Bizarr Issue 350F long read please help!

veloracermike

Coast to Coast
So a couple weeks back I took my 350F out and had an weird issue with what seemed like the bike was running out of gas. It had been sitting for about 4 days. It started fine and ran great, I had to run up to the north part of town so I took the freeway. About 8 miles into a 10 mile trip the bike began to miss at anything past 3/8 throttle. I got off the freeway and made the rest of the trip on surface streets nursing it along. I arrived and was at the place for about 20min. Came out and the bike fired right up. Rode it about two blocks revving it with full throttle and it was fine. Came to a stop light where it idled perfectly. I revved to to leave the light and it just fell on it's face. I couldn't get it past 1/4 throttle. I was around the corner from the shop I use so I nursed to the shop. We tinkered with it for about an hour and at that point I just left it at the shop (while I was there we put in line and took out the inline filter/checked the breather/checked the flow out of the tank all were good). Three days later he called and told me that A) my floats were adjusted to the wrong amount (too little flow) and that one of my exhaust valves was nearly closed (I really don't undersand how). Now the last time I had rode the bike (4 days earlier all was fine). He said that he took the bike out for several hard runs and it was perfect. I was away on business so I picked it up yesterday and this is what happened.

The shop is about 4 mi from the freeway. The bike started from dead cold easily and idled like a clock. I let it warm up and instantly noticed that the bike was running better than ever. Perfect throttle response in all rpm ranges and just nice smooth delivery. It's the best it's ran since I got it...just perfect. I get on the freeway and just nail it through the gears and get it up to 70 and hold it there for the next 8 mi. I come up on some traffic and roll off the throttle and then back on, when I get back the bike kinda hiccups then clears out for about a mile then it starts to sputter again and right back to where it was when it ended up in the shop. I call him and tells me to let it cool off over night and try riding it again this time with the gas cap open. So this morning I do that. Bike fires right up, let it warm up, roll out of the neighborhood and again just brilliant. Bike is like a swiss watch. Get out on the highway and for about 5 miles the bike is just awesome then it starts to sputter and runs like crap again so I limp it home and in the garage it sits. I'm calling my mechanic in the morning but I'd like to get some feedback before I do...any thoughts?
 
How old are the coils? Maybe they are over heating and then failing until they cool down again.
 
Not sure how old they are, I just went out and pulled the plugs and they are pretty nicely brown and fairly even across the cylinders.
 
I had a similar problem with my CB350F -- but it was overheating. Problem was some crud partially blocking a main jet. Bike ran great for about the same distance as yours, but then started losing power, etc. I could nurse it along. Did some of the same stuff you did (checked valves, changed filters -- it seemed like a fuel flow issue, and in the end, I guess it was), but finally opened up the carbs and cleaned out the jets and I've been fine ever since. I run on a stock airbox on this bike, so I just pull the float bowls off without taking the carbs off to access everything in the float bowl.

Does it seem like it's overheating? Sounds like the same symptoms, including letting cool off and having it run great again.
 
I'll pm you re the 400

When it was in the shop he went through the carbs. If its a clogged jet he lied.


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Assuming this turns out to be coils. You guys recommend Dyna's or stock. If stock any suggestions on where to get them. I did a google search and could only find used ones


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I'm not familiar with the coil setup for the 350f but on the twin the cheap coils from mikesxs do the job nicely
 
Dime City maybe? I don't know if 750 coils would work, they would probably be easier to find though. Personally, I would go with Dyna coils and be done with it.
 
They carry the Dyna's. Just don't want to drop 155 on coils to find out that isn't it.

How does one test a coil for an over heating issue?


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I've never had a problem with stock coils, and I've never had coils overheat. Not saying it might not be it, or that it doesn't happen... but still, check your jets yourself. Free and easy to do, just to rule it out, before dropping whatever you're going to drop on coils. If it is coils, I have a set of stock CB350F coils that are in perfect order (took them off a low mile bike, rebuilt it completely with a CB400F engine and dyna coils) that I will sell for cheap.

I should add: my '73 CB350F is mostly stock (airbox included), but with CB400F exhaust and peg set up, and clubmans.
 
if getting the dyna make sure that they are the same OHMs as stock or get the right resistor packs for them
 
Okay if this is an ignition or coil issue shouldn't I be seeing some black and wet plugs? All four of my plugs are near perfect in color with number 1 slightly lean.
 
Well kids I think I found the issue. It was the coils but not overheating or a coil going bad. I tried a few things this morning and did some runs with no change in symptoms. I decided just for the hell of it I'd check all the connections. The bike has a custom wiring harness so it's pretty straight forward. I unplugged and plugged everything ignition related and took it out for several high speed runs. Zero sputtering. Then I took it out for about 45min for around town riding and the bike runs just great. So it was coil related in the end. Really appreciate all the help, the coil direction was a big help.
 
SONICJK said:
Don't you love it when it's that simple?

Yep, the weather here is finally something cooler than hell and I just want to ride!!! It's running great and I am a happy happy camper. Thanks again all!
 
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