1974 H2B Performance at Low RPM

[Renn_73]

Finally I have my hands on an H2B which I rode yesterday. No problems developing full power but riding it around the backstreets it was a challenge as it seemed not a smooth as it should have been and chugged a bit before it smoothed out. Obviously dropping it down a cog always sorted that out but then I was flying again. Is this a common trait of these bikes or can a bit of carb tuning synchronisation help? It was 40 years since I rode one and my recent Z900 was obviously so different and before you say it I prefer the KH750 HB as it was so much more involving and challenging to ride. I can read vacuum gauges as well as the next man and adjusting the carburettors (I have seen several You tube Videos) is well within my capabilities. My guess is the carbs are not all opening together. The bike is other wise pretty immaculate so i am wondering if this was a thing the previous owner didn't manage to resolve and just lived with it. PS i try and change down using engine braking to control the bike and get it under load with more rpm and then use the throttle progressively which helps. After an hour I got it to a stage where I was riding it smoothly by doing this. Any advice or experience would be greatly appreciated. Mark

[Wolfie]

Just do a search on here using 'Carbs' or similar, there must be thousands of stories about Carb setting up, some good endings some bad endings.. some go on for years (I'm in that list)..

MrAxl is the website for Triples Resources.. it's all in there..

H2s are known for poor running and surging, some will resolve by simple carb sync, some will resist all attempts to stop it. There are many "cures" some work on one bike and not on another and vice versa..

Just start with a basic sync on the tickover then set the liftoff at around 9 - 10mm, if it still surges you're probably in for the long haul.

[Renn_73]

Thanks i'll try that. What a reference library of manuals. Many thanks. I've started with the maintenance manual. Who are the go to specialists for 750 Triples. Are there any down South ?

[BIG H]

The first thing to do is check & adjust the ignition timing if required.
you will waste a lot of time,effort & money messing about with carbs when half the problem is
the timing not set right.
Fitting an Ivan's jet kit made massive improvement to my H2C

[Wolfie]

H2s are known for poor running and surging, some will resolve by simple carb sync, some will resist all attempts to stop it. There are many "cures" some work on one bike and not on another and vice versa..

Just to confirm the above statement, Ivan's made very little difference to mine, it would still surge and give a big kick when rolling off the throttle at speed..

The last attempt by fitting 2.0 Cutaway slides has just about sorted it although it's lost some horses in the process, AND it can still be temped into surging every now and then.

[scouse]

Link to Ivan's website.
http://www.ivansperformanceproducts.com/
Chain tension and worn cush drive rubbers, will exaggerate the hunting and surging
Gary T

[Nigel S]

The first thing to do is check & adjust the ignition timing if required.
you will waste a lot of time,effort & money messing about with carbs when half the problem is
the timing not set right.
Fitting an Ivan's jet kit made massive improvement to my H2C

I totally agree with the Ivan's performance improvements. They have transformed my H2c as well. Money well spent I think.
But some have seen no improvement.

[Renn_73]

On balance i think the Ivan kit from those that have it fitted seem to in the majority to confirm it does improve the low speed performance with a trade off against high end. This in my opinion is not a bad thing as screaming the bike at max rpm can only lead to premature wear. For every 1000 rpm there is an exponential rise in load on components. I am going to give the kit a try but first synchronize the carbs. Many thanks for all your suggestions and I'll let you know how i get on.

[scouse]

On balance i think the Ivan kit from those that have it fitted seem to in the majority to confirm it does improve the low speed performance with a trade off against high end. This in my opinion is not a bad thing as screaming the bike at max rpm can only lead to premature wear. For every 1000 rpm there is an exponential rise in load on components. I am going to give the kit a try but first synchronize the carbs. Many thanks for all your suggestions and I'll let you know how i get on.

Personally with a such a low redline I wouldn't bother about causing too much stress on the engine

Gary T

[Nigel S]

On balance i think the Ivan kit from those that have it fitted seem to in the majority to confirm it does improve the low speed performance with a trade off against high end. This in my opinion is not a bad thing as screaming the bike at max rpm can only lead to premature wear. For every 1000 rpm there is an exponential rise in load on components. I am going to give the kit a try but first synchronize the carbs. Many thanks for all your suggestions and I'll let you know how i get on.

Personally with a such a low redline I wouldn't bother about causing too much stress on the engine

Gary T

I have to say that my H2c in standard spec with Ivan's kit installed was clocked at 120 by a Ducati multi strada. 7000 rpm in 5th gear. On a nice cool evening.

So I have not seen any issue with high speed and the Ivan's kit. Good all round plus from me.

[Neil the Don]

Here's the thing. Ivans .

It's not exactly a simple kit thst you fit and it solves everyrhing. You are paying for a whole load of parts you will not use. As the kit has an assortmentof parts to fit depending on standsrd spec or running with chambers etc ??

The crucial thing is that the original needle is a failry crude thing with limited steps on it . The Zivan needle is ground with more steps for a mote gradual progress of fuel being squirted in. Lets say for simplicity the o.e.m. needle is a 3 step , and the Ivans is a five step ? ( Some may argure it's a five to seven step )

So , with thst in mind you all have an option . Steve st Motocarb also has a five ,( or seven) step needle for sale. Its a modern grind genuine Mikuni needle. And it' s also aproven mod thst works well on the H2s.
So you could save yourself a bit of money , and talk to Steve a t Motocarb ??

Just a thought !!

[Eric]

Good post Neil

[Tilly H2C]

H2s are known for poor running and surging, some will resolve by simple carb sync, some will resist all attempts to stop it. There are many "cures" some work on one bike and not on another and vice versa..

Just to confirm the above statement, Ivan's made very little difference to mine, it would still surge and give a big kick when rolling off the throttle at speed..

The last attempt by fitting 2.0 Cutaway slides has just about sorted it although it's lost some horses in the process, AND it can still be temped into surging every now and then.

I have been all around the houses with mine, I might even write a story for Malc!

I have returned to the Ivans kit a number of times and to be honest it just doesnt suit my bike at all, I know im not hacksawing spark plugs up to look for the 'smoke ring' but the plugs are bordering on snow white after a 70mph plug chop, any attempts to richen this up and i'm heading for a 4 stroking bike at lesser speeds. If you measure an Ivans needle you will see why it runs so lean around half throttle

I also ended up with '2.0' slides, (which really want smaller PJ) a different needle set up, and like above I also know where to find the surge if I go looking for it

I tried the UFO set up which can make the bike very good at small throttle openings, but overall really requires a different style of needle

A carb balance is essential after EVERY adjustment that involves removing carbs or carb top, even moving the needle clip can upset the balance, the throttle cable run is not the best and accidently giving the slide a 360 degree turn whilst altering the clip will put the balance way out

Something like a Gunsons carb balancer is very good although be carefull not to set it too restrictive to alter the airflow

[Wolfie]

]I noticed the other day (first time on the M62 since the Slides change) that it now hunts at higher speeds.

I keep saying 'That's it now I've run out of ideas", then think of something else..

Next in line now might be a set of moo reeds before he stops producing them..

Having fitted reeds elsewhere they have really smoothed the drive at lower RPM/throttle settings (but shown up other issues) Doh!

[Tilly H2C]

I think the issue is that the PJ circuit comes back into play once you start to close the throttle, at least thats what I think happens with mine, I have the twist grip marked off in 1/8th throttle openings, I find it only happens at less than 1/8th throttle openings when decellerating, closed altogether and its fine. trying to set the PJ circuit to give the correct fuelling at 1500 and 5000rpm is a big ask

It's 'just' a matter of finding the correct balance between slide/needle/PJ that reduces the above but also allows it to run clean without 4 stroking lower down, I have ridden 2 'perfect' tuned bikes that just 4 stroke up to about 1/4 throttle

[Rickm]

Out of interest, what is this "4 stroking" that you mention and what causes it ?

[Wolfie]

I think it was Motocarb who told me that the Surging is due to a weak condition at small throttle openings, so he was converting some 2.0cuataway slides and these are what I bought.

They are the first things that have made a serious improvement in the slow speed riding, although I can feel it is now rich at small openings and stutters (which is what i presume you mean by 4 stroking) when driving but doesn't go "rawp... rawp... rawp.." with the accompanying power pulsing on overrun.

I can feel that there are some ponies missing with the rich condition, maybe they will return when I smallen the Pilot Jet.

But then.. maybe the surging will return too..

As a slight aside.. we had a chips ride on Thurs and the best riding H2 in the world came out to play. A bike with super power delivery, smooth well balanced, like sh*t off a shovel when opened up, picks the front wheel up with little effort, but best of all. not even a hint of surging or hunting.
And looks awesome too, fair makes me sick it does.

[Tilly H2C]

What is that 'perfect' bike Wolfie?

[Wolfie]

This one.....

IMAG1566.jpg

[Tilly H2C]

not a standard one then

To be honest taking the rubber 1-3 inlet off does improve matters as it stops the inlets interfeering with each other at small throttle openings.

4 stroking is what 2 strokes do when they run too rich at slow speeds, they 'miss' a cycle due to lack of air and fire every other stroke or '4 stroke', just watch some two stroke youtube videos and you can hear them 'stuttering' when going along on a small thrttole before clearing as the throttle is opened

[Tilly H2C]

PS: When mine was bad it would 4 stroke at small throttle openings, then ping when accelerating before settling into a surging detonating f*****g mess at any cruise speed