Loss of Power at higher speeds and running lean

[IanFrancisco]

Re: Loss of Power at higher speeds and running lean

Here?s some info on the carb work I did

Stock Pilot = 15 -- replaced with 17.5
Stock Main = 115 -- replaced with 120
I put one shim on the needle
Air screws are set at 2.5 turns out

On my '80 GS450 with the Mikuni carbs the factory service manual shows a spacer/shim in the slides which lowers the needle, leaning out the mixture. The PO had made a note that this spacer had been removed. When I cleaned my carbs I tried to raise the needles to richen it up and couldn't. The slides aren't built that way, they seem overly complex with their spring-loaded arrangement. Wish the needles had normal grooves and an e-clip. Maybe there are different carbs on your bikes but I don't think so. I bought a set of carbs on eBay from an '82 that were identical. My bike ran great at idle and wfo but seemed fuel starved at mid-throttle openings, hesitated and lost power. The only way I could richen it up without rejetting was to raise the float level some, which did the trick. I'm running stock everything from airbox to jets to exhaust. With the stock 16/45 gearing I can still get from 0-60mph in around 5.5 seconds, 5.3 was what Cycle World reported in their tests at the time. That equates to about 8500 rpm in third gear. Fast enough for me!

As far as balancing the carbs, I didn't mess with mine. I'll bet that the "bench-balancing" method of getting the clicks as the butterflies snap shut to be exactly in unison (sounding like one click) and using a .005 feeler gauge to measure the gap would work great on these mildy tuned engines.

[Anonymous]

Re: Loss of Power at higher speeds and running lean

I was able to shim my needles and successfully raise them. It took some thinking, but if you put the spacers below the spring then you will raise the needle. I also set my float heights to 26mm as that is what I found was recommended for my jetting changes.

BTW -- I have the BS-34 carbs.

Here?s some info on the carb work I did

Stock Pilot = 15 -- replaced with 17.5
Stock Main = 115 -- replaced with 120
I put one shim on the needle
Air screws are set at 2.5 turns out

On my '80 GS450 with the Mikuni carbs the factory service manual shows a spacer/shim in the slides which lowers the needle, leaning out the mixture. The PO had made a note that this spacer had been removed. When I cleaned my carbs I tried to raise the needles to richen it up and couldn't. The slides aren't built that way, they seem overly complex with their spring-loaded arrangement. Wish the needles had normal grooves and an e-clip. Maybe there are different carbs on your bikes but I don't think so. I bought a set of carbs on eBay from an '82 that were identical. My bike ran great at idle and wfo but seemed fuel starved at mid-throttle openings, hesitated and lost power. The only way I could richen it up without rejetting was to raise the float level some, which did the trick. I'm running stock everything from airbox to jets to exhaust. With the stock 16/45 gearing I can still get from 0-60mph in around 5.5 seconds, 5.3 was what Cycle World reported in their tests at the time. That equates to about 8500 rpm in third gear. Fast enough for me!

As far as balancing the carbs, I didn't mess with mine. I'll bet that the "bench-balancing" method of getting the clicks as the butterflies snap shut to be exactly in unison (sounding like one click) and using a .005 feeler gauge to measure the gap would work great on these mildy tuned engines.