Stumbly Bumbly

[ninskrillz]

Ok so after a few weeks of a break from working on the bike I decided to fire it up. It started a bit rough from sitting but smoothed out once warm.

I noticed it was smoking a little bit of greyish white smoke on decel on one cylinder and with the throttle on another. I also noticed quite a bit of condensation from the left cylinder.

If there’s some sort of leak from the valves or rings could that possibly cause an overly lean situation and the stumble I’ve been dealing with?

 

[ninskrillz]

Welp I just realized after taking the carbs off for some reason the right carb is a 3.0 slide and the left is a 2.0 slide. I guess that’s what happens when you don’t thoroughly check your stuff and trust that one part means a same parts on the other side!

 

[ninskrillz]

Also upon further inspection the carbs have 159 P6 needle jets.

 

[grizld1]

Congratulations. It's great to see that you thought to check the brass in those carbs all by yourself.

 

[ninskrillz]

Congratulations. It's great to see that you thought to check the brass in those carbs all by yourself.

LOL! Yeah should have been done before I even thought about putting them on - never would have thought they’d have two completely different slides. Life’s always giving new lessons! Thanks for your help hopefully this will solve my issue.

 

[ninskrillz]

Ok - so I’ve gotten my carbs together with matching slides and other internals. I’ve dropped my pilot to a 20 and it runs better. I’ve tried every main jet from 175-200 with no improvement.

I might have isolated the problem to the left cylinder. It feels much weaker and less cadence in its note at idle. The exhaust gases also feel cooler. I did a test by blocking each exhaust pipe completely and the right side made the bike choke and die where as the left didn’t affect it much at all, maybe lowing idle very slightly. Upon switching ignition boxes/coils, the problem persisted and got the same results of the exhaust blocking test.

If this is an ignition problem the only part that wasn’t tested in some way are the pickups on the rotor.

 

[Oldfartaussie]

Bike used to stumble and backfire so I removed the bs38s and fitted vm34 round slide carbs and it ran great except it stumbles at 4000rpm but pulls strongly from 5000rpm. Removed points ignition and installed boyer bransden micro unit and it ran great except it still stumbled around 4000rpm but otherwise excellent. Replaced the C type cam chain with the E type, adjusted cam chain and set tappets to .06 &.03 and now it idles slowly around 1000rpm, pulls poorly low down and the stumble around 4000rpm is worse but still goes great from 5000rpm. I haven't touched the carbs so the cam chain adjustment and tappets settings must have made it worse .?

 

[Jan_P]

OK not read through but thinking out load
Carbs is serviced and replaced I have never almost in 35 years had carburetor problems to speak of
Ignitions is serviced and replaced that I have had massive problems with
Is compression as it should be ?
In ninskrillz machine the problem is on the left side regardless switching ignition wires
I dont remember doing it on the bike but on a car one should be able to stop it via stopping exhausts with a rag or as some jokers used to do a potato or apple plug at the exhaust end not heard if for a while though.
Leaking intake or exhaust ???

 

[gggGary]

Raise the needles a notch. See what that does.

 

[gggGary]

Bike used to stumble and backfire so I removed the bs38s and fitted vm34 round slide carbs and it ran great except it stumbles at 4000rpm but pulls strongly from 5000rpm. Removed points ignition and installed boyer bransden micro unit and it ran great except it still stumbled around 4000rpm but otherwise excellent. Replaced the C type cam chain with the E type, adjusted cam chain and set tappets to .06 &.03 and now it idles slowly around 1000rpm, pulls poorly low down and the stumble around 4000rpm is worse but still goes great from 5000rpm. I haven't touched the carbs so the cam chain adjustment and tappets settings must have made it worse .?

Raise the needles one notch see what that does.

 

[Jan_P]

Raise the needles one notch see what that does.

Wort trying and is not so difficult to do ..But if it is one side only questions remains.
The last few days I have thought about the jetting so the needle step increases fueling in the midrange.
So this sounds as a good idea
The main jet is for the full open
Has been posted her before but ... about so can help

In that line

http://www.iwt.com.au/mikunicarb.htm

 

[ninskrillz]

OK not read through but thinking out load
Carbs is serviced and replaced I have never almost in 35 years had carburetor problems to speak of
Ignitions is serviced and replaced that I have had massive problems with
Is compression as it should be ?
In ninskrillz machine the problem is on the left side regardless switching ignition wires
I dont remember doing it on the bike but on a car one should be able to stop it via stopping exhausts with a rag or as some jokers used to do a potato or apple plug at the exhaust end not heard if for a while though.
Leaking intake or exhaust ???

Yeah I thought it was suspect that if the right side is plugged it will choke out and stop running but the left didn’t.

 

[Oldfartaussie]

Raise the needles a notch. See what that does.

Pulled the plugs and both were black/sooty so I dropped the needles a notch- went 1 groove up. Haven't ridden it yet but also backed off cam chain tensioner a touch then reset tappets, both exhaust were out to .08 thou since setting just the other day to .06 so I mustn't have tightened them correctly. See how it goes tomorrow.

 

[Jan_P]

Pulled the plugs and both were black/sooty so I dropped the needles a notch- went 1 groove up. Haven't ridden it yet but also backed off cam chain tensioner a touch then reset tappets, both exhaust were out to .08 thou since setting just the other day to .06 so I mustn't have tightened them correctly. See how it goes tomorrow.

Please report .If Plugs get less black . And throttle response accelerating from middle rev. .This is exactly what I am Planning to do
Check the idle setting + circuit
Move the clip one step leaner
Leaving the main jet at 135 which can be to large ..but I take it step vise
Since they overlap a bit Leaning needle and jet can sum up getting it to lean Dont want that

 

[Oldfartaussie]

Bike ran much better after dropping the needle 1 notch, stumble has gone, just a bit sluggish up to about 5000rpm, above that it pulls strongly. Pulled the plugs and just a touch of soot on the tips but the electrodes are on the light side of tan.

 

[ninskrillz]

I noticed a strange occurrence that might possibly be affecting my spark, but could just be a normal.

I took the right spark plug out to redo the compression test (was 180 on both cylinders) and had the wire hanging about a half an inch from the head. When I was kicking the bike over to perform the compression test the wires were arcing to the head from where the wire meets the cap.

Is this a normal thing to happen if the spark plug is not connected and the cap is close enough to a ground? Could there be an issue with my wires/caps? They’re brand new.

 

[gggGary]

Is this a normal thing to happen if the spark plug is not connected and the cap is close enough to a ground?

yup, why you always have grounded sparkplugs in both wires when kicking over an engine with the iggy on. Um why WAS the ignition on? ;^)

 

[ninskrillz]

yup, why you always have grounded sparkplugs in both wires when kicking over an engine with the iggy on. Um why WAS the ignition on? ;^)

With the powerdynamo it’s always on unless the coils are grounded - much like a dirt bike with a momentary kill switch