Author Topic: Carbs or coils or neither '76 250  (Read 922 times)

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Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #15 on: April 25, 2019, 04:32:20 PM »
The carbs seemed in good condition and cleaned up well. I know some parts in the carbs are new, whether they are oe or not I don't know as it was my uncles bike and he has sadly passed away.
I'll see if the gaskets, coils, leads and caps make any difference then i'll start delving back into the carbs again.
I've attached a photo of one of the carbs but its not that great, I will take another if needed.

Offline tractorman

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Re: Carbs or coils or neither '76 250
« Reply #16 on: April 25, 2019, 05:35:55 PM »
Not a great photo, but I thought the 250B used Hi Top carbs, they don't look like Hi Tops, and the idle screw looks different to my 250B carbs as well

Offline tractorman

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Re: Carbs or coils or neither '76 250
« Reply #17 on: April 25, 2019, 05:38:34 PM »
May be Hi Tops but the wrong idle screw.

Offline 5port

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Re: Carbs or coils or neither '76 250
« Reply #18 on: April 25, 2019, 08:25:28 PM »
Hi again.  Allens performance or motocarb are both good suppliers for Mikuni.  The Mikuni 5L3 Needle is rare but worth trying to get.  However, you can try the common gen Mikuni 5L1 Needle but, that has a difference of +1.5 on the clip position so if you need to try the 5L1 instead of the 5L3, for your standard setting of clip 3 you would use clip 4.5 with a 5L1. ;)  You can try the clip positions 4 and clip 5 to with the 5L1 too see how that goes, it might be good but, you can get the .5 by adding 0.5mm washer under the clip if needed to get the +0.5 adustment. 

5port
« Last Edit: April 26, 2019, 10:22:30 AM by 5port »
5port

Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #19 on: April 27, 2019, 08:04:09 AM »
Thanks 5port. I'll get in touch with them once I've fitted the electrical things.
I took some more photos of carbs, I hope they help.

Offline 5port

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Re: Carbs or coils or neither '76 250
« Reply #20 on: April 27, 2019, 08:55:40 AM »
OK,  The Main jet washer is the Mikuni part VM20/169,  Allens do the genuine part about £1 ea, yes a pound for a washer but, it is thicker than a standard 10mm brass washer  and they do work.  what happens with the old washer is that they get dished and then don't seal around the bottom of the Main jet and the Needle jet.  That can be enough to let fuel past that upsets the mixture very rich.  I always change these now.  You will see that the washer has a sharp outer edge on one face, that goes  against the Needle jet side, the rounded outer edge goes against the Main jet side.  Cheers

5port
5port

Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #21 on: April 27, 2019, 10:58:52 PM »
Thanks 5port, are they right carbs?
Once I get the electrics replaced i'll get the carb bits. Cheers.

Offline tractorman

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Re: Carbs or coils or neither '76 250
« Reply #22 on: April 28, 2019, 08:25:06 AM »
They are Hi Tops, so the right carbs. I was confused by the tick over screws, they are different to the ones on my 250B.

Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #23 on: May 15, 2019, 03:41:39 AM »
Bit of an update,

I've replaced coils, leads and plugs. Bike now starts and idles a lot better. It revs ok (not crisply, feels restricted) with no load so next avenue is to get the original carb bits.

Offline Barnett

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Re: Carbs or coils or neither '76 250
« Reply #24 on: May 15, 2019, 03:19:24 PM »
6 ohms on the coils did sound quite high btw.
Yamaha 1974 RD125 (AS3) fully restored 2018 on road
Kawasaki 1977 z650 B1 on road
Yamaha 1972/3 U.S. early RD350 ongoing project.

Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #25 on: May 16, 2019, 12:08:29 AM »
I'm going to order the correct carb bits from motocarb or Allens. What should I get to be sure carbs are ok? Needles, main jets...

Offline 5port

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Re: Carbs or coils or neither '76 250
« Reply #26 on: May 19, 2019, 09:05:19 AM »
Thanks 5port, are they right carbs?
Once I get the electrics replaced i'll get the carb bits. Cheers.

They should have 522 00 stamped on the casting where the choke plunger goes in.  ;)

5port
5port

Offline 5port

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Re: Carbs or coils or neither '76 250
« Reply #27 on: May 19, 2019, 09:20:51 AM »
I'm going to order the correct carb bits from motocarb or Allens. What should I get to be sure carbs are ok? Needles, main jets...

Hi, Here is some of the info from my earlier post,
 "RD250/400C onwards and 521/522 have remote air corrector feeds from the filterbox.  This makes some difference, especially to the remote feed carbs if you have the wrong gaskets for the early bikes without the holes in! 
Your 95 Main is correct if you have the correct air filter element with the baffles in. 
Here is the stock spec for your carbs:
Carb code: 522, Main jet 95 (std Baffled) 120 (non-std unbaffled), Needle 5L3- Clip in 3rd groove from top, Needle jet 175-O8, Slide 2.0, Pilot jet 25, Air screw 1.25 turns out from lightly seated, Floatsetting, 16mm (lever type)  23mm (one-piece type)."

You need to work methodically with good tools and on a bench/table to do carbs properly.  Be particular about what type of airfilter you use and the Main jet.  The filter with nothing in the centre is unbaffled and needs about a 120 Main jet on the RD250.  The filter box needs to run with the lid on or, the jetting is changed.
You might well have the correct Needles and Needle jets.  The OE Mikuni 5L3 Needle is difficult to find so, be careful with them if you have them.  I would suggest that you replace the Pilot jets and Main jets with new gen Mikuni, then you know they are correct and not worn/bored-out/partly blocked etc.  Get those VM20/169 gen Mikuni jet washers as well!  Cheers

5port 
« Last Edit: May 19, 2019, 07:08:23 PM by 5port »
5port

Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #28 on: May 19, 2019, 08:30:01 PM »
Thanks 5port,

I've sent a list of bits to motocarb, Pilot jets, Main jets, Needle jet, needles, VM20/169 washers and also a pair of 120 main jets so i'm covered if i change the filter. Hopefully this will sort things out.



Offline tidyrob69

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Re: Carbs or coils or neither '76 250
« Reply #29 on: July 12, 2019, 02:56:00 AM »
It's been a while but I've not had the time to look at it. I've fitted pilot jets, main jets, needle jets and washers. I've blasted them all with carb cleaner whilst apart. I've set the float height too- I assume its measured from the face of the carb the gasket sits on to the outer face of the brass lever plate. And I've fitted the correct gaskets.
I noticed there is small brass pick up pipe missing off one of the carbs, should this be the case, does one have and one not or should they both have them fitted. See picture which shows missing tube (would go in hole next to verniers) and also shows how I measured float height.