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4rt Restrictors


gii
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Took the plunge recently and bought a 4RT. I'm getting along with it quite nicely, love the suspension and the power characteristics 99% of the time, the exception is hillclimbs. The bike doesn't rev high and doesn't develop power, it produces low and midrange torque by the bucketload, but when you need to really fly up a hill it won't.

The bike is exactly as it came out of the box, investigation shows 3 diametric restrictors in the exhaust and one immediately after the throttle body.

The one after the throttle body was the surprise, it's a disk completely filling the intake with a tiny (guess 10-13mm dia) hole punched in it low down. This I assumed was the problem, in my mind it acts as another fixed throttle and would be effectively allowing the bike to run at max 1/4 throttle.

So I removed it, expecting the same bottom end characteristics but a freer revving motor though still constrained by the exhaust restrictors.

However, the bike wouldn't run properly without it, response was very poor and laggy and the bike wouldn't rev at all, missfiring and popping back above about 3000rpm. Put the disk back in and everything is back to normal.

Has anyone else removed just this disk? and if they did, how did they get the bike to run right? I don't want to take out the exhaust restrictors and get my arms stretched, and I don't want to buy an adjustable throttle body - the bike was expensive enough and should be capable of running right. I just want the nice soft + torquey motor I have but with a petrol engine top end instead of the diesel version I have now.

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I have one of the first 4rt's ...its taken me about a year to getting just right, but she;s fine once you do.

then this buddy of mine bought a 06.....the bloody thing runs great right out of the crate!

it nalso has ALL restrictors out!!!

get rid of stock air cleaner....install one from a 315!!!

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GII

sounds like you bike has not had the pink wire mod (the electronic resistor munch talks about)

that is an absolute must i hav also removed the middle restrictor between the pipe and silencer only because it kept rattling,however it did not afect noise or power noticeably.

leave all the others in and the bike is really smooth try hill climbing in a higher gear it takes a bit of adjustment but is worth the effort,

viva montesa

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OK, Iwas slightly innaccurate, The bike is exactly as it came out of the box but with the lights etc removed and a kill switch fitted. I presume this means that the electronic restrictor circuit has been removed or bypassed?

However the physical restrictors are as described and the bike does not run properly with the inlet restrictor removed. I intend running with all of the exhaust restrictors in to begin with removing only if necessary. The bike runs perfectly well low and midrange with the inlet restrictor, just doesn't rev hard and produce power for hills. Do I have to do something else after removing the inlet restrictor to get it to run properly. And is there an acid test to chek the removal of the electronic restrictor?

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Ahah!

I think I've got it.

2 wiring diagrams in the handbook, one with lights, one without.

When the lights are attached, the white/green wire from the throttle body titled 's/w map' is earthed, when the lights are removed the link to earth is removed too.

'Cept on mine the link has been carefully replaced.

I asked for the bike with all the restrictors in so I could remove them one at a time till I had the performance I wanted.

Looks like I got exactly what I asked for.

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Mmm,

Not having a big enough hill in my garage, I resorted to a multimeter. Found that the White/green wire was earthed so went looking for the earth and found the link.

Just got to get the tickover back down now

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  • 2 weeks later...
 

Yep, there are no downsides to it, I believe it's the way the bike is normally presented to the owner by the dealer.

With the inlet restrictor in place the engine cannot flow enough air to rev high, it feels a bit like a diesel hitting the rev limiter.

If you just remove the restrictor plate but leave the SW/Map pin earthed the bike doesn't run properly.

Remove the earth link too and the bike is noticeably smoother at the bottom end, stronger in mid range and will also rev high.

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Just done the mods as suggested, WOW what a difference only rode bike around the garden and up a small wall, I have had probs with the bike stalling occasionaly this tendancy has vanished and i can now have the tickover set much lower . There is now no popping or back firing on the over run . i rode a trial yesterday and had the bike flat out in top along a gravel track cant guess the speed it was doing but it wasent great. I am sure this will be improved . Thanks for the help

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Have been out playing on the mont again last night, one thing i have noticed is the bike is running MUCH cooler since removal of inlet restrictor, the cooling fan is now running much less frequently. Is there any change in the fuel consumption of bike , with the mods done???

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GII... this topic you have started explains a lot . I test rode a 4rt about a year ago and it exhibited all the idiosynchrisies you first described .

i.e. snatchy take up just above idle and then dying on it's a*** when you went to rev it out. This formed my opinion of the bike.

So I thought the bike was just too expensive to put up with those short-comings .

Well...... last week I was on Mr Harlands new mount.......with a re-mapped throttle body....what a difference.

A silky smooth bottom end,strong mid-range and a freed up top end.

I had real problems handing it back.

I think I've found the 'Holy Grail ' for me:- An easy to use trials bike!

Now I've just got my bloody house sale to complete..bugger.

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I think it's a smashing bike,

With the inlet disc and electronic restrictor removed but all the exhaust restrictors in it suits me perfectly. If I wanted more power I could remove the exhaust restrictors (they're not an insignificant reduction in diameter). I too have ridden Mr Harlands velocipede, now programmed with the Laia Sanz settings, but to be honest I think it could get me into trouble, not quite Aprilia Climber 280 on re-heat trouble, but easily 'I feel 2 feet behind the bike' trouble!. The standard settings seem to give me more time, and the strong tickover (mines set at 1200 rpm - seems ok) allows me to keep trickling through sections with the throttle closed and the clutch out.

In a road car too much power is just about enough, but I'm starting to realise that trials bikes are different, less power can mean less dabs.

Slightly off topic but 2 riders who have spent time and cash on their bikes making quite radical changes have been kind enough to trust me to ride them, both made a change that was both noticeable and surprising. - The real swinger for me buying the bike was the suspension, after several trys on friends bikes, this was the bit that impressed, but these 2 bikes had a change that moved the game on another step - they'd fitted an Ohlins rear shocker. And you can feel the difference.

This does seem to be a bike that suits the clubman well but can be built upon.

Only bit I miss about removing the inlet and electronic resistrictor is the popping and banging on the overrun - it used to make me smile wider! Mercedes program the AMG cars with a missfire on overrun just for that reason!

Edited by GII
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Any info on cost/availability for the Ohlins rear shock?? I reckon you are onto something there, the front suspension is just incredible (lightyears ahead of my GasGas) but I always feel the back needs a little more something.

Just changed the front fork oil, the old stuff came out like air-ated chip pan oil. The difference is like day and night, the front wheel feels like it is glued to the ground again.

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