GP200 running weak when warm

[john.t5]

I've had an ongoing problem with my GP200 - standard Indian top end, 28mm Delorto, JL pipe. I just fitted new Mec Eur crank, Asso piston and all new bearings seals, chain, etc etc. The thing is it runs sweet when started up but then after a couple of miles starts to feel a bit gutless, plug chops show it's running weak at 1/4 -1/2 throttle. It also takes a little long to return to tick over, suggesting it's weak on the mixture there too. There is no sign of leaking around the base or head gasket and the only thing I can think of checking now is the inlet manifold drawing in air.

Anyone come across anything similar or have any ideas - I'm meant to be taking it to Southport at the weekend then Killarney at the end of the month so I need to sort it or burn it

[shocky]

have you checked for fuel starvation or a blocked jet or s**t/water in the carb

[john.t5]

Cheers Shocky, just fitted a fast flow tap and the carb is clean, tried a 30mm carb and it does exactly the same.

[Bilko]

John, how many miles since rebuild? Did you re torque the head to make sure?

I've had this issue mate.

[john.t5]

Bilko I've only done 30 miles, thing is it was pretty similar before rebuild, as you know I had it set up over rich last year for 4 nations. I had the top end off again on Friday night to check it after a light seize so all torqued down right. There are no signs of leaks around the head or base, only thing I can think of is the manifold expanding and either the manifold is warped or the gasket face on the barrel isn't perfect, going to look at it today again

[Bilko]

Hello John, I certainly didn't want to sound condescending or anything. I know you know your stuff mate.

I made a cock up of mammoth proportions with the 250 that's going to cost me a fortune and wanted to check you weren't missing anything.

I know what a pain in the arse it is stripping and rebuilding and checking everything over and over.

[john.t5]

I appreciate any suggestions Bilko - I know how easy it is to miss the simple things and someone else may think of something you miss. I'm kinda stuck on the idea it's something to do with the inlet manifold so that's what today's mission centers around!!

What are you gonna have on the road for the 4 Nations now? It's not too long away

[goldeneye]

my GP200 engine was doing the same a few years back. after rebuilding it about three times, with different top ends, carbs, the lot and being totally sick of it, it came down to a hairline crack in the mag side transfer port area, that would only show the problem after the engine warmed up, usually after about ten miles. ended up getting a new casing and swopping the lot over, been fine since. in fact , i tell a lie, scotty DSC swopped everything over, because i was gonna take a hammer to it, i was that sick of it! hope its not this on yours, but another thing to look for.

[Bilko]

I've nothing else on the road, John so the 4 nations is out for me and Jackie.

[shocky]

might be worth checking that the spogit or the barrel isnt touching the mag flange transfere port cut out 200 cut outs are bigger than 150 ones i had it on 2 rapido cylinders