Inconsistent combustion question 72 GT380

[JFISHSOLEVIBE]

Howdy guys! Back again with another question regarding my 72 380.

Last I checked in it was in final stages of rebuild, with me returning to riding from an accident.

Well at this point the bike is 100% assembled, including the Newtronic Electro ignition.

Now, the bike starts up easily, but what I am experiencing is inconsistency on the left side and center cylinders firing. I know that the carbs are clean and the only "performance mod" on the bike is pods on the carbs. My "bad" cylinders plugs are showing slight firing, slight fuel fouling, clearly not getting a complete burn.

I know this is a pretty broad question, but What should I be lookin for? The coils were replaced with new stock coils. Plugs are new, electronic ignition, stock exhaust.

Is this likely a fuel issue or a spark issue? Could a timing issue result in misfiring on the 2 and 3 cylinders? Number 1 cylinder is definitely firing strong.

As always thank you guys for being such a helpful group!

John

[Craig380]

I'd first check the battery is fully charged and you're getting at least 13V at idle - I seem to remember that Newtronics ignitions need to see at least 12V when running, otherwise they get temperamental.

Check the carb sync very carefully, make sure all three slides are lifting exactly in sync, and to the same height. If one slide is 'leading' the others, that causes all sorts of fun. Luckily, this is easier with pods and the 3 cable set-up on the earlier carbs.

If these basics check out OK, then I would see how she behaves on a gentle ride, keeping her below half throttle and 5,000 rpm. If it smooths out above quarter throttle with all cylinders working in harmony, it points to a blockage or lean condition on the pilot circuits, so you can try tweaking the pilot screws. Have you altered the jetting / carb set-up for the pods?

[JFISHSOLEVIBE]

Thank you kindly for the reply.

I hadn't even thought of the battery. That is very possible, considering its a new battery perhaps my initial charge didnt push it up to a full 13v. I will make sure I get that squared away first.

The jetting wasn't altered, so it's all stock minus the pod filters. I will double check the sync on the carbs and Ill report my results!



Thanks!!
John

[JFISHSOLEVIBE]

I neglected to add this to my original question... Could bad spark plug leads or resister caps cause such intermittent firing? Just wnna make sure I'm covering the bases . Thanks again!

[GT750Battleship]

Hi,yes bad plug caps,dud leads,bad connections in headlight & elsewhere,sorry it could be anything,but sounds electrical..had a misfire on my 750..only solved by checking with a volt meter & renewing male/female connections in the headlight shell.. !!

Cheers,
GT750Battleship.

[JFISHSOLEVIBE]

Update! Rechecked all my electrical, fixed a known short on the battery leads and combustion is good!!

Curiously, the bike seems to run fairly well on just about any advance setting on the ignition. I've leaned it toward the retarded side to be safe.

Follow up question to that being said, I have notice that as the bike heats up, tbe revs at idle climb substantially. After riding for a big idle is rising up to 4-5k. My carb throtttles are all synced, and set -3.5 turns on out idle screws, and -1.75 turns out on fuel circuit.

Could the ignition be causing the sped up idle? Seems unusual but I can't figure out what else it might be. Floats are all set properly, throttle cables have slack, new boots on the engine side of carb so I shouldn't have any air leaks. Can't figure this one out!

Thanks guys!

[JFISHSOLEVIBE]

Okay so idle seems to be fine! Played around with cable routing and throttle stop screws and have it set up pretty well for idle.

Next and seemingly last hurdle is my low rev power. Now I rode this bike for a few years prior to the teardown and I recall that it never had a alot of guts in the lower revs, but I'm seeing a pretty solid flat spot between 1000-3000rpm. 3500-5500 is ovviously the sweet spot, but my wuestion is: is what I'm experience normal performance? Seems particularly sluggish, this is apparent when stopping on an incline and having to really juice the bike to get away from a stop. I backed out my pilot screws a bit to try to feed the pilot circuit some extra fuel but I didn't see a huge difference. I am running the pod filters, so is it possible that its not getting enough fuel whilst feedin from the pilot jet?