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bike missing at 1/8th throttle

  • Thread starter Thread starter chandler
  • Start date Start date
C

chandler

Guest
hello all i rebuilt my 1979 gs 1000 e about a year ago have K&N filters a kerker header with competition baffle and a dynojet stage 3 kit bike has been running great but within the past couple months i am getting a flatspot at 1/8t throttle when crusing and barley turning the throttle it is misfiring and feels sluggish untill i get a load back on the engine . have a dyna iggy with brand new b8es plugs 2nd set thought it might have been a plug but did same thing with another set. carbs are all rebuilt and float heights are correct. this problem has come on slowly over the past few months driving me crazy trying to find it .
could it be the intake Orings ???

thanks
steve
 
Have you trimmed the ends of the spark plug wires?

Unscrew the caps, trim about 6mm from the ends of the wires, screw the caps back on.

.
 
i am not using the ngk caps i have dyna boots wich dont have resistors in them and i use BR8ES plugs . the wires and caps are new
 
Brands don't really matter, but it's nice to know they are new.
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O-rings possible. With the engine idling, spray some carb cleaner around the junction of the boots to the head and see if it affects the idle.

The slow onset of this condition might also indicate a buildup of varnish or dirt in one or more of the carbs. You might try some cleaner in the fuel, such as Berrymans or Techron (I don't recommend others).

Also, 1/8 throttle is completely on the pilot circuit and your mixture screws should be effective in this region of operation. Try resetting for fastest idle, or consider playing with them: Turn them out (richer) by 1/2 turn and see if that helps; If that makes it worse, turn them back in 1/2 plus another 1/2 (leaner) and see what that does.

I believe this has VM (slide) carbs? They also have an air mixture screw, but recommend starting with the fuel side unless you suspect some dirt got in the air side - unlikely with a good air filter.
 
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His bike has VMs, so it might be better to try the fuel screws in smaller increments (i.e., 1/8 turn) since they start out at about 1 turn out. 1/2 turns are a big change on the fuel screw.

If the problem emerged slowly without any changes to the jetting, I'd look pretty hard at those intake boots and rings. Jetting problems should happen when jets change. If it ran well before but stopped, and you didn't change anything in between, then something else has affected the mix. A new leak in the boots is a likely cause, especially if the flat spot is lean (instead of bogging). If it's a richness issue (you should do a plug chop as this happens), then you have a fuel invasion or blocked air passage, dirty filter, etc. that is cutting off the air supply.

If you can recreate the stumble, try giving it a touch of choke. If that smoothes it out, probably lean. If it gets worse, rich. Again, a plug chop for the pilot circuit is the best method. Ride around at low throttle for about 20 minutes, then chop the throttle and coast to a stop as you pull into your garage. Check the plugs for signs of rich/lean.

AJ said:
O-rings possible. With the engine idling, spray some carb cleaner around the junction of the boots to the head and see if it affects the idle.

The slow onset of this condition might also indicate a buildup of varnish or dirt in one or more of the carbs. You might try some cleaner in the fuel, such as Berrymans or Techron (I don't recommend others).

Also, 1/8 throttle is completely on the pilot circuit and your mixture screws should be effective in this region of operation. Try resetting for fastest idle, or consider playing with them: Turn them out (richer) by 1/2 turn and see if that helps; If that makes it worse, turn them back in 1/2 plus another 1/2 (leaner) and see what that does.

I believe this has VM (slide) carbs? They also have an air mixture screw, but recommend starting with the fuel side unless you suspect some dirt got in the air side - unlikely with a good air filter.
Click to expand...
 
If it was running ok before and you haven't changed anything it's either an air leak (O rings, split hose etc), blockage in the airbox or you have got crap in one of your pilot jets. I wouldn't go fiddling with any of those screws - something has changed and it won't be sorted by turning a screw or 2.
 
I concur with AJ and MC's assesment. 1/8 throttle you are still on the pilot jet circuit. Your symptoms seem indicative of a slightly lean condition. Try running/riding the bike with a bit of choke and see if the symptoms improve. Then try removing the pod filters and see if it gets worse. If it does, you're lean and somehow got a little varnish or gunk in one or more of your carb's pilot jet circuits.
 
yes my bike does have the 26 VM carbs...thanks guys will do what you all said and will let you know how it runs .
 
Pods are properly oiled?

I read somewhere that as a last resort, or even as a troubleshooting experiment, wrap some tape around the outside pods to lessen the airlow, which will slightly richen your mixture. Or wrap tape around all four. 3/4" masking tape should be enough, and one strip width (you don't want to cut off all the air). That might be easier than actually changing the mixture at each carb, it will give you a quick and dirty look at the effect of richening.
 
Does it reappear at idle or over say 3,000 RPMs? Then i would deduce its a malfunction of power modulation thats effecting the flux capacitors. :eek::eek::eek::):):)
 
hey chuck you might be right LOL i was thinking more of a vortex making the diodes flow backwards LOL

ok this is what i have done i had a new set of Orings for the intake boots i pulled off the carbs and changed the Orings on the intakes one looked suspect so i replaced the entire intake rubber have bike back together now runs much better did a plug chop a WOT plugs looke great did it a few more times at half still looked good but still has that eratic idle and about 1/8th throttle feels very flat
then i pulled out the choke it started cutting out but then pulled it out about halfway it ran better holding the throttle at the 1/8th position my air screws on the side are at 1.5 turns and my fuel screws on the bottom are at 1 turn i also have 17.5 pilot jets in it along with the dynojet kit ..
another thing when bike is idleing the exhaust is burning my eyes and i hear poping out of the header wich makes me think it is very lean
 
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