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Spark plug problem

Old 06-28-2005, 05:49 AM
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Spark plug problem

Hi guys,

I really need help on this one. I have a '98 Firestorm, and a few problems that come with it. Maybe they are related!
1- Can't do more than about 65 miles with a tank.
2- The plug of the back cylinder gets soot up with a black powdery dirt. That often and needs to be cleaned or the cylinder stops working. Spark plugs are new!
3- People who follow me on the road say the bike smells fuel.
4- Sometimes when I start the engine, and put the bike in first gear (with the stand up) the engine shuts down.

The bike does'nt burn oil, I checked the air filter, looks good. Idle is stable at 1000 rpm. When spark plug clean, power is stable there is no loss.

What do you think is my problem ????
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Old 06-28-2005, 06:42 AM
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Re: Spark plug problem

Sounds too me like you have a carb problem and are running way too rich on the back cylinder.
I'd speculate that cylinder is getting way more gas than it can burn and as a result, you are getting low mpg, the plug eventually fouls and then you are running on one cylinder.
Does the engine pull smoothly from 1/2 throttle up through high rpms when you have a new plug in it?
Could there be an obstruction to the free flow of air to that cylinder?
An over rich condition can be too little air or too much fuel - both will result in a fuel/air mixture where all the fuel will not be burned. The unburned fuel will foul the plug and get blown out the exhaust.

I've never been into the carbs on the SH but suspect maybe a stuck float. If the float sticks up, it will result in too much gas in the float bowl and therefore too much gas through the carb and into the cylinder.

Have you dropped the bike recently? That can sometimes cause a float to stick.

Keep us posted, I'd like to know what you find.

Thanks.
Brian A


edit to add: all the above is based upon the assumption that you have a good healthy spark. If your ignition system is not working properly then you know where you have to focus your efforts.
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Old 06-28-2005, 06:56 AM
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Re: Spark plug problem

Thanks for your quick response Brian,

I have had the bike for about 3 months and never droped it. The bike doesn't have any scratch and doesn't look like it's been droped by the last owner.

It does make sense that the carb is not doing it's job properly.
Do you think a carb cleaner in the fuel or directly in the carb could solve the problem or I really need to take it out. (looks like a dirty job)


Do you think could cause the engine to shut down as soon as I engage 1st gear without releasing the clutch (like if the stand was still down) or is it a totally different problem ?
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Old 06-28-2005, 08:11 AM
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Re: Spark plug problem

Hi Quebecer, glad to see another VTR owner from Quebec here

On the other hand, sorry to hear that you have some trouble with your "TempÍte de Feu"

And yes, as Brian said, that seem to be a carb problem!

Habitually, carb cleaner in gas are crap!! IMO. You can try one of them, but that will not be my choice. Yes, I think your shut down problem can be related, even if you don't release the cluth, if you pass gear, the engine is no more running "free" and this make it forced a bit so like at idle the RPM is low, only a little bad fuel or air mixture can cause the engine to shut down. Try to give a little bit of trottle when you pass the gear with the clutch and watch if it will do this also?

What is the milleage of your VTR?
If it pass 50 000Km, do you know if the valve adjustement have been done?
Is your bike have a jet kit from the previous owner?
What's the color of the other spark plug compare to the back cylinder one?
What spark plug number you have?
Have you checked the trumpet between the carb and the cylinder, is this one is craked or vented?

And finnaly, do you know a good garage?
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Old 06-28-2005, 08:15 AM
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Re: Spark plug problem

Originally Posted by Quebecer";p=&quot View Post
I have had the bike for about 3 months
Since you haven't had the bike long do you know much about the history?
Has this problem been with you from the start?
Did the bike sit unused for any length of time?
Has it been rejetted?

You might want to pull the carbs and take a look yourself at the jet sizes and look at the needles to see how they are setup. Of course you could then clean things up while you're inside. You might just open things up and stumble on an obvious glitch....
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Old 06-28-2005, 08:24 AM
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Re: Spark plug problem

I did try to give it some trottle when passing 1st gear, no change, engine shuts down anyway.
The bike has 30 000 km on it and a valva adjustment has been done at 27 000 km as well as a complete tune up.
I don't have a clue if the previous owner installed a jet kit or not. My other spark plug looks good.
I will check the trompet tonight as well as the spark plug number even if it's the one that the Honda guy gave me. We never know.

If carb cleaners in gaz are crap, are the ones spayed directly in the carb better ??

I do know a good mechanic, the only problem is that he spends to much time on his bike on the road instead of the one in his garage !!! It can take long before I get the bike back.

The Honda mechanics are so damn expansive.

I unfortunatly don't have any history on the bike. All I know is that the previous owner rode about 1500 km in 03 and didn't really ride it 04.
This would meen that it spent a lot of time in the garage.
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Old 06-28-2005, 09:27 AM
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Re: Spark plug problem

Did you said that you ride it since three month and he never do this before?

Because if the bike don't ride in 2004 and have do only 1500Km in 03! It could sound like some cristalized gaz in the carb and the only way to get back of this it's by a complete carb clean out, and yes unfortunatelly, it will require the carb removal... sorry!

Do you know how it have been stored in winter?

Do the last check-up on previous things and we will see...
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Old 06-28-2005, 09:39 AM
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Re: Spark plug problem

I changed the spark plugs about 2 weeks after getting the bike, I thought that was the problem. I did fix it but it laster about a month and fell on one cylinder again. I took the plug out to find out it was as dirty as the ones I had replaced a month before (only in the back cylinder).

I know the bike was stored with fuel stabilizer during the winter. The previous owner had it stored at the dealer. (I guess they did the right storing procedures there)

When I bought the bike, it was it's first start since the last season, it coughed a bit for a few minutes but I rode it came back home without any problem.
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Old 06-28-2005, 09:41 AM
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Re: Spark plug problem

Yes, you can expect carb problems if the bike sat and was not ridden for 1 year. The gas will age and cause problems with the proper movement of needles/slide assembly.

Proper cleaning will require removal and, at least , partial disassembly.

Brian A

edit to add; it appears you were posting a response while I was typing the above.
If the bike was properly prepared for storage, that might lessen the chance for carb problems. But, based on my experiences, I still tend to think you have a carb problem.
Be careful if you use any of the spray type cleaners for the internals. I believe some of them can have a bad effect on the rubber seals, etc.
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Old 06-28-2005, 11:11 AM
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Re: Spark plug problem

Thanks a lot for your help guys, now I know where to concentrate.

Do you think this is something someone handy could do or I really need to bring the bike to a shop and get it done by a pro. The only carb i've played with was on my motocross : 1979 honda XL185 . Let's say that the Storm's looks a bit complicated compared to the '79 one.

Of course I do want to save money !!! I found the Shop manual on internet, all the pictures are in there.

Now, if I take it out, what do I need to do with it, take pieces apart and clean them (with carb cleaner I guess)?, change gaskets? What do I do with the needle?(do I expect it to be stuck somewhere and I only have to free it?

I kinda need a <Carbs for dummies> crash course . :
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Old 06-28-2005, 11:26 AM
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Re: Spark plug problem

I'v never opened a SH carb but assume it to be a CV carb like others I have worked on.
The bottom should come off and expose the float and float bowl. Remove the flaot bowl and clean insides thoroughly.
The top of the carb should come off and expose the top of the slide and the rubber air seal (boot).
Gently pull the slide out of the top of the carb. The jet needle will remain with the slide.
Carbs vary quite a bit when it comes to low speed (idle) circuits, but in general you'll have an idle circuit, a jet needle for for 1/4 to 3/4 throttle and then the main jet for wide open throttle.
All these circuits / components must be free of build-up and any dirt.

You should be able to remove the main jet once you have the float bowl off. You might have to remove the float to access the jet. Be careful with the float. Be sure you don't alter where it sits and how far up/down it travels once you have it reinstalled. Changing float level can change fuel/air mixture.

Anyways, once you get it all apart, clean everything well and make sure all air passages are clean and clear. Some are very small and even a little build up or debris can cause problems.

If you are careful, you can reuse the gasekts. But, it is always smart to use new ones if you can get them.

Best of luck.

Brian A
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Old 06-28-2005, 11:50 AM
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Re: Spark plug problem

Thanks a lot guys,

It's the first time I use this forum and I am impressed in the quality of the answers I can get.

You guys where very helpful.
Many thanks.
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Old 06-28-2005, 12:14 PM
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Re: Spark plug problem

If you do have it narrowed down to a gummed up carb, here's an easy "trick" to try first. I picked this up on a vintage bike list where they deal with reviving old/stored bikes all the time.

Get some Yamaha brand carb cleaner. This stuff is not dumped into the tank rather it is pored directly into the carbs via the fuel line(s).

1) remove fuel lines (go ahead and do both carbs)
2) select run switch to "off"
3) mix cleaner with FRESH gas as per directions on bottle
4) drain float bowls on each carb and close
5) using a small funnel, slowly pour mix into the lines until full
6) rock/shake bike and gently tap carbs with a block of wood or something similar
7) crank bike and roll open throttle but don't let it start (switch is still set to off, right?) to pull mix thru carb jets. Don't overheat starter! Let bike sit for a bit and let the chemicals work
8 ) drain float bowls and repeat steps 1-7
9) install new or cleaned plugs
10) replace fuel lines to tank with fresh gas
11) set switch to run
12) cross fingers
13) start

Tougher cases sometimes need an overnight sitting with the mix. Horrible carbs have been revived by removing and soaking in a bucket but it's best to rebuild those as they are usually in dire need of it.

Oh yeah, set idle speed to 11-1200rpm
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Old 06-28-2005, 01:02 PM
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You can expect a carb problem from a sitting bike but not this carb problem. This is probably caused by:

Jetting mistake
Stuck needle valve or other float problem
Sticking carb slide or bent/unclipped needle.

It can also be an ignition problem but I'd R&R and clean/inspect the carbs. When you do, write down the jet numbers and check the position of the needles.
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Old 06-28-2005, 06:33 PM
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Here's what I would do first. Seeing as how the bike ran fine for about a month after replacing the plugs, I would suspect either a weak ignition coil, or the pilot screw for the rear cylinder is adjusted just a bit too rich.

Try first swapping the coils, front to rear. Clean the plugs (carb cleaner and a rag should do for wet fouled plugs). Ride the bike till the problem repeats. If the front plug is fouled this time, the coil is toast.

After that,if the rear is still fouling, you could try twisting on the fuel screw. In is less fuel/leaner idle mixture.

One more thing I read about somewhere, and I am not 100% sure on the details, is that a faulty sidestand switch COULD cause this type of problem, as the kill function of the switch only cuts off ONE coil (though I am not sure about it).

Just keep in mind one thing when working on problems that seem a little strange. ELECTRICAL malfunctions are the most likely culprit whenever intermittent problems appear.
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Old 06-28-2005, 08:01 PM
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Another thing I thought of is that the enrichner might be hung open. I've never heard of this happening but the symptoms could match.

You can follow the cable from the choke pull to find it. Make sure it is pushing all the way in.
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Old 06-29-2005, 06:42 AM
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Re: Spark plug problem

I will check my choke cable tonight. As of the coils, BearHunter was talking about, I don't think that would be the problem. You see since the problem has been there since I got the bike. I never did more that 65 miles with a full fuel tank. There clearly is a problem with my carb. I'm not too sure doing it myself, I'm not sure I should trust my mechanical expertise. I would'nt want to make it worst. Damn Honda says it can take from 2.5 to 4 hours to do. They charge a nice 69$ CAD an hour. Ouch!!!!

As of the sidestand switch, I find the comment really interesting. I did take it off and tryied different possitions to see if it would keep cuting the engine. Positive, it did. Now, are you saying that even with the stand up, one coil could still receive the message to shut off. That would meen that my side stand switch is faulty. Is there a way to test that??
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Old 06-29-2005, 06:57 AM
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Oh, I missed the 65 miles comment before. You almost certainly have a sticking float valve or sticking or loose needle or sticking slide. You have a carb malfunction; I'm voting for a small piece of debris in the float valve.
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Old 06-29-2005, 02:09 PM
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Re: Spark plug problem

In my opinion if your not sure of your mechanical abilities I wouldn't attempt a carb re and re on your own.
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Old 06-29-2005, 05:59 PM
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Well, I think whoever wrote the thing that I read about the sidstand switch only cutting off one coil was misinformation. I tested this last night by running the engine up to 6 grand with the clutch in and in 1st gear, at a standstill. Then when I put down the sidestand the engine just cut out immediately. If only one coil was cut, then the engine would still run when given that much throttle.

You can 86 this idea.
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Old 06-29-2005, 08:18 PM
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This problem is not because the small jets are blocked.
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