AIRCOOLEDRDCLUB FORUM

Tech Zone => Aircooled RD Tech Help 250cc and Above => Topic started by: Ian Anderson on November 21, 2020, 09:57:05 AM

Title: RD350B choke plunger
Post by: Ian Anderson on November 21, 2020, 09:57:05 AM
Hi all,

Having sent my choke plunger away to have a viton seal fitted the Royal Mail promptly lost it despite it being sent via a tracked service. Twice in the last few months they have managed to achieve this, the first with my dating certificate sent to the DVLA. Words fail me.

Anyway back to the matter in hand, I am now without a choke plunger and need to source a replacement. There are a number on EBay and I can buy the complete lever assembly from Motocarb. The correct item is VM15/62, I believe. However can someone please supply me with all the measurements of the plunger so I double check the items on EBay before I either buy one of these or just go for the Motocarb item.

Thanks in advance.

Ian
Title: Re: RD350B choke plunger
Post by: psoidon on November 21, 2020, 10:46:41 AM
I think the correct part is - Cold Start Plunger VM26/116 ... the Dust Cap / Choke is VM20/455.
Allens have them £7.86 & £5.63 respectively.
Arrived next day. 

Title: Re: RD350B choke plunger
Post by: Ian Anderson on November 21, 2020, 10:53:55 AM
Thanks for that. However VM26/116 is the part number for the threaded nut, VM20/455 is the dust cap.

Ian
Title: Re: RD350B choke plunger
Post by: psoidon on November 21, 2020, 05:05:44 PM
Well Allens don't agree -
[attachimg=1]

Also here is new and old side by side on the invoice from Allens ... same size and fits perfectly !

[attachimg=2]

Regards Ian
Title: Re: RD350B choke plunger
Post by: Ian Anderson on November 21, 2020, 05:27:17 PM
Splendid,  thank you.

Interesting how different suppliers can give different part numbers for the same item. The attached image is from an authorised Mikuni supplier.
[attachimg=1]
Title: Re: RD350B choke plunger
Post by: Phil S on November 21, 2020, 07:16:52 PM
Will this plunger fit the VM28 RD400 carbs?

Thank you
Title: Re: RD350B choke plunger
Post by: Ian Anderson on November 21, 2020, 09:49:23 PM
While one could assume the plunger would be the same it would be prudent to email them: tech@allensperformance.co.uk
I’m sure they would be able to confirm one way or another whether it is suitable.
Ian.
Title: Re: RD350B choke plunger
Post by: 5port on November 22, 2020, 03:42:31 AM
Worth remembering that the RD carbs are bespoke Yamaha parts and some parts are not Mikuni standard parts.  The choke parts are particularly difficult to know if you can use them.  I am not certain which, if any of those Mikuni spares are the correct part.  You might find a NOS Yamaha part or, possibly buy a used carb for the spares.  Cheers

5port
Title: Re: RD350B choke plunger
Post by: Paulrs on November 22, 2020, 09:45:05 AM
5port is right to say some parts on a mikuni are bespoke to yamaha (but possibly also used by other manufacturers) so spares can be a little complicated. 
As Ian suggests it is worth contacting Allens or Motocarb about a part before buying it by part number, or in my opinion before buying overpriced NOS or used.  I used Motocarb purely because I couldn't get a reply from Allens on the day I called (to be fair to Allens it was early in lockdown 1), got to say Steve at Motocarb knew the Mikuni well and exactly what parts fitted my carbs. 
Title: Re: RD350B choke plunger
Post by: Ian Anderson on November 22, 2020, 09:49:12 AM
Given that Psoidon has already bought the parts, compared them and has provided photographic evidence I am confident that the parts are ok.
Can I ask what evidence to you have that the choke plunger would be different it would be nice to know?
There is not really an option for sourcing NOS parts so I will get them and report back whether they fir and work so others will be able to purchase with confidence.
I will also check with Allen’s tech department as they are better placed to advise whether they will fit or not.

Kind regards,

Ian
Title: Re: RD350B choke plunger
Post by: 5port on November 22, 2020, 11:38:45 AM
Given that Psoidon has already bought the parts, compared them and has provided photographic evidence I am confident that the parts are ok.
Can I ask what evidence to you have that the choke plunger would be different it would be nice to know?
There is not really an option for sourcing NOS parts so I will get them and report back whether they fir and work so others will be able to purchase with confidence.
I will also check with Allen’s tech department as they are better placed to advise whether they will fit or not.

Kind regards,

Ian

That looks like a good post by Psoidon.  The Yamaha part is 278-14171-00.  Cheapest Yamaha NOS I see is about £20.  You got to be careful though, suppliers do make mistakes.  A few years ago, some were clueless about spares like this.   :D
Also, if that VM26/116 is the correct part to be the same, the price is good, probably about £10 inc post.
Cheers

5port 
Title: Re: RD350B choke plunger
Post by: psoidon on November 22, 2020, 12:55:54 PM
I replied to Ian in a separate email, but for everyone else it probably helps if I post it here as well -


Yes it is not easy to find on their site  ... start at their shop homepage - https://www.allensperformance.co.uk/shop/ (https://www.allensperformance.co.uk/shop/)
then Spare Parts by Carb Model  -> Mikuni  -> VM Carb -> VM26-8639
It's about half way down that page.
The RD carbs are VM26 type, that model is the only one current VM26 with a choke lever rather than the pull knob,

I took a punt that it was the right one and it all looks good to me.
They have changed the actual rubber seat slightly, but it all fits as it should and I think it will work.

The bike is tucked up for the winter so I have not run it yet, but anything should be better than the 46 year old one that was in there ;-)

I'm also getting the one repaired by Rob, I have two sets of carbs, one with the Dale A mods and the original set.
I'll decide which plunger to use on each set when I get the repaired one back.

As always it is good to know if the parts are still available, but figuring out the Mikuni number system is a minefield.

I hope this helps

Regards Ian
Title: Re: RD350B choke plunger
Post by: psoidon on November 22, 2020, 01:08:57 PM
Here is a photo of the seats, new one on the right

Sorry about the quality, it's not easy to photo.

[attachimg=1]

Regards Ian
Title: Re: RD350B choke plunger
Post by: Gr8uncleal on November 22, 2020, 01:50:28 PM
Are you able to post dimensions Ian?

Thanks.
Title: Re: RD350B choke plunger
Post by: 5port on November 22, 2020, 02:03:49 PM
Mikuni numbering is complicated.  I think parts are generally numbered originally by the type and venturi size.  However, where they are then later used on another carb type, they carry the original number with them.  That is why you see Mikuni VM26 part numbers on the RD250/350/400 carbs that are all VM28 carbs but specifically bespoke Yamaha models and so, many parts are Yamaha only numbered, others are Mikuni numbered as well.
Cheers

5port
Title: Re: RD350B choke plunger
Post by: psoidon on November 22, 2020, 05:54:47 PM
Dimensions are identical, like I say the only difference is the seat.
The older part has more of a rolled edge, it looks like the newer one has a slightly different method of retaining the rubber seal.
If you look at an older part, you can see the wear at the point of contact with the carb body, looks to be about 2mm so I can't see the bigger seat making any difference.
My guess is it is just an easier manufacturing process.

At £7.86 its worth a try ;-)

Ian
Title: Re: RD350B choke plunger
Post by: Gr8uncleal on November 22, 2020, 06:36:24 PM
Thanks Ian, but what are the dimensions (length & diameter), or am I having a senior moment and have missed them?!
Title: Re: RD350B choke plunger
Post by: psoidon on November 22, 2020, 07:41:56 PM
Overall length is 40mm, dia of base 8mm, dia of shaft 4.8mm

Ian
Title: Re: RD350B choke plunger
Post by: Gr8uncleal on November 22, 2020, 08:28:16 PM
Thanks, much appreciated.
Title: Re: RD350B choke plunger
Post by: Ian Anderson on November 23, 2020, 10:44:57 PM
Attached picture shows the number of common parts across carbs. Hence the difficulty in picking the correct number.
Title: Re: RD350B choke plunger
Post by: 5port on November 24, 2020, 07:22:01 PM
And that is just the start of it!  That is just the generic Mikuni VM parts! most bikes have bespoke carbs for their production, and many parts are different. Think of the RD rubber cap on the top of the carb, the one with pleats, a RD specific part and most parts are.  The RD Carb bodies are different to the generic Mikuni VM, etc,etc. 
Cheers

5port