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Engine swap: Question for the pros

  • Thread starter Thread starter GS_Bill
  • Start date Start date
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GS_Bill

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I appreciate any input that anyone has to this question. Thanks in advance!

I swapped a GS1100GK motor into an 82 GS1100G frame. I am using the carbs from the 82 motor. The bike starts up and runs idles and revs fine while parked. When driving the bike, it seems to lack power almost like it is running on three cylinders. I have verified that all four cylinders are getting spark. The plugs look a brownish gray, which would tend to indicate a lean condition to me. When taking off from a start the bike has plenty of power, when cruising at 30-40 mph, the bike has no power when I give it more gas, and almost wants to stall. It seems like it is running a little hot too.

My question to all of you is: can anyone verify that the carbs have the same internals from 82 to the 84? I find conflicting results from bike bandit, partsfish, and other online fische sites, specifically needle and pilot. Any other ideas what could be causing this problem?

-Bill
 
As a general rule, if a bike idles and revs fine with no load, but tries to stall or lacks power under load, that's a fuel flow, fuel level, or lean symptom. Poor float bowl venting can also effect fuel flow. I can't see the plugs, but you say they look a bit lean and the bike seems to be running hotter. That also suggests a fuel flow or lean condition.
I don't know if the carbs have any changes from '82 to '84 other than what you see, or the engines for that matter, that could cause problems like this.
Your test results at cruising speeds of 30 to 40 may suggest a pilot circuit mixture problem. At those speeds, the throttle is at a minimal opening. If the mixture screws have already been adjusted using the highest rpm method at factory recommended idle, and you're sure the float levels are good and the carbs are clean, and the bowls are venting correctly, then I think the pilot jet is too small. If your mixture screws don't effect the rpm's as they should, that also suggests you need to change the pilot jets. But as basic maintanance, the venting/clean carbs/float level adjustments should be done/verified first. Then see how the mixture screws react to adjustment. Generally, if you do acheive highest rpm when the screws are in a range of approx' 3/4 to 2 turns out, the pilot jet size is OK. If below or over that range, or if the screws seem to have no effect, the pilots are the wrong size.
The air jets can factor in here too, but more commonly the pilots are changed.
 
I read through my shop manual last night, it appears that there is different ignition timing from 82 to 84. Both bikes have electronic ignition, but it appears the the timing is different by 4 degrees from '82 to '84. So my question is what controls the timing on these bikes? Is it a component that is housed on the frame, or the engine? All of the electronics that are on the engine are '84, while all of the components on the frame are '82.
 
I'm not concerned with changing the timing. I am wondering where the timing is controlled? Is it controlled my a module on the motor, or on the frame. As I stated before the chassis electrical is all 1982 while the motor is all 1984. Is there a conflict between the motor electrical and the chassis electrical?
 
The timing is controlled by the "ignitor" unless you have a mechanical advance. I think.

You'd want to use the ignitor and mech advance (if it exists) from the donor bike. Then you're guaranteed the correct ignition timing.
 
That was what I was thinking. Can anyone else verify?

Thanks,
Bill
 
Or do yourself a favor and get a Dyna S. ;-) Of course you'd still need to work out a mechanical advance...
 
They could be jetted different due to different air boxes possibly
 
Under the signal generator cover is where the pickups are for the ignition.. but I would assume that you are running lean, try running the bike with just a hair of choke, and see if it runs better..
 
I think your model reaches full advance by about 2300 rpm, which is acheived as you rev it in neutral. It idles and revs well in neutral. It appears to be working. I don't see where actual load effects the sparking/timing, only engine rpm. I can't answer how the '82 and '84 parts could effect each other. There must be timing marks to shoot with a gun to see if it's firing at the right time??
I still think the loss of power under load is fuel related.
 
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