Bike dumps power at WOT

[BZNrider]

I have an 81SH (BS34). Did the Mikes 1.5" headpipes w/ dynaglide mufflers and pod air filters. The jetting is stock except for 135 mains. The carbs were sync'ed by a shop.

The bike is running a bit rich, I can smell -some- unburned fuel on idle and the plugs are a bit dark but never wet looking. My mixture screws are set 2 1/2 turns out. My real concern is that when I grab a handful (greater than 3/4) of throttle, the bike falls on its face. I lose a lot of my power and cannot maintain speed. The bike surges slightly when this happens. Even up at 70, the bike pulls the best at 3/4 to 7/8 throttle.

I thought that these carbs were fairly lean to begin with and I did not 'rich' them out too much, but I think it may be pouring too much fuel in at WOT. I read somewhere that the needles can wear and make the bike run rich? Is this possible?

The diaphragms look fine and the carbs are very clean. I thought that the floats may have been improperly adjusted but I measured them tonight and they were fine. The carbs never leak. The bike idles great and starts fine, pops slightly on deceleration (right side only).

Any ideas?

 

[Patches]

Is the rubber plug over the pilot jet? If this is missing it can cause these carbs to run rich. Did you check the mixture screw to make sure the o ring and washer were still there? Have you tried turning the mixture screws in to see if it kills that cylinder (dead cylinder method)?

 

[BZNrider]

Rubber plug is present and not cracked. I replaced the o-rings and washers two years ago.

 

[XSLeo]

Those Dyna mufflers are as or more restrictive than the stock mufflers. Try the stock jets and adjust the air mixtures screws.

 

[BZNrider]

Those Dyna mufflers are as or more restrictive than the stock mufflers. Try the stock jets and adjust the air mixtures screws.

Is this true? Would mufflers designed for a much larger engine be more restrictive? I was starting to think that the bike might be running too lean at WOT and to rich at mid ranges from ???

 

[weekendrider]

While not in his signature I believe Leo owned/owns a dyna so I'd take his word on it.

 

[Classic]

Welcome from another MN XS rider. I rode an '82 with exactly the same problem and I'm not sure if the owner ever got it sorted....

 

[grizld1]

If you can't determine if your mix is rich or lean at WOT I don't know how to help you, except to suggest that you put the stock components back on your motorcycle. You're making an error to assume that the breakup is due to carburetion unless you've done a thorough job of inspecting the ignition (from the fuse box down).

 

[XSLeo]

Yes, I have an "03 Dyna. I put different mufflers on the Dyna. I tried the Dyna Mufflers on my 75 XS. I had K&N pods on it so I was up 1 on the pilot and two up on the mains. The bike showed signs of to rich.
I put the stock mufflers back on. The Dyna mufflers didn't look as good as the stock mufflers.
The Dyna's do have a larger engine but they are also built to much stricter emissions and sound standards than our XS's.
If you were to drill or knock out the baffle plate in the Dyna mufflers, then they will be more of a straight thru muffler, Kinda like a glass pack.
Have you read the carb guide? www.amckayltd.com/carbguide.pdf
It has a tuning guide in it. This might help you understand the carbs better.

 

[gggGary]

Since it is a WFO problem run it WFO pull the clutch, kill switch the engine, and pull the plugs after you safely stop. AKA plug chops. Then you should know if you are rich or lean.

 

[littlebill31]

If I put my 1200 sportster mufflers on (bologna cut) I have to add more air to the mix. I have cut pipes normally. Also, I can't use the choke with these mufflers. I only used them for inspection, but they make the bike run very rich when installed.