Allens Performance Ltd.

Allens Mikuni VM28-57 carburettor specially prepared with a custom made, radiused air entry

February 21st, 2020

For your viewing pleasure, a specially prepared, bespoke Allens Mikuni VM28-57 carburettor  with a custom made, radiused air entry.

A generous radius helps to guide air into the carburettor entry, massively reducing turbulence and allowing the pressure drop caused by the engine to draw more air than it otherwise could. Due to production practicalities the carb manufacturers rarely put a particularly nice shape on the rear of the carb. This can be rectified, but a new piece has to be made, pressed on, holes filled, then turned, shaped and blended in. A lot of lumps and bumps that disturb airflow have been removed. In this case, the air hole for the cold start fast idle has been blocked up and smoothed over. A little compromise in the name of high performance.

An extra difficulty with modifying this type of carburettor is that the inside diameter of the carb is not concentric with the outside. This means more metal is removed from the top than the bottom. It’s very tricky to make sure there is still enough metal left in order to avoid the whole thing falling apart.

The front spigot has also been modified to fit a rubber that the customer provided.


Mikuni VM28-57 carburettor with custom made radiussed air entry


A picture of the standard carb below is a great comparison:

Mikuni VM26-8639 Carburettor

26J Yamaha Mikuni TZ Reverse Slide Replica Carburettors Built to Order

January 26th, 2017

Fantastic! Finally it’s possible to get a close match for the reverse slide carburettors most sought after by TZ riders rather than put up with tired old orignals. Genuine Mikuni VM carbs modified and set up to suit.

We can also supply slides only if you prefer, or even carbs fitted with conventional brass slides.

Plenty of other TZ carb parts available, just ask for more details…
Mikuni VM38 26J Reverse Slide Replica Carbs Built by Allens Performance Ltd

Jimmy Doom Special Doomster Engine

September 4th, 2016

Feast your eyes on the Mammoth Vee Twin of Doom!

Here you can see a prototype for a run of extra special engines conceived and developed by the most eccentric Cylinder Head guru in the North, Jimmy Doom.

The bore/stroke of 4.250″ x 4.250″ gives a total capacity of 120 cu in (around 2 litres.) 2.100″ valves are fed by VM44 carbs supplied by Allens Performance Ltd. Cam lift is 0.650″ and the exhaust headers are a full 2″ diameter.

Doomsters are destined for a new wave of muscle bike so watch this space!


Endurance Legends 4 hour endurance race review, Snetterton circuit, 17th and 18th of October 2015

October 24th, 2015

Thanks be to Darin Frow and Rob Beale of Classic Bike Trackdays/Endurance Legends for taking up the massive labour of love and financial commitment required

to make this event happen. The Classic Racing Motorcycle Club also got behind the idea and made it possible. I’ve heard talk for years about the desire and concept to bring classic motorcycle endurance racing to the UK, but it still caught me by surprise when it actually happened!

Allens Performance Classic Endurance Honda VFR750 RC24 Team

The Allens Performance classic Endurance Legends race team conisiting of Alan Hudson, Chris Withey, Steve Panter, Simon Hindley, Nolan Freebury and the Honda RC24 VFR750


In order to give ourselves the best chance, I decided to find a nice, reliable (haha) Honda VFR750 and enter the F2 class. Although the bike was purchased early in the year, the various parts and work all came together very late in the day. I tried the bike on the road months ago, but the practice on Saturday morning at Snetterton was the first time our VFR had ever actually taken to the track.


Previously a 70,000, 3 owner non running bike bought for £400, it seemed very fit and willing. Dyno testing and a little rejetting of the carburettors further confirmed that it was producing 90hp at the rear wheel. Obviously 70,000 miles is enough to get these old Hondas nicely loosened up!


Race preparation involved the usual service, removal of road specific pats, lockwiring of certain fasteners, swapping coolant for water, adding a race exhaust, rearsets race bodywork, Avon AM22/23 tyres, new pads, a new Nitron shock at the back, Hyperpro springs and S1 Suspension cartridge emulators in the forks.


Conditions were fairly good for qualifying. We got 12th of 16. The carburettor setup was spot on. There were no glitches or flat spots, just seamless drive! Straight line speed wasn’t an issue but we all needed to gel with the untested bike. We reasoned that in a four hour race the starting position was not crucial in any case. Gear selection issues were our biggest problem but we managed to mitigate the issue before race day arrived.


Simon Hindley dismounting after his session


In the garage Alan Hudson had us all well organised, sorting out who was responsible for each task, keeping track of laps, lap times and even cooking a fried breakfast! Nolan Freebury kept the bike topped up with fuel, wearing full leathers for fire protection and wielding the quick fill tank. (After Alan repaired it!) Nolan has since decided that he must get his Clubman’s licence in order to compete next year!


The weather could have been a lot better! Words that spring to mind are damp, greasy wet, wetter and cold. A garnish of oil here and there too! Since this event was run under the umbrella of the Classic Racing Motorcycle Club, wet tyres were not permitted! So, with caution I executed the start (running across the track to the bike was a novelty) and all seemed to go well. The track was wet but drying slowly. I was able to pass quite a few bikes on the first lap while feeling fairly safe about it. A few laps later, he track began to dry and I was able to push harder. However, arriving at the bomb hole amidst the wreckage of Phase One’s formula one bike did give me pause for thought!


Getting the bike safely onto its stand

Just as it seemed that the track would get dry, the rain returned with a vengeance! I had eventually remembered to check for the pitboard and missed it the first time it was shown. It’s safe to say that visibility was not good! I did my first ever pit stop. I was careful to halt at the stop line and observe the pit lane speed limit. It was actually a relief to step off the bike and relax while the next rider, Chris Withey mounted up. I was flabbergasted when the guys told me that our team was running second in class! I was almost on cloud nine! I tried not to get too excited, a I knew there was plenty of time for things to go wrong.


HRC Screwdriver releases the tank cap

Unfortunately, soon after I began to clean my helmet it became apparent that Chris was having problems. He’d broken down at Corrams and manfully pushed our big old VFR back to the pitlane in the rain. Our first suspicion was that the wet weather had caused us some ignition problems. We sprayed everything with a good deal of silicone, wrapped a few things in tape and the bike ran. Off he went again and stopped halfway up the pitlane. Another fiddle and the bike flew off while the rest of us bit our nails furrowed our brows. Chris and the VFR didn’t reappear for quite a while. Eventually they returned in the recovery van!

Precious minutes were wasted while we tore bodywork off, checked and rechecked electrical parts, consulted wiring diagrams, pulled hair out, all to no avail! Eventually it was discovered that pulling the wiring loom around at the front of the bike caused the problem to disappear. We got it cable tied in an operational position and sent the bike out again.


I was told that the drama cost us over twenty laps! Although the bike gave no further problems, the damage was done. Despite all three of us riding at a good pace considering conditions, it was impossible to catch the others teams except in cases where they had their own problems. The most dramatic event was a miscalculation of fuel load leading to an unfortunate splutter around Corrams before Chris made his stop. We worked out what had happened and refilled the bike! Brows were mopped after that pitstop.


Drama and unwelcome ignition problems!

Simon Hindley was our rider at the helm during the final leg of the race. Although the whole race had been run in challenging weather and we’d all had our share of scary moments, conditions were getting worse and worse with each lap. He did well to keep the bike off the ground and it seemed the closer he got to the flag, the more slippery and difficult the circuit got! The whole team was overjoyed when Simon crossed that finishing line on the final lap!

We’re successfully addicted. Next year we hope we can get a real result!

Writing: by Steve Panter

Pictures by Claire Mackintosh, Clickers Photography Ltd. All rights reserved.


Joy after Simon finishes the race!



Cheerful team in Parke Ferme


Suzuki XF650 Freewind Special Carb Set with TPS

December 15th, 2014

Another job to keep the Allens workshop busy! Not the billet Throttle position sensor adaptor on this special rack of smoothbore Keihin CR33 carbs for a Suzuki XF650 Freewind engine powered CCM. Pictured here next to the original Mikuni BSR CV carbs

.Special Rack of CR33 Smoothbores for Suzuki XF650 Freewind CCM with TPS

What are Jets/valves/metering screws?

December 10th, 2014

Jet: A component controlling flow of a fluid, restricting by means of a calibrated orifice size. In the case of a carburettor this fluid could be fuel or air.

Float Valve: A component designed to allow or prevent the flow of fuel. A float valve prevents fuel flow when the level in your float chamber is correct. Exactly like your toilet cistern.

Metering Screw: A tapered screw allowing adjustable flow restriction of fluid. (In this case fuel and/or air.)