SIL 200 now won't rev over 3000rpm when warm

[sideout]

Here's a funny thing....

New SIL 200 engine with Jetex on standard jets and Indian Big Bore exhaust. Has been going fine for 300 miles but coming home from work the other night, after waiting at some traffic lights it started 4 stroking when going through the gears (above ~3000 revs).

So far I've changed:
plug
plug cap
ht lead
CDI
even cleaned the carb jets and it's still the same.
Does anyone think it may be the pick up on the stator? Do they fail like this?

Cheers for any replies

Nigel

[coaster]

The pickup would probably just fail completely or cause intermittent cutting out. It could be CDI related but first I would check that the air filter is not dirty, air scoop not obstructed and also that the air hose hasn't gone soft, they have been known to collapse when sucking air under load.

[Andy Pickering]

Does it rev freely when cold..or more importantly with choke on..

[sideout]

The pickup would probably just fail completely or cause intermittent cutting out. It could be CDI related but first I would check that the air filter is not dirty, air scoop not obstructed and also that the air hose hasn't gone soft, they have been known to collapse when sucking air under load.

Air filter is new, as is the air hose. I've checked the scoop is unobstructed. Thanks Coaster.

Does it rev freely when cold..or more importantly with choke on..

I've just started it up and it revs freely when cold and with the choke on. What were you thinking? Cheers Lam46.

[DaveTomo]

I'd check the carb,It should bog down with the choke on once started up and warm,up to about 3/4 throttle maybe not so noticeable after that up to full throttle ,but if it revs better with the choke on I'd check the jetex if its needing more fuel to rev.Hope you get it sorted

[Andy Pickering]

That should tell you its on the fuel side thus eliminating elect..any chance you borrow a carb off a mate to have a comparison..

[sideout]

Thanks for the suggestions guys, some new things to try tomorrow. This afternoon I've disconnected the electrics, other than the ignition feed to the CDI and no change.
I've checked the choke operation, but I'll take another look before I swap the carb over (I have another one I can try).

Colin's (not a.k.a. Jon ) point about the air hose collapsing seems to fit the symptoms perfectly, I've just got to come up with a way of testing it

Went about 2 miles to the garage this afternoon, the same trip as yesterday and exactly the same symptoms. Fine on the way, put 5L of unleaded in a can on the sprint rack, went in and paid for it and pulling away onto the road again it started 4 stroking above 3k. (I know because it does it above 30mph in top: ~10mph per 1000rpm with 5.22 gearing.)

I'll report back! Thanks for the input, much appreciated

Cheers,

Nigel

[wack 63]

I've had this a couple of times and it has been the pick up.

[eibargum]

I've had this a couple of times and it has been the pick up.

Yep, that would be my guess, come across this a couple of times on mates scoots, borrow a working stator off somone to try.

[coaster]

Jon's point about the air hose collapsing seems to fit the symptoms perfectly, I've just got to come up with a way of testing it

It's Colin actually Nig

Try removing the air filter hose and take it for a quick spin to see if the 4 stroking goes away, that should tell you if it is induction related. If it runs ok without the hose then try it with the hose back on but with the air filter removed.

With regard to the pickup or LT coil being the cause, it's easy to test them with a multi meter without removing the stator.