Mikuni HSR42 to Mikuni HSR45 Upgrade

[rbirkey]

In 2014, I purchased a pair of Mikuni HSR 42 flat-side carburetors for my 2008 Triumph Bonneville from Bonneville Performance. These opened up the intake side of the engine from 36mm to 42mm and enabled it to breath and make better use of the airbox I had removed, and free-flow exhaust system installed. There was a noticeable increase in power and performance in addition to the reliability and more instant response one gets from a flat-side carb.

In the winter of 2015-2106, I had Bonneville Performance rebuild my engine, bumping it up to 1100cc, along with head/valve work, cams, balanced crank, etc. I reused the Mikuni HSR42s on it for the first few months in 2016. To gain better low end idle and top end power I bumped the pilot jets to 25 and main jets to 147.5. After discussing this with Bonneville Performance owner, Bill Gately at the Lima Half Mile race, I decided to upgrade to the Mikuni HSR45 setup with 150 main jets, needles 96 center, and pilot jets at 25.

I installed these on the Bonneville last night and am very pleased with the results. The engine runs much smoother and even at idle and there is a marked additional "pull" on acceleration all the way up into the 6,000+ RPM range. The engine feels like it is working "effortlessly" and is just begging for more gas and air! I am very happy with this upgrade!

 

[bluesforchallah]

That sounds like some seat of the pants real good time right there. I bet that bike hauls ass. Though I've never dealt with him personally, It seems Bill Gately really knows his stuff.

 

[rbirkey]

Chris,

I plan to have the 1100 cc engine dyno'd soon and will post the results. I expect it to produce over 100 HP and in the mid 70's ft. lbs. of torque.

I met Bill Gately online when I purchased some of his performance products. I was impressed with the customer service I received and his knowledge that he shared when I ran into some difficulties with the install. He eventually invited me to attend the Springfield Mile flat track race to watch his Triumph factory sponsored AMA Pro Flat Track team compete. I was hooked from that day forward, and have been helping him and the team ever since. He's the most knowledgeable person I know on all things Bonneville!