Topic: '78 750 Sporadic power loss

[WaleFab]

Heya, I've exhausted all my resources, including reading similar posts here, consulting my dad (40+yrs mechanic), forums, friends, my own knowledge, and D all the above...

Issue is the following.

Bike runs great then randomly will run like a bag, everyonce and a while. some days its completely fine, like it was this morning when i first went out and rode to a cafe for breakfast. Left the cafe and it started doing it again.

These are the specs, items and alterations I've tried to fix the issue...

OEM coils and wires and lead plugs, I've snipped 1/2" off the end of the wires to expose new wires
confirmed the spark plug gap
Routed the blue and yellow and B/W wires to the opposite side of the downtube under the tank.
I run the NEWTRONICS Optic ignition setup.
I have the Danmoto 180 dash, and disconnected the Tach pickup wires (which were connected to the blue ign wire) and taped them off completely... BUT today when it was running like a bag, I noticed the RPM gauge on the 180 was still getting a signal, not everytime it was running #$%*ty, but some, which i find extremely weird considering theres no direct signal going to the gauge... When i did disconnect the 180 for the Tach wired I wasn't getting any issue, up until now..
The carbs seem in good shape and are clean.
The controls are GSXR that go with the front end, and the wires start and stop switch is in good order.

Truly bashing my head against the wall on this one because the bike DOES run really really good, but just randomly will spurt and grovel and pop...

please help me haha

Truly throw out any ideas that you can think of !!
Im looking into picking up some 3ohm coils and wires in the meantime. but considering the bike runs top notch 90% of the time, I'm sure its not the issue...

thanks in advance.

[flybox1]

carb model?
Jetting? mixture screw setting? bowl fuel level confirmed?
intake?
exhaust?
is there a specific throttle position where this happens more frequently?
does it occur more often with a specific air temp or ride duration?

[WaleFab]

Factory carbs. Jetting done proper, no flat spots. Doesn't matter where in the throttle range.
UNI pods and full 4-1 stubbied.
The bike had the exact same setup minus the ignition (was Boyer brandson) as last year and ran fine. Bike was hit in sept and I rebuilt it using the newtronics, since the Boyer was destroyed.

Doesn't seem to matter when or how long it's been ridden, sometimes does it a few min into riding , sometimes after an hour, then it'll go for days with no problems then acts up randomly again...

The fact that it runs top notch at best the. Randomly like crap leads me to more electrical than a carb issue...

[flybox1]

Air, Fuel, Spark. Its gotta be one, so start ruling out stuff.
We cant rule out your carbs as you didnt provide enough details
Make sure all harness connectors are free of corrosion and tight.
Anyway, if you think your bike is back to where it should be, and the only thing different is the ignition, well, there's your place to start.

[harisuluv]

Hi Walefab.  There are plenty of people who will help you, but you're going to have to give us more information.

"Jetting done proper" is basically something that is completely uninformative.  If you want to talk about jets--give us sizes, needle position.

Seems to me that you are saying that they only thing that was changed was the ignition module.  So basically it was running fine, then you changed the igntion module and now it doesn't run fine.

I would suspect the ignition.

However, that's assuming that everything you told us is accurate, and you are more or less dismissing the carbs as a problem, although they can't be ruled out IMO. 

[WaleFab]

Thanks for the replies guys!!
I can't recall the jetting sizes off top of my head, but got them from 6sigma on eBay. Custom jetting kit catering to elevation and mods. I HIGHLY suggest them if anyone's looking to take the headache out of s dewing with jetting when running pods/exhaust mods.
All in all, I ended up pulling the carbs apart this afternoon and did a once over on it, there was a slight bit of debris found under carb 2 pilot but that was about it. Regardless I did a relative overhaul on everything, synced carbs, adjusted air/fuel, dialed carbs in @2000rpm all bang on the same (fluid filled gauges are unreal for syncing, no needle bounce), put it together and took it out for a boot.

2hours on the bike and it's running better than it was when it was running fine this morning, the real test will be over the course of the week if I end up having any issues again with it as it is a sporadic issue to begin with...

Thanks again for the insight! Hoping to do a build thread on my bike (assuming recovering my hard drive works out and I get my pics back :-/ )

[flybox1]

Glad it works better, but you still haven't provided any of the information we asked for 
Why did you adjust the air/fuel screws?  Did your plug color warrant the change?
Vacuum sync should be done at the LOWEST comfortable rpm.  ~1200rpm for my bike.

[WaleFab]

Truly Not trying to be difficult haha and I know you're just trying to help but I can confirm there are no jetting issue. I ran the bike like this (pods , exhaust and jets) last year prior to the accident and had zero issues all season with the bike.

Bike ran top notch all night last night on my 2 hour boot... Today I went to take it out and didn't make it down the alley before it started acting up again, popping and backfiring and misfiring for a few seconds then it was fine, then it'd do it again... SO FRUSTRATING. Safe to say I can rule out the carbs though considering the breakdown and cleaning I did and that its fine 90% of the time...

Should I pick up new coils or contact NEWTRONICS ya think?

Maybe I'll throw my points plate back on in hopes to eliminate the ignition... Then if it still acts up I'll look into coils perhaps. The coil wires seem in good shape and doesn't seem to effect the run it when I jiggle them around or anything...

These intermittent issues are the worst

[flybox1]

Throw in a points plate and see if the problem persists
just you hope it goes away, because if we have go go back to carbs....

[calj737]

What is the single indicator of an electrical problem (to me) is that you taped off the BLUE wire (tach sensing wire) and still got an intermittent signal. That would suggest to me, that despite your unwillingness to share/provide carb data, the ignition is shorting out. Given that it's intermittent, I think it quite simple to track your wires under the tank, from under the points cover, and start doing continuity tests and resistance tests. Its also possible that the "damage that wrecked the Boyer" created some internal damage on the advancer cam (unbeknownst to you).

As for it being carbs, well, that may well be true. But since you can't/dont/won't provide those answers, lets chase our electrical tails a while...

[WaleFab]

hahaha, I appreciate the input.
Ive rectified that my yellow wire had a relatively poor crimp on the connection to the coil, and 2/3 cyl were bagging out. I redid it and the issue seemed to be rectified for a while, and mostly is like 98%! the issue came forth mildly on saturday, after I had breakfast. started the bike after eating (rode to the brunch spot with no issues) and was instantly running on 2 cyl. shut it off, and tried again 2 times, and it was fine. did it again today same scenario (ran fine first ride out to coffee shop then on 2 cyl after starting it after, shut off, started again fine on all 4)
I have to pull one of my forks this week to have the seal checked since its got less than 800km on brand new seals (GSXR oem) and its leaking and ill pull my carbs at the same time to give you my jetting numbers since you guys are die hard horny for them hahahahaha jk.

when i had the tank off sourcing the wiring issues it started with 2/3 bagging out and literally pushed on the ignition wires (blue and yellow) and picked up on all 4, then took my finger off and back to 2/3... so investigated and ya the yellow wire had a #$%*ty crimp on it, if i recall my buddy was crimping that for me at the time and it wasnt done properly (M crimped, it was just "smooshed" crimped).

Calj737, the Boyer setup doesnt use the advance place from the OEM points setup, advance curve is programmed to the module. The shaft that is threaded into the crank was bent, pickups smashed and plate broken (bike went down on its right side). I refurbished the original advance plate as the NEWTRONICS setup required it, it was in great free shape once i was done with it.
I havent had any electric tach signal since fixing the yellow connection, likely wouldnt hurt to scope out the blue one aswell and redo its crimping connection as im sure buddy buggered that one up aswell.

side note, where is the best place on here to do a build blog of my bike?

thanks

[calj737]

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