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350LC transfer port heights


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Just popped the barrels on the 350lc and done a quick measure on the main transfer heights .

lh barrel 42.4 one side 43.0 on the other.

rh barrel 42.6 one side 43.6 other.

differences seem a lot to me, but will they make a significant difference on a road bike engine ?

 

Opinions please !

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Tom Mac

Assuming the barrels are "standard" I doubt it would make "that" much difference, but if they've been ported already I'd be getting them matched by someone who knows what they are doing.

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46 minutes ago, Tom Mac said:

Assuming the barrels are "standard" I doubt it would make "that" much difference, but if they've been ported already I'd be getting them matched by someone who knows what they are doing.

That is one of the options I am thinking !

Exhaust ports are up at 28mm , barrels have been relined because of lumps out of transfer ports.

I guess the new liners have been matched to the bodged original porting job.

If this was going to be a "Fast" engine I would definitely be getting the barrels to a proper grown up tuner, but as this is for road use, top end not particularly important (but obviously nice), I am more concerned with not loosing bottom end and having a bigger than usual midrange flat spot.

So after a "nicely" running road engine, that is fairly reliable. I have no desire to go back to the days of feeding highly tuned LC`s on a constant diet of pistons and cranks !

I had a Terry becket "Road Tuned" LC in the 80`s that I put about 10,000 miles on before blowing it up abusing it on the track, so think that is possible.

To add confusion, It will be running on the YPVS microns it came with , as I have no standard 4L0 pipes, or have the option of a set of 31K YPVS standard pipes

Torn between getting it back together and see how it goes, (so close !) or spending more and waiting till it is "Right".

 

 

Edited by DougW
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I agree with Rich, lifted exhaust ports and Microns will be lightswitch powerband material. I'd say it would be worth matching the transfers though, as that usually improves drive and smoothness, which is what you're after. If it's any help I can do that for you?

 

 

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Match the bottom of the transfers to the crankcases😉

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  • 2 weeks later...
DougW
On 12/25/2020 at 9:56 AM, Martin77 said:

I agree with Rich, lifted exhaust ports and Microns will be lightswitch powerband material. I'd say it would be worth matching the transfers though, as that usually improves drive and smoothness, which is what you're after. If it's any help I can do that for you?

 

 

Thanks Martin.

As the people who re lined the barrels seem to think those measurements are “ normal” I’m going use the standard ypvs pipes to run it in and see how it goes. Once I have a few hundred miles on it I’ll get it dyno’d and make a decision on whether to whip the barrels off and let someone such as yourself tidy it up.

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Martin77

Sounds like a plan..

To be fair to the people who relined the cylinders, if I were given a tuned (good or otherwise) cylinder and asked to reline it, I would be inclined to copy what was there, otherwise the customer might be a bit miffed to have it returned to standard in the process. (Just being devil's advocate here... I've seen some terrible relining jobs!)

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DougW

 

Meanwhile , this has arrived.

What could possibly go wrong ?

 

20210104_131214x.thumb.jpg.8fb9bb6812871ce40670f5ff41a97589.jpg

 

(I don`t think I will risk touching the LC Barrels myself, but I have the Stan Stephens write up of the DT175 and a couple of victim barrels to play with)

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  • 2 weeks later...
DougW

Update.

Looked at fitting the PV exhausts, brackets need repositioning, but boy are they heavy.

So microns on.

Repacked, not too loud at low revs... 3 heat cycles in sounds good even with throttle slides not balanced and air screws just set at 1.5.

It has the original 4L0 carbs that have been modified in a professional looking way to the original or the dealer Yamaha mod, will have to see how it feels.

Got a set of disks to clean up, fit to the nice eBay front wheel I picked up, wait for a better covid situation, MOT , few hundred miles then Dyno time.

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2T Institue

I just remembered something , the Yamaha parallel twins respond well to at the junction of the A transfer inner wall and bore step that down about 5mm

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DougW
On 1/20/2021 at 2:42 AM, 2T Institue said:

I just remembered something , the Yamaha parallel twins respond well to at the junction of the A transfer inner wall and bore step that down about 5mm

I think they had been lowered on my barrels pre re-linering, back to standard looking now with the re-lined barrels.

3 stationary heat cycles in now, sounded worryingly crisp with a few blips up to 8,000 ish yesterday. (-1 C here then) 

Its got the original 4L0 180 mains in that it came with at the moment, thinking of putting a couple of 220`s in for peace of mind and see how it feels.

Got to wait now until covid situation a bit less serious and get an MOT for it to do some running in with a bit of load.

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  • 4 weeks later...
fabiostar

i wouldnt be doing any riding with microns and standard mains.... easier to rejet than re piston.

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DougW

It has 190 mains in that it came with , it had been running that jetting for a while judging by the bore wear and Amount of carbon. A few minor scuffs on pistons no major signs os seizing.

It has the first 4L0 carbs that have some professional looking mods to the pilot circuit that don’t match anything I have seen on web, like the dealer mods. Can’t remember precise details but it’s got the bigger pilots.

giving it a few blips up to 8,000 when air temp around 1 C it did sound worryingly crisp to me ( been playing with RM and KTM 2t jetting for last 15 years so have a fair idea about 2t sounds on different jetting now)

With that in mind I have a pair of genuine Mikuni 210 jets to go in before it sees any high revs.

Counting down the days to March 1st when it’s insured and can take it for MOT. 

I have an 18 year old son to set an example too, so no illicit late night test runs, like the neighbour used to do with his racing F2 sidecar, or someone a little closer to home on unregistered race bikes....

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