GPZ500 D1 More woes...(Borderline unusable)

[alex965]

Following on from my previous wall of text, on the mechanics recommendation I ordered and fitted a new r/h ignition coil to the bike and for a day or so it was running fine again. The previous bogging down on heavy throttle and the 'kangaroo hopping' effect had disappeared.

Fast forward a day and a new, similar problem has now developed. When cold, although the bike starts quite readily, it will bog down and stall easily. Pulling away is a challenge and it will intermittently just lose power and bog down completely for no apparent reason. The choke has little effect in helping this when the bike is stone cold. Issues with power loss continue seemingly at random even when warm, but it is almost guaranteed to lose power if I try to accelerate heavily.

The exhaust is now producing a different sound, sort of deeper and gruntier, which doesn't sound particularly healthy.

Also, it now loves to violently backfire which, although hilarious when it scared the sh1t out of a carpark of people the other night, is getting a bit embarrassing. I am really at a loss now, I have no idea what is causing this and would greatly appreciate any advice or input.

To recap, this is what has been done to the bike so far:
.Compression test done by mechanic, both cylinders have good compression and mechanic has said overall the engine is in good order.

.New spark plugs.

.Mechanic has cleaned and balanced both carbs.

.New r/h ignition coil fitted by me on mechanic's advice.

Also, one more thing, when the mechanic handed my bike back to me, he had forgotten to reattach the air filters to the carbs, I only noticed after riding about 15 miles with the air filters off It didn't occur to me a professional mechanic would forget something like that, I reattached them as soon as I noticed but is it possible this is contributing to the present problem?

Thanks all.
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Passed A2 licence 19th Dec '14.

[UncleFester]

[alex965]

It did sort of raise some alarm bells when I discovered the air filters dangling loose. But tbf to him, when I took the bike in, it wouldn't start- the starter motor would spin the engine but it would just backfire repeatedly.
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Passed A2 licence 19th Dec '14.

[stinkwheel]

Couple of things to check

One is the main fuse holder on the top of the starter solenoid. Pull it off and check for signs of corrosion around the terminals that attach to the main fuse. This has corroded to oblivion on all three of the kawasaki 500s I've owned.

Is it running on both cylinders? Sounds like it's running on one (down on power, low, loud exhaust note, possible smell of fuel from exhaust) and only firing on the other occasionally (BANG!). Put a drop of oil on each header pipe and start the engine. See if one of them is remaining cold/cool (oil fails to burn off).

Also have a good look in the fuel tank with a torch, see if you can see any water in the bottom. Crack open the carb drain screw and catch the fuel that runs out. Look for water droplets. Another member on here had terrible problems with water contaminated fuel (due to a fault with the tank rather than the fuel itself). Engines don't run well on water.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Snod Blatter]

If you've messed with the coils and it ran well again for a short while then you're probably on the right track. Maybe a plug cap is faulty/broken? Did you tighten it onto the HT lead properly/enough? Are all the connections to and from the coil clean?
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1994 CB250, 1984 CBX250RS-E, 1989 K100RS, 1995 TRX850, 2016 Z250SL

[TheManWithThe...]

Similar to the above suggestion, my er5 suffered a similar issue of suddenly dropping to one cylinder and having power surges that was fixed by replacing the HT lead on the offending cylinder when my mechanic noticed it was arcing and not delivering the current to the spark plug properly.

The carbs were also balanced at the same time, so note it may have been one or the other, but it may be worth looking at the HT leads as it should be fairly cheap just for a punt on the chance of it solving the problem.
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MBK Nitro 50, Sold. Kawasaki ER-5, Honda ST1100
"Anyone can jump a motorcycle! The trouble begins when you try to land it..."

[alex965]

Many thanks for all the suggestions. As yet, I can't see any signs of water contamination in the fuel.

The HT lead was replaced along with the ignition coil and although it gave some improvement, that seemed to disappear quickly.

I did have the new coil off again and took some fine sandpaper to both the parts of the coil that attach to the frame, and the frame itself where it attaches to the coil. It wasn't too bad in the first place but I got it down to bare metal against bare metal in the end. That, again, seemed to improve the bike a little for a day, now it's gone back to running like crap again.

I don't know if this is a relevant clue, but ever since this problem developed, the choke has very little effect on the rpm at all. When I started up the bike, the choke would keep the rpm around 3-4k, now I have to have the choke on, and give the bike light throttle to get it started and warmed up.

I've picked my brain, and remembered, when the mechanic had a look at the bike, he did state that it seemed to have a tendancy to only fire on one cylinder, and that it is the r/h cylinder that was dropping off- hence why I replaced ignition coil. He said he also found a lot of crap in the r/h carb before he cleaned it out and balanced the carbs.

Stinkwheel, thanks in particular. I'm going to check the fuse box today and see what I can find.

I am really at a loss. The bike is my daily form of transport and I really don't want to have to take it to a mechanic again because, in my experience, it's usually these vague problems that end up racking hours and hours of labour fees for a part that is probably available for £10 on fleabay
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Passed A2 licence 19th Dec '14.

[UncleFester]

Are you sure there isn't a seal away between the carb on that side and the body of the block? Or one of the carb rubbers with a small split in it?

If the choke is having little to no effect that would suggest you have an air leak somewhere.
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2017 Z1000SX

[alex965]

[alex965]

Have just double checked air filters, one had come loose, they've both been sorted now and the seals are properly on.

Started the bike up and left it to idle for a minute or so, l/h header pipe was scolding hot, r/h header pipe was lukewarm. So it's definitely still got issues with the r/h cylinder.

Took it out for a spin and after getting the air filters properly air tight it is a big improvement. No bogging down, no loss of power, no evident back firing. I think it is intermittently running on one cylinder low down the rev range but as soon as I open it up, it happily buzzes up to 80-90mph and beyond without any hesitation.

That may have also had something to do with my half hearted squirting of gt85 into some electrical connections that looked filthy in what I think is the fuse box above the solenoid? (was inside the l/h side fairing as you are sitting on the bike). I think it might be worth going through the connections there thoroughly and getting them pristine.
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Passed A2 licence 19th Dec '14.

[UncleFester]

If it's only warm then you might have a duff plug / fouled lead / poor connection so that's where i'd start.

Have you pulled the plug on that side to see what condition it is in?

Are you sure the carb on that side isn't suffering at light throttle openings? Are you sure your mechanic balanced them properly ......
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2017 Z1000SX