Joining Air Boxes on RD250D/350

[Whitey]

So, as an update…

Replaced Air filter with baffled type, removed 250D type duct that connects two halves of air box with a straight thru modified connector, and drilled out fixed 1.0 air corrector jets and replaced with 0.5 jets. Replacing the fixed air corrector jets with treaded swappable jets was much more straight forwarded than I imagined and went well. Also, needle now 4th from top.



Unfortunately the original #25 pilot jets that I had and had been suggested I use were badly worn and one looked as though it had been opened up. So, I’ve had to fit the some new #27.5 pilot jets I have until I can order the #25’s. Wondering if I can use the air screw to compensate fir this as it’s only one size up.

Likewise, the throttle slides are still #2.5 as I’m struggling to find #2.0 atm.

So, took it for a spin around the block a few times and it was picking up quite well. Only just got it warm but it was starting to feel good.

I’ll give it a proper run tomorrow morn and report back….


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[Whitey]

Ok, an update in the 250/350 tuning journey, fir those who are interested ….

I managed to get a pair of 2.0 slides , (along with lots of other bits and bobs) thanks to fellow forum members.

Once fitted the mix seems very rich and I had to open up the air screws to 2 1/4 before I could get any sort of decent mix.

Here is the set up as it stands:

Air Box Mods:
250D Airbox
Modified / Cut down connector duct (Opened up)
Baffled Air Filter

Carb:
1A2 Carbs
#25 Pilot
#0.5 Air corrector Jet
#2.0 Cutaway slides
5L3 Needles
4th Clip down
175-08 Needle Jet
#135 Main

I was hoping to get a better result but looking at the set up, I think the richer slides and air corrector jet along with the #135 Main are making it too rich. Std 350 runs a #105 and 250D a #115.

I know that the main is mainly for  3/4-WOT but could it be making too rich further down.

Anyone have an opinion?


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[5port]

Ok, an update in the 250/350 tuning journey, fir those who are interested ….

I managed to get a pair of 2.0 slides , (along with lots of other bits and bobs) thanks to fellow forum members.

Once fitted the mix seems very rich and I had to open up the air screws to 2 1/4 before I could get any sort of decent mix.

Here is the set up as it stands:

Air Box Mods:
250D Airbox
Modified / Cut down connector duct (Opened up)
Baffled Air Filter

Carb:
1A2 Carbs
#25 Pilot
#0.5 Air corrector Jet
#2.0 Cutaway slides
5L3 Needles
4th Clip down
175-08 Needle Jet
#135 Main

I was hoping to get a better result but looking at the set up, I think the richer slides and air corrector jet along with the #135 Main are making it too rich. Std 350 runs a #105 and 250D a #115.

I know that the main is mainly for  3/4-WOT but could it be making too rich further down.

Anyone have an opinion?


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The 135 MJ is large, a 400C/D with similar airbox only runs 120.  That isn't necessarily an exact read across but bear it in mind.
Have you got new gen Mikuni jets?  You can't reliably tune with old ones you don't know are not messed-about. So, the 350B runs 2.0 Slides and 25 pilots at 1.25 turns. Sounds to me that your Pilots are possibly bigger than you think? Next is Needles and Needle jets, both can be worn.
Also, going back to the old bogey of the tiny angled Orifice for the Pilot jet, it must be clear.

Cheers

5port 

[D Peacock]

I found zero performance / jetting difference between using the Y boot and separate foam pods. I went with the seperate pods in the end for easier servicing. On a bike with standard porting and carbs the airbox will give a quiter more civilised ride however.

[Whitey]

#25 pilots are both new and gen.

As the air screws are having a fairly direct effect when turned I’m figuring that the passages are clear, I have given them several good squirts and cleans.

I could try new needle jets and needles if I can find them, but thought the MJ might be a quick fix to try as I’m trying to fix low running first before I move onto WOT settings.


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[Whitey]

I found zero performance / jetting difference between using the Y boot and separate foam pods. I went with the seperate pods in the end for easier servicing. On a bike with standard porting and carbs the airbox will give a quiter more civilised ride however.

That interesting and an option… if that’s the case, I could dispense with the 250D air box and go to pods. The 250D air box is the only part of  the air/fuel system that isn’t as per a 350 atm - (current MJ excepted)

[mention]D Peacock [/mention] Which make and type of foam pods did you use, and did you extend them away from the carbs with connecting tubes/pipes?

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[5port]

#25 pilots are both new and gen.

As the air screws are having a fairly direct effect when turned I’m figuring that the passages are clear, I have given them several good squirts and cleans.

I could try new needle jets and needles if I can find them, but thought the MJ might be a quick fix to try as I’m trying to fix low running first before I move onto WOT settings.


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Well, I can't see why your set-up is that different to my 350 conversion that runs the jetting I gave you in reply #16 and is the 350B jetting. The air filterbox is the same on my 350 conversion, although I am not certain if you are running the baffled filter, as I said you should, so that might be an issue?
Overall, setting-up is going to need doing whatever you do. The airbox with filter should be easier than no air filter, or foam socks or Y-Boot K&N with your Bleed type carbs.  The standard bleed type are notoriously tricky with no normal air filter, ask Dale A, or Dave Friest et al.  That is why they bothered to use the Primary-type carb conversion.
I think Dan has carbs with the Primary conversion.
So, what air filter element have you got fitted?

5port 
 

[Whitey]

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Well, I can't see why your set-up is that different to my 350 conversion that runs the jetting I gave you in reply #16….
So, what air filter element have you got fitted?

5port

It’s the baffled type and agreed, it’s a very similar set up to yours, that’s why I was hoping for a better result.

The only difference I can see is the main jet.

I’ll get what jets I can, have a fiddle and report back….

Oh, noted re. bleed type needle jets and good call, if I do go down the pods route I’ll mod my carbs to Primary type.

Thanks all


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[5port]

OK.  Because so much of this is experimentation, try the unbaffled air fliter with the 25's and Idle air at 1.5 turns.  As you say, the MJ should not be a problem but, it might come down a bit with experiment. You might consider also going to the bottom Needle groove if it really is rich at low/mid throttle.

5port

[D Peacock]

I used Ramair foam pods, no spacer, just straight onto the carbs.

[Whitey]

I used Ramair foam pods, no spacer, just straight onto the carbs.

Thanks, did you modify your carbs to Primary Needle Jets?


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[D Peacock]

I use carbs with Primary needle jets, they are aftermarket VM’s.

[Whitey]

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[Whitey]

Just a short update on this project…
I had a temporary good result with returning to 2.5 Slides, 120 Main and everything else the same, but the good result wasn’t consistent.

So, I’m pulling the re-build back a few stages and working through a few bugging issues like leaky fuel tap, overflowing fuel bowl, potential bad connection in ignition, and some brake and suspension upgrades.

I’m also going to go through the carbs again to make sure everything is clear and refurb the choke and move back to oil pump and not pre-mix - Then I’ll further fine tune the jetting.

Thanks to all for their help this far


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[5port]

"Overflowing fuel bowl".  You don't have a hope of setting the jetting with a flooding issue, which is likely to be a sticking float valve that needs polishing. Any other problems with fuel or ignition must be sorted.  Generally, inconsistent response shows that there are problems.  Another thing is battery. The points ignition is a bit touchy and you must have a fresh fully charged battery and have good timing and points gaps etc.
I would expect that one of the standard 350 set-ups will be close, and I think it would be the "350B" with remote air feeds etc.

Hope you get on OK.
 
5port