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4rt improvement underway. Any thoughts ?


Monty Wise One
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I'm improving my 4rt after riding it for a year as standard and knowing it can be turned into a greater bike with some nice alterations. First thing, I know it's already a great bike and Toni Bou could win on it but I want to make it better for myself, mr ordinary. I've got an ohlins shock sorted, I've already sourced a PTB, leads and software. Now I'm looking at exhaust systems to get the most out of it. I spoke to Trials enduro direct today to source an S3 titanium front pipe but they're out of stock for 4-6 weeks. I'm ordering a set of heavier springs for my tech forks as I'm happy with them apart from being soft for me. I'm not buying a Termi system as I'm not rich but Bharat anyone any advice.

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10 minutes ago, Monty Wise One said:

I'm improving my 4rt after riding it for a year as standard and knowing it can be turned into a greater bike with some nice alterations. First thing, I know it's already a great bike and Toni Bou could win on it but I want to make it better for myself, mr ordinary. I've got an ohlins shock sorted, I've already sourced a PTB, leads and software. Now I'm looking at exhaust systems to get the most out of it. I spoke to Trials enduro direct today to source an S3 titanium front pipe but they're out of stock for 4-6 weeks. I'm ordering a set of heavier springs for my tech forks as I'm happy with them apart from being soft for me. I'm not buying a Termi system as I'm not rich but Bharat anyone any advice.

Toni Bou could probably win on a rigid framed Bantam! As for your bike, you obviously love it! What about some top end engine work; polishing and porting with some appropriate mods to enhance low end torque and throttle response. What fuel are you using, pump gas or other? You don’t mention tyres, which to some riders is most important. Have you had the suspension (current) set up by someone who knows what they are doing, you may have already done this yourself perfectly well, what suits one does not always suit another??I know of one rider who spent most of his time just getting the wheel bearings as friction free as possible, alignment in the hubs, selective bearings etc, worth at least 3-4 hp he would say.

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Well, my Öhlins is going to be supplied by Andy Dawson, just waiting for the correct spring from the factory. I’ve got the twin programmable throttle body and various maps and the option of making a map once I’ve ridden the existing ones and assessed what’s good for me. I’m thinking of perhaps an S3 280 kit to enhance it. The mitani kit from H&D looks good, very exotic and importantly light weight. I’m thinking long term as I improve ( if ) I will have a great bike to continue riding. It’s not a lesson in spending money, I was intending to upgrade to a new bike which was going to cost £2k. I had a work out for some nice parts and it works out better to spend on the 4rt. I see it as a sensible choice. 

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As an added note. One of my riding buddies is rebuilding his repsol rt after it snapped the lug off the kickstart stop in the crankcase. New case imported from ?? Italy after a slow postal trip.more importantly it was half the cost of the same part from Honda UK.  He is polishing the port on his head while in pieces, he’s well versed in CRF motocross rebuilds so I’ll see how it goes. 

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Mitani exhaust is a massive saving on weight, seems to run a little smoother and looks great. Will you need two? It might not be such a good idea to do everything at once, if something isn't working for your riding style you won't know what it is. Think i would rather put new Michelin's on the back more often than put a big bore kit on. Titanium hollow spindles, now they are great when you fall off you can see right through them.

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21 minutes ago, windlestone1 said:

Mitani exhaust is a massive saving on weight, seems to run a little smoother and looks great. Will you need two? It might not be such a good idea to do everything at once, if something isn't working for your riding style you won't know what it is. Think i would rather put new Michelin's on the back more often than put a big bore kit on. Titanium hollow spindles, now they are great when you fall off you can see right through them.

If I start paying £500 for a spindle I’d need locking up. The big bore kit will add torque more than crazy power. The best fix would be a lower Idle speed that would not flame out. 

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Can be done apparently.  I think it's H&D  that have a spacer for the generator that supposedly allows a slow tickover but I have never heard of anyone trying one.

Correction, I think it was here www.montesa4rt.nl which seems to be no more.  They had lots of useful info too.  Can any of our Dutch members tell us what happened? And indeed if the spacer worked.

Edited by 2stroke4stroke
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I saw in another post that your bike is a 2016 4RT260. Something I'm curious about is the 2-Map Programmable TB/ECU. Is it for 2016+ bikes or is the standard one programmable?

What I'm trying to understand -- because I haven't seen details for newer optional PTB/ECUs and am still not clear on whether or not the standard 2016+ TB/ECUs are programmable -- is if an optional PTB/ECU for 2015 and earlier bikes will work correctly.

The reason is the fuel pump system changed in 2016. Earlier fuel pump systems used an external (attached to injector assembly) fuel pressure regulator driven by intake port vacuum. The purpose is to keep injector fuel pressure at a constant value above intake port vacuum. So the injector always has a (nearly) constant pressure difference from its input to output.

The 2016+ fuel pump system doesn't have the external, intake vacuum controlled pressure regulator. It has a pop-off valve in the internal fuel pump assembly to keep pressure (nearly) constant going to the injector input. If this is uncorrected, it means there's a higher pressure across the injector when there's higher intake vacuum. That would change the amount of fuel delivered in a given squirt duration. But I suspect there's some correction with the 2016+ ECUs, based on MAP sensor input, to offset the fuel discharge duration and compensate for fuel differential pressure variability at the injector. It's just electronic correction rather than vacuum driven diaphragm correction.

With a programmable TB/ECU, the user can add / remove fuel from the basic amount based on two variables, rpm and throttle opening percent. The user doesn't have the ability to correct fuel amount based on intake vacuum, that's done behind the scenes. And I suspect the 2016+ TB/ECUs have some additional correction to mimic the external pressure regulator on 2015 and earlier 4RTs.

I haven't seen a detailed explanation from Montesa / Honda. So all of the above is just guesswork. Anyone have real information from the Honda engineers?

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You wont turn it into a great bike from an ordinary one, all you can do is tune it to your style and or requirements. There is nothing wrong with standard.

With a ptb they can be tuned to exactly what you want from docile smooth to harsh hitting hard, but the power should be fine for anyone less than very very good expert.

Be careful what you do.

Edited by nigel dabster
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My description of a great bike isn’t to be confused with a bike for TrialGP, I’m thinking of great as in better equipment like a factory version. The PTB is from an older model and is a twin map. The oem unit has 2 maps but they’re not changeable, with the old TMPTB the variations with advancing and retarding the ignition and leaner or richer fuelling and the combination of both has a noticeable change on grip and delivery. The pipe will smooth out the delivery. The 280 kit will be the last addition if I feel I would like it. One of the Montesas I’ve ridden with a 280 kit feels much livelier but hasn’t lost any mild manners in tighter stuff , the mapping will be set up for that purpose. Currently one 2016 model 260 with PTB and mitani system is a much more responsive bike in the same sections. Definitely worth the work. 

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I would suggest you need to advise us  what sort of sections and ability/level you are riding at.

I didn't like my 09 280 and put it back to 250 standard. I do like the 300RR but its a much better beast than a over bored 250 I feel.

If its a std 260 then Ohlins and a PTB with map, larger front pipe helps match a softer map, to suit unless you are expert level I would say good Tyres and possobly swap from the motad to Did rims. Dump the Dunlops/X11 and fit X lights..

To be honest I liked my 260 std map with S3 front pipe.

I found front Tech forks on the std 260 ok  -  I'm probably 14.5 stone.

Above set up I found is great for clubman national class on rocky type going.

If doing more mud and climbs then the extra cc maybe worth it.  

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