Stalls following some maintenance

[fatjames]

Good morning all,

Following on from my mechanical fun on the weekend I seem to have developed an issue keeping the bike running. First, let me give you some background as to what work I've done.

Work done - I snapped one of the exhaust studs going into the rear elbow. This is yet to be fixed and is only being held one with one of the bolts. There were no gaskets in there, these have been replaced with copper o ring style gaskets.
I've wrapped the exhaust, although this was a few weeks ago and hasn't been an issue.
I changed the oil (10/40) and filter (HiFlo Filtro)
I changed the fuel and air filter.
I checked and adjusted the valve clearances.
And I replaced the spark plugs (and gapped them correctly)

Symptoms - I was riding for about 10 mins, had a chance to get upto about 40, stopped for some lights and as I pulled off the bike spluttered a bit, followed by a loud back fire and then the bike stalled. It started on the button straight away after. This happened a few times, but progressed to happen mid ride.
This happened again after coming down from high speeds on a motorway.
This morning it seemed even worse, the bike was giving me the impression I could save the stall with revs but it just spluttered, dropped to about 5mph and I couldn't bring the revs back up, this time the back fire was so loud I though the engine had blown up! Again, the bike was happy to start again on the button.

Conclusion - I'm hoping its due to air getting into the exhaust at the elbow joint and all can be fixed once my new irwin set arrives?

Does anyone have any ideas? Prior to this, the bike was running fine, except the loud ticking (thought it was the valves)

I've posted this on viragotechforum too, but that site is not quite as busy as here

Thanks all, and sorry for the long post.
FJ

[Eddie Hitler]

Chucking it out there as it has happened to me, exactly the same symptoms but turned out to be a dodgy ignition barrel. Theres a metal plate and 2 screws, it somehow wasn't making contact and the bike stuttered/backfired like mad.

Replaced and worked perfectly. May not be your problem but it had my head scratching for a while, worth a look. Bike was a FZR600.

[fatjames]

Thanks, I'll have a look.

[.....]

Are you sure there were no exhaust gaskets already in there? It can be very hard to tell sometimes but if you carefully pick at them with something like a small screwdriver you can see that they are actually there after all.

[fatjames]

[DrDonnyBrago]

The old gaskets are probably so caked in old crap that they are impossible to see. I was adamant that mine had no gaskets, they had just got caked in white powdery stuff and blended in with the rest of the head. If (and they almost certainly are) they are still in there then the new gaskets probably wont seal as well. If you are going to be disturbing a lot of hard dusty shite in that area, block up your exhaust ports with some clean tissue to stop bits going in to the engine.

If you have a weak seal and only one stud on one of the downpipes then the leak could throw out the fuelling, you should be able to feel leaking exhaust gases or shut the door and turn off the lights in the garage. Light a cigarette and use a torch to see if the smoke is being blown away by the leaks.

Also check that you haven't knocked one of the carb/throttle body rubbers loose and that the airbox is seated properly. Worth checking that the air filter is in properly too.

TBH I'd put off most of that until the exhaust stud had been sorted properly as it may solve it.

[fatjames]

[daemonoid]

Checked there's no air getting in the carb? The symptoms are very similar to my fiat when I left it at a dodgy mechanic who failed to screw the carb back on properly.

Big air gap between the carb and the top of the engine, lost the throttle adjust bolt too. Exactly the same issues as you've had, but also had low power when cold.
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@thomasgarrard | www.straitjkt.com | www.racingseven.com

[mysterious_rider]

Hm my zzr has the worst seal to the head. EVA. Runs alright.... I'd be more inclined to double check the tappets were adjusted correctly.

Good luck with her mate.

[fatjames]

[mysterious_rider]

Out of interest what fuel filter did you use? Are you using the same one that was on there or a different one?

[fatjames]

[mysterious_rider]

Hm. Well I don't know if you added any tubing (on my gs, I added some tubing to make taking the tank off easier, and added a fuel filter, a small car one) and It caused weird running like what you said. Also when the tank got near reserve it would refuse to run without constant throttle.

Just something else to eliminate. Might be putting stress on the fuel system if it's not fed by a pump.

[fatjames]

It's a good point, the more I can eliminate the better.

Thanks

[fatjames]

My conclusion on this was the exhaust. I was really hoping that once that was fixed, everything would be ok again. So I spent most of yesterday extracting the broken stud, replacing the gaskets (there were a some in there under the ones I put in!) and re fitting the exhaust.
This did not fix the issue. The bike is still bogging down and following a loud backfire, stalling.

There is a good spark. No kinks or breaks in the fuel lines, breather cables etc. Loads of fuel. Good battery. etc etc

And ideas?

Thanks
Fatjames

[DrDonnyBrago]

Lol, knew the old gaskets would still be there .

My guess is "still" that the carb/throttle body rubbers have been knocked loose or that the airbox isn't fitted properly.

How confident are you that you did the valve clearances properly?

[fatjames]

[.....]

Did you set them with a stone cold engine on the compression stroke?

[fatjames]

[fatjames]

Just a quick question RE: the valves. The Haynes manual shows 3 markings, 1. T (tdc) 2. F 3. Mark
For the front cylinder, should it be on the mark, or on F?
I assumed F but now have doubts.
FJ

[neil.]

Should be on T. F is when the spark happens, just before TDC.
____________________
CBT February 2008 | A2 June 2008 | Yamaha YBR125 (written off) | Honda CBF125 (current)

[fatjames]

[Johnser]

all good suggestions.

quick and painless test - change the spark plugs back to the old ones. its unusual for a plug to be duff out of the box but it'll at least rule it out.

does sound like an air/fuel issue to me. maybe changing the fuel filter dislodged some crap in the lines which is blocking a carb jet.

or maybe the air filter caused a carb rubber to not seal/split?

[iooi]

Not pulled the HT leads or damaged them have you ?
Spark plug caps OK?
____________________
Just because my bike was A DIVVY, does not mean i am......

[fatjames]