Restrictor Plates in Intake Boot

[thunderbolt]

I have become aware in doing the CCT stopper mod and then pulling the camshafts to do some shim changes that there is a restrictor plate in each of the intake boots between the carb and the cyl head. This obviously reduces performance in some way.



Seeing as the earlier models do not have this restrictor does that mean they have more HP? If not, what is the point of the restrictor?

Do the carbs that do not have this restriction have different jetting, needles, etc? I have noticed that some of the bikes have 48 pilot jets whereas mine are 45s. Has this to do with these plates being in place?

If I was to remove these restrictors what other alterations would I need to make if there is extra power available. Rejetting, etc/

Thanks for any info.

[8541Hawk]

The restrictor plates are normally installed in countries that have a 100 BHP limit in place for bikes.
As far as the carbs, all the bits are the same. So just get a set of unrestricted isolators and you are good to go.
For the pilots, I really can't tell you as either 45s or 48s were installed at different times and for different countries.

IMHO these bikes run better with 48 pilots but there are those out there that also say that is incorrect and to run 45s

[AMCQ46]

If you are in a hurry, you can pull the restrictions out of the rubber boots and then refit the rubbers

[VTRDark]

I'm not entirely convinced that they are restrictors. I think they are there to either speed up airflow/velocity or to help prevent intake reversion.

I wouldn't physically remove the complete plates, unless your testing, If you don't want the extra metal then cut it out keeping the outer circumference/ring of metal around the intake rubber. This then retains some ridgety to the intake rubber, hence the earlier model still have the ring.

(:-})

[kenmoore]

I removed them from my bike when I did the engine work.

Eventually I ordered a new set of inlet rubbers and I took them out of those as well.

No problems to date and a mod that is viewed as a necessity here in Oz.

Someone said that they were there for noise regs here in Oz.

In Oz our bikes were listed as having 105 BHP, I have seen restrictors advertised that only give the bike 33BHP!

My thoughts are that they rob the engine of power and That is why I took them out.

Just used a set of pliers and yanked them out!

[Virt]

I don't have them in mine, ripped them out, have no issues with the bike because of it

Sent from my GT-I9505 using Tapatalk

[fabiostar]

just noticed this thread. my 97 bike aint got them but my mates 05 has? so can these be ripped outa his engine as my bike seems a lot perkier than his at any revs?.

[8541Hawk]

Well all I can say is that is what Honda said they were for when they appeared in '98 ... though in the end it really doesn't matter.

They can be removed with no issues or retuning, though if your jetting is off with them in it will also be off with them out.

As for removing the metal bit altogether, that isn't such a good idea.
On the standard, un-restricted, isolator (or intake boot) the metal ring has the same I.D. as the carb throat.
It is there to give a solid mount when you push the carbs in place.

If you remove it, now there is nothing but the rubber lip to stop the carb when you seat it home.
While this might not ever cause issue, it might and you gain nothing due to the carb I.D. being the limiting factor in that part of the intake...... So I run them stock and have no issues

[thunderbolt]

...... So I run them stock and have no issues

So when you say you "run them stock"" does this mean the metal insert is still in the rubber boot, but the restrictor portion has been removed or standard where there was no restrictor.

[VTRDark]

Standard on earlier models is with the metal insert, just with the crescent moon shape bit cut out from the plate and leaving an outer ring. On the later 2001 onwards models they decided to put that later style plate in.

It's perfectly OK to remove them, after all none us have a standard system once we put an aftermarket exhaust on which changes pulse waves anyway I doubt you will notice much if any difference from removing it, and if there is any difference I suspect it will be at idle/low speeds. Possibly a little cough, splutter, uneven idle, which is most likely what Honda where trying to resolve by installing them. Note there are other ways of tuning out the carb fart/cough, splutter whatever you want to call it.

I see it like the so called, we'll call it a restrictor as we all know what's being spoken about then, restrictor in the right hand side header pipe accept this is on the inlet side.

(:-})

[8541Hawk]

...... So I run them stock and have no issues

So when you say you "run them stock"" does this mean the metal insert is still in the rubber boot, but the restrictor portion has been removed or standard where there was no restrictor.

Yes. Here in the US you can not get the restriced isolators as they were never used here.
What you do get is isolators with a ring that has a 48mm I.D. , so it adds support but does not block the air flow.

That is why I have said there is no real advantage to removing them.
It is probably just me but I also feel the carbs are a bit more secure with them in as, again to me, the carbs seem to be able to move around a bit more with the metal bits removed.

I will also say that I have run without them installed with no issues found, except I felt the carbs were bouncing around a bit, though YMMV

In the end it is another one of those issues of run whatever makes you sleep the best as I doubt you could notice the difference of either set up while riding the bike.

[thunderbolt]

[/quote]

Yes. Here in the US you can not get the restriced isolators as they were never used here.
What you do get is isolators with a ring that has a 48mm I.D. , so it adds support but does not block the air flow.

That is why I have said there is no real advantage to removing them.
It is probably just me but I also feel the carbs are a bit more secure with them in as, again to me, the carbs seem to be able to move around a bit more with the metal bits removed.

I will also say that I have run without them installed with no issues found, except I felt the carbs were bouncing around a bit, though YMMV

In the end it is another one of those issues of run whatever makes you sleep the best as I doubt you could notice the difference of either set up while riding the bike. [/quote]

Thanks Hawk, I am thinking I will leave them as is. You are probably correct in that it might not make much difference one way or another. Probably degreeing the cams would have an overall better boost to power and smoothness of the motor.

[thunderbolt]

Yes. Here in the US you can not get the restriced isolators as they were never used here.
What you do get is isolators with a ring that has a 48mm I.D. , so it adds support but does not block the air flow.

That is why I have said there is no real advantage to removing them.
It is probably just me but I also feel the carbs are a bit more secure with them in as, again to me, the carbs seem to be able to move around a bit more with the metal bits removed.

I will also say that I have run without them installed with no issues found, except I felt the carbs were bouncing around a bit, though YMMV

In the end it is another one of those issues of run whatever makes you sleep the best as I doubt you could notice the difference of either set up while riding the bike.

Thanks Hawk, you are probably correct. The bike will run ok either way. Degreeing the cams to the way Mr Honda originally intended them would probably show a greater gain.

[thunderbolt]

Note there are other ways of tuning out the carb fart/cough, splutter whatever you want to call it.

(:-})

Thanks Carl,

Do you have any tuning tips on the above statement? I would be interested if you have.

Thanks

[VTRDark]

You have started already..... First and foremost is the timing and Valve clearances. I believe carb farts occur during the Valve overlap period and the scavenging effect causing intake reversion. More of a problem with bigger carbs at idle speed/low down revs.

The next thing is to move onto Carb tuning. Carbs should be dialled in according to the timing of the engine, including the intake and exhaust systems hence doing the timing and clearances first. Carb farts can often get confused with a lean condition, especially within the Pilot circuit including the correct adjustment for the fuel Mixture (fuel screw adjustment). You will find that a Carb sync/balance, then TPS adjustment and then another Carb balance/sync to finish off will all help.

Fuel Screw/Mixture Adjutsment

How to Adjust the Throttle Position Sensor (TPS)

(:-})