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Engine will not go above ~6000rpm?!?!

  • Thread starter Thread starter flyanimator
  • Start date Start date
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flyanimator

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I had written this on my other post, but since i guess it is a new problem I decided to put it in a new thread.

This may not be related to my original problem of the rich mixture or the low volatage to the coils, but here it goes. I performed the coil relay mod on my bike AFTER cleaning all the electrical connections with a dremel and a small wire brush attachment and now my bike runs but will not rev past around 6000 rpms:eek:. May the modification or another electrical issue have caused this:confused:? Just to ad some relevant info; the filter box to carb boots are old and hard so they are not fitted on all the way and ambient air leaks into the carbs. This was present before the previous problem and subsequent actions to correct it but it did rev all the way up to the ~9k rpm redline without a problem (although i rarely take her above 6k rpm). I've read that this problem can present itself when changing to pods on bike with certain kinds of carbs or maybe even all carb'd bikes due to a lack or reduction of vacuume needed for proper carb function. Might this be the case in my situation:confused:? This is all under a no load situation (bike is on centre stand). I have not yet tested it on the road to see if power has been affected in any other rev range. Please help:cry:!!! Thanks.
-Rudy

P.S. I am getting about 12.8v at the coils at idle with the coil relay modification with less that .1v drop from battery.
 
You should not be trying to rev it to 9000 rpms with no load on the engine
 
It's not that I'm trying to rev it to 9k, the problem is that it won't go past 5500-6000 rpm. where before it would. Might this be a coil issue? Since they are old I would imagine they were fine and dandy with the reduced voltage and may have had a "heart attack" with 12v once the voltage drop issue was resolved with cleaning the contacts and the relay mod. Is this a possibility or am I just talking nonsense? Can coils fail from one moment to the next. I will be testing the coils in a bit for primary and secondary resistance and see what that comes up with. One other note on the problem: when the engine was peaking at ~6k rpm it felt like it was bogged down and that was at WOT.
-Rudy
 
I have to second the thing about revving under no-load. I blew up a REALLY nice V8 doing that once. Hope you have a roller bearing crank.
What bike is it? maybe put it in your signature.
Did you change to pods yet? Could be part of the problem. Check all the plugs for wetness/color and spark. Could be a couple mixed up wires from the coil relay.
 
Make sure your mechanical advance isn't sticking.
Are your carb slides moving freely?
Did you change the main jet?
Is your battery good?
 
air flow

air flow

These bikes are very susceptible to changes in air flow. For instance, I had a bike running great until I fixed a leak in the exhaust. Following that exhaust repair it would run great up to 4500 RPM and just hold there. Wouldn't go any higher until I re-jetted the carbs with smaller jets.

Anything that changes the airflow even a little can affect the way it runs and pods or a significant leak in the filter box will make a big difference. Try to fix that leak and see if that makes a difference. Then consider what else may have changed the air flow either in the intake side or the exhaust side.

It could be as simple as adjusting your mixture screws. It could be something that really needs to be fixed, like the boots, or it could be somewhere in between or a combination of things.

check for air leaks, check the timing, then check the valves...keep looking. It's there somewhere.
 
Thanks Larry, I appreciate your advice. Sometimes it gets a little frustrating fixing something wrong with the bike and having one or more problems arise from the repair. Guess that I just have to take it step by step and stay calm. The weather here has just been so great these past few days and I wish I was out riding instead of being stuck in the garage trying to diagnose the source of the gremlins.

Just to give some more relevant information:

Carb clean and sync 2 weeks ago, have not messed with them since then.

Original problem was crappy fuel mileage and extremely rix mixture; voltage at coils was less than 8v and was corrected by cleaning all electrical contacts and coil relay modification.

air box to carb boots were not seated even marginaly well before the coil voltage issue was fixed, but the engine did not hang up the way it does now.

The battery is good and cranks the engine well. Engine starts up quickly without any issues. The carbs have not been modified and have all stock spec. internals.

I think thats it. I'll be testing the coils and other things during the rest of this weekend so I will update as sone as I have the info.
Thanks

-Rudy
 
adjusted valves, runs smoother but didn't take care of the problem.

adjusted valves, runs smoother but didn't take care of the problem.

Ok i just adjusted the valves yesterday, and as suspected the intake valves needed adjustment so I set them to .004" (exhaust valves were in spec.). The engine seems to run a little smother but I am still have the cutoff problem at higher rpms. I will be pulling the carbs this weekend (hopefully) to make sure tthe shop that sync'd them did everything right and to catalogue the jets and adjust if necessary. I will also be reading up here on the forum on how to inspect or adjust the timing as well as reviewing my service manual. I would imagine that the enggine needs a timing advance at higher rpms, is this correct? If anyone has done this recently or has any tips on techniques or tools that will help make this job easier, please chyme in and let me know what I should look out for. Thanks.
-Rudy
 
Sounds like a shaftie.

Just trying to start trouble. lol
 
Haha, no it's a chain drive 1980 GS1100L. It was only produced for one year apparently so I don't know f many people have some experience with them or if they are similar to any of the other bikes (maybe the 850's).
 
Take it for a ride and give it a little choke. If it runs better - too lean. Start checking the intake boots and the carb to air box boots. Replace them if needed. These are great bikes, you need to do repairs properly. That includes having the airbox fit properly.
 
I need to order them soon. I read a thread on here where someone described having used short sections of various diamaters of radiator hose sealled with silicone as filter box to carb boots. Can I use these as replacements or at least as a temporary fix until I can order replacement boots?
 
Well, if you order them today, and spend a day or so checking your carbs, that box will show up before you know it and you'll have one more problem nsolved.
 
I had this problem on my G with good carbs... It turned out to be the igniter box. I tested against the instructions in Clymers & it showed a fault. Wouldn't pull past 6k, eventually started missing on plug 3.
Fix is to get a Dyna S.. $120.

:)
 
Thanks for the tip Dan. I have a feeling mine has the same or similar problem (some part of the ignition). I will be testing the ignitor box and various other ignition components tomorrow and will post the findings on here. Is the dyna s ignition a direct fit or do you have to mess with the harness to connect it?
-Rudy
 
Pretty much a direct fit, you have to cut out the signal generator (just unplug & the ignitor) then run the 3 wires up to the required points.
It's pretty easy.

Dan :)
 
Dan, one more question about the dyna s ignition. Does this eliminate the need for the ignitor box. I was looking at it and it looks like it all fits where the signal generator goes under the right side cover on the engine. Just wondering, but I guess it is a self contained unit.
 
I've been testing the ignition system and my coils seem to have a much higher resistance on the secondary side. My left coil reads at ~115K ohms and the right coil gives me ~126K ohms. The primary side reads within spec at 4.5 ohms though.

My question is if this increased resistance is causing my engine to not go above 6k rpm. I would imagine that with this kind of resistance the engine would just not fire at all but I'm no expert. I was hoping some of the pro's on here wouldchyme in on the subject.

I tested the signal generator too and it reads in at 322 ohms (manual says between 250 and 360 is good). I wanted to test the ignitor box but the manual says that the coils need to be in good order for this so I think my coils would distort the results or lead me to believe that my ignitor is bad when it may not be.

I also had a question on the dyna s ingnition. I know many of the members on here recomend the dyna s ignition when the ingitor is faulty. Please correct me if I'm wrong, but does the dyna s eliminate the need for an ignitor or would I have to replace the ingiotor when I install the dyna s ingnition.

Thanks for all of your advice,
-Rudy
 
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Just finished testing the ignitor and came up with some confusing results. The manual states that by connectingthe blue wire on the ignitor with the positive lead on the tester and the neg lead with the green wire, No. 3 cylinder sparks and reversing the polarity of the tester the No. 4 cylinder sparks. With the leads set to have #3 go off it sparks but the #4 cylinder gives off a very weak spark as well. Then with the leads set to have #4 spark, none of them spark. I know this is not the way it should be working but I wonder if this may be as a rsult of my coils being over 100K ohms on the secondary side.

Any thoughs on this? All input is greatly appreciated.

I'm looking into the dyna s ignition and a set of green dyna coils. Does anyone have a used working set that they would be willing to part with? I would like to buy new ones but I'm a college student and my budget is pretty slim.

-Rudy
 
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