and OD of the stock carbs' outlets to continue, but I can hopefully get a smooth transition inside the manifold.

 

Can anybody help me out with this? I need the ID and OD of the carb outlet where I'd be clamping the hose in the above setup.... Seriously, this could save XJ owners a lot of time and money if the prototype works right...

 

I've got my carbs off about to do a clean and rebuild while I wait on my boots and new bolts to arrive. 82 XJ650J Maxim. I'm new to XJ's and carb work, period, so, if I have what you need, let me know and I can throw some calipers on her and give you some numbers. I can even PM you my phone number and we can do it live.

I haven't looked at these carbs to see make. I would assume that given the year and exact model that only a certain carb was used. But I know some of these bikes had Mikuni and some had ... another that I can't remember. You'll have to tell me how to identify mine and see if they are what you need.

On a side note, I'm picking up a parts motor with the same carb and he's throwing a bunch of other carbs, too. If this year/model isn't what you want, maybe I'll have it soon.

 

PS - if someone came up with a set of design files for something like this, I'm sure there's GOT to eventually be a MFG that would be willing to produce these... at the very least, we could use the designs to buy these at local machine shops (or make them ourselves for those of you equipped and inclined to do so).

Wish I could machine and had a mill and a lathe!!!!!!!

 

The prototypes will be hand made with basic tools, but I will have the flanges machined if there is enough interest. I just need these measurements. Surely somebody has a set of carbs on a bench somewhere that they can get some measurements off of!

 

Ok, I've pulled a joint off the junk engine I have. I can probably get some good measurements from it if I can find my dial calipers. It's been a while since I've worked a machine shop, so this is not a commonly used tool for me... they're here somewhere though.

The next issue at hand: clearance.

I need to know how much clearance there is behind the stock air box. If there is no extra room to move the air box back, it will increase the difficulty of this project exponentially. I've searched for pictures of the setup, but can't find good shots to show what I'm looking for.

The stock joints are offset. They cast rubber over metal flanges and made up the difference between the differing centerlines of the carbs vs. the ports in the rubber part.

I can make them with the angles, but it will be a major PITA to actually get accurate measurements of this from the stock joints. If this is the case and I am unable to use the flex of the hoses to make up the differences in centerlines, these units will unfortunately have to be for pod setups only.

So, what I need: Somebody to chime in with their knowledge of the stock airbox mounting area. Can it be moved rearward any, if at all? The more clearance here, the better!

 

I didn't get them machined, I did them myself, learned heaps too.

I could help with 750 measurements from the standard set up, but not all XJs are the same, what you trying to fit them on?

 

the 650 and 750 carbs are the same.

 

I can get carb measurements from my stock joints, I need airbox clearances, in other words, how far back can the stock airbox be moved, if at all? Any and all xj bike models welcome here, the more info the better. I want them to be sort of universal if possible. I'm sure they wont work across the board due to differences in heads, but it's still worth knowing.

That's pretty awesome for homebrew darkfibre! What tools did you use?

 

Really wish this would happen.

From what I understand, the airbox doesn't move back much! I've never gone and unbolted its mounts to try, though. I'm about to remove my carbs, I'll try and do it and let you know if you're still interested.

 

I found the carb joints on boats.com and they are an exact match to the old ones.

 

part # and price please
someday i might need some

 

http://www.boats.net/parts/search/Yamaha/Motorcycle/1982/XJ750RJ/INTAKE/parts.html

http://www.apachemotorcycles.com/fiche_section_detail.asp

The Apache link won't take you directly to the parts fiche, and they don't have the model listed for all years. Look up a 1983 XJ750MK for the intake boots.

They were listed as NLA a few months ago, but aren't now.

 

I discovered years ago that "boats.net" and "boats.com" simply carry a dated version of the Yamaha dealer parts fiche. I tried on two occasions to order from them and it turned out they had no stock, no access to parts, and they tied my money up for a bit until the orders got cancelled. If someone has actually gotten hard-to-find parts from them I'd like to hear about it. On order isn't the same as "parts in hand."

If you're looking for truly "still available from Yamaha" parts, try Babbitt's. If it shows as available in the fiche, it doesn't necessarily mean THEY have it, but that somebody in the Yamaha dealer network does, and they'll get it for you (might take a while.) But be prepared to pay close to Yamaha MSRP: http://www.yamahapartshouse.com/

You can get intake manifolds of varying quality from eBay; pay Yamaha some BIG bucks for a set; or get in touch with XJ4Ever.

Plus, if money is no issue, there are a couple~three NOS suppliers around that have all SORTS of cool stuff for beaucoup $$$.

I prefer XJ4Ever. Quality parts, in stock, and not a $15 minimum to ship every blasted order.