Difficult to start GPz1100 - suggestions please

[martinz1000r]

So my Unitrak GPz is back together and looks good but it is a pig to start.

It's on carbs from my ELR (34 mm CV) replacing DTI injection which are clean and off a running bike. I look to have a reasonable spark and plenty of nice new fuel.

It will only start with the aid of easy start. It runs ok but wont tick over. If it stalls it will not start again without the aid of another dose of easy start. Makes no difference in terms of choke position or throttle position.

It has a Harris pipe with street baffle and is rumored to have mild porting work to the head (no idea if this is true).

When it does start there is no smoke or noises that should not be there.

Suggestions please!

[Ginger Bear]

Martin, may be worth double checking the valve timing & check you have not mixed the cams up. I'm not suggesting your stupid or anything, but it wouldn't be the first time it's happened.

Also, did the carbs run well before? have they sat around for ages & got gummed up? Could be worth trying another set if you have some spare, just to eliminate your CV's.

[martinz1000r]

It did not have the engine apart and when it does go it sounds very smooth so I dont think this is the issue.

I can try another set of carbs as I have the RS38 that you sold me but the carbs on it were cleaned before fitting and looked pretty good.

[Ginger Bear]

Probably worth swapping the carbs out then, just to rule out the CV's.

[Rich]

sounds like an idle system problem / incompatibility, check the pilot jets/airways are clean, fuel heights are correct, that you are getting fuel.

[PAULJAC47]

If the carbs have air vents try blowing gently down them into carbs,then
try to start with no choke,if it does suspect chokes,also guess your pilot circuit as others have said may be blocked,be carefull with easy start can cause bore washing!!!Paul J

[z1bman]

hi have you done a compression test ? compression test should be the first thing to be checked with the throttle fully opened this will show if your piston rings + valve clearance + valve timing are correct . also check your ignition coils they are prone to giving trouble on these models if you remove your plug caps from the HT lead +hold the HT lead against the engine with some insulated pliers the spark should jump at least an 8mm gap + be a bright blue crisp spark. does the engine spin over quickly when you press the starter button? another common problem is the alternator windings frequently burn them selves out + cause a weak spark + a big drain on the starter motor make sure you have got battery voltage at the ignition coils = 12volts

[martinz1000r]

No but can do if considered worth it.

[martinz1000r]

So I tested the compression and got the following:

no.1 @ 60psi
no.2 @ 85psi
no.3 @ 40psi
no.4 @ 60psi

I know this is far too low and inconsistent. Putting a little oil in to the spark plug holes and repeating the exercise sends the gauge up to about 200 psi so this suggests to me that the rings are ok?

What next guys? Going to check valve clearances/timing. Am I on the right track or any other recommendations?

[martinz1000r]

Actually just thinking with the oil test that says to me that rings / bore are shagged and head is fine.

Can someone confirm before I start major spanner works for no reason!

[Ginger Bear]

Martin, you've got it right, those bores are 'Donald ducked'

[martinz1000r]

Anyone want to buy a rather tasty looking GPz streetfighter with a f**ked engine?

[z1bman]

100% piston rings + bore. you might just get away with changing the piston rings with you compression readings. rings are probably broken or worn as thin as a razor blade. try a new set of rings inside the bore + check the ring end gap

[Pigford]

YOU DID DO COMP CHECK WITH A HOT MOTOR AND THROTTLE WIDE OPEN

[martinz1000r]

cold motor coz it is such a pig to start. Throttles were wide open.

In fact it would not start at all today.