T5 help..please!

I have recently fitted a new 172 kit to my T5 classic.

After putting the engine back in, I found that it was running really rough and struggling to reach anything above mid revs. The throttle was very slow to respond. On closer inspection of the carb (24/24 G), I found that the mixture screw had pushed the threads through so that some metal was poking out into the inlet of the carb… so I bought a new carb and decided to go for a 26/26 G instead.

After fitting the new carb last night, the engine has a flat spot as soon as you pull the throttle. I have tried every possible setting of the mixture screw, but the flat spot won’t go away. It even backfires and stops as I am adjusting the mixture screw. It will tickover OK, indicating that there isn’t an air leak problem anywhere.

The timing was on 14 degrees, so I put it back to standard in an attempt to stop the backfiring, but it didn’t work.

Over the last two months I have replaced practically every part of the engine with new parts… new crank, bearings, oil seals, CDI box, HT lead, spark plug cap… I could go on forever.

Can anyone help?.. / suggest things to try. :\


…so either you have an air leak, (check the carb base is absolutely flat on its sit and that the screws that fits it press it well on the cases and gasket…and all the other suggestions the others gave you ), or you have a problem with the slow jet. Check it is well in its place, that it is clean and of the correct size.

What way are you turning the stator plate clockwise to retard anti clockwise to advance are you useing a strobe light my t5 is set on 15

have you had the cylinder head reprofiled to go with the 172 kit

Well… this evening I borrowed a friends 24/24G carb and tried it… and it seems to have cured all my problems (hopefully).

The flat spot has gone… only a very minor one now every now and again which I hope I’ll be able to sort out by playing with the mixture screw.

How important is it to put the timing to 14 degrees? It is currently back on standard which I did in an attempt to stop the backfiring the other night.

Sounds silly, but nothing is blocking the air bellows? have you tried it without the bellows? how does the choke affect it?
Sounds like you’ve had enough!!! is there anybody near you that you could swap parts?
try without the petrol cap on(breather might be blocked)
If I think of anything else(which you’ve probably already thought of!!!)I’ll get back to you.
Good luck!![:look:]

Dont use sealer if using the auto lube, the oil way under the carb box is easly blocked with the sealer!

When choke is on… all seams fine… no flat spot… no backfiring.

how are you setting the timeing .Have you checked the wires from the stator to coil to see if they are not broken my t5 the wires seamed ok tryed to checked the resistance with a multimeter as described on page 78 in haynes manual no reading the wires seamed ok the plastic outer was ok the wire in side had broken soldered on new wires ok now


please tell us what happen with the choke on.

What way are you turning the stator plate clockwise to retard anti clockwise to advance are you useing a strobe light my t5 is set on 15

Yes… the cylinder was profiled to match the kit

The same happend to me, so i put on 2 new gaskets and sealer, the carb to carb box and carb box to engine(did not do the 1st time i put the carb on). 128 main jet and 160 air jet, alot better but i am going play around a bit more when i’ve got a bit of time.