Plugs

[Sean]

shoud i use a hotter spark plug than the standard?

Over the past few days my bike has been running badly, i put new plugs in lastnight (hotter than the standard plugs) and it helped some what, especially after i went to the gas pump and filled it up. My bike (this may sound stupid) runs better on the first 1/2 tank than it does on the last 1/2.

[mark]

By running badly, what do you mean? Did it start running badly all of the sudden? You could have a number of problems (electrical etc.) Need to be more specific.

I'd go back to standard plugs and look for the actual problem you are having. Don't just throw in hotter plugs. Check to make sure that all your plugs are actually firing. What color were the standard spark plugs when you pulled them? That will tell you about your mixture. As far as the gas tank issue goes, check that you're breather tube isn't clogged or twisted somehow. You could also check the flow of your petcock when the tank is down close to reserve and see if you have some kind of a problem with your petcock assembly.

Year, make and model would be helpful too.

[scotty]

By running badly, what do you mean? Did it start running badly all of the sudden? You could have a number of problems (electrical etc.) Need to be more specific.

I'd go back to standard plugs and look for the actual problem you are having. Don't just throw in hotter plugs. Check to make sure that all your plugs are actually firing. What color were the standard spark plugs when you pulled them? That will tell you about your mixture. As far as the gas tank issue goes, check that you're breather tube isn't clogged or twisted somehow. You could also check the flow of your petcock when the tank is down close to reserve and see if you have some kind of a problem with your petcock assembly.

Year, make and model would be helpful too.

Mark you seem like a very stable sort. Why not benchmark

Oh yes listen to marks advice and read the sticky at the beginning of the tech forum on how to get lots of responsces

[Sean]

Plugs

1) 1982 GS850G with 45000 miles
2) No recent engine or electrical work has been done
3) old plugs were "dusty" black (carbon fouled)
4) runs smoother with the choke slightly engaged
5) have some backfiring
6) I have the original owners manual (i'm the 3rd owner) with detailed and dated maintanance records, the original owner ran hotter plugs when the bike had less than 5000 miles on it.
7) the bike runs poorly regardless of the position of the petcock (run or res.)
8) When i first start the bike it has a very muffled sound with and the bike will die if i don't let off the throttle.
9) once out on the road, with the choke slightly engaged the bike runs like a dream, but when you diengage the choke completely it becomes sluggish in throttle response.

[scotty]

Wow, thats the way to post a question with info

[scotty]

I think you should check your plug wires and caps if you have them for starters at least
sooty plugs and running better with choke on is confusing me a bit.

[scotty]

Just an afterthought. On a newly aquired used bike, I usually run a few tanks through with a GAS TREATMENT added to the gasoline. NOT CARB CLEANER.

[Sean]

Plugs

I have ran a complete bottle of "STABIL" gas treatment, which took 4-5 tank fill ups to accomplish.

Could the filter screen in the petcok be dirty causing a fuel starvation issue?

[mark]

Other points.

Your aircleaner box needs to be sealed perfectly for your 850 to run right. Make sure you're seals on the outside of the box haven't deteriorated. Check the clamps on the carburetors to make sure they are tight. Check your air cleaner that its oiled right and clean.

Manifold boot O-Rings could be bad and causing an air leak. You can spray some water on them when the bike is running to see if air is being sucked in at that point.

You've got good spark right? Nice blue spark at each plug. I assume you haven't messed with the air screws on your carb or something. If that is the case, if the motor is in reasonably good mechanical condition, what it sounds like is that the carbs need a good cleaning. Theres a good section on the homepage on cleaning your carbs.

[LW_Icarus]

everything mark said, and- the pilot jets are likely restricted. its a small hole to begin with and if the bike sat any amount of time there is probably some blockage. mine had symptoms similar to yours until I got mine completeley clean.

don't run hotter plugs. don't run hotter plugs. don't run hotter plugs. its not a hotter spark, its simply how much of the combustion heat the plug will transfer to the head. the stock heat range should work fine.

it could be the petcock screen plugged causing it to run outta gas, but Id suspect itd die after a few moments of running hard if that was the case.

[Sean]

Plugs

One thing that i did not put in previous post (last reply got the old brain going).

After i run through the gears agressivly, let of the gas, then go back to hammer on it it does act as if it may die, then it will finally straighten out a little. as long as the choke is slightly engaged.

According to the previous owner the bike did set for a long while, almost 2 years and maybe ridden once a month. (at least in a garage and out of the weather).
Would cleaning the screen in the petcock be the first thing i need to go after before having the carbs cleaned? (doesnot make much sense to clean the carbs if the petcok screen is not for sure to be clean)

[LW_Icarus]

Id likely start in the carbs. these GSs are finicky anyway about what mixture ya feed them, and after sitting a couple years Im almost positive they'll be obstructed.

mine looked sparkly clean inside, and still the pilots were 90% blocked with deposits. no cleaning solvent I used touched it. had to run a thin wire through it.

you can pull the petcock but at that point Id get a rebuild kit or a new one and be done with it. if the screen is blocked chances are there will be junk throughout the fuel system at this point anyway. whats the inside of the tank look like?

[Sean]

Plugs

from what i can see with a flashligt there is no apparent rust.

I will probaly replace the petcock and have the carbs cleaned and re senc'ed, sense from all the replies i've gotten seems to be a deffinite thing that needs to be done.

thanks to all for the info provided.

[KEITH KRAUSE]

Just another thought...how does the bike idle? Do the rpm's rise quite a bit as the engine becomes hot? The idle should be set at around 1,000/1,100 rpm's to start this check.
As others said, please put the correct heat range plugs in there.

[DaveDanger]

I'd have thought you guys would have jumped on this already, but I'm going to wade in anyhow . If it takes some amount of choke to make it SEEM to run better, then it's too lean. regardless of what the specific cause is, it's too lean. Having to engage the choke in however small an amount is artificially richening the mixture. It's a classis symptom of lean mixture. I'm not one of those guys that reaches for a can of starting fluid (ether) at the drop of a hat, but it does come in handy for chasing intake leaks. Simply crank and run the engine, and very lightly spray the starting fluid at the typical suspect areas around the engine... airbox gaskets, intake tubes, even around the carb bodies themselves. If there's even the tiniest hole somewhere sucking air, you'll hear the rpm rise instantly when the starting fluid is drawn in. Fix the leak and continue checking till you have no more leaks.
Next, (and this did get mentioned) plug heat range has nothing whatsoever to do with combustion temperature in a cylinder head. Absolutely nothing. It has to do with the actual temperature of the electrodes in the head of the plug. They will either be more recessed in a ceramic insulator (cooler plug) or more exposed (hotter plug). If you had an engine that had a slight tendancy to foul plugs, you might go with a hotter range plug to help burn off oily deposits or carbon. Or if your engine has a tendancy to pre-ignition from some other cause (generally aggressively timed ignition in a racing engine) you might go to a cooler heat range to help keep the near-molten electrodes from acting like glow-plugs. Aside from that, I'd also agree that the factory recommendations for plug range are the best way to go.