Advice For Anyone Running With Stock Dual Hitatchi Carbs

[MadMax2020]

I don't know if a stiff/tough throttle is a hugely common problem with those of us 1st gen riders and others that run with stock hitachi carbs, but I do know that mine was so bad it felt like it was seized and would suddenly snap open after a lot of force and I recently helped someone else on this forum with the same problem. Maybe it is a more common issue than I realised so here is what I did to fix it.

In between the 2 carbs, where the 2 link arms actually link up is a solid steel bushing (in the green circle) that is supposed to roll up and down the "U" shaped channel in the plate that joins the carbs together at the bottom. In my opinion this is a bad design, I found a bearing that can replace this bushing and now my throttle is smother and free-er than ever, possibly even than factory.

CARB_D~2.JPG

Try to pick up a " 688 2rs w6 " bearing. The w6 refers to the width of the bearing being 6mm, the original part is 7mm wide and has 2 x 1mm thick washers either side of it so all I did was change the washers to new ones that were 1.5mm thick to compensate for the bearing being narrower. You can also use this chance to take out some of the play by adding super thin M8 shim washers so that the whole thing isn't as loose. Standard/common type 688 2rs bearings are 4mm & 5mm thick, if you can't find the " W6 " bearing then I'm sure that a 5mm thick one will work with thicker spacer washers. I certainly wouldn't recommend using a 4mm one.

You can check if this bushing is the cause of your stiff throttle by trying to operate both sides of the carbs at once. Try rotating the left carb by its stop lever while you roll the throttle, if it is easy when both carbs are being opened up at the same time, then it is the original solid bushing binding and not rolling freely.

If this is what is wrong with your throttle and you do not want to remove your carbs again and change the bushing for a bearing like I did, then you could possibly just try to spray the bushing with your choice of spray lube/grease (ideally one with a straw so you do not end up caking your carbs with grease).

Please check the easier things first, for example;- that the throttle cable moves freely, that the plastic throttle tube isn't binding on the handlebars and that the cable hasn't become dislodged inside the switchgear - because no one I know really looks forward to removing their twin carbs on these bikes.

I hope this helps some of you out there while you have the carbs out of your bike or even if ya' don't I suppose .

[cat3]

Pics?


Sent from my iPad using Tapatalk HD

[bstig60]

Not a bad idea, but if you keep the bushing clean and use a little silicone lubricant on it you won't have a problem. I think you will find the bearing will get corrosion and dirt in it too........ over time.........

[MadMax2020]

Here are some pics, but there is not much to see tbh.

100_3667.JPG

This picture was taken from the back of the carbs as they would be sitting on the bike (I think, imagine that it is anyway) making the right carb the one with the throttle cable. In trying to figure out what was binding or jamming on my carbs, one of the things I tried was operating the carb by the throttle cable arm WITHOUT the bottom joining plate with the " U " channel and what I saw was that when the cable arm is operated, this bushing/pivot point went straight back almost perfectly horizontally heading for the rear of the bike (right towards you from from the vantage point of the picture) and the butterfly valve for the left carb didn't move at all. So when we first roll on our throttles, this bushing is being pushed into the rear most edge of the U channel at almost a 90 degree angle to it which is not a good starting point to get a solid bushing to start rolling from and this assembly rolling down the channel is what operates the 2 valves at the same time. This to me explains why my throttle was always tough to open up, but then would suddenly give after enough force was used. Not a comfortable way to ride though.

100_3675.JPG

This is actually a standard 5mm thick bearing that I ordered before I found the " W6 " 6mm bearing.

100_3676.JPG

When I measured this to know what size bearing I was looking for, I got a reading of 15.8mm across the outer edges and 15.6mm at the worn section.

When I got the bearings in I checked that they all fit in the " U " channel without getting jammed and they did with about 0.1mm or 0.2mm clearance. So right away I have taken out a lot of play that causes these carbs to be somewhat out of balance at the low end.

Not a bad idea, but if you keep the bushing clean and use a little silicone lubricant on it you won't have a problem. I think you will find the bearing will get corrosion and dirt in it too........ over time.........

Mine was clean, but it wasn't greased or lubed in the slightest. I have no doubt that it would have been better if I had just chucked some grease on it and I did advise people as such if they don't want to try the bearing mod, but having done this mod myself I thought I would share it with others for if they want to try it. I don't know if anyone else has done this before me, but I do know that I will be using a bearing from now on as the difference is night and day and I'm sure the bearing makes for an easier and lighter throttle than the greased bushing. I invite others to try it if they want to and then they can also compare.

The bearing is a 2rs type, so it's totally sealed and it's not running at high rpm, so I think that it will take years and/or loads of miles and use for the rubber seals to perish/fail.

[crdnick]

Not a bad idea, but if you keep the bushing clean and use a little silicone lubricant on it you won't have a problem. I think you will find the bearing will get corrosion and dirt in it too........ over time.........

and then it becomes a bushing like before.... its a sealed bearing, it should last for YEARS.

i did it, i did have to take the carbs off, but i just held carbs in the throttle open position and was able to swap the parts with no disassembly. pop off the c-clip and go.

[turnrightonred]

I don't know if a stiff/tough throttle is a hugely common problem with those of us 1st gen riders and others that run with stock hitachi carbs, but I do know that mine was so bad it felt like it was seized...

It sounds like the bracket may have been installed backwards. Although the linkage will work when assembled backwards. the roller will bind and wear. The number one (rear) carburetor should be bolted to the side of the bracket that says "rear" and vice versa for the number two carb.

Properly assembled, there should be very little friction and silky smooth operation.