Occasional acceleration issues at 5k rpm's

cmills83

XS650 Addict
Messages
342
Reaction score
22
Points
18
Location
Santa Barbara, CA
I recently finished my build and am test riding the bike. Most of the time it's fine but occasionally I can't accelerate past 5k rpms, the bike just loses power and won't rev any higher. Usually its fine and I can take it up to redline. I am running k&n pod filters, aftermarket 2->1 exhaust and the Mikes XS Heiden Dyno Jet Kit. Any ideas?
 
Thanks for the replies. The ignition is the stock 1980 electronic ignition.

It seems to be occurring in 2nd and 3rd, I don't think I ran it hard in first yet. I was just going down the street from my house so I think I topped out at about 50mph.
 
Well, Myself am not even able to start diagnosing your bike with little info. I can tell you that there are members here who know your bike very well. So my advise is to further test, check what you are able, investigate this sites tech by searching. Then repost a detailed thread that is as informative as needed. Get the attention of the guys who know and will participate in your thread ! XS650.com is a treasure trove of info and seems to very much "help those who help themselves" ! Good luck, RT
 
Can't really post much else as of now, thought this seemed like a pretty specific issue. I was hoping that if someone had a similar issue they would post some insight into what they did to resolve it. Next weekend I plan on cleaning the carbs again, checking the slides and checking the timing and ignition.
 
Assuming you have stock CV carbs, the slides may not be lifting properly. The rubber diaphragm may have small hole(s).
Test by lifting slide to top, hold thumb covering the oval port....................slide should only drop very slowly.
 
Thanks, I will give that a try. I remember doing this test when I reassembled the carbs but I did notice one had some pin holes but still seemed to pass the test. Are the diaphragms repairable at all?
 
Thanks, I will give that a try. I remember doing this test when I reassembled the carbs but I did notice one had some pin holes but still seemed to pass the test. Are the diaphragms repairable at all?
Not repairable in my opinion, although I have heard of people trying to do that. If its got holes, its time to buy new diaphragms. Do a "search" on the site here..................lots of information................I think JBM is a popular choice.
 
I use dielectric grease, which is silicone grease, on my diaphragms , as it's one of the best things to put on rubber. I also use it on my car door seals, and on the sunroof seals.
 
I might suggest removing the Dyna Jet parts and using Mikuni parts instead.
I have read that a lot of the Dyna Jet parts are not up to the Mikuni specs. This can lead to issues.
Leo
 
Dyna jet, Mikes XS, Mikuni. they are all manufactured in similar fashion. (lathe) Instead of labeling which is "good", accept that some of each are made better than others of each. All depends on the cutting tool condition of that day and who made them. I have used all these brands with great success over the years. Take the initiative to inspect carefully ! Clean it up if needed. I've found for example a Qtip shank will polish or say de-burr a too sharp or dirty edge break on a needle & seat. Inspect cross holes, edges, Trust only yourself ! I would never just install carb componets assuming the quality is good.. If a component looks suspicious, get a different one.. It's kinda like "measure twice, cut once" Inspect Your components ! Trust no mfg just because of the name. Success is on You !
 
Obviously, good diaphragms are a necessity, but I see other red flags waving in the background with your set-up. Basically, all the components you've chosen can cause tuning problems on their own. All together, well, good luck with that.
 
Interesting info, thanks guys. I replaced the right diaphragm and the bike seems to be good to go. I'll probably keep the jet/needle kit unless I run into issues then will take a look at the Mikuni's
 
Back
Top