Rough Idle & Charging Issue 1991 GSF 400 M

[Craig806]

Before I start, thank you all, I’ve been reading this forum for awhile now and the info and people in here have been VERY helpful in all the work ive done on the bike thus far. Sorry for the super long explanation here. This is my first bike and I love it but it’s a whole bag of problems. I rode it for about 300 miles in total before it started to idle rough and stall at idle then break down (dead battery due to charging issue) … I let it sit in my parking lot for three weeks before I had it towed to a guy who works on older bikes out of his garage. Two and half months later I finally (don’t even get me started on that ) got it back and I’m a few hundred dollars poorer and still have the same problems.  The mechanic admittedly said he is not the best at the electrical. I’ll try not to go into my many gripes about the mechanic. I approached the charging and rough idle / stalling issues from a few angles but I’ve exhausted almost all the money I can afford to put into this. Below I describe what I’ve done for both the issues and where I think I need to look next. Please let me know if I’m missing anything or if you have any better suggestions or if I did anything dumb. I’m not a mechanic and I’ve never worked on a motorcycle,  but I can follow instructions, like tinkering, and don’t mind getting my hands dirty.

UNDERCHARGING: When I got the bike back from the mechanic his latest diagnosis was that my charging system was indeed fine but there was an electrical short somewhere causing the undercharging.  That weekend I bought a multi meter performed a quick test with the bike off and confirmed there was a short drawing power within the connection to the fuse box. I pulled the pieces, thoroughly cleaned them and put in new fuses and the short was gone.  Afterwards a quick check of the voltage showed the bike was charging properly at about 13.5v. I was very proud of myself although the rough idle remained.  After a few days of working on the rough idle (described below), the undercharging issue reared its ugly head again . Next I ran though the electrosport charging system test (thanks stormi). First the wiring between the reg/rec and the battery failed. So I wired it directly to the battery and retested. It showed fine. I got to the point where I tested the stator and… due to the rough idle I couldn’t get a steady AC voltage to compare the wires to confirm. It was fluctuating close to where it should be (and my mechanic supposedly tested it very thoroughly and removed it to inspect) so I decided that was good for now and moved on. Then the reg/rec failed the diode test. I suppose I will buy a new mosfet type reg/rec and wire direct to the battery and avoid the factory harness per this link I found in this forum (http://www.triumphrat.net/speed-triple-forum/104504-charging-system-diagnostics-rectifier-regulator-upgrade.html) (Thanks tomx611) Before buy the new reg/rec, is there some other issue I should look into first or should I look at this from another angle? My battery is new.

ROUGH IDLE / STALLING AT IDLE: In neutral or when I’m using the clutch at a red light the rpms will fluctuate and gradually decrease to a stall if I don’t rev the engine. The bike runs fine in all gears at all speeds and only has this problem when idling.  First I pulled the K&N air filter, cleaned it and replaced it. No change. So I took out the filter and sea foamed the intakes. No change. I noticed some light surface rust in the tank so I set to remove the rust. I removed and drained the tank, filled it with nuts and bolts shook it around for about half an hour and found there was much more then only light rust. Afterwards I soaked it in vinegar for 4 days, rinsed with water and baking soda, then rinsed with fresh gas, allowed it to dry, filled with new gas and reinstalled. I cleaned the fuel strainer on the petcock, the in line filter appeared to be clean and it was new so I blew it out and put it back in. With everything re-assembled I took it for a ride, no change. Added sea foam to the gas tank and took it for another ride, no change. The bottom two pipes on the exhaust headers were almost pancake flat due to the prior owner so I thought that couldn’t be helping anything. I located an almost unused stock exhaust locally on craigslist for a steal at $80 (what luck huh?). I removed the old dented system (lighter aftermarket headers with a Yoshimura can) and put the stock one on with fresh gaskets and bolts and it still idles rough. I then tried adjusting the idle screw to let it idle higher at 2,000 – 2,500 and… it helps a little but it still idles rough and comes to a stall. My next move I suppose will be replacing the spark plugs or cleaning the carbs.  Although, The mechanic supposedly inspected the plugs and carbs already.  Should I do the plugs or carbs first? Anything simple left to look into? Any pointers for the carb cleaning? I’m dreading that.

[Maniac]

I'd get that regulator issue fixed before I started throwing more money at it, it's possible that will fix both problems.

[canyonbreeze]

Adjusting the valves worked wonders for my cold idle smoothness when I first got the bike.

[tomx611]

Hi Craig

Did you check the 4 exhaust from engine, they all got temperature? if one is cold, seems got problem of carb for the unstatable of RPM.

if 4 are hot, then please check any leakage from the air box to the engine intake boots.

intake boots between engine o ring,
intake boots and carb body
airbox boots and carb connection

my bike tried carb balance cap loss, and the idle unstatable and stop.
also may be check the carb cover, i found that it's not smooth between the cover and carb body. ( also you can check there's any damage on the diaphragms) you can use some sand paper and add some air vacuum grease.

those points are easy to check. if those are ok, then you should break apart your carb or open the engine cover to fix it.
Good luck

[banditv]

there is nothing wrong wit the factory style reg/rect, just completely rewire it from stator leads to the battery when you replace it.
you ned to check the stator output voltage with the reg/rect disconnected and your multimeter set on the ac scale. i made the mistake of using the dc scale and completely misdiagnosed my charging probs.
65/70 odd volts ac is what you are looking for between each phase.

get the carbs balanced by someone who knows what they are doing and if need be, replace the diaphrams, cause after 20 years they are prob as still as a board and wont be responding as they should be.
i just replaced the diaphrams in my 250 and it made such a difference. its a new bike, so responsive and revs so clean its funny.
if you are game enough to pull the carbs off, check and reset the idle mixture screws to 2 or 2 1/4 turns out from lightly seated.

[Craig806]

Thanks for the suggestions

Maniac -I went ahead and ordered the new reg/rec. I would like to think the new reg/rec would solve both problems but the bike still had a rough idle when the charging system was testing ok the week before.

Canyon Breeze- If I get to the point where I need to clean the carbs, I’ll probably make it a weekend project by adjusting the valves and changing the plugs too. Who knows when they were last checked or adjusted.

Tomx611- I will definitely fire it up tonight to check the pipes to see if any are cold. This may seem like a silly question, but how do I check those points for potential leaks?

Banditv- New diaphragms will be on the to-do list if im pulling the carbs.

Few additional questions:
-How do I check for leaks in the places Tomx611 suggested?
-If I do try to clean the carbs, aside from the cleaning materials, are their any special tools or replacement parts, gaskets, sealants, lubricants, etc that I will need to purchase? My fiancé would kill me if I had disassembled carbs sitting on the kitchen table while waiting for a special part or tool in the mail.
-If I try to adjust the valves - same question as above – anything special I need on hand?

[canyonbreeze]

For the carbs it would be good to have bowl gaskets, float valves and the several o-rings.

For the valves just make sure to have very thin feeler gauges, 0.005 and 0.007.

My idle mixtures like to be a 3-3/4 to 4 turns out.  At 2 to 3 turns the acceleration sucks.

[Craig806]

Success on the charging issue!  The New mosfet reg/rec came in the mail today. I cut the stator output wires, fitted the new connector and wired the new reg/rec direct to the battery with a 30amp fuse. The charging voltage is GREAT. It’s right at 14.5v at 5k rpm.  The new one is a bit larger but I fitted it in the original location at an angle. The bike is drivable again. If only I wasn't getting a hurricane this weekend...

The rough idle diminished but it’s still there. I adjusted the idle speed to 2k rpms. It can hold idle steady there for the most part. If I try to adjust it even a hair lower the rpms fluctuate then drop and the bike stalls. Do you think it will cause any damage to ride it like this?

I noticed that the top of the airbok does not sit flush to the bottom, the plastic on the top or bottom is slightly warped so it doesn't create a good seal.  Could this contribute to the idle problem? I wouldnt think so.

I checked the pipes per Tomx611’s suggestion and they are all hot – how do I check for those possible leaks he mentioned?

[tomx611]

Hi Craig

Seems your charging system is fine. i also connect a second wire from the battery negative terminal to the starter, i found the original one was a little burn.

About the leak check, i never tried. i just watch in some forum to spray some carb cleaner to the connect points, if any leakage, the RPM will change. CARB CLEANER is flammable, i think you should very very CARE on it.

fixed the leak point if still unstatable IDLE, seems should be change the o rings, clean the jets.
as your bike is 10 yr old, seems you need prepare float boat gaskets and needle valves.



Link for carb cleaner leak check
http://www.gixxer.com/forums/showthread.php?t=621

very useful link on carb, most similar as bandit 400 carbs, i also changed all the old O rings of my carbs.
http://www.gixxer.com/forums/showthread.php?t=159718



hope these can help you

[canyonbreeze]

My airbox top doesn't sit flush, has never seemed to be a problem.  I put some duct tape around the joint to seal it.

2k idle is a little high but shouldn't do any damage.  I think recommended is 1300~1500.  I read somewhere that lower than that and the oil pump volume is too low.  Mine will idle at ~500 RPM when cold, it wouldn't do that before I adjusted the valves.  Goes up to ~1500 when warmed up.  I use the throttle when cold to keep it up.