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'98 SZR 660 4SU won't start


Langkjaer
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My son and I, are in the process of  repairing an older Yamaha SZR 660.

Last season it ran fine, right up to a point where it would not start. It was set aside, but now we're looking at it, to fix the issue.

We found that the bike, was fitted with an unoriginal electric fuel pump, and some wiring/relay for this. This pump was deemed faulty, as it could not produce pressure.

We ordered a new fuel pump, which is an vacuum operated one, like the original one. To this also a set of new fuel lines, and a new fuel cock.

After the fitment for these parts, a new spark plug, removal of wiring for the electric fuel pump, and some repairing of other damaged electrical wires. The bike will still not start.

It cranks just fine, and if we spray some start spray, into the carburetors. We can then from time to time, get it to run very shortly.

Where do we go from here? All help is appriciated.

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Sounds like you're still not getting fuel. 

Have you checked or cleaned the carbs?

Is there a way to prime the system, there's sometimes a third position on the fuel tap for this

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  • 6 months later...
On 6/25/2021 at 2:19 PM, Langkjaer said:

My son and I, are in the process of  repairing an older Yamaha SZR 660.

Last season it ran fine, right up to a point where it would not start. It was set aside, but now we're looking at it, to fix the issue.

We found that the bike, was fitted with an unoriginal electric fuel pump, and some wiring/relay for this. This pump was deemed faulty, as it could not produce pressure.

We ordered a new fuel pump, which is an vacuum operated one, like the original one. To this also a set of new fuel lines, and a new fuel cock.

After the fitment for these parts, a new spark plug, removal of wiring for the electric fuel pump, and some repairing of other damaged electrical wires. The bike will still not start.

It cranks just fine, and if we spray some start spray, into the carburetors. We can then from time to time, get it to run very shortly.

Where do we go from here? All help is appriciated.

hello,

have just bought one in November 21 and hope to help.

Your electrical circuit seem oK if you getit  to run a few short times. You have fuel flow to the carb with the vacuum pump I understand.

So my advice is to dismantle the carb and clean it. They... sell gaskets and seals.

But I have yet to discover the weird carb device details.

bon courage à vous.

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on the electrical side,

the darter and ignition are subject to a set of switches  operated by : prop stand, clutch lever, Neutral. some Diodes are included (2 +1) in the circuit. The switches can be bypassed if you have the scheme and if you are prepared to work the related wiring(see: colours of wires)   or connectors.

Now the fuel pump will  need enough crankshaft turns  to pump fuel up to the carbs .Its is operated by the successive pressure pulses in the inlet tract. So need a strong battery or the help of a car battery although there is not much space to connect to the usual m/c battery lugs.

Cheers.

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