Twin carb KR set up

I was over on the Sporty forum talking about Simons dual carb heads and thought I would show you folks the carb set up I'm going to use for the dome motor I'm building. Have always like the MKII Amals and they fit the manifold spacing perfectly. Even the choke link length and Mikuni rubber spigot bolt spacing is correct.
Mike

34mm Mk2 Amals are a good carb, I use them a lot

Nice... I did have nearly the same set-up on the KHK some years back...

A good idea with square Spanish Amals on a H-D is to install the heavier brass slides... I know of and I have had quite a few stuck slides on the fully opened position... Kill button at the ready!!! I've also seen extentions fitted on the top to fit longer/stronger springs...

Now, Mike, don't take this personnaly/litteraly, I'm only after more info, but the H-D race shop couldn't make the domes work at the time, what are you doing today that you think will make them work?

Patrick

Hi Mike,

Just went on the Sporty page to look at your Tillotsons... I did run that as well on the KHK... I started with them "à la KRTT", chamber vertical... wouldn't start easy, no iddle to speak of etc... In fact, all the woes reported at the time on the factory KRTTs... Then put them "à la Sportster", chamber underneath, bit wider set up, probably not doable with the factory manifold... Night and day, everything went back to normal...

Patrick

Patrick
I will make a note of the heavier slide idea.
With regards your remarks on the dome motor nothing taken personally. This exercise is primarily to find out for my self how the dome motors made more HP but they have such a bad reputation that in talking to some of the guy's that rode them seems to always come down to a carburetion issue. I had a very brief talk with Mert Lawill but was not able to cover anything in depth. That will happen on another day. He ran dual mikuni carbs on his dirttracker in 69 and claims it worked well with a HP increase over the Tillotsons. If you look closley in On any Sunday you can see him on this bike at San Jose with two air cleaners splayed out and flopping around on what were hose mounts. It should be interesting to talk to him as he and Jim Belland were there at the end for the KR era. As an anicdote Mert said if HD would have let him run the KR in 70 instead of the iron XR he may have gotten the #1 plate again.
The plan, finances allowing, is to dyno this motor with dome and switch back to flat tops with a set of #7 heads and see what we find. I just cannot imagine that dual carbs by themselves won't be a big improvement . With the stock manifold your always jetting on the rich side because of the poor distribution of the stock "Y" on these motors.
Mike

Nice... I did have nearly the same set-up on the KHK some years back...

A good idea with square Spanish Amals on a H-D is to install the heavier brass slides... I know of and I have had quite a few stuck slides on the fully opened position... Kill button at the ready!!! I've also seen extentions fitted on the top to fit longer/stronger springs...

Now, Mike, don't take this personnaly/litteraly, I'm only after more info, but the H-D race shop couldn't make the domes work at the time, what are you doing today that you think will make them work?

Patrick

Hi Mike,

Thanks for the update.

As you might know, racers could be cagey at the time!!! H-D did advertise a bit the domes, the pistons and special heads were available in the parts books, but as far as I can acertain, they only try to use the domes at Daytona 69 where most of the factory guys reverted to flat during the extra week before the delayed race...

Can't remember where I read it, but the dome was tried in the fall of 68 on the dyno with the factory special one cylinder KR and it was reported as a success, but as usual, big difference between dyno read-outs and actual performance on the tracks!!! Another 69 problem was that they somehow had less time than in the fall of 67 and they did try too many things at once, megaphones, domes...

Lawwill might be right about Mikunis vs Tillotsons... Tillotsons are all or nothing, not strong in the mid-range so there might have been an advantage to switch to other set-ups on flat tracks where torque did matter... I did talk a few times with Mert, but that was some time ago, during his racing bicycles years, he did not seem too keen to peer in the past, classical stance of a still very competitive man!!! He's now back in the motorcycle fold so might be more willing, hope you'll manage to talk with him again. That old KR of his was also raced in 70 when the Waffle Iron was broken, there's some photos of Mert on it with #1 plate in actual races, same for his protégé, Mark.

Keep us informed as you progress... Is that engine of yours for racing or just to play around? I also saw the Garage Company, Japanese owner, has got a dome 69 engine restored last year, do you know anything about that one?

All the best from Patrick

For racing. We run a KR in Vintage dirttrack. Thanks
Mike

Hi Mike,

Thanks for the update.

As you might know, racers could be cagey at the time!!! H-D did advertise a bit the domes, the pistons and special heads were available in the parts books, but as far as I can acertain, they only try to use the domes at Daytona 69 where most of the factory guys reverted to flat during the extra week before the delayed race...

Can't remember where I read it, but the dome was tried in the fall of 68 on the dyno with the factory special one cylinder KR and it was reported as a success, but as usual, big difference between dyno read-outs and actual performance on the tracks!!! Another 69 problem was that they somehow had less time than in the fall of 67 and they did try too many things at once, megaphones, domes...

Lawwill might be right about Mikunis vs Tillotsons... Tillotsons are all or nothing, not strong in the mid-range so there might have been an advantage to switch to other set-ups on flat tracks where torque did matter... I did talk a few times with Mert, but that was some time ago, during his racing bicycles years, he did not seem too keen to peer in the past, classical stance of a still very competitive man!!! He's now back in the motorcycle fold so might be more willing, hope you'll manage to talk with him again. That old KR of his was also raced in 70 when the Waffle Iron was broken, there's some photos of Mert on it with #1 plate in actual races, same for his protégé, Mark.

Keep us informed as you progress... Is that engine of yours for racing or just to play around? I also saw the Garage Company, Japanese owner, has got a dome 69 engine restored last year, do you know anything about that one?

All the best from Patrick

I've never had problems with Amals sticking open, but then again I use methanol not petrol, so there is a lot of fluid in the carb generally. Plus, I would reckon the general vibration and banging about on a 500cc single racing on grass or vintage speedway would tend to deal with a problem like that anyway

Hi 45brit,

!!! Wonder then why Amal supplies heavy brass slides!!! It is a problem with single carb on twins, I've experienced it...

That's why I've got this fetish about only using butterflies on my H-Ds. I did like the square Amal, but it looks a bit too modern on me old gear... Choke was perfect for starting, but I've yet to see a carb with a more wicked response than the Tillotson... After a few years with them, it sorts of grows on you!!! Its iddle/mid range circuit's not the most refined, probably why guys can't start bikes where it's fitted... Usually traced, as any other carb, to a too weak starting mixture.

Patrick

the brass slides do provide a better sliding action, but it's not because they are heavier, it's because they have a different metal-to-metal interface. I use the brass ones because they resist methanol better, and they tend to be better shaped - more accurate, that is.

I usually take a new slide and give it the gentlest of wipes with a polishing cloth before I put it in and it seems to improve the action. Track-racing bikes need to snap shut straight away on release of the twist-grip, and they need to have the slide firmly seated at "slack wire" so you can start them - they are push-started, or started by oulling the back wheel on a stand, and it is important to get a quick start, first bump.