Idle's great, w/throttle, pops and sputters...

Hello,
I just recently restored my '79 KZ400 from frame up, except for engine (had only 5k miles). The bike ran great before and after. I ran out of gas the other night (I thought I did)...and it was sputtering and popping like crazy. Put gas in, 3.9 gal 87 octane, and it still presents the same problem and left me stranded. I am at sea level. The carbs were thoroughly cleaned before the rebuild and just last night. I though maybe something got stuck in a jet. This was not the case. All three jets were clear, so I reassembled and the bike, itis still causing me problems. It will idle great but with any amount of fuel it will pop and hesitate with it in gear or not. I re-timed it, cleaned the point and still same problem. Idle screws are set at stock + 1/2. (It ran great at this setting). I did bench time the carbs but have not on the bike. I did notice while I was timing it the light would be steady then miss a few and the engine would hesitate at that moment. I am suspecting the my stock coil is bad. I checked all my wiring and it is good. This morning now, it wont start at all. Both plugs do get wet with fuel and both sides get hot while running and it has spark, but looks weak.

I do stress the it was perfectly after the rebuild and was running very strong.
I am out of ideas, any help?

Tank vent clear?

Are you using a see-through paper fuel filter?

I have a see through brass type filter on it now after the fact. I emptied the float bowls first to make sure the fuel would run through. Fuel does pass through when trying to start it. As far as the tank vent, I am not sure. I did try to start it with the cap off though.

Still no luck on a fix. I am most likely going to put a new coil on it since the spark was weak and intermittent.

Anyone have any ideas for a single fire dual coil? I have looked at the Dyna ones.

I'm not sure if it's still available, but Z1 enterprises had a nice 4-ohm coil made by Emgo for about $40. It's very similar to the stock points coils.

Thanks for the info. I decided to just order a 7thgeardesigns.com electronic ignition system and be done with points. I am hoping this fixes my issue. If not I wanted to upgrade it anyways.

Would you think that I got bad gas? How do you check?

ShaCvet wrote: Would you think that I got bad gas? How do you check?

Drain the tank and the bowls... refill with a gal of KNOWN good fuel, set the petcock to prime, wait a min to let the bowls fill and fire away. Take her for a ride and see if your sputtering goes away...

I just went through similar iterations.

My petcock screen was non-existent. Had dirty carbs as a result. Rectified that - to then realize I had a bad coil. My symptoms were - when bike gets got, cycl 2/3 die. Bike runs rough cant hold idle and dies. Your issue will be either air, fuel, or spark. I am leaning towards fuel and spark. Start with fuel --- dump your tank wash it was gas make sure you have good flow through your fuel filter when petcock is on---

I am not a model specific knowledge person but your bike is close to the age of mine, and there are things you need to look into when replacing a coil - like... do you have points? electronic... will you need different wires? suppression caps? ... and how deep do you want to go. I opted to replace everything then I could guarantee all the parts would work together with the right ohms and spark delivery. Call Z1 if you are looking for coils and they will direct you to your options.

Thanks All.

Earlier this week I decided to order an electronic ignition from 7thgeardesigns.com. I am hoping this fixes the issue. Fuel flow is normal and I have cleaned the carbs throughout, twice. I will be replacing the fuel, sure my nissan will run on it :laugh:

Will keep posted.