backfireing centry

gadget · Post by **gadget** » Mon Jun 26, 2006 3:22 pm

Hi i have a silver centry plus (wpcl) seems a little under powered , engine not sounding quite right. points were set at 20 thou and plug also but would not start. so adjusted points to 25 thou and plug left at 20 thou and runs . been on test on 14ft boat but engine doesnt seem 100 % and backfires every few mins. any ideas what might cause this .

thanks nigel

bgsats · Post by **bgsats** » Tue Jun 27, 2006 8:47 pm

Weak mixture/wrong carb. or needle, incorrect fuel /oil mix - do you measure it out? Should be 10:1 - new unleaded fuel and 2 stroke oil not multigrade - preferably outboard 2 stroke but any 2 stroke would get it running OK if nothing else is wrong. Weak coil also a possibility, borrow one known to be working if poss. to check this!

Post by **John@sos** » Wed Jun 28, 2006 9:49 am

Check the screw on the ignition backplate is not loose and the timing out, also that the backplate is rock steady and does not move up and down. Points and plug should be 20 thou.

Mixture could well be wrong. weak mix will do it, as will not enough oil to seal the crank, thus it will suck in air there and run weak .....

Regards
John
SOS

gadget · Post by **gadget** » Wed Jun 28, 2006 10:46 am

thanks bgsats and john, has given me a few pointers for the weekend. it has an amal 2 jet carb and run on marine 2 stroke 10-1 mix. only thing , according to the manual the float chainber should be on the boat side not the tank side . the carb is also on the left side if the engine is on the transom and you are in the boat facing it. coil resistance is ok , will play at the weekend in the back garden (dont want to anoy the neighbours too much )
thanks will let you know how it goes

gadget · Post by **gadget** » Mon Jul 03, 2006 3:20 pm

Hi have been playing at the weekend. started from scratch. mix 10-1 unleaded petrol and mairne 2 stroke oil , measured, new fuel pipe, cleaned fuel filters and amal 2 jet carb, float working correctly , checked compression (50 psi) checked for leakes in the crank case, non found, new spark plug , lead and cap. coil resistance 5Kohm to base plate . continuity check from base plate to cylinder head. spun flywheel with electric drill for 5 mins. cleaned points. measured points are opening 2.5mm before tdc. base plate checked for correct position and checked sucurity. all commponents on base plate seated correctly. set points to 20 thou runs like a pig. set to 25 thou runs ok at half throttle any more and it backfires. plug set at 20 thou. ignition system wypac2 . (1)question is there a condensor in the wypac 2 system as i cannot see one near ther points. (2) any other ideas to what could be causing the backfire nearly tearing my hair out . thanks a deserate seaguller .

albert · Post by **albert** » Tue Jul 04, 2006 8:16 pm

(2) any other ideas to what could be causing the backfire nearly tearing my hair out . thanks a deserate seaguller .[/quote]

Sometimes it helps when you open the gap of the spark plug a bit more to let's say o.3 thou. But don't ask me how that works.
Once a had troubles like you and found after a long time that a cleaned the points too much! Where the arm turns, it is necessary to keep it a little bit greasy. If not, the points cannot follow the speed of the engine: they have to open and close many times per minute.
Also a weak or broken spring could be the problem.

Maybe this helps?

gadget · Post by **gadget** » Wed Jul 05, 2006 10:01 am

Thanks albert will give your ideas a go at the weekend . concerning the spring how would i know if it was weak , is there something i could guage it against . thanks again nigel

albert · Post by **albert** » Wed Jul 05, 2006 2:19 pm

gadget wrote:Thanks albert will give your ideas a go at the weekend . concerning the spring how would i know if it was weak , is there something i could guage it against . thanks again nigel

If the spring causes your troubles, you have problems with making higher revs. Then your motor will run on low revs pretty good but will not reach higher ones. Ones I had such troubles with a Bosch ignition. Never had this with a Villiers, about Wipac, I do not know..

Hope this helps you..

Happy Seagulling, Albert

gadget · Post by **gadget** » Wed Jul 05, 2006 4:28 pm

Thanks albert will try plug first then check the spring, will collect a selection of springs before the weekend and if all fails will try to replace the spring . thanks again nigel

Charles UK · Post by **Charles UK** » Thu Jul 06, 2006 12:07 am

would be very supprised to find a Seagull ignition with a weak spring, I've owned 30 or 40 of them & never had a spring problem.
The only possible reasons I can think of are incorrect timing, too far retarded or a build up of carbon crud in the exhaust port & the top of the exhaust tube that gets very hot when at higher revs, igniting the lost fresh fuel/air charge,
Or realy tired piston rings.

Drop the exhaust tube to check that ther is no build up of carbon around exhaust port, this was common when 30 grade motor oil was standard 2 stroke fuel mix at a 10:1 ratio

gadget · Post by **gadget** » Tue Jul 18, 2006 10:10 am

thanks albert and charles uk. have cleaned exhust ports( fairly clean to start with) have greased the cam the points touch. timeing checked points opening at 2.5 mm before tdc (measured using a gauge) points 20 thou and plug tried at 20 , 23, 25 thou.(20 thou for both seems to be better at lower revs) still having problems above half throttle with backfireing. only thing left to check would be the points spring. have you guys got any more ideas this one is just foxing me ,but i'll get there eventualy.
thanks in hope nigel

albert · Post by **albert** » Tue Jul 18, 2006 4:48 pm

Hello Gadget,

What a puzzle.
Does your 2 jet amal have the right powerjet? If it is converted to 25:1, running on 10:1 will produce a lean mixture.
In that case, going back to 25:1 will not solve the problem when your engine is not in the best condition.
You have to take a bigger jet (45 or 50 I believe)
So, take a look to the powerjet...

Regards,

Albert

gadget · Post by **gadget** » Wed Jul 19, 2006 9:06 am

Hi albert checked jets they are correct for 10-1 mix which i have been using. going to try the spring some time this week . thanks nigel

headcase · Post by **headcase** » Wed Jul 19, 2006 9:48 pm

Hi gadget, I had a similar problem recently with a century, a good spark and the engine would start and run well for about 20 seconds and then start misfiring and backfiring. A replacement coil from John SOS cured the problem. Ignition coils either work or don't but the incorporated condenser, if faulty, will give a useful looking spark outside the engine that soon fails when under compression

gadget · Post by **gadget** » Thu Jul 20, 2006 10:53 am

thanks headcase i will check every thing out this weekend ,if still no luck then i'l contact john re replacement coil. thanks nigel