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Old 05-10-2002, 21:29   #1 (permalink)
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frown Please Help - Suzuki GSXR750 Missing on 1 cyl

please, Please, PLEASE Help !

I just recently bought a 1991 Suzuki GSXR750 (Water Cooled), and have just had it for over 1 week now.

Anyway, A couple of days ago, the thing started missing on the way home from work, and by the time I got home (10 minutes after it started missing), One of the cylinders stopped firing completely.

The Bike still idles, but unfortunately with only 3 cyls, it just doesnt have any torque. (wont go anywhere)

O.K. For a bit of background on the bike, (From what I can tell).
Its using stock Mikuni Carbs (4x - I think they are SU's, not sure though). These carbs have been rejetted, a K&N Air Filter has been fitted, and a staintune Carbon Fibre Muffler has also been fitted.
As for Rejetting of the carbs, I dont think that it was tuned properly, as the spark plugs were replaced the day that I picked up the Bike (I saw them do this), and only after 400Km, they are as black as black.

Anyway, First thing I checked was ignition, by pulling each plug off, to see if the engine died. Engine died on all 3 cylinders except cyl 4, so I am assuiming that the problem is with Cyl 4.
I changed all the spark plugs with new ones (Just in case), and tried the test again.
Same symptoms as above.
Took off the Ignition lead for cyl 4, and checked it with a new plug, outside of the engine, and could not see any spark.
Tried grounding the lead to the chassis, and there was a very weak intermittant spark.
I then went to replace the ignition lead (With motorbikes, they use solid copper Ignition leads, with suppressed boots), So I bought myself some Ignition wire, and a new NGK Boot, and made myself a new lead.
The cylinder still doesnt want to fire, and with the new plug on the lead, outside of the engine, there is still no spark. BUT grounding the ignition wire to the chassis, there definitely is a stronger spark, and it is no longer intermittant.

The Suzuki has 2 coil packs, and they operate in a very similar arrangement to the EF/AU Triple Coil pack, in the way that 2 opposing cyls share the one coil pack. I am assuming that the Coil pack is OK, as Cyl 1 (The cyl that shares the same coil pack with Cyl 4), is running perfectly.

With all the above F!@#$ing around, the engine isnt running any better than before (still only 3 cyls firing, and cyl 4 does not even backfire, or intermittantly fire), so I am now assuming that maybe its a fuel problem ?????

Does anyone have ANY idea's ?????
Or alternatively does anyone know of any motorcyle mechanics in Sydney, or know of any motorcyle forums that could help, or know where I can purchase a gun with a bullet that I can put through my head ?????

Please help, as I am absolutely desperate !
Cheers
Matti
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Old 05-11-2002, 00:33   #2 (permalink)
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Sometimes with bike leads if you pull them off the wrong way it can stuff them up completely. I reckon you should replace that dodgy lead with a newie and see what happens then.

Also, the spark plug boot is easy to pull off the lead, same with the coil end of the lead. Check whether it is pushed in all the way. If the coil was dodgy then youd drop 2 cyls and it would really run liek shit.

This may seem like a dumb question, but did you put the leads back on the right way?? Everything is so close together it is easy to do...

Is the plug from cyl 4 wet with fuel when you pull it out? Did you break the insulator when you took it out or put it in? Is the plug cross threaded?

I cant see it being fuel somehow...:oo1:
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Old 05-11-2002, 02:58   #3 (permalink)
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The coil pack could still be buggered - I've heard of Commodores losing one ignition output from one of the the dual packs.
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Old 05-11-2002, 05:48   #4 (permalink)
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Many years ago, when i was riding bikes, i had occasional spark problems. One thing that helped at times was to pull the ignition lead a small amount from the sparkplug,creating a small gap. This in fact causes a better spark in the plug. Worth a try to see if the faulty cylinder fires.
Don't know the principle behind it, but it also worked on lawnmowers.

Jon
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Old 05-12-2002, 01:57   #5 (permalink)
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Honestly, thankyou guys for all your help !
I understand this is not a Ford Related problem, but I really appreciate you giving this one a go ! :s5

Quote:
Originally posted by Road Warrior

Also, the spark plug boot is easy to pull off the lead, same with the coil end of the lead. Check whether it is pushed in all the way. If the coil was dodgy then youd drop 2 cyls and it would really run liek shit.
This may seem like a dumb question, but did you put the leads back on the right way??
Yeah, I think you are right with this one, I even tried swapping the leads on that one Coil pack just in case, but still the exact same problem.

Quote:
Is the plug from cyl 4 wet with fuel when you pull it out? Did you break the insulator when you took it out or put it in? Is the plug cross threaded?
Funnily enuf, the spark plug was not wet.
I Changed all the plugs, as the Original ones were Black and sooty (Carbs running very rich), and after many times of cranking and idling, the plug on the miss firing cyl looks brand new ??

Quote:
I cant see it being fuel somehow...:oo1:
I would have to agree with you, but I think I have tried almost everything in terms of Ignition, so this is the only other thing that I think could go wrong ???

Quote:
The coil pack could still be buggered - I've heard of Commodores losing one ignition output from one of the the dual packs.
- This is a very good point, I havent tried swapping the coil packs yet, to see if maybe one is faulty, but I will give this a go next ! (Fingers crossed)

Quote:
pull the ignition lead a small amount from the sparkplug,creating a small gap. This in fact causes a better spark in the plug. Worth a try to see if the faulty cylinder fires.
Gave this one a go as well, Still the same problem, but you can definitely here the sparks coming from the boot to either the rocker cover, or plug ! (Wasnt doing this before I replaced the Ignition lead and Boot !)

Hmmmmm - Im am now wondering if it is a Fuel problem ?
I have some very small fuel filters fitted, and they seem fine, I even tried blowing air through them just to make sure that they were still flowing - They seem fine.
Is it possible/common that the Needles/Venturi can get clogged with crap ????

A friend said that I should try some carb cleaner, and rev the Sh!t out of it, to try and dislodge any possible crap ????
I might also give this a go tommorow !

Again, thankyou for all your help !
Im a little peeved that I had this trouble sooo soon, as I only got to ride the bike for 400 odd Kays, (6 Days total). And it has been off the road almost longer than it has been on !

Cheers
Matti
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Old 05-12-2002, 04:52   #6 (permalink)
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Aha!! So is plug #4 bone dry, even after cranking the motor over? It should be wet with fuel. If is is dry, then that number 4 mikuni might have some crap in it, especially if you ran the fuel right down. For heavens sake, DONT start messing with the Mikunis unless you REALLY know what your doing...get a bike shop to check it out, preferably a different one with a dyno, as it looks like the one you went to might have botched it.

Also, you said that you had little fuel filters fitted ijn the fuel lines? Take them out and see what happens. Most bikes have a brass gauze filter inside the fuel tank, so you dont need those funny little see thru inline filters. They are probably restricting the fuel flow.
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Old 05-12-2002, 05:06   #7 (permalink)
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I had similar probe years ago on a Honda.The needle droped out of the carrier/piston so it wouldn't richen up the mixture as the piston [in carb similar to S,U]opened.Thats if its a constant velocity type carb.Didn't do the rings much good, I guess it got alittle hot..
Possibly easier to try another carb?
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Old 05-14-2002, 02:26   #8 (permalink)
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Quote:
Originally posted by Road Warrior
For heavens sake, DONT start messing with the Mikunis unless you REALLY know what your doing...get a bike shop to check it out, preferably a different one with a dyno, as it looks like the one you went to might have botched it.
Yeah, I know exactly what you mean,
At least with the Falcon, all I need to do is short the STI input, and the computer gives me some codes, so as I have something to go by, Playing with carbs, Ummmmmmm, Errrrrrrrrrr, This stuff is a little before my time.

I finally found a Suzuki Forum (If only I could find one as good as FF ! then my life would be complete), and another guy had exactly the same problem, at exactly the same time (Give or take a few hours), on exactly the same piston, on exactly the same bike !!!! Freaky stuuf, as he tried pretty much everything that I have tried, and found out that the Coil was stuffed !)

I sent him a message, and he said that his plugs were dry, which confused him as well, (He put it down to the amount of air the Cyl was pumping around, causing the plug to be dry ??????) and he tried the Coils as a last resort to pulling out the carbs.

Im gonna try and swap the coils, to see if that changes the symptoms, and if not, then I guess she be going off to get a Dyno Tune :crazy1:
Hopefully I can afford it ?!?!?!?
[/B][/QUOTE]

Cheers and Thanx for all your help Again !!!!
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