engine misses at lower rpm's

[Anonymous]

I've been riding my '81 gs850 every day to work for the past 2 years (22 miles each way) and have had similar stalling and missing problems. I've had good success in fixing them. Here's what I did:
1. replaced the 20-year-old coils with new ones and new wires. Dyna coils are a good choice. 2. rebuilt my airbox so that it's scrupulously clean. Look closely and you might find (as I did) that there is rust coming down from the breather tube at the top. Easy to miss! Little rust particles love to stick in the idle jets. 3. Replaced the ignition switch, which was causing high resistance in the system (and a lot of heat, I might add!). This seemed to do the trick. Sometimes I get a miss at idle in one of the carbs. I just unscrew the idle mixture screw and give it a blast from the compressor. Works every time! Just for your reference, at sea level, my idle screws are out 2 1/2 turns. I have played with that adjustment extensively, and that is the best for my bike. I guess what I'm trying to say is that your problem lies in the carbs. Let us know what you find.

[Anonymous]

engine misses

i'm going out now to look at the idle circuit. where the airbox vent hose goes into the top of the engine, i noticed the wire clamp was loose and the hose wasn't tight around the tube. could this be part of the problem? i'll fix it anyway.

[Anonymous]

engine misses

the o-ring on the needle valve (not to be confused with the needle jet) was worn to about nothing on 2 carbs. you would think that i would of had overflow problems, but i never did. could this effect my problem? the carbs look pretty clean so far but i need to spray carb cleaner to check jets/holes. i had the super fine rust (very small amount) in bowls. carbs were spotless 2 weeks ago.

[Anonymous]

The super fine rust in the float bowls is leaking past your in-line fuel filter (you have one?). The rust from the airbox is only visible inside the upper portion of the airbox itself, and then only if you take the rubber side seals off. Since you weren't flooding and your plugs aren't fouled, I suspect a combination of dirty idle jets and poor spark caused by low voltage to the coils. I say this because I have had similar problems on other bikes of the same age. As a fair warning, my other bikes are British!

[Anonymous]

engine misses

i did install an inline fuel filter about a month ago and i always suspect it as far as starving the carbs of fuel. it's a briggs & stratton filter (large & clear) rated to 80 h.p., to work best it should sit vertically but due to space issues it sits more horizontally. the gas hose leaving it always looks full of fuel though. do you recommend taking the airbox apart and cleaning then containing the rust with grease or something ?

[lartross]

I was following your thread because I recently installed new needles and plugs [in whatever it is they plug into], readjusted my floats [they were set pretty high-like at 15mm instead of 23]and, now my bike has an intermittent that sounds like your symptoms. Runs really strong, with beautiful, white plug deposit, then, starts acting as if a cylinder is cutting out. I have new Dyna coils and recently had a mechanic check my carbs and fix a starting problem I couldn't find. He had set the floats hi...maybe that's what it took to make it run, but, it wasn't nearly as strong as it is now, when it's running right. Last night, coming home at midnight, it ran crappy...this morning, I looked at the plugs...it ran like a dream half way to work...then started cutting out. Hope you find the solution and that it works for me. If I stumble onto it, I'll let y'all know. Larry

[KEITH KRAUSE]

Hi. The loose clamp on your crankcase breather hose is not a problem. If your bike is similar to my '79 1000, you have some folded up mesh screen
inside your crankcase breather cavity. This screen can rust and you may get some rust seeping into the airbox. I've never seen anything beyond a "staining" enter the airbox, certainly nothing that would clog the jets,
but I suppose it could get worse than I've seen. If you have rust, I would take a better look at your tank. That's most likely where the rust is coming from. I'm not familiar with the design of your float needle valves, but a worn o-ring would cause a rich mixture, not a lean problem.
I know this problem is frustrating for you and time consuming, but you need to check or re-check several things. Some suggestions have been made, but you don't always respond if you have actually checked out the suggestion. We keep "assuming" something was checked and we start trying something else. Earlier you said the carbs were clean, but now they have rust. This makes it hard to troubleshoot. I'm sure the rust was a surprise to you.
For a problem that feels like lower rpm fuel starvation, lean sparkplugs, is intermittent, and considering the rust, this is what I would check.
Remember, I don't have a perfect understanding of your style carbs.
Inspect the tank. If any rust, Kreem coat it or do similar to remove/stop the rust.
Clean the gas cap vent.
Clean/check the petcock operation. Is ANY fuel entering the vacuum line?
(This would indicate a damaged diaphragm and it would not always fully open the petcock.)
Remove the fuel filter, at least temporarily, until the problem is solved.
Take the carbs apart and clean everything, blow out the passages, pay close attention to the pilot circuit and the floatbowl venting.
Check all parts in the carbs, especially the moving parts, floats/needle valves/ throttle valves/pistons and diaphragms.
Check the intake boots/manifolds/o-rings, if OK, grease the o-rings with hi-temp axle grease and tighten the clamps good, install the vent tube(s) and CORRECT size fuel line.
Synch' the carbs.
If all this is done correctly, I can't think of anything else that would give you a lean condition as you describe. I would still double-check the electrical connections too.
Good luck, keep us up on this! (I love a good mystery.)

[Anonymous]

engine misses

as of last night the problem may be fixed! this problem would have been easier to deal with if the tramsmission didn't go the first week or so that i owned the bike. three exaust studs broke, and the premuffler broke. this was the first time i ever did a tranny rebuild and it took a few steady weeks. i did fix all that stuff though. ok, back to this problem. some things that i tried that didn't correct the problem are: flushed gas tank with gas (only very minor surface rust visible); disassembled & cleaned gas cap venting; disassembled & cleaned the petcock-i never had fuel in the vacume line which was good; disassembled & cleaned carbs (with the exception(mistake) of the choke plungers & the needle valve (also called the fuel valve); left floats at about 23.4mm's; disassembled & cleaned cam chain tensioner (why not); adjusted fuel metering screws to between 3 & 3 1/2 turns out (the spark plug electrodes were white & bike coughed thru carbs occasionally)-the UNI air filter in the stock airbox may have leaned the minture somewhat; installed a fuel filter (briggs & stratton rated up to 80 hp) along with new fuel & vacume hoses; cleaned electrical grounds, connections at coil & signal generator; metered charging system which was ok; replaced spark plug boots (2 of the old ones bad electrically); i sprayed carb cleaner and propane gas (at different times) around intake system revealing nothing; i even ran the bike down the street with a funnel full of gas in place of the gas tank; with all that stuff done, the bike still had intermittent missing/stumbling moments at lower rpm's. so, with help from "Kieth" and others within this thread i went after the carbs & intake again yesterday. i rode for about 6 hours today with no missing/stumbling problem. although i need a few more rides to be certain, i feel pretty good about it. last night after doing the stuff i'll list next, the bike ran stronger than ever before for me. i nailed it a couple times in 1st gear and the front wheel came off the ground, without clutching it. here is what i did yesterday that seems to have the gs and me happy again: cleaned out the intake track, up to the intake valve, on the engine with carb cleaner and a rag (it was sticky with residue-why not), replaced the flattened out o-rings on the rubber intake manifolds; wrapped tin, cut to size, around the rubber intake manifold where the clamps fasten to let the clamps have more bite on the rubber; totally disassembled carbs & fully blew out the idle/pilot circuit passages within the carb using carb cleaner (along with all other passages); replaced the o-rings on the needle valves (also called fuel valves), 2 of which were almost completly gone; replaced the rubber plugs which fit into the pilot jets tube; i set the floats to as close to 22.4mm's as possible (raising bowl fuel level); left the fuel metering screws at 3 & 3 1/2 turns out (plugs look much better); i rearranged the fuel filter to let gravity be more effective. and there you have it. the way it feels now i think this did the trick. a couple more rides will prove it. what i need to do now is throw a timing light on it, readjust the fuel metering screws, sync the carbs (tool delivered yesterday), then do a final adjust on the fuel metering screws. i'll post conclusions after more test riding. i would recommend doing this stuff anyway just for the performance benefit that a 20 something year old bike deserves. thanks again Kieth & everyone else involved. p.s.: if you look at Kieth's first post, most of the stuff was recommended early on.

[KEITH KRAUSE]

Hi. I sure hope you have it running good, you've put a lot of effort into it!
Just for my information, you said " I replaced the rubber plugs that fit into the pilot jets tube". What exactly do you mean? Can you describe them better?
Like I said before, I don't have much experience with your carbs, but this made me curious.

[Anonymous]

engine misses

hey Keith. when you pull the bowl off the bottom of the carb, you have the pilot jet which sits somewhat recessed into the tube which it screws into. the end of that tube sits in the bowls gas. at that end of the tube there is a cylinder shaped rubber plug about 4mm's long that blocks the end of the tube, preventing gas to enter. sounds crazy, i know. so where does the pilot get its gas? well, when the main jet is removed you see a hole connecting the main jets tube to the pilots tube, therefore it appears that all the pilot jet fuel enters via the main jet first. maybe this controls splashing & uneven gas feed to the pilot as the main jet sits deeper into the gas supply. this plug was discontinued later on. i imagine "bike bandit" would show it. i have web-tv, not a computer, and am unable to "attach" pictures, etc.

[KEITH KRAUSE]

Hi. Thanks for the info. I was aware that the pilot is fed through the main. I just did'nt understand the rubber plug thing.
Again, hope you fixed it!

[lartross]

I finally figured mine out! My plug wire cores were burned away on 3 of the 4 wires where they plugged into the coils. Seems they had enough carbon trail left to work, unloaded. On the road... ran like *@%^$*@%^$*@%^$*@%^$. Hope this helps y'all! Larry

[Anonymous]

engine misses

a couple more rides since my last post and it's still running without misses/stumbling. thanks again all. i'll keep posting any changes.

[Anonymous]

engine misses

well, several hundred miles more & no problems. i would say at this point that the bike is fixed. thanks again to all involved.

[KEITH KRAUSE]

Glad to hear the bikes running good. See ya.