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Honda C90 - Back firing. - John v2011

Hi

When I slow down, my Honda has a tendency to back fire. It doesn't do it all the time though. I have recently had my bike serviced but it still does it. Any ideas?

John

Honda C90 - Back firing. - tdc

What year,what mileage?

If you have a real oldun with c/b points and condenser then could be dirty /badly gapped/worn/burnt-out points or faulty condenser(which is essentially a tight wad of rolled-up tin foil which absorbs excess current not used by the ignition,thereby preventing excess wear/arcing at the points)

The odds are you have electronic ignition so next thing to check is all the wiring for loose connections at the junctions or corrosion.

Then check the tappets,an easy job on all stepthru models,Haynes manual will show you how.With high mileage,tight valve clearances can occur and will cause back-firing,clearance does reduce as valve faces/valve seats wear....talking from experience on this model.

There is a screw at the bottom of the carb float-bowl which when slackened drains petrol through a plastic pipe you should have attached.Use a clean jar to collect contents of float-bowl and leave petrol tap on to flush through a little before re-tightening the screw.If a lot of crud comes out you may have some muck in a jet.

Lastly(or maybe firstly!) give your silencer a thump with your fist(preferably when cool :) )If it rattles then your baffles are collapsing.You`ll`ve noticed a noisy exhaust note if this is the case...only likely with high mileage.If the silencer is falling to bits internally then it will affect both exit of gasses and mixture.

Good luck and let me know what you find.

Honda C90 - Back firing. - craig-pd130

All good advice above, it can also be a sign of a weak fuel / air mixture, check the airfilter isn't holed and is correctly mounted. Could also be a leak at the exhaust pipe's junction with the cylinder head (unlikely as you'd hear the exhaust quite loudly)

Honda C90 - Back firing. - John v2011

Hi

Bike is 14 years old and has done less than 30k miles.

Looking back, the problem did appear to start when the bikes original exhaust was damaged and replaced by a local mechanic with one he had salvaged from a scrapped C90. Having said that though, the exhaust has just been changed again with a nice new one (Albeit from China) but it is still back-firing. Thanks for your feedback.

John

Honda C90 - Back firing. - tdc

Hi John,

Great little engines which usually outlast the rest of the bike due to rot getting at the inside of the front forks and around the rear suspension mounting area of the frame thanks to good old British weather.Waxoyl from new helps.

However 30`000 miles is not low mileage for such a small 4-stroke engine,although unlike their 2-stroke rivals they can attain much higher miles if ridden carefully and serviced regularly. Owned several of them over the years amongst the 60-odd(sometimes very odd)bikes I`ve owned.

As mentioned earlier,check that the valve clearances haven`t closed up.For removal of the alloy inspection covers to check the tappets,have always used a socket on which I`d ground the front face down....standard socket with its radiused lead-in can slip and chew up the alloy cover`s hex head which is quite shallow.

Best of Luck,

Oz

Honda C90 - Back firing. - cub90man

hello peeps!

Oz, I have a question for you.

My bike is jumping from 3rd gear to 2nd. also it backfires a little sometimes, which Ive just read possible solutions, and the clutch is slipping. I know from previous ownership that you can hold the gears inbetween (clutch engaged) on manual bike as when I was young and adventurous(stupid) thats how we used to wheelie them. my bike has Nothing inbetween. Is it possibl the clutch has something to do with gears or is that just the fork selector? and new clutch plates needed? cheers.

ps my bike is 1990 9000 miles.

cheers

Honda C90 - Back firing. - rtyerter

Could also be a leak at the exhaust pipe's junction with the cylinder head.

Edited by Avant on 13/08/2013 at 23:29

Honda C90 - Back firing. - steve the grease

My Honda 50 used to do this.

Even a tiny leak where the exhaust pipe bolts on to the cylinder head will cause a backfire on the over run . The engine drags through fuel which doesn't burn on the over run , the air leak enables it to burn in the exhaust making a pop bang sort of noise.

There is a copper compression washer where the exhaust pipe bolts in, no one ever changes them and usually it's OK, yours leaks a tiny bit of air and so bang , pop bang.

Usually comes as part of a gasket set, but surely available from a Honda dealer, or ask mechanic to use exhaust assembly paste , should do the job , a tube only a few quid.

Honda C90 - Back firing. - martint123

Agreed, air leaking in somewhere in the exhaust system. Start searching nearest the cyclinder head and work backwards.

Honda C90 - Back firing. - jeffreyburkholderRoom

I get it started and get into the grass and after a couple minutes when encountering thicker stuff it will bog a bit and backfire through the carb