Burnt Plugs

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rwhc80
750 GT
Posts: 174
Joined: Sat May 16, 2009 7:19 am
Location: Melbourne Australia

Burnt Plugs

Post by rwhc80 »

G,day Guys, could do with some suggestions here for a Bosch squarecase engine issue.

The bike started destroying plugs some time ago on the front cylinder, every 50 kms or so. originally thought it was fouling the plug but now realise it is burning them out, as the recently re-chromed header pipe is now badly blued for 300 mm from the head. rear pipe is still perfect.

So far remedies have been, 40mm carbs off and cleaned twice, ( 145 Mains 65 Idle ) timing checked, heads off, new exhaust guides, seals ect, re-shimmed, and vavles lapped in. Thought when we took the heads off the burnt exhaust valve was the problem, compression was 70 psi in front 145 rear. Now realise it was a sympton not the cause.

any ideas ?? cheers Rick
I have desmo disease, I just hope they never find a cure !!!

MartinMille BANNED
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Post by MartinMille BANNED »

Rick

Before I read the entire post I was going to reply when the blue pipe was mentioned , you are running way to lean hence the extra heat turning the header blue , the rest of your post states you have burned a valve , valves only burn out due to a lean mixture or incorrect valve adjustment (shims) to tight

Who did the shimming ?

Who tuned the carbs for you?
Have a read of this , it will put you on the right spot with tuning the carbs or get them done by a pro

http://www.bevelheaven.com/~BB/phpBB2/v ... c.php?t=10

Cheers Marty

rwhc80
750 GT
Posts: 174
Joined: Sat May 16, 2009 7:19 am
Location: Melbourne Australia

Post by rwhc80 »

Thanks Marty,

I think its a given the front cylinder is lean, but trying to start with most obvious reason for that ? I guess a process of elimination, and given the extent of knowledge out there on these old bikes, surely this has happened to a few others. As for the shims, we did them so I know their ok, and besides, the problem existed before the heads were removed and re-shimmed.
Would the tip be to start by looking at the carbs again ??

Cheers
Rick
I have desmo disease, I just hope they never find a cure !!!

MartinMille BANNED
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Post by MartinMille BANNED »

The only thing left then is the carbs , are you running any valve saver additive with your fuel at all. ? try adding some upper cylinder lube to help cool the valves

Cheers Marty

hedton
Mariana
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Joined: Mon May 14, 2007 1:47 am

Post by hedton »

Martin Mille / SSD wrote:The only thing left then is the carbs , are you running any valve saver additive with your fuel at all. ? try adding some upper cylinder lube to help cool the valves

Cheers Marty
My friend rode a 350 Ducati with petrol from Shell called V-power.
His Duke was wrecked 2 times before hi noticed that the rubber on the valve in the carb had melted. Hope that this hasn't happened to you.

Best regards

hedton

BEVEL DAVE
Diana
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Joined: Sat Jun 13, 2009 7:22 pm
Location: SYDNEY, AUSTRALIA

Post by BEVEL DAVE »

You said timing was chaecked???

What was actually checked & was the advance checked for the front cyl. in the process???
Retarded timing can do the same things & generate a lot of heat. The initial timing may be fine but the fr. cyl. may not be advancing.

Dave

wdietz186
Cagiva Alazzura
Posts: 703
Joined: Sun Sep 10, 2006 5:40 pm

Post by wdietz186 »

Rick, In your carb cleaning did you happen to check the float level? If it is too low it can cause the mixture to go lean at crusing speeds and will seem to go flat when accelerating hard. Also inspect the screen under the inlet fitting and make sure the petcocks flow ok.Another thought,Did the exhaust seat require much cutting to get a good seat?It is possible the seat is warping when hot causing the valve to burn.There isn't much meat around the seat on the port floor and they can loosen/warp when they get too hot.And you are sure you don't have any vacuum leaks right?

rwhc80
750 GT
Posts: 174
Joined: Sat May 16, 2009 7:19 am
Location: Melbourne Australia

Post by rwhc80 »

Thanks Guys,
In order, Marty-, Not using valve saver as yet.
Hedton-, Just premium fuel, normally BP. 95 octane. we have the same issue with Shell Optimax not recommended for bikes.
Bevel Dave - Checked Advance, no problem there.
Wdietz186- Float Levels have been checked and are OK, seats had a bit of cutting due to new guides, but I beleive they should be OK, ( Will keep in mind though) Vacuum leaks worth checking, but new o-rings went into inlet spacers ( alloy type ) Fuel flow I have not checked, damn good advice that's next on the list.

Excellent feedback, thanks all, I will let you know how it goes.
Cheers Rick.
I have desmo disease, I just hope they never find a cure !!!

BEVEL DAVE
Diana
Posts: 62
Joined: Sat Jun 13, 2009 7:22 pm
Location: SYDNEY, AUSTRALIA

Post by BEVEL DAVE »

What needle & needle jet???
Where is the needle position???

Dave.

paulh
Cucciolo - the Lil Pup
Posts: 11
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Location: Central Queensland, Australia

Post by paulh »

Has the engine been detonating at all? Has it pinged, rattled or knocked under load, especially in top gear roll ons? I ask these questions because the plug condition that you describe can be the result of a moderate to severe detonation problem. Have you used a stobe light on your engine to check the timing on each cylinder? Is your engine modified e.g. high compression pistons, modified combustion chambers?
This is just another angle to investigate and if nothing else it is food for thought.

bobnorton
860 GT / GTS
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Location: bromley kent

Post by bobnorton »

Check your tank cap is venting, this can cause weak mixture and blue pipes, simple to fix.

rwhc80
750 GT
Posts: 174
Joined: Sat May 16, 2009 7:19 am
Location: Melbourne Australia

Post by rwhc80 »

Thanks again guys

In order, Bevel Dave- Needle is a K4, set on centre slot, 145 jet
Paulh - No evidence of detonation that we could find, engine pulls like a train with no pinging until plug goes again,then simply runs on 1 cylinder bike is almost standard except for slight port job and yes we used a strobe to check timing advance.
Bobnorton- haven't checked fuel flow yet as wdietz186 suggested, but I hope to do tonight. I will check cap venting at the same time thanks.

Will advise on outcome
Cheers
Rick
I have desmo disease, I just hope they never find a cure !!!

rwhc80
750 GT
Posts: 174
Joined: Sat May 16, 2009 7:19 am
Location: Melbourne Australia

Post by rwhc80 »

OK, we may finally be getting some where,

Checked the fuel flow from the SS taps tonight and it appeared a little slow. I decided to do a comparison with my Darmah, and ran this test : The Darmah filled a 200 mls jar in 20 seconds.
The tap to rear cyclinder on the SS put 60mls in the jar in 20 seconds and the tap to the front cylinder put approx 90 mls in the jar.

Not sure what the flow rate should be, but I assume it indicates some sort of problem ? I guess at this stage it's not a definite until I get the taps removed and check them out.

again will keep you all informed,
Cheers Rick
I have desmo disease, I just hope they never find a cure !!!

MartinMille BANNED
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Post by MartinMille BANNED »

Rick
With that flow rate one would think that the rear cylinder would be running hot, less fuel - Lean running

Back to basics

Timing might be fine but an ignition box could be failing under load changing your advance curve giving you a leaner burn

Are you sure that you are not sucking AIR as this is the usual culprit for burning valves

Marty

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Craig in France
Cagiva Gran Canyon
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Location: Montpellier, France

Post by Craig in France »

rwhc80 wrote: I decided to do a comparison with my Darmah ...
Hi Rick,

If you've also got a Dramah, can you not just temporarily put the front carb from the Dramah on to the SS and see if the problem persists?

That way, you'd at least know whether it was the carb that was faulty - or something else.

P.s Or swap the ignition box to test that ...?

Ciao

Craig

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