Three-Seventy

[archloafer]

Just been looking at some of the other projects people are doing on this part of the forum - all great stuff. This thread might not be particularly interesting in comparison!

Couple of years ago I heard someone mention that Ron of Fahron was looking to retire, so I got a 250 top end and sent it up to him for a 370 conversion. Got it back in the middle of last year - time now to put it all together.

I guess everyone has seen examples of his work. I'm a 250 owner, have had little to do with 350s. Look at the size of those bores!







All cleaned up and sent off for powder coating - should be getting them back early next week.

I thought about going all-in and getting PWKs and some mid range pipes, but decided to get some 31k carbs and stick with the allspeeds I already have, for the time being. This combination might well be enough for what I want, which is a bike with more useable power than my peaky 275.

Thanks to reedpete for these:



I stripped them down this evening and am taking them to be ultrasonically cleaned tomorrow morning.



I took the brass balls out of the back - no drill press, couple of small slippages (!), not too bad fortunately. Also tapped the holes for grub screws.



I've got a few replacement parts already - gaskets, float bowl and drain screws / washers, new o-rings for the idle screws. Float valves and seats are £40-odd from Yamaha, each! I called Allen's and they have none in stock, waiting on a delivery, *might* be a couple of weeks. Don't want to use Keyster stuff and I read on here that Tourmax used to be OK but might not be anymore. Had a scout around and found someone on eBay selling NOS ones for a not-exactly-cheap but acceptable price, so got a couple of those on the way.

I was looking for o-rings for the air screws (Allen's also waiting on those) and stumbled across some complete gen Yam screw sets, from the US, about half what they cost here. International postage was expensive, but as luck would have it my wife is over there at the moment so I got them posted to her and she will bring them over. Bonus. As a reward I will give her the old set and she can make a nice pair of earrings out of them.

Couple of questions:

Standard 31k jetting likely to be OK for this setup?

Needle clips are on the bottom notch - my inclination would be to move them to the middle to begin with?

Cheers - David

[4l04ever]

Standard air box?

[archloafer]

Mar 9, 2024 8:44:05 GMT 1 4l04ever said:

Standard air box?

Yeah, standard. Snorkel removed.

[4l04ever]

I always use the Tourmax needle valves and seats. Not had any problems so far.

I would either put the snorkel back in or go up a few more jet sizes to start with. Maybe 25 pilots and 260 mains? These will probably be a bit rich, but better to start rich and work your way back down. Try clips in the middle to start with so you can go either way and see if it improves or not.

[jon]

Is it just me that can’t see the pictures?

Jon

[4l04ever]

Mar 9, 2024 10:36:21 GMT 1 jon said:

Is it just me that can’t see the pictures?

Jon

Yes....I can see them from my PC on Firefox.

[midlifecrisisrd]

No probs with the pics on my phone on Chrome

Steve

[JonW]

Just you Jon...

[stusco]

I cant see them on safari on my ipad

[archloafer]

Mar 9, 2024 10:36:21 GMT 1 jon said:

Is it just me that can’t see the pictures?

Jon

Odd. What platform / browser are you using? The photo's are shared from a public folder on Dropbox, fyi.

[zig]

nice work



ZiG

[lcmarky]

Nice.. I have a Fahron 400cc re-lined barrels and re-profiled head in my hybrid. If I were you, I'd swap out those carbs for some Keihin PWK jobbies.

Very pleased with the motor & off to see Mutt's Nutts for a dyno in April.

[lcmarky]

Squish Solder 1 by KTM Marky, on Flickr

..bores did you say!

[archloafer]

Mar 12, 2024 18:25:57 GMT 1 lcmarky said:

Nice.. I have a Fahron 400cc re-lined barrels and re-profiled head in my hybrid. If I were you, I'd swap out those carbs for some Keihin PWK jobbies.

Very pleased with tow motor & off to see Mutt's Nutts for a dyno in April.

I have heard good things about PWKs. At the moment though I just want to get it running and ride it. I might look at some further upgrades later on in the year, depending on how I like it as it is.

I will (hopefully - not booked anything yet) be taking mine to 2T engineering for a bit of dyno time. Seems to be the closest to me with some 2-stroke knowledge.

What sort of power are you anticipating you will get out of yours?

[archloafer]

Mar 12, 2024 18:27:14 GMT 1 lcmarky said:

Squish Solder 1 by KTM Marky, on Flickr

..bores did you say!

Bores indeed! Lovely stuff. Cool squish measuring method. I suppose you can do that with o-rings - not really possible with a normal single-use head gasket. I'll be using the traditional solder through the spark plug hole technique.

[4l04ever]

The solder on the top of the pistons can be inaccurate due to having to remove the head to check the solder, as there is some play in the head to cylinder fitment which can affect the squish. If you fit an LC head loosely, you can move the head around a few mm left/right and front/back compared to the cylinders. If you go through the plug hole, once you are good, you can leave it at that.

[lcmarky]

I torqued mine down to measure..

[4l04ever]

Every time you remove and refit the head (including torquing it down each time), it ends up in a slightly different place, so the squish changes. This is the case because on LC top ends there are no alignment dowels.

[archloafer]

Picked up the carbs. Really pleased with how they have come up.




Float valve kits arrived, in little protective johnnies. Different to the ones that came out of the carbs (on the right), which look more like 4l0/4l1, to my eye at least.






Not encountered the valves with the wire clip before - I'm assuming this is correct.




1mm short, something amiss.




Part no is correct. Got other stuff to do so will have to re-visit this, soon. Will put the old valves and seats back in and measure the float height, take it from there. The new seat does look slightly different to the old one - might end up having to use the new valve in the old seat, perhaps. Bit wary about bending the floats.


Cleaned up the idle screws with a scotchbrite mop on a Dremel, fitted the new o-rings. Discovered that my Dremel now has only 2 speeds, off and full-tilt! Hoping the switch is replaceable.






Left one came out of the 31K, middle out of my box of old carb bits so would have been from the 250 carbs, right is one I bought when I refurbed the 250 carbs a few years back. I put the new (ish) one into the 31Ks, the decent looking middle one into the 250s and the dirty one in with the spares.




Grub screws in with a bit of stud lock. Nearly ready - just waiting for the new mixture screws, figure out the float height issue. I was hoping to keep the 250 carbs complete, but I might borrow the cable guides, which are in better nick, and the rubber caps, which are relatively new.




Got the top end back from the powder coaters. Some scuffs and scratches evident that weren't there before






I cleaned off the masking residue with white spirit, went round the edge of the mating surfaces carefully with a stanley blade to remove the powder that had bled under the masking. Then gently went over the top of the head and the inlets with some 400 grit, then 600 grit wet and dry on a flat thing, with plenty of GT85. Did the surface of the head and the top and bottom of the barrels with some fine (grey) scotchbrite... and plenty of GT85. All now looking good.












The small patch of bubbling on the head is due to 'outgassing' - gas released from the alloy when it is heated. It was worse than shown above when they first did it so I asked them to have another go. They could have done it yet again to try and get it perfect, but there's no guarantee that would be the case. Might well have come out worse again. Anyway, it's at the back so won't be visible when on the bike, and the coating is solid.

[midlifecrisisrd]

Hi

Not unusual for the float height to be different after new seats and valves

Just adjust the tang on the floats that operates the valve

Totally normal to adjust them

Steve

[tony2stroke]

As you say David, the right needle valve looks like a 4l0 4l1 item, 2.5, the left looks correct for 31k 31w, 2.8 mine is (genuine mikuni) they both fit both carbs, the needle is slightly fatter around main body on 31k with a rubber tip, I would say hence the slightly larger 0.3 valve seat, so I would not recommend using that needle in the 4l0 seat, or vice versa, adjust the float tab to the new correct needle valves, they had the wrong ones to start with, now you have the correct ones.


Is your new valve seat 2.8 or 2.5? Just to clarify.

[archloafer]

Mar 18, 2024 9:49:36 GMT 1 midlifecrisisrd said:

Hi

Not unusual for the float height to be different after new seats and valves

Just adjust the tang on the floats that operates the valve

Totally normal to adjust them

Steve

Thanks Steve - that's reassuring. I was looking at the floats yesterday thinking of the best way to adjust them. Seems blindingly obvious now

[archloafer]

Mar 18, 2024 10:28:58 GMT 1 tony2stroke said:

As you say David, the right needle valve looks like a 4l0 4l1 item, 2.5, the left looks correct for 31k 31w, 2.8 mine is (genuine mikuni) they both fit both carbs, the needle is slightly fatter around main body on 31k with a rubber tip, I would say hence the slightly larger 0.3 valve seat, so I would not recommend using that needle in the 4l0 seat, or vice versa, adjust the float tab to the new correct needle valves, they had the wrong ones to start with, now you have the correct ones.


Is your new valve seat 2.8 or 2.5? Just to clarify.

Hey Tony. I would have to take the seat out to check, which I will do next time I'm in the garage. They are genuine Yam parts so odds-on that they are correct.

[steve63]

Top work and nice photos 

[abar121]

Just lovely!

I have a 370 from Ron waiting now to be fitted. Can't wait to get on with it

[wallcraft]

Very nice…. are these 370’s all mid-range tunes that Ron specifies?

Seen some were the cylinder spigot is shaped leading into the transfer ports and some that aren’t like above pictures, what’s the difference in performance?👍

[4l04ever]

There are 3 different models of 4L1 cylinders, so that could be a difference.

[4l04ever]

You can file original LC 4L0 needle valve seats down so you can use the YPVS needles in them.

[archloafer]

Slight problem. I have allspeeds, as already mentioned, which were working OK on the 250. That has the the later type barrels with the wide copper gasket.

The 370 barrels are early type with the thin gasket. Looking at them I can see how it would work with standard pipes - the flange would push the end of the pipe against the crush ring gasket and then the flange itself would come into contact with the flat gasket. That isn't going to work as well with the barrel stubs.

The ID of the stub is only slightly smaller than the OD of the gasket.






The un-compressed gasket has a gap between it and the OD of the recess in the barrel, to allow it to expand when compressed I assume.




It's going to be tricky to line everything up with the barrels in place on the engine and get the stubs to make useful contact with the gasket.

Also, worse, is that the stubs don't sit flat against the barrels. Bent.




This will be due to the gaskets on the 250 not compressing right down, and me over-tightening the nuts


I spoke to the guy who did the carb cleaning about this (that would be Stewart of Stewart's Motorcycles in Hampton - good bloke). I brought them in to him and he gave them a donk on his fly press. Bloody steel, kept springing back. Applied a bit of heat and tried again. Better (one slightly better than the other) but still not as flat as I want them to be.






He thought about sticking them in the lathe and machining them flat, but decided they would be a bit on the thin side afterwards. Ho-hum.

I will have another go at straightening them. I don't have a press, but I do have a vice and some thick, flat bits of metal that I can squeeze them between. Maybe a bit more heat would help. The hottest thing I have is a mapp gas torch, which should be enough.

If this doesn't work then I suppose I will need to look at getting some more stubs made. Any likely candidates? I'm thinking someone who makes pipes would be best, rather than a general fabricator of things.

[archloafer]

Mar 18, 2024 22:12:02 GMT 1 wallcraft said:

Very nice…. are these 370’s all mid-range tunes that Ron specifies?

Seen some were the cylinder spigot is shaped leading into the transfer ports and some that aren’t like above pictures, what’s the difference in performance?👍

Interesting - I've heard people on here talk about 'fast road' and other tunes in relation to 370 conversions, but when I spoke to Ron on the phone he said that he does them all the same Perhaps with some necessary variation, depending on what you send him, as Rob has pointed out.