Author Topic: power cutting out at wide open throttle  (Read 1168 times)

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Offline dankeller

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  • 1978 xs500
    • toronto, on, canada
power cutting out at wide open throttle
« on: June 15, 2016, 11:09:49 PM »
I noticed this problem when going on the highway recently.  When I turn the throttle wide open the power starts to cut in and out.  What can cause this? I thought it was a dirty carb, so I put my spare clean one in, but it seems to do the same. I tried this on with the new carb at 60-80 km/hr. But it's still there.

I have normal power from idle to 3/4 throttle. Then from 3/4 to wide open, the power goes for a second then cuts out and in. I don't try it for too long for fear of breaking something.

The main jets are clean. On the old carb I had a 140 main, and on the new one its the correct 132.5.

Where should I look? What should I look for.

Thanks.

Offline dankeller

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Re: power cutting out at wide open throttle
« Reply #1 on: June 17, 2016, 02:54:44 AM »
I rode longer on the new carbs and wide open throttle was working fine for short bursts.  So I guess some thing is clogged somewhere in my other set of carbs.

Offline dankeller

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Re: power cutting out at wide open throttle
« Reply #2 on: May 25, 2017, 04:22:56 AM »
Just to complete my thread, my original set of carbs (carbs no. 1) were paired with pod filters when I got the bike.  I eventually put an air box back on the bike because of the advice on this forum (with which I now agree). As I worked through issues I got a second set of "refurbished" carbs, which I used in the bike for the last couple years.  At the start of this season I was having issues with carbs no. 2 (leaking float valve, popping on decel, not getting good power at full throttle) which I thought were due to them being dirty, so I swapped in the first set of carbs. Some of said issues disappeared, but wide open throttle on the highway resulted in significant power cutting out, and cutting back in when throttle was reduced.

I checked the carbs no. 1 which I had out at this point and discovered the main jets were the wrong size (140 instead of 132.5). So put in the right main jets and also replaced the pilot jets, mixture screws, and float valves (I used a keyster kit for another model but which had at least these parts), cleaned the carb bodies good, set the float heights, and swapped the carbs no. 1 into the bike. After synching them and testing them I found wide open throttle now worked fine, and popping on deceleration was no longer noticeable.

So in summary I conclude that the wide open throttle bogging issue with my carbs no. 1 was caused by the wrong size main jets (too big) for the stock airbox setup. I haven't yet investigated the problem in the carbs no.2, but I suspect they need a cleaning.