Need some expert help!

A place to discuss matters related to Honda Helix scooters.

Need some expert help!

Postby kenyrider » Wed Sep 11, 2019 9:11 am

95 Honda Helix. 23,000 miles, mostly mine.

For at least two years I've had a gremlin in this machine. It loses power, especially up a hill. Full throttle sometimes wont even get over 45, sometimes its 60... IT sounds like a blanket over the engine, (when it runs right its more hallow and throaty sounding). You can feel compression on the engine even after it slowly accelerates, way slower than it should. If it gets up to a decent speed (short of its general max of 70-72) you will feel like someone is stomping the back brake here and there, like its misfiring. It also when doing this is going through gas nearly twice as fast, likely as its just dumping it unsparked. when you let off the throttle, even at 25, it pops like a damn popcorn maker out the tailpipe.

The oddest thing about it, is other days you turn it on and its fine! sometimes mid crappy ride, it will just suddenly lurch and take off and run perfectly! no backfiring whatsoever, proper acceleration, top speed, sounds normal, like there was a pea stuck in a drinking straw and it finally clears. I am at my wits end with this thing.

As I'd gotten from advice here in the past, here is what I've done: all OEM parts from bike bandit, etc

Good gas, seafoam
got a rebuild kit for the carb from wincycles
cleaned and rebuilt carb, new jets, floats, seal
new autobystarter
replaced muffler seal and checked muffler for leaks-its fine
new ignition coil
my carb tubes, when hot, could be pulled off pretty easy even with clamps on so i replaced the tubing and clamps (actually ran worse that day)
new spark plug.
checked fuel filter.. can blow through it easily
no rust in gas tank
replaced the carbuerator insulator
replaced fuel pump
replaced air filter a while back (wasn't even really dirty)
i tried taking the plug out top of block to check the high side timing, it seemed to look right (cant imagine timing going in and out, would just be right or wrong)
ive had the air intake plastic on and off a million times.. nothing impeding, all looks ok.
cant see any arcing from anything electrical.
spark seems to be good. although i do notice with the vibration that the positive connection on the end of the ignition coil can come loose, but have made sure to push it on fully.

this clearly to most people sounds like a fuel or air issue. but ive replaced most everything there i can think of.
this issue is always the same.. its not like i fix one thing and then it causes something else. its always done the SAME THING. and then just fixes itself, sometimes mid ride! I can go home with it running great. then turn on next day and its CRAP!
Sometimes bumps in the road seem to affect it.
I've also noticed at times recently, if i only throttle halfway, let the bike slowly get up to speed way slower than it should, and back off the throttle a notch, it will correct itself and lurch forward and drive fine. some days that doesnt work. last saturday in colorado it was dry and 82 degrees and it ran perfect all day. even took it on the highway. next day back to crap. The funny thing is, it certainly hates rain and humidity.. that makes it run the worst, but while it loves cold morning dry air, and will run well(normal) at least halfway to work, then at the end of a day when its dry and not humid, but 100 degrees it will run great then too!
the only thing i can definitely tell, is it hates humidity or rain.

Does ANYBODY have any ideas what could be happening?

Thanks!
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Re: Need some expert help!

Postby GrahamH » Wed Sep 11, 2019 9:39 am

Did you replace the HT lead and spark plug cap when you fitted the new coil? I had a Suzuki 2 stroke that hated wet weather and had to spray the HT lead/spark plug with WD40 to prevent misfiring.....sounds a little similar. Maybe when the problem occurs stop and give it a good spray to overcome the dampness.

Also check for electrical earths, clean and retighten any connections and if in doubt add an extra earthing wire, it can't do any harm.

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Re: Need some expert help!

Postby zozman » Wed Sep 11, 2019 2:58 pm

This is the classic fuel delivery/drivability issue which plagues older bikes.

After rebuilding carburetors for years, sometimes I get a carburetor to rebuild and no matter what I do it just is difficult to get it tuned properly. I had a cold-blooded one like that once. I just replaced it with another I had in storage already rebuilt.

First, I would check the carburetor vacuum piston for pin hole leaks in the rubber sheath or sloppiness in upward travel possibly a bind. This may be contributing to your acceleration issue.

Next, look for vacuum leaks from the intake to the carburetor.

If those check out, I would replace your carburetor assembly with the Honda OEM Helix carburetor 16100-KFR-842, $233.11 (this appears to be $10 higher than last year!). This eliminates any parts overlooked on the rebuild or blocked carburetor passages issues not addressed.

Once you replace the carburetor and some or all of the issues still exist, then I'd look at replacing the CDI.

zoz
87 & 98 Helix
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Re: Need some expert help!

Postby millican » Thu Sep 12, 2019 1:30 pm

zozman, I have a question about the OEM carburetor. (I wouldn't consider the knock-off units.) I've cleaned and rebuilt my carb a couple of times recently. It has a new bystarter, air cut-off valve (old one tested at 0psi!), gaskets, and that diaphragm piston. Getting that cover on while keeping that piston in place is pretty tricky, I must add. Buying one of those special screwdrivers and going through the idle-drop adjustment procedure helped, but I'm still having problems at highway speeds. It just cuts out and jerks a bit when you let off the throttle.

After all that: my question is this:
Does the new OEM carb come already mostly tuned? Do you still have to go through the idle-drop and enrichment adjustments with a new carb? Taking an engine apart is fine, but carbs I just can't get right. I have all the parts for another complete carb and might try putting that together and seeing what happens for poops and giggles, but I suspect I'll just need a new carb.
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Re: Need some expert help!

Postby zozman » Fri Sep 13, 2019 5:42 am

The OEM Honda carburetors are tuned to specifications at the final assembly point and rarely need any adjustment.

zoz
87 & 98 Helix
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Re: Need some expert help!

Postby millican » Fri Sep 13, 2019 9:18 am

Thanks!
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