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TOPIC: Bike redlining when started?

Bike redlining when started? 30 Jun 2019 13:21 #806718

  • dan4sman
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Hi everyone,

I'm hoping that someone with more knowledge than I have could help me with a problem that I'm having. My bike is an 81 kz750 ltd 4 cyl with Keihin cv34 carbs. I bought the bike a few months back and have slowly been restoring it to get it running again, the previous owner had it sitting in a garage for about 10 years or so not running. I finally got the bike running, but my issue is that whenever the bike is started, it goes straight to redlining (although I'm not exactly sure what the RPMs are as he also ripped out the tach, although its way too high without a doubt, as in gas is starting to pour out of the exhaust pipe heads), and I can't figure out why.

A few other details: I have pods on the bike currently (I've jetted to 70/125), I've cleaned out the carbs multiple times now with no help, and, recently today, I tried removing vacuum lines 1 and 4 on the carbs and capped them, and then ran another piece of tubing between the vacuum fittings (I think these are vacuum fittings?) further up the engine near the valve cover. This seemed to have no effect on the problem, as the issue continued whether or not the vacuum lines were on 1 and 4 or not. I still cannot seem to figure out the problem.

One thing I suspect that MIGHT be the problem (which is where if someone could chime in who knows more about these bikes would be awesome) is that the previous owner had broken off part of the choke return spring that's between carbs 2 and 3, and re-wrapped the spring around the spring housing again in order to get some tension behind the spring. As far as I can tell, this isn't a problem as the choke seems to function properly, although I did take a look at the valves that are opened and closed with the choke, and noticed that they seem to move slightly in and out (they're not all the way closed with the bike running), although I assume that this is normal behavior? If this isn't someone please let me know. If I go to close the valves or slow them down (by pressing in on the lever that returns all 4 choke valves) as the bike is running, it stalls out pretty easily. I think that I have put this assembly back correctly as well--I'll include a picture in hopes that that helps.I have seen an instructional forum that someone made about turning that choke lever into a more mechanical lever, and was thinking that that might not be a bad idea to try.

If anyone has any suggestions please let me know, and thank you!!

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Bike redlining when started? 30 Jun 2019 13:23 #806719

  • dan4sman
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Oops, forgot to include a picture of the choke lever setup between carbs 2 and 3. Here it is:

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Bike redlining when started? 30 Jun 2019 13:49 #806720

  • Nessism
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Sounds like the throttle is hanging up. You might want to check the cable routing and make sure the throttle stop screw is backed off to the point where the throttle butterflies are only cracked open a sliver. Lastly, if you haven't changed the carb boots doing so would be money well spent in order to avoid air leaks.
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Bike redlining when started? 30 Jun 2019 16:07 #806725

  • dan4sman
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Thanks for the advice. I will for sure check out the throttle cable routing and make sure that that isn't the source of the problem. I'll take another look at the boots as well and make sure that those are okay. I'll report back with any changes.

Dan

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Bike redlining when started? 30 Jun 2019 16:08 #806726

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Also, I've tried twice now on the choke lever picture but don't see it... I think I got it this time.
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Bike redlining when started? 02 Jul 2019 08:49 #806839

  • dan4sman
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Hi again,

well your suggestion did work! I was able to get the idle speed down significantly--to a point where with some adjustments it should be idling fine. Although, now I have a follow up, and I think independent problem. Now when the bike is started, it feels like (by temperature of touching the pipes) that it is not firing on cylinder 1 and 4. Also, a small puddle of gas is coming out from the head of the first pipe, and its causing some smoking issues as the bike is running. Obviously I don't want to leave the bike running this way for very long. Strangely enough, before I was having a problem where the bike was firing on ONLY 1 and 4, and 2 and 3 were not firing. I thought I had fixed this issue, since I figured out that the PO had flipped the spark plug wires from cylinders 2 and 3--flipping them back to their correct spots seemed to have amended the problem. Because the bike was able to previously fire on 1 and 4, it makes me think that the issue is not electrically related. I can go back and check later today to make sure I have spark on those cylinders, but I should, as that was one of the first things I checked when I got the bike.

Also, I had removed the vacuum system and plugged up carbs 1 and 4, as well as plugging the vacuum lines from the valve covers by making a line between them. I thought maybe the firing issue on 1 and 4 had something to do with that, so I replaced back the original vacuum system, but that didn't seem to change anything, Am I safe to plug these back up and remove the factory system?

Any thoughts on this would be great, thanks.

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Bike redlining when started? 11 Sep 2019 17:56 #810728

  • TexasKZ
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Plugging the vacuum ports is fine as long as the plugs fit tightly and that they are on the vacuum ports and not the bowl vents.
Switching the 2 & 3 spark plug wires because the fire at the same time. So do 1 & 4, so I suspect there is a problem with that coil or its wiring.
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