bike is stumbling

[soulrydemike]

im having an issue with my 79 special. just replaced my friction plates and clutch springs and been working with some jetting issues. clutch solved high end slipage but but it is still seeming to "starve" for fuel on the high end so ill have to rejet(prob cause the pod filters and debaffled pipes with custom super traps). so now that the clutch is working great, as I was pulling hard throught he gears enjoying the readily available power, the bike stumbled or seemed to jerk somewhere in the rear end. or at least thats whet it felt like.

any ideas on what could cause this?

[Clerek]

Don't know but if I need to rejet because of pod filters and straight pipes, I may have a problem. Or I could just live with that extra little available power...

-Rick

[XSokieSPECIAL]

I thought i was running out of fuel at top end too, but yesterday I found the real problem.

I had a wire in the ignition pick up coil that had rubbed a tiny pinhole in the insulation an was occasionally grounding out on the head of a screw. For a long time it seemed to only do it when I was on the throttle in high gear. Felt just like the engine was starving.

Yesterday it kept dropping 2 cyls and back firing when I was just cruising. That was embarassing, I was riding right next to 3 Harleys when it started acting up.

[mro]

Stumbling SF...
Pick up coil wires (see tech tip) can look good but be broken, loose contact and regain in a way that you may think you have a fuel problem.

Ignition switch or electrical plug not making proper contact.
Tip over switch, (usually just goes bad tho)
Coil going south, fouled plug(s)
Vacuum leak
Pod filters that have an inner lip which obstruct air flow into carb
Kinked fuel hose, bad petcock/octopus valve not allowing enough fuel
Partially clogged petcock filters

That’s just a few of the things that can cause a stumble, but since your monkeying with the carbs and have intake/exhaust mods most likely it’s cause is the carbs... (thinking you have done a good maintenance and check of the rest of the bike)

“or seemed to jerk somewhere in the rear end”
You did at least check the fluid levels in the final and middle drives?
The zirk fitting near the front of the final drive may have been put there for looks, cause it does not lube anything. Have to pull the drive shaft to grease it’s splines and same for the gears on the wheel and final drive.

mro
Have you posted any pics of your SF?

[GARTHXS]

sync

You need to sync and retune your pilot mix first after you have the carbs off and definatly lube everything up

[soulrydemike]

i definitely need to re-sync the carbs.
i will check out he ignition coil for sure and i should probably redo the fuel lines.
as for the jerk that it did. it did it again to day. i was in second at around 5000 and she jerked pretty hard then again a few seconds later. it only happens in second when im getting on the throttle pretty hard. will lubing the splines and final drive help maybe? cause its a pretty quick jerk, which almost sounds like a miss fire or back fire. but not the rumbling back fire like when im down shifting. more of like a potato gun pop, if that makes sense.

[GARTHXS]

misfire

Maybe a misfire or second gear slip

[DGXSER]

I would second the broken pick up coil wire(s).

[TopCatGr58]

Not seeing the forrest for the trees?!

Hey Mike,

You said a "skipping" type sensation under strong throttle in 2nd GEAR....
Hmmmmmm could it be the dreaded 2nd gear skipping problem due to worn gear dogs and slots... .....me thinks so!

See the tech tips for the Dremmel 1st and 2nd gear fix. Sorry that you didn't discover that BEFORE you worked on your clutch, you were almost half way to doing the gear fix when you pulled your clutch!
T.C.

[DenyP]

I would still sugguest addressing jetting if you have not done so since going to pods and no baffels in the exhaust. This may not be the cause of the specific problem - but will be a problem never-the-less.

Deny

[GARTHXS]

baffled?

I would still sugguest addressing jetting if you have not done so since going to pods and no baffels in the exhaust. This may not be the cause of the specific problem - but will be a problem never-the-less.

Deny

He has a custom supertrapp type setup. I have seen it

[3Phase]

He has a custom supertrapp type setup. I have seen it

It is as fast as it looks, I have ridden it! <shameless >

Mike, the problem under heavy load: is it only in 2nd gear or does it happen in other gears?

Now that you've fixed the clutch and eliminated the slip you can check your main jets and work your way through the tuning tree. Have you found out what type of low speed jets are in your carbs and are they the stock #42.5 or did someone put in the larger #45 size?

Here's a link to the Factorypro CV Carburetor Tuning Guide that shows the basics of CV carburetor tuning but remember that the intake and exhaust have to be tuned along with the carburetors. That will make it more interesting but should give you a better tune in the long run.

You can't do too much with the pod filters except ensure that the rubber fittings don't cover the air jets in the carburetor inlet bell but that exhaust that you made is totally tunable!

Here is Trbig's post with pictures that show the blocked inlet problem with some pod filters. Happy tuning!


Regards,

Scott

[soulrydemike]

Mike, the problem under heavy load: is it only in 2nd gear or does it happen in other gears?

Now that you've fixed the clutch and eliminated the slip you can check your main jets and work your way through the tuning tree. Have you found out what type of low speed jets are in your carbs and are they the stock #42.5 or did someone put in the larger #45 size?

so far its only under heavy load in second gear. as im powering through second it makes a strange pop as it stumbles. thats the only reason i dont thinks its a drive train issue.

i feel that the hight end stumble/starvation feeling is mostly the carbs and hopefully the pick up coil fix will dial that.

could the pick up coil issue cause that hard stumble or does it feel more like the light clutch slip/lean carb stumble?

I havent checked the other jets, but i did put the 117.5s in the middle two and the 112.5s in the outer. still need to resync though to see how she is really feeling. she's pullin like a beast with the new clutch though. now i just need to figure out this new damn issue.

[GARTHXS]

pick up coils

If you have a multi meter you can check them at the small plug on the tci I think its the white and yellow to the white and red if you set the mm at 20ohm it should read somthing like .760

[Ivan]

When my second gear started to go, it would make a pop and the bike would feel like the switch was turned off for just an instant.

Later on, it got to where it would shift its self from 2nd to 3rd under hard accelleration.

Finally it got to the point that it wouldn't stay in second, just pop out of gear, and trying to hold it in with your toe sounded like a machine gun going off and hurt like all get out.

I am guessing you are in the very early stages of second gear going south. Not a big deal to fix.