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General Category >> Rubber Side Down! >> RPM's bottom out when going in to 1st gear
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Message started by troyrr on 07/23/17 at 23:58:01

Title: RPM's bottom out when going in to 1st gear
Post by troyrr on 07/23/17 at 23:58:01

This might be an easy one for your guys who are more experienced. I'm still new to the whole turning of the wrench thing.

Anyway, I've been working an 1987 LS650 for far too long. Here is what I've got so far.

1. The bike starts up fine and idles perfectly.

2. When I drop it into 1st gear the RPM's drop to almost nothing and the bike eventually shuts down.

3. Carb. Tried 2 and 3 washers on the needle. 52.5 and 150 jet. It runs very rich. 1 turn on the adjustor screw at the moment. Actually, I've tried all the jets I've got in different combinations and I still get the same 1st gear low RPM problem. Cone filter.

4. Exhaust - 18" muffler with a 13" baffle. Stock header.

5. Swapped out the spark plug, just in case.

6. Battery is about a year old and fully charged as of last week.

7. Adjusted the valves with a new feeler gauge from Harbor Freight.

8. I've got a 2nd carb. It may need a gasket. It's next on my To-Do list.

9. I got ahold of a 36mm Mikuni round slide carb. Thought I might try for the upgrade with the UFO, but I wanted to make sure there wasn't something else I've missed. All I have is the carb at the moment.

10. Thought I might have some bad fuel. Ran to the gas station and got some fresh 91 octain.

11. Swapped out the O Ring on the Intake Manifold.

12. Petcock. Bought the Raptor 660. Tested it yesterday. Flows like a river. Bought a 2nd petcock just in case. I haven't installed it yet.

12. Replaced the metal gasket on the header pipe.

13. Heat wrap on the header. I've rechecked the entire exhaust. Can't find any leaks.

I haven't looked at the kickstand switch, but I've read on here that it can be a problem, although I don't think the symptoms are the same as mine.

That's it. That's my brain dump. I just want to ride. Is that so wrong?!?!

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 07/24/17 at 00:49:28

Does it try to walk when you put it in gear?
What if you give it gas?
Have you adjusted the idle speed?

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 07/24/17 at 09:17:07

Yes, it does roll forward when in gear.

Two weeks ago I was able to drive it around the block. It was backfiring badly. I had flames shooting out the exhaust. It wouldn't go over 20 mph.

When it is in gear, while I have the clutch pulled in, I try to give it gas and it, I don't know how to describe it, gasping and wheezing? Like it's not getting enough air or fuel, or both. I can't tell which.

I have repeatedly checked the floats. The seem fine, but maybe I need to take a closer look. I checked the float needle and little filter. There is no obstructions of any kind.

Title: Re: RPM's bottom out when going in to 1st gear
Post by Dave on 07/24/17 at 09:27:40

Those kind of symptoms can result from a battery that has low voltage, as the ignition circuit can't reliably make a spark.

That may not be your problem - but it is worth checking the battery voltage with the engine off, and then running to see if the charging circuit is working.

Also your cone filter could be a problem.....is it the kind that obstructs the oval opening at the top of the carb inlet? If you block that opening the slide can't operate properly, and the air jets can't get air.

Title: Re: RPM's bottom out when going in to 1st gear
Post by batman on 07/24/17 at 11:03:56

Dave 's advice is along the same thoughts I had.I'm wondering why you've jetted the carb 52.5/150 the stock jetting for the big carb( 86-87)being 47.5/155. I think the 52.5 pilot jet may be to big ,I'd try a 50 .I also think Dave may be right about the cone filter,you could try removal (for a test ) .you need to look at the clutch adjustment it shouldn't be grabbing.If it were the kickstand switch the bike would die immediately ,It wouldn't slow and then die.

Title: Re: RPM's bottom out when going in to 1st gear
Post by ero4444 on 07/24/17 at 13:55:14

does it run well without the air filter?

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 07/25/17 at 08:59:54

I ran it without the cone filter. No change.

I didn't have a 50 Pilot Jet, so I used the 47.5. I checked the floats again and made some small adjustments. It made absolutely no difference. I still get the exact same symptoms.

I did notice the headlight dims by almost 50% when I kick it into 1st gear. It gets a bit brighter, but thats when the RPM's bottom out. It's still gasping when I turn the throttle.

I'm going to borrow a volt meter from work and test the battery. I bought the battery in November. The ignition coil is brand new but that doesn't always mean it's good. The spark plug is new and I gapped it according to Clymers.

At this point I'm thinking it's NOT the carb. It's electrical.

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 07/25/17 at 09:13:29

Did you remove All of the filters parts? The problems arise from the rubber mount covering passages.

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 07/25/17 at 09:16:12

If it's trying to walk you need to adjust the clutch.

Your idea of Idling Great might not be what it likes, it needs to be around 1100 rpm.

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 07/25/17 at 10:40:15

The filter is one piece. It doesn't come apart. I removed the clamp and filter entirely.

It doesn't walk in 1st gear.

As far as idle, I understand it's supposed to be less like a Harley and more like a sewing machine. The idle screw is the one part on the carb I really haven't messed with.

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 07/25/17 at 11:23:22

Sounds like you're headed in the right direction.
I'd stand it up, play with the gas, and drop it in gear just as I goosed it, if you can get it to rev up in neutral.
The clutch safety must be okay, and the sidestand is maybe not.. If that thing is messing up it Could, possibly, be killing it without just shutting it off like a switch, have you tried putting it up before dropping in gear?

Title: Re: RPM's bottom out when going in to 1st gear
Post by batman on 07/25/17 at 19:21:04

The bike won't run very well without a filter either,I just thought you might be able to get it in gear without stalling.

Title: Re: RPM's bottom out when going in to 1st gear
Post by Savageman on 07/25/17 at 22:26:58

You might try adjusting the clutch (less free play). And also raising the idle speed a little. It isn't supposed to idle like a Harley but faster at 1100 rpm. You could also adjust the idle mixture screw. It shouldn't be rocket science.

Title: Re: RPM's bottom out when going in to 1st gear
Post by IslandRoad on 07/26/17 at 00:48:23

The idle speeds, that people have reported here on the forum, vary from 1100-1500. I run mine at around 1300-1400 warm. At 1100 the engine will stumble if I have to chop the throttle.

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 07/27/17 at 08:42:21

Ok. I've tested the battery. At Rest, it measures 12 volts. With the motor running and in 1st gear, it measures 11.33 volts. Withing seconds of shutting down the bike it immediately goes back to 12 volts.

Sidestand Switch - It looks like the previous owner already took care of that one. It was already looped back on the wiring harness.

I guess that leaves the Clutch Switch which I will look at tonight.

I may need to purchase some new controls because the hand brake lever doesn't activate the brake light. If there is a problem with the clutch switch it may need to be replaced.

Title: Re: RPM's bottom out when going in to 1st gear
Post by stewmills on 07/27/17 at 08:46:53

Maybe try spraying some WD40 in the brake switch. Had the same problem on my Ninja, and after I sprayed it and worked the switch a little it started working and has been good for over a year now.

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 07/27/17 at 09:07:36

tested the battery. At Rest, it measures 12 volts. With the motor running and in 1st gear, it measures 11.33 volts. Withing seconds of shutting down the bike it immediately goes back to 12 volts.

Not that good.

That the sidestand APPEARS to be modified is no comfort.

A crappy job could be the problem.

The battery needs checked out.

Title: Re: RPM's bottom out when going in to 1st gear
Post by Dave on 07/27/17 at 09:38:13

6D6B76606B6B190 wrote:

Well that isn't right.....when the bike is running and the charging system is working - the voltage should be up over 13 volts....even over 14 volts is normal.

I don't know at what voltage the igniter/black box system stops working - but that could be your problem.

Can you leave your charger on the bike as you start it and see what happens?

Title: Re: RPM's bottom out when going in to 1st gear
Post by Savageman on 07/27/17 at 16:11:42

It seems as if you are off track with the advice that is being given to you. Your responses dont match advice. You need to keep on track and follow advise without jumping around. Then you dont know where you are at.

Title: Re: RPM's bottom out when going in to 1st gear
Post by batman on 07/27/17 at 16:12:55

It sounds like you need a new battery,or you need to test the alternator,with the bike running voltage has to be higher than 12 ( 11.33 ain't cutting it)or you can't recharge the battery, and 12v on the battery at rest sounds low ,it should be 12.3 - 12.5 if fully charged.Either your battery isn't accepting the voltage (weak cell?) or the bike isn't generating enough voltage .( you can bypass the clutch switch by connecting the two wires together,but if your able to start the bike the clutch switch is working,other wise the starter wouldn't run).Charge the battery,make sure the cables are clean and tight, don't forget the ground cable where it bolts to the motor (just above the oil level site glass) then try testing again.

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 08/02/17 at 08:23:54

Tested the Rectifier with a multimeter. There are no problems.

Tested the Stator and I'm getting resistance.

If the training videos I've watched are right, that means the Stator is bad. This would explain the problems with the battery voltage dropping and not charging. It could also explain why the bike runs rough when in gear, and why the headlight is so dim.

Title: Re: RPM's bottom out when going in to 1st gear
Post by Gary_in_NJ on 08/02/17 at 09:07:27

40465B4D4646340 wrote:
Ok. I've tested the battery. At Rest, it measures 12 volts. With the motor running and in 1st gear, it measures 11.33 volts. Withing seconds of shutting down the bike it immediately goes back to 12 volts.

At 12 VDC the battery may be toast. At 11.33 VDC I'm surprised the ECU has enough power to keep the bike running.

I'd put the battery on a charger to confirm that it can charge to, and hold, 12.8VDC.

The output of the electrical system should be around 13.5 VDC at idle and 14VDC or higher at 3,000 rpm.

At 11.33VDC you have a charging issue for sure. If you are handy with a multi meter it's actually fairly easy to figure out what isn't working.

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 08/02/17 at 09:22:08

When testing the Stator coil I am getting NO resistance.

Title: Re: RPM's bottom out when going in to 1st gear
Post by Gary_in_NJ on 08/02/17 at 09:39:47

Each of the yellow wires should have no continuity to ground. There should however be continuity between the three stator wires. I would also check the output (in VAC) from each lead to ground. At 5,000 rpm you should see 100VAC at each yellow wire.

If that checks out OK you can move on to the regulator / rectifier. To test the Regulator / Rectifier remove the R/R from the bike so you can check the internal rectifier diodes. Put your digital meter on diode check and follow the meter test instructions. Check positive wire to yellows wires then reverse the test leads. You will get no continuity one way and about .5 volt drop fwd continuity the other. Now repeat the test negative wire to yellows. You should get the opposite results for no continuity and fwd continuity with a .5 volt drop.

There is not test that I know of that specifically tests the regulator portion of the R/R other then checking everything else - and if the above tests check out OK, but you still have low output, then you are safe to assume that the regulator is at fault.

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 08/02/17 at 12:09:11

20263B2D2626540 wrote:

When testing the Stator coil I am getting NO resistance.

This is where telling exactly where your test leads are connected would help.

Title: Re: RPM's bottom out when going in to 1st gear
Post by batman on 08/02/17 at 13:36:14

again the stater is tested by by placing the leads between two of the yellow leads ( three readings) there should be 1 0r 2 ohm resistance (the resistance of the coil wires) ,no resistance means you have an open circuit (bad coil).

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 08/02/17 at 13:57:28

No resistance or continuity?

Title: Re: RPM's bottom out when going in to 1st gear
Post by verslagen1 on 08/02/17 at 15:14:11

2C2F3A232F207A764E0 wrote:

Actually if you have an open circuit on 1 branch, it'll read 2x ohms because it's reading the other 2 branches.
Or if you have less than an Ohm, then you have a short.
You should have 3 equal readings for the 3 branches.
And an infinite or open circuit on any of the 3 branches and ground.

And give the ohm meter a chance to settle on a reading, measuring thru a coil is weird.

Title: Re: RPM's bottom out when going in to 1st gear
Post by troyrr on 10/05/18 at 14:07:16

Ok, I got it figured out. I know it's been a long time since I updated, but with the wife, kids, work, wife's work, my time and budget are both limited.

Anyway, the main problem was the fact that the engine was missing a gasket just below the jug. Gone. As in, it wasn't installed bu the previous mechanic/owner.

I was getting low compression, around 90 psi, so I figured it must be the piston rings. Then i thought, since I'm going to be doing the piston rings I might as well install a new Cam Chain, and clean up and grind the valves. So I did.

Once I got the engine apart I realized there was no gasket!!! I already had the full OEM gasket set, so replacing it was no problem. Actually, swapping out the cam chain was a lot harder. Cleaning the valves were actually fun by comparison.

Anyway, being a total noob at this I am pretty proud of myself and I just wanted to thank all you guys who contribute and moderate this site for all your help. Also, Youtube was a big help. I think my next project might be getting my hands on a bigger tool box.

The bike runs great. I've gone through the valve calibration enough times, and re-jetting to be comfortable with the process. Thanks again, fellas!

Title: Re: RPM's bottom out when going in to 1st gear
Post by Gary_in_NJ on 10/05/18 at 20:58:29

Awesome!

Title: Re: RPM's bottom out when going in to 1st gear
Post by justin_o_guy2 on 10/06/18 at 05:55:59

You fought and won.
I'm impressed. That's not a piddling little job. I hope you get many trouble free miles out of it.