Different Methods to 33bhp Restrict a Bike

[Swifte]

I'm looking at a couple of 70s Hondas I quite like between 350-500cc. Information on their actual bhp is varied some saying 30bhp others 41bhp most in between 30-40bhp etc.

Some of them are all only slightly above 33bhp (I'm still restricted).

Point is this, these bikes were made before the days of restrictor kits. I've heard that there are other ways of restricting bikes than just putting a carb metal plate restrictor in the rubber inlet manifolds.

I read somewhere that you can restrict the throttle so you cannot open it fully and that mechanics actually do this officially when restricting bikes.

I doubt these bikes being as old as they are actually produce the bhp they are supposed to but I have to prove that they are less than 33bhp in court in case of an event (touch wood that will never happen).

Anyhow anyone know of any methods to restrict old 70s bikes? Do you reckon its necessary?

Would appreciate any info, thanks.

[G]

[Swifte]

[calyx]

[Kickstart]

Hi

Not only do some disappear with age, they were quite small horses anyway.

However most newer carbed bikes have CV carbs and are easily restricted with a washer after the carbs. This limits the air flow through the carbs and with a CV carb they sort the fueling out themselves to a large extent.

Anything older is likely to be running slide carbs, and putting a washer after the carb on these will restrict airflow. But probably do nothing for the fueling landing up with it running badly.

Easiest way after that is probably to limit how far the carbs can open, but that isn't that simple. Easiest way is probably to cut a length of pipe (possibly fuel pipe) and put it over the throttle cable between the top of the carb and the carb slide. However long the pipe would need to be to limit the power would take experimentation.

Also depending on how the carbs operate this might be difficult. Some will have a linkage going to each carb from a central point where the cable connect. It might be easier or more difficult, but you would need to examine the actual setup on that bike to work it out first.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[mysterious_rider]

No point restricting a 40bhp bike. Being old it's bound to have lost a few bhp's. Just ride it.

[MarJay]

Something that no one has mentioned in this thread yet:

A lot of people don't even bother with the 33bhp restriction. There is no requirement for proof of restriction legally, and so a lot of people seem to take the risk. I know that police are a little more aware of the law these days than they were back in 1998 when I took my bike test, but even so if you've only got a few weeks left of restriction, and the bike you're looking at is listed around 40bhp I wouldn't worry too much. Japanese horses are generally very optomistic, and nobody knows if the 33bhp power figure is at the crank or at the wheel anyway.

Plenty of people on this forum saw out their restriction periods on 600s and in some cases 1000cc bikes. I'm not saying thats what you should do, but I'm saying some people have done it.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[c_dug]

[Ingah]

It's also 25kW (slightly over 33.5BHP). Adding a little bit more leeway, along with the fact that it seems that the police allow ~10% on the rare occassion they dyno a bike for restriction, as dyno's are notoriously inaccurae.
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-- Ingah

[johnsmith222]

A friend of mine rode about for a year and a half on a sports touring style motorcycle that is 99 or 100 bhp.( claimed)

He didn't restrict it and rode it everywhere like he stole it (not anymore though.)

He's no longer restricted so it's not an issue and he never got caught.

I advise that you pick a reasonably sensible bike. Think maybe something like a thundercat or the likes. Get a grey helmet and wear a high visability vest and wear textiles, or leather that doesn't look sporty. The sort of stuff you see plod wear. Make sure you keep the bike legal as far as MOT and tax and pay insurance. Don't bother with a loud can or small numberplate. Avoid tinted visors while you're at it.

You are trying to convey an appearance of being a sensible, safety conscious rider. Not only does this appearance help when stopped, but also stops you getting pulled over in the first place.

[Paulington]

[sebastianw]

To those of you who don't mind the risk - you will be riding without insurance and without a licence. Keep away from me because I don't want to have to pay for repairs due to accidents which are not my fault

[Kickstart]

[Rogerborg]

[chris-red]

I mate of mine had a DR500 for the 70's (I Think) he had it seized because he couldn't prove it was 33bhp, it was 37 at the crank when new.
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[Kickstart]

[Rogerborg]

Cheerfully corrected, sir, thank you.

[Kickstart]

Hi

. It is hardly the most easy to read document.

The civil debt is down to the person who had insurance though. It isn't the innocent 3rd party that suffers from it.

There are all sorts of odd clauses in the rta. For example your insurance isn't valid until the certificate is delivered in the prescribed form (s147). And for real fun check s144a which basically makes trade insurance for any vehicle impossible.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Cheeseybeaner]

[Cheeseybeaner]

[dean36014]

Well I can speak with a little experience here unfortunately. I had a bmw F650, 48 bhp as standard. Bought it from a dealer who had it restricted for me by a dyno place in Birmingham. they restricted it by drilling a tiny little hole in each carb slider which somehow reduces the power output made, in this case down to 31 bhp. Only documentation was a dyno printout showing the bike details, power curve and stated maximum horse power. Unfortunately on november 3rd this year, while stationary in a queue of traffic at a give way junction, a 20 year old lass decided to plough into the back of me at 30 mph, smashing/sandwiching me into the car in front. Police called, ambulance, gear cut off me, spinal board etc, etc. The police are prosecuting the girl, but then the issue of my resticted licensce came up. They checked with the supplying dealer, with the dyno place how it was done, checked my paperwork, and finally had a carb slider removed off the bike to check the hole was still in it, the bike was too bent to be dyno'd. All this was to make sure that i was legally entitled to be on the road so that the prosecution of the car driver could proceed with no unexpected surprises. I'm of no doubt i would have been done if i was not all legal even though i was the innocent party. On the other side of the coin, the police were fanatstic at the scene helping the ambulance staff, kept me reguarly updated as to what was happening, and apologised about all the hassle it was causing. At the end of the day I knew i was legal so wasn't overly bothered, but it was a real eye opener. I've got a few friends who went the restricted licensce route and never bothered with the restiction, and they were all thankfull it never happened to them.

[Swifte]

[dean36014]

It all amounted to that the fact they could only take her to court and prosecute her if the other party was legally entitled to be on the road.
As for documentation, i don't think there is anything that will legally prove the bike is restricted. My new bike has been restricted by the dealer, supplied with a restriction certificate, a copy of which is held by the dealer, by myself, and a third copy sent to the manufacturer. All of this amounts to nothing, as i could immediately remove the kit after collecting the bike, yet still hold all the correct paperwork. Theres nothing obvious on the bike that shows where the restrictor is fitted, so the police only really have the option of having the bike dyno'd to prove its under the limit. As the police themselves admitted to be its a real grey area, the policeman who dealt with my case got advice himself to make sure he understood it all correctly. His opinion of it all would be it would be a lot easier if it was a cubic capacity restriction rather than a bhp restiction as it would be alot easier to manage.
At no point did the police ever make me feel threatened by it all. After all I could have chose to buy a bike that was under the 33 bhp limit, but chose to go the through the grey zone. You just need to be aware what could potentially happen, in my case i was completely stationary, couldn't filter to the front of the queue as there was no room. She would have smashed into the car in front of me anyway even if i wasn't there as she was completely distracted and admitted to it under police caution at the scene. I'm still slightly in shock in that I never broke any bones, and never got crushed by the car what hit me, as i was bounced of the car in front into a safe area. Looking back at it, and i've had a long time to do this, the funniest thing that sticks in my mind is that while in A+E, still strapped to the spinal board the first people I got them to ring was work to explain I was going to be late! Hopefully I'll be back to work sometime next week, but so far I've lost £1500 in take home pay(difference between normal pay and sick pay), £850 worth of bike gear cut of me at the scene, and one massive dent to my pride. i just hope the solicitors dealing with it get there finger out as i could seriously do with a cash injection now!

[ncrn]

I had a ZZR250 when I was restricted, I didn't get the thing checked for its actual horse power when I got it (perhaps naively) as I figured it was older than me, so the chance of it still making its estimated 37bhp (or similar I can't remember exactly) was quite unlikely. I didn't ever get pulled over in that time, I didn't get in any accidents either but that may have been more luck than judgement.

My insurance never once asked if I had the restriction even though I told them I was on a restricted license, I found this slightly odd.. I would have thought the easiest way to police the law would be for an insurance company to require proof that your bike is not 33bhp before insuring you.
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[robocog]

Only experience I have is:

Bought a 76 Honda twin (CJ360t) before I had even taken my CBT or even thought about getting a license (as I just liked the "look" of the machine)

Should have had 34 hp when brand spanking new
Assumed that it would have lost a few HP since then so just rode it on my restricted licence as soon as I had passed
(only took my test to ride the thing)

My only other bike I could compare it to was the CG125 which I took my test on and commuted/pleasure rode

Power wise it felt like perhaps double the "poke" of the CG but with similarly crap brakes

Got bored V quickly with it and I'd go as far as to say it wasn't confidence inspiring and I felt my learning curve has flattened off
Cornering never felt smooth and nice on it...I put it down to lack of experience

Got a GPZ500 , popped the 33hp restrictors in...
World of difference power wise and handling wise
I felt my learning curve and confidence had had a big boost
Cornering became smooth and confident with very little input (and became a pretty much subconscious event)
I had to be careful with the throttle again

The CJ hasn't barely moved a wheel since getting it
Almost every aspect of it is far inferior in comparison and is a good example of progress in the last 20 years

Everytime I have taken it out I wish I had taken the GPZ

I'm guessing (as the GPZ is a relatively old design) If I were to have a chance of a ride on something even more modern I'd again be blown away (but maybe just not to the extent of comparing the 2 machines I have?)

I would also take early Honda power figures with a pinch of salt
The CJ I have although has more getup and go than the CG125 is deffo way down on power compared to my restricted GPZ500

I'd also say that if you are finding a modern(ish) bike uninspiring don't sell it till you have at least ridden a dull 70's commuting machine

BTW my CJ360 is still for sale if your adamant its something you want...Taxed tested and running, just totally naff, a bit scruffy and unbelievably uninspiring
(I'm not very good at selling am I?)


Regards
Rob
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Needs a bigger garage...